PCSK9 Knockdown can improve myocardial ischemia/reperfusion injury by inhibiting autophagy

Background: and Aim This study aims to investigate the effect and mechanism of proprotein convertase subtilisin/Kexin type 9 (PCSK9) on myocardial ischemia-reperfusion injury (MIRI) and provide a reference for clinical prevention and treatment of acute myocardial infarction (AMI). METHODS: We established a rat myocardial ischemia/reperfusion (I/R) model and AC16 hypoxia/reoxygenation (H/R) model. A total of 48 adult male Sprague-Dawley rats were randomly assigned to three groups (n=16): control, I/R, and I/R +SiRNA. In I/R and I/R +siRNA groups, myocardial ischemia was induced via occlusion of the left anterior descending branch (LAD) of the coronary artery in rats in I/R group for 0.5 h and reperfused for three days. To assess the myocardial injury, the rats were subjected to an electrocardiogram (ECG), cardiac function tests, cardiac enzymes analysis, and 2,3,5-triphenyl tetrazolium chloride (TTC)/Evan Blue (EB) staining. Meanwhile, hematoxylin-eosin (HE) staining was used to detect morphological changes in cardiomyocytes in each group, and the level of myocardial fibrosis was quantified using Masson trichrome staining. Differences in the expression of autophagy-level proteins and Bcl-2/adenovirus E1B 19-kDa interacting protein (Bnip3) signaling-related proteins were determined by protein blotting. RESULTS: I/R and H/R injury increased the expression level of PCSK9, activated the downstream Bnip3, and subsequently triggered autophagy. In vitro and in vivo experimental studies revealed that siRNA knockdown of PCSK9 resulted in reduced expression of the autophagic protein Beclin-1, light chain 3 (LC3) compared to normal control-treated cells and control-operated groups. Simultaneously, the presentation of the autophagic pathway Bnip3 was downregulated. Furthermore, PCSK9-mediated small interfering RNA (siRNA) group injected into the left ventricular wall significantly improved cardiac function and myocardial infarct size, as well as the expression of mRNA of Recombinant Human Interleukin-1β（IL-1β. Moreover, Nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) was significantly downregulated and reduced the inflammatory response compared with the I/R group. CONCLUSIONS: In ischemic/hypoxic circumstances, PCSK9 expression was dramatically increased. PCSK9 knockdown alleviated MIRI via the Bnip3-mediated autophagic pathway and improved inflammatory response, myocardial infarct size, and cardiac function.