Epigenetic control of vascular smooth muscle cells in Marfan and non-Marfan thoracic aortic aneurysms

Abstract

AimsHuman thoracic aortic aneurysms (TAAs) are characterized by extracellular matrix breakdown associated with progressive smooth muscle cell (SMC) rarefaction. These features are present in all types of TAA: monogenic forms [mainly Marfan syndrome (MFS)], forms associated with bicuspid aortic valve (BAV), and degenerative forms. Initially described in a mouse model of MFS, the transforming growth factor-β1 (TGF-β1)/Smad2 signalling pathway is now assumed to play a role in TAA of various aetiologies. However, the relation between the aetiological diversity and the common cell phenotype with respect to TGF-β signalling remains unexplained.Methods and resultsThis study was performed on human aortic samples, including TAA [MFS, n = 14; BAV, n = 15; and degenerative, n = 19] and normal aortas (n = 10) from which tissue extracts and human SMCs and fibroblasts were obtained. We show that all types of TAA share a complex dysregulation of Smad2 signalling, independent of TGF-β1 in TAA-derived SMCs (pharmacological study, qPCR). The Smad2 dysregulation is characterized by an SMC-specific, heritable activation and overexpression of Smad2, compared with normal aortas. The cell specificity and heritability of this overexpression strongly suggest the implication of epigenetic control of Smad2 expression. By chromatin immunoprecipitation, we demonstrate that the increases in H3K9/14 acetylation and H3K4 methylation are involved in Smad2 overexpression in TAA, in a cell-specific and transcription start site-specific manner.ConclusionOur results demonstrate the heritability, the cell specificity, and the independence with regard to TGF-β1 and genetic backgrounds of the Smad2 dysregulation in human thoracic aneurysms and the involvement of epigenetic mechanisms regulating histone marks in this process.

Modifications of Chromatin Dynamics Control Smad2 Pathway Activation in Aneurysmal Smooth Muscle Cells

“…13 In accordance with these observations, we show here that the inhibition of H3 HAT by garcinol or CPTH2 induced a specific decrease in Smad2 1a expression in aneurysmal VSMCs (Online Figure VB), but the Smad2 1b variant was not modified (Online Figure VC).…”

“…A significant decrease in nucleosome occupancy was found at position −200 bp and +100 bp of SMAD2 in aneurysmal media compared with control (P<0.01). These data suggest that the increased expression of Smad2 previously observed 13 is because of activation of the SMAD2 promoter by the simultaneous recruitment of p53 and H3 hyperacetylation.…”

“…Finally, Smad2 overexpression was linked to modifications in the histone code on the SMAD2 promoter in nuclei of aortic VSMCs. 13 However, molecular mechanisms controlling SMAD2 promoter activation were not well characterized in this previous study. The purpose of the present study is to identify the molecular mechanisms controlling SMAD2 promoter activation in human aneurysms.…”

“…13 The increased expression of Smad2 was associated with modifications of the histone code within its promoter. Using in silico analysis of the Smad2 promoter, p53 and Myc consensus binding sites seemed to be of relevant interest.…”

“…1,5 Importantly, development of aneurysms of the ascending aorta in human patients has been linked to TGF-β pathway dysregulation, mutations in genes coding for key actors of the TGF pathway, including FBN1 (fibrillin-1), TGFBR1/R 2 (TGF-β receptor type 1 and type 2), 6,7 SMAD3, 8 and TGFB2 (TGF-β type 2), 9,10 as well as tissue fibrinolytic system activation 11,12 and constitutive Smad2 overexpression and activation. 13 …”