Abstract
The mechanisms underlying vascular dysfunction in adipose tissue (AT) in obesity are not clearly understood. Our hypothesis is that in response to pro-inflammatory cytokines (PIC) present in obese AT, endothelial cells (EC) can de-differentiate and acquire a mesenchymal-like phenotype (EndoMT) that leads to endothelial dysfunction. To test our hypothesis, we measured endothelial and mesenchymal markers of CD31 + CD34 + EC isolated from omental (OM) and subcutaneous (SC) AT of bariatric subjects (BAMVEC) using RT-PCR and western blot. Permeability and oxidative metabolism were determined by ECIS and Seahorse analyzer XF e 24, respectively. BAMVEC isolated from both OM and SC fat showed very low protein expression of vWF and VE-Cadherin (EC markers) and abundantly expressed αSMA and the EMT transcription factor twist-1. To determine effects of PIC on EndoMT, commercially available primary endothelial cells from AT (HAMVEC) were treated in vitro with PIC (2.5ng/mL TNFα, IFNγ and TGFβ) for 1, 3 or 6 days. We found progressive down-regulation by >2-fold (p<0.001) of the EC markers vWF, VE-Cadherin, and Occludin compared to controls. As early as 1 day of PIC treatment twist-1 (p<0.001) and snail1 (p<0.05) showed an increase by >2-fold. Similarly, OM and SC BAMVEC expressed >2-fold increase in the mesenchymal genes twist-1, FSP1, αSMA, and snail1 compared to untreated HAMVEC. Metabolically, BAMVEC had increased ATP production and maximal respiration compared to HAMVEC suggesting increased oxidative phosphorylation, a marker of mesenchymal-like cells. PIC stimulation of HAMVEC yielded significant increases in endothelial permeability and motility (p<0.001). Notably, there were no significant differences in any of the markers between OM and SC BAMVEC. These results show that EC in obese AT exhibit a mesenchymal-like phenotype which may account for functional changes such as increased permeability and migration and are not depot specific. Using primary EC from human AT we showed that prolonged exposure to PIC induces a phenotype similar to CD31+CD34+ EC from obese AT. This supports the concept that AT inflammation can promote EC de-differentiation in vivo and our in vitro model is suitable for future studies to uncover the relevant mechanisms.
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