OC 10.5 - Aging Activates Platelet mTOR to Induce Platelet Hyperreactivity

Background: Aging is an independent risk factor for the development of cardiovascular disease. We hypothesized that aging promotes platelet hyperreactivity and increases thrombotic risk.

Aims: In this study, we examined the mammalian target of rapamycin (mTOR) as a mechanistic regulator of platelet hyperreactivity in aging.

Methods: Platelets from young ( < 45y) and aged (>70y) humans were isolated to examine platelet aggregation and mTOR signaling. Young (8-12 weeks) and aged (>18 months) wild-type (WT; mTORfl/fl) and platelet-specific mTOR knockout mice (KO; mTORfl/fl-Pf4-Cre) were used to examine platelet activation. A microvascular thrombosis model using collagen and epinephrine was employed.

Results: In aged humans and mice, we observed significant (p < 0.01) basal activation of the mTOR pathway, including phosphorylation of AKT, 70S6K and 4E-BP1. Aged platelets from humans and mice had significantly greater integrin activation and P-selectin expression when activated. Additionally, aged human and murine platelets had significant greater aggregation compared to younger controls. Inhibition of mTOR either with torin-1 in aged humans or genetic deletion in aged mice reversed this platelet hyperreactivity. In a collagen-epinephrine thrombosis model, aged WT mice succumbed significantly (p < 0.001) faster compared to young WT mice, while aged KO mice had similar times to death as young WT mice. Mechanistically, we observed a significant increase in RAC-GTP (p < 0.05) and phospho-p47phox (p < 0.01) downstream of mTOR activation in aged WT mice. Additionally, we observed increased reactive oxygen species (ROS) in resting platelets and megakaryocytes in aged WT mice compared to young WT and young or aged KO mice. Increased ROS led to significantly greater phospho-p38 and thromboxane generation in aged WT mice compared to young controls (p < 0.05). Phospho-p38 and thromboxane generation upon activation were unchanged when comparing aged and young KO mice.

Conclusion(s): Aging induces platelet mTOR activation, leading to increased platelet hyperreactivity mediated through increased activation of p38 and thromboxane generation.