Adiponectin is protective against endoplasmic reticulum stress-induced apoptosis of endothelial cells in sepsis

Endoplasmic reticulum (ER) stress is a critical molecular mechanism involved in the pathogenesis of sepsis. Hence, strategies for alleviating this stress may be essential for preventing cardiovascular injuries under sepsis. Adiponectin is secreted by adipocytes and its levels are decreased in sepsis. The purpose of this study was to investigate the protective effects of adiponectin treatment on endothelial cells and its mechanism. Male Wistar rats underwent cecal ligation and puncture (CLP) before being treated with adiponectin (72 and 120 μg/kg). The levels of malondialdehyde (MDA) in plasma, histological structure, and apoptosis of endothelial cells were evaluated. In vitro, human umbilical vein endothelial cells (HUVECs) were treated with adiponectin at 10 and 20 μg/mL for 24 h after stimulation by lipopolysaccharide (LPS). The levels of reactive oxygen species (ROS), ultrastructure, rate of apoptosis, the expression of inositol-requiring enzyme 1α (IRE1α) protein, and its downstream molecules (78 kDa glucose-regulated protein (GRP78), C/EBP homologous protein (CHOP), and caspase-12) were detected. The results showed that the levels of MDA and ROS induced by CLP or LPS stimulation were increased. Furthermore, endothelial cell apoptosis was increased under sepsis. The IRE1α pathway was initiated, as evidenced by activated IRE1α, increased GRP78, and up-regulated CHOP and caspase-12 in HUVECs. Following treatment with adiponectin, the number of apoptotic endothelial cells was markedly decreased. These findings demonstrated that treatment with adiponectin decreased apoptosis of endothelial cells caused by sepsis by attenuating the ER stress IRE1α pathway activated by oxidative stress.

内质网应激（Endoplasmic reticulum (ER) stress）是参与脓毒症发病机制的关键分子机制。因此，缓解该应激的策略或许是预防脓毒症相关性心血管损伤的核心手段。脂联素（adiponectin）由脂肪细胞分泌，其在脓毒症患者体内的表达水平显著降低。本研究旨在探究脂联素干预对内皮细胞的保护作用及其潜在分子机制。

本研究选用雄性Wistar大鼠，采用盲肠结扎穿刺术（cecal ligation and puncture，CLP）构建脓毒症模型，随后分别以72 μg/kg和120 μg/kg的脂联素进行干预。检测各组大鼠血浆丙二醛（malondialdehyde，MDA）水平、内皮细胞组织学结构及细胞凋亡情况。

体外实验中，将人脐静脉内皮细胞（human umbilical vein endothelial cells，HUVECs）用脂多糖（lipopolysaccharide，LPS）刺激24小时后，分别以10 μg/mL和20 μg/mL的脂联素进行处理。检测各组细胞内活性氧（reactive oxygen species，ROS）水平、细胞超微结构、凋亡率，以及肌醇需求酶1α（inositol-requiring enzyme 1α，IRE1α）蛋白及其下游分子（78kDa葡萄糖调节蛋白（78 kDa glucose-regulated protein，GRP78）、C/EBP同源蛋白（C/EBP homologous protein，CHOP）及半胱氨酸天冬氨酸蛋白酶12（caspase-12））的表达水平。

研究结果显示，CLP建模或LPS刺激可显著升高血浆及细胞内MDA和ROS水平；同时脓毒症状态下内皮细胞凋亡率显著升高，且IRE1α通路被激活，具体表现为IRE1α活化、GRP78表达上调，以及HUVECs中CHOP和caspase-12的表达水平显著升高。经脂联素干预后，凋亡的内皮细胞数量显著减少。

本研究结果证实，脂联素可通过减轻氧化应激激活的内质网应激IRE1α通路，进而抑制脓毒症诱导的内皮细胞凋亡。