Augmented afferent arteriole (AA) vasoconstriction induced by chymase‐dependent ANGII formation in diabetic renal disease

Abstract

The leptin receptor deficient db/db mouse is a genetic model of type II diabetes with progressive renal disease. We hypothesized that chymase is the major enzymatic pathway responsible for intrarenal ANGII formation in diabetes. Renal ACE activity was reduced in diabetic compared to control db/m mice (5±3 vs 37±8 AFU/min/mg), while ACE2 activity was similar. Urinary albumin excretion (822±187 vs 28±4 μg/d) was elevated, while GFR (0.65±0.04 vs 1.00±0.13ml/min/g KW, n=6, 7, P<0.02) was reduced by 35% in diabetic compared to control mice. AA diameters of in vitro blood perfused juxtamedullary nephrons were significantly larger in diabetic compared to control kidneys (14.3±0.4 vs 12.3±0.3 μm). AA responses to ANGI±AT1 receptor blocker (100 μM Candesartan, CV), ±ACE inhibitor (1mM Captopril) ±serine protease inhibitor (1mM PMSF) were measured. AA vasoconstriction to 10, 100, 1000nM ANGI was similar in both groups (‐9±2, ‐29±4, ‐28±3% diabetic, n=11; ‐10±2, ‐24±4, ‐26±3% control, n=12) due to conversion of ANGI→ANGII. AA vasoconstriction produced by ANGI→ANGII was significantly attenuated by CV, Captopril, and Captopril+PMSF (‐4±2, ‐3±5, ‐5±5% at 100nM ANGI), but not by PMSF alone (‐22±4%) in control kidneys. AA vasoconstriction produced by ANGI→ANGII was significantly attenuated by CV, PMSF, and Captopril+PMSF (‐4±3, ‐6±6 ‐6±3 % at 100nM ANGI), but not by Captopril alone (‐20±4%) in diabetic kidneys. AA vasoconstriction to the chymase‐specific [Pro11, D‐Ala12]ANGI was significantly augmented in AA of diabetic compared to control kidneys (‐16±5,‐28±5% vs ‐3±2,‐13±2% at 100, 1000nM). The AA responses to [Pro11, D‐Ala12]ANGI were blocked by CV in both. In summary, we have identified a novel role for renal chymase activity in diabetes. We propose that a switch from ACE‐dependent to chymase‐dependent intrarenal ANGII formation contributes to diabetic renal vascular disease.