The Effects of Dopamine D2 Receptor Specific Deletion in the Renal Proximal Tubule of Mice are Sex Dependent

Abstract

We have reported that the dopamine D2 receptor (D2R) has a major effect in preventing inflammation and injury in the mouse kidney and in human renal proximal tubule cells (hRPTCs). Lack of or decreased expression of D2R in the mouse kidney or in hRPTCs carrying genetic variants of the receptor that decrease its expression results in an increase in inflammatory factors and injury markers. Because dopamine is synthesized in the RPT and regulated by D2R, we developed a model to determine the effects of D2R in the RPT by generating Drd2fl/fl, PSGLT2::Cre+ mice (D2RPT-/-) that lack D2R only in the RPT and Drd2 fl/fl, PSGLT2::Cre- (D2RPT+/+) mice that do not have the deletion. We hypothesized that the D2R plays a role in the protection of females from renal injury, relative to males. We studied male and female mice on normal salt (NS; 0.4% NaCl) and high salt (HS; 4% NaCl) diets. On NS diet, male D2RPT-/- had higher D2R protein expression in the renal cortex than male D2RPT+/+ (0.85 ± 0.06 vs 0.49 ± 0.11, D2R/GAPDH; n=5; P<0.05) and female D2RPT-/- had higher D2R expression than female D2RPT+/+ (2.95 ± 0.69 vs 1.72 ± 0.35, D2R/GAPDH; n=5; P<0.05). HS increased D2R expression in both male groups (D2RPT+/+ 0.49 ± 0.11 vs 1.04 ± 0.08; n=3-5; P<0.05; D2RPT-/- 0.85 ± 0.06 vs 1.28 ± 0.19, D2R/GAPDH; n=3-5, P<0.05) but decreased its expression in both female groups (D2RPT+/+ 1.72 ± 0.35 vs 0.91 ± 0.05; n=4-5; P<0.05; n=5; D2RPT-/- 2.95 ± 0.69 vs 0.95 ± 0.04, D2R/GAPDH; n=4-5, P<0.05). The transcription factor Nurr1 is involved in the regulation of D2R expression. Nurr1 expression on NS was higher in females of both groups (D2RPT+/+ 1.57± 0.29; D2RPT-/-1.96 ± 0.20, Nurr1/GAPDH; n=4-5; P<0.05) than in males (D2RPT+/+ 0.24 ± 0.05; D2RPT-/-0.38 ± 0.17, Nurr1/GAPDH). HS increased Nurr1 expression in males (D2RPT+/+0.24± 0.05 vs 1.36 ± 0.22; D2RPT-/-0.38± 0.17 vs 0.89 ± 0.19, Nurr1/GAPDH; n=4-5; P<0.05), tended to decrease it in female D2RPT+/+ (1.57± 0.29 vs 1.26 ± 0.19, Nurr1/GAPDH) but decreased significantly in D2RPT-/- (1.96 ± 0.20 vs 0.76± 0.11 ratio Nurr1/GAPDH; n=4-5; P<0.05). The mRNA expression of the injury marker Kim-1 on NS was lower in female than in male mice and was increased in both males and females with D2RPT-/- (1.69 ± 0.09 and 0.36 ± 0.02 fold-change) compared with D2R PT+/+ (1.02 ± 0.03 and 0.15 ± 0.01 fold-change). On HS, there was a decrease in females with D2RPT-/- (0.36 ± 0.02 vs 0.13 ± 0.01 fold-change; n=4-5; p<0.05) and an increase in males with D2RPT-/- (1.69 ± 0.09 vs 3.34 ± 0.56 fold-change; n=4-5; p<0.05). These results show that renal D2R expression is higher in female mice then males and HS diet resulting in increased inflammation and injury elicits an increase in the expression of the receptor in males but a decrease in females. Nurr1 expression is related to D2R expression on NS but has a different response to HS in males and females. The expression of Kim-1 was lower in females than in males regardless of diet and genotype suggesting that increased basal levels of the D2R results in a protective effect. Our findings indicate that the D2R is part of the protective response to renal injury in females.