Changes in insulin, glucagon and ER stress precede immune activation in type 1 diabetes

Abstract

It is unknown whether there is a gene signature in pancreas which is associated with type 1 diabetes (T1D). We performed partial pancreatectomies on 30 day preinsulitic, diabetes-prone BioBreeding (BBdp) rats to prospectively identify factors involved in early prediabetes. Microarrays of the biopsies revealed downregulation of ER stress, metabolism and apoptosis. Based on these results, additional investigations compared gene expression in control (BBc) and BBdp rats age ~8, 30 and 60 days using RT-qPCR. Neonates had increased ER stress gene expression in pancreas. This was associated with decreased insulin, cleaved caspase-3 and Ins1 whereas Gcg and Pcsk2 were increased. The increase in ER stress was not sustained at 30 days and decreased by 60 days. In parallel, the liver gene profile showed a similar signature in neonates but with an early decrease of the unfolded protein response (UPR) at 30 days. This suggested that changes in the liver precede those in the pancreas. Tnf and Il1b expression was increased in BBdp pancreas in association with increased caspase-1, cleaved caspase-3 and decreased proinsulin area. Glucagon area was increased in both 30 day and 60 day BBdp rats. Increased co-localization of BIP and proinsulin was observed at 60 days in the pancreas, suggesting insulin-related ER dysfunction. We propose that dysregulated metabolism leads to ER stress in neonatal rats long before insulitis, creating a microenvironment in both pancreas and liver that promotes autoimmunity.

Dysregulated liver lipid metabolism and innate immunity associated with hepatic steatosis in neonatal BBdp rats and NOD mice

“…The potential dysregulation in the target tissue very early in life suggests it is of developmental origin 7 . Our previous findings in the pancreas of very young diabetes-prone BBdp rats support this conclusion and similar prediabetic changes in liver suggest a role for this organ in diabetogenesis 3 .…”

“…The majority of tissue-resident macrophages in the body, Kupffer cells, reside in the liver and play a role in immune regulation, antimicrobial defenses and glucose homeostasis. Because we observed immune changes in liver and macrophages are important players in pancreas of young BBdp rats 3,10 , we investigated the macrophage marker CD68 + in neonate and 30 day liver. There was a decrease in macrophage cells in neonates which persisted at 30 days (Fig.…”

“…In the present study we further investigated changes in hepatic immunity and metabolism in very young BBdp rats compared with control BBc rats and also in NOD mice compared with C57BL/6J control mice. The overall findings indicated that in addition to disrupted metabolism and ER stress in the pancreas 3 , very young BBdp rats demonstrated deficiencies in hepatic macrophages and increased proinflammatory cytokines, suggesting the usual tolerogenic state was impaired. This was accompanied by hepatic steatosis.…”

“…Type 1 diabetes (T1D) is a multi-system disease involving the pancreas, gut, diet and microbial agents 1,2 . We recently identified a gene signature in the pancreas of very young diabetes-prone BB rats 3 . Surprisingly, several of the genes identified in pancreas were also different in the liver, with some hepatic gene changes preceding those observed in pancreas.…”

“…The liver is the central mediator of metabolism and plays a major role defending against pathogens, in part attributable to its large collection of phagocytes 4 . Although the role of liver metabolism in glucoregulation is well-recognized, it has not been linked to early development of T1D until recently 3 .…”