Liraglutide protects pancreatic β cells from endoplasmic reticulum stress by upregulating MANF to promote autophagy turnover

Aims: This study was conducted to determine the relationship between mesencephalic astrocyte-derived neurotrophic factor (MANF), autophagy and endoplasmic reticulum (ER) stress, and whether liraglutide (LRG) can protect beta cells, promote autophagy and alleviate ER stress by regulating MANF expression. Main methods: Human serum samples were collected from healthy controls (NC), simple hyperlipidemia (HLD), and newly diagnosed type 2 diabetes (T2D). The MANF levels were detected using ELISA. In vitro, after the mouse islet MIN6 cells were treated with glucose (GLU), palmitate (PA), thapsigargin (TG), LRG, and chloroquine (CQ), cell proliferation was detected using cell counting kit-8 (CCK-8), apoptosis-related protein cleaved caspase 3 (C-cas-3), ER stress, and autophagy-related proteins were detected by Western blotting, MANF, insulin, and C-cas-3 proteins were detected via immunofluorescence. Subcellular structures and autophagosomes were examined using electron microscopy. Key findings: Compared with the NC group, the MANF levels in the HLD and T2D groups increased significantly. After ER stress induced by GLU, PA, and TG, cell viability decreased, while MANF, c-cas3, ERS, and autophagy-related proteins increased, which was related to the concentration of GLU, PA, and TG. Compared with the BSA group, the number of mitochondria and autophagosomes in the PA group increased and the mitochondria were damaged. In the PA and TG plus CQ groups, the effect was further exaggerated. But after co-treatment with LRG, the effects of GLU, PA, and TG were attenuated. Significance: LRG protects islet beta cells from ER stress by upregulating MANF to promote autophagy turnover.