Ranganathan Punithavathi, Jayakumar Calpurnia, Li Dean Y, Ramesh Ganesan
Vascular Biology Center, Georgia Regents University, Augusta, GA, USA.
J Cell Mol Med. 2014 Jul;18(7):1290-9. doi: 10.1111/jcmm.12280. Epub 2014 Apr 10.
The netrin-1 administration or overexpression is known to protect colon from acute colitis. However, the receptor that mediates netrin-1 protective activities in the colon during colitis remains unknown. We tested the hypothesis that UNC5B receptor is a critical mediator of protective function of netrin-1 in dextran sodium sulfate (DSS)-induced colitis using mice with partial deletion of UNC5B receptor. DSS colitis was performed in mice with partial genetic UNC5B deficiency (UNC5B(+/-) mice) or wild-type mice to examine the role of endogenous UNC5B. These studies were supported by in vitro models of DSS-induced apoptosis in human colon epithelial cells. WT mice developed colitis in response to DSS feeding as indicated by reduction in bw, reduction in colon length and increase in colon weight. These changes were exacerbated in heterozygous UNC5B knockout mice treated with DSS. Periodic Acid-Schiff stained section shows damages in colon epithelium and mononuclear cell infiltration in WT mice, which was further increased in UNC5B heterozygous knockout mice. This was associated with large increase in inflammatory mediators such as cytokine and chemokine expression and extensive apoptosis of epithelial cells in heterozygous knockout mice as compared to WT mice. Overexpression of UNC5B human colon epithelial cells suppressed DSS-induced apoptosis and caspase-3 activity. Moreover, DSS induced large amount of netrin-1 and shRNA mediated knockdown of netrin-1 induction exacerbated DSS-induced epithelial cell apoptosis. Our results suggest that UNC5B is a critical mediator of cell survival in response to stress in colon.
已知给予或过表达网蛋白-1可保护结肠免受急性结肠炎的侵害。然而，在结肠炎期间介导网蛋白-1在结肠中发挥保护作用的受体仍不清楚。我们使用UNC5B受体部分缺失的小鼠，检验了UNC5B受体是网蛋白-1在葡聚糖硫酸钠（DSS）诱导的结肠炎中发挥保护功能的关键介质这一假说。对部分基因UNC5B缺陷的小鼠（UNC5B(+/-)小鼠）或野生型小鼠进行DSS结肠炎实验，以研究内源性UNC5B的作用。这些研究得到了DSS诱导人结肠上皮细胞凋亡的体外模型的支持。野生型小鼠在喂食DSS后出现结肠炎，表现为体重减轻、结肠长度缩短和结肠重量增加。在用DSS处理的杂合UNC5B基因敲除小鼠中，这些变化加剧。高碘酸-希夫染色切片显示野生型小鼠结肠上皮受损和单核细胞浸润，在UNC5B杂合基因敲除小鼠中进一步加重。与野生型小鼠相比，这与杂合基因敲除小鼠中细胞因子和趋化因子等炎症介质表达大幅增加以及上皮细胞广泛凋亡有关。UNC5B在人结肠上皮细胞中的过表达抑制了DSS诱导的凋亡和半胱天冬酶-3活性。此外，DSS诱导大量网蛋白-1表达，而shRNA介导的网蛋白-1诱导敲低加剧了DSS诱导的上皮细胞凋亡。我们的结果表明，UNC5B是结肠对应激作出反应时细胞存活的关键介质。
