2668-P: Serpinb13 Impairs Glucose Tolerance and Dedifferentiates Beta Cells in Subacute Model of Insulin-Dependent Diabetes

Introduction and Objective: The primary role of Clade B serpins, a family of intracellular proteinase inhibitors, is to protect cells from harmful enzymes. Our laboratory has found that secretion of the natural autoantibody to serpinB13, a member of Clade B, leads to positive clinical outcomes in type 1 diabetes (T1D), suggesting that serpinB13, once released into the extracellular milieu, has detrimental effects on beta-cell biology. Methods: To assess the impact of extracellular serpinB13 on pancreatic islets, we injected 4-week-old immunodeficient male B6 mice with multiple low doses of streptozotocin (STZ, 55 mg/kg b.w x 5), thereby causing gradual destruction of beta cells. At regular intervals for 3 weeks, the animals were also simultaneously injected (10 micrograms per injection) with either recombinant serpinB13 or non-inhibitory Clade B serpin, chicken ovalbumin (OVA). During the 4th week after first STZ injection, mice were subjected to the glucose tolerance test (GTT), and their pancreases examined by IF microscopy. Image analysis was performed using Visiopharm software. Results: We found marked deterioration in GTT performance in animals who received serpinB13, as compared with OVA control. The weights of the pancreas and total body remained the same between the groups, but compared with OVA-treated mice, serpinB13-treated mice had reduced beta-cell mass (p=0.0156) and insulin staining intensity (p<0.0001). The serpinB13-treated animals were also characterized by a lower intensity of staining of Pdx-1 transcription factor (p<0.0001) and frequency of Pdx-1 expression in insulin-positive cells (p=0.0007). Conclusion: Our data demonstrate that extracellular serpinB13 dedifferentiates beta cells during limited injury of pancreatic islets and are consistent with our published observations that inhibition of serpinB13 with antibodies promotes early beta-cell development. Ultimately, these findings support of the idea that serpinB13 is an attractive target for developing a novel approach to preventing and treating T1D.