The Role And Mechanism Of TLR9 In Ventricular Remodeling After Myocardial Infarction In Mice

Background: In myocardial infarction,ischemic injury of myocardial cells leads to hypertrophy and fibrosis,which leads to thickening or dilating of the heart area to irreversible myocardial remodeling.The heart function gradually deteriorates and eventually develops into heart failure.Excessive inflammation caused by Damage Associated Molecular Patterns(DAMP)is considered to be one of the main causes of cardiac insufficiency and remodeling.Toll-like receptors(TLRs)involved in the activation of the natural immune system play an important role.Toll-like receptors,as the pattern recognition receptors,play a crucial role in identifying microbial-related molecular patterns and promoting immune responses.Toll-like receptor-9(TLR9)activates the innate immune system by binding to specific ligands.It not only regulates the inflammatory response and angiogenesis but is also closely related to autophagy and apoptosis.This experiment aims to explore the role of TLR9 in acute myocardial infarction,focusing on the effects and mechanisms of TLR9 on myocardial remodeling after acute myocardial infarction,and to provide a reference for subsequent scientific research and clinical guidance.Methods: Left anterior descending coronary artery ligation was used to model acute myocardial infarction.WT and TLR9 KO mice(23.5 ～ 27.5g,male)were subjected to LAD ligation surgery and Sham surgery,as well as WT mice which were injected intraperitoneally with low dose ODN1826 and PBS pretreatment.Evaluating28 Days survival situation.The heart function of mice in each group was evaluated by echocardiography and hemodynamics after modeling.3% TTC staining to determine the area of myocardial infarction;cardiac left ventricular protein was extracted,and fibrosis,apoptosis,and angiogenesis-related protein levels were detected by western blotting respectively;total cardiac left ventricular RNA was extracted and RT-PCR was used to detect fibrosis-related m RNA levels;WGA staining and PSR staining were used to evaluate cardiac morphology;immunofluorescence and immunohistochemical staining were used to detect fibrosis,apoptosis,and expression of angiogenesis-related proteins.Results: The expression level of TLR9 was significantly increased after myocardial infarction,and it was mostly concentrated in the infarcted and marginal regions and showed low expression in the non-infarcted regions.TLR9 deletion reduced the survival rate of myocardial infarction in mice,increased myocardial rupture rate,increased cardiac dilatation,decreased EF and FS,and the differenceswere statistically significant compared with WT mice(P<0.05);Reduced expression of α-SMA,smad3,and col 1 in acute myocardial infarction in TLR9 knockout mice(P<0.05 vs.WT-MI);compared with WT-MI mice,the TUNEL-positive cells in TLR9KO-MI mice were increased significantly(P<0.05);Bax was higher,Bcl-2 and Bcl-xl were lower,Bcl-2 / Bax and Bcl-xl / Bax ratio were lower in TLR9KO-MI mice.Immunofluorescence results showed that in the infarcted heart tissue of WT mice,the expression of TLR9 co-localized with the expression of HIF-1a,and the expression levels of both rises.The results of immunohistochemical staining showed that HIF-1α,VEGFA,and CD31 had significantly fewer positive cells in the heart of TLR9KO-MI mice than in wild type mice(P<0.05).PCNA and CD31 dual immunofluorescence staining revealed that endothelial cells of TLR9KO-MI mice had insufficient proliferation compared to wild type mice.Western blot also confirmed that HIF-1α,VEGFA,CD31,and PCNA proteins were significantly down-regulated in TLR9KO-MI mice compared to wild-type mice(P<0.05).The number of CD31-positive and α-SMA-positive cells in TLR9KO-MI mice was significantly lower than that in wild type mice(P<0.05).TLR9 agonists have a cardioprotective effect on mice after AMI by increasing fiber repair and angiogenesis,reducing apoptosis.Conclusion: TLR9 is essential for the repair of acute myocardial infarction,and it is related to fiber repair,apoptosis and angiogenesis after myocardial infarction.TLR9 agonists have potential therapeutic prospects for acute myocardial infarction.