Altered gene signature for ER stress, metabolism and apoptosis precedes immune activation in pancreas and suggests a hepatic clue to diabetogenesis

It is important to identify defects in whole pancreas of subjects who develop type 1 diabetes (T1D) that distinguish them from genetically susceptible individuals who remain disease-free. It is unclear which biological processes are impaired and when this first occurs. Pancreas biopsies from diabetes-prone BioBreeding (BBdp) rats were obtained at 30 days. Animals were monitored for diabetes until 150 days and biopsies were retroactively identified as originating from nondiabetic or prediabetic rats. Microarray data revealed downregulation of ER stress, metabolism and apoptosis. Additional investigations compared control (BBc) and BBdp rats age ~8, 30 and 60 days using RT-qPCR, immunoblotting and immunohistochemistry. BBdp neonates showed increased pancreatic unfolded protein response (UPR). This was associated with decreased insulin and increased glucagon and Pcsk2 expression, which persisted until 30 days. At 30 days, pro-inflammatory genes Tnf and Il1b were upregulated in BBdp pancreas in association with increased caspase-1, cleaved caspase-3 and decreased proinsulin⁺ area. Parallel analyses of neonatal liver showed a similar gene profile, however UPR gene expression was downregulated at 30 days in association with increased pro-inflammatory genes: Nlrp3, Il1b and Tnf. This suggests that changes in the liver may precede those in the pancreas, which did not show strain-related decreases in the UPR until 60 days. In vitro experiments indicate that treatment with chemical chaperones before inducing ER stress upregulated genes involved in pro-apoptotic and inflammatory processes such as Foxo3, Txnip and Nlrp3. These results suggested that dysregulated metabolism and ER stress response present in neonatal liver and pancreas long before insulitis could create the ideal microenvironment to promote autoimmunity. (Funded by CIHR)