Prevention of rupture of atherosclerotic plaque by Candesartan in rabbit model / 中华病理学杂志

<p><b>OBJECTIVE</b>To evaluate Candesartan therapeutic effect against atherosclerotic plaque rupture and to explore the related mechanisms.</p><p><b>METHODS</b>Thirty-four New Zealand White male rabbits were randomly divided into three groups: the control group, the model control group and the Candesartan intervention group. The control group rabbits were fed with a normal diet. Rabbits of the latter two groups were fed with a 1% high-cholesterol diet and received a balloon catheter injury respectively one week after the cholesterol feeding. Candesartan (0.5 mgⁱkg⁻¹ⁱd⁻¹) was given to the Candesartan group rabbits 2 days before the performance of the balloon catheter injury. By the end of 12(th) week of the experiment, Russell's viper venom was used for rabbits of both the model control and the Candesartan groups in order to induce rupture of the plaques developed and followed by sacrifice of all the rabbits of the 3 groups. The aortas were removed and fixed for histological evaluation. Immunohistochemistry of MMP-9, macrophage markers and collagen were performed. The protein expression of MMP-9 was determined using Western blot analysis.</p><p><b>RESULTS</b>In the model control group, 7 of 9 rabbits with a total of 12 plaques developed rupture and thrombosis of the plaques after the induction. In contrast, only 2 of 10 rabbits with a total of 3 plaques demonstrated rupture and thrombosis in the Candesartan group (P < 0.05). The control group rabbits did not have plaque rupture and thrombosis. Compared with the model group, both the percentage area of MMP-9 and macrophages in the plaques were significantly decreased in the Candesartan group (12.35% ± 4.28% vs 32.58% ± 9.16%, P < 0.05; 13.87% ± 4.91% vs 23.8% ± 7.45%, P < 0.05). There was an increased percentage of collagen content in total plaques of the Candesartan group (30.27% ± 11.36% vs 4.18% ± 1.28%, P < 0.01). Compared with the model group, the protein expression of MMP-9 was significantly decreased in the Candesartan group (P < 0.01).</p><p><b>CONCLUSION</b>Candesartan has a preventive value against atherosclerotic plaque rupture in hypercholesterolemic rabbits, likely through its reduction of MMP-9 expression, inhibition of macrophage accumulation and increase of collagen content within the plaques.</p>

Rac1 accelerates endothelial cell senescence induced by hypoxia in vitro / 生理学报

To investigate the role and mechanism of Rac1 protein in the process of the human umbilical vein endothelial cell (HUVEC) senescence, we used hypoxia as a model for modulating HUVECs entering replicative senescence in vitro. Premature senescence of HUVECs was evidenced by detecting the SA-beta-Gal activity and PAI-1 expression. Meanwhile, cell cycle distribution and cell proliferation rate were investigated by flow cytometry assay and BrdU staining. The results indicated that the HUVECs became enlarged and flattened, both SA-beta-Gal activity and PAI-1 expression increased obviously, while cell proliferation was inhibited and G(1) phase cell cycle arresting occurred when HUVECs were treated with continued hypoxia for 96 h. Accompanied with these changes, the expression of activated Rac1 increased obviously in cells after hypoxia. All these observations suggested that endothelial senescence could be induced by continued hypoxia and it might correlate with the activity of Rac1. To further define the relationship between Rac1 and HUVEC senescence, HUVECs were transiently infected with the constitutively active form of Rac1 (V12Rac1) or dominant negative form of Rac1 (N17Rac1) using retrovirus vector pLNCX-V12Rac1 or pLNCX-N17Rac1. We observed the changes of these three kinds of HUVECs (HUVECs, N17Rac1-HUVECs, V12Rac1-HUVECs) after hypoxia for 48 h and 96 h, the expression and localization of serum response factor (SRF), which is one of the downstream signal molecules of Rac1, were also investigated. The results obtained indicated that after continued hypoxia for 48 h, HUVECs infected by V12Rac1 showed obvious senescence accompanied with SA-beta-Gal activation, PAI-1 expression increase, G(1) phase arrest and cell proliferation inhibition which were similar to HUVECs after continued 96-hour hypoxia treatment, while the senescence of HUVECs infected by N17Rac1 was significantly inhibited even if the cells were exposed to hypoxia for more than 96 h. All the results identified that the activation of Rac1 might accelerate HUVEC senescence induced by hypoxia and that inactivation of Rac1 could partly block the cell senescence. To further investigate the mechanism of HUVEC senescence induced by Rac1, we detected the expression of total SRF (tSRF) and nuclear SRF (nSRF) in these three kinds of HUVECs by immunofluorescent analysis and Western blot assay after hypoxia. The results showed that the expression of nSRF decreased obviously and the nuclear translocation of SRF was inhibited in HUVECs infected by V12Rac1 compared with those in the normal HUVECs. In contrast, the expression of nSRF increased obviously in the HUVECs infected by N17Rac1. These results suggest that activation of Rac1 accelerates endothelial cell senescence and inhibition of Rac1 activity prevents HUVECs from entering senescence induced by hypoxia, while the nuclear translocation of SRF regulated by Rac1 might play an important role in the process of senescence.

Serum response factor participates in RhoA-induced endothelial cell F-actin rearrangements / 生理学报

RhoA is one of the main members of RhoGTPase family involved in cell morphology, smooth muscle contraction, cytoskeletal microfilaments and stress fiber formation. It has been demonstrated that RhoA modulates endothelial cell permeability by its effect on F-actin rearrangement, but the molecular mechanism of rearrangement of actin cytoskeleton remains unclear. Recent studies prove that RhoA/Rho kinase regulates smooth muscle specific actin dynamics by activating serum response factor (SRF)-dependent transcription. To further investigate the molecular mechanism of the rearrangement of vascular endothelial cell actin cytoskeleton, we explored the relationship between the activation of SRF and F-actin rearrangement induced by RhoA in human umbilical vein endothelial cells (HUVECs). HUVECs were infected with the constitutively active forms of RhoA (Q63LRhoA) or the dominant negative forms of RhoA(T19NRhoA) using retrovirus vector pLNCX-Q63LRhoA or pLNCX-T19NRhoA, the positive clone was obtained by G418 selection. The expression and distribution of SRF in normal and infected cells were evaluated by immunohistochemistry and Western blot in complete medium and in serum-free medium. The effect of F-actin polymerization was detected by Rhodamine-Phalloidine staining. Infection of PLNCX-Q63LRhoA induced F-actin rearrangement and stress fiber formation in HUVECs, as well as enhanced the expression of SRF in the nuclei. In contrast, the cells infected with T19NRhoA showed no distinct changes. With serum deprivation, the expression of SRF increased obviously in both normal and infected HUVECs, but the subcellular localization of SRF was evidently different. In HUVECs, the localization of SRF was in the nuclei after 3 d with serum deprivation, but it was redistributed outside the nuclei after 5 d with serum deprivation. In cells infected with Q63LRhoA, the immunolocalization of SRF was always in the nuclei compared with HUVECs infected with T19NRhoA, which was almost always localized in the cytoplasm. In HUVECs, the rearrangement of F-actin and formation of stress fiber increased after 3 d with serum deprivation, but appeared decreased and unpolymerized after 5 d with serum deprivation. The polymerization of F-actin and the formation of stress fiber in HUVECs infected with Q63LRhoA kept during the period of serum-free culture, whereas the rearrangement of F-actin in cells infected with T19NRhoA was not found. These results suggest that RhoA influences endothelial F-actin rearrangement in part by regulating the expression and subcellular localization of SRF.