ACAA2

ACAA2 is a mitochondrial thiolase that catalyzes the final step of fatty acid β-oxidation (FAO), and its abundance and activity serve as a regulatory node coupling lipid catabolism to cellular stress responses (PMID:35813467, PMID:39733992). In hepatocytes, Egr1 transcriptionally upregulates Acaa2 to drive mitochondrial respiration and FAO, and Acaa2 is the downstream effector through which Egr1 protects against acetaminophen-induced liver injury (PMID:35813467). ACAA2 protein stability is controlled by the ubiquitin–proteasome system: assembly of a Cullin1/FBXO42 E3 ligase complex promotes its ubiquitin-mediated degradation, which is restrained by CAND1, and preserving ACAA2 limits non-alcoholic fatty liver disease (PMID:37528093). ACAA2 thiolase activity is further tuned by post-translational and protein–protein inputs — the mitochondrial Shc isoform p46Shc represses its activity, reducing β-oxidation and β-hydroxybutyrate output while raising reactive oxygen species, and lactylation modulates its activity during cardiac hypertrophic stress (PMID:39733992, PMID:40858063). Consistent with a protective metabolic role, loss of ACAA2 in cardiomyocytes causes lipid droplet accumulation, impaired oxidative respiration, and heightened oxidative stress (PMID:40858063, PMID:40149900). Beyond its mitochondrial role, ACAA2 also localizes to the nucleus, where it binds thyroid hormone receptor β1 (TRβ1) and acts as a ligand-dependent transcriptional coactivator without altering TR DNA binding, and OGT-mediated O-GlcNAc glycosylation governs its nucleocytoplasmic distribution (PMID:34474245, PMID:38656551). ACAA2 expression is additionally set by miRNA regulatory axes, and gain or loss of ACAA2 modulates proliferation, apoptosis, and tumor behavior in epithelial and cancer cells (PMID:29323178, PMID:38656551).

1. 2018 Medium

   Established that ACAA2 levels are set by miRNA control and that its level dictates lipid synthesis and cell fate, framing it as more than a constitutive housekeeping enzyme.

   Evidence Dual-luciferase miR-152 target validation plus ACAA2 overexpression/knockdown in mammary epithelial cells

   PMID:29323178

   Open questions at the time

   • Does not address thiolase mechanism or whether phenotypes depend on FAO flux
   • Single cell type, no in vivo confirmation
2. 2021 Medium

   Revealed a non-canonical nuclear function for this mitochondrial enzyme by identifying it as a ligand-dependent coactivator of TRβ1, linking metabolic enzyme identity to transcriptional regulation.

   Evidence GST pull-down on cardiac tissue with LC-MS/MS, luciferase reporter assay, nuclear localization confirmation

   PMID:34474245

   Open questions at the time

   • Mechanism of nuclear import not defined
   • Direct target genes of the ACAA2/TRβ1 complex not identified
   • Whether thiolase catalytic activity is required for coactivation unknown
3. 2022 High

   Defined an upstream transcriptional driver, showing Egr1 directly upregulates Acaa2 to sustain FAO and that ACAA2 is the obligate downstream mediator of Egr1 hepatoprotection.

   Evidence ChIP-seq, RNA-seq, liver-specific Egr1 KO and adenoviral OE, Acaa2 knockdown epistasis, Seahorse and fatty acid analysis

   PMID:35813467

   Open questions at the time

   • Does not address post-transcriptional control of ACAA2
   • Cardiac/other tissue generalization untested in this study
4. 2022 Low

   Added a ceRNA layer to ACAA2 regulation, showing a lncRNA/miRNA axis relieves repression of ACAA2 to suppress tumor progression.

   Evidence Luciferase, RNA immunoprecipitation, FISH, western blot, and functional assays in esophageal squamous cell carcinoma (lncRNA-centric study)

   PMID:36162992

   Open questions at the time

   • Primary subject is the lncRNA, not ACAA2; direct enzymatic relevance not tested
   • Single lab, single study
   • ACAA2-specific causality not isolated from the broader axis
5. 2023 High

   Identified the degradation machinery controlling ACAA2 stability, defining a Cullin1/FBXO42 E3 ligase complex opposed by CAND1 and linking ACAA2 preservation to protection against NAFLD.

   Evidence Reciprocal Co-IP of the Cullin1/FBXO42/ACAA2 complex, hepatocyte-specific CAND1 KO/KI mice, ACAA2 overexpression rescue

   PMID:37528093

   Open questions at the time

   • Ubiquitination site(s) on ACAA2 not mapped
   • Substrate-recognition determinant of FBXO42 for ACAA2 unknown
6. 2024 Medium

   Showed that ACAA2 thiolase activity is directly repressible, with p46Shc inhibiting activity to reduce β-oxidation and ketogenesis while promoting ROS and mitochondrial damage.

   Evidence In vitro thiolase activity assay, p46Shc-inducible and dominant-negative transgenic mice, Oroboros respirometry, electron microscopy

   PMID:39733992

   Open questions at the time

   • Whether p46Shc physically binds ACAA2 directly not established
   • Molecular basis of activity inhibition unresolved
7. 2024 Medium

   Demonstrated that O-GlcNAcylation by OGT controls ACAA2 nucleocytoplasmic distribution and that ACAA2 abundance drives ovarian cancer growth, connecting a post-translational modification to its dual localization and oncogenic output.

   Evidence OGT overexpression with immunofluorescence/fractionation, ACAA2 gain/loss of function, nude mouse xenograft, RNA-seq implicating DIXDC1/WNT-β-Catenin

   PMID:38656551

   Open questions at the time

   • O-GlcNAc site(s) not mapped
   • Direct link between glycosylation, localization, and the WNT axis remains correlative
   • Whether nuclear ACAA2 here is the TRβ1 coactivator pool untested
8. 2025 Medium

   Extended modification-based control to the heart, showing ACAA2 lactylation changes during hypertrophic stress and that ACAA2 loss worsens lipid accumulation, oxidative stress, and respiratory impairment, with transcriptional input from FOXO4.

   Evidence Immunoprecipitation for lactylation, RNAi knockdown and overexpression in cardiomyocytes, Seahorse, ELISA substrate assays, FOXO4 knockdown epistasis, Oil Red O staining

   PMID:40149900 PMID:40858063

   Open questions at the time

   • Lactylation site(s) and effect on catalytic mechanism not mapped
   • Causal contribution of lactylation vs. abundance to phenotype not separated
   • FOXO4 regulation of ACAA2 not shown to be direct

• How ACAA2's mitochondrial thiolase function and its nuclear TRβ1 coactivator role are coordinated — and whether the array of modifications (ubiquitination, O-GlcNAc, lactylation) constitute a unified switch governing localization and activity — remains unresolved.
• No structural model integrating catalytic and coactivator functions
• Modification crosstalk not dissected
• Tissue-specific hierarchy of regulators unknown