Pathology of Pancreatic Β-Cells and Diabetes in Premature Aging Cisd2 Knockout and Naturally Aging Wild-Type Mice (III)---Morphometric Evaluation of Ultrastructural Heterogeneity in Β-Cells

Aging which affects all organ systems is one of the most complex phenotypes in biomedical sciences. Application of genetically modified mouse models will help elucidate the genetic pathways of human aging. Cisd2 is a previously uncharacterized novel gene. Significantly, the Cisd2 gene is located on human chromosome 4q where a genetic component for longevity maps. Recently, the Cisd2 gene has been identified as the second causative gene associated with Wolfram syndrome (WFS, MIM 222300), patients with a homozygous mutation of the Cisd2 gene have been classified as WFS2 (MIM 604928). WFS is highly variable in its clinical manifestations, which include diabetes mellitus, diabetes insipidus, optic atrophy, and deafness. Our group had previously generated Cisd2 knockout premature aging mice and demonstrates for the first time that Cisd2 is involved in mammalian lifespan control. Cisd2 deficiency in mice causes mitochondrial outer membrane breakdown and dysfunction accompanied by autophagic cell death and these events precede the two earliest manifestations of nerve and muscle degeneration; together, they lead to a panel of phenotypic features suggestive of premature aging. Thus, this Cisd2 knockout mouse provides an animal model for mechanistic investigation of Cisd2 protein function and will help with a pathophysiological understanding of aging. Degenerations of nervous and muscle systems, which usually exacerbates with age, are the two major phenotypes associated with aging. Importantly, Cisd2 knockout mice exhibit a progressive neurodegenerative phenotype that includes optic nerve defects. Regarding glucose homeostasis, we found that Cisd2 knockout mice display a milder phenotype, namely, impaired glucose tolerance and decreased insulin secretion. In this grant, we will introduce the Cisd2 mutant allele into DBA/2 or 129/Sv diabetes-prone strains of mice (generation of congenic strains of Cisd2 knockout mice with a diabetes-sensitive background by backcrossing into the DBA/2 or 129/Sv inbred mice), which may contain genetic modifier(s) that increase susceptibility to diabetes. Recently, our results showed that Cisd2 deficiency causes significant mitochondrial outer membrane breakdown and ER stress accompanied by significant autophagy in diabetes-prone mice pancreatic β-cells at age 5~7 months. However, the damaged organelles induce autophagy as a cytoprotective response to eliminate the dysfunctional organelle, or excessive autophagy may cause pancreatic β-cells to death, that is accompanied by decreased insulin secretion, impaired glucose tolerance, and finally induce diabetes needs to be thoroughly clarified. In this grant proposal, by morphometric examination, we will systematically evaluate the ultrastructural alternations and heterogeneity changes of pancreatic β-cell in the premature aging Cisd2 knockout mice with diabetes-prone congenic background and compare with the wild-type mice in naturally aging process by using STZ challenge and transmission electron microscope (TEM). In addition, we will perform biochemical test for the changes of mitochondrial functions in pancreatic β-cells to correlate the evidence of morphometry. We anticipate that we will have a complete panel of ultrastructural database and basic biochemical results within three years. These investigations will help evaluate the feasibility of using Cisd2 mutant mice as an animal model for screening of agents associated with pancreatic β-cell disorder and might eventually provide clues about how to slow the age-associated diabetes process.

Project ID:PC10207-0351
External Project ID:NSC102-2320-B182-009