Intrarenal dopamine modulates progressive angiotensin II-mediated renal injury

Abstract

It is well-recognized that excessive angiotensin II (ANG II) can mediate progressive renal injury. Previous studies by us and others have indicated that dopamine may modulate actions of ANG II in the kidney. The current studies investigated whether altering intrarenal dopamine levels affected ANG II-mediated renal fibrosis. We utilized a model of increased intrarenal dopamine, catechol-O-methyl-transferase knockout (COMT KO) mice, which have increased kidney dopamine levels due to deletion of a major intrarenal dopamine-metabolizing enzyme. In wild-type mice, chronic ANG II infusion increased renal expression of both of the major dopamine-metabolizing enzymes, COMT and monoamine oxidase. After 8 wk of ANG II infusion, there were no significant differences in blood pressure between wild-type and COMT KO mice. Compared with wild-type, COMT KO mice had decreased albuminuria and tubulointerstitial injury. In response to ANG II infusion, there was decreased expression of both glomerular and tubulointerstitial injury markers (fibronectin, connective tissue growth factor, fibroblast-specific protein-1, collagen I, podocyte vascular endothelial growth factor) in COMT KO mice. We recently reported that ANG II-mediated tubulointerstitial fibrosis is mediated by src-dependent epidermal growth factor receptor (EGFR) activation. In aromatic l-amino acid decarboxylase knockout (AADC KO) mice, a model of intrarenal dopamine deficiency due to selective proximal tubule AADC deletion, which inhibits intrarenal dopamine synthesis, ANG II infusion further increased expression of p-src and pTyr845-EGFR. In contrast, their expression was markedly attenuated in COMT KO mice. These results demonstrate a role for intrarenal dopamine to buffer the detrimental effects of ANG II upon the kidney.

Fig. 1.

Dopamine-mediated alterations in expression of the angiotensin system in cultured proximal tubule cells. A and B: PCR identified the existence of the components of angiotensin system (A) and dopamine system (B) in cultured mouse proximal tubule cells. C: dopamine inhibited angiotensinogen (AGT) expression and increased angiotensin-converting enzyme (ACE)2 expression. AADC, aromatic l-amino acid decarboxylase; COMT, catechol-O-methyl-transferase; MAO, monoamine oxidase.

Fig. 2.

Urinary ANG II excretion was inhibited by activation of the intrarenal dopaminergic system. Gludopa, a renal specific dopamine precursor, inhibited urinary ANG II excretion in wild-type mice. Compared with wild-type mice, urinary ANG II excretion was reduced in COMT knockout (KO) mice. *P < 0.05 vs. control wild-type mice, n = 4 in each group.

Fig. 3.

ANG II activated renal dopamine-metabolizing system and decreased renal dopamine levels. A: chronic ANG II infusion led to increases in expression of MAO and COMT. B: at baseline, renal dopamine levels were higher in COMT KO mice than in wild-type. ANG II infusion decreased renal dopamine levels in wild-type but not COMT KO mice (*P < 0.05 vs. control wild-type, n = 4 in each group).

Fig. 4.

ANG II-mediated albuminuria was significantly attenuated in COMT KO mice. A: SDS-PAGE gel electrophoresis indicates significantly less urinary protein excretion in ANG II-treated unilaterally nephrectomized (UNX) COMT KO mice than in the ANG II-treated UNX wild-type mice. Loading volume was determined using urinary creatinine as an internal control. B: 24-h urinary albumin excretion (UAE) was significantly lower in ANG II-treated UNX COMT KO mice than ANG II-treated UNX wild-type mice (*P < 0.01 vs. wild-type control; †P < 0.01 vs. corresponding UNX mice; ‡P < 0.01 vs. ANG II-treated UNX wild-type mice, n = 6 in each group).

Fig. 5.

ANG II-mediated renal injury was markedly attenuated in COMT KO mice. ANG II infusion led to significantly less interstitial fibrosis (A) and glomerular sclerosis (B) in COMT KO mice than in wild-type mice (*P < 0.01 vs. wild-type, n = 4).

Fig. 6.

ANG II-mediated elevations of mediators and markers of fibrosis were attenuated in COMT KO mice. A: immunohistochemistry showed that ANG II-induced elevations of fibronectin, connective tissue growth factor (CTGF), fibroblast-specific protein-1 (FSP-1), collagen I, and vascular endothelial growth factor (VEGF) were significantly attenuated in COMT KO mice. B: immunoblotting indicated that ANG II-induced increases in fibronectin, FSP-1, and CTGF were attenuated in COMT KO mice.

Fig. 7.

ANG II-mediated activation of Src-epidermal growth factor receptor (EGFR) signaling was attenuated by intrarenal dopamine. A: activation of Src and EGFR induced by ANG II was attenuated in COMT KO mice. B: ANG II-induced increases in NADPH oxidase 1 (NOX-1) expression were inhibited in COMT KO mice. Control and ANG II-infused samples were from the same gel. C: activation of Src and EGFR induced by ANG II was augmented in AADC KO mice.

Fig. 8.

Intrarenal dopamine antagonizes ANG II-induced renal injury at multiple levels. ANG II induces renal injury through activation of AT₁ receptors. Intrarenal dopamine may antagonize ANG II-induced renal injury through inhibition of AT₁ expression and decreases in intrarenal ANG II production due to inhibition of expression of both AGT and renin.