Humoral factors by human bone marrow-derived MSC enhance beta cell proliferation via ERK1/2 signalling

Background and aim: We previously demonstrated that human telomerase-immortalised MSC (hMSC-TERT) migrate towards injured rat INS-1E beta cells and promote their survival via preservation of functional active phospho (p)-AKT levels. Both cell lines display a valid model since they closely resemble results from primary rat MSC and islets. Since some studies indicate that MSC also mediate proliferation of beta cells, we here tested whether hMSC-TERT-derived factors promote proliferation of INS-1E and explored the signalling mechanims involved.

Methods: Cocultures were performed using inserts with 0.4 µm pores to allow only soluble factors but not cells to pass the membrane. Proliferation was analysed by MTS assay, counting cell numbers and determining the percenatge of Ki-67+ nuclei. p-AKT and p-ERK1/2 levels were measured by Western blot.

Results: Cocultured hMSC-TERT significantly increased viability, percentages of Ki67+ nuclei and numbers of INS-1E after 5 days. Within 24h hMSC-TERT did not alter p-AKT levels of non-injured INS-1E but substantially increased p-ERK1/2 levels. Activation of p-ERK1/2 was still effective under starving conditions (2.8 mM glucose and 1% FBS) and under high glucose (20 mM) conditions. hMSC-TERT-enhanced expansion of normally cocultured INS-1E was reduced to normal levels by addition of the ERK1/2-inhibitor U0126. Notably, proliferation of alone cultured INS-1E was only marginally affected by U0126.

Conclusion: hMSC-TERT-derived factors feature a beta cell regenerative potential since they promote both survival via preservation of p-AKT and proliferation via activation of p-ERK1/2 signalling. Inhibition of MSC-mediated increase in beta cell expansion by the inhibitor U0126 suggests that p-ERK1/2 plays a very central role in this scenario.