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 β-cell–specific killing by autoreactive T-cells. Less is known about β-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 β-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 β-cells to glucagon-positive α-cells was about 4:1 in nondiabetic mice. Islets isolated from newly diabetic mice exhibited the expected severe β-cell depletion accompanied by phenotypic β-cell changes (i.e., hypertrophy and degranulation), but they also revealed a substantial loss of α-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 β-cell numbers in recently diabetic mice revealed an altered endocrine cell composition that is consistent with a prominent and unexpected islet α-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.