Biomedical subjects

Xiu-Fen Ming

Publications and source records attributed to Xiu-Fen Ming.

10 recordsLinked to original sources

PubMed2006

Endothelial arginase: a new target in atherosclerosis.

Decreased endothelial nitric oxide (NO) bioavailability as it relates to endothelial dysfunction plays an important role in various cardiovascular disorders, including athero-sclerosis. Recent research has provided evidence that endothelial dysfunction in atherosclerosis is not primarily caused by decreased endothelial NO synthase (eNOS) gene expression, but rather deregulation of eNOS enzymatic activity, which contributes to the increased oxidative stress in atherosclerosis. Among other mechanisms, the substrate L-arginine is an important limiting factor for NO production. Emerging evidence demonstrates that L-arginine is not only converted to NO via eNOS, but also metabolized to urea and l-ornithine via arginase in endothelial cells. Hence, arginase competes with eNOS for the substrate L-arginine, resulting in deceased NO production. There are an increasing number of studies showing that enhanced arginase gene expression and/or activity contribute to endothelial dysfunction in various cardiovascular disorders, including atherosclerosis. Thus, endothelial arginase may represent a new therapeutic target in atherosclerosis.

Animals↗

PubMed2006

Recent advances in understanding endothelial dysfunction in atherosclerosis.

Over the last two decades, it has become evident that decreased bioavailability of endothelial nitric oxide (NO) produced from endothelial NO synthase (eNOS), referred to as endothelial dysfunction, plays a crucial role in the development and progression of atherosclerosis. Much progress has been made in understanding the mechanisms of decreased endothelial NO bioavailability at the levels of regulation of eNOS gene expression, eNOS enzymatic activity and NO inactivation. Initial studies suggest that increasing eNOS gene expression would improve endothelial NO release in the hope of inhibiting the progression of atherosclerosis. Recent experimental studies, however, do not always support this therapeutic concept and show some evidence that overexpression of eNOS in atherosclerosis may be even harmful for the disease progression.Thus, recent research to improve endothelial function in atherosclerosis has focused on regulation of eNOS enzymatic activity and prevention of NO inactivation by oxidative stress. Since the role of oxidative stress in endothelial NO bioavailability has been reviewed in a large number of comprehensive articles, this article focuses on the relevant regulatory mechanisms of eNOS enzymatic activity that are emerging to play a role in endothelial dysfunction in atherosclerosis.

Animals↗

PubMed2005

Sirolimus increases tissue factor expression but not activity in cultured human vascular smooth muscle cells.

BACKGROUND: Sirolimus-eluting stents (CYPHER stents) demonstrated remarkable efficacy in reducing restenosis rates in patients with coronary artery disease. There is a concern of sub-acute and late stent thrombosis. Tissue factor (TF) is critical in thrombosis. This study investigated the effect of sirolimus on TF expression and activity in cultured human vascular smooth muscle cells (SMCs). METHODS: SMCs were cultured from human saphenous veins and aortas. Quiescent cells were stimulated with sirolimus (0.1 - 20 ng/ml) over 24 hours. Cellular TF expression and activity released into culture medium were measured. The effect of sirolimus on activation of mammalian target of rapamycin (mTOR) was measured by phosphorylation of the substrate p70s6k at T389, and activation of RhoA was measured by pull-down assay. RESULTS: Sirolimus increased TF protein level in cultured human SMCs in a concentration and time-dependent manner (about 2-fold, p < 0.01) reaching maximal effect at 5 ng/ml. The stimulation of TF expression by sirolimus was associated with inhibition of basal activity of mTOR. No effects of sirolimus on RhoA or p38mapk activation that are positive regulators of TF in vascular wall cells were observed. The stimulation of TF expression by sirolimus (20 ng/ml) was prevented by the HMG-CoA reductase inhibitor fluvastatin (1 micromol/L). However, no increase in TF activity released from SMC into culture medium was observed after sirolimus treatment. CONCLUSION: Although sirolimus stimulates TF protein expression in human SMC associated with inhibition of mTOR, it does not enhance TF activity released from the cells, suggesting a relatively safe profile of CYPHER stents. The inhibition of TF expression by fluvastatin favors clinical use of statins in patients undergoing coronary stenting.

Aorta↗

PubMed2004

Thrombin stimulates human endothelial arginase enzymatic activity via RhoA/ROCK pathway: implications for atherosclerotic endothelial dysfunction.

BACKGROUND: Arginase competes with endothelial nitric oxide synthase (eNOS) for the substrate l-arginine and decreases NO production. This study investigated regulatory mechanisms of arginase activity in endothelial cells and its role in atherosclerosis. METHODS AND RESULTS: In human endothelial cells isolated from umbilical veins, thrombin concentration- and time-dependently stimulated arginase enzymatic activity, reaching a 1.9-fold increase (P<0.001) at 1 U/mL for 24 hours. The effect of thrombin was prevented by C3 exoenzyme or the HMG-CoA reductase inhibitor fluvastatin, which inhibit RhoA, or by the ROCK inhibitors Y-27632 and HA-1077. Adenoviral expression of constitutively active RhoA or ROCK mutants enhanced arginase activity (approximately 3-fold, P<0.001), and the effect of active RhoA mutant was inhibited by the ROCK inhibitors. Neither thrombin nor the active RhoA/ROCK mutants affected arginase II protein level, the only isozyme detectable in the cells. Moreover, a significantly higher arginase II activity (1.5-fold, not the protein level) and RhoA protein level (4-fold) were observed in atherosclerotic aortas of apoE-/- compared with wild-type mice. Interestingly, l-arginine (1 mmol/L), despite a significantly higher eNOS expression in aortas of apoE-/- mice, evoked a more pronounced contraction, which was reverted to a greater vasodilation by the arginase inhibitor l-norvaline (20 mmol/L) compared with the wild-type animals (n=5, P<0.001). CONCLUSIONS: Thrombin enhances arginase activity via RhoA/ROCK in human endothelial cells. Higher arginase enzymatic activity is involved in atherosclerotic endothelial dysfunction in apoE-/- mice. Targeting vascular arginase may represent a novel therapeutic possibility for atherosclerosis.

Animals↗

PubMed2004

Endothelial nitric oxide synthase gene transfer restores endothelium-dependent relaxations and attenuates lesion formation in carotid arteries in apolipoprotein E-deficient mice.

Nitric oxide (NO) and monocyte chemoattractant protein-1 (MCP-1) exert partly opposing effects in vascular biology. NO plays pleiotropic vasoprotective roles including vasodilation and inhibition of platelet aggregation, smooth muscle cell proliferation, and endothelial monocyte adhesion, the last effect being mediated by MCP-1 downregulation. Early stages of arteriosclerosis are associated with reduced NO bioactivity and enhanced MCP-1 expression. We have evaluated adenovirus-mediated gene transfer of human endothelial NO synthase (eNOS) and of a N-terminal deletion (8ND) mutant of the MCP-1 gene that acts as a MCP-1 inhibitor in arteriosclerosis-prone, apolipoprotein E-deficient (ApoE(-/-)) mice. Endothelium-dependent relaxations were impaired in carotid arteries instilled with a noncoding adenoviral vector but were restored by eNOS gene transfer (p < 0.01). A perivascular collar was placed around the common carotid artery to accelerate lesion formation. eNOS gene transfer reduced lesion surface areas, intima/media ratios, and macrophage contents in the media at 5-week follow-up (p < 0.05). In contrast, 8ND-MCP-1 gene transfer did not prevent lesion formation. In conclusion, eNOS gene transfer restores endothelium-dependent vasodilation and inhibits lesion formation in ApoE(-/-) mouse carotids. Further studies are needed to assess whether vasoprotection is maintained at later disease stages and to evaluate the long-term efficacy of eNOS gene therapy for primary arteriosclerosis.

Adenoviridae↗

PubMed2004

Reconstituted high-density lipoprotein inhibits thrombin-induced endothelial tissue factor expression through inhibition of RhoA and stimulation of phosphatidylinositol 3-kinase but not Akt/endothelial nitric oxide synthase.

Endothelial cells express negligible amounts of tissue factor (TF) that can be induced by thrombin, which is important for acute coronary syndromes. Recent research suggests that endothelial TF expression is positively regulated by RhoA and p38mapk, but negatively by Akt/endothelial nitric oxide synthase (eNOS) pathway. High-density lipoprotein (HDL) is atheroprotective and exerts antiatherothrombotic effect. This study investigated the effect of a reconstituted HDL (rHDL) on endothelial TF expression induced by thrombin and the underlying mechanisms. In cultured human umbilical vein and aortic endothelial cells, thrombin (4 U/mL, 4 hours) increased TF protein level, which was reduced by rHDL (0.1 mg/mL, 43% inhibition, n=3 to 7, P<0.01). Activation of RhoA but not p38mapk by thrombin was prevented by rHDL. rHDL stimulated Akt/eNOS pathway. The phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 abolished the activation of Akt/eNOS and reversed the inhibitory effect of rHDL on TF expression. Adenoviral expression of the active PI3K mutant (p110) reduced TF expression stimulated by thrombin without inhibiting RhoA activation, whereas expression of the active Akt mutant (m/p) further facilitated TF upregulation by thrombin. Moreover, a dominant-negative Akt mutant (KA) reduced thrombin's effect and did not reverse the rHDL's inhibitory effect on TF expression. Inhibition of eNOS by N(omega)-nitro-L-arginine methyl ester (100 micromol/L) did not affect the rHDL's effect. In conclusion, rHDL inhibits thrombin-induced human endothelial TF expression through inhibition of RhoA and activation of PI3K but not Akt/eNOS. These findings implicate a novel mechanism of antiatherothrombotic effects of HDL.

Adenoviridae↗

PubMed2003

A novel mechanism of tumor suppression by destabilizing AU-rich growth factor mRNA.

The occurrence of pathologically stable mRNAs of proto-oncogenes, growth factors and cyclins has been proposed to contribute to experimental and human oncogenesis. In normal resting cells, mRNAs containing an AU-rich element (ARE) in their 3' untranslated region are subjected to rapid degradation. Tristetraprolin (TTP) is an RNA-binding zinc-finger protein that promotes decay of ARE-containing mRNAs. Here we report that TTP acts as a potent tumor suppressor in a v-H-ras-dependent mast cell tumor model, where tumors express abnormally stable interleukin-3 (IL-3) mRNA as part of an oncogenic autocrine loop. Premalignant v-H-ras cells were transfected with TTP and injected into syngeneic mice. TTP expression delayed tumor progression by 4 weeks, and late appearing tumors escaped suppression by loss of TTP. When transfected into a fully established tumor line, TTP reduced cloning efficiency in vitro and growth of the inoculated cells in vivo. Transgenic TTP interfered with the autocrine loop by enhancing the degradation of IL-3 mRNA with concomitant reduction of IL-3 secretion. Our data establish the ARE as an antioncogenic target in a model situation, underline the importance of mRNA stabilization in oncogenesis and show for the first time that tumor suppression can be achieved by interfering with mRNA turnover.

3' Untranslated Regions↗

PubMed2003

PKC is required for activation of ROCK by RhoA in human endothelial cells.

Rho/Rho-kinase (ROCK) complex formation is the only proposed mechanism for ROCK activation. Rho/ROCK and PKC can exhibit a convergence of cellular effects such as suppression of endothelial nitric oxide synthase (eNOS) expression. We, therefore, investigated the role of PKC in RhoA/ROCK complex formation and activation linked to eNOS expression in cultured human umbilical vein endothelial cells. We showed that expression of constitutively active RhoA (Rho63) or ROCK (CAT) suppressed eNOS gene expression. This effect of Rho63 but not that of CAT was abolished by phorbol ester-sensitive PKC depletion. Accordingly, depletion or inhibition of PKC prevented ROCK activation by Rho63 without affecting RhoA/ROCK complex formation. Similarly, suppression of eNOS expression and activation of ROCK, but not RhoA by thrombin were prevented by PKC inhibition or depletion. These results indicate that RhoA/ROCK complex formation alone is not sufficient and PKC is required for RhoA-induced ROCK activation leading to eNOS gene suppression.

Alkaloids↗

PubMed2003

Small G proteins as novel therapeutic targets in cardiovascular medicine.

Small G proteins are implicated in regulation of endothelial function, smooth muscle cell contraction, proliferation, and migration, as well as cardiomyocyte hypertrophy. Targeting small G proteins and their downstream signaling could constitute promising therapeutic approaches in cardiovascular disorders such as atherosclerosis, restenosis, hypertension, vasospasm, and cardiac hypertrophy.

Animals↗

PubMed2002

Rho GTPase/Rho kinase negatively regulates endothelial nitric oxide synthase phosphorylation through the inhibition of protein kinase B/Akt in human endothelial cells.

Endothelial nitric oxide synthase (eNOS) is an important regulator of cardiovascular homeostasis by production of nitric oxide (NO) from vascular endothelial cells. It can be activated by protein kinase B (PKB)/Akt via phosphorylation at Ser-1177. We are interested in the role of Rho GTPase/Rho kinase (ROCK) pathway in regulation of eNOS expression and activation. Using adenovirus-mediated gene transfer in human umbilical vein endothelial cells (HUVECs), we show here that both active RhoA and ROCK not only downregulate eNOS gene expression as reported previously but also inhibit eNOS phosphorylation at Ser-1177 and cellular NO production with concomitant suppression of PKB activation. Moreover, coexpression of a constitutive active form of PKB restores the phosphorylation but not gene expression of eNOS in the presence of active RhoA. Furthermore, we show that thrombin inhibits eNOS phosphorylation, as well as expression via Rho/ROCK pathway. Expression of the active PKB reverses eNOS phosphorylation but has no effect on downregulation of eNOS expression induced by thrombin. Taken together, these data demonstrate that Rho/ROCK pathway negatively regulates eNOS phosphorylation through inhibition of PKB, whereas it downregulates eNOS expression independent of PKB.

Adenoviridae↗