在正常情况下,大部分肝细胞处于G0期,很少分裂,但是当受到某些机械,病毒,药物等刺激时,G0期细胞可以进入G1期,启动细胞周期。大鼠进行2/3肝切除后,剩余肝脏仍可代偿性的长到原来大小,并恢复其功能,这个过程称为肝再生(Liver regeneration,LR)。很多激素,细胞因子,蛋白,信号通路参与肝再生过程,迄今为止,对肝再生过程还没有非常明确的了解,尤其是启动和终止阶段 [ 1-3 ] 。
溶酶体是广泛存在于真核细胞中对细胞功能有重要作用的细胞器,自噬(Autophagy)是溶酶体介导的降解受损或冗余细胞成分为小分子物质的过程,降解后的物质可以被重新利用。这些功能主要是溶酶体膜蛋白和内腔中的酸性水解酶类来执行的。迄今为止,发现至少50种溶酶体酸性水解酶 [ 4 ] ,这些水解酶直接行使催化功能,但溶酶体膜蛋白的作用也极其重要,比如,维持溶酶体内酸性环境,选择性的运输需要被降解的物质,介导溶酶体膜和其他膜的融合等 [ 5 ] 。自噬参与了机体很多重要的生理过程,如细胞发育,分化,衰老,死亡等 [ 6 ; 7 ] 。越多的越多的证据表明,自噬和人类的一些疾病和肿瘤发生有很大关系 [ 8 ] 。所以,自噬在细胞和机体的生命中扮演着重要角色。
关于肝再生与自噬的研究已有不少报道 [ 9-13 ] ,研究发现,正常小鼠70%肝切除后,发生积极自噬而免于细胞老化,并通过维持健康的线粒体形态刺激线粒体代谢,通过氧化磷酸化为肝再生提供能量 [ 14 ] 。还有研究发现,肝再生早期,线粒体通透性没有明显改变,而24h之后内膜通透性降低,氧化磷酸化偶联增强,效率提高 [ 15 ] 。为了解大鼠2/3肝切除肝再生与自噬的关系,自噬相关信号通路及相关蛋白在肝再生不同时间点的变化,并阐明其机制,本研究借助同位素标记相对和绝对定量(isobaric tags for relative and absolute quantitation,iTRAQ)结合质谱(mass spectrometry,MS)方法检测了大鼠肝再生2、6、12、24、30和36小时等6个时间点自噬相关蛋白的表达变化,并分析了他们的表达模式和相互作用及其与肝再生的关系。根据实验结果我们提出溶酶体和线粒体可能有共存的形式,且从分子水平阐释其存在的可能机理。除了自噬,真核细胞还有一种降解蛋白质的系统,现在有研究发现两种蛋白降解体系之间有着某种联系 [ 16-19 ] ,但是机理有待阐明。我们首次在蛋白水平分析了大鼠肝再生自噬与泛素介导的蛋白酶体途径之间可能的联系。
大鼠肝切除后,合成活动旺盛,需要大量的能量供应。和能量相关的AMPK信号通路激活,以对抗这种应激状态。而和自噬直接相关的溶酶体膜蛋白和大量酸性水解酶表达上调,线粒体内膜相关蛋白表达增强,意味着线粒体功能并未受到大的影响,根据以上分析,
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