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Role of the alpha4 integrin (CD49d) in Type-1 Diabetes mellitus prevention and treatment

Periodic Report Summary 2 - CD49D IN DIABETES (Role of the alpha4 integrin (CD49d) in Type-1 Diabetes mellitus prevention and treatment)

Type I (autoimmune) diabetes remains an important cause for morbidity and mortality. For reasons unknown, its incidence continues to increase in the Western world, and the age of onset continues to decrease. Insulin substitution remains the only, albeit cumbersome and imperfect, treatment; a cure remains elusive.

Based on evidence provided by us and others on the role of the alpha4 integrin VLA4 in leukocyte trafficking, we proposed that VLA4 blockade, using appropriate pharmacological tools, may prolong, potentially indefinitely, the honeymoon period between first manifestation of diabetes (while considerable islet cell mass remains intact) and complete destruction of islet cells and complete exogeneic insulin dependence.

To test this hypothesis, a mouse strain susceptible to autoimmune Type I-like diabetes (NOD) was to be genetically altered by floxing the second exon of the alpha4 integrin gene, further referred to as a4f/f. These mice were to be crossed to mice with cre recombinase expressed under the control of the tie2 promoter, to allow ablation of a4 specifically in hematopoietic cells, by deleting the gene in hemangioblasts. We proposed to test whether this mouse would be protected from spontaneous Type I diabetes. Alternatively, we will cross a tamoxifen-inducible cre into the NOD.a4f/f background, to allow drug-induced ablation of VLA4 at selected time points. Ablation at the first sign of diabetes is proposed to halt diabetes and allow, based on the considerable regenerative potential of pancreatic islets, complete reconstitution and normoglycemia.

Based on mouse husbandry costs at the time that the project was proposed, adequate funds should have been available to allow sufficiently large breeding cohorts and genotyping for selection of future breeding pairs for a speed congenic approach. However, mouse prices have more than quintupled (EUR 0.25 to GBP 1.89 per week), so that only a conventional breeding program with whole-genome typing for purity after the 10th generation was permissible. The NOD.a4f/+ mice have now been generated and analysed by extensive microsatellite screening; they are pure NOD except for the floxed allele (a4f/+). They were interbred to generate NOD.a4f/f. As soon as whole genome screening arrays of the two NOD.cre+ strains (under the control of the hemangioblast-specific Tek-promotor, tek-cre or a tamoxifen-inducible cre, tam-cre) become available, we will select potential founders for the a4f/f x cre breeding program, and diabetes studies will follow promptly. Thus far we have provided evidence that female NOD.a4f/f mice retain their propensity for spontaneous development of diabetes.