[Overexpression of human EP4 receptor in vascular smooth muscle cells attenuates angiotensin II-induced hypertension in mice].

Prostaglandin E2 (PGE2) plays an important role in cardiovascular system. PGE2 regulates blood pressure through its 4 G protein coupled receptors, i.e., EP1, EP2, EP3, and EP4. The aim of this study was to investigate the role of EP4 receptors in vascular smooth muscle cells (VSMC) in blood pressure regulation. VSMC-specific human EP4 transgenic (VSMC-hEP4 Tg) mice were generated and genotyped. The systolic blood pressure (SBP) of the VSMC-hEP4 Tg mice and the wild-type (WT) littermates was measured under normal, low-salt (LSD) and high-salt diet (HSD) conditions using a tail-cuff method. Both WT and VSMC-hEP4 Tg mice were administered with a chronic infusion of angiotensin II (Ang II) with an osmotic pump and SBP levels were monitored every week. The mean arterial blood pressure (MAP) of WT and VSMC-hEP4 Tg mice upon Ang II intravenous infusion was measured via carotid arterial catheterization. Ang II-induced vasoconstriction of the mesenteric arterial rings from WT and VSMC-hEP4 Tg mice was measured using the multi myograph system. The effect of PGE1-OH (a selective EP4 agonist) on Ang II-induced phosphorylation of myosin phosphatase target subunit 1 (MYPT1) was detected by Western blot. The effect of two additional EP4 specific agonists (CAY10580 and CAY10598, 0.5 mg/kg) on blood pressure of WT mice was measured by carotid arterial catheterization. The results showed that the VSMC-hEP4 Tg mice were successfully generated and their basal SBP levels were lower than those of WT mice. Although blood pressure levels were significantly altered in WT mice under LSD and HSD, little change was observed in the VSMC-hEP4 Tg mice. After a chronic infusion and an acute intravenous injection of Ang II, SBP levels of VSMC-hEP4 Tg mice were significantly lower than those of WT mice. In addition, both CAY10580 and CAY10598 significantly reduced MAP levels of WT mice. Ex vivo study showed that treatment of isolated mesenteric arteries with PGE1-OH inhibited Ang II-induced phosphorylation of MYPT1. Collectively, these results demonstrate that specific overexpression of human EP4 gene in VSMCs significantly reduces basal blood pressure levels and attenuates Ang II-induced hypertension, possibly via inhibiting Ang II/AT1 signaling pathway. Our findings suggest that EP4 may represent an attractive target for the treatment of hypertension.

Endothelial cell prostaglandin E2 receptor EP4 is essential for blood pressure homeostasis.

Prostaglandin E2 and its cognate EP1-4 receptors play important roles in blood pressure (BP) regulation. Herein, we show that endothelial cell-specific (EC-specific) EP4 gene-knockout mice (EC-EP4-/-) exhibited elevated, while EC-specific EP4-overexpression mice (EC-hEP4OE) displayed reduced, BP levels compared with the control mice under both basal and high-salt diet-fed conditions. The altered BP was completely abolished by treatment with l-NG-nitro-l-arginine methyl ester (l-NAME), a competitive inhibitor of endothelial nitric oxide synthase (eNOS). The mesenteric arteries of the EC-EP4-/- mice showed increased vasoconstrictive response to angiotensin II and reduced vasorelaxant response to acetylcholine, both of which were eliminated by l-NAME. Furthermore, EP4 activation significantly reduced BP levels in hypertensive rats. Mechanistically, EP4 deletion markedly decreased NO contents in blood vessels via reducing eNOS phosphorylation at Ser1177. EP4 enhanced NO production mainly through the AMPK pathway in cultured ECs. Collectively, our findings demonstrate that endothelial EP4 is essential for BP homeostasis.

VSMC-specific EP4 deletion exacerbates angiotensin II-induced aortic dissection by increasing vascular inflammation and blood pressure.

Prostaglandin E2 (PGE2) plays an important role in vascular homeostasis. Its receptor, E-prostanoid receptor 4 (EP4) is essential for physiological remodeling of the ductus arteriosus (DA). However, the role of EP4 in pathological vascular remodeling remains largely unknown. We found that chronic angiotensin II (AngII) infusion of mice with vascular smooth muscle cell (VSMC)-specific EP4 gene knockout (VSMC-EP4-/-) frequently developed aortic dissection (AD) with severe elastic fiber degradation and VSMC dedifferentiation. AngII-infused VSMC-EP4-/- mice also displayed more profound vascular inflammation with increased monocyte chemoattractant protein-1 (MCP-1) expression, macrophage infiltration, matrix metalloproteinase-2 and -9 (MMP2/9) levels, NADPH oxidase 1 (NOX1) activity, and reactive oxygen species production. In addition, VSMC-EP4-/- mice exhibited higher blood pressure under basal and AngII-infused conditions. Ex vivo and in vitro studies further revealed that VSMC-specific EP4 gene deficiency significantly increased AngII-elicited vasoconstriction of the mesenteric artery, likely by stimulating intracellular calcium release in VSMCs. Furthermore, EP4 gene ablation and EP4 blockade in cultured VSMCs were associated with a significant increase in MCP-1 and NOX1 expression and a marked reduction in α-SM actin (α-SMA), SM22α, and SM differentiation marker genes myosin heavy chain (SMMHC) levels and serum response factor (SRF) transcriptional activity. To summarize, the present study demonstrates that VSMC EP4 is critical for vascular homeostasis, and its dysfunction exacerbates AngII-induced pathological vascular remodeling. EP4 may therefore represent a potential therapeutic target for the treatment of AD.

[Role of prostaglandin E2 receptor 4 in cardiovascular diseases].

Prostaglandin E2 (PGE2) is a cyclooxygenase metabolite of arachidonic acid. It acts as a bioactive lipid and plays an important role in regulating many biological processes. PGE2 binds to 4 different G protein-coupled receptors including prostaglandin E2 receptor subtypes EP1, EP2, EP3 and EP4. The EP4 receptor is widely expressed in most of human organs and tissues. Increasing evidence demonstrates that EP4 is essential for cardiovascular homeostasis and participates in the pathogenesis of many cardiovascular diseases. Here we summarize the role of EP4 in the regulation of cardiovascular function and discuss potential mechanisms by which EP4 is involved in the development of cardiovascular disorders with a focus on its effect on inflammation.

Protective effects of dioscin against cartilage destruction in a monosodium iodoacetate (MIA)-indcued osteoarthritis rat model.

BACKGROUND: Osteoarthritis (OA) is a disabling disease of joint with no clear treatment. The finding of medicine be of benefit to joint is an important topic for osteoarthritis prevention and treatment. The present study was designed to explore the therapeutic effects and possible underlying mechanism of dioscin, a natural steroidal saponin, on osteoarthritis. METHODS: OA models were created via intra-joint injection of monosodium iodoacetate (MIA) in rats. After the administration of dioscin, the effects of dioscin were estimated with western blotting, qRT-PCR and histologic staining. RESULTS: The results showed that dioscin exerted cartilage and extracelluar matrix (ECM) protective effects via suppressing ER-stress, oxidative stress, apoptosis and inflammation. More significantly, it also ameliorated the progress of OA via inhibiting Wnt/ß-catenin pathway and up-regulating PPAR-γ expression. CONCLUSION: Our work showed the good protective effects of dioscin on MIA-induced OA for the first time. Dioscin is a promising drug on OA treatment although further researches are needed in the future.