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Articles by Z Xie
Total Records ( 6 ) for Z Xie
  A. N Wansapura , V Lasko , Z Xie , O. V Fedorova , A. Y Bagrov and J. B Lingrel

Endogenous Na+ pump inhibitors are thought to play important (patho)physiological roles and occur in two different chemical forms in the mammalian circulation: cardenolides, such as ouabain, and bufadienolides, such as marinobufagenin (MBG). Although all Na+-K+-ATPase isoforms (1-4) are sensitive to ouabain in most species, in rats and mice the ubiquitously expressed 1 Na+-K+-ATPase is resistant to ouabain. We have previously shown that selective modification of the putative ouabain binding site of either the 1 or 2 Na+-K+-ATPase subunit in mice substantially alters the cardiotonic influence of exogenously applied cardenolides. To determine whether the ouabain binding site also interacts with MBG and if this interaction plays a functional role, we evaluated cardiovascular function in 1-resistant/2-resistant (1R/R2R/R), 1-sensitive/2-resistant (1S/S2R/R), and 1-resistant/2-sensitive mice (1R/R2S/S, wild type). Cardiovascular indexes were evaluated in vivo by cardiac catheterization at baseline and during graded infusions of MBG. There were no differences in baseline measurements of targeted mice, indicating normal hemodynamics and cardiac function. MBG at 0.025, 0.05, and 0.1 nmol·min–1·g body wt–1 significantly increased cardiac performance to a greater extent in 1S/S2R/R compared with 1R/R2R/R and wild-type mice. The increase in LVdP/dtmax in 1S/S2R/R mice was greater at higher concentrations of MBG compared with both 1R/R2R/R and 1R/R2S/S mice (P < 0.05). These results suggest that MBG interacts with the ouabain binding site of the 1 Na+-K+-ATPase subunit and can thereby influence cardiac inotropy.

  S Wang , M Zhang , B Liang , J Xu , Z Xie , C Liu , B Viollet , D Yan and M. H. Zou

Rational: AMP-activated protein kinase (AMPK) is an energy sensor and ubiquitously expressed in vascular cells. Recent studies suggest that AMPK activation improves endothelial function by counteracting oxidative stress in endothelial cells. How AMPK suppresses oxidative stress remains to be established.

Objective: The aim of this study is to examine the effects of AMPK in regulating NAD(P)H oxidase, oxidative stress, and endothelial function.

Methods and Results: The markers of oxidative stress, NAD(P)H oxidase subunit expression (gp91phox, p47phox, p67phox, NOX1 to -4), NAD(P)H oxidase–mediated superoxide production, 26S proteasome activity, IB degradation, and nuclear translocation of nuclear factor (NF)-B (p50 and p65) were examined in cultured human umbilical vein endothelial cells and mouse aortas isolated from AMPK2 deficient mice. Compared to the wild type, acetylcholine-induced endothelium-dependent relaxation was significantly impaired in parallel with increased production of oxidants in AMPK2–/– mice. Further, pretreatment of aorta with either superoxide dismutase (SOD) or tempol or apocynin significantly improved acetylcholine-induced endothelium-dependent relaxation in AMPK2–/– mice. Analysis of aortic endothelial cells from AMPK2–/– mice and human umbilical vein endothelial cells expressing dominant negative AMPK or AMPK2-specific siRNA revealed that loss of AMPK activity increased NAD(P)H oxidase subunit expression (gp91phox, p47phox, p67phox, NOX1 and -4), NAD(P)H oxidase–mediated superoxide production, 26S proteasome activity, IB degradation, and nuclear translocation of NF-B (p50 and p65), whereas AMPK activation by AICAR or overexpression of constitutively active AMPK had the opposite effect. Consistently, we found that genetic deletion of AMPK2 in low-density lipoprotein receptor knockout (LDLr–/–) strain markedly increased 26S proteasome activity, IB degradation, NF-B transactivation, NAD(P)H oxidase subunit overexpression, oxidative stress, and endothelial dysfunction, all of which were largely suppressed by chronic administration of MG132, a potent cell permeable proteasome inhibitor.

Conclusions: We conclude that AMPK2 functions as a physiological suppressor of NAD(P)H oxidase and ROS production in endothelial cells. In this way, AMPK maintains the nonatherogenic and noninflammatory phenotype of endothelial cells.

  M. R Mahjoub , Z Xie and T. Stearns

Centrioles form the core of the centrosome in animal cells and function as basal bodies that nucleate and anchor cilia at the plasma membrane. In this paper, we report that Cep120 (Ccdc100), a protein previously shown to be involved in maintaining the neural progenitor pool in mouse brain, is associated with centriole structure and function. Cep120 is up-regulated sevenfold during differentiation of mouse tracheal epithelial cells (MTECs) and localizes to basal bodies. Cep120 localizes preferentially to the daughter centriole in cycling cells, and this asymmetry between mother and daughter centrioles is relieved coincident with new centriole assembly. Photobleaching recovery analysis identifies two pools of Cep120, differing in their halftime at the centriole. We find that Cep120 is required for centriole duplication in cycling cells, centriole amplification in MTECs, and centriole overduplication in S phase–arrested cells. We propose that Cep120 is required for centriole assembly and that the observed defect in neuronal migration might derive from a defect in this process.

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