167-LB: The Contribution of a- to ß-Cell Transdifferentiation in Gestational ß-Cell Expansion in Mouse

Introduction: Pregnancy is characterized as a state of insulin resistance. To compensate for this, endocrine pancreatic β-cell mass (BCM) expansion occurs and is maximal at gestational day 18 (GD18) in mouse. There is evidence through lineage tracing of α-cells that they can replenish β-cells following β-cell loss/stress by α to β-cell transdifferentiation. In this study we sought to track the fate of α-cells during pregnancy to determine the contribution of α to β-cell transdifferentiation in gestational BCM expansion.

Hypothesis: α to β-cell transdifferentiation will be higher during pregnancy compared to a non-pregnant animal.

Materials and Methods: Glucagon-Cre/Rosa26-eYFP mice were time-mated and a non-pregnant group was age-matched to these animals. Pancreata were removed on GD9, 12, 18, and postpartum day 7 for fluorescence immunohistochemistry. Tissue sections were immunostained for insulin, YFP, glucagon, DAPI and analyzed by manual cell counting. All insulin-expressing cells were counted and separated into either islets (≥6 β-cells) or clusters (1-5 β-cells).

Results: There were more transitional cells (Insulin⁺YFP⁺Glucagon⁺) in clusters during pregnancy compared to a non-pregnant animal (13.31±4.53%vs.9.14±2.01%). Furthermore, there were more differentiated β-cells with an α-cell origin (Insulin⁺YFP⁺Glucagon^-) during pregnancy compared to a non-pregnant animal (16.73±5.28% vs.5.79±3.27%).

Discussion and Conclusions: The data show more transitional cells during pregnancy, followed by an increase in β-cells differentiating from α-cells. Our previous experiments found that BCM expansion occurs in part due to neogenesis from β-cell progenitors located in clusters. Since there were more transitional cells localized to clusters, it is plausible that α to β cell transdifferentiation is enriched in clusters. This study provides mechanistic insights into the pathology of β-cell deficiency in pathological pregnancies such as gestational diabetes.