Department of Biological Sciences, College of Natural Sciences, Kongju National University, Gongju, Chungnam Do 314‑701, Republic of Korea.
Mol Med Rep. 2019 Dec;20(6):5249-5256. doi: 10.3892/mmr.2019.10773. Epub 2019 Oct 25.
Gallotannin (GT) is a class of polyphenols with antioxidant, anticancer, and antiviral activities. 2‑Deoxy‑D‑glucose (2DG), a glucose‑derived molecule, can inhibit glucose metabolism and induce endoplasmic reticulum (ER) stress. GT in primary‑cultured chondrocytes enhances expression of type II collagen, an indicator of differentiation, and cyclooxygenase‑2 (COX‑2), which mediates inflammatory reactions. In contrast, 2DG reduces type II collagen and COX‑2 expression while driving ER‑stress‑induced unglycosylation. In the present study, it was investigated whether GT could attenuate 2DG‑induced dedifferentiation and ER‑stress. Following treatment with GT and 2DG, chondrocytes were assessed using western blotting, RT‑PCR, immunofluorescence, and alcian blue staining. GT restored type II collagen expression that was reduced by 2DG, inhibited ER‑stress‑induced COX‑2 unglycosylation, and induced COX‑2 expression. The expression of a glucose‑regulated protein, GRP78, which is an indicator of reduced ER‑stress, was decreased. To link the GT signaling pathway with pathways that inhibit 2DG‑induced dedifferentiation and ER‑stress, inhibitors were treated in chondrocytes. The results revealed that, among the different signaling pathways triggered by ER‑stress, the p38 kinase pathway was involved in the inositol‑requiring enzyme 1 (IRE1) downstream signaling pathway. Following inhibition of the IRE1 pathway, type II collagen expression was increased and COX‑2 expression was decreased. In addition, after examining the splicing of X‑box binding protein 1 (XBP‑1) which is dependent on IRE1 activation induced by ER‑stress, it was revealed that GT inhibited the increase of XBP‑1s after splicing due to 2DG‑induced ER stress. GT in chondrocytes inhibited 2DG‑induced dedifferentiation and ER‑stress‑induced COX‑2 unglycosylation while regulating differentiation and inflammation via the ER‑stress‑induced p38 kinase pathway downstream from the IRE1 pathway.
没食子单宁（GT）是一类具有抗氧化、抗癌和抗病毒活性的多酚。2-脱氧-D-葡萄糖（2DG），一种葡萄糖衍生的分子，可以抑制葡萄糖代谢并诱导内质网（ER）应激。GT 在原代软骨细胞中增强了分化标志物 II 型胶原和环氧化酶-2（COX-2）的表达，后者介导炎症反应。相比之下，2DG 降低了 II 型胶原和 COX-2 的表达，同时驱动 ER 应激诱导的去糖基化。在本研究中，研究了 GT 是否可以减轻 2DG 诱导的去分化和 ER 应激。用 GT 和 2DG 处理软骨细胞后，通过 Western blot、RT-PCR、免疫荧光和茜素蓝染色评估。GT 恢复了 2DG 降低的 II 型胶原表达，抑制了 ER 应激诱导的 COX-2 去糖基化，并诱导了 COX-2 的表达。葡萄糖调节蛋白 78（GRP78）的表达减少，这是 ER 应激减轻的一个指标。为了将 GT 信号通路与抑制 2DG 诱导的去分化和 ER 应激的信号通路联系起来，在软骨细胞中用抑制剂进行处理。结果表明，在 ER 应激触发的不同信号通路中，p38 激酶通路参与了肌醇需求酶 1（IRE1）下游信号通路。抑制 IRE1 通路后，II 型胶原表达增加，COX-2 表达减少。此外，在检查了 X 盒结合蛋白 1（XBP-1）的剪接之后，发现 XBP-1 的剪接依赖于 ER 应激诱导的 IRE1 激活，这表明 GT 抑制了由于 2DG 诱导的 ER 应激导致的 XBP-1s 的增加。GT 在软骨细胞中抑制了 2DG 诱导的去分化和 ER 应激诱导的 COX-2 去糖基化，同时通过 IRE1 通路下游的 ER 应激诱导的 p38 激酶通路调节分化和炎症。
