SUN-299 TUBULAR ANGIOTENSIN II TYPE 1 RECEPTOR-ASSOCIATED PROTEIN AMELIORATES DIABETIC GLOMERULAR INJURIES IN STREPTOZOTOCIN-INDUCED MICE

Abstract

Activated tissue renin-angiotensin system and enhanced infiltration of immune cells, especially macrophages, are critical factors in the development and progression of diabetic nephropathy. We previously identified that angiotensin II type 1 (AT1) receptor-associated protein (ATRAP) specifically binds to the AT1 receptor and suppresses the over-activation of AT1 receptor signaling. ATRAP is abundantly expressed in renal tubules, but rarely in glomeruli. ATRAP regulates blood pressure abnormality through the alteration of renal sodium handling in animal models of activated renin-angiotensin system. However, the role of ATRAP in the pathophysiology of progressive kidney diseases, such as diabetic nephropathy, is poorly elucidated. Our aim was to determine the protective role of ATRAP in a mouse model of diabetic nephropathy. To examine the effect of ATRAP deficiency on systemic and renal phenotypes under diabetic conditions, diabetes was induced in wild-type mice (WT) and systemic ATRAP knock-out mice (KO) by intraperitoneal injection of streptozotocin 55 mg/kg for 5 consecutive days. To examine the causal relationships between diabetic glomerular injury and numbers of alternatively-activated macrophages (M2Mφ) in the tubulointerstitium, which reduce inflammation and aid tissue repair, we performed adoptive transfer of ex vivo polarized M2Mφ into diabetic WT and KO at 8 and 16 weeks after streptozotocin injection. To examine whether tubular ATRAP regulates tubulointerstitial M2Mφ expression in diabetic nephropathy, diabetes was also induced in proximal tubule-specific ATRAP knock-out mice (PKO) and their littermate wild-type mice (CTL). All mice were sacrificed at 24 weeks after streptozotocin injection. The glycemic and blood pressure status of diabetic WT and KO mice were comparable throughout the study period. We confirmed increased urinary albumin excretion, increased glomerular area, decreased podocyte number (estimated by WT1 immunohistochemistry) and increased foot process width in diabetic KO compared with diabetic WT mice (Figure). The severity of tubulointerstitial injury was comparable in diabetic WT and KO mice. The number of CD206 positive-cells, a marker of M2Mφ, in the tubulointerstitium was increased in diabetic WT mice, but suppressed in diabetic KO. Adoptive transfer of M2Mφ almost completely diminished the glomerular injuries present in diabetic KO, which was equivalent to those in M2Mφ-treated diabetic WT. Moreover, the number of tubulointerstitial CD206 positive-cells in diabetic KO was restored by the adoptive transfer of M2Mφ. The number of tubulointerstitial CD206 positive-cells in diabetic PKO was significantly lower than in diabetic CTL mice. These results suggest that mainly renal tubular ATRAP plays a protective role in the progression of diabetic glomerular injury via enhancing the numbers of tubulointerstitial M2Mφ, indicating that ATRAP may be a novel therapeutic target for diabetic nephropathy.