Bardet-Biedl syndrome obesity: BBS4 regulates cellular ER stress in early adipogenesis
Bardet-Biedl syndrome obesity: BBS4 regulates cellular ER stress in early adipogenesis
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DOI：
10.1016/j.ymgme.2019.03.006
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发表时间：
2019-04-01
影响因子：
3.8
通讯作者：
Birk, Ruth
中科院分区：
文献类型：
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作者：
Anosov, Mariana;Birk, Ruth
背景Bardet-Biedl综合征（BBS）是一种常染色体隐性遗传的纤毛病，表现为早期肥胖发作。BBS肥胖的病因涉及中枢和外周缺陷，其机制大多尚未阐明。我们先前显示了BBS 4在脂肪形成中的表达，在分化的第3天达到峰值。肥胖的特点是细胞应激，促进pathological consequences.Aims：我们着手测试可能的作用，BBS 4在脂肪细胞内质网（ER）应激诱导的展开蛋白反应（UPR）.Methods：BBS 4沉默（SiBBS 4）和过度表达（OEBBS 4）前脂肪细胞鼠细胞系进行ER应激诱导（衣霉素，TM）在脂肪形成。结果：计算机模拟结果显示，BBS 4基因中含有一个ER定位序列，该序列可作为ER定位的参考。我们通过免疫细胞化学和细胞蛋白分级分离证实了BBS 4在脂肪细胞中的ER定位。此外，我们证明，BBS 4的表达显着上调ER应激，所示的蛋白质和转录水平。SiBBS 4脂肪细胞在分化的第3天表现出典型的ER-应激和显著的XBP-1下调的ER肿胀。在ER应激后，SiBBS 4脂肪细胞表现出XBP-1 ER保留，不能易位到细胞核，并且核活性裂解的ATF 6 α耗尽。BBS 4没有改变高尔基体中SW和S2 P对ATF 6 α的加工。值得注意的是，SiBBS 4细胞表现出显着减少下游激活磷酸-IRE 1 α，独立的ER-stress.Conclusions：在第3天的脂肪形成，符合其峰值表达的时间，BBS 4是本地化的ER，并参与ER应激反应和贩运。BBS 4耗竭导致ER肿胀，XBP-1和ATF 6 α的细胞内核易位受损。因此，BBS 4影响早期脂肪形成中的ER应激反应，改变ER应激反应和脂肪细胞ER表型。
Background. Bardet-Biedl syndrome (BBS) is an autosomal recessive ciliopathy, presenting with early obesity onset. The etiology of BBS obesity involves both central and peripheral defects, through mechanisms mostly yet to be deciphered. We previously showed BBS4 expression in adipogenesis, peaking at day 3 of differentiation. Obesity is characterized by cellular stress which promotes pathological consequences.Aims: We set out to test a possible role of BBS4 in adipocyte endoplasmic reticulum (ER) stress-induced unfolding protein response (UPR).Methods: BBS4 silenced (SiBBS4) and overexpressing (OEBBS4) pre-adipocyte murine cell lines were subjected to ER-stress induction (Tunicamycin, TM) during adipogenesis. ER-stress UPR was analyzed at the transcript, protein and biochemical levels (microscopy, immunocytochemistry, western blotting, quantitative RT-PCR and X-box binding protein 1 (XBP-1) splicing).Results: In silico analysis showed that BBS4 harbors an ER localization sequences indicative of ER localization. We verified BBS4's ER localization in adipocytes by immunocytochemistry and cellular protein fractionation. Furthermore, we demonstrated that BBS4 expression is significantly up-regulated by ER-stress, as indicated by protein and transcript levels. SiBBS4 adipocytes exhibited swollen ER typical to ER-stress and significant XBP-1 down-regulation at day 3 of differentiation. Following ER-stress, SiBBS4 adipocytes exhibited XBP-1 ER retention, failure to translocate to the nucleus and depletion of the nuclear active cleaved ATF6 alpha. BBS4 did not alter ATF6 alpha processing by SW and S2P in the Golgi. Notably, SiBBS4 cells demonstrated significant reduction in the downstream activated phospho-IRE1 alpha, independent of ER-stress.Conclusions: At day 3 of adipogenesis, coinciding with the timing of its peak expression, BBS4 is localized to the ER and is involved in the ER stress response and trafficking. BBS4 depletion results in swollen ER with impaired intracellular nucleus translocation of XBP-1 and ATF6 alpha. Thus, BBS4 affects the ER stress response in early adipogenesis, altering ER stress responsiveness and the adipocyte ER phenotype.