Department of General Surgery, Third Xiangya Hospital, Central South University, Changsha, 410013, China.
Department of General Surgery, Third Xiangya Hospital, Central South University, Changsha, 410013, China.
Biochem Biophys Res Commun. 2019 Oct 1;517(4):629-635. doi: 10.1016/j.bbrc.2019.07.079. Epub 2019 Aug 3.
Type II diabetes is a complex, chronic, and progressive disease. Previously, we demonstrate that FXR inhibits GLP-1 secretion via interacting with CREB to inhibit the transcriptional activity of CREB, thus promoting the development of type II diabetes. Epigenetic modifications, such as DNA methylation, histone acetylation, and post-transcriptional RNA regulation, are essential mediators contributing to diabetes-associated morbidity and mortality. Thus, we attempted to investigate the epigenetic mechanisms of FXR modulating GLP-1 secretion. Firstly, the involvement of histone acetylation, DNA methylation, and post-transcriptional regulation in FXR inhibiting GLP-1 secretion was verified. As FXR overexpression significantly inhibited the activity of GCG 3'-UTR, we hypothesize that miRNA might participate in the mechanism. Two online tools and real-time PCR revealed that FXR promoted miR-33 expression. Moreover, miR-33 inhibited the expression of GCG and CREB1 through direct targeting in STC-1 cells. FXR overexpression in STC-1 cells significantly reduced the mRNA expression and protein levels of both GCG and CREB1, as well as the secretion of GLP-1; miR-33 inhibition exerted opposing effects. More importantly, the effects of FXR overexpression were significantly reversed by miR-33 inhibition, indicating that FXR inhibited GLP-1 secretion through promoting miR-33 expression, therefore inhibiting the expression of miR-33 targets, GCG and CREB1. In conclusion, we provide a novel epigenetic mechanism by which FXR inhibits the secretion of GLP-1 through miR-33 and its two downstream targets, GCG and CREB1. These findings might provide innovative strategies for improving type II diabetes, which needs further in vivo and clinical investigation.
2 型糖尿病是一种复杂的、慢性的、进行性疾病。之前，我们证明 FXR 通过与 CREB 相互作用抑制 GLP-1 分泌，从而抑制 CREB 的转录活性，促进 2 型糖尿病的发展。表观遗传修饰，如 DNA 甲基化、组蛋白乙酰化和转录后 RNA 调控，是导致糖尿病相关发病率和死亡率的重要介质。因此，我们试图研究 FXR 调节 GLP-1 分泌的表观遗传机制。首先，验证了组蛋白乙酰化、DNA 甲基化和转录后调控在 FXR 抑制 GLP-1 分泌中的作用。由于 FXR 过表达显著抑制了 GCG 3'-UTR 的活性，我们假设 miRNA 可能参与了这一机制。两个在线工具和实时 PCR 显示，FXR 促进了 miR-33 的表达。此外，miR-33 通过直接靶向在 STC-1 细胞中抑制 GCG 和 CREB1 的表达。FXR 在 STC-1 细胞中的过表达显著降低了 GCG 和 CREB1 的 mRNA 表达和蛋白水平，以及 GLP-1 的分泌；miR-33 抑制则产生相反的效果。更重要的是，miR-33 抑制显著逆转了 FXR 的过表达作用，表明 FXR 通过促进 miR-33 的表达来抑制 GLP-1 的分泌，从而抑制 miR-33 靶标 GCG 和 CREB1 的表达。总之，我们提供了一种新的表观遗传机制，即 FXR 通过 miR-33 及其两个下游靶标 GCG 和 CREB1 抑制 GLP-1 的分泌。这些发现可能为改善 2 型糖尿病提供创新策略，需要进一步的体内和临床研究。
