Endothelial MRTF-A Moderates The Crosstalk Between BRG1and ASH2 To Promote Angiotensin Ⅱ Induced Pathologicalhypertrophy

Objective: Angiotensin Ⅱ(Ang Ⅱ)induces cardiac hypertrophy and fibrosis in part by stimulating endothelin(ET-1)transcription.Numerous studies have addressed the involvement of the epigenetic machinery in the regulation of ET-1 transcription.It remains enigmatic,however,how Ang Ⅱ-dependent ET-1 transcription is epigenetically modulated.Our recent study has established a role for MRTF-A in regulating Ang Ⅱ-induced ET-1 transcription in vascular endothelial cells and pathological hypertrophy.Growing evidence supports the connection between MRTF-A and different branches of the epigenetic machinery.Accordingly,we hypothesized that in endothelial cells,MRTF-A contributes to Ang Ⅱ-induced ET-1 transcription,which induced pathological cardiac hypertrophy,by regulating the crosstalk between chromatin 3emodeling proteins and histone H3K4 methylation complex.Methods:Mrna levelsand protein levels ET-1and hypertrophic marker geneswere examined by real-time quantitative PCR(Qpcr),ELISA,and Western Blot in Eahy926 cells,pulmonary microvascular endothelial cells(PMVECs)and mouse embryonic fibroblasts(MEF).HMT assays were performed to measure histone methyltransferase activities.Ch IP and Re-Ch IP assays were performed to examine the occupancies of proteins on gene promoters.Results:In response to Ang Ⅱ stimulation,core components of the mammalian chromatin remodeling complex(Brahma-related gene 1,or Brg1,and Brahma or Brm)and histone H3K4 methylation complex(Ash2,absent,small,or homeotic discs 2,or Ash2 and WD domain repeat 5,or Wdr5)were recruited to the ET-1 promoter region in endothelial cells.Over-expression of Brg1/Brm or Ash2/Wdr5 enhanced while depletion of Brg1/Brm or Ash2/Wdr5 attenuated Ang Ⅱ-induced ET-1 transactivation.Endothelial-specific knockdown of Brg1/Brm or Ash2/Wdr5 ameliorated cardiac hypertrophy.More importantly,Brg1/Brm interacted with Ash2/Wdr5 on the ET-1 promoter to catalyze H3K4 methylation.The crosstalk between Brg1/Brm and Ash2/Wdr5 was mediated by myocardin-related transcription factor A(MRTF-A).Conclusion:In conclusion,our data have unveiled an epigenetic complex that links ET-1 transactivation in endothelial cells to Ang Ⅱ-induced cardiac hypertrophy and fibrosis.