Beta-cell death is an important pathogenic element in diabetes. Our data demonstrate that endoplasmic reticulum (ER) stress contributes to beta-cell death in patients with diabetes. ER stress is caused by imbalance between the demand placed on the ER by the load of client proteins and the ability of the ER to meet that demand. The """"""""unfolded protein response"""""""" (UPR) is an adaptive response that counteracts ER stress. ER-associated protein degradation (ERAD), a component of the UPR, contributes to the survival of ER-stressed cells. Inositol Requiring 1 (IRE1) is a central regulator of the UPR. Our data show not only that IRE1 has an important function in insulin biosynthesis, but that a heavy load of client protein, insulin, causes a high baseline level of ER stress in beta-cells. This means that only a slight additional increase in ER stress is likely to lead to beta-cell death. Such an example is Wolfram syndrome (WFS). The pathogenesis of WFS, a rare form of juvenile diabetes, has been attributed to mutations in the WFS1 gene. Most of those mutations occur in exon 8, which encodes the protein's transmembrane and C-terminal luminal domains. We hypothesize that mutations in WFS1 lead to misfolding of protein in the ER, cause an increase in ER stress, and consequently lead to beta-cell death.
In Aim 1, we will examine the roles of ERAD in beta-cell death in WFS.
In Aim 2, we will determine the function of IRE1 signaling in beta-cells.
In Aim 3, we will study the molecular mechanisms of ER stress-mediated beta-cell death. The proposed studies will elucidate the relationship between ER stress and diabetes. Understanding this relationship will move us closer to our ultimate goal of developing drugs that block ER stress-mediated beta-cell death.
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