Siat7A Promotes Cardiac Hypertrophy By Activating HIF-1α Through The Endoplasmic Reticulum Stress Signaling Pathwa

Background: Hypertension is a very common chronic disease in China,and severe hypertension as a risk factor leads to heart damage,brain damage and kidney damage,and results in vascular lesions.According to statistics,over 245 million adults in China suffer from hypertension in 2020,and hypertrophic cardiomyopathy accounts for 7%.Sialyltransferase 7A(Siat7A)is the only gene that shows persistently elevated expression via studying the hypertrophic myocardium of hypertensive rats in different genetic backgrounds.Our previous study found that Siat7 A upregulated hypoxia-inducible factor-1α(HIF-1α)expression in hypertrophic cardiomyocytes and demonstrated that Siat7 A promoted myocardial hypertrophy by activating endoplasmic reticulum stress.However,whether or not protein kinase RNA-like ER kinase(PERK),inositol-requiring enzyme 1(IRE1),and activating transcription factor 6(ATF6),which are members of the endoplasmic reticulum stress signaling pathway,are involved in the development of myocardial hypertrophy is unclear.Whether Siat7 A regulates HIF-1α by activating these three signaling pathways to initiate endoplasmic reticulum stress in hypertrophic cardiomyocytes.Therefore,we investigated the interaction between PERK,IRE1,ATF6 and HIF-1α in the process of myocardial hypertrophy.Methods: Paraffin sections were made from hypertension-induced hypertrophic myocardial tissues selected from autopsy specimens.Paraffin sections were made from hypertrophic myocardial tissues in Wistar rats.Hematoxylin-Eosin(HE)staining and Immunohistochemistry(IHC)staining were performed to detect Siat7 A,GRP78 and HIF-1α expression in myocardial tissues.Lentivirus overexpressing Siat7 A,knocking down Siat7 A or knocking down HIF-1α was transfected into AC16 cells.4-phenylbutyric acid(4-PBA)was used to treat AC16 cells or cells of overexpressed Siat7 A.Quantitative Real-time PCR technique was used to detect the expression of ANP,BNP,β-MHC,Siat7 A,GRP78 and HIF-1α at the m RNA level;Western Blot technique to detect the protein levels ANP,PERK,p-PERK,90 k D and 50 k D expression of ATF6,IRE1,Siat7 A,GRP78 and HIF-1α;Immunocytochemistry technique to detect the expression of α-actinin,GRP78 and HIF-1α.Results: Increased expressions of Siat7 A,GRP78 and HIF-1α were detected in hypertensive cardiac hypertrophic tissue in autopsy specimens.Increased protein expression of ANP,GRP78,p-PERK,50 k D of ATF6,IRE1,Siat7 A and HIF-1α were detected in AC16 cells treated with 1μM Ang II for 24 h.Increased expression of ANP,GRP78,p-PERK,50 k D ATF6,IRE1,Siat7 A and HIF-1α in both AC16 cells and rats myocardial tissues with Siat7 A overexpression after administration of Ang II treatment.ANP,GRP78,p-PERK,50 k D ATF6,IRE1,Siat7 A and HIF-1α were decreased in both AC16 cells and rats myocardial tissues with Siat7 A knockdown after administration of Ang II treatment.0m M,1m M,2m M,5m M 4-PBA was used to treat AC16 cells for 2h followed by treatment of 1μM Ang II,and then ANP,GRP78,p-PERK,50 k D ATF6 and IRE1 protein expression were detected to be decreased in those cells,while Siat7 A protein expression was not significantly altered.The higher the concentration of 4-PBA,the more obvious the decrease in ANP,GRP78,p-PERK,50 k D ATF6 and IRE1.Treatment of Siat7 A overexpressed cells with 5m M 4-PBA for 2h followed by administration of 1μM Ang II resulted in decrease in the m RNA expressions of ANP,BNP,β-MHC,GRP78 and HIF-1α,and decrease in the protein expressions of ANP,GRP78,p-PERK,50 k D of ATF6,IRE1 and HIF-1α in those cells.The fluorescence intensity of α-actinin,GRP78 and HIF-1α was diminished and the expression of Siat7 A was not significantly altered.Treatment of HIF-1α knockdowned cells after administration of 1μM Ang II resulted in decrease in the m RNA expressions of ANP,BNP,β-MHC and HIF-1α,decrease in the protein expressions of ANP and HIF-1α,however,the protein expressions p-PERK,50 k D ATF6 and IRE1 were not significantly altered,and expressions of Siat7 A and GRP78 were not significantly altered.Conclusions:(1)Three endoplasmic reticulum membrane receptors,including PERK,IRE1 and ATF6,were activated during myocardial hypertrophy.(2)Siat7A mediates HIF-1α expression through PERK,IRE1,and ATF6 signaling pathways to promote myocardial hypertrophy.