The ubiquitously expressed G protein α-subunit Gsα mediates the intracellular cAMP response to glucagon-like peptide 1 (GLP1) and other incretin hormones in pancreatic islet cells. We have shown previously that mice with β-cell-specific Gsα deficiency (βGsKO) develop severe early-onset insulin-deficient diabetes with a severe defect in β-cell proliferation. We have now generated mice with Gsα deficiency throughout the whole pancreas by mating Gsα-floxed mice with Pdx1-cre transgenic mice (PGsKO). PGsKO mice also developed severe insulin-deficient diabetes at a young age, confirming the important role of Gsα signaling in β-cell growth and function. Unlike in βGsKO mice, islets in PGsKO mice had a relatively greater proportion of α-cells, which were spread throughout the interior of the islet. Similar findings were observed in mice with pancreatic islet cell-specific Gsα deficiency using a neurogenin 3 promoter-cre recombinase transgenic mouse line. Studies in the α-cell line αTC1 confirmed that reduced cAMP signaling increased cell proliferation while increasing cAMP produced the opposite effect. Therefore, it appears that Gsα/cAMP signaling has opposite effects on pancreatic α- and β-cell proliferation, and that impaired GLP1 action in α- and β-cells via Gsα signaling may be an important contributor to the reciprocal effects on insulin and glucagon observed in type 2 diabetics. In addition, PGsKO mice show morphological changes in exocrine pancreas and evidence for malnutrition and dehydration, indicating an important role for Gsα in the exocrine pancreas as well.
Tao Xie, Min Chen and Lee S Weinstein
Da-Long Ren, Ai-Ai Sun, Ya-Juan Li, Min Chen, Shu-Chao Ge and Bing Hu
Neutrophil migration to inflammatory sites is the fundamental process of innate immunity among organisms against pathogen invasion. As a major sleep adjusting hormone, melatonin has also been proved to be involved in various inflammatory events. This study aimed to evaluate the impact of exogenous melatonin on neutrophil migration to the injury site in live zebrafish and further investigate whether ERK signaling is involved in this process. Using the tail fin transection model, the fluorescently labeled neutrophil was in vivo visualized in transgenic Tg(lyz:EGFP), Tg(lyz:DsRed) zebrafish. We found that exogenous melatonin administration dramatically inhibited the injury-induced neutrophil migration in a dose-dependent and time-dependent manner. The inhibited effect of melatonin on neutrophil migration could be attenuated by melatonin receptor 1, 2, and 3 antagonists. The ERK phosphorylation level was significantly decreased post injury when treated with melatonin. The blocking of ERK activation with inhibitor PD0325901 suppressed the number of migrated neutrophils in response to injury. However, the activation of ERK with the epidermal growth factor could impair the inhibited effect of melatonin on neutrophil migration. We also detected that PD0325901 significantly suppressed the in vivo neutrophils transmigrating over the vessel endothelial cell using the transgenic Tg(flk:EGFP);(lyz:DsRed) line labeled as both vessel and neutrophil. Taking all of these data together, the results indicated that exogenous melatonin had an anti-migratory effect on neutrophils by blocking the ERK phosphorylation signal, and it led to the subsequent adhesion molecule expression. Thus, the crossing of the vessel endothelial cells of neutrophils became difficult.
Xin-gang Yao, Xin Xu, Gai-hong Wang, Min Lei, Ling-ling Quan, Yan-hua Cheng, Ping Wan, Jin-pei Zhou, Jing Chen, Li-hong Hu and Xu Shen
Impaired glucose-stimulated insulin secretion (GSIS) and increasing β-cell death are two typical dysfunctions of pancreatic β-cells in individuals that are destined to develop type 2 diabetes, and improvement of β-cell function through GSIS enhancement and/or inhibition of β-cell death is a promising strategy for anti-diabetic therapy. In this study, we discovered that the small molecule, N-(2-benzoylphenyl)-5-bromo-2-thiophenecarboxamide (BBT), was effective in both potentiating GSIS and protecting β-cells from cytokine- or streptozotocin (STZ)-induced cell death. Results of further studies revealed that cAMP/PKA and long-lasting (L-type) voltage-dependent Ca2 + channel/CaMK2 pathways were involved in the action of BBT against GSIS, and that the cAMP/PKA pathway was essential for the protective action of BBT on β-cells. An assay using the model of type 2 diabetic mice induced by high-fat diet combined with STZ (STZ/HFD) demonstrated that BBT administration efficiently restored β-cell functions as indicated by the increased plasma insulin level and decrease in the β-cell loss induced by STZ/HFD. Moreover, the results indicated that BBT treatment decreased fasting blood glucose and HbA1c and improved oral glucose tolerance further highlighting the potential of BBT in anti-hyperglycemia research.
Jinn-Yang Chen, Deng-Yuan Jian, Chih-Chan Lien, Yu-Ting Lin, Ching-Heng Ting, Luen-Kui Chen, Ting-Chia Hsu, Hsuan-Min Huang, Yu-Ting Wu, Tse-Ting Kuan, Yu-Wen Chao, Liang-Yi Wu, Seng-Wong Huang and Chi-Chang Juan
Obesity is a risk factor that promotes progressive kidney disease. Studies have shown that an adipocytokine imbalance contributes to impaired renal function in humans and animals, but the underlying interplay between adipocytokines and renal injury remains to be elucidated. We aimed to investigate the mechanisms linking obesity to chronic kidney disease. We assessed renal function in high-fat (HF) diet-fed and normal diet-fed rats, and the effects of preadipocyte- and adipocyte-conditioned medium on cultured podocytes. HF diet-fed and normal diet-fed Sprague Dawley rats were used to analyze the changes in plasma BUN, creatinine, urine protein and renal histology. Additionally, podocytes were incubated with preadipocyte- or adipocyte-conditioned medium to investigate the effects on podocyte morphology and protein expression. In the HF diet group, 24 h urinary protein excretion (357.5 ± 64.2 mg/day vs 115.9 ± 12.4 mg/day, P < 0.05) and the urine protein/creatinine ratio were significantly higher (1.76 ± 0.22 vs 1.09 ± 0.15, P < 0.05), increased kidney weight (3.54 ± 0.04 g vs 3.38 ± 0.04 g, P < 0.05) and the glomerular volume and podocyte effacement increased by electron microscopy. Increased renal expression of desmin and decreased renal expression of CD2AP and nephrin were also seen in the HF diet group (P < 0.05). Furthermore, we found that adipocyte-conditioned medium-treated podocytes showed increased desmin expression and decreased CD2AP and nephrin expression compared with that in preadipocyte-conditioned medium-treated controls (P < 0.05). These findings show that adipocyte-derived factor(s) can modulate renal function. Adipocyte-derived factors play an important role in obesity-related podocytopathy.