| 摘要: | 雖然降低血中低密度脂蛋白(LDL)對於降低動脈血管粥狀硬化之罹病率及死亡率已有公認的好處，但直到最近的臨床證據，仍未能證明獨立血清高密度脂蛋白（HDL）升高的利益。也有零星的證據顯示高密度脂蛋白在高濃度的情況下可能損失對心血管的保護作用。本研究目的在探討高密度脂蛋白濃度，對體外(in vitro)以及體內(in vivo)實驗時對人類內皮前驅細胞（EPCs）和相關的血管生成(vasculogenesis)功能造成的影響。在我們的研究中所使用的細胞是由人體週邊血液中循環的單核細胞所衍生成的內皮前驅細胞。高密度脂蛋白能恢復氧化態低密度脂蛋白（oxLDL）對後期血管內皮前驅細胞(late EPC)存活度所造成的損害﹔且恢復的效果隨著高密度脂蛋白的劑量上升而提高。在不含有氧化態低密度脂蛋白的實驗中，低濃度高密度脂蛋白（5-50μg/mL,相當於人體血中濃度0.5-5mg/dL）會透過活化PI3K/Akt/eNOS訊息傳遞路徑加強內皮前驅細胞Tube formation之功能性；中度到高濃度的高密度脂蛋白則透過激活Rho-associated kinase（ROCK）促使內皮前驅細胞老化和抑制PI3K/Akt及p38 MAPK訊號傳遞路徑阻礙Tube formation之功能性。ROCK抑製劑Y27632或statins類藥物，除了可以阻斷高濃度之高密度脂蛋白誘導內皮前驅細胞老化之外﹔在體內及體外實驗中，也可以在高濃度高密度脂蛋白之環境下恢復Tube formation以及內皮前驅細胞血管生成的能力。本實驗結果證明高密度脂蛋白能保護內皮前驅細胞受到氧化低密度脂蛋白造成的損傷。然而更重要的是本文提出高密度脂蛋白的潛在危險及其可能機轉：在沒有氧化低密度脂蛋白存在的環境下，中到高濃度的高密度脂蛋白會透過激活ROCK訊息傳遞路徑損害內皮前驅細胞和相關的血管生成之功能。
Recent clinical evidence failed to demonstrate the benefits of elevation of serum high density lipoprotein (HDL), suggesting potential loss of protective effects of HDL at high concentrations. This study aimed to investigate the concentration-related effects of HDL on in vitro and in vivo function of human endothelial progenitor cells (EPCs) and related angiogenesis. Early and late-outgrowth EPCs were generated from human circulating mononuclear cells. Oxidized low density lipoprotein (oxLDL) reduced viability of late-outgrowth EPCs, which was reversed dose-dependently by HDL. In the absence of oxLDL, HDL at low concentrations (5-50μg/mL, equal to 0.5-5mg/dL in human) enhanced EPC tube formation by activating PI3K/Akt/eNOS pathways. Moderate to high concentrations (400-800μg/mL) of HDL paradoxically enhanced EPC senescence and impaired tube formation by activating Rho-associated kinase (ROCK) and inhibiting PI3K/Akt and p38 MAPK pathways. ROCK inhibitors, either Y27632 or statins, prevented high HDL-induced EPC senescence and improved in vitro tube formation as well as in vivo capacity of angiogenesis of EPCs. While protecting EPCs from the injury of oxLDL, moderate to high concentrations of HDL paradoxically impaired EPCs and related angiogenesis in the absence of oxLDL by activating ROCK pathways, providing mechanistic evidence of potential hazard effects of HDL. |
