Abstract 035: Increasing Renal AcSDKP by Eliminating the ACE N-Domain Blocks Renal Inflammation and Sodium Retention During Diabetic Nephropathy

Abstract

Angiotensin-converting enzyme (ACE) plays a key role in renal inflammation and sodium retention associated with diabetic nephropathy. Although most effects of ACE have been classically related to angiotensin (Ang) II synthesis, studies highlight an Ang II-independent role of ACE in inflammation. Indeed, ACE has two catalytic domains, the N- and C-domains, that can process a wide diversity of substrates besides Ang I. Here, we study the relative contributions of ACE domains to renal inflammation and sodium retention during diabetic nephropathy. Diabetes was induced with streptozotocin in wild-type (WT) mice and mice lacking either a functional ACE N-domain (NKO) or C-domain (CKO) (n=5-8). After 6 months of diabetes, we evaluated the natriuretic response to volume expansion. For this, mice were injected with 0.9% NaCl equivalent to 10% of their body weight. After 5 hours, diabetic NKO mice excreted 30% more urinary sodium in response to the saline challenge compared to diabetic WT or CKO mice ( P <0.05). This enhanced natriuretic response was associated with a 47% reduction ( P <0.05) of renal epithelial sodium channel (ENaC) cleaved (active) α and γ subunits. Further, diabetic NKO displayed lower levels of renal fibrosis (46% reduction, P <0.05), IL-1β (56% reduction, P <0.05), TNFα (50% reduction, P <0.05) and albuminuria (53% reduction, P <0.01) compared to WT and CKO diabetic mice. This protective phenotype was not associated with changes in renal Ang II levels (WT: 237 ± 73; NKO: 283 ± 53 CKO: 245 ± 39 fmol/g kidney, P =NS). We next evaluated whether the anti-inflammatory tetrapeptide N-acetyl-seryl-asparyl-lysyl-proline (AcSDKP), an ACE N-domain specific substrate, mediates the protective phenotype of NKO. For this, diabetic mice were treated with the prolyl oligopeptidase inhibitor, S17092 (10 mg/kg, IP), that prevents the synthesis of AcSDKP. In diabetic NKO mice receiving S17092, sodium excretion in response to a saline challenge, ENaC α and γ subunit cleavage, renal inflammation and renal injury were indistinguishable from equally treated diabetic WT mice. In summary, these data indicate that increasing AcSDKP by blocking the ACE N-domain improves sodium handling and ameliorates diabetic kidney disease independently of intrarenal Ang II regulation.