Background: Islet beta-cells are almost completely destroyed when patients with type 1 diabete are diagnosed. To date, insulin substitute therapy is still one of the main treatments. The cure of type 1 diabetes requires beta-cell regeneration from islet cell precursors and prevention of recurring autoimmunity. Therefore, beta-cell regeneration and proliferation emerge as a new research focus on therapy for type 1 diabetes. Islet beta-cell regeneration and development are controlled by many growth factors, especially insulin-like growth factor-1 (IGF-1).
Methods: Recombinant adenovirus encoding rat IGF-1 (rIGF-1) was constructed and transduced into rat beta-cells, RINm5F cells. Western blotting analysis and ELISA were used to detect rIGF-1 protein. Streptozotocin (STZ) was used to induce RINm5F cell destruction. The level of nitric oxide (NO) was detected in cell culture supernatants by the Griess reaction. Islet cell function was evaluated by glucose-stimulated insulin production. Flow cytometry analysis was further used to investigate the apoptosis of RINm5F cells. Thiaoollyl blue viability assay was applied to determine cell viability.
Results: The recombined adenovirus-rIGF-1 was successfully constructed and the titer was 4.0 x 10(8) pfu/ml. The rIGF-1 protein was effectively expressed in the RINm5F cells and cell culture supernatants. rIGF-1 expression remarkably inhibited STZ-induced islet cell apoptosis and significantly decreased the level of NO. Furthermore, IGF-1 expression also significantly protected insulin secretion and cell proliferation in a time-dependent manner.
Conclusions: Our study suggests that locally produced rIGF-I from RINm5F cells may be beneficial in maintaining beta-cell function, protecting beta-cells from the destruction of apoptosis factors and promoting beta-cell survival and proliferation. IGF-I might be considered as a candidate gene in gene therapy for type 1 diabetes. In addition, it appears that the apoptosis induced by STZ may be NO-dependent.