Role of Thioredoxin 1 in Impaired Renal Sodium Excretion of hD 5 R F173L Transgenic Mice

Background Dopamine D 5 receptor (D 5 R) plays an important role in the maintenance of blood pressure by regulating renal sodium transport. Our previous study found that human D 5 R mutant F173L transgenic ( hD 5 R F173L ‐TG) mice are hypertensive. In the present study, we aimed to investigate the mechanisms causing this renal D 5 R dysfunction in hD 5 R F173L ‐TG mice. Methods and Results Compared with wild‐type D 5 R‐TG ( hD 5 R WT ‐TG) mice, hD 5 R F173L ‐TG mice have higher blood pressure, lower basal urine flow and sodium excretion, and impaired agonist‐mediated natriuresis and diuresis. Enhanced reactive oxygen species production in hD 5 R F173L ‐TG mice is caused, in part, by decreased expression of antioxidant enzymes, including thioredoxin 1 (Trx1). Na + ‐K + ‐ATPase activity is increased in mouse renal proximal tubule cells transfected with hD 5 R F173L , but is normalized by treatment with exogenous recombinant human Trx1 protein. Regulation of Trx1 by D 5 R occurs by the phospholipase C/ protein kinase C (PKC) pathway because upregulation of Trx1 expression by D 5 R does not occur in renal proximal tubule cells from D 1 R knockout mice in the presence of a phospholipase C or PKC inhibitor. Fenoldopam, a D 1 R and D 5 R agonist, stimulates PKC activity in primary renal proximal tubule cells of hD5R WT ‐ TG mice, but not in those of hD 5 R F173L ‐TG mice. Hyperphosphorylation of hD 5 R F173L and its dissociation from Gαs and Gαq are associated with impairment of D 5 R‐mediated inhibition of Na + ‐K + ‐ATPase activity in hD 5 R F173L ‐TG mice. Conclusions These suggest that hD 5 R F173L increases blood pressure, in part, by decreasing renal Trx1 expression and increasing reactive oxygen species production. Hyperphosphorylation of hD 5 R F173L , with its dissociation from Gαs and Gαq, is the key factor in impaired D 5 R function of hD 5 R F173L ‐TG mice.