{"gene":"AMPD1","run_date":"2026-06-09T22:02:43","timeline":{"discoveries":[{"year":1990,"finding":"The AMPD1 gene product in rat is alternatively spliced via a novel pathway: the 12-base exon 2 is excluded or included in a tissue-specific and stage-specific pattern. Alternative splicing proceeds through an RNA intermediate that generates an alternative 5' splice donor site at the exon 1-exon 2 boundary not present in the primary transcript. In human AMPD1, the analogous intermediate was a poor splicing substrate due to differences in exon 2 sequences, so human AMPD1 was not alternatively spliced.","method":"Transfection and minigene analysis, RNA intermediate characterization","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct RNA intermediate characterization with minigene constructs, replicated across rat and human sequences in a single rigorous mechanistic study","pmids":["2398891"],"is_preprint":false},{"year":1991,"finding":"Two steps in RNA processing control the ratio of AMPD1 alternative transcripts: (1) exon 2 recognition in the primary transcript (influenced by its small size and suboptimal splice sites, and by a slow-removal intron 2 that plays a permissive role); and (2) nucleocytoplasmic partitioning of an RNA intermediate (exon 1-exon 2-intron 2-exon 3) — nuclear retention of this intermediate is associated with accumulation of the exon-2-containing mature mRNA, while cytoplasmic escape leads to the alternative transcript.","method":"Transfection with native, mutant, and chimeric minigene constructs; subcellular fractionation of RNA intermediates","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods (minigene mutagenesis, nuclear/cytoplasmic fractionation) in a single rigorous mechanistic study","pmids":["1922051"],"is_preprint":false},{"year":1993,"finding":"Muscle-specific expression of AMPD1 is controlled by two distinct cis-acting elements within 100 nucleotides of the transcriptional start site. One element (-100 to -79) acts as a tissue-specific enhancer resembling an MEF2 binding motif and interacts with proteins predominantly in myoblast/myotube nuclei; an A/T core within it is essential for enhancer activity. The second element (-60 to -40) acts as a stage-specific promoter element essential for muscle-specific expression, interacting with a protein restricted to differentiated myotube nuclei.","method":"Promoter deletion and mutation analysis by transfection, electrophoretic mobility shift assay (EMSA) for protein-DNA interaction","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis of cis elements combined with protein-DNA binding assays; multiple orthogonal methods in one study","pmids":["8355716"],"is_preprint":false},{"year":1994,"finding":"Mutational analysis of AMPD1 demonstrated that the catalytic site and a regulatory site (likely an ATP binding site) are located in the highly conserved carboxy terminus. The amino terminus has a profound influence on catalytic activity and on binding of AMPD1 to myosin. Alternative splicing in the amino-terminal region generates isoforms exhibiting differential sensitivity to effector molecules such as ATP.","method":"Site-directed mutagenesis, deletion mutant expression and enzymatic assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro mutagenesis with activity assays but single lab, single study; inference on ATP binding site from activity data without direct structural validation","pmids":["7802626"],"is_preprint":false},{"year":2000,"finding":"Positive and negative elements mediate alternative splicing of AMPD1 exon 2. Exon 2 is intrinsically defective due to three combined defects: a suboptimal 3' splice acceptor site, a suboptimal 5' splice donor site, and its small size. The defective exon can only be recognized in the presence of the adjacent downstream intron. Improving any single defect relieves exon masking.","method":"Minigene transfection with systematic mutation of splice sites and exon sequences","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — systematic minigene mutagenesis in a single lab, multiple constructs tested","pmids":["10767559"],"is_preprint":false},{"year":2000,"finding":"Two novel missense mutations (R388W in exon 9 and R425H in exon 10) of AMPD1 result in undetectable AMPD enzyme activity when expressed prokaryotically, establishing these residues as functionally critical for catalytic activity and identifying AMPD1 as essential for normal skeletal muscle metabolism and development.","method":"Prokaryotic expression of mutant constructs with enzyme activity assay","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro expression with activity assay; single patient and single lab","pmids":["11102975"],"is_preprint":false},{"year":2001,"finding":"In subjects homozygous for the AMPD1 mutant allele (MM), AMP deaminase activity was nearly absent in skeletal muscle during sprint exercise, resulting in no significant net ATP catabolism, no IMP accumulation, no postexercise plasma ammonia increase, and a dramatic ~25-fold increase in skeletal muscle adenosine compared to normal homozygotes (NN). Heterozygotes showed intermediate enzyme activity and IMP accumulation.","method":"Muscle biopsy with direct enzyme activity assay; nucleotide and adenosine measurement; plasma ammonia measurement during Wingate exercise test","journal":"Journal of applied physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct biochemical measurement in human muscle biopsies with multiple metabolic endpoints across three genotype groups","pmids":["11408438"],"is_preprint":false},{"year":2002,"finding":"A second AMPD1 mutant allele, G468T (causing a Q156H substitution), was identified in compound heterozygous patients with myoadenylate deaminase deficiency. Baculoviral expression of the G468T mutant produced an enzyme with labile catalytic activity, and Western blot of patient muscle detected no immunoreactive AMPD1 polypeptide, demonstrating this allele is dysfunctional.","method":"Baculoviral expression with enzyme activity assay; Western blot of patient muscle biopsy","journal":"Neuromuscular disorders","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro expression with activity assay plus patient tissue validation; single lab","pmids":["12117480"],"is_preprint":false},{"year":2003,"finding":"The C34T (Glu12Stop) nonsense mutation in AMPD1 reduces cardiac AMP-deaminase activity to approximately half of wild-type in heterozygous heart failure patients, without changing the activity of other adenosine-regulating enzymes. In homozygous mutant subjects, exercise-induced increase in blood adenosine was significant, whereas heterozygotes and wild-type subjects showed no significant change, indicating local cardiac metabolic effects predominate over systemic adenosine changes.","method":"Direct enzyme activity assay in cardiac tissue; SSCP genotyping; LC/MS measurement of blood adenosine","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct tissue enzyme activity measurement with genotype stratification, orthogonal systemic adenosine quantification by LC/MS","pmids":["14499869"],"is_preprint":false},{"year":2005,"finding":"A novel intronic deletion (IVS2-(4-7)delCTTT) in AMPD1 disrupts splicing, generating multiple alternatively spliced AMPD1 transcripts from patient skeletal muscle, including deletions in exon 3, complete deletion of exon 3 or exons 3-4, and activation of a cryptic splice site with an insertion at the 5' end of exon 4, demonstrating that intronic sequences flanking exon 3 are essential for normal AMPD1 splicing.","method":"AMPD1 mRNA characterization from skeletal muscle biopsy; allele-specific PCR; direct sequencing","journal":"Molecular genetics and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — mRNA-level characterization with sequencing in patient tissue; single case/lab, no in vitro reconstitution","pmids":["16040263"],"is_preprint":false},{"year":2007,"finding":"In subjects heterozygous for the 34C>T AMPD1 variant, forearm reactive hyperemia following ischemia was significantly augmented and ischemia-reperfusion injury (measured by 99mTc-annexin A5 scintigraphy detecting externalized phosphatidylserine) was significantly reduced compared to wild-type controls, consistent with increased ischemia-induced intracellular adenosine formation due to reduced AMPD1 activity.","method":"Venous occlusion plethysmography for forearm blood flow; 99mTc-annexin A5 scintigraphy for tissue injury quantification; in vivo human experiment with genotype-stratified cohorts","journal":"European heart journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal in vivo functional readouts in genotype-stratified human subjects; single lab","pmids":["17376785"],"is_preprint":false},{"year":2008,"finding":"AMPD1 genotype-deficient individuals (MM or compound heterozygotes) exhibited a greater and faster post-exercise blood flow response and a more than twice-faster fall in blood flow during recovery (T1/2: 7.8 min vs. 16.1 min in normal homozygotes) following sprint exercise, consistent with AMPD1 deficiency increasing adenosine formation and augmenting exercise-induced hyperemia.","method":"Common femoral artery ultrasonography before and after 30-s Wingate cycling test in genotype-stratified human subjects","journal":"European journal of applied physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct vascular imaging with functional outcome, genotype stratification; small sample, single lab","pmids":["18224333"],"is_preprint":false},{"year":2014,"finding":"Pharmacological inhibition of AMPD (in isolated rat muscle) or genetic deletion of Ampd1 (in mouse skeletal muscle) potentiated exercise-induced rises in AMP, AMP:ATP ratio, and AMPK Thr172 and ACC Ser218 phosphorylation during electrical stimulation. Enhanced AMPK activation was moderate and muscle-type dependent (observed in soleus but not EDL from Ampd1 knockout mice), suggesting control by factors beyond adenine nucleotide changes alone.","method":"Pharmacological inhibition with direct nucleotide measurement; Ampd1 knockout mouse muscle (incubated EDL and soleus); immunoblot for AMPK/ACC phosphorylation; electrical stimulation","journal":"Chemistry & biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — genetic KO plus pharmacological inhibition with direct biochemical readouts (nucleotide levels, phosphorylation) in isolated muscle; multiple orthogonal approaches","pmids":["25459662"],"is_preprint":false},{"year":2014,"finding":"Genetic disruption of AMPD1 in mice fed a high-fat diet leads to less severe insulin resistance, improved glucose tolerance, enhanced insulin clearance, and elevated phosphorylated AMPK in skeletal muscle compared to wild-type mice, demonstrating AMPD1 modulates insulin sensitivity through the AMP/AMPK axis in skeletal muscle.","method":"AMPD1-deficient mouse model; glucose tolerance test; insulin tolerance test; immunoblot for phospho-AMPK in skeletal muscle","journal":"BMC endocrine disorders","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with functional metabolic assays and biochemical phosphorylation readouts; single lab","pmids":["25511531"],"is_preprint":false},{"year":2015,"finding":"AMPD1 deficiency in mice on high-fat diet activates the AMPK/Akt/mTORC1/p70 S6 kinase axis specifically in skeletal muscle (not liver or white adipose tissue), and increases Raptor-bound mTOR in skeletal muscle, mechanistically linking AMPD1 to insulin signaling via this pathway.","method":"AMPD1-deficient mouse model; immunoprecipitation of mTOR followed by immunoblot for Raptor; phosphorylation assays for AMPK, Akt, p70 S6K by immunoblot","journal":"BMC endocrine disorders","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and phosphorylation assays with genetic KO model; single lab, no in vitro reconstitution","pmids":["25887856"],"is_preprint":false},{"year":2016,"finding":"A knockout-first cassette insertion in the Ampd1 locus caused neonatal lethality in mice by disrupting expression of neighboring genes Man1a2 and Nras, not from AMPD1 loss per se. Mice with the critical exon deleted (Ampd1tm1d) survived to adulthood. E18.5 Ampd1tm1a/tm1a mice showed elevated AMP and near-complete absence of IMP in skeletal muscle, directly confirming AMPD1's catalytic role in AMP-to-IMP conversion in vivo.","method":"Conditional knockout mouse model; RNA-seq for neighboring gene expression; metabolite measurement (AMP, IMP) in skeletal muscle by biochemical assay","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with direct metabolite quantification and RNA-seq for off-target effects; multiple constructs and controls","pmids":["27775065"],"is_preprint":false},{"year":2022,"finding":"AMPD1 knockdown (~35%) in mouse EDL (but not SOL) skeletal muscle impaired time-to-peak tension and half-relaxation time during maximal tetanic contractions. In EDL, AMPD1 knockdown exaggerated the AMP response to LOW and MOD duty-cycle contractions (+100% and +54%, respectively) and increased AMPK Thr172 phosphorylation (+25% and +34%) and downstream substrate phosphorylation, in an intensity-dependent manner.","method":"Electroporation of AMPD1-specific miRNA into contralateral EDL and SOL muscles in mice; isometric contractile function assay; immunoblot for AMPK/substrate phosphorylation; direct AMP measurement","journal":"Journal of applied physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — acute in vivo gene knockdown with contralateral muscle controls, multiple contractile and biochemical readouts, sex-stratified analysis","pmids":["36107988"],"is_preprint":false},{"year":2023,"finding":"Berberine suppressed AMPD1 expression and promoted adenylosuccinate synthetase (ADSL) expression in fructose-treated rats and L6 cells, increasing intracellular AMP and AMP/ATP ratio to activate AMPK, thereby alleviating insulin resistance. This identifies AMPD1 as a mechanistic target of berberine in the AMP-AMPK pathway.","method":"In vivo rat model and L6 cell culture; gene expression by qPCR/Western blot; AMP/ATP ratio measurement; AMPK activation by phosphorylation assay","journal":"Food and chemical toxicology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological manipulation with mechanistic biochemical readouts in both in vivo and cell models; single lab","pmids":["36931587"],"is_preprint":false}],"current_model":"AMPD1 encodes the skeletal muscle-specific isoform of AMP deaminase, which catalyzes the deamination of AMP to IMP and ammonia; its expression is controlled by MEF2-like and stage-specific cis-elements, and its exon 2 is subject to alternative splicing through an RNA-intermediate mechanism involving both exon recognition (governed by suboptimal splice sites and exon size) and nucleocytoplasmic partitioning; the catalytic and regulatory (ATP-binding) sites reside in the conserved carboxy terminus while the amino terminus influences catalytic activity and myosin binding; loss of AMPD1 activity (via the common C34T or other mutations) elevates intracellular AMP and adenosine in skeletal muscle and heart, augments AMPK activation, modulates mTORC1/p70 S6K and Akt signaling to improve insulin sensitivity, and enhances ischemia-induced vasodilation and cardioprotection through increased local adenosine production."},"narrative":{"mechanistic_narrative":"AMPD1 encodes the skeletal-muscle isoform of AMP deaminase, which catalyzes the deamination of AMP to IMP and ammonia and thereby governs adenine nucleotide flux during muscle energy stress [PMID:27775065, PMID:11408438]. Its catalytic site and a regulatory ATP-binding site reside in the conserved carboxy terminus, while the amino terminus modulates catalytic activity and myosin binding [PMID:7802626]. Muscle-restricted expression is driven by two cis-elements near the transcription start site — an MEF2-like tissue-specific enhancer and a stage-specific promoter element active in differentiated myotube nuclei [PMID:8355716] — and the gene's exon 2 is subject to a distinctive alternative splicing mechanism controlled by exon recognition (suboptimal splice sites and small exon size) and by nucleocytoplasmic partitioning of an RNA intermediate [PMID:2398891, PMID:1922051, PMID:10767559]. Loss of AMPD1 activity, through the common C34T (Glu12Stop) nonsense allele or other catalytic mutations, abolishes net ATP catabolism and IMP accumulation during exercise and instead elevates intracellular AMP and adenosine in skeletal muscle and heart [PMID:11408438, PMID:14499869, PMID:11102975, PMID:12117480]. The resulting rise in the AMP:ATP ratio potentiates AMPK Thr172 phosphorylation and downstream ACC, Akt, and mTORC1/p70 S6 kinase signaling, improving insulin sensitivity and glucose tolerance [PMID:25459662, PMID:25511531, PMID:25887856], while increased local adenosine production enhances ischemia-induced vasodilation and confers cardioprotection [PMID:17376785, PMID:18224333]. Catalytically inactivating mutations cause myoadenylate deaminase deficiency [PMID:12117480, PMID:11102975].","teleology":[{"year":1990,"claim":"Established that AMPD1 transcripts are diversified by a non-canonical splicing route, defining how isoform diversity arises and revealing a species difference between rat and human exon 2 handling.","evidence":"Transfection and minigene analysis with RNA intermediate characterization in rat and human sequences","pmids":["2398891"],"confidence":"High","gaps":["Did not identify trans-acting splicing factors","Functional consequence of exon 2 inclusion/exclusion on enzyme activity not resolved here"]},{"year":1991,"claim":"Resolved the two-step control of alternative transcript ratio — exon 2 recognition plus nucleocytoplasmic partitioning of an RNA intermediate — explaining how subcellular RNA localization gates the mature mRNA pool.","evidence":"Minigene mutagenesis with nuclear/cytoplasmic RNA fractionation","pmids":["1922051"],"confidence":"High","gaps":["Machinery driving nuclear retention vs cytoplasmic escape unidentified","Physiological tissue context of partitioning not addressed"]},{"year":1993,"claim":"Defined the cis-regulatory basis of muscle-specific transcription, identifying an MEF2-like enhancer and a differentiation-stage promoter element with their bound nuclear factors.","evidence":"Promoter deletion/mutation transfection and EMSA","pmids":["8355716"],"confidence":"High","gaps":["Binding proteins not molecularly identified","Interplay with splicing regulation not examined"]},{"year":1994,"claim":"Mapped catalytic and regulatory domains, placing the active and ATP-binding sites in the carboxy terminus and assigning the amino terminus a role in activity and myosin binding.","evidence":"Site-directed mutagenesis and deletion mutant enzymatic assays","pmids":["7802626"],"confidence":"Medium","gaps":["ATP-binding site inferred from activity, not structurally validated","Myosin-binding interface not delineated at residue level"]},{"year":2000,"claim":"Showed exon 2 is intrinsically defective through three combined features and is only recognized with help from the adjacent intron, clarifying the molecular logic of exon masking.","evidence":"Systematic minigene splice-site and exon mutagenesis","pmids":["10767559"],"confidence":"Medium","gaps":["Single lab","Trans-acting regulators of masking not identified"]},{"year":2000,"claim":"Identified disease-causing missense mutations (R388W, R425H) that abolish enzyme activity, linking specific residues to catalytic competence and to muscle metabolic dysfunction.","evidence":"Prokaryotic expression of mutants with activity assay","pmids":["11102975"],"confidence":"Medium","gaps":["Single patient and single lab","In vivo consequences not directly measured"]},{"year":2001,"claim":"Demonstrated in human muscle that loss of AMPD1 activity abolishes exercise IMP/ammonia production and instead causes a ~25-fold adenosine rise, defining the in vivo metabolic phenotype of deficiency.","evidence":"Muscle biopsy enzyme/nucleotide/adenosine measurement and plasma ammonia during Wingate exercise across three genotypes","pmids":["11408438"],"confidence":"High","gaps":["Downstream signaling consequences not assessed here","Vascular/clinical outcomes not measured"]},{"year":2002,"claim":"Validated a second dysfunctional allele (G468T/Q156H) producing labile enzyme and absent muscle polypeptide, expanding the mutational spectrum of myoadenylate deaminase deficiency.","evidence":"Baculoviral expression with activity assay plus patient muscle Western blot","pmids":["12117480"],"confidence":"Medium","gaps":["Single lab","Mechanism of protein instability not defined"]},{"year":2003,"claim":"Extended the deficiency phenotype to the heart, showing C34T halves cardiac AMP-deaminase activity and that local cardiac adenosine effects predominate over systemic changes.","evidence":"Cardiac tissue enzyme assay with SSCP genotyping and LC/MS blood adenosine","pmids":["14499869"],"confidence":"High","gaps":["Causal link to heart-failure outcome not established","Tissue adenosine not directly measured"]},{"year":2007,"claim":"Provided in vivo human evidence that the C34T variant augments reactive hyperemia and reduces ischemia-reperfusion injury, connecting reduced AMPD1 activity to vascular and cytoprotective benefit.","evidence":"Forearm plethysmography and 99mTc-annexin A5 scintigraphy in genotype-stratified subjects","pmids":["17376785"],"confidence":"Medium","gaps":["Single lab","Intracellular adenosine increase inferred not directly measured in this readout"]},{"year":2008,"claim":"Confirmed augmented and faster-resolving exercise hyperemia in AMPD1-deficient individuals, reinforcing the adenosine-mediated vasodilatory consequence of deficiency.","evidence":"Femoral artery ultrasonography before/after Wingate cycling in genotype-stratified subjects","pmids":["18224333"],"confidence":"Medium","gaps":["Small sample, single lab","Direct adenosine quantification not performed"]},{"year":2014,"claim":"Linked AMPD1 loss to energy-sensing signaling, showing deletion or inhibition potentiates exercise-induced AMP, AMP:ATP ratio, and AMPK/ACC phosphorylation in a muscle-type-dependent manner.","evidence":"Ampd1 knockout mouse muscle plus pharmacological inhibition with nucleotide and phospho-immunoblot readouts during electrical stimulation","pmids":["25459662"],"confidence":"High","gaps":["Moderate effect implies additional regulators of AMPK beyond nucleotide levels","Mechanism of soleus vs EDL difference unexplained"]},{"year":2014,"claim":"Demonstrated metabolic benefit of AMPD1 deficiency, with improved glucose tolerance and insulin clearance and elevated muscle phospho-AMPK on high-fat diet.","evidence":"AMPD1-deficient mice with glucose/insulin tolerance tests and phospho-AMPK immunoblot","pmids":["25511531"],"confidence":"Medium","gaps":["Single lab","Tissue-specific contribution to whole-body phenotype not dissected"]},{"year":2015,"claim":"Defined the downstream signaling axis, showing AMPD1 deficiency activates AMPK/Akt/mTORC1/p70 S6K and increases Raptor-bound mTOR selectively in skeletal muscle.","evidence":"AMPD1-deficient mice with mTOR Co-IP for Raptor and phosphorylation immunoblots","pmids":["25887856"],"confidence":"Medium","gaps":["Co-IP without reciprocal validation","Direct molecular coupling of AMPK to mTORC1 in this context not reconstituted"]},{"year":2016,"claim":"Provided definitive in vivo confirmation of catalytic function and corrected a misattributed lethal phenotype, showing elevated AMP and near-absent IMP in muscle while neonatal lethality arose from disruption of neighboring Man1a2/Nras.","evidence":"Conditional knockout mouse alleles with RNA-seq of neighboring genes and AMP/IMP metabolite measurement","pmids":["27775065"],"confidence":"High","gaps":["Adult-survivable allele's metabolic phenotype only partially characterized","Residual AMP deaminase from other isoforms not quantified"]},{"year":2022,"claim":"Showed acute AMPD1 knockdown impairs contractile kinetics and intensity-dependently exaggerates AMP and AMPK signaling in fast-twitch EDL, tying AMPD1 to muscle performance and energetic sensing.","evidence":"Contralateral in vivo miRNA electroporation of EDL/SOL with contractile and phospho-immunoblot readouts and direct AMP measurement","pmids":["36107988"],"confidence":"High","gaps":["Fiber-type basis of EDL-specific effect unresolved","Chronic vs acute knockdown effects may differ"]},{"year":2023,"claim":"Identified AMPD1 as a pharmacological target, with berberine suppressing AMPD1 (and inducing ADSL) to raise AMP/ATP ratio, activate AMPK, and relieve insulin resistance.","evidence":"Rat and L6 cell models with expression, AMP/ATP ratio, and AMPK phosphorylation readouts","pmids":["36931587"],"confidence":"Medium","gaps":["Single lab","Direct drug-AMPD1 binding not demonstrated; effect may be indirect transcriptional"]},{"year":null,"claim":"The trans-acting factors controlling exon 2 splicing and RNA partitioning, the proteins binding the muscle-specific cis-elements, and the precise molecular coupling of AMP accumulation to mTORC1 remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Splicing regulators unidentified","Transcription factors at cis-elements not molecularly defined","AMPK-to-mTORC1 coupling not reconstituted"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[6,15,5,7]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[6,15]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[6,15]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[6,15,13]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,1,4]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[12,14]}],"complexes":[],"partners":["MYH (MYOSIN)"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P23109","full_name":"AMP deaminase 1","aliases":["AMP deaminase isoform M","Myoadenylate deaminase"],"length_aa":747,"mass_kda":86.5,"function":"AMP deaminase plays a critical role in energy metabolism","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P23109/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/AMPD1","classification":"Not Classified","n_dependent_lines":11,"n_total_lines":1208,"dependency_fraction":0.009105960264900662},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/AMPD1","total_profiled":1310},"omim":[{"mim_id":"615511","title":"MYOPATHY DUE TO MYOADENYLATE DEAMINASE DEFICIENCY; MMDD","url":"https://www.omim.org/entry/615511"},{"mim_id":"610681","title":"PHOSPHOFRUCTOKINASE, MUSCLE TYPE; PFKM","url":"https://www.omim.org/entry/610681"},{"mim_id":"605320","title":"6-@PHOSPHOFRUCTO-2-KINASE/FRUCTOSE-2,6-BISPHOSPHATASE 4; PFKFB4","url":"https://www.omim.org/entry/605320"},{"mim_id":"601937","title":"NUCLEAR RECEPTOR COACTIVATOR 3; NCOA3","url":"https://www.omim.org/entry/601937"},{"mim_id":"245340","title":"ERYTHROCYTE LACTATE TRANSPORTER DEFECT","url":"https://www.omim.org/entry/245340"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"skeletal muscle","ntpm":538.0},{"tissue":"tongue","ntpm":202.3}],"url":"https://www.proteinatlas.org/search/AMPD1"},"hgnc":{"alias_symbol":["MAD","MADA"],"prev_symbol":[]},"alphafold":{"accession":"P23109","domains":[{"cath_id":"3.20.20.140","chopping":"129-157_271-322_615-780","consensus_level":"medium","plddt":91.3854,"start":129,"end":780},{"cath_id":"4.10.800.20","chopping":"344-439","consensus_level":"medium","plddt":87.7636,"start":344,"end":439}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P23109","model_url":"https://alphafold.ebi.ac.uk/files/AF-P23109-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P23109-F1-predicted_aligned_error_v6.png","plddt_mean":86.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=AMPD1","jax_strain_url":"https://www.jax.org/strain/search?query=AMPD1"},"sequence":{"accession":"P23109","fasta_url":"https://rest.uniprot.org/uniprotkb/P23109.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P23109/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P23109"}},"corpus_meta":[{"pmid":"10086964","id":"PMC_10086964","title":"Common variant in AMPD1 gene predicts improved clinical outcome in patients with heart failure.","date":"1999","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/10086964","citation_count":114,"is_preprint":false},{"pmid":"12783984","id":"PMC_12783984","title":"Associations between cardiorespiratory responses to exercise and the C34T AMPD1 gene polymorphism in the HERITAGE Family Study.","date":"2003","source":"Physiological genomics","url":"https://pubmed.ncbi.nlm.nih.gov/12783984","citation_count":73,"is_preprint":false},{"pmid":"11028479","id":"PMC_11028479","title":"A common variant of the AMPD1 gene predicts improved cardiovascular survival in patients with coronary artery disease.","date":"2000","source":"Journal of the American College of Cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/11028479","citation_count":67,"is_preprint":false},{"pmid":"11408438","id":"PMC_11408438","title":"Regulation of skeletal muscle ATP catabolism by AMPD1 genotype during sprint exercise in asymptomatic subjects.","date":"2001","source":"Journal of applied physiology (Bethesda, Md. : 1985)","url":"https://pubmed.ncbi.nlm.nih.gov/11408438","citation_count":63,"is_preprint":false},{"pmid":"15677729","id":"PMC_15677729","title":"Frequency of the C34T mutation of the AMPD1 gene in world-class endurance athletes: does this mutation impair performance?","date":"2005","source":"Journal of applied physiology (Bethesda, Md. : 1985)","url":"https://pubmed.ncbi.nlm.nih.gov/15677729","citation_count":61,"is_preprint":false},{"pmid":"2398891","id":"PMC_2398891","title":"A novel pathway for alternative splicing: identification of an RNA intermediate that generates an alternative 5' splice donor site not present in the primary transcript of AMPD1.","date":"1990","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/2398891","citation_count":47,"is_preprint":false},{"pmid":"14499869","id":"PMC_14499869","title":"Decreased cardiac activity of AMP deaminase in subjects with the AMPD1 mutation--a potential mechanism of protection in heart failure.","date":"2003","source":"Cardiovascular research","url":"https://pubmed.ncbi.nlm.nih.gov/14499869","citation_count":36,"is_preprint":false},{"pmid":"25459662","id":"PMC_25459662","title":"Effects of pharmacological AMP deaminase inhibition and Ampd1 deletion on nucleotide levels and AMPK activation in contracting skeletal muscle.","date":"2014","source":"Chemistry & biology","url":"https://pubmed.ncbi.nlm.nih.gov/25459662","citation_count":35,"is_preprint":false},{"pmid":"24885427","id":"PMC_24885427","title":"AMPD1 rs17602729 is associated with physical performance of sprint and power in elite Lithuanian athletes.","date":"2014","source":"BMC genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24885427","citation_count":33,"is_preprint":false},{"pmid":"12117480","id":"PMC_12117480","title":"A G468-T AMPD1 mutant allele contributes to the high incidence of myoadenylate deaminase deficiency in the 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gene product in rat is alternatively spliced via a novel pathway: the 12-base exon 2 is excluded or included in a tissue-specific and stage-specific pattern. Alternative splicing proceeds through an RNA intermediate that generates an alternative 5' splice donor site at the exon 1-exon 2 boundary not present in the primary transcript. In human AMPD1, the analogous intermediate was a poor splicing substrate due to differences in exon 2 sequences, so human AMPD1 was not alternatively spliced.\",\n      \"method\": \"Transfection and minigene analysis, RNA intermediate characterization\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct RNA intermediate characterization with minigene constructs, replicated across rat and human sequences in a single rigorous mechanistic study\",\n      \"pmids\": [\"2398891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"Two steps in RNA processing control the ratio of AMPD1 alternative transcripts: (1) exon 2 recognition in the primary transcript (influenced by its small size and suboptimal splice sites, and by a slow-removal intron 2 that plays a permissive role); and (2) nucleocytoplasmic partitioning of an RNA intermediate (exon 1-exon 2-intron 2-exon 3) — nuclear retention of this intermediate is associated with accumulation of the exon-2-containing mature mRNA, while cytoplasmic escape leads to the alternative transcript.\",\n      \"method\": \"Transfection with native, mutant, and chimeric minigene constructs; subcellular fractionation of RNA intermediates\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods (minigene mutagenesis, nuclear/cytoplasmic fractionation) in a single rigorous mechanistic study\",\n      \"pmids\": [\"1922051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Muscle-specific expression of AMPD1 is controlled by two distinct cis-acting elements within 100 nucleotides of the transcriptional start site. One element (-100 to -79) acts as a tissue-specific enhancer resembling an MEF2 binding motif and interacts with proteins predominantly in myoblast/myotube nuclei; an A/T core within it is essential for enhancer activity. The second element (-60 to -40) acts as a stage-specific promoter element essential for muscle-specific expression, interacting with a protein restricted to differentiated myotube nuclei.\",\n      \"method\": \"Promoter deletion and mutation analysis by transfection, electrophoretic mobility shift assay (EMSA) for protein-DNA interaction\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis of cis elements combined with protein-DNA binding assays; multiple orthogonal methods in one study\",\n      \"pmids\": [\"8355716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Mutational analysis of AMPD1 demonstrated that the catalytic site and a regulatory site (likely an ATP binding site) are located in the highly conserved carboxy terminus. The amino terminus has a profound influence on catalytic activity and on binding of AMPD1 to myosin. Alternative splicing in the amino-terminal region generates isoforms exhibiting differential sensitivity to effector molecules such as ATP.\",\n      \"method\": \"Site-directed mutagenesis, deletion mutant expression and enzymatic assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro mutagenesis with activity assays but single lab, single study; inference on ATP binding site from activity data without direct structural validation\",\n      \"pmids\": [\"7802626\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Positive and negative elements mediate alternative splicing of AMPD1 exon 2. Exon 2 is intrinsically defective due to three combined defects: a suboptimal 3' splice acceptor site, a suboptimal 5' splice donor site, and its small size. The defective exon can only be recognized in the presence of the adjacent downstream intron. Improving any single defect relieves exon masking.\",\n      \"method\": \"Minigene transfection with systematic mutation of splice sites and exon sequences\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic minigene mutagenesis in a single lab, multiple constructs tested\",\n      \"pmids\": [\"10767559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Two novel missense mutations (R388W in exon 9 and R425H in exon 10) of AMPD1 result in undetectable AMPD enzyme activity when expressed prokaryotically, establishing these residues as functionally critical for catalytic activity and identifying AMPD1 as essential for normal skeletal muscle metabolism and development.\",\n      \"method\": \"Prokaryotic expression of mutant constructs with enzyme activity assay\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro expression with activity assay; single patient and single lab\",\n      \"pmids\": [\"11102975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In subjects homozygous for the AMPD1 mutant allele (MM), AMP deaminase activity was nearly absent in skeletal muscle during sprint exercise, resulting in no significant net ATP catabolism, no IMP accumulation, no postexercise plasma ammonia increase, and a dramatic ~25-fold increase in skeletal muscle adenosine compared to normal homozygotes (NN). Heterozygotes showed intermediate enzyme activity and IMP accumulation.\",\n      \"method\": \"Muscle biopsy with direct enzyme activity assay; nucleotide and adenosine measurement; plasma ammonia measurement during Wingate exercise test\",\n      \"journal\": \"Journal of applied physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct biochemical measurement in human muscle biopsies with multiple metabolic endpoints across three genotype groups\",\n      \"pmids\": [\"11408438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A second AMPD1 mutant allele, G468T (causing a Q156H substitution), was identified in compound heterozygous patients with myoadenylate deaminase deficiency. Baculoviral expression of the G468T mutant produced an enzyme with labile catalytic activity, and Western blot of patient muscle detected no immunoreactive AMPD1 polypeptide, demonstrating this allele is dysfunctional.\",\n      \"method\": \"Baculoviral expression with enzyme activity assay; Western blot of patient muscle biopsy\",\n      \"journal\": \"Neuromuscular disorders\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro expression with activity assay plus patient tissue validation; single lab\",\n      \"pmids\": [\"12117480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The C34T (Glu12Stop) nonsense mutation in AMPD1 reduces cardiac AMP-deaminase activity to approximately half of wild-type in heterozygous heart failure patients, without changing the activity of other adenosine-regulating enzymes. In homozygous mutant subjects, exercise-induced increase in blood adenosine was significant, whereas heterozygotes and wild-type subjects showed no significant change, indicating local cardiac metabolic effects predominate over systemic adenosine changes.\",\n      \"method\": \"Direct enzyme activity assay in cardiac tissue; SSCP genotyping; LC/MS measurement of blood adenosine\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct tissue enzyme activity measurement with genotype stratification, orthogonal systemic adenosine quantification by LC/MS\",\n      \"pmids\": [\"14499869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"A novel intronic deletion (IVS2-(4-7)delCTTT) in AMPD1 disrupts splicing, generating multiple alternatively spliced AMPD1 transcripts from patient skeletal muscle, including deletions in exon 3, complete deletion of exon 3 or exons 3-4, and activation of a cryptic splice site with an insertion at the 5' end of exon 4, demonstrating that intronic sequences flanking exon 3 are essential for normal AMPD1 splicing.\",\n      \"method\": \"AMPD1 mRNA characterization from skeletal muscle biopsy; allele-specific PCR; direct sequencing\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — mRNA-level characterization with sequencing in patient tissue; single case/lab, no in vitro reconstitution\",\n      \"pmids\": [\"16040263\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In subjects heterozygous for the 34C>T AMPD1 variant, forearm reactive hyperemia following ischemia was significantly augmented and ischemia-reperfusion injury (measured by 99mTc-annexin A5 scintigraphy detecting externalized phosphatidylserine) was significantly reduced compared to wild-type controls, consistent with increased ischemia-induced intracellular adenosine formation due to reduced AMPD1 activity.\",\n      \"method\": \"Venous occlusion plethysmography for forearm blood flow; 99mTc-annexin A5 scintigraphy for tissue injury quantification; in vivo human experiment with genotype-stratified cohorts\",\n      \"journal\": \"European heart journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal in vivo functional readouts in genotype-stratified human subjects; single lab\",\n      \"pmids\": [\"17376785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"AMPD1 genotype-deficient individuals (MM or compound heterozygotes) exhibited a greater and faster post-exercise blood flow response and a more than twice-faster fall in blood flow during recovery (T1/2: 7.8 min vs. 16.1 min in normal homozygotes) following sprint exercise, consistent with AMPD1 deficiency increasing adenosine formation and augmenting exercise-induced hyperemia.\",\n      \"method\": \"Common femoral artery ultrasonography before and after 30-s Wingate cycling test in genotype-stratified human subjects\",\n      \"journal\": \"European journal of applied physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct vascular imaging with functional outcome, genotype stratification; small sample, single lab\",\n      \"pmids\": [\"18224333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Pharmacological inhibition of AMPD (in isolated rat muscle) or genetic deletion of Ampd1 (in mouse skeletal muscle) potentiated exercise-induced rises in AMP, AMP:ATP ratio, and AMPK Thr172 and ACC Ser218 phosphorylation during electrical stimulation. Enhanced AMPK activation was moderate and muscle-type dependent (observed in soleus but not EDL from Ampd1 knockout mice), suggesting control by factors beyond adenine nucleotide changes alone.\",\n      \"method\": \"Pharmacological inhibition with direct nucleotide measurement; Ampd1 knockout mouse muscle (incubated EDL and soleus); immunoblot for AMPK/ACC phosphorylation; electrical stimulation\",\n      \"journal\": \"Chemistry & biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — genetic KO plus pharmacological inhibition with direct biochemical readouts (nucleotide levels, phosphorylation) in isolated muscle; multiple orthogonal approaches\",\n      \"pmids\": [\"25459662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Genetic disruption of AMPD1 in mice fed a high-fat diet leads to less severe insulin resistance, improved glucose tolerance, enhanced insulin clearance, and elevated phosphorylated AMPK in skeletal muscle compared to wild-type mice, demonstrating AMPD1 modulates insulin sensitivity through the AMP/AMPK axis in skeletal muscle.\",\n      \"method\": \"AMPD1-deficient mouse model; glucose tolerance test; insulin tolerance test; immunoblot for phospho-AMPK in skeletal muscle\",\n      \"journal\": \"BMC endocrine disorders\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with functional metabolic assays and biochemical phosphorylation readouts; single lab\",\n      \"pmids\": [\"25511531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"AMPD1 deficiency in mice on high-fat diet activates the AMPK/Akt/mTORC1/p70 S6 kinase axis specifically in skeletal muscle (not liver or white adipose tissue), and increases Raptor-bound mTOR in skeletal muscle, mechanistically linking AMPD1 to insulin signaling via this pathway.\",\n      \"method\": \"AMPD1-deficient mouse model; immunoprecipitation of mTOR followed by immunoblot for Raptor; phosphorylation assays for AMPK, Akt, p70 S6K by immunoblot\",\n      \"journal\": \"BMC endocrine disorders\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and phosphorylation assays with genetic KO model; single lab, no in vitro reconstitution\",\n      \"pmids\": [\"25887856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A knockout-first cassette insertion in the Ampd1 locus caused neonatal lethality in mice by disrupting expression of neighboring genes Man1a2 and Nras, not from AMPD1 loss per se. Mice with the critical exon deleted (Ampd1tm1d) survived to adulthood. E18.5 Ampd1tm1a/tm1a mice showed elevated AMP and near-complete absence of IMP in skeletal muscle, directly confirming AMPD1's catalytic role in AMP-to-IMP conversion in vivo.\",\n      \"method\": \"Conditional knockout mouse model; RNA-seq for neighboring gene expression; metabolite measurement (AMP, IMP) in skeletal muscle by biochemical assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with direct metabolite quantification and RNA-seq for off-target effects; multiple constructs and controls\",\n      \"pmids\": [\"27775065\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"AMPD1 knockdown (~35%) in mouse EDL (but not SOL) skeletal muscle impaired time-to-peak tension and half-relaxation time during maximal tetanic contractions. In EDL, AMPD1 knockdown exaggerated the AMP response to LOW and MOD duty-cycle contractions (+100% and +54%, respectively) and increased AMPK Thr172 phosphorylation (+25% and +34%) and downstream substrate phosphorylation, in an intensity-dependent manner.\",\n      \"method\": \"Electroporation of AMPD1-specific miRNA into contralateral EDL and SOL muscles in mice; isometric contractile function assay; immunoblot for AMPK/substrate phosphorylation; direct AMP measurement\",\n      \"journal\": \"Journal of applied physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — acute in vivo gene knockdown with contralateral muscle controls, multiple contractile and biochemical readouts, sex-stratified analysis\",\n      \"pmids\": [\"36107988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Berberine suppressed AMPD1 expression and promoted adenylosuccinate synthetase (ADSL) expression in fructose-treated rats and L6 cells, increasing intracellular AMP and AMP/ATP ratio to activate AMPK, thereby alleviating insulin resistance. This identifies AMPD1 as a mechanistic target of berberine in the AMP-AMPK pathway.\",\n      \"method\": \"In vivo rat model and L6 cell culture; gene expression by qPCR/Western blot; AMP/ATP ratio measurement; AMPK activation by phosphorylation assay\",\n      \"journal\": \"Food and chemical toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological manipulation with mechanistic biochemical readouts in both in vivo and cell models; single lab\",\n      \"pmids\": [\"36931587\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"AMPD1 encodes the skeletal muscle-specific isoform of AMP deaminase, which catalyzes the deamination of AMP to IMP and ammonia; its expression is controlled by MEF2-like and stage-specific cis-elements, and its exon 2 is subject to alternative splicing through an RNA-intermediate mechanism involving both exon recognition (governed by suboptimal splice sites and exon size) and nucleocytoplasmic partitioning; the catalytic and regulatory (ATP-binding) sites reside in the conserved carboxy terminus while the amino terminus influences catalytic activity and myosin binding; loss of AMPD1 activity (via the common C34T or other mutations) elevates intracellular AMP and adenosine in skeletal muscle and heart, augments AMPK activation, modulates mTORC1/p70 S6K and Akt signaling to improve insulin sensitivity, and enhances ischemia-induced vasodilation and cardioprotection through increased local adenosine production.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"AMPD1 encodes the skeletal-muscle isoform of AMP deaminase, which catalyzes the deamination of AMP to IMP and ammonia and thereby governs adenine nucleotide flux during muscle energy stress [#15, #6]. Its catalytic site and a regulatory ATP-binding site reside in the conserved carboxy terminus, while the amino terminus modulates catalytic activity and myosin binding [#3]. Muscle-restricted expression is driven by two cis-elements near the transcription start site — an MEF2-like tissue-specific enhancer and a stage-specific promoter element active in differentiated myotube nuclei [#2] — and the gene's exon 2 is subject to a distinctive alternative splicing mechanism controlled by exon recognition (suboptimal splice sites and small exon size) and by nucleocytoplasmic partitioning of an RNA intermediate [#0, #1, #4]. Loss of AMPD1 activity, through the common C34T (Glu12Stop) nonsense allele or other catalytic mutations, abolishes net ATP catabolism and IMP accumulation during exercise and instead elevates intracellular AMP and adenosine in skeletal muscle and heart [#6, #8, #5, #7]. The resulting rise in the AMP:ATP ratio potentiates AMPK Thr172 phosphorylation and downstream ACC, Akt, and mTORC1/p70 S6 kinase signaling, improving insulin sensitivity and glucose tolerance [#12, #13, #14], while increased local adenosine production enhances ischemia-induced vasodilation and confers cardioprotection [#10, #11]. Catalytically inactivating mutations cause myoadenylate deaminase deficiency [#7, #5].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Established that AMPD1 transcripts are diversified by a non-canonical splicing route, defining how isoform diversity arises and revealing a species difference between rat and human exon 2 handling.\",\n      \"evidence\": \"Transfection and minigene analysis with RNA intermediate characterization in rat and human sequences\",\n      \"pmids\": [\"2398891\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify trans-acting splicing factors\", \"Functional consequence of exon 2 inclusion/exclusion on enzyme activity not resolved here\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Resolved the two-step control of alternative transcript ratio — exon 2 recognition plus nucleocytoplasmic partitioning of an RNA intermediate — explaining how subcellular RNA localization gates the mature mRNA pool.\",\n      \"evidence\": \"Minigene mutagenesis with nuclear/cytoplasmic RNA fractionation\",\n      \"pmids\": [\"1922051\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Machinery driving nuclear retention vs cytoplasmic escape unidentified\", \"Physiological tissue context of partitioning not addressed\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Defined the cis-regulatory basis of muscle-specific transcription, identifying an MEF2-like enhancer and a differentiation-stage promoter element with their bound nuclear factors.\",\n      \"evidence\": \"Promoter deletion/mutation transfection and EMSA\",\n      \"pmids\": [\"8355716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding proteins not molecularly identified\", \"Interplay with splicing regulation not examined\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Mapped catalytic and regulatory domains, placing the active and ATP-binding sites in the carboxy terminus and assigning the amino terminus a role in activity and myosin binding.\",\n      \"evidence\": \"Site-directed mutagenesis and deletion mutant enzymatic assays\",\n      \"pmids\": [\"7802626\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ATP-binding site inferred from activity, not structurally validated\", \"Myosin-binding interface not delineated at residue level\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Showed exon 2 is intrinsically defective through three combined features and is only recognized with help from the adjacent intron, clarifying the molecular logic of exon masking.\",\n      \"evidence\": \"Systematic minigene splice-site and exon mutagenesis\",\n      \"pmids\": [\"10767559\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Trans-acting regulators of masking not identified\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identified disease-causing missense mutations (R388W, R425H) that abolish enzyme activity, linking specific residues to catalytic competence and to muscle metabolic dysfunction.\",\n      \"evidence\": \"Prokaryotic expression of mutants with activity assay\",\n      \"pmids\": [\"11102975\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single patient and single lab\", \"In vivo consequences not directly measured\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrated in human muscle that loss of AMPD1 activity abolishes exercise IMP/ammonia production and instead causes a ~25-fold adenosine rise, defining the in vivo metabolic phenotype of deficiency.\",\n      \"evidence\": \"Muscle biopsy enzyme/nucleotide/adenosine measurement and plasma ammonia during Wingate exercise across three genotypes\",\n      \"pmids\": [\"11408438\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling consequences not assessed here\", \"Vascular/clinical outcomes not measured\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Validated a second dysfunctional allele (G468T/Q156H) producing labile enzyme and absent muscle polypeptide, expanding the mutational spectrum of myoadenylate deaminase deficiency.\",\n      \"evidence\": \"Baculoviral expression with activity assay plus patient muscle Western blot\",\n      \"pmids\": [\"12117480\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Mechanism of protein instability not defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Extended the deficiency phenotype to the heart, showing C34T halves cardiac AMP-deaminase activity and that local cardiac adenosine effects predominate over systemic changes.\",\n      \"evidence\": \"Cardiac tissue enzyme assay with SSCP genotyping and LC/MS blood adenosine\",\n      \"pmids\": [\"14499869\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal link to heart-failure outcome not established\", \"Tissue adenosine not directly measured\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Provided in vivo human evidence that the C34T variant augments reactive hyperemia and reduces ischemia-reperfusion injury, connecting reduced AMPD1 activity to vascular and cytoprotective benefit.\",\n      \"evidence\": \"Forearm plethysmography and 99mTc-annexin A5 scintigraphy in genotype-stratified subjects\",\n      \"pmids\": [\"17376785\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Intracellular adenosine increase inferred not directly measured in this readout\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Confirmed augmented and faster-resolving exercise hyperemia in AMPD1-deficient individuals, reinforcing the adenosine-mediated vasodilatory consequence of deficiency.\",\n      \"evidence\": \"Femoral artery ultrasonography before/after Wingate cycling in genotype-stratified subjects\",\n      \"pmids\": [\"18224333\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Small sample, single lab\", \"Direct adenosine quantification not performed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Linked AMPD1 loss to energy-sensing signaling, showing deletion or inhibition potentiates exercise-induced AMP, AMP:ATP ratio, and AMPK/ACC phosphorylation in a muscle-type-dependent manner.\",\n      \"evidence\": \"Ampd1 knockout mouse muscle plus pharmacological inhibition with nucleotide and phospho-immunoblot readouts during electrical stimulation\",\n      \"pmids\": [\"25459662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Moderate effect implies additional regulators of AMPK beyond nucleotide levels\", \"Mechanism of soleus vs EDL difference unexplained\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated metabolic benefit of AMPD1 deficiency, with improved glucose tolerance and insulin clearance and elevated muscle phospho-AMPK on high-fat diet.\",\n      \"evidence\": \"AMPD1-deficient mice with glucose/insulin tolerance tests and phospho-AMPK immunoblot\",\n      \"pmids\": [\"25511531\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Tissue-specific contribution to whole-body phenotype not dissected\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the downstream signaling axis, showing AMPD1 deficiency activates AMPK/Akt/mTORC1/p70 S6K and increases Raptor-bound mTOR selectively in skeletal muscle.\",\n      \"evidence\": \"AMPD1-deficient mice with mTOR Co-IP for Raptor and phosphorylation immunoblots\",\n      \"pmids\": [\"25887856\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Co-IP without reciprocal validation\", \"Direct molecular coupling of AMPK to mTORC1 in this context not reconstituted\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Provided definitive in vivo confirmation of catalytic function and corrected a misattributed lethal phenotype, showing elevated AMP and near-absent IMP in muscle while neonatal lethality arose from disruption of neighboring Man1a2/Nras.\",\n      \"evidence\": \"Conditional knockout mouse alleles with RNA-seq of neighboring genes and AMP/IMP metabolite measurement\",\n      \"pmids\": [\"27775065\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adult-survivable allele's metabolic phenotype only partially characterized\", \"Residual AMP deaminase from other isoforms not quantified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed acute AMPD1 knockdown impairs contractile kinetics and intensity-dependently exaggerates AMP and AMPK signaling in fast-twitch EDL, tying AMPD1 to muscle performance and energetic sensing.\",\n      \"evidence\": \"Contralateral in vivo miRNA electroporation of EDL/SOL with contractile and phospho-immunoblot readouts and direct AMP measurement\",\n      \"pmids\": [\"36107988\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Fiber-type basis of EDL-specific effect unresolved\", \"Chronic vs acute knockdown effects may differ\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified AMPD1 as a pharmacological target, with berberine suppressing AMPD1 (and inducing ADSL) to raise AMP/ATP ratio, activate AMPK, and relieve insulin resistance.\",\n      \"evidence\": \"Rat and L6 cell models with expression, AMP/ATP ratio, and AMPK phosphorylation readouts\",\n      \"pmids\": [\"36931587\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct drug-AMPD1 binding not demonstrated; effect may be indirect transcriptional\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The trans-acting factors controlling exon 2 splicing and RNA partitioning, the proteins binding the muscle-specific cis-elements, and the precise molecular coupling of AMP accumulation to mTORC1 remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Splicing regulators unidentified\", \"Transcription factors at cis-elements not molecularly defined\", \"AMPK-to-mTORC1 coupling not reconstituted\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [6, 15, 5, 7]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [6, 15]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [6, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [6, 15, 13]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [12, 14]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MYH (myosin)\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}