The Role Of CaMKⅡδ-MEF2 Signaling Pathway In Aerobic Exercise-induced Improvement Of Cardiac Hypertrophy In Hypertension

Purpose:Hypertension can cause cardiac hypertrophy,which is a major risk factor for cardiovascular disease,and is one of the most common chronic diseases.Long-term high blood pressure can lead to increased pre-and post-load,causing the myocardium to be mechanically pulled,prompting the release of humoral factors.Mechanical traction and humoral factors alter the Ca²⁺concentration in cells through receptors or receptors on the cell membrane,activate multiple signal transduction pathways including CaMKⅡδ-MEF2 in cells,and induce stimulation signals to cause cardiac hypertrophy.In this study,CaMKⅡδ-MEF2 signaling pathway was used as the entry point to explore the mechanism of aerobic exercise to improve hypertensive cardiac hypertrophy.Methods:Three-month-old spontaneously hypertensive male rats and 3-month-old Wistar Kyoto male rats were randomly divided into normal control group（WKY-SED）,normal aerobic exercise group（WKY-EX）,and hypertensive control group（SHR-SED）,hypertension Aerobic Exercise Group（SHR-EX）.After 12weeks of treadmill exercise training,the blood pressure of the tail artery of each group was measured.Determination of body function in the body using the Millar pressure-volume measurement system.HE staining was used to observe the morphology of myocardial cells and the thickness of ventricular wall.Western Blot was used to determine the expression of CaM,CaMKⅡδ,p-CaMKⅡδ,HDAC4,p-HDAC4 and MEF2 proteins.Cellular immunofluorescence was used to determine the spatial localization of CaMKⅡδand MEF2 proteins.Results:1.Basic indicators:The heart rate of SHR-SED group was significantly higher than that of WKY-SED group（p<0.05）.The heart rate SED group of SHR rats was significantly higher than that of EX group（p<0.05）.Systolic and diastolic blood pressure were higher in the SHR-SED group than in the WKY-SED group（p<0.05）.The systolic blood pressure and diastolic blood pressure of the WKY-EX group were significantly lower than those of the WKY-SED group（p<0.05）.The systolic and diastolic blood pressures of the SHR-EX group were significantly lower than those of the SHR-SED group（p<0.05）.2.Heart morphology:The myocardial cells in the WKY-SED group were neatly arranged,the morphology was normal,and the nucleus staining was clear.Compared with the WKY-SED group,the cardiomyocytes in the SHR-SED group were slightly larger than the WKY-SED group,and the cells were sparse,and the cells were sparsely arranged.The myocardial fibers showed bifurcation rupture,and the nucleus stained with hypertrophy or pyknosis.The WKY-EX group has the most densely arranged cardiomyocytes and smaller intercellular spaces.The cardiomyocytes in the SHR-EX group were closer to the cardiomyocytes in the normal morphology than the SHR-SED group in the arrangement and single cell morphology.3.Cardiac function:Compared with the WKY-EX group,the WKY-SED group had a shorter duration of the rapid ejection period than the WKY-SED group.The curved annular area of the SHR-EX group is larger than that of the SHR-SED group.The ESPVR slope Ees of the SHR group was larger than that of the WKY group,while the slope of the WKY quiet group and the exercise group was almost indistinguishable.The slope of ESPVR in SHR-EX rats was milder than that in SHR-SED rats.4.Western Blot:The expression of CaM protein in cardiomyocytes of SHR-SED group was higher than that of WKY-SED group（p<0.01）.In addition,the expression of CaM protein in cardiomyocytes of SHR-EX group was significantly lower than that of SHR-SED group（p<0.01）.The expression of CaMKⅡδprotein in SHR-SED group was significantly higher than that in WKY-SED group（p<0.01）.The expression of CaMKⅡδprotein in WKY-EX group was higher than that in WKY-SED group（p<0.01）.The expression of CaMKⅡδprotein in myocardium of SHR-EX group was lower than that of SHR-SED group（p<0.01）.The phosphorylation level of CaMKⅡδwas significantly higher in SHR-SED than in WKY-SED group（p<0.05）,while the phosphorylation level in SHR-EX group was significantly lower than that in SHR-SED group.The amount of HDAC4 protein measured by the SHR-SED group was significantly higher than that of the WKY-SED group（p<0.05）.The expression level of the WKY-EX group was significantly lower than that of the WKY-SED group（p<0.01）.The expression of HDAC4 in the myocardium of SHR exercise group was significantly lower than that in the quiet group（p<0.01）.The ratio of p-HDAC4/HDAC4 in the WKY-EX group was greater than that in the WKY-SED group（p<0.05）.The expression of MEF2protein in myocardium of SHR-SED group was significantly higher than that of WKY-SED group（p<0.01）.Interestingly,the two WKY rats were compared,and the MEF2 protein in the WKY-EX group was higher than that in the WKY-SED group（p<0.01）.The SHR-SED group was significantly more than the SHR-EX group than the SHR-EX group（p<0.01）.Conclusion:Regular moderate-intensity aerobic exercise can inhibit the expression and activation of CaMKⅡδprotein and regulate its downstream HDAC4and MEF2 to achieve a positive effect on improving cardiac function in hypertensive cardiac hypertrophy.Therefore,the CaMKⅡδ-MEF2 signaling pathway is one of the mechanisms by which aerobic exercise regulates hypertensive cardiac hypertrophy.