Identifying pancreatic islet cells that acquire a beta-cell like phenotype is important for developing new diabetes therapies. Our studies have revealed a novel serpinB13 protease inhibitor antibody, that augments cathepsin L protease activity, resulting in Notch1 receptor cleavage and mobilization of endocrine progenitor cells to become beta cells in the embryonic pancreas. It is unclear, however, whether a similar induction of additional beta cells occurs with exposure to serpinB13 monoclonal antibody (mAb) in later life.
To explore the exact source (s) of new beta cells in response to serpinB13 mAb after birth we developed a novel, multicolor flow cytometry analysis approach to study pancreatic islets. Five-week old normal Balb/c mice were injected with serpinB13 mAb (or control IgG) , and sacrificed at 8 weeks for islet isolation. Islet cell suspensions were stained with a viability dye, and a panel of antibodies to CD31, CD45, cytokeratin 19, EpCAM, insulin (Ins) , glucagon (Glu) , somatostatin (SS) , c-peptide, and four transcription factors, Maf-A, Nkx6.1, NeuroD1, and Pdx-1.
Exposure to the serpinB13 mAb caused a significant increase in the number of hormonal-negative (e.g., Ins-Glu-SS-c-peptide-) cells (p=0.0011) , and hormonal negative, but c-peptide positive, cells (p=0.002) . At least one of four transcription factors examined were positive in 5-10% and 10-30% of these populations, respectively. At the same time, there was a trend in the drop of Glu+ and SS+ cells. The average number of pancreatic islets, and the total islet cellularity per mouse, was augmented in animals receiving serpinB13 mAb.
Although additional studies are necessary to characterize the hormonal negative cells and assess whether Glu+ and SS+ cells transdifferentiate to beta cells, these findings demonstrate that enhanced tissue plasticity and beta-cell output can be achieved in the pancreas following treatment with antibodies to protease inhibitors.
Y.Kryvalap: None. S.Z.Meng: None. J.Czyzyk: None.