Effects of angiotensin II on connexin 43 of VSMCs in arteriosclerosis

Mechanism of genistein regulating the differentiation of vascular smooth muscle cells into osteoblasts via the OPG/RANKL pathway

Objective

The present study aimed to investigate the mechanism of genistein, a tyrosine kinase inhibitor, regulating the differentiation of vascular smooth muscle cells (VSMCs) into osteoblasts via the OPG/RANKL (Osteoprotegerin/Receptor Activator of Nuclear Factor-κB Ligand) pathway.

Methods

The mouse VSMCs were isolated, purified and cultured. We constructed the LV5-Tnfrsf11b overexpression lentiviral vector and LV3-OPG-309 interference lentiviral vector. The OPG overexpression was induced and the growth of VSMCs infected with the lentiviral vector was observed. The VSMC calcification and control group were treated with different doses of genistein. The mRNA and protein expression levels of OPG, α-SM-actin (smooth muscle actin), ALP (alkaline phosphatase) and OPN (osteopontin) were detected in VSMCs after treatment using RT-PCR and Western Blot.

Result

We induced OPG overexpression and performed lentiviral vector infection of the VSMCs to suppress OPG expression, respectively, which was followed by treatment with genistein. The results showed that the relative expression of OPG was the highest in the VSMC calcification +genistein +OPG overexpression-inducing treatment group. It was the lowest in the VSMC calcification +OPG expression-suppressing treatment group. The relative expression of ALP was the highest in the VSMC calcification +OPG expression-suppressing treatment group, and the lowest in the VSMCs+genistein treatment group.

Conclusion

OPG gene plays an important regulatory role in the growth of VSMCs, by suppressing the calcification of VSMCs. Genistein could regulate the differentiation of VSMCs into osteoblasts via the OPG/RANKL pathway in a dose-dependent manner.

Connexin43 siRNA promotes HUVEC proliferation and inhibits apoptosis induced by ox-LDL: an involvement of ERK signaling pathway

Oxidized low-density lipoprotein (ox-LDL), one of the most important risk factors of atherosclerosis, is a highly antigenic, potent chemoattractant that facilitates the development of atherosclerosis. Gap junctions also play an important in the development of atherosclerosis. In this study, we investigated the effects of ox-LDL on connexin43 and the mechanisms of connexin43 siRNA-inhibited apoptosis induced by ox-LDL in human umbilical vein endothelial cell (HUVEC), to clarify the role of connexin43 in atherosclerosis. Our results showed that ox-LDL significantly inhibited the growth and promoted apoptosis of HUVEC in a dose-dependent manner. Also, ox-LDL upregulated the expression of connexin43. Furthermore, knockdown connexin43 by siRNA promoted proliferation and inhibited apoptosis in ox-LDL-stimulated HUVEC. Moreover, the level of phosphor-ERK1/2 and connexin43 was remarkably attenuated by a ERK pathway inhibitor (PD98059). These results suggest that connexin43 siRNA promotes HUVEC proliferation and inhibits apoptosis induced by ox-LDL, and ERK signaling pathway appears to be involved in these processes.

Inhibition of oxidized-phospholipid-induced vascular smooth muscle cell proliferation by resveratrol is associated with reducing Cx43 phosphorylation

Abnormal proliferation of vascular smooth muscle cells (VSMCs) is an important factor during the progression of atherosclerosis. In this study, we investigated the effects of resveratrol on atherosclerosis-associated proliferation of VSMCs. We utilized an oxidized phospholipid, 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine (POVPC) to induce abnormal proliferation of VSMCs. Our results showed the treatments with resveratrol dose-dependently abolished POVPC-induced VSMC proliferation, as evidenced by the decreased [(3)H]thymidine incorporated into VSMCs and reduced percentage of 5-ethynyl-2'-deoxyuridine (EdU)-positive VSMCs. Cell cycle analysis demonstrated that resveratrol inhibited POVPC-induced increase in the S phase cell population and DNA synthesis. Our study further indicated that POVPC-induced VSMC proliferation was associated with a significant increase in the phosphorylation of Cx43, which was a consequence of activation of MAPK signaling. Interestingly, treatment with resveratrol abolished POVPC-induced phosphorylation of Cx43 as a result of inhibiting activation of Src, MEK, and ERK1/2. Our results provided a novel mechanism by which resveratrol may contribute to cardiovascular protection.

Effects of Losartan on expression of connexins at the early stage of atherosclerosis in rabbits

AIM

to investigate effects of Losartan on expression of connexin 40 and 43 (Cx40 and Cx43), in arteries at the early stage of atherosclerosis in a rabbit model.

METHODS

A total of 28 male New Zealand white rabbits were divided into following groups: control group, high fat diet group, and Losartan group (10 mg/kg/day). Losartan was administrated in food for two weeks. Iliac arteries were obtained for immunohistochemistry, transmission electron microscopy, Western blot, and reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Transmission electron microscopy revealed abundant gap junctions between neointimal smooth muscle cells (SMCs), which were markedly reduced by treatment. RT-PCR and Western blot assay showed that the mRNA and protein expression of Cx40 and Cx43 were elevated in the neointimal area at the early stage of atherosclerosis. The mRNA and protein expression of Cx43 were significantly down-regulated by losartan treatment but those of Cx40 were not markedly changed.

CONCLUSION

Cx40 and Cx43 in the neointimal SMCs were up-regulated at the early stage of atherosclerosis. Losartan (an angiotensin-converting enzyme inhibitor) could reduce neointima proliferation and down-regulate the elevated protein expression of Cx43, suggesting the rennin-angiotensin system (RAS) plays an important role in the remodeling of gap junction between ventricular myocytes under pathological conditions.

Eprosartan in the Primary Prevention of Cardiac Allograft Vascular Disease: A Double-Blind Prospectively Randomized Study using Intravascular Ultrasound

The angiotensin blocker (ARB) eprosartan (600 mg once daily) and the calcium antagonist diltiazem (90 mg twice daily) were studied in a 24-month prospective, randomized, double-blind trial involving 53 heart transplant patients. The study compared their effects on the development of post-transplant cardiac allograft vasculopathy, a condition that frequently impairs long-term post-transplantation survival and where angiotensin blockers might be expected to play a preventive role. From baseline to month 12, the mean plaque volume increased by 7.7 mm3 for eprosartan-treated patients and by 34.4 mm3 for diltiazem-treated patients, but the eprosartan-related trend for reduced myointimal hyperplasia was not statistically significant. The trend in favour of eprosartan for secondary parameters (mean intimal index, vessel volume, lumen volume and coronary flow reserve) also failed to reach significance. The lack of effect might be due to a lower than planned sample size and observation periods due to recruitment difficulties. A larger study is required to confirm these preliminary findings.

Losartan reduced connexin43 expression in left ventricular myocardium of spontaneously hypertensive rats

OBJECTIVE

To assess the effect of angiotensin II type 1 (AT(1)) receptor antagonist losartan on myocardium connexin43 (Cx43) gap junction (GJ) expression in spontaneously hypertensive rats (SHRs) and investigate possible mechanisms.

METHODS

Sixteen 9-week-old male SHRs and 8 age-matched male Wistar-Kyoto (WKY) rats were included in this study. SHRs were randomly divided into two groups to receive losartan at 30 mg/(kg x d) by oral gavage once daily for 8 weeks (SHR-L) or vehicle (0.9% saline) to act as controls (SHR-V); WKY rats receiving vehicle for 8 weeks served as normotensive controls. At the end of the experiment, rats were sacrificed and the hearts were removed. Expressions of Cx43 and nuclear factor-kappaB p65 (NF-kappaB p65) proteins in all three groups were observed and further investigations on the effect of angiotensin II type 1 receptor antagonist losartan (30 mg/(kg x d), 8 weeks) on Cx43 expression were conducted with Western blot and immunohistochemistry. NF-kappaB p65 protein in nuclear extracts was determined by Western blot.

RESULTS

Left ventricular (LV) hypertrophy was prominent in SHRs, Cx43 and NF-kappaB p65 protein expressions were obviously upregulated and Cx43 distribution was dispersed over the cell surface. Treatment with losarton reduced the over-expressions of Cx43 and NF-kappaB p65 in LV myocardium. The distribution of Cx43 gap junction also became much regular and confined to intercalated disk after losartan treatment.

CONCLUSION

Cx43 level was upregulated in LV myocardium of SHR during early stage of hypertrophy. Angiotensin II type 1 receptor antagonist losartan prevented Cx43 gap junction remodeling in hypertrophied left ventricles, possibly through the NF-kappaB pathway.

Involvement of connexin 43 in angiotensin II-induced migration and proliferation of saphenous vein smooth muscle cells via the MAPK-AP-1 signaling pathway

Proliferation and migration of vascular smooth muscle cells (VSMCs) lead to intimal thickening and influence the long-term patency of venous graft post coronary arterial bypass graft. There is increasing evidence that connexins are involved in the development of intimal hyperplasia and restenosis. We assessed connexin 43 (Cx43) expression and its role in angiotensin II-induced proliferation and migration of smooth muscle cells and the signal pathways involved in human saphenous vein bypass conduits. Angiotensin II significantly increased gap junctional intercellular communication and induced the expression of Cx43 in human saphenous vein SMCs in a dose- and time-dependent manner through angiotensin II type 1 receptor. The effect of angiotensin II was blocked by siRNA of ERK 1/2, p38 MAPK and JNK, respectively. Overexpression of Cx43 markedly increased the proliferation of saphenous vein SMCs. However, siRNA for Cx43 inhibited angiotensin II-induced proliferation, cyclin E expression and migration of human saphenous vein SMCs. In dual-luciferase reporter assay, angiotensin II markedly activated AP-1 transcription factor, which was significantly attenuated by a dominant-negative AP-1 (A-Fos) with subsequent inhibition of angiotensin II-induced transcriptional expression of Cx43. These data demonstrate the role of Cx43 in the proliferation and migration of human saphenous vein SMCs and angiotensin II-induced Cx43 expression via mitogen-activated protein kinases (MAPK)-AP-1 signaling pathway.