Schultz Kelly, Fanburg Barry L, Beasley Debbie
Molecular Cardiology Research Institute, Department of Medicine, Tufts-New England Medical Center, Box 8486, 750 Washington Street, Boston, MA 02111, USA.
Am J Physiol Heart Circ Physiol. 2006 Jun;290(6):H2528-34. doi: 10.1152/ajpheart.01077.2005. Epub 2006 Jan 6.
Hypoxia is thought to be a stimulus for the excessive proliferation of vascular smooth muscle cells (VSMC) that contributes to pulmonary hypertension, but the mechanisms involved are unknown. Here we tested whether hypoxia-inducible factor 1-alpha (HIF-1alpha), a master regulator of the transcriptional response to hypoxia, is involved in the enhanced mitogen-induced proliferative responses of hypoxic VSMC. Exposure to moderate hypoxia (5% O(2)) enhanced the proliferative responses of human pulmonary artery SMC (HPASMC) to mitogens including platelet-derived growth factor (PDGF), fibroblast growth factor 2 (FGF-2), and epidermal growth factor (EGF), compared with those in normoxia (20% O(2)). Moderate hypoxia elicited increased cellular HIF-1alpha levels, shown by Western blot analysis, and also enhanced PDGF-, FGF-2-, and EGF-induced expression of HIF-1alpha. Knockdown of HIF-1alpha or HIF-1beta levels in HPASMC with specific small interfering RNAs inhibited FGF-2-stimulated proliferation of HPASMC incubated in either 5% or 20% O(2) but failed to inhibit the comitogenic effect of hypoxia. Knockdown of HIF-1alpha similarly inhibited PDGF-stimulated proliferation, whereas HIF-2alpha knockdown had no effect on HPASMC proliferation. Knockdown of HIF-1alpha expression also inhibited growth factor-induced expression of cyclin A. We conclude that HIF-1alpha promotes proliferative responses of human VSMC to FGF-2, PDGF, and EGF by mechanisms that may involve HIF-1-dependent expression of cyclin A, but HIF is apparently not crucial to the enhancement of FGF-2-, PDGF-, and EGF-induced proliferation of VSMC that occurs during hypoxia.
缺氧被认为是导致血管平滑肌细胞（VSMC）过度增殖从而引发肺动脉高压的一个刺激因素，但其涉及的机制尚不清楚。在此，我们测试了缺氧诱导因子1α（HIF-1α），一种缺氧转录反应的主要调节因子，是否参与了缺氧VSMC中丝裂原诱导的增殖反应增强。与常氧（20% O₂）环境下相比，暴露于中度缺氧（5% O₂）环境增强了人肺动脉平滑肌细胞（HPASMC）对包括血小板衍生生长因子（PDGF）、成纤维细胞生长因子2（FGF-2）和表皮生长因子（EGF）在内的丝裂原的增殖反应。通过蛋白质印迹分析显示，中度缺氧引起细胞HIF-1α水平升高，同时也增强了PDGF、FGF-2和EGF诱导的HIF-1α表达。用特异性小干扰RNA敲低HPASMC中HIF-1α或HIF-1β水平，可抑制在5%或20% O₂环境中培养的HPASMC受FGF-2刺激的增殖，但未能抑制缺氧的协同促增殖作用。敲低HIF-1α同样抑制了PDGF刺激的增殖，而敲低HIF-2α对HPASMC增殖没有影响。敲低HIF-1α表达也抑制了生长因子诱导的细胞周期蛋白A的表达。我们得出结论，HIF-1α通过可能涉及细胞周期蛋白A的HIF-1依赖性表达的机制促进人VSMC对FGF-2、PDGF和EGF的增殖反应，但HIF显然对缺氧期间发生的FGF-2、PDGF和EGF诱导的VSMC增殖增强并不关键。
