Knock down of PCSK9 can improve myocardial ischemia/reperfusion injury by inhibiting autophagy

Abstract Purpose: To investigate the effect and mechanism of proprotein convertase subtilisin/Kexin type 9 (PCSK9) on myocardial ischemia-reperfusion injury (MIRI) and to 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 into 3 groups (n=16): control（scrambled RNAi was use）, ischemia/reperfusion(I/R), and I/R +SiRNA. In the I/R and I/R +siRNA groups, myocardial ischemia was induced by occlusion of the left anterior descending branch (LAD) of the coronary artery in rats in the I/R group for 0.5 hours reperfused for 3 days. To assess myocardial injury, rats were subjected to the electrocardiogram (ECG), cardiac function, cardiac enzymes, and 2,3,5-triphenyl tetrazolium chloride (TTC) /Evan Blue (EB) staining. Meanwhile, hematoxylin-eosin (HE) staining was used to detect morphological changes of cardiomyocytes in each group, and the level of myocardial fibrosis was quantified by Masson trichrome staining. Differences in expression of autophagy level proteins and Bcl-2/adenovirus E1B 19-kDa interacting protein (BNIP3) signaling-related proteins were determined by protein blotting.Results: PCSK9 mRNA and protein levels were significantly upregulated during cardiomyocyte hypoxia in vitro and in vivo. Immunohistochemistry confirmed that PCSK9 expression was increased in rat hearts 3 days after anterior descending branch ligation. 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 control-treated cells and sham-operated groups, at the same time, the presentation of the autophagic pathway BNIP3 was also downregulated. Furthermore, the 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）and 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 myocardial infarct size and cardiac function.