Protein phosphatase 2A參與ketamine抑制大鼠血管平滑肌細胞增生的機轉探討

The role of protein phosphatase 2A in ketamine-mediated inhibitory effects on rat vascular smooth muscle cell proliferation

洪碩凰(Shou-Huang Hung)

指導教授 ： 許準榕

臺北醫學大學/醫學院/醫學科學研究所/碩士(2012年)

https://doi.org/10.6831/TMU.2012.00051

摘要

先前的研究指出，血管平滑肌細胞在一些心血管疾病，例如粥狀動脈硬化及血管再窄化的病程中扮演相當重要的角色。血小板衍生生長因子-BB（PDGF-BB）會從血管受損的內皮細胞釋放，進而刺激血管平滑肌細胞增生和遷移，導致內膜異常增厚及伴隨著血管狹窄。Ketamine，一般用於人或動物之速效作用、非巴比妥類藥物的解離性 ( dissociative ) 麻醉劑。本篇論文中，我們探討 ketamine 對於 PDGF-BB 所誘導的血管平滑肌細胞增生機轉，且進一步觀察 PP2A ( Protein Phosphatases 2A ) 是否參與其中。本篇論文發現 ketamine 可以抑制 PDGF-BB 所誘導的蛋白激酶 ( AKT ) 及胞外訊息調控激酶1/2 ( ERK1/2 ) 的磷酸化，而 PP2A 的抑制劑 okadaic acid ( OA )及 PP2A siRNA 皆能有意義地回復ketamine所抑制 PDGF-BB 誘導的 AKT 及 ERK1/2 磷酸化。另ㄧ方面，我們也發現nSMase 抑制劑 3-o-methyl sphingomyelin ( 3-OME ) 會隨著濃度相關性回復 ketamine 所抑制的 PDGF-BB 誘導之 AKT 及 ERK1/2 的磷酸化，暗示 ketamine 可能經由活化 nSMase 使得細胞內 ceramide 增加，進一步活化 PP2A，最終使得 AKT 以及 ERK1/2 的磷酸化程度下降而抑制 PDGF-BB 誘導的細胞增生。此外本論文發現 ketamine 也有可能是透過抑制 PP2A Tyr307的磷酸化及 Leu309 去甲基化之蛋白修飾作用，使得PP2A的活性增加。同時我們也發現在約 55 kDa 的位置有一個protein tyrosine的磷酸化程度會隨著 ketamine 濃度增加而明顯減少，因此由實驗結果推測 ketamine 可能是經由抑制某 Src-family protein kinase 成員的活性，使得 PP2A 的去磷酸化而變成活化態，進而達到抑制大鼠血管平滑肌細胞的增生作用。

關鍵字

K他命 ； 血管平滑肌細胞 ； 增生

並列摘要

Previous studies have indicated that vascular smooth muscle cells ( VSMCs ) play a critical role in the progression of vascular diseases such as atherosclerosis and vascular stenosis. Platelet-derived growth factor-BB ( PDGF-BB ) released from damaged endothelium stimulated VSMC proliferation and migration leading to neointima formation and subsequent vascular stenosis. Ketamine is a common drug used in human and veterinary medicine. It is known as a rapid-acting, non-barbiturate and dissociative anesthetic. In this study, we investigated the effects of ketamine on PDGF-induced VSMC proliferation. We demonstrated that ketamine concentration-dependently inhibited PDGF-induced rat VSMC proliferation. Ketamine was also shown to attenuate PDGF-induced Akt and ERK1/2 phosphorylation. In addition, the inhibitory actions of ketamine were restored in the presence of protein phosphatase 2A ( PP2A ), okadaic acid ( OA ). Selectively ketamine PP2A using PP2A siRNA also restored ketamine’s inhibitory effects on Akt and ERK1/2 phosphorylation. In addition, 3-o-methyl sphingomyelin ( 3-OME ), a neutral sphingomyelinase ( nSMase ) inhibitor, was also shown to suppress ketamine actions in PDGF-induced VSMCs. It suggests that ketamine may cause nSMase-ceramide-PP2A cascade activation. Furthermore, ketamine was shown to decrease PP2A Tyr307 phosphorylation, Leu309 demethylation and tyrosine-phosphorylation of 55-kDa, leading to PP2A activation. Taken together, these results suggest that ketamine may cause PP2A activation to dephosphorylate Akt and ERK1/2 inhibit cell proliferation in rat VSMCs exposed to PDGF.

並列關鍵字

pp2a ； ketamine ； vscular smooth muscle cells ； proliferation

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