The expression of fluorochromes in the beta cells of hemizygous Ins1-EGFP transgenic mice elicit pathophysiological changes which may complicate interpretations if islets from this model are used in transplantation studies. These pathophysiological changes alter the normal pathogenic progression in the NOD mouse model of autoimmune diabetes. Preliminary studies indicate that hemizygous mice are not suitable as recipients of diabetogenic T cells.
Donating investigator reports transgenic mice develop normally and behave similarly to controls with respect to glucose tolerence and and pancreatic insulin content. Histology confirms transgenic mice have normal islet architecture with coexpression of insulin and GFP. The enhanced GFP reporter allows the beta cells to be easily identified and purified for further studies.
Studies completed at The Jackson Laboratory indicate there is strong non-mosaic expression of green fluorescent protein in NOD/LtJ-Tg(Ins1-EGFP/GH1)14Hara/HaraJ islets. 100% of homozygous Ins1-EGFP transgenic males and females, identified by qPCR, become diabetic by 9 weeks of age. Pancreatic histopathology of homozygous mice shows beta cell loss without insulitis.
Hemizygous Ins1-EGFP mice are viable and are used for breeding. A 30-week incidence study comparing NOD/LtJ controls with mice hemizygous for the Ins1-EGFP transgene shows severely depressed diabetes incidence in these hemizygotes, with males atypically at greater risk than females. Glucose tolerance in prediabetic, Ins1-EGFP transgenic hemizygous 8-week-old males is selectively impaired compared to wild type controls. Although these 8-week-old Ins1-EGFP transgenic and wild type males did not differ in plasma insulin content; a significant decline was noted in hemizygous Ins1-EGFP transgenic males compared to normoglycemic wildtype males when sampled at 30 wk. Adoptive transfer of highly diabetogenic CTL (AI4 TCRTg Rag) CD8+ T cells produced diabetes within 8 days post-injection into NOD/Lt females, but failed to produce any diabetes or even home to islets weeks after injection into hemizygous females. Pancreatic histopathology of 31 week old, non-diabetic, hemizygous Ins1-EGFP transgenic males and females indicate peri and intra islet fibrosis, peri-insulitis and depleted beta cell granulation in 70% of the animals, while only 30% of the mice have intra islet insulitis.
This model provides a valuable tool for studying beta-cell biology, including identification of progenitor cells.
