College of Animal Science and Technology, Northwest Agriculture and Forestry University, Yangling 712100, China.
J Anim Sci. 2023 Jan 3;101. doi: 10.1093/jas/skad101.
Docosahexaenoic acid (DHA) lessens adipose tissue lipid deposition partly by inducing adipocyte apoptosis in grass carp, but the underlying mechanism remains unclear. Endoplasmic reticulum (ER) stress and unfolded protein response (UPR) is the novel pathway for inducing apoptosis. This study aimed to explore the potential role of ER stress in DHA-induced apoptosis in grass carp (Ctenopharyngodon idellus) adipocytes. DHA induced apoptosis by deforming the nuclear envelope, condensing the chromatin, and increasing the expression of apoptosis-related proteins and genes in vivo and in vitro (P < 0.05). However, the ER stress inhibitor, 4-phenylbutyric acid (4-PBA), effectively suppressed DHA-induced apoptosis (P < 0.05), indicating that ER stress mediates DHA-induced adipocyte apoptosis. Furthermore, we observed that 200 μM DHA significantly up-regulates the transcripts of B cell lymphoma-2 (BCL-2) related ovarian killer (BOK) in vitro (P < 0.05). BOK is a pro-apoptotic protein in the BCL-2 family, which governs the mitochondria apoptosis pathway. Hence, we hypothesized that BOK might be an important linker between ER stress and apoptosis. We cloned and identified two grass carp BOK genes, BOKa and BOKb, which encode peptides of 213 and 216 amino acids, respectively. BOKa primarily localizes in ER and mitochondria in the cytoplasm, while BOKb localizes in the nucleus and cytoplasm of grass carp adipocytes. Moreover, 200 μM DHA treatment up-regulated the mRNA expression of BOKa and BOKb, whereas 4-PBA suppressed the DHA-induced expressions. These results raised the possibility that BOK participates in DHA-induced adipocyte apoptosis through ER stress signaling, in line with its localization in ER and mitochondria. Two UPR branches, the inositol-requiring enzyme 1 (IRE1α) and activating transcription factor 6 (ATF6) signaling pathways, are possibly important in DHA-induced adipocyte apoptosis, unlike protein kinase RNA-activated-like ER kinase. The study also emphasized the roles of BOKa and BOKb in IRE1α- and ATF6-mediated apoptosis. This work is the first to elucidate the importance of the ER stress-BOK pathway during adipocyte apoptosis in teleost.
二十二碳六烯酸 (DHA) 通过诱导草鱼脂肪细胞凋亡来减少脂肪组织脂质沉积，但具体机制尚不清楚。内质网 (ER) 应激和未折叠蛋白反应 (UPR) 是诱导凋亡的新途径。本研究旨在探讨 ER 应激在 DHA 诱导草鱼 (Ctenopharyngodon idellus) 脂肪细胞凋亡中的潜在作用。DHA 在体内和体外通过使核膜变形、染色质浓缩以及增加凋亡相关蛋白和基因的表达来诱导凋亡 (P < 0.05)。然而，ER 应激抑制剂 4-苯丁酸 (4-PBA) 可有效抑制 DHA 诱导的凋亡 (P < 0.05)，表明 ER 应激介导 DHA 诱导的脂肪细胞凋亡。此外，我们观察到 200 μM DHA 显著上调了体外 B 细胞淋巴瘤-2 (BCL-2) 相关卵巢杀伤因子 (BOK) 的转录物 (P < 0.05)。BOK 是 BCL-2 家族中的一种促凋亡蛋白，可调控线粒体凋亡途径。因此，我们假设 BOK 可能是 ER 应激和凋亡之间的重要连接子。我们克隆并鉴定了两种草鱼 BOK 基因，BOKa 和 BOKb，分别编码 213 和 216 个氨基酸的肽。BOKa 主要定位于细胞质的内质网和线粒体中，而 BOKb 则定位于草鱼脂肪细胞的核和细胞质中。此外，200 μM DHA 处理上调了 BOKa 和 BOKb 的 mRNA 表达，而 4-PBA 则抑制了 DHA 诱导的表达。这些结果表明，BOK 通过 ER 应激信号参与 DHA 诱导的脂肪细胞凋亡，与其在 ER 和线粒体中的定位一致。两条 UPR 分支，肌醇需求酶 1 (IRE1α) 和激活转录因子 6 (ATF6) 信号通路，在 DHA 诱导的脂肪细胞凋亡中可能很重要，而不是蛋白激酶 RNA 激活样内质网激酶。该研究还强调了 BOKa 和 BOKb 在 IRE1α 和 ATF6 介导的凋亡中的作用。这项工作首次阐明了 ER 应激-BOK 途径在硬骨鱼脂肪细胞凋亡中的重要性。
