Mechanisms of insulin-dependent diabetes locus 9-mediated protection from type 1 diabetes

Open Access
Author:
Berry, Gregory John
Graduate Program:
Microbiology and Immunology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 18, 2014
Committee Members:
  • Hanspeter Waldner, Dissertation Advisor
  • Hanspeter Waldner, Committee Chair
  • Laura Carrel, Committee Member
  • Todd Schell, Committee Member
  • Neil David Christensen, Committee Member
  • Jianxun Song, Committee Member
  • Laura Carrel, Special Member
Keywords:
  • Type 1 Diabetes
  • NOD mouse
  • Insulin-dependent diabetes locus 9
  • B cells
Abstract:
There is currently no cure for type 1 diabetes (T1D), a chronic autoimmune disease typically diagnosed in children that results in destruction of the insulin-producing beta cells of the pancreas and hyperglycemia and serious life-long health complications. A cure for this debilitating disease has remained ellusive in part due to its complex genetics. Linkage studies have identified over 25 Insulin dependent diabetes (Idd) regions known to be associated with T1D development. We focused on one of these regions, a ~200 gene region called Idd9. This region contains genes known to regulate lymphocyte function and development and can confer greater than 90% protection from T1D in nonobese diabetic (NOD) mice, a spontaneous T1D animal model of human T1D in which the NOD Idd9 is exchanged with the same region from a T1D-resistant mouse strain. The goal of this dissertation was to further elucidate the mechanisms by which Idd9 confers protection from T1D development in NOD mice. We investigated the role of this region in the regulation of islet-specific, autoimmune CD4+ T cells and the role of a sublocus of this region, Idd9.3, in overall T1D development. To identify the role of Idd9 in the regulation of diabetogenic, islet-specific CD4+ T cells, we developed novel NOD.B10 Idd9 (line 905) congenic mice that harbor predominantly islet-reactive CD4+ T cells expressing the BDC2.5 T cell receptor (BDC-Idd9.905 mice). We compared these BDC-Idd9.905 mice containing the Idd9 from the T1D-resistant C57BL/10 (B10) mouse to BDC2.5 TCR transgenic (BDC2.5) mice containing the NOD-derived T1D-susceptible Idd9. Overall, these findings identified Eno1, Rbbp4, and Mtor as candidate genes in the regulation of diabetogenic islet-specific CD4+ T cells and suggest their role in T1D pathogenesis. Idd9.3 contains 19 genes instead of the ~200 found on full-length Idd9, allowing us to more easily focus in on individual genes to identify specific genes and genetic mechanisms contributing to T1D. We used congenic NOD mice containing the T1D-resistant B10 Idd9.3 (NOD B10 Idd9.3) and compared them to NOD mice and found that NOD.B10 Idd9.3 mice had a vast reduction in B cells. Constitutive expression of MicroRNA-34a (miR-34a), one of the genes on Idd9.3, had previously been shown to mediate an early B cell developmental block by repressing the B cell developmental transcription factor Foxp1. We therefore set out to determine whether the B cell development block in NOD.B10 Idd9.3 mice was controlled by the miR-34a-Foxp1 axis. We investigated miR-34a expression and Foxp1 levels in developing B cells of NOD.B10 Idd9.3 mice and found a significant increase in miR-34a expression that directly correlated with a decrease in Foxp1 levels. This finding implicated miR-34a and its repression of Foxp1 as a likely mechanism underlying the B cell paucity seen in NOD.B10 Idd9.3 mice. We also show that reduced B cell numbers and impaired B cell APC function in NOD.B10 Idd9.3 mice directly correlates with inefficient diabetogenic CD4+ T cell proliferation as compared to NOD mice, likely due to reduced numbers and ability of B cells to act as APCs. Therefore, miR-34a-mediated B cell paucity may contribute to inefficient priming of diabetogenic CD4+ T cells, resulting in T1D protection in NOD.B10 Idd9.3 mice. Overall, our studies of Idd9 and Idd9.3 have led to the identification of novel Idd9 candidate genes and identification of novel mechanisms by which these genes may contribute to T1D protection.