Regulation of Endothelial Cell Differentiation and Activation by TGF-ß

Endothelial cell activation in the glomerulus is the major determinant of disease in the hemolytic uremic syndrome and in other thrombotic microangiopathies, including preeclampsia and eclampsia These diseases are associated with significant morbidity and mortality, and their mechanisms are as yet poorly understood. In addition, a number of vasculitic disorders can affect the microvasculature of the kidney, and liberation of cytokines in many forms of immune complex mediated glomerulonephritis involves endothelial cell activation. Interruption of the TGF - Beta signaling cascade has been proposed as a therapeutic option for the treatment of progressive glomerular sclerosis/fibrosis in immune-mediated disease. However TGF - Beta1 normally suppresses endothelium-dependent recruitment of leukocytes and inhibit production of inflammatory cytokines by endothelial cells. This proposal aims to examine the hypothesis that the functional response of differentiated endothelial cells to TGF - Beta differs from that of cytokine activated endothelial cells. We propose that these changes in TGF - Beta responsiveness are brought about by selective expression of type I TGF - Beta receptor isoforms and by altered expression of cytoplasmic TGF - Beta signaling proteins, the Smads. The hypothesis is based on prior findings in Dr. Ballermann`s laboratory showing that glomerular capillary endothelial cells exposed to chronic shear stress in vitro undergo differentiation which is accompanied by reduced TGF - Beta type II receptor, and enhanced YO 5-3 (a Smad family member) expression. We further propose that activation of endothelial cells during immune injury returns them to a less differentiated phenotype and that changes in the TGF - Beta signaling cascade during activation may represent the critical determinants of TGF - Beta1`s immunosuppressive action. For that reason we will explore TGF - Beta1 signaling and function in differentiated (shear-stress treated) and proliferating as well as in differentiated (shear-stress treated) and cytokine-activated glomerular endothelial cells.