Cybulsky Andrey V, Takano Tomoko, Papillon Joan, Bijian Krikor, Guillemette Julie, Kennedy Chris R J
Div. of Nephrology, Royal Victoria Hospital, 687 Pine Ave. West, Montreal, Quebec, Canada H3A1A1.
Am J Physiol Renal Physiol. 2009 Oct;297(4):F987-95. doi: 10.1152/ajprenal.00055.2009. Epub 2009 Jul 29.
Focal segmental glomerulosclerosis (FSGS) may be associated with glomerular epithelial cell (GEC; podocyte) apoptosis due to acquired injury or mutations in alpha-actinin-4. This study addresses how FSGS-associated mutant alpha-actinin-4 may induce GEC injury, focusing on endoplasmic reticulum (ER) stress and metabolism of mutant alpha-actinin-4 via the ubiquitin-proteasome system. In a model of experimental FSGS induced by expression of an alpha-actinin-4 K256E transgene in podocytes, we show induction of ER stress, including upregulation of ER chaperones (bip, grp94), phosphorylation of the eukaryotic translation initiation factor-2alpha subunit, and induction of the proapoptotic gene C/EBP homologous protein-10 (CHOP). To address mechanisms of ER stress, we studied signaling in cultured GEC and COS cells expressing alpha-actinin-4 K256E. Previously, we showed that expression of this alpha-actinin-4 mutant in GEC increased apoptosis. In the present study, we show that alpha-actinin-4 K256E upregulates grp94 and CHOP expression in COS cells and significantly exacerbates induction of bip and CHOP in GEC in the presence of tunicamycin. ER stress was associated with aggregation and ubiquitination of alpha-actinin-4 K256E and impairment of the ubiquitin-proteasome system. In addition, alpha-actinin-4 K256E exacerbated apoptosis in the context of mild proteasome inhibition. Thus alpha-actinin-4 K256E triggers several metabolic abnormalities, which may lead to GEC injury and glomerulosclerosis.
局灶节段性肾小球硬化（FSGS）可能与由于获得性损伤或α-辅肌动蛋白-4突变导致的肾小球上皮细胞（GEC；足细胞）凋亡有关。本研究探讨了与FSGS相关的突变α-辅肌动蛋白-4如何诱导GEC损伤，重点关注内质网（ER）应激以及通过泛素-蛋白酶体系统对突变α-辅肌动蛋白-4的代谢。在通过在足细胞中表达α-辅肌动蛋白-4 K256E转基因诱导实验性FSGS的模型中，我们显示了ER应激的诱导，包括ER伴侣蛋白（bip、grp94）的上调、真核翻译起始因子-2α亚基的磷酸化以及促凋亡基因C/EBP同源蛋白-10（CHOP）的诱导。为了探讨ER应激的机制，我们研究了在表达α-辅肌动蛋白-4 K256E的培养GEC和COS细胞中的信号传导。此前，我们表明这种α-辅肌动蛋白-4突变体在GEC中的表达增加了细胞凋亡。在本研究中，我们表明α-辅肌动蛋白-4 K256E上调了COS细胞中grp94和CHOP的表达，并在衣霉素存在的情况下显著加剧了GEC中bip和CHOP的诱导。ER应激与α-辅肌动蛋白-4 K256E的聚集和泛素化以及泛素-蛋白酶体系统的损伤有关。此外，在轻度蛋白酶体抑制的情况下，α-辅肌动蛋白-4 K256E加剧了细胞凋亡。因此，α-辅肌动蛋白-4 K25
