SMAD SIGNALING IN ANGIOTENSIN II-MEDIATED RENAL FIBROSIS

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DESCRIPTION (provided by applicant): Ang II plays a pivotal role in the development of end-stage renal disease. It is known that Ang II acts by stimulating TGF-b to mediate renal fibrosis. However, our preliminary studies showed an additional signaling pathway that may be required for renal fibrosis induced by Ang II. We found that Ang II is able to activate the TGF-b signaling pathway, Smad2 and SmadS. This response leads to increased collagen production by two mechanisms: 1) an acute pathway (5-30 minutes) via activation of the ERK/p38 MAP kinases; and 2) a late mechanism (24 hours) that acts through autocrine TGF-b and leads to fibrosis. Furthermore, we also find that mice null for SmadS are protected against renal fibrosis, while mice that are conditionally deleted for Smad2 enhance SmadS signaling and renal fibrosis in response to Ang II. Thus, we hypothesize that Smad signaling is a key to the development of renal fibrosis in response to Ang II. We plan to test this hypothesis and to determine the new role for the Ang Il-Smad signaling pathway in renal fibrosis by pursuing three specific aims. In Aim 1, we will study that Ang II activates Smads via an acute (5-30 mins) ERK/p38 MAPKdependent and a late (20 hrs) classic TGF-b-dependent pathways. In Aim 2, we will dissect the functional role of TGF-b-dependent and independent Smad signaling pathways in Ang ll-induced renal fibrosis in mesangial cells (MC) and tubular epithelial cells (TEC) that do or do not express TGF-b or TbRII, and in conditional TbRII KO mice. In Aim 3, we will dissect the specific role of Smad2 or SmadS in Ang ll-mediated renal fibrosis. This will be examined in mouse embryonic fibroblasts, MC, and TEC that do or do not express Smad2 and SmadS and in SmadS KO and conditional Smad2 KO mice. We expect that the outcomes obtained from this study will support the central hypothesis and provide new insights into the pathogenesis of Ang ll-mediated renal fibrosis and valuable information for the development of new therapeutic strategies to combat renal fibrosis by targeting Smad signaling.