Oxidative stress induced by chronic hyperglycemia in type 2 diabetes plays a crucial role in progressive loss of β-cell mass through β-cell apoptosis. Glucagon like peptide-1 (GLP-1) has effects on preservation of β-cell mass and its insulin secretory function. GLP-1 possibly increases islet cell mass through stimulated proliferation from β-cell and differentiation to β-cell from progenitor cells. Also, it probably has an antiapoptotic effect on β-cell, but detailed mechanisms are not proven. Therefore, we examined the protective mechanism of GLP-1 in β-cell after induction of oxidative stress. The cell apoptosis decreased to ~50% when cells were treated with 100 µM H2O2 for up to 2 hr. After pretreatment of Ex-4, GLP-1 receptor agonist, flow cytometric analysis shows 41.7% reduction of β-cell apoptosis. This data suggested that pretreatment of Ex-4 protect from oxidative stress-induced apoptosis. Also, Ex-4 treatment decreased GSK3β activation, JNK phosphorylation and caspase-9, -3 activation and recovered the expression of insulin2 mRNA in β-cell lines and secretion of insulin in human islet. These results suggest that Ex-4 may protect β-cell apoptosis by blocking the JNK and GSK3β mediated apoptotic pathway.

No abstract

Estrogen (17β-estradiol) has been implicated in maintaining insulin sensitivity. It is thought to act predominantly through genomic pathways and regulate the expression of various genes via binding to estrogen receptors (ERs)-α and -β. 17β-estradiol has been reported to simultaneously stimulate protein kinase B (Akt) and adenosine monophosphate-activated protein kinase (AMPK) in ex vivo skeletal muscle. Since data regarding the interaction between AMPK and the insulin receptor substrate-1 (IRS-1)/Akt pathway are controversial, the correlation between AMPK activation and insulin signaling remains unclear. In this study, we examined whether 17β-estradiol simultaneously stimulates the activation of AMPK and IRS-1/Akt in 3T3-L1 adipocytes as well as the 17β-estradiol-ER-induced interaction between the AMPK and IRS-1/Akt pathway in 3T3-L1 adipocytes not exposed to insulin. 17β-estradiol (10⁻⁷ M) rapidly activated AMPK and IRS-1/Akt in 3T3-L1 adipocytes, while the ER-α/β non-specific antagonist, ICI 182.780 (10 µM), and the AMPK antagonist compound C (20 µM) reversed the estrogen-induced activation of AMPK and tyrosine (Tyr)-IRS-1/Akt in these cells. Moreover, 17β-estradiol increased the expression of the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), adiponectin, uncoupling protein 2 (UCP2) and glucose transporter 4 (GLUT4) genes 24 h after treatment, whereas the ER-α/β non-specific antagonist, ICI 182.780 (10 µM), and the AMPK antagonist compound C (20 µM) reversed the estrogen-induced increase in the expression of these genes. These results indicate that 17β-estradiol activates AMPK through an ER and activates Akt through AMPK activation in 3T3-L1 adipocytes, despite the absence of insulin. Furthermore, 17β-estradiol regulates the expression of genes related to glucose metabolism through ER-AMPK activation in these cells.

No abstract

No abstract