Clusterin Over-expression Induces Differentiation of Pancreatic Ductal Cells into Insulin-Producing Cells

초록

Recently we reported that clusterin is up-regulated in the process of tissue remodeling induced by various tissue injuries. It may be implicated that clusterin could be involved in the regeneration of pancreatic endocrine cells including insulin secreting beta cells by stimulation of their differentiation and proliferation during the pancreas regeneration. In the present study, we investigated the effect of clusterin overexpression on differentiation of insulin beta cells from duct cells by clusterin cDNA transfection into duct cells isolated from rat pancreas. To examine clusterin action on ductal cell differentiation and proliferation, we assessed the population of differentiated insulin-producing cells using immunocytochemistry and cellular insulin contents by northern blot analysis. Insulin secretion was measured in culture media using radioimmunoassay as well as western blot analysis after immunoprecipitation. We found that the number of insulin producing cells increased 11.5 fold when clusterin was over-expressed, while glucagon cell showed only a slight increase. Insulin expression, both insulin mRNA and peptide levels, was increased in clusterin transfected cells. However, glucagon and cytokeratin 20, a specific marker for ductal cells, were not expressed in those insulin secreting cells, indicating that they were developed as a fully differentiated cell type. In addition, they showed extensive proliferation on day 4 after transfection as determined by PCNA immunostaining. We also found that clusterin induced-insulin secretion of beta cells is modified by glucose stimulation, indicating cellular response for glucose sensing in differentiated beta cells. In conclusion, we suggest that clusterin could stimulate not only differentiation of precursor cells in the pancreatic duct, but also proliferation of predifferentiated beta cells, and those differentiated beta cells are functional cells secreting insulin in response to glucose stimulation.