Dynamic Changes in Pancreatic Endocrine Cell Abundance, Distribution, and Function in Antigen-Induced and Spontaneous Autoimmune Diabetes

OBJECTIVE Insulin deficiency in type 1 diabetes and in rodent autoimmune diabetes models is caused by beta-cell-specific killing by autoreactive T-cells. Less is known about beta-cell numbers and phenotype remaining at diabetes onset and the fate of other pancreatic endocrine cellular constituents. RESEARCH DESIGN AND METHODS We applied multicolor flow cytometry, confocal microscopy, and immunohistochemistry, supported by quantitative RT-PCR, to simultaneously track pancreatic endocrine cell frequencies and phenotypes during a T-cell-mediated beta-cell-destructive process using two independent autoimmune diabetes models, an inducible autoantigen-specific model and the spontaneously diabetic NOD mouse. RESULTS The proportion of pancreatic insulin-positive beta-cells to glucagon-positive alpha-cells was about 4:1 in nondiabetic mice. Islets isolated from newly diabetic mice exhibited the expected severe beta-cell depletion accompanied by phenotypic beta-cell changes (i.e., hypertrophy and degranulation), but they also revealed a substantial loss of alpha-cells, which was further confirmed by quantitative immunohistochemisty. While maintaining normal randomly timed serum glucagon levels, newly diabetic mice displayed an impaired glucagon secretory response to non-insulin-induced hypoglycemia. CONCLUSIONS Systematically applying multicolor flow cytometry and immunohistochemistry to track declining beta-cell numbers in recently diabetic mice revealed an altered endocrine cell composition that is consistent with a prominent and unexpected islet alpha-cell loss. These alterations were observed in induced and spontaneous autoimmune diabetes models, became apparent at diabetes onset, and differed markedly within islets compared with sub-islet-sized endocrine cell clusters and among pancreatic lobes. We propose that these changes are adaptive in nature, possibly fueled by worsening glycemia and regenerative processes.