Platelet Jak2-deficiency accelerates atherosclerosis with increased inflammatory response.

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, of which atherosclerosis is the major pathology. Chronic inflammation underlies atherosclerosis, and Janus kinase 2 (Jak2) is a critical signaling node that mediates this process. Jak2 activating mutation has recently been implicated in clonal hematopoiesis of indeterminate potential as an emerging major CVD risk factor. While platelets' role in hemostasis and thrombosis is well-established in CVD, the essential role of platelet Jak2 in mediating inflammation in atherosclerosis is unknown. To this end, we assessed the in vivo role of platelet Jak2 in atherosclerosis using ApoE mice with platelet Jak2 deficiency. These mice developed accelerated atherosclerosis in the aortic roots and arches with no significant changes in metabolic parameters. Systemically, there were increased numbers of inflammatory cells including various leukocytes and platelets. Given the prominent role of macrophages in atherogenesis, we also assessed bone marrow (BM)-derived macrophages from these mice which exhibited upregulated expression of proinflammatory genes in response to lipopolysaccharide (LPS). Furthermore, flow cytometric analysis of the BM showed significant expansion of hematopoietic stem and progenitor cells (HSPCs), suggesting platelet Jak2 effect on HSPC expansion. Together, these results show that platelet Jak2 attenuates atherogenesis likely through pleiotropic effects including regulation of inflammation in myeloid cells.