The PI3K/Akt1-FoxO1 Translocation Pathway Mediates EXf Effects on NIT-1 Cell Survival.

EXf, a glucagon-like peptide 1 (GLP-1) receptor agonist, stimulates ß-cell proliferation and reduces apoptosis in diabetic animal models, but the underlying mechanisms are not fully understood. We constructed a FoxO1-GFP fusion protein expression plasmid and transiently transfected it into NIT-1 cells to investigate whether FoxO1 mediates EXf effects on NIT-1 cell survival. Our results showed that EXf could increase cell viability by inhibiting apoptosis and stimulating proliferation, and it could also promote the translocation of the FoxO1-GFP fusion protein from the nucleus to the cytoplasm in NIT-1 cells. However, the above effects of EXf were suppressed by the inhibitor of PI3K. Comparative transcription analysis showed up-regulation of igf-1r, irs-2, pI3k, akt1 and pdx-1 in NIT-1 cells after EXf treatment. Moreover, the up-regulation of PI3K and phosphorylation of Akt1 upon EXf treatment was confirmed by Western blot, both phenomena were abrogated by wortmannin, an inhibitor of PI3K. In summary, FoxO1 may mediate the effects of EXf on NIT-1 cell survival by activating the PI3K/Akt1 pathway.

Long-term treatment with EXf, a peptide analog of Exendin-4, improves ß-cell function and survival in diabetic KKAy mice.

EXf is a C-terminally truncated fragment of Exendin-4 with two amino acid substitutions. Previous studies showed that EXf controls plasma glucose level acting as a glucagon-like peptide 1 (GLP-1) receptor agonist. The purpose of this study was to evaluate the effects of EXf on ß-cell function and survival in diabetic KKAy mice. EXf treatment significantly improved the glucose intolerance and reduced non-fasting and fasting plasma glucose levels, as well as plasma triglyceride levels in diabetic KKAy mice. In hyperglycemic clamp test, EXf-treated mice displayed an increased glucose infusion rate and first-phase insulin secretion. Treatment with EXf also led to a significant restoration of islet morphology, an increase in Ki67 expression in ß-cells, and a reduction in the number of TUNEL positive ß-cells. In the pancreas, comparative transcription analysis showed up-regulation of Akt1. The up-regulation of phosphorylated Akt1 was confirmed by Western blot, and changes in the protein levels of members of the Akt1 pathway, such as PI3K, Bim, Bcl-2, Bax, Caspase-3, and Caspase-9, PDX-1, were observed as well. Therefore, EXf treatment could improve ß-cell function and survival in diabetic KKAy mice, likely as a result of islet morphology restoration, stimulation of ß-cell proliferation, and inhibition of ß-cell apoptosis.