PYGL

PYGL encodes liver glycogen phosphorylase, the enzyme that mobilizes hepatic glycogen by liberating glucose-1-phosphate, and loss-of-function mutations in its conserved catalytic residues cause glycogen storage disease type VI (Hers disease) with hepatic glycogen accumulation (PMID:9529348). Its activity is positively controlled by reciprocal covalent modification: O-GlcNAcylation at Ser430 and phosphorylation at the activating Ser15 mutually reinforce one another, with both modifications rising under glucagon or hypoxic conditions and falling under glucose/insulin (PMID:34939084). Beyond hormonal control, PYGL transcription is driven by HIF1α under hypoxia (PMID:37063425, PMID:38545181) and by FOXO3a binding directly to its promoter (PMID:35439639), and is repressed by promoter hypermethylation in a model of maternal diet-induced metabolic dysfunction (PMID:34673295). By processing glycogen stores to feed glycolysis, PYGL couples glycogenolysis to downstream cellular programs: it fuels NADPH oxidase-driven oxidative stress and neutrophil-mediated inflammation (PMID:32126244), sustains neuronal glycolytic plasticity and the synaptic vesicle cycle [PMID:bio_10.1101_2025.04.10.648039], and in multiple cancers drives glycolytic flux that promotes EMT, metastasis, proliferation, and therapy resistance (PMID:37063425, PMID:39525037, PMID:38545181, PMID:41974649). PYGL physically interacts with lactate dehydrogenase A (LDHA), an interaction that can be disrupted pharmacologically to accelerate LDHA degradation and reduce glycolytic flux (PMID:42056865).

1. 1998 High

   Establishing that PYGL is a disease gene answered whether hepatic glycogen accumulation could arise from a defect in the glycogen-degrading enzyme itself, linking PYGL catalytic function to human metabolic disease.

   Evidence Sequencing of GSD VI patients identifying active-site missense mutations (N338S, N376K) at absolutely conserved residues and splice-site mutations

   PMID:9529348

   Open questions at the time

   • Does not resolve the enzyme's regulatory inputs
   • No structural mechanism for how each mutation impairs catalysis
2. 2022 High

   Identification of Ser430 O-GlcNAcylation answered how nutrient signaling tunes PYGL activity, revealing a post-translational layer beyond classical Ser15 phosphorylation.

   Evidence Site-directed mutagenesis of Ser430, OGT/OGA manipulation, phosphorylation and phosphorylase activity assays in HEK293T and HCT116 cells

   PMID:34939084

   Open questions at the time

   • Mechanism of mutual reinforcement between O-GlcNAcylation and pSer15 not structurally defined
   • Physiological significance in liver not tested
3. 2022 Medium

   Demonstrating direct FOXO3a binding to the PYGL promoter answered how transcriptional inputs couple glycogenolysis to lipogenic metabolism under selenium supranutrition.

   Evidence ChIP of FOXO3a at the PYGL promoter and SELENOF/PYGL RNAi epistasis with lipid accumulation readouts

   PMID:35439639

   Open questions at the time

   • Generality of the SELENOF-AKT1-FOXO3a-PYGL axis beyond selenium context unknown
   • Direct enzymatic contribution to lipogenesis not isolated
4. 2021 Medium

   Linking Pygl promoter methylation to maternal diet answered how environmental/epigenetic programming can suppress hepatic glycogenolysis and produce offspring metabolic defects.

   Evidence Mouse maternal high-fat/high-sucrose dietary model with bisulfite methylation analysis, expression profiling, and osteocalcin rescue via CREBH/ATF4

   PMID:34673295

   Open questions at the time

   • Causal contribution of Pygl downregulation vs other genes to phenotype not isolated
   • Human relevance of the methylation event unestablished
5. 2020 Medium

   Inhibiting Pygl in zebrafish answered whether glycogen processed by phosphorylase functions as a substrate source for inflammatory oxidative stress, connecting glycogenolysis to NADPH oxidase and NF-kB.

   Evidence Pharmacological Pygl inhibition in zebrafish skin inflammation models with neutrophil, ROS, and Nfkb readouts

   PMID:32126244

   Open questions at the time

   • Mechanistic link from glucose-1-phosphate to NADPH oxidase substrate supply not biochemically traced
   • Mammalian inflammation relevance untested
6. 2023 Medium

   Placing PYGL downstream of HIF1α answered how hypoxic tumor cells mobilize glycogen to feed glycolysis and drive EMT and metastasis.

   Evidence HIF1α and PYGL gain/loss-of-function, glycogen and glycolysis assays, 2-DG rescue, and in vivo liver metastasis models in pancreatic cancer

   PMID:37063425

   Open questions at the time

   • Single cancer type
   • Whether glycogenolysis is rate-limiting for metastasis in vivo not quantified
7. 2024 Medium

   Confirming HIF1α-driven PYGL transcription across glioma and ccRCC established the hypoxia-PYGL-glycolysis axis as a recurrent oncogenic dependency and a therapeutic target for restoring drug sensitivity.

   Evidence ChIP of HIF1α at PYGL promoter, PYGL knockdown with Seahorse/apoptosis assays, and CP-91149 inhibition restoring sunitinib sensitivity

   PMID:38545181 PMID:39525037

   Open questions at the time

   • No structural model of HIF1α occupancy at the PYGL locus
   • Resistance-reversal mechanism beyond glycolytic suppression not defined
8. 2026 High

   Identifying PYGL's allosteric inhibitor binding site and its physical interaction with LDHA answered how PYGL is coupled to glycolytic flux at the protein level, defining a druggable PYGL-LDHA node.

   Evidence Molecular docking, SPR, CETSA, mutagenesis of Glu162/Arg247/Glu273, Co-IP of PYGL-LDHA, proteasome rescue, and xenografts in NSCLC

   PMID:42056865

   Open questions at the time

   • Reciprocal validation and stoichiometry of the PYGL-LDHA complex not fully resolved
   • Whether the interaction is direct or scaffold-mediated unclear
9. 2026 Medium

   Placing PYGL downstream of extracellular ATP-P2Y12-AhR signaling answered how a receptor-driven pathway converges on glycogenolysis to confer endocrine therapy resistance.

   Evidence P2Y12/AhR inhibition, PYGL knockdown, glycolysis and endocrine resistance assays in ER+ breast cancer cells and organoids

   PMID:41974649

   Open questions at the time

   • Direct transcriptional vs indirect control of PYGL by AhR not distinguished
   • Mechanism of glycolysis-to-resistance coupling not defined
10. 2025 Medium

    Demonstrating a cell-autonomous neuronal requirement for the PYGL ortholog answered whether neuronal glycogenolysis sustains glycolytic plasticity and synaptic function under metabolic stress.

    Evidence RNAi screen in C. elegans with single-neuron HYlight glycolytic sensor imaging, mitochondrial epistasis, and synaptic vesicle cycle assays (preprint)

    PMID:bio_10.1101_2025.04.10.648039

    Open questions at the time

    • Ortholog study not yet peer-reviewed
    • Conservation of neuronal glycogenolytic plasticity in mammals untested

• How the multiple transcriptional, epigenetic, and post-translational inputs are integrated to set PYGL activity in a tissue- and context-specific manner, and the structural basis of its LDHA interaction, remain open.
• No structural model integrating Ser15/Ser430 modifications with catalysis
• Direct vs indirect nature and stoichiometry of PYGL-LDHA complex unresolved
• Tissue-specific hierarchy of HIF1α, FOXO3a, and methylation control unknown