Timed IGF-1 Pulses Enhance Mitochondrial Genome Repair in Aging via AMPK‑POL G Axis

Intermittent, low‑dose IGF-1 administration aligned with the nadir of endogenous GH secretion can improve mitochondrial genome stability in older adults without provoking chronic insulin resistance. We're proposing that brief IGF-1 spikes activate the IGF‑1R/PI3K/Akt pathway transiently, which in turn phosphorylates and activates AMPK through LKB1 when cellular ATP dips during the trough of GH secretion. Activated AMPK phosphorylates POLG and TFAM, boosting mitochondrial replication and repair of lesions 5. This repair shift reduces heteroplasmy load and lowers senescence markers p16 and p21, mirroring the acute protective effect observed in vitro 2. Because the IGF-1 signal is short‑lived, downstream mTORC1 activity doesn't sustain the proliferative shift that drives insulin resistance; instead, the concurrent rise in AMPK suppresses S6K1, preserving insulin signaling 3. Sex differences may emerge because estrogen amplifies AMPK activation, predicting a larger benefit in post‑menopausal women receiving estradiol replacement alongside the IGF-1 pulse regimen.

To test this hypothesis we propose a randomized, double‑blind, crossover trial in adults aged 65‑80 with baseline mtDNA heteroplasmy >5 % (measured by duplex sequencing). Participants receive either subcutaneous recombinant IGF-1 (20 µg) or placebo at 02:00 h, when endogenous GH is at its lowest, three times per week for 12 weeks, separated by a 12‑week washout. Primary outcomes are change in mtDNA copy number, heteroplasmy fraction, and POLG/TFAM protein levels in peripheral blood mononuclear cells. Secondary outcomes include fasting insulin, HOMA‑IR, lean body mass (DXA), circulating senescence‑associated secretory phenotype cytokines (IL‑6, TNF‑α), and physical performance (gait speed, hand‑grip strength). We're predicting the IGF-1 pulse arm will show a ≥15 % rise in mtDNA copy number, a ≥20 % drop in heteroplasmy, and improved insulin sensitivity relative to placebo, without increases in fasting glucose or adiposity. Failure to detect these changes would falsify the mechanistic link between timed IGF-1, AMPK‑POL G activation, and mitochondrial genome repair.

If confirmed, this approach can't be seen as contradictory to the longevity benefits of reduced IGF-1 signaling; rather, it shows that strategic, hormonally timed IGF-1 exposure can harness the repair arm of the pathway while avoiding the metabolic costs of chronic elevation. This strategy could be combined with existing AMPK activators (exercise, metformin) to amplify mitochondrial protection and delay the onset of sarcopenia and metabolic disease in aging populations.