Hypothesis

Aging-associated lysosomal dysfunction accelerates degradation of the mitochondrial citrate carrier (CiC/SLC25A1), depleting nuclear acetyl-CoA and driving histone hypoacetylation. We propose that pharmacological or genetic activation of the lysosomal master regulator TFEB restores CiC stability by enhancing lysosomal proteostasis and transcriptionally upregulating CiC expression, thereby replenishing nuclear acetyl-CoA from mitochondrial citrate. This mechanism operates in parallel with acetate-fueled nuclear ACSS2 activity, creating a bipartite supply route that can synergistically elevate histone acetylation at neuroprotective and osteogenic loci. Consequently, combined TFEB activation (e.g., via mTORC1 inhibition or TFEB overexpression) and partial ACLY inhibition (e.g., low-dose CMS121) should yield greater lifespan extension and reduced aging biomarkers than either intervention alone, without triggering global hyperacetylation-associated oncogenesis.

Mechanistic rationale

1. TFEB sustains CiC levels – TFEB drives lysosomal biogenesis and upregulates chaperone-mediated autophagy, reducing misfolded protein load that targets CiC for lysosomal degradation. TFEB also directly binds promoters of SLC25A1 (CiC) and ACSS2, increasing their transcription (supported by ChIP-seq data showing TFEB occupancy at metabolic gene loci).
2. Dual acetyl-CoA sources – Restored CiC exports citrate to cytosol where ACLY generates acetyl-CoA; simultaneously, acetate supplied exogenously fuels nuclear ACSS2. The two pathways converge on nuclear acetyl-CoA pools, providing redundancy that buffers against age-related fluctuations in mitochondrial output.
3. Epigenetic outcome – Elevated nuclear acetyl-CoA increases H3K9ac and H3K27ac at promoters of TFEB target genes (e.g., lysosomal genes, antioxidant enzymes) and osteogenic regulators (Runx2, Sox9), establishing a positive feedback loop that reinforces lysosomal function and chromatin openness.
4. Safety window – Partial ACLY inhibition prevents excess cytosolic acetyl-CoA diversion to lipid synthesis, limiting oncogenic lipogenesis, while TFEB-mediated lysosomal activation promotes clearance of damaged organelles, reducing tumorigenic stress.

Experimental plan (testable & falsifiable)

In vitro: Treat senescent human mesenchymal stem cells with acetate (5 mM) ± TFEB overexpression (lentiviral) ± low-dose CMS121 (0.5 µM). Measure:

• CiC protein half-life by cycloheximide chase + immunoblot.
• Nuclear acetyl-CoA levels via LC-MS.
• Global H3K9ac/H3K27ac by ELISA.
• Osteogenic differentiation (Alizarin Red) and senescence-associated β-galactosidase.

In vivo: Use SAMP8 mice (accelerated aging) divided into four groups (n=15 each): control, TFEB overexpression (AAV-TFEB, liver-brain), CMS121 low dose (10 mg/kg/day), combined TFEB + CMS121. Monitor over 12 months:

• Survival curves.
• Brain and bone histology (H3K9ac, neuronal markers, trabecular bone volume).
• Mitochondrial citrate export (CiC immunoblot of nuclear fractions).
• Cancer incidence (histopathology).

Predictions: Combined treatment yields (i) ≥30 % increase in median lifespan vs. control, (ii) ≥2‑fold rise in nuclear acetyl-CoA, (iii) restored H3K9ac at neuroprotective promoters, (iv) reduced senescence markers, and (v) no increase in tumor burden relative to single-agent groups.

Falsifiability: If TFEB activation fails to stabilize CiC (no change in CiC half-life or nuclear citrate export) or if combined therapy does not surpass the efficacy of either monotherapy in lifespan or epigenetic marks, the hypothesis is refuted.

Potential impact

Demonstrating a lysosomal-Citrate carrier axis would reveal a novel node linking organelle quality control to epigenetic metabolism, guiding combinatorial gerotherapeutic strategies that avoid the pitfalls of single-pathway modulation.

References [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC12402629/ [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC8068152/ [3] https://www.genengnews.com/news/epigenetic-changes-in-aging-stem-cells-rejuvenated-by-acetate/ [4] https://pubmed.ncbi.nlm.nih.gov/33917812/ [5] https://elifesciences.org/articles/47866