Mesenchymal stem cell (MSC)-mediated activation of ERK1/2 signaling does not contribute to maintained survival of cocultured alloxan-treated INS-1E beta cells

Introduction: Injury-activated MSC secrete tissue protective factors which contribute to re-establishment of the local microenvironment. We previously demonstrated that cocultured telomerase-immortalised human MSC (hMSC-TERT) promote survival of alloxan (ALX)- or streptozotocin-treated INS-1E beta cells via AKT signalling. hMSC-TERT further mediated proliferation via ERK1/2 signalling. Here we investigated whether ERK1/2 signalling contributes to survival during ALX-mediated beta cell stress.

Methods: Cocultures employed hMSC-TERT and INS-1E, and used inserts with 1 µm pores that allow only humoral factors but not cells to pass the membrane. Cellular stress was induced by ALX. Viability was measured by MTS assay and p-ERK1/2 levels by western blotting. ERK1/2 phosphorylation was blocked by established concentrations of the specific inhibitor U0126.

Results: INS-1E beta cells responded to ALX by strong transient upregulation of p-ERK1/2 levels after 30 min. 24h exposure to 3.3 and 6.6 mM ALX reduced viability of INS-1E by about 30 and 60%, respectively. Cocultured hMSC-TERT increased p-ERK1/2 levels in INS-1E within 4h and significantly maintained viability. Exposure of INS-1E beta cells to10µM U0126 for 2h prior coculture completely depleted p-ERK1/2 pathway activation but did not change viability levels of untreated and ALX-treated INS-1E.

Conclusion: MSC enhance survival of ALX-treated INS-1E beta cells independent of ERK1/2 signalling. This indicates that MSC mediate protection of injured beta cells mainly via maintenance of p-AKT levels.