Plasma growth factors maintain constitutive translation in platelets to regulate reactivity and thrombotic potential.

Mechanisms of proteostasis in anucleate circulating platelets are unknown, and may regulate platelet function. We investigated the hypothesis that plasma-borne growth factors/hormones (GFH) maintain constitutive translation in circulating platelets to facilitate reactivity. Bio-orthogonal non-canonical amino acid tagging (BONCAT) coupled with LC/MS/MS analysis revealed constitutive translation of a broad-spectrum translatome in human platelets dependent upon plasma or GFH exposure, and in murine circulation. Freshly-isolated platelets from plasma showed homeostatic activation of translation initiation signaling pathways: phosphorylation of p38/ERK upstream kinases, essential intermediate MNK1/2, and effectors eIF4E/4E-BP1. Plasma starvation led to loss of pathway phosphorylation, but it was fully restored with 5-minute stimulation by plasma or GFH. Cycloheximide or puromycin infusion suppressed ex vivo platelet GpIIb/IIIa activation and P-selectin exposure with low thrombin concentrations and low-to-saturating concentrations of ADP or thromboxane analogue, but not convulxin. ADP-induced thromboxane generation was blunted by translation inhibition, and secondary-wave aggregation was inhibited in a thromboxane-dependent manner. Intravenously-administered puromycin reduced injury-induced clot size in cremaster muscle arterioles, and delayed primary hemostasis following tail tip amputation but did not delay final hemostasis after subsequent rebleeds, nor final hemostasis following jugular vein puncture. In contrast, these mice were protected from injury-induced arterial thrombosis and thrombin-induced pulmonary thromboembolism (PE), and adoptive transfer of translation-inhibited platelets into untreated mice inhibited arterial thrombosis and PE. Thus, constitutive plasma GFH-driven translation regulates platelet GPCR reactivity to balance hemostasis and thrombotic potential.