Sequestosome 1 (SQSTM1) also known as ubiquitin-binding protein p62 (p62) is a cargo protein involved in the degradation of misfolded proteins via selective autophagy. Disruption of autophagy and resulting accumulation of misfolded proteins in the endoplasmic reticulum (ER) leads to ER stress. ER stress is implicated in several neurodegenerative diseases and obesity. As knockout of p62 (p62KO) reportedly induces obesity in mice, we examined how p62 contributes to ER stress and the ensuing unfolded protein response (UPR) in hypothalamus using mouse organotypic cultures in the present study. Cultures from p62KO mice showed significantly reduced formation of LC3-GFP puncta, an index of autophagosome formation, in response to the chemical ER stressor thapsigargin compared to wild-type (WT) cultures. Hypothalamic cultures from p62KO mice exhibited higher basal expression of the UPR/ER stress markers CHOP mRNA and ATF4 mRNA than WT cultures. Thapsigargin enhanced CHOP, ATF4, and BiP mRNA as well as p-eIF2α protein expression in both WT and p62KO cultures, but all peak values were greater in p62KO cultures. A proteasome inhibitor increased p62 expression in WT cultures and upregulated the UPR/ER stress markers CHOP mRNA and ATF4 mRNA in both genotypes, but to a greater extent in p62KO cultures. Therefore, p62 deficiency disturbed autophagosome formation and enhanced both basal and chemically induced ER stress, suggesting that p62 serves to prevent ER stress in mouse hypothalamus by maintaining protein folding capacity.

译文

Sequestosome 1 (SQSTM1) 也称为泛素结合蛋白p62 (p62) 是一种通过选择性自噬参与错误折叠蛋白降解的货物蛋白。自噬的破坏和内质网 (ER) 中错误折叠的蛋白质的积累导致ER应激。ER应激与几种神经退行性疾病和肥胖症有关。据报道,由于p62 (p62KO) 的敲除会导致小鼠肥胖,因此我们在本研究中使用小鼠器官型培养物检查了p62如何促进下丘脑的内质网应激和随后的未折叠蛋白反应 (UPR)。与野生型 (WT) 培养物相比,来自p62KO小鼠的培养物显示出响应于化学ER应激源thapsigargin的LC3-GFP点形成显着减少,这是自噬体形成的指标。p62KO小鼠的下丘脑培养物显示出UPR/ER应激标记物CHOP mRNA和ATF4 mRNA的基础表达高于WT培养物。Thapsigargin在WT和p62KO培养物中均增强了CHOP,ATF4和BiP mRNA以及p-eIF2α 蛋白的表达,但在p62KO培养物中所有峰值均较大。蛋白酶体抑制剂在两种基因型中均增加了WT培养物中的p62表达,并上调了UPR/ER应激标记物CHOP mRNA和ATF4 mRNA,但在p62KO培养物中更大程度。因此,p62缺乏干扰了自噬体的形成,并增强了基础和化学诱导的ER应激,表明p62通过维持蛋白质折叠能力来预防小鼠下丘脑的ER应激。

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