Hypothesis

Enhancing CARnitine Acetyltransferase (CRAT) in senescent immune cells breaks the mitochondria‑inflammaging loop and extends healthspan

Mechanistic rationale

Age‑associated immune cells accumulate damaged mitochondria that release mtDNA into the cytosol, activating the cGAS‑STING pathway and driving inflammaging [2]. This process is amplified when inflammatory cytokines impair mitochondrial OXPHOS and autophagy in tissues such as skeletal muscle [1]. A key node linking mitochondrial acetyl‑CoA flux to inflammasome activity is the carnitine acetyltransferase (CRAT) enzyme, which buffers acetyl‑CoA levels by transferring acetyl groups to carnitine. When CRAT activity falls, excess acetyl‑CoA promotes protein acetylation of NLRP3, lowering its activation threshold and increasing ROS‑driven mtDNA release [3]. Conversely, boosting CRAT restores acetyl‑CoA/carnitine balance, reduces NLRP3 acetylation, limits mtDNA efflux, and dampens cGAS‑STING signaling.

We propose that restoring CRAT specifically in senescent immune cells uncouples the immune‑driven arm of aging from downstream tissue dysfunction, thereby slowing aging phenotypes even without altering systemic carnitine levels.

Testable predictions

1. Genetic overexpression of CRAT in hematopoietic stem cells (HSCs) of aged mice will reduce the proportion of senescent CD8+ T cells and macrophages expressing p16^INK4a^ and SA‑β‑gal.
2. These mice will show lower serum IL‑6, TNF‑α, and circulating cell‑free mtDNA compared with age‑matched controls.
3. Mitochondrial ROS production in sorted immune cells will decrease, and NLRP3 acetylation levels will be reduced.
4. Functional readouts such as grip strength, treadmill endurance, and frailty index will improve, and median lifespan will increase by at least 15 %.
5. The benefits will persist when animals are placed on a carnitine‑deficient diet, demonstrating independence from systemic carnitine pools.

Experimental design

• Use a Vav‑Cre‑inducible CRAT transgene (Rosa26‑LSL‑CRAT) crossed to aged (20‑month) mice; induce expression at 18 months via tamoxifen.
• Include control groups: Vav‑Cre‑only, tamoxifen‑treated wild‑type, and a group receiving L‑carnitine supplementation.
• Primary outcomes: flow cytometry for senescence markers, ELISA for cytokines, qPCR for cGAS‑STING transcripts, Seahorse assay for mitochondrial ROS, Western blot for acetyl‑NLRP3.
• Secondary outcomes: physiological performance tests, frailty scoring, survival monitoring.
• Statistical plan: power analysis targeting n = 15 per group to detect 20 % changes with α = 0.05, power = 0.8.

Potential outcomes and falsifiability

If CRAT overexpression fails to reduce immune senescence markers, inflammasome activity, or circulating mtDNA, and does not improve physical performance or lifespan, the hypothesis is falsified. Conversely, observing the predicted improvements would support the notion that immune‑intrinsic metabolic remodeling can uncouple inflammaging from systemic aging, positioning CRAT as a leverage point for geroprotective intervention.