Hypothesis

Endothelial-specific microRNA‑126 (miR-126) functions as an upstream controller that synchronizes the hallmarks of aging by maintaining endothelial nitric oxide (NO) bioavailability. When miR-126 declines with age, eNOS becomes uncoupled, shifting from NO to superoxide production, which triggers a cascade of oxidative stress, NF‑κB‑mediated inflammation, cellular senescence, and mitochondrial dysfunction. Crucially, miR-126 loss also alters the cargo of endothelial-derived extracellular vesicles (EVs), enriching them with pro‑senescence miRNAs and DAMPs that disseminate the vascular stress signal to distant tissues.

Mechanistic Rationale

1. miR-126 suppresses ADAM9 and SPRED1, thereby stabilizing VEGF‑PI3K‑Akt signaling that phosphorylates eNOS at Ser1177, promoting coupled NO synthesis.
2. In aged endothelium, reduced miR-126 lifts repression of ADAM9, increasing shedding of VEGF receptors and diminishing Akt activation, leading to eNOS uncoupling.
3. Uncoupled eNOS elevates superoxide, which reacts with NO to form peroxynitrite, nitrating eNOS and further impairing its function—a positive feedback loop.
4. Oxidative stress activates NF‑κB, driving expression of adhesion molecules and SASP factors that reinforce senescence.
5. Simultaneously, miR-126‑deficient endothelial cells package higher levels of miR-34a and miR-146a into EVs; these miRNAs are known to induce senescence and inflammation in recipient cells.
6. Thus, a single endothelial miRNA loss couples NO dysregulation with a systemic pro‑aging EV signature, positioning miR-126 as the putative upstream controller.

Testable Predictions

• Prediction 1: Endothelial‑specific overexpression of miR-126 in aged mice will restore eNOS coupling (increased NO, decreased superoxide), reduce arterial stiffness, and improve circulating NO metabolites.
• Prediction 2: Same manipulation will lower systemic markers of inflammation (IL-6, TNF‑α), senescence (p16^INK4a, SA‑β‑gal in liver, kidney, brain), and mitochondrial ROS.
• Prediction 3: EVs isolated from miR-126‑overexpressing endothelia will carry reduced miR-34a/146a and, when administered to young mice, will not induce senescence, whereas EVs from aged WT endothelia will.
• Prediction 4: Longitudinal tracking will show extended median lifespan and delayed onset of frailty indices in miR-126‑overexpressing mice.

Falsifiability

If endothelial miR-126 overexpression fails to improve NO bioavailability or does not attenuate downstream hallmarks (inflammation, senescence, mitochondrial dysfunction) despite confirmed vascular delivery, the hypothesis that miR-126 is a master upstream controller is refuted. Conversely, if rescuing miR-126 only improves vascular parameters without affecting systemic hallmarks, it would suggest that vascular NO loss is necessary but not sufficient, supporting a more modular network rather than a single controller.