Effect And Mechanism Of Glucagon-like Peptide-1on Pancreatic Beta Cell Proliferation, Apoptosis And Autophagy

To investigate the effect of GLP-1on pancreatic beta-cell proliferation, apoptosisand autophagy, and its mechanism, we use INS-1beta-cell line as study object, andtreated it with the long-acting GLP-1analogue liraglutide.Part1. GLP-1promotes pancreatic beta cell proliferation via AMPK/mTORsignaling.INS-1beta-cell line was treated with liraglutide in the presence of11.1or30mmol/Lglucose. Cell proliferation was evaluated by Cell Counting Kit-8. AMPK/mTOR pathwayand its downstream effectors P70S6K,4EBP1protein expression levels were tested bywestern blotting. Based on the above, we evaluated the change of cell proliferation afterusing mTOR pathway inhibitors: the AMPK activator AICAR or the mTOR inhibitorrapamycin. Result:1. GLP-1promoted INS-1cell proliferation in the presence of11.1and30mmol/L glucose.2. GLP-1decreased AMPK expression, increased mTOR and itsdownstream effectors, P70S6K and4EBP1protein expression.3. mTOR pathwayinhibitors decreased mTOR and its downstream effectors expression, and significantlyreduced GLP-1induced cell proliferation. Conclusion: GLP-1promotes beta cellproliferation under normal and high glucose, and AMPK/mTOR pathway may beinvolved in this process.Part2. GLP-1promotes pancreatic beta cell autophagy through inhibition of5’-AMP-activated protein kinase under high glucoseINS-1beta-cell line was treated with liraglutide under high glucose (30mmol/L), andautophagy related indicators were investigated, including autophagy related proteinsexpression (LC3, Atg7and P62), MDC staining, LC3immunofluorescence andautophagosomes observed by transmission electron microscope. Furthermore, to discussthe mechanism of GLP-1regulates beta cell autophagy, changes of above indicators were evaluated after using lentiviral transfection or AICAR to enhance AMPK activity. Results:1. GLP-1increased cellular LC3II/I ratio, Atg7protein expression, and decreased P62protein expression. In addition, GLP-1increased the number of positive MDC stainingcells, positive LC3immunofluorescence cells and autophagosomes observed bytransmission electron microscope. These results suggest that GLP-1promotes beta cellautophagy.2. Activation of AMPK abated GLP-1induced enhancement of INS-1cellautophagy. Conclusion: GLP-1may promote pancreatic beta cell autophagy throughinhibition of AMPK under high glucose.Part3. GLP-1prevents pancreatic beta cell apoptosis from high glucosethrough promoting autophagyINS-1beta-cell line was treated with liraglutide under high glucose (30mmol/L), andcell apoptosis related indicators were investigated, including Bcl-2, Bax, caspase-3protein expression and Hoechst33342staining. Furthermore, changes of above indicatorswere evaluated after inhibition of autophagy by3-MA (autophagy inhibitor). Result:1.GLP-1increased Bcl-2protein expression, and decreased Bax, Caspase-3proteinexpression. In addition, GLP-1reduced the number of apoptotic cells tested by Hoechst33342staining.2. Inhibition of autophagy by3-MA abated GLP-1induced anti-apoptosiseffect in INS-1cells. Conclusion: GLP-1prevents beta cell apoptosis from high glucoseand cell autophagy may be involved in it.In conclusion, GLP-1promotes beta cell proliferation via AMPK/mTOR signalingpathway, and increases beta cell autophagy through inhibition of AMPK. In addition,GLP-1prevents beta cell apoptosis from high glucose, and enhancement of autophagy byGLP-1may be one of the reasons. GLP-1may protect beta cells from high glucosethrough the above mechanisms, which provide some basic evidence for clinicalprevention and treatment of type2diabetes.