Abstract
We have previously reported that age-associated oxidative stress via protein kinase C (PKC) increases D1 receptor (D1R) phosphorylation and causes D1R-G protein uncoupling in renal proximal tubules (RPTs) of old Fischer 344 rats. This results in reduced ability of D1R agonist SKF-38393 to inhibit Na+-K+-ATPase in RPTs of old rats. Here, we studied the effect of treadmill exercise on markers of oxidative stress, PKC, D1R phosphorylation, D1R-G protein coupling, and Na+-K+-ATPase activity in RPTs of adult and old rats. We found increased levels of malondialdehyde, a marker of oxidative stress, in RPTs of old rats, which decreased during exercise. Nuclear levels of nuclear erythroid-related factor (Nrf)-2 and nuclear factor (NF)-kappaB in RPTs, transcription factors involved in antioxidant enzyme gene transcription, increased in exercised old rats. This was accompanied by an increase in the activity and expression of antioxidant enzymes, superoxide dismutase and heme oxygenase-1. Age-related decrease in the levels of D1R mRNAs and proteins was attenuated during exercise. Furthermore, exercise in old rats decreased PKC activity and D1R phosphorylation and increased SKF-38393-mediated [35S]guanosine 5'-O-(3-thiotriphosphate) binding (an index of D1R-G protein coupling). SKF-38393 also caused inhibition of Na+-K+-ATPase in these animals. Also, exercise caused a decrease in proteinuria and increase in phosphaturia in old rats. These results suggest beneficial effects of exercise in terms of increasing antioxidant defenses, decreasing oxidative stress, and improving kidney function in general and D1R function in particular in aging. Both Nrf-2 and NF-kappaB seem to play key role in this phenomenon.