Department of Surgery, University of Michigan Medical Center , Ann Arbor, Michigan.
Department of Physiology and Pathophysiology, Peking University Health Science Center , Beijing , China.
Am J Physiol Gastrointest Liver Physiol. 2019 Jan 1;316(1):G123-G131. doi: 10.1152/ajpgi.00056.2018. Epub 2018 Nov 8.
Leucine-rich repeat G protein-coupled receptors (LGRs) and their endogenous ligands R-spondin1-4 (Rspo) are critical in embryonic development and in maintenance of stem cells. The functions of the Rspo-LGR system in differentiated cells remain uncharacterized. In this study, the expression profiles of LGRs and Rspos were characterized in mature hepatocytes. A liver-specific knockout of LGR4 in mouse was generated and used to study hepatic ischemia/reperfusion-induced injury (HIRI) as well as lipopolysaccharide/ D- galactosamine (LPS/D-Gal)-induced liver injury. We have demonstrated that, in adult liver, LGR4 is expressed in hepatocytes and responds to Rspo1 with internalization. Rspo1 is responsive to various nutritional states and to mTOR signaling. Activation of LGR4 by Rspo1 significantly reduced tumor necrosis factor-α (TNFα)-induced cell death, and levels of NF-κB-p65 and caspase-3 in cultured hepatocytes. Knockdown of hepatic LGR4 rendered hepatocytes more vulnerable to TNFα-induced damage in cultured primary cells and in the setting of HIRI and LPS/D-Gal-induced liver injury. Rspo1 potentiated both basal and Wnt3a-induced stabilization of β-catenin. Disruption of β-catenin signaling reversed the protective effects of Rspo1 on TNFα-induced hepatocyte toxicity. LGR4 knockdown increased nuclear translocation of NF-κB-p65 in response to acute injury. Overexpression of IKKβ attenuated the protective effects of Rspo1 on TNFα-induced cell death. In conclusion, the Rspo1-LGR4 system represents a novel pathway for cytoprotection and modulation of stress-induced tissue damage. NEW & NOTEWORTHY Functional LGR4 is present in mature hepatocytes. R-spodin1 protects hepatocytes from tumor necrosis factor-α-induced cell death. Liver-specific knockdown of LGR4 renders liver more susceptible to acute injury. LGR4 protects hepatocytes from injury by inhibition of NF-κB signaling.
富含亮氨酸重复的 G 蛋白偶联受体（LGRs）及其内源性配体 R 螺旋 1-4（Rspo）在胚胎发育和干细胞维持中起着关键作用。然而，Rspo-LGR 系统在分化细胞中的功能仍未被描述。在本研究中，我们对成熟肝细胞中的 LGRs 和 Rspos 的表达谱进行了表征。我们生成了一种肝脏特异性 LGR4 敲除小鼠，用于研究肝缺血再灌注损伤（HIRI）以及脂多糖/半乳糖胺（LPS/D-Gal）诱导的肝损伤。我们已经证明，在成年肝脏中，LGR4 在肝细胞中表达，并对内源配体 Rspo1 发生内化反应。Rspo1 对各种营养状态和 mTOR 信号有反应。Rspo1 激活 LGR4 显著降低了培养的肝细胞中肿瘤坏死因子-α（TNFα）诱导的细胞死亡，以及 NF-κB-p65 和 caspase-3 的水平。在培养的原代细胞以及 HIRI 和 LPS/D-Gal 诱导的肝损伤中，肝 LGR4 的敲低使肝细胞更容易受到 TNFα 诱导的损伤。Rspo1 增强了 Wnt3a 诱导的 β-连环蛋白的稳定性。β-连环蛋白信号的破坏逆转了 Rspo1 对 TNFα 诱导的肝细胞毒性的保护作用。LGR4 的敲低增加了 NF-κB-p65 对急性损伤的核易位。IKKβ 的过表达减弱了 Rspo1 对 TNFα 诱导的细胞死亡的保护作用。总之，Rspo1-LGR4 系统代表了一种新的细胞保护和应激诱导组织损伤调节的途径。
