NOS1β in the macula densa contributes to the sex differences in decline of GFR with aging

Abstract

Kidney function indicated by glomerular filtration rate (GFR) decline with aging. The descent of GFR begins at age about 40, and accelerates after age 60 to 70, but females have a much slower decline in GFR compared with males. The mechanisms underlying the decline in GFR with aging and the sex differences have not been clarified yet. In present study, we hypothesized that the expression of NOS1β in macula densa (MD) decreases with aging, which enhances tubuloglomerular feedback (TGF) responsiveness and contributes to declines of GFR. Females are protected by a lower rate of decrease in NOS1β expression compared with age‐matched males, resulting in the relatively retarded decline in kidney function with aging. First, we measured NOS1β protein level in both young mice (3 months) and aged mice (18 months) by Western Blot. The expression of NOS1β was reduced by 83±7.9% in aged male mice, but only reduced by 27±14.3% in aged females. TGF, as indicated by the change in proximal tubular stop flow pressure, was 6.1±0.8mmHg in young male mice and significantly enhanced to 8.7±1.2mmHg in aged males, but there was no significant changes in females with aging (5.9±1.2mmHg vs 6.8±1.6mmHg). GFR in conscious mice were measured by plasma FITC‐inulin clearance after a single bolus injection of FITC‐inulin. GFR was reduced by 36% in aged male mice, which was from 236±9.7 μl/min in young male mice to 150±7.6 μl/min in aged male mice, but only reduced by 17% in aged female mice, which was from 182±9.2 μl/min in young to 151±13.5 μl/min in aged females. Histology with PAS staining showed obvious glomerulosclerosis in aged mice. But the injury in aged male mice was much more severe than that in age matched females, with a higher glomerular injury score (1.4±0.5 vs 0.8±0.4). To further determine the role of MD NOS1β in the decline of GFR and sex differences with aging, we repeated the experiments in MD specific NOS1 knockout (MD‐NOS1KO) mice, which were developed by our laboratory. GFR was decreased more rapidly by 47% in aged male KO mice and by 39% in aged female KO mice, but the sex difference was diminished in the KO mice. Glomerular injury is more severe in both male and female MD‐NOS1 KO mice with a higher injury score (2.1±0.6, 1.7±0.5) than age matched wild type mice (1.4±0.5, 0.8±0.4). There was also no significant sex difference in MD‐NOS1KO mice. In conclusion, NOS1β in MD protects against decline of GFR with aging by modulating TGF response. The decreased expression of NOS1β in MD contributes to the decline of GFR in aged male mice. The relatively higher MD NOS1β level in female mice delays the decrease of GFR with aging.