Narimasa Miho

Beneficial Effect of T-Type Calcium Channel Blockers on Endothelial Function in Patients with Essential Hypertension

Endothelial function is impaired in essential hypertension. T-type but not L-type voltage-gated Ca2+ channels were detected in the vascular endothelium. The purpose of the present study was to clarify the role of T-type Ca2+ channels in endothelial function. We studied flow-mediated vasodilation (FMD) and sublingual nitroglycerin (NTG)-induced vasodilation in the brachial artery. Forty patients with essential hypertension were randomly assigned to treatment with efonidipine, a T- and L-type Ca2+ channel blocker, or with nifedipine, an L-type Ca2+ channel blocker. Twenty healthy normotensive individuals were included as a control group. In patients with essential hypertension, FMD was attenuated and NTG was similar that of compared to healthy controls. After 12 weeks, the decrease in mean blood pressure in the efonidipine and nifedipine groups were similar. The endothelial function index, a ratio of FMD/NTG, was significantly increased by efonidipine (73±24 to 94±20%) but unchanged by nifedipine. Urinary excretion 8-hydroxy-2′-deoxyguanosine (8-OHdG) and serum malondialdehyde-modified low-density lipoprotein (LDL) were decreased by efonidipine but unchanged by nifedipine. These results suggest that a T-type Ca2+ channel blocker, but not an L-type Ca2+ channel blocker, may improve vascular endothelial dysfunction in patients with essential hypertension via a reduction in oxidative stress.

Angiotensin II-Induced Osteopontin Expression in Vascular Smooth Muscle Cells Involves Gq/11, Ras, ERK, Src and Ets-1

Recent studies suggest that osteopontin (OPN) plays a critical role in the progression of atherosclerotic plaques and that angiotensin II (Ang II) is a potent upregulator of OPN expression. The goal of the present study was to characterize the signaling mechanisms whereby Ang II increases OPN expression in vascular smooth muscle cells (VSMC). YM-254890, a specific inhibitor of Gq/11, potently suppressed Ang II−induced OPN expression and ERK1/2 activation. Among dominant-negative (DN) mutants of small G proteins, only DN-Ras suppressed Ang II−induced OPN promoter activity. DN-MEK1 markedly inhibited Ang II−induced OPN promoter activity, while neither DN-JNK nor DN-p38 MAP kinase had any effect. DN-Src and DN-Fyn suppressed Ang II−induced OPN promoter activity. YM-254890 inhibited Ang II−induced Src and Ras activation, and PP2, a selective inhibitor for the Src kinase family, inhibited Ras activation, suggesting that the Gq/11-Src-Ras axis is the upstream signaling cascade for Ang II−induced OPN expression. Finally, small interfering RNA against Ets-1 suppressed Ang II−induced OPN expression. In conclusion, these data suggest that Ang II−induced OPN expression in VSMC is mediated by signaling cascades involving Gq/11, the Ras-ERK axis, and the Src kinase family, and by the transcription factor, Ets-1. These signaling molecules may represent therapeutic targets for the prevention of pathological vascular remodeling.

Mnk1 Is Required for Angiotensin II–Induced Protein Synthesis in Vascular Smooth Muscle Cells

Abstract— Angiotensin II (Ang II) stimulates protein synthesis in vascular smooth muscle cells (VSMCs), possibly secondary to regulatory changes at the initiation of mRNA translation. Mitogen-activated protein (MAP) kinase signal–integrating kinase-1 (Mnk1), a substrate of ERK and p38 MAP kinase, phosphorylates eukaryotic initiation factor 4E (eIF4E), an important factor in translation. The goal of the present study was to investigate the role of Mnk1 in Ang II–induced protein synthesis and to characterize the molecular mechanisms by which Mnk1 and eIF4E is activated in rat VSMCs. Ang II treatment resulted in increased Mnk1 activity and eIF4E phosphorylation. Expression of a dominant-negative Mnk1 mutant abolished Ang II–induced eIF4E phosphorylation. PD98059 or introduction of kinase-inactive MEK1/MKK1, but not SB202190 or kinase-inactive p38 MAP kinase, inhibited Ang II–induced Mnk1 activation and eIF4E phosphorylation, suggesting that ERK, but not p38 MAP kinase, is required for Ang II–induced Mnk1-eIF4E activation. Further, dominant-negative constructs for Ras, but not for Rho, Rac, or Cdc42, abolished Ang II–induced Mnk1 activation. Finally, treatment of VSMCs with CGP57380, a novel specific kinase inhibitor of Mnk1, resulted in dose-dependent decreases in Ang II–stimulated phosphorylation of eIF4E, protein synthesis, and VSMC hypertrophy. In summary, these data demonstrated that (1) Ang II–induced Mnk1 activation is mediated by the Ras-ERK cascade in VSMCs, and (2) Mnk1 is involved in Ang II–mediated protein synthesis and hypertrophy, presumably through the activation of translation-initiation. The Mnk1-eIF4E pathway may provide new insights into molecular mechanisms involved in vascular hypertrophy and other Ang II–mediated pathological states.