Dicer Neosynthesis Regulates Platelet Reactivity: A Mechanism Altered in Type 2 Diabetes

Despite being anucleate, platelets contain mRNAs and synthesize new proteins. Platelets also contain microRNAs and Dicer (ribonuclease III enzyme Dicer-1), an enzyme required for microRNA maturation. The expression of Dicer and some microRNAs is reduced in platelets from patients with type 2 diabetes (T2DM). However, the role of Dicer in the regulation of platelet function and in T2DM-associated platelet hyperreactivity is unclear. We aimed to assess whether Dicer levels are regulated in platelets upon activation, if they modulate mRNA translation by triggering pre-microRNA maturation, and whether these mechanisms are deranged in T2DM platelets.

Dicer expression in ultrapurified platelets was assessed by Western blotting, flow cytometry, and liquid chromatography-tandem mass spectrometry. P2Y₁₂ (purinergic receptor P2Y₁₂) expression was assessed by Western blotting and microRNA-223 and P2RY12 transcript by real-time polymerase chain reaction. In vivo experiments were performed in Dicer-deficient and wild-type mice with alloxane-induced diabetes.

Thrombin-activated platelets from healthy individuals rapidly neosynthesize Dicer, leading to increased maturation of microRNA-223 and concomitant consumption of pre-microRNA-223. An increase in microRNA-223 was associated with a reduction of P2RY12 mRNA, one of its main targets, and platelet P2Y₁₂ expression and function. All these mechanisms were significantly deranged in platelets from patients with T2DM. Similar alterations were also observed in platelets from Dicer-deficient and diabetic mice. ADP-induced platelet pulmonary thromboembolism was decreased in mice previously infused with low-dose thrombin.

The Dicer-triggered decrease in P2Y₁₂ after thrombin stimulation may represent a self-regulatory mechanism of platelet activation to prevent undesired thrombus formation. The derangement of this self-regulatory mechanism in T2DM may contribute to the platelet hyperreactivity and enhanced thrombotic complications of patients with T2DM. Our results show that the complex regulatory role of microRNA neoformation during platelet activation, when deranged, may contribute to cardiovascular disease.