| Abstract: | 狹心症為全世界性最重要的單ㄧ疾病死因之一。儘早打通血管以重建 血流灌注為拯救缺氧之心肌所必需。然而,成功重建血流灌注亦可能 導致某些心肌細胞迅速死亡,此種再灌注導致之細胞死亡降低了成功 早期重建血流的療效, 因此,降低致死性再灌流損傷為心血管疾病研 究之重要課題。細胞內鈣離子濃度過高為 缺氧—再灌注 病理變化之 特徵之一,並為導致細胞壞死或凋亡之重要因素,而鈉鈣交換通道則 在生理狀態下及缺氧—再灌注時均為鈣離子重要交通孔。含鈣過高之 粒腺體可起動細胞壞死或凋亡,而細胞內質網與粒腺體間有附著及鈣 離子交通,此二者間之相互作用可能在缺氧—再灌注時引起粒腺體內 鈣離子過高而導致細胞死亡。另在心臟衰竭之治療,保存心肌細胞之 存活亦為重要之原則,而此時常需使用之傳統強心劑,則可能因具昇 高細胞內鈣離子濃度作用,不利心肌細胞之存活,而導致病人死亡率 昇高。Levosimedan為一新型的強心劑,具有鈣離子敏感化血管擴張 及對缺氧—再灌注損傷具保護性作用;但其對鈣離子平衡及細胞凋亡 之影響及作用機轉則不明。我們的研究首先建立人類心肌細胞培養模 型,以免在動物細胞實驗因物種不同而引起之結果差異。在人類心臟 前驅細胞衍生之心肌細胞缺氧再氧化時,針對Levosimedan對細胞凋 亡及鈉鈣交換通道活性之影響進行研究。在再氧化時給予Levosimedan 可減少細胞凋亡,並降低 缺氧—再氧化導致之鈉鈣交換通道反向作 用增加。並可見鈉鈣交換通道遠離開細胞膜,此為鈉鈣交換通道活性 降低之原因之一。同時因缺氧—再氧化導致之細胞內質網壓力反應昇 高,亦可因投予 Levosimedan或鈉鈣交換通道核糖核酸抑制而降低,但兩者並無加成作用。此結果顯示Levosimedan可藉抑制鈉鈣交換通 道反向作用,降低缺氧—再氧化導致之細胞內質網壓力反應昇高及細 胞凋亡。並暗示鈉鈣交換通道反向作用導致之細胞內鈣離子濃度昇高, 為內質網壓力反應,及內質網與粒腺體之鈣離子交通導致粒腺體內鈣 離子過高,而引發細胞凋亡之決定性因素。此ㄧ結果應在後續研究中 予以証實。
Ischemic heart disease is the leading cause of death worldwide as a single disease entity. To salvage cardiomyocytes suffering acute ischemic insult, it is mandatory to restore blood supply as early as possible. Paradoxically reperfusion per se inflicts additional damages on the cells. Rapid death of ischemic but still viable cardiomyocytes may ensue following successful reestablishment of blood flow. This lethal reperfusion injury diminishes the benefit of early reperfusion and is an important subject of investigation. Ca2+ overload, a prominent feature of cells subject to ischemia-reperfusion(I/R) that originates from a preceding intracellular Na+ accumulation and the action of reverse mode Na+-Ca2+ exchanger(NCX) on the plasma membrane, could lead to necrosis or apoptosis. NCX plays an important role in controlling Ca2+ homeostasis, both under physiological conditions and during I/R. The mitochondrion, when containing excessive Ca2+, triggers necrosis or apoptosis. Because there are attachments and Ca2+ communications between endoplasmic reticulum (ER) and mitochondria, interactions of these 2 organelles might affect mitochondrial Ca2+ content, which, when excessive, could to cell death during I/ R. Preserving cardiomyocyte viability has also become an paradigm in treatment of heart failure, while the use of conventional inotropes, which enhances cardiac contractility by increasing intracellular Ca2+ concentration, could decrease patient survival. Levosimendan, a known calcium sensitizer with positive inotropic and vasodilating properties, might also be cardioprotective during I/R. Its effects on calcium homeostasis and apoptosis in I/R injury remain unclear. A human cardiomyocyte culture model was established to avoid inconsistencies arising from species difference if animal cells were used for experiments. We probed effects and underlying mechanisms of levosimendan on apoptosis and NCX activity in cultured human cardiac progenitor cells(hCPC)-derived cardiomyocytes undergoing anoxia-reoxygenation (A/R), simulating I/R in vivo. Administration of levosimendan decreased apoptosis of hCPC-derived cardiomyocytes induced by A/R. The increase in reverse-mode NCX activity after A/R was curtailed by levosimendan, and NCX1 was translocated away from the cell membrane. Concomitantly, ER stress response induced by A/R was attenuated in hCPC-derived cardiomycytes treated with NCX-targeted siRNA or levosimendan with no synergistic effect. Results indicated levosimendan inhibited reverse-mode NCX activity to protect hCPC- derived cardiomyocytes from A/R-induced ER stress and cell death, and also suggested that during A/R heightened NCX reverse mode action-induced intracellular Ca2+ increase plays an decisive role in apoptosis induced by ER stress response and mitochondrial Ca2+ overload resulting from ER- mitochondrial communication. Confirmation of results awaits further studies. |
