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, promote their survival and reduce their apoptosis via p-AKT-Bcl2/Bax signalling pathway. Both cell lines are valid models since they closely resemble results from primary rat MSC and rat islets. Here, we further tested whether hMSC-TERT promote the proliferation and function of INS-1E, and investigated the underlying mechanism.

Methods: Cocultures were performed by inserts with 0.4 µm pores to allow soluble factors but not cells to pass the membrane. Proliferation was analysed by MTS assay, counting cell numbers and determining the percentage of Ki-67+ nuclei. Protein levels were tested by western blot. Insulin levels were measured by ELISA.

Results: hMSC-TERT significantly increased viability, percentages of Ki67+ nuclei and numbers of INS-1E after 5 day coculture. 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 both starving conditions (2.8 mM glucose and 1% FBS) and high glucose (20 mM) conditions. Enhanced proliferation of INS-1E by cocultured hMSC-TERT was abolished to normal levels by application of the ERK1/2 inhibitor U0126. Cocultured hMSC-TERT enhanced both the basal and high glucose-stimulated insulin secretion of INS-1E.

Conclusion: hMSC-TERT-derived factors feature a beta cell regenerative potential since they enhance insulin secretion and promote proliferation of INS-1E via 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.