Patients with type II diabetes are susceptible to fracture; however, these patients typically have normal bone mineral density. Thus, such fractures cannot be entirely explained by advanced glycation end products (AGEs)-induced osteoblast apoptosis. Autophagy is a molecular process allowing cells to degrade unnecessary or dysfunctional cellular organelles, and closely interacts with apoptosis. The aim of this study was to determine whether autophagy participated in the pathology of AGEs-treated osteoblasts, and the possible mechanism of such an involvement. Osteoblastic MC3T3-E1 cells were used. Autophagy was evaluated by detecting the level of LC3 via western blotting and immunofluorescence. p62/SQSTM1 expression was also assessed by western blotting. The autophagy inducer rapamycin (RA) and the autophagy inhibitor 3-methyladenine were used to determine whether autophagy has effect on AGEs-induced apoptosis. N-Acetylcysteine (NAC), reactive oxygen species (ROS) inhibitor, was used to determine whether ROS and mitochondrial damage were involved in autophagy regulation. The results showed that the autophagy level was increased in MC3T3-E1 cells treated with AGEs, as represented by an increase in both the total LC3 level and the LC3II/LC3I ratio, as well as a decrease in p62/SQSTMI expression. Further inducing autophagy by RA attenuated AGEs-induced apoptosis. The antioxidant NAC suppresses AGEs-induced autophagy in osteoblastic MC3T3-E1 cells. These results demonstrate that autophagy participates in the pathology of AGEs-treated osteoblasts, and may play a protective role in AGEs-induced apoptosis in osteoblastic MC3T3-E1 cells. ROS and mitochondrial damage are essential in upregulating AGEs-induced autophagy.
Lei Yang, Hongzheng Meng, and Maowei Yang
Xiu-Lei Mo, Rui Yang, and Ya-Xiong Tao
The melanocortin-4 receptor (MC4R) is a G protein-coupled receptor critical for maintaining energy homeostasis. Transmembrane domain 3 (TM3) of MC4R contains residues that were suggested to be essential in ligand binding and signaling. Several MC4R mutations in TM3 are associated with human obesity. To gain a better understanding of the functions of TM3, we analyzed the functions of 26 residues in TM3 using alanine-scanning mutagenesis. We showed that all mutants had normal cell-surface expression. Four mutants were defective in ligand binding and signaling and six mutants had normal ligand binding but impaired cAMP production. L140A had increased basal cAMP level. To further characterize the function of L140, we generated 17 additional L140 mutants. Fifteen L140 mutants had significantly decreased cell-surface expression, with L140R and L140V expressed normally. Ten L140 mutants had increased basal cAMP activities. Four L140 mutants were defective in ligand-stimulated cAMP generation. Interestingly, with the ERK1/2 pathway, we showed that nine constitutively active mutants had similar levels of basal pERK1/2 as that of WT, and two signaling defective mutants had similar levels of pERK1/2 as that of WT upon agonist stimulation, different from their cAMP signaling properties, suggesting biased signaling in these mutant receptors. In summary, we identified 13 residues in TM3 that were essential for ligand binding and/or signaling. Moreover, L140 was critical for locking MC4R in inactive conformation and several mutants showed biased signaling in cAMP and ERK1/2 signaling pathways.
Lingxia Pang, Lianghui You, Chenbo Ji, Chunmei Shi, Ling Chen, Lei Yang, Fangyan Huang, Yahui Zhou, Jun Zhang, Xiaohui Chen, and Xirong Guo
Excessive adipocyte differentiation and proliferation are closely associated with the onset of obesity, which has been partially linked to microRNA expression. In previous studies, using miRNA microarray screening, we found that miR-1275 was significantly decreased in human mature adipocytes. In this study, we examined the role of miR-1275 in adipogenesis. Our results indicated that miR-1275 can inhibit the differentiation of human visceral preadipocytes without affecting their proliferation. ELK1, an E-twenty-six (ETS)-domain transcription factor associated with adipocyte differentiation, was strongly suppressed by miR-1275 in human visceral adipocytes. This was demonstrated via a dual-luciferase reporter assay and pointed to ELK1 as a direct target of miR-1275. Furthermore, miR-1275 expression was significantly diminished in the visceral adipose tissue of overweight and obese human subjects accompanied by a negative correlation with body mass index. These results suggest that miR-1275 could play a future role in the management of obesity, as a novel therapeutic target or biomarker.
Guoqing Lei, Linxi Chen, Miao Peng, Bolin Zeng, Qiaoxi Yang, Hening Zhai, and Geyang Xu
GLP-1 is a potent glucose-dependent insulinotropic hormone derived from intestinal L cells. Inflammatory Interleukin-27 (IL-27), a pleiotropic two-chain cytokine, is composed of EBI3 and IL-27 p28 subunits. IL-27 has a protective effect on pancreatic β-cell function. The relationship between IL-27 and GLP-1 is still unexplored. Here we showed interleukin-27-stimulated GLP-1 production via the Stat3-mTOR-dependent mechanism. Interleukin 27 receptor subunit alpha (IL-27 Rα) was detected in ileum and STC-1 cells. Co-localization of EBI3 and GLP-1 was observed not only in mouse ileums but also in human ileums and colons. Third-ventricular infusion of IL-27 increased ileal and plasma GLP-1 in both lean C57BL/6J mice and diet-induced obese and diabetic mice. These changes were associated with a significant increase in Stat3-mTOR activity. Treatment of STC-1 cells with IL-27 contributed to the increments of Stat3-mTOR signaling and GLP-1. Interference of mTOR activity by mTOR siRNA or rapamycin abolished the stimulation of GLP-1 production induced by IL-27 in STC-1 cells. Stat3 siRNA also blocked the stimulus effect of IL-27 on GLP-1. IL-27 increased the interaction of mTOR and Stat3 in STC-1 cells. Our results identify Stat3-mTOR as a critical signaling pathway for the stimulation of GLP-1 induced by IL-27.
Zhiyu Ma, Ying Zhang, Juan Su, Sheng Yang, Wenna Qiao, Xiang Li, Zhihai Lei, Ling Cheng, Na An, Wenshao Wang, Yanyan Feng, and Jinlong Zhang
Neuromedin B (NMB), a mammalian bombesin-related peptide, has numerous physiological functions, including regulating hormone secretions, cell growth, and reproduction, by binding to its receptor (NMBR). In this study, we investigated the effects of NMB on testosterone secretion, steroidogenesis, cell proliferation, and apoptosis in cultured primary porcine Leydig cells. NMBR was mainly expressed in the Leydig cells of porcine testes, and a specific dose of NMB significantly promoted the secretion of testosterone in the primary Leydig cells; moreover, NMB increased the expression of mRNA and/or proteins of NMBR and steroidogenic mediators (steroidogenic acute regulatory (STAR), CYP11A1, and HSD3B1) in the Leydig cells. In addition, specific doses of NMB promoted the proliferation of Leydig cells and increased the expression of proliferating cell nuclear antigen and Cyclin B1 proteins, while suppressing Leydig cell apoptosis and decreasing BAX and Caspase-3 protein expression. These results suggest that the NMB/NMBR system might play an important role in regulating boar reproductive function by modulating steroidogenesis and/or cell growth in porcine Leydig cells.
He-jun Zhao, Xia Jiang, Li-juan Hu, Lei Yang, Lian-dong Deng, Ya-ping Wang, and Zhi-peng Ren
This study aimed to determine whether and how the glucagon-like peptide 1 receptor (GLP-1R) agonist liraglutide affects the chemoresistance and chemosensitivity of pancreatic cancer cells to gemcitabine in vitro and in vivo. The GLP-1R and protein kinase A (PKA) levels were compared between the human pancreatic cancer cell line PANC-1 and the gemcitabine-resistant cell line PANC-GR. The in vitro effects of liraglutide on the cell proliferation and apoptosis as well as the nuclear factor-kappa B NF-κB expression levels of PANC-GR cells were evaluated. In addition, a mouse xenograft model of human pancreatic cancer was established by s.c. injection of PANC-1 cells, and the effects of liraglutide on the chemosensitivity were evaluated in vitro and in vivo. In contrast to PANC-1 cells, PANC-GR cells exhibited lower expression levels of GLP-1R and PKA. Incubation with liraglutide dose dependently inhibited the growth, promoted the apoptosis, and increased the expression of GLP-1R and PKA of PANC-GR cells. Similar effects of liraglutide were observed in another human pancreatic cancer cell line MiaPaCa-2/MiaPaCa-2-GR. Either the GLP-1R antagonist Ex-9, the PKA inhibitor H89, or the NF-κB activator lipopolysaccharide (LPS) could abolish the antiproliferative and proapoptotic activities of liraglutide. Additionally, each of these agents could reverse the expression of NF-κB and ABCG2, which was decreased by liraglutide treatment. Furthermore, liraglutide treatment increased the chemosensitivity of pancreatic cancer cells to gemcitabine, as evidenced by in vitro and in vivo experiments. Thus, GLP-1R agonists are safe and beneficial for patients complicated with pancreatic cancer and diabetes, especially for gemcitabine-resistant pancreatic cancer.