The major focus of this proposal will be the study of glucose-regulated insulin biosynthesis in experimental animals, and evaluation of the genes which mediate these responses in man. The hypothesis to be tested is that defects in these regulatory genes are responsible for part of the inherited susceptibility to non-insulin-dependent diabetes mellitus (NIDDM). There are 4 specific aims: 1) Rats will be infused with glucose or saline for 24 hours, and genes differentially expressed between control and hyperglycemic islets defined by fingerprinting technique for mRNAs. This method allows cloning and characterization of glucose-regulated genes in rats, which will serve as candidates for the impaired glucose responsiveness in NIDDM. 2) Human islet beta-cell genes which mediate glucose-regulated insulin biosynthesis will be assessed in NIDDM. These include the receptor for glucagon-like polypeptide-1 (GLP- 1), a potent gut potentiator of glucose-stimulated insulin synthesis and secretion, and Islet-1(Isl-1), a rat developmental regulatory homeodomain protein which is a transcriptional activator of insulin biosynthesis. Human cDNA and genomic clones have been isolated for both of these genes. The role of these genes will be evaluated in NIDDM using simple sequence repeat polymorphisms (SSRPs) in genomic clones, through population studies and linkage in families, along with direct genomic sequencing of DNA from patients. Genes for other islet transcription factors and glycolytic enzymes will also be evaluated. 3) Trinucleotide repeats in exonic genes can disrupt function, and are the basis for a new type of mutagenesis. We have isolated 6 novel triplet repeat human islet cDNAs. These genes will be placed on the human genome linkage map, and their role in NIDDM determined. 4) Mapping NIDDM susceptibility genes is complicated because of multifactorial etiology. An alternative strategy is to map genes involved in monofactorial disorders of islet beta-cell function. Persistent hyperinsulinemic hypoglycemia of infancy is a rate autosomal recessive disorder characterized by severe neonatal hypoglycemia. The etiology of the islet beta-cell dysfunction is unknown. Wolfram syndrome is a rate autosomal diabetes is early onset of islet beta-cell hypoplasia in the absence of islet cell antibodies. The genes for these disorders will be mapped in multiplex pedigrees by whole genome searches with SSRP markers at 10cM intervals, through combined linkage analysis and homozygosity mapping. The hypothesis to be tested is that genes essential for normal islet beta-cell growth and development are mutated in these disorders. Defects in these genes may contribute to susceptibility to other forms of diabetes. The long-range goal of these studies is to provide a molecular genetic classification of NIDDM. This strategy promises to yield important information about the etiology of this disease, thus enhancing opportunities for more rational genetic counselling, for better prediction of risk, and for better therapy and intervention.
Showing the most recent 10 out of 116 publications
