Role of oxidative stress in defective renal dopamine D1 receptor-G protein coupling and function in old Fischer 344 rats

2006 ◽  
Vol 291 (5) ◽  
pp. F945-F951 ◽  
Author(s):  
Riham Zein Fardoun ◽  
Mohammad Asghar ◽  
Mustafa Lokhandwala
Keyword(s):  
Oxidative Stress ◽  
G Protein ◽  
D1 Receptor ◽  
Serine Phosphorylation ◽  
D1 Receptors ◽  
Adult Rats ◽  
G Protein Coupling ◽  
Protein Coupling ◽  
Age Related ◽  
Old Rats

Aging is associated with an increase in oxidative stress. Previously, we have reported that dopamine failed to inhibit proximal tubular Na-K-ATPase and to promote sodium excretion in old rats (Beheray S, Kansra V, Hussain T, and Lokhandwala MF. Kidney Int 58: 712–720, 2000). This was due to uncoupling of dopamine D1 receptors from G proteins resulting from hyperphosphorylation of D1 receptors. The present study was designed to test the role of oxidative stress in the age-related decline in renal dopamine D1 receptor function. We observed that old animals had increased malondialdehyde (MDA) levels, a biomarker of oxidative stress, and decreased D1 receptor number and protein in the proximal tubules (PT) compared with adult rats. In old rats, there was increased G protein-coupled receptor kinase-2 (GRK-2) abundance, increased basal serine phosphorylation of D1 receptors, and defective D1 receptor-G protein coupling in PT membranes. Interestingly, supplementation with an antioxidant, tempol (1 mmol/l in drinking water for 15 days), lowered MDA levels and normalized D1 receptor number and protein in old rats to the level seen in adult rats. Furthermore, tempol decreased GRK-2 abundance and D1 receptor serine phosphorylation and restored D1 receptor-G protein coupling in PT of old rats. The functional consequence of these changes was the restoration of the natriuretic response to D1 receptor activation in tempol-supplemented old rats. Therefore, in old rats, tempol reduces oxidative stress and prevents GRK-2 membranous abundance and hyperphosphorylation of D1 receptors, resulting in restoration of D1 receptor-G protein coupling and the natriuretic response to SKF-38393. Thus tempol, by lowering oxidative stress, normalizes the age-related decline in dopamine receptor function.

scholarly journals Exercise activates redox-sensitive transcription factors and restores renal D1 receptor function in old rats

2009 ◽  
Vol 297 (5) ◽  
pp. F1174-F1180 ◽  
Author(s):  
Liza George ◽  
Mustafa F. Lokhandwala ◽  
Mohammad Asghar
Keyword(s):  
Oxidative Stress ◽  
Transcription Factors ◽  
G Protein ◽  
Skf 38393 ◽  
Antioxidant Defenses ◽  
Heme Oxygenase 1 ◽  
Related Factor ◽  
G Protein Coupling ◽  
Protein Coupling ◽  
Old Rats

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)-κB 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-κB seem to play key role in this phenomenon.

Tempol reduces oxidative stress and restores renal dopamine D1-like receptor- G protein coupling and function in hyperglycemic rats

2006 ◽  
Vol 291 (1) ◽  
pp. F58-F66 ◽  
Author(s):  
Aditi Marwaha ◽  
Mustafa F. Lokhandwala
Keyword(s):  
Oxidative Stress ◽  
G Protein ◽  
Sodium Excretion ◽  
Receptor Activation ◽  
Serine Phosphorylation ◽  
G Protein Coupling ◽  
Protein Coupling ◽  
Agonist Stimulation ◽  
Renal Dopamine ◽  
And Function

Dopamine via activation of renal D1-like receptors inhibits the activities of Na-K-ATPase and Na/H exchanger and subsequently increases sodium excretion. Decreased renal dopamine production and sodium excretion are associated with hyperglycemic conditions. We have earlier reported D1-like receptor-G protein uncoupling and reduced response to D1-like receptor activation in streptozotocin (STZ)-treated hyperglycemic rats (Marwaha A, Banday AA, and Lokhandwala MF. Am J Physiol Renal Physiol 286: F451–F457, 2004). The present study was designed to test the hypothesis that oxidative stress associated with hyperglycemia increases basal D1-like receptor serine phosphorylation via activation of the PKC-G protein receptor kinase (GRK) pathway, resulting in loss of D1-like receptor-G protein coupling and function. We observed that STZ-treated rats exhibited oxidative stress as evidenced by increased lipid peroxidation. Furthermore, PKC activity and expression of PKC-βI- and -δ-isoforms were increased in STZ-treated rats. In addition, in STZ-treated rats there was increased GRK2 translocation to proximal tubular membrane and increased basal serine D1-like receptor phosphorylation. Supplementation with the antioxidant tempol lowered oxidative stress in STZ-treated rats, led to normalization of PKC activity, and prevented GRK2 translocation. Furthermore, tempol supplementation in STZ-treated rats restored D1-like receptor-G protein coupling and inhibition of Na-K-ATPase activity on D1-like receptor agonist stimulation. The functional consequence was the restoration of the natriuretic response to D1-like receptor activation. We conclude that oxidative stress associated with hyperglycemia causes an increase in activity and expression of PKC. This leads to translocation of GRK2, subsequent phosphorylation of the D1-like receptor, its uncoupling from G proteins and loss of responsiveness to agonist stimulation.

Oxidative stress reduces renal dopamine D1 receptor-Gq/11α G protein-phospholipase C signaling involving G protein-coupled receptor kinase 2

2007 ◽  
Vol 293 (1) ◽  
pp. F306-F315 ◽  
Author(s):  
Anees Ahmad Banday ◽  
Mustafa F. Lokhandwala
Keyword(s):  
Oxidative Stress ◽  
Atpase Activity ◽  
Phospholipase C ◽  
G Protein ◽  
Lipoic Acid ◽  
Skf 38393 ◽  
G Protein Coupling ◽  
Protein Coupling ◽  
Obese Rats ◽  
G Protein Coupled

The dopamine D1 receptors (D1R), expressed in renal proximal tubules, participate in the regulation of sodium transport. A defect in the coupling of the D1R to its G protein/effector complex in renal tubules has been reported in various conditions associated with oxidative stress. Because G protein-coupled receptor kinases (GRKs) are known to play an important role in D1R desensitization, we tested the hypothesis that increased oxidative stress in obese Zucker rats may cause GRK2 upregulation and, subsequently, D1R dysfunction. Lean and obese rats were given normal diet or diet supplemented with antioxidant lipoic acid for 2 wk. Compared with lean rats, obese rats exhibited oxidative stress, D1R were uncoupled from Gq/11α at basal level, and SKF-38393 failed to elicit D1R-G protein coupling, stimulate phospholipase C (PLC), and inhibit Na-K-ATPase activity. These animals showed increased basal protein kinase C (PKC) activity and membranous translocation of GRK2 and increased GKR2-Gq/11α interaction and D1R serine phosphorylation. Enzymatic dephosphorylation of D1R restored SKF-38393-induced adenylyl cyclase stimulation but not PLC activation. Treatment of obese rats with lipoic acid restored D1R-G protein coupling and SKF-38393-induced PLC stimulation and Na-K-ATPase inhibition. Lipoic acid treatment also normalized PKC activity, GRK2 sequestration, and GKR2-Gq/11α interaction. In conclusion, these data show that oxidative stress increases PKC activity causing GRK2 membranous translocation. GRK2 interacts with Gq/11α and acts, at least in part, as a regulator of G protein signaling leading to the D1R-Gq/11α uncoupling, causing inability of SKF-38393 to stimulate PLC and inhibit Na/K-ATPase. Lipoic acid, while reducing oxidative stress, normalized PKC activity and restored D1R-Gq/11α-PLC signaling and the ability of SKF-38393 to inhibit Na-K-ATPase activity.

Exercise decreases oxidative stress and inflammation and restores renal dopamine D1 receptor function in old rats

2007 ◽  
Vol 293 (3) ◽  
pp. F914-F919 ◽  
Author(s):  
Mohammad Asghar ◽  
Liza George ◽  
Mustafa F. Lokhandwala
Keyword(s):  
Oxidative Stress ◽  
G Protein ◽  
Sch 23390 ◽  
D1 Receptor ◽  
Skf 38393 ◽  
Receptor Function ◽  
Protein Activation ◽  
G Protein Activation ◽  
Anti Oxidant ◽  
Old Rats

Recently, we reported that oxidative stress decreases D1 receptor numbers and G protein activation in renal proximal tubules (RPT), resulting in diminished natriuretic response to dopamine in old rats. We tested the hypothesis that exercise in old rats will decrease oxidative stress and restore natriuretic response to D1 receptor agonist, SKF 38393. Old (23 mo) rats were subjected to rest (sedentary) or to treadmill exercise followed by measurement of oxidative stress [malondialdehyde (MDA)], inflammation [C-reactive protein (CRP)], anti-inflammation (IL-10), antioxidant enzyme [superoxide dismutase (SOD)], and natriuretic response to SKF 38393. We found that MDA levels decreased and total SOD activity and Cu/ZnSOD protein increased in RPT of exercised rats. Exercise increased the nuclear levels of Nrf2 transcription factor (which binds to anti-oxidant response elements) in RPT. The levels of CRP decreased and IL-10 increased in RPT of exercised rats. Furthermore, exercise increased the basal bindings of [3H]SCH 23390 and [35S]GTPγS (indexes of D1 receptor number and G protein activation, respectively) together with D1 receptor and Gαq proteins in RPT membranes. Moreover, SKF 38393 increased sodium excretion in exercised rats. Also, exercise decreased the levels of proteins in the urine of old rats. These results demonstrate that exercise decreases oxidative stress, inflammation, and proteinuria and increases anti-oxidant defense and D1 receptor function in old rats. Therefore, exercise may prove beneficial in preventing age-associated increases in oxidative stress, inflammation, and preserving kidney function, in general, and renal D1 receptor responsiveness, in particular.

scholarly journals Renal proximal tubules from old Fischer 344 rats grow into epithelial cells in cultures and exhibit increased oxidative stress and reduced D1 receptor function

2008 ◽  
Vol 295 (5) ◽  
pp. C1326-C1331 ◽  
Author(s):  
Mohammad Asghar ◽  
Annirudha Chillar ◽  
Mustafa F. Lokhandwala
Keyword(s):  
Oxidative Stress ◽  
Primary Cultures ◽  
D1 Receptor ◽  
Zucker Rats ◽  
Receptor Function ◽  
Adult Rats ◽  
Fischer 344 ◽  
Old Rats ◽  
Obese Zucker Rats ◽  
F344 Rats

Earlier we reported defects in D1 receptor function in renal proximal tubules (RPTs) of aged Fischer 344 (F344) and obese Zucker rats. However, the defects in the receptor function in RPTs of obese Zucker rats do not pass onto primary cultures of RPTs from these animals. Here, we determined whether the defects in D1 receptor function in RPTs of aged F344 rats pass onto the primary cultures. RPTs from aged (24-mo) and adult (6-mo) F344 rats were grown into primary cultures. The microscopic studies showed that cells in cultures from adult and old rats were healthy as determined by the shape and size of the cells and nuclei. D1 receptor agonist SKF-38393 produced inhibition of 86Rb (rubidium) uptake, index of Na-K-ATPase activity, in cells from adult rats, but this was reduced in old rats. Also, SKF-38393 increased the [35S]GTPγS binding, index of receptor activation, in the membranes of cells from adult rats but to a lesser extent from old rats. Furthermore, there was a downward trend in the levels of D1 receptor numbers and in the receptor proteins in old rats. Interestingly, gp 91phox subunit of NADPH oxidase and cellular protein carbonyl levels (oxidative stress marker) were higher in cultures from old rats. These results show that RPTs from adult and old F344 rats grow into epithelial cells in cultures. Furthermore, cells in cultures from old rats are at a higher level of oxidative stress, which may be contributing to the reduced D1 receptor function in the cells from old compared with adult rats.

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