Abstract 39: The Macula Densa PGE2 Activates Adult Renal CD44+ Mesenchymal Stromal Cell (MSC) Migration and Differentiation to Renin Producing cells via EP4 Receptor and Wnt Canonical Signaling

Abstract

Background: We have previously shown that CD44+ MSCs exist in the adult kidney and that under chronic sodium deprivation these cells migrate to the juxtaglomerular (JG) area and differentiate to new renin expressing cells. The mechanisms mediating these biological processes remain elusive. Renin expression and release by JG cells is initiated at the Macula densa (MD) primarily by the release of PGE2. Interestingly, renal MSC expresses the PGE2 receptor EP4. Here, we hypothesized that MD-derived PGE2 acting via the EP4 is responsible for the migration of renal MSCs and their differentiation to renin expressing cells. Methods: MSCs were isolated by FACS from the kidney of C57BL/6 adult mice and co-cultured in a transwell system with the MD cell line MMDD1 at normal or low NaCl medium. For the in vivo study, wild type and EP4 knockout mice were fed a low salt diet and given furosemide to induce JG hyperplasia. Renin, CD44 and B-catenin stabilization were detected by immunochemistry staining and Western blot analysis. Results: Low salt stimulation of MMDD1 cells significantly increased MSC migration in transwell assays (P<0.05). These effects were abrogated by addition of a COX2 inhibitor (NS398) to MMDD1 cells or an EP4 receptor antagonist (AH23848) to the MSCs. Treatment of MSCs with a PGI2 receptor antagonist (CAY 10441) had no effect on this migratory response. Furthermore, direct addition of PGE2, but not PGI2 to MSCs increased cell migration as compared to controls (P<0.05). PGE2 did not affect proliferation of MSCs but did induce renin expression, suggesting that PGE2 plays an important role in promoting the migration and differentiation of renal MSCs. PGE2 treatment also resulted in increased beta catenin stabilization and activation of canonical Wnt signaling; a pathway that plays an important role in progenitor cell migration and differentiation. Finally, the absence of the EP4 receptor in mice attenuated expansion, migration of renal CD44+ cells and JG hyperplasia induced by sodium deprivation. Conclusion: The MD/ PGE2/ EP4 axis plays a key role in the activation of MSCs and their differentiation to renin producing cells. This process could potentially be an important physiologic mechanism of maintaining blood pressure under conditions of sodium deprivation.