Role of Thioredoxin 1 in Impaired Renal Sodium Excretion of hD5R F173L Transgenic Mice

Background-Dopamine D-5 receptor (D5R) plays an important role in the maintenance of blood pressure by regulating renal sodium transport. Our previous study found that human D5R mutant F173L transgenic (hD(5)R(F173)(L)-TG) mice are hypertensive. In the present study, we aimed to investigate the mechanisms causing this renal D5R dysfunction in hD(5)R(F173L) -TG mice. Methods and Results-Compared with wild-type D5R-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 D5R occurs by the phospholipase C/ protein kinase C (PKC) pathway because upregulation of Trx1 expression by D5R does not occur in renal proximal tubule cells from D1R knockout mice in the presence of a phospholipase C or PKC inhibitor. Fenoldopam, a D1R and D5R agonist, stimulates PKC activity in primary L renal proximal tubule cells of hD5R wl -TG mice, but not in those of hD 5 R-F731L-TG mice. Hyperphosphorylation of hD(5)R(F173L) and ; its dissociation from Gas and Gaq are associated with impairment of D5R-mediated inhibition of Na+-K+-ATPase activity in hD5R(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 G alpha s and G alpha q, is the key factor in impaired D5R function of hD(5) R-F173L-TG mice.