DEXI, a candidate gene for type 1 diabetes, modulates rat and human pancreatic beta cell inflammation via regulation of the type I IFN/STAT signalling pathway

Abstract

Aims/hypothesis: The initial stages of type 1 diabetes are characterized by an aberrant islet inflammation that is in part regulated by the interaction between type 1 diabetes susceptibility genes and environmental factors. Chromosome 16p13 is associated with type 1 diabetes and CLEC16A has been considered the etiologic gene in the region. However, recent gene expression analysis indicates that SNPs in CLEC16A modulate the expression of a neighbouring gene with unknown function named DEXI. We presently evaluated the role of DEXI in beta cell responses to “danger signals” and determined the mechanisms involved. Methods: Functional studies based on silencing or overexpression of DEXI were performed in rat and human pancreatic beta cells. Viral double-stranded RNA-driven beta cell inflammation and apoptosis were evaluated by RT-PCR, western blot and luciferase assays. Results: DEXI-silenced beta cells exposed to double-stranded RNA (PIC; a by-product of viral replication) showed reduced STAT1 activation and lower production of pro-inflammatory chemokines that was preceded by a reduction in IFN expression. Exposure to PIC increased chromatin-bound DEXI and IFN promoter activity. This effect on IFN promoter was inhibited in DEXI-silenced betacells, suggesting that DEXI is implicated in the regulation of IFNtranscription. In a mirror image of knockdown experiments, DEXI overexpression led to increased STAT1 and pro-inflammatory chemokine expression. Conclusions: These observations support DEXI as the aetiological gene in the type 1 diabetes-associated 16p13 genomic region and provide the first indication of a link between this candidate gene and the regulation of local antiviral immune response in beta cells. Moreover, our results provide initial information on the function of DEXI.