Background: Proprotein convertase subtilisin/kexin 9 (PCSK9), mainly secreted by the liver and released into the blood, elevates plasma low-density lipoprotein (LDL) cholesterol by degrading LDL receptor. Pleiotropic effects of PCSK9 beyond lipid-metabolism have been shown. However, the direct effects of PCSK9 on platelet activation and thrombosis, as well as the underlying mechanisms, still remain unclear. Methods: We detected the direct effects of PCSK9 on agonists-induced platelet aggregation, dense granule ATP release, integrin αIIbβ3 activation, α granule release, spreading, and clot retraction. These studies were complemented by in vivo analysis of FeCl3-injured mouse mesenteric arteriole thrombosis. We also investigated the underlying mechanisms. Using myocardial infarct (MI) model, we explored the effects of PCSK9 on microvascular obstruction and infarct expansion post-MI. Results: PCSK9 directly enhances agonists-induced platelet aggregation, dense granule ATP release, integrin αIIbβ3 activation, P-selection release from α granules, spreading, and clot retraction. In line, PCSK9 enhances in vivo thrombosis in a FeCl3-injured mesenteric arteriole thrombosis mouse model, while PCSK9 inhibitor evolocumab ameliorates its enhancing effects. Mechanism studies revealed that PCSK9 binds to platelet CD36 and thus activates Src kinase and mitogen-activated protein kinase (MAPK)- extracellular signal-regulated kinase 5 and c-Jun N-terminal kinase, increases the generation of reactive oxygen species, as well as activates the p38MAPK/cytosolic phospholipase A2/cyclooxygenase-1/thromboxane A 2 signaling pathways downstream of CD36 to enhance platelet activation. Using CD36 knockout mice, we showed the enhancing effects of PCSK9 on platelet activation are CD36 dependent. Consistently and importantly, aspirin abolishes the enhancing effects of PCSK9 on platelet activation and in vivo thrombosis. Finally, we showed that PCSK9 activating platelet CD36 aggravates microvascular obstruction and promotes MI expansion post-MI. Conclusions: PCSK9 in plasma directly enhances platelet activation and in vivo thrombosis, as well as MI expansion post-MI, by binding to platelet CD36 and thus activating the downstream signaling pathways. PCSK9 inhibitors or aspirin abolish the enhancing effects of PCSK9, supporting the use of aspirin in patients with high plasma PCSK9 levels in addition to PCSK9 inhibitors to prevent thrombotic complications.

The field of small interfering RNA (siRNA) as potent sequence-

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.