UBC Theses and Dissertations
Gene therapy for diabetes : targeting the gut for insulin replacement Lam, Ada Wing-Yi
Type 1 diabetes mellitus (T1DM), a chronic metabolic disorder characterized by hyperglycemia, is caused by the autoimmune destruction of insulin-producing pancreatic p-cells. The most common current treatment for T1DM is insulin administration; however, ideal blood glucose levels are rarely achieved in these individuals who are therefore at increased risk for developing debilitating complications of diabetes. Gene therapy may provide a means for achieving prolonged regulated production and delivery of insulin within the body. Targeting meal-responsive gut K-cells as an alternative insulin source has been previously demonstrated to protect mice against streptozotocin- (STZ)-induced diabetes. However, since insulin is a potential auto-antigen, genetically modified insulin-producing K-cells may trigger an autoimmune response. In this thesis, the possibility of autoimmune destruction of modified K-cells was investigated using the non-obese diabetic (NOD) mouse model of T1DM. Transgenic NOD mice containing a rat GIP promoter/mouse insulin transgene showed insulin-immunoreactivity in their gut K-cells. However, quantification of these cells indicated that only a portion apparently possessed the proinsulin processing enzymes CPE (39.3%) and/or PC2 (27.8%), suggesting proinsulin processing may be impaired in the majority of K-cells. Regardless, the presence of bioactive insulin coming from the gut of female transgenic NOD mice was evident as these mice maintained lower random blood glucose levels following STZ-treatment (16 ± 6 mM) and had a 2.5-fold lower incidence of spontaneous diabetes (25.5% at 12-months of age) compared to non-transgenic female NOD mice (30 mM and 66.2% at 12-months of age, respectively). Moreover, despite clear autoimmune destruction of β-cells, insulin-producing gut K-cells were still abundant in transgenic NOD mice. Furthermore, when duodenal sections from non-transgenic and transgenic female NOD mice were examined, no detectable differences were observed between the genotypes for villus and crypt lengths and ratio, K-cell distribution along the crypt-villus axis, nor the density of leukocytes along the villus or within the gut epithelium. Overall, these findings suggest that there is no autoimmune targeting or destruction of insulin-producing K-cells in transgenic NOD mice and thus further support targeting K-cells for insulin replacement as a potential treatment for T1DM.