P-55/BO-06 : Transcriptional Regulation of Hyperglycemia induced EndMT: Role of MRTF-A and ATF3

posted Jan 26, 2017, 5:50 AM by sourav ghosh   [ updated Jan 26, 2017, 6:29 AM ]

Vibhuti Sharma1, Nilambra Dogra2, Uma Saikia1, Madhu Khullar3
(1) Department of Histopathology, Department of Experimental Medicine and Biotechnology, PGIMER, Chandigarh, India (2) National Centre for Human Genome Studies and Research, Panjab University, Chandigarh, India

Constant exposure of vascular endothelial cells to high blood glucose levels in a diabetic condition may result in diabetes associated microvascular complications. Under pathological conditions endothelial cells are known to contribute to fibrosis by transitioning into myofibroblasts by a process termed as endothelial to mesenchymal transition (EndMT). Molecular mechanisms and the transcriptional mediators controlling EndMT in heart during development or disease remain relatively undefined. Myocardin related transcription factor-A (MRTF-A) is known to facilitate serum response factor (SRF) in the transcription of contractile and cytoskeletal genes during fibrosis, therefore its specific role in cardiac EndMT might be of importance. Activating transcription factor 3 (ATF3) activation during cardiac EndMT is speculated, since it is known to immediately respond to various stress signals or stimuli such as TGF-β and directly control the expression of primary EMT marker genes snail, slug and twist. Although the role of TGF-β has been established in inducing EndMT mediated cardiac fibrosis, the contribution of hyperglycemia (HG) to this transition is not clearly defined. In the present study, the effect of hyperglycemia on the mesenchymal transitioning of cardiac endothelial cells and potential involvement of fibrosis associated transcription factors MRTF-A and ATF3 during that transition was explored.

EndMT changes were examined in type-II diabetic rat heart sections, as well as cardiac autopsy tissues of diabetic subjects. Protein expression and localization of transcription factors MRTF-A and ATF3 was also observed in these tissue sections. Nuclear localization of transcription factor MRTF-A was observed in the vascular endothelium of diabetic hearts, parallel with an increase in interstitial collagen deposition. Transcription factor ATF3 was induced and specifically expressed in the small cardiac vessels of diabetic hearts. However, ATF3 expression was not observed in large cardiac vessels. In vitro results showed HG mediated EndMT response in cell specific manner. Prominent EndMT features were observed in cardiac microvascular endothelial cells (CMVECs) upon HG treatment, as compared to the aortic endothelial cells (AECs). ATF3 induction in response to HG treatment was specifically observed in CMVECs. HG stimulated EndMT marker gene slug expression through ATF3 was also observed.
Our study suggests HG as a potent stimulus of cardiac EndMT and an important contributor to diabetes associated cardiac fibrosis. In addition, differential effects of HG treatment on macrovascular and microvascular endothelial cells were observed. Results suggest that HG induced EndMT more significantly in CMVECs as compared to AECs. Further, role of transcription factor ATF3 in HG mediated EndMT in CMVECs is indicated but needs further investigation in order to determine its exact role in the transition.