Platelet mitofusin-1 mediates endothelial cell dysfunction in pulmonary arterial hypertension via the NLRP3 inflammasome and interleukin-1B Free

Pulmonary arterial hypertension (PAH) is a chronic and progressive disorder driven by metabolic and endothelial cell dysfunction (ECD) and is characterized by angioproliferative vasculopathy in pulmonary arterioles that lead to increased pulmonary artery pressure, pulmonary vascular resistance, and ultimately right heart failure. Platelets and platelet activation have been implicated in PAH pathogenesis. Thrombocytopenia or deletion of platelet-specific complement in animal models attenuate hypoxia and monocrotaline-induced PAH. However, clinical trials using anti-coagulants to treat PAH patients show conflicting results, suggesting that platelets contribute to PAH pathogenesis outside of their classically studied thrombotic roles. Platelets are metabolically active mediators of inflammatory signaling and modulate vascular wall function through the release of cytokines and vasoactive products. However, it remains unclear whether platelet-mediated inflammatory signaling or a specific platelet secretome contributes to PAH pathogenesis. A recent publication from our lab showed that platelets from PAH patients have metabolic dysfunction characterized by increased fatty acid oxidation (FAO) and mitochondrial oxident (mtROS) production. We now hypothesize that this platelet metabolic dysfunction leads to increased inflammatory signaling and altered secretome release in PAH patients. We show that platelets from PAH patients have an increase in protein levels of the mitochondrial GTPase mitofusin-1 (MFN1), which promotes FAO and mtROS production. Notably, platelet-specific MFN1 knockout mice (MFN1^flox/flox/PLF4-Cre) show significantly attenuated hypoxia-induced PAH compared to wildtype mice. On a mechanistic level, we show that in human platelets, hypoxia increases the translation of MFN1 mRNA. This increased MFN1 interacts with the platelet NLRP3 inflammasome, which in turn activates interleukin-1B (IL-1B) via caspase-1. Using a co-culture model of human platelets and pulmonary artery endothelial cells, we show that platelet secretion of IL-1B induces pulmonary ECD characterized by proliferation and activation. All-together, these data elucidate a novel mechanism by which platelet MFN1 activates the NLRP3 inflammasome to mediate IL-1B secretion and endothelial/vascular dysfunction. Ongoing ex vivo and murine studies are further elucidating the cross-talk between platelet metabolic and inflammatory signaling and determining mechanisms to inhibit this pathway. These studies will serve as a foundation to develop strategies to modulate platelet immunometabolic signaling to prevent PAH initiation and progression.