Renal c-fos expression induced by angiotensin II is enhanced in spontaneously hypertensive rats

Role of bradykinin in renoprotective effects by angiotensin II type 1 receptor antagonist in salt-sensitive hypertension

To elucidate whether bradykinin is involved in the renoprotective effect produced by angiotensin II type 1 receptor antagonist (AT1A) in chronic salt-sensitive hypertension, Dahl salt-sensitive rats receiving a high-salt (8%) diet were treated either with an AT1A (candesartan, 1 mg/kg/day), a bradykinin B2 receptor antagonist (BKB2A; FR172357, 30 mg/kg/day) or a combination of AT1A and BKB2A for 7 weeks. None of the treatments changed the markedly increased systolic blood pressure induced by a high-salt diet. However, chronic treatment with AT1A significantly improved the histological hallmarks of renal damage-i.e., glomerular sclerosis and cell proliferation-despite the presence of severe hypertension. This beneficial action of AT1A was abolished by the concomitant administration of BKB2A. In agreement with these histologically based findings, increases in levels of creatinine clearance induced by AT1A were also reversed back to the basal levels when BKB2A was administered in conjunction with AT1A. Furthermore, urinary excretions of nitrate plus nitrite and prostaglandin E2 increased moderately in response to the administration of AT1A alone, but not in combination with BKB2A. Thus, the blockade of bradykinin signaling abrogates the renoprotective actions of the angiotensin II type 1 (AT1) receptor antagonism. Collectively, these data show that when AT1 action is chronically blocked, endogenous bradykinin plays a pivotal role in preventing the progression of glomerular injury in salt-sensitive hypertension.

Increased angiotensin II-mediated Src signaling via epidermal growth factor receptor transactivation is associated with decreased C-terminal Src kinase activity in vascular smooth muscle cells from spontaneously hypertensive rats

We investigated whether upregulation of Src by Ang II leads to increased extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and whether these processes are associated with altered activation of C-terminal Src kinase (Csk), a negative regulator of Src. Furthermore, the role of epidermal growth factor receptor (EGFR) transactivation by angiotensin II (Ang II) was determined. Ang II-mediated c-Src phosphorylation was significantly greater (approximately 4-fold, P<0.01) in SHR than in Wistar-Kyoto rats (WKY). Ang II increased Csk phosphorylation 2-to 3-fold in WKY but not in SHR. Treatment of the cells with AG1478, a selective EGFR tyrosine kinase inhibitor, decreased Ang II-mediated c-Src phosphorylation, particularly in SHR. Phosphorylation of cortactin and Pyk2/focal adhesion kinase, Src-specific substrates, was increased by Ang II >3-fold, with significantly greater responses in SHR than in WKY (P<0.05). Ang II-induced ERK1/2 activation was significantly augmented (P<0.05) and sustained in VSMCs from SHR. PP2, a selective Src inhibitor, attenuated these effects and normalized the responses in SHR. Irbesartan, a selective Ang II type 1 receptor blocker, but not PD123319, a selective Ang II type 2 receptor blocker, inhibited Ang II actions. Our results demonstrate that c-Src phosphorylation and Src-dependent ERK1/2 signaling by Ang II are increased in VSMCs from SHR. These processes are associated with blunted Ang II-induced phosphorylation of Csk. EGFR transactivation contributes to Ang II-mediated Src-dependent ERK1/2 signaling. In conclusion, altered regulation of Ang II type 1 receptor-activated c-Src by Csk may be an important upstream modulator of abnormal ERK1/2 signaling in VSMCs from SHR.

Src is an important mediator of extracellular signal-regulated kinase 1/2-dependent growth signaling by angiotensin II in smooth muscle cells from resistance arteries of hypertensive patients

The role of c-Src in growth signaling by angiotensin (Ang) II was investigated in vascular smooth muscle cells (VSMCs) from arteries of hypertensive patients. c-Src and extracellular signal-regulated kinase 1/2 (ERK1/2) activity, proto-oncogene expression, activating protein-1 (AP-1) DNA-binding activity, and DNA and protein synthesis were studied in Ang II-stimulated VSMCs derived from small peripheral resistance arteries of normotensive subjects (NTs, n=5) and age-matched untreated hypertensive patients (HTs, n=10). Ang II type 1 (AT(1)) and type 2 (AT(2)) receptor status was also assessed. Ang II dose-dependently increased the synthesis of DNA and protein, with enhanced effects in VSMCs from HTs. PD 098,059, a selective inhibitor of the ERK1/2 pathway, attenuated Ang II-stimulated growth in HTs. The effects of PD 098,059 were greater in HTs than in NTs. In NTs, Ang II transiently increased ERK1/2 phosphorylation, whereas in HTs, Ang II-stimulated actions were augmented and sustained. PP2, a selective Src inhibitor, reduced ERK1/2 activity and normalized ERK1/2 responses in HTs. Ang II-induced c-Src phosphorylation was 2- to 3-fold greater in HTs than in NTs. In HTs but not NTs, kinase activation was followed by overexpression of c-fos and enhanced AP-1 DNA-binding activity. PD 098,059 and PP2 attenuated these responses. AT(1) receptor expression was similar in NTs and HTs. In HT cells transfected with c-fos antisense oligodeoxynucleotide, Ang II-stimulated growth was reduced compared with sense oligodeoxynucleotide. Our findings suggest that augmented Ang II-stimulated VSMC growth is mediated via hyperactivation of c-Src-regulated ERK1/2-dependent pathways, leading to overexpression of c-fos mRNA and enhanced AP-1 DNA-binding activity. Because AT(1) receptor expression was unaltered in HTs, increased Ang II signaling may be a postreceptor phenomenon. These data define a signal transduction pathway whereby Ang II mediates exaggerated growth in VSMCs from HTs.

Differential activation of extracellular signal-regulated protein kinase 1/2 and p38 mitogen activated-protein kinase by AT1 receptors in vascular smooth muscle cells from Wistar-Kyoto rats and spontaneously hypertensive rats

OBJECTIVES

The present study investigates effects of angiotensin II on activation of extracellular signal-regulated protein kinase (ERK) 1/2, p38 mitogen activated-protein kinase (p38MAPK) and c-Jun amino terminal kinase (JNK) in vascular smooth muscle cells from spontaneously hypertensive rats (SHR).

METHODS

Vascular smooth muscle cells (VSMC) from mesenteric arteries of Wistar-Kyoto (WKY) rats and SHR were studied. Angiotensin II-induced phosphorylation of ERK1/2, JNK and p38MAPK were assessed by Western blot analysis. c-fos mRNA expression by angiotensin II was determined by reverse transcriptase-polymerase chain reaction in the absence and presence of PD98059, selective inhibitor of ERK1/2-dependent pathways and SB202190, selective p38MAPK inhibitor.

RESULTS

Angiotensin II increased phosphorylation of ERK1/2 and p38MAPK, but not JNK. Responses were significantly increased in SHR compared with WKY. Irbesartan, AT1 receptor antagonist, but not PD123319, AT2 receptor blocker, abolished angiotensin II-induced effects. PP2, selective Src inhibitor, decreased angiotensin II-mediated activation of MAP kinases. Angiotensin II increased c-fos mRNA expression in SHR and had a small stimulatory effect in WKY. These actions were inhibited by PD98059, whereas SB202190 had no effect.

CONCLUSIONS

Angiotensin II-induced activation of vascular ERK1/2 and p38MAPK is increased in SHR. These effects are mediated via AT1 receptors, which activate Src-dependent pathways. Overexpression of c-fos mRNA in SHR is due to ERK1/2-dependent, p38MAPK-independent pathways. Our results suggest that angiotensin II activates numerous MAP kinases in VSMCs and that differential activation of these kinases may be important in altered growth signaling in VSMCs from SHR.