Hypothesis

Epigenetic derepression of complement genes is the upstream driver that links epigenetic drift to multiple hallmarks of aging via mitochondrial C3aR signaling.

Mechanistic model

1. Age‑dependent loss of H3K27me3 at promoters of C3, C5aR1 and related complement components in microglia and astrocytes leads to transcriptional derepression.
2. Secreted C3a and C5a bind the mitochondrial isoform of C3aR (mtC3aR) on neurons, skeletal muscle and endothelial cells.
3. mtC3aR activation inhibits complex I of the electron transport chain, lowering ATP production and increasing mitochondrial ROS.
4. Energy deficit and oxidative stress trigger proteostatic collapse, activation of NF‑κB‑driven inflammasome signaling, and senescence‑associated secretory phenotype (SASP).
5. These downstream events manifest as the classic hallmarks: mitochondrial dysfunction, chronic inflammation, loss of proteostasis, cellular senescence, stem cell exhaustion, and altered intercellular communication.

Testable predictions

• Prediction 1: In aged mouse brain, ChIP‑seq will show reduced H3K27me3 enrichment at the C3 promoter correlating with elevated C3 protein in microglia.
• Prediction 2: Targeted restoration of H3K27me3 using CRISPR‑dCas9‑EZH2 (or a small‑molecule EZH2 activator) specifically in GFAP+ astrocytes will normalize C3 secretion, improve mitochondrial respiration (measured by Seahorse OCR), and reduce ROS.
• Prediction 3: Pharmacological blockade of mtC3aR (with a selective antagonist) in aged mice will rescue ATP levels and extend healthspan even when epigenetic derepression persists.
• Prediction 4: Simultaneous epigenetic rescue and mtC3aR antagonism will produce additive improvements across multiple hallmarks (e.g., grip strength, cognitive performance, frailty index) compared with either intervention alone.

Falsifiability

If epigenetic restoration fails to lower complement expression or if mtC3aR blockade does not ameliorate mitochondrial dysfunction despite confirmed target engagement, the hypothesis that epigenetic drift drives aging primarily through complement‑mediated mitochondrial inhibition would be refuted.

Broader impact

Demonstrating a single upstream node (epigenetic control of complement) that coordinates multiple age‑related pathologies would shift therapeutic strategy from symptomatic treatment to precision epigenomic reprogramming, complementing recent successes with epigenetic clocks as biomarkers.

Key references

• Epigenetic drift drives transcriptional dysregulation loss of H3K36me3 silencing
• PRC2 manipulation rescues glycolysis and extends lifespan in Drosophila PRC2 complex restores glycolysis and extends lifespan
• Complement C3a elevation in AMD and mitochondrial inhibition systemic C3a elevation in AMD
• Epigenetic loss leads to mitochondrial/protein synthesis downregulation age-related loss of epigenetic fidelity drives multiple downstream hallmarks
• Proteostatic collapse as upstream driver of cell aging proteostatic collapse acts as a driver of cell aging upstream of other failures
• Lack of single‑node interventions reversing all hallmarks no interventions targeting a single upstream node have yet demonstrated reversal of all hallmarks simultaneously