Anti-apoptotic action of exendin-4 in INS-1 beta cells: comparative protein pattern analysis of isolated mitochondria

Glucagon like peptide-1 (Glp-1) exhibits beneficial effects on beta cell mass by both enhancing proliferation and inhibiting apoptosis. The precise mechanism of the anti-apoptotic effect of Glp-1 and Glp-1 mimetics like exendin-4 has remained elusive. Here, we studied cytokine-induced apoptosis in the pancreatic beta cell line INS-1 and performed a comparative mitochondrial protein pattern analysis using two-dimensional difference gel electrophoresis (2D-DIGE). Cytokine incubation of INS-1 cells increased caspase-3 activity about 3-fold, which was reduced by 60% in the presence of exendin-4. Production of reactive oxygen species in response to cytokines was completely prevented after preincubation with exendin-4. Highly purified mitochondria were obtained and mitochondrial proteins were labeled with Cy-dyes and separated on overlapping zoom 2D gels spanning a pH-range of 4-9. Protein spots with significant changes after cytokine and exendin-4 treatment were identified by MALDI mass spectrometry. Comparing all treatment conditions, comparative mitochondrial proteome analysis allowed to identify 33 different proteins, which were significantly altered between comparison groups. Changes in protein patterns revealed involvement of cytokine-induced electron transport chain damage. Thus, cytochrome bc1 complex subunit I and ATP synthase subunit beta were downregulated by 30-40%. This was abrogated by the presence of exendin-4. In conclusion, this study provides further insights into the role of mitochondria in cytokine-induced apoptosis. We show here that exendin-4 significantly counter-regulates the reduced abundance of electron transport chain proteins, leading to a reduction of oxidative stress and most likely contributing to the anti-apoptotic action of this drug.