Respiratory dysfunction by AFG3L2 deficiency causes decreased mitochondrial calcium uptake via organellar network fragmentation
Respiratory dysfunction by AFG3L2 deficiency causes decreased mitochondrial calcium uptake via organellar network fragmentation
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DOI：
10.1093/hmg/dds214
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发表时间：
2012-09-01
影响因子：
3.5
通讯作者：
Casari, Giorgio
中科院分区：
文献类型：
--
作者：
Maltecca, Francesca;De Stefani, Diego;Casari, Giorgio
线粒体蛋白AFG3L2与脊髓小脑共济失调蛋白（paraplegin）在线粒体内膜形成同聚和异聚复合物，称为m - AAA蛋白酶。这些复合物负责错误折叠蛋白质的质量控制，并参与OPA1蛋白水解切割的调节，而OPA1蛋白水解切割是线粒体融合所必需的。AFG3L2的突变会导致28型脊髓小脑性共济失调以及一种儿童复杂神经退行性综合征。在这项研究中，我们证明了在小鼠胚胎成纤维细胞（MEFs）中AFG3L2的缺失会降低线粒体对Ca - 2的摄取能力。这一缺陷既不是细胞内Ca - 2稳态整体改变的结果，也不是线粒体内Ca - 2内化驱动力降低的结果，因为胞质Ca - 2瞬变和线粒体膜电位未受影响。此外，在透化细胞中进行的实验表明，Afg3l2缺失细胞中线粒体Ca - 2的摄取速度未改变，这表明存在有功能的Ca - 2摄取机制。我们的研究结果表明，Afg3l2缺失细胞中Ca - 2处理缺陷是由线粒体网络碎片化引起的，这是呼吸功能障碍以及随后OPA1加工的结果。这使得许多线粒体与内质网没有连接，因此没有Ca - 2升高，阻碍了Ca - 2沿线粒体网络的正常扩散。通过过表达OPA1恢复Afg3l2缺失的MEFs中的线粒体碎片化，可以挽救受损的线粒体Ca - 2缓冲能力，但无法恢复呼吸功能。通过将线粒体形态与Ca - 2稳态联系起来，这些发现为强调AFG3L2突变导致神经退行性变的分子机制提供了新的线索。
The mitochondrial protein AFG3L2 forms homo-oligomeric and hetero-oligomeric complexes with paraplegin in the inner mitochondrial membrane, named m-AAA proteases. These complexes are in charge of quality control of misfolded proteins and participate in the regulation of OPA1 proteolytic cleavage, required for mitochondrial fusion. Mutations in AFG3L2 cause spinocerebellar ataxia type 28 and a complex neurodegenerative syndrome of childhood. In this study, we demonstrated that the loss of AFG3L2 in mouse embryonic fibroblasts (MEFs) reduces mitochondrial Ca-2 uptake capacity. This defect is neither a consequence of global alteration in cellular Ca-2 homeostasis nor of the reduced driving force for Ca-2 internalization within mitochondria, since cytosolic Ca-2 transients and mitochondrial membrane potential remain unaffected. Moreover, experiments in permeabilized cells revealed unaltered mitochondrial Ca-2 uptake speed in Afg3l2(/) cells, indicating the presence of functional Ca-2 uptake machinery. Our results show that the defective Ca-2 handling in Afg3l2(/) cells is caused by fragmentation of the mitochondrial network, secondary to respiratory dysfunction and the consequent processing of OPA1. This leaves a number of mitochondria devoid of connections to the ER and thus without Ca-2 elevations, hampering the proper Ca-2 diffusion along the mitochondrial network. The recovery of mitochondrial fragmentation in Afg3l2(/) MEFs by overexpression of OPA1 rescues the impaired mitochondrial Ca-2 buffering, but fails to restore respiration. By linking mitochondrial morphology and Ca-2 homeostasis, these findings shed new light in the molecular mechanisms underlining neurodegeneration caused by AFG3L2 mutations.