Diabetes is one of five major diseases in the advanced countries, and its influence is increasing yearly in other countries as well. Pancreatic β cells in charge of blood glucose control are known to deal with an increase in the amount of necessary insulin in the body due to obesity, pregnancy, diabetes and the like by increasing the cell mass by hypertrophy, neogenesis, growth and apoptosis suppression. Since the current therapeutic drug for diabetes is mainly a symptomatic therapy for controlling the blood glucose level, diabetes is difficult to completely cure once it is developed. With such background, the development of a therapeutic drug for diabetes, which has a pancreatic β cell proliferation accelerating effect as a main action and aims at complete cure of diabetes, is expected.
In recent years, it is suggested that various miRNAs are expressed in animal cells and play biologically important roles. For example, miR-375 has been reported to suppress the amount of insulin secreted from pancreatic β cells in a glucose-dependent manner (non-patent document 1).
As for miR-199b*, reports have documented that the level of miR-199b-prec expression decreases in a lung cancer tissue (non-patent document 2), miR-199b-5p functions as a regulatory factor of Notch signal via the regulation of HES1 expression in a myeloma cell line (non-patent document 3), the level of miR-199b expression decreases during differentiation of human leukemia HL-60 cells by 4-hydroxynonenal (non-patent document 4), mmu-miR-199b is expressed in goat skin cells (non-patent document 5), the expression level of miR-199b is significantly low in human ciliary cancer cells as compared to normal cells (non-patent document 6) and the like. Furthermore, a diagnostic method of breast cancer by using miR-199b (patent document 1), a diagnostic method of lung cancer by using miR-199b-prec (patent document 2), a therapeutic method of cancer using hsa-mir-199a (patent document 3) and the like have been reported.