Spirulina and Acetyl-CoA Metabolism: ACLY, Histone Acetylation, and Metabolic Epigenetics

Acetyl-CoA Sources: ACLY, ACSS2, and PDH

Nuclear/cytosolic acetyl-CoA is generated by three principal routes: (1) ATP-citrate lyase (ACLY): citrate exported from the TCA cycle is cleaved to acetyl-CoA and oxaloacetate. ACLY is phosphorylated and activated by Akt Ser454, coupling PI3K signalling to acetyl-CoA production for lipogenesis and histone acetylation; (2) acetyl-CoA synthetase 2 (ACSS2): acetate (from histone deacetylation, dietary, or microbial) is converted to acetyl-CoA using ATP; (3) nuclear-cytoplasmic PDH complex (PDH/PDHA1): a fraction of pyruvate dehydrogenase translocates to the nucleus under growth signals, generating acetyl-CoA directly from pyruvate. AMPK phosphorylates and inactivates ACLY (Ser455, conflicting literature; AMPK Ser454 from Akt is activating), and activates PDHA kinase PDK4 (reducing PDH flux) while suppressing lipogenesis.

Histone Acetyltransferases: CBP/p300, PCAF, Tip60

Histone acetyltransferases (HATs/KATs) transfer the acetyl group from acetyl-CoA to histone lysines, neutralising the positive charge, loosening chromatin, and creating binding sites for bromodomain reader proteins: CBP (CREBBP) and p300 (EP300) are transcriptional co-activators for NF-kB/p65 (p300 acetylates p65 Lys122/123/218/221/ 310, stabilising it), HIF-1alpha (p300/CBP Cys800, critical for VEGF induction), and p53 (Lys373/382 acetylation, activating). PCAF (KAT2B) acetylates H3K9 and H3K14. KAT5 (Tip60/PLIP) acetylates H4K16 (activating) and ATM Lys3016 (activating DDR). Nrf2 requires CBP/p300 for its transactivation activity; PCB-Nrf2-CBP interaction competes with NF-kB-p300 co-activation.

AMPK and the Acetyl-CoA Epigenetic Checkpoint

During nutrient depletion, AMPK activation suppresses ACLY (reducing acetyl-CoA from citrate), induces SIRT1 (via NAMPT-NAD+, deacetylating histones and transcription factors), and activates HDAC class IIa (via AMPK phosphorylation, nuclear export). The net effect is global histone deacetylation and chromatin compaction at growth genes (c-Myc targets, cyclin D1, ACLY itself), while maintaining open chromatin at AMPK/Nrf2 target loci through Nrf2-CBP interactions. Spirulina's AMPK activation thus reprogrammes the epigenome toward stress-resistance and catabolic gene programmes.

BET Bromodomain Proteins: Reading Acetyl-Lysine

Bromodomain and extra-terminal (BET) proteins BRD2, BRD3, and BRD4 read H3K27Ac and H4K16Ac marks, recruiting RNA Pol II to super-enhancers driving oncogenes (c-Myc, BCL-2) and inflammatory genes (IL-6, MCP-1). BRD4-NF-kB interaction at the IL-6 promoter is disrupted by BET inhibitors (JQ1, ABBV-075). Spirulina's suppression of NF-kB-p300-driven H3K27Ac at inflammatory gene super-enhancers (via PCB IKKbeta inhibition) reduces BRD4 recruitment, effectively mimicking partial BET inhibitor effects without direct BRD4 binding.

Protein Acetylation Beyond Histones

Protein acetylation occurs on thousands of non-histone proteins: SIRT1 deacetylates p53 Lys382 (pro-apoptotic deactivation), FOXO Lys (nuclear retention for anti- oxidant gene induction), PGC-1alpha (activating SIRT1 deacetylation at Lys183/ Lys450/Lys480), and AMPK-beta1 (Lys43 CBP acetylation, AMPK complex stabilisation). CBP/p300 acetylation of PCNA Lys164 switches DNA damage repair from error-prone TLS to accurate HR. The spirulina-Nrf2-CBP/p300 interaction thus has broad non-histone acetylation consequences affecting DNA repair, metabolism, and apoptosis regulation.

Acetate and Metabolic Flexibility

Under glucose deprivation, tumour cells upregulate ACSS2 to scavenge acetate (from fermentation or histone deacetylation), maintaining acetyl-CoA for both histone acetylation and fatty acid synthesis. ACSS2 nuclear translocation occurs under hypoxia. Spirulina's gut microbiome effects (butyrate production by Bifidobacterium/Firmicutes from spirulan prebiotics) provide both a HDAC inhibitor (butyrate) and an acetate source (from butyrate oxidation), influencing nuclear acetyl-CoA via ACSS2, linking the microbiome effects back to chromatin regulation.