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

Abstract

Objective: Insulin deficiency in type 1 diabetes and in rodent autoimmune diabetes models is caused by ß-cell specific killing by autoreactive T cells. Less is known about ß-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 (q)RT-PCR, to simultaneously track pancreatic endocrine-cell frequencies and phenotypes during the T cell-mediated ß-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⁺ ß-cells to glucagon⁺ α-cells was about 4:1 in non-diabetic 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 also revealed a substantial loss of α-cells, that 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 spontanteous autoimmune diabetes models, became apparent at diabetes onset, and differed markedly within islets compared to 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.