Intestinal Region-Specific and Layer-Dependent Induction of TNFα in Rats with Streptozotocin-Induced Diabetes and after Insulin Replacement

Abstract

Tumour necrosis factor alpha (TNFα) is essential in neuroinflammatory modulation. Therefore, the goal of this study is to reveal the effects of chronic hyperglycaemia and insulin treatment on TNFα expression in different gut segments and intestinal wall layers. TNFα expression was mapped by fluorescent immunohistochemistry and quantitative immunogold electron microscopy in myenteric ganglia of duodenum, ileum and colon. Tissue TNFα levels were measured by enzyme-linked immunosorbent assays in muscle/myenteric plexus-containing (MUSCLE-MP) and mucosa/submucosa/submucous plexus-containing (MUC-SUBMUC-SP) homogenates. Increasing density of TNFα-labelling gold particles is observed in myenteric ganglia from proximal to distal segments and TNFα tissue levels are much more elevated in MUSCLE-MP homogenates than in MUC-SUBMUC-SP samples in healthy controls. In the diabetics, the number of TNFα gold labels is significantly increased in the duodenum, decreased in the colon and remained unchanged in the ileal ganglia, while insulin does not prevent these diabetes-related TNFα changes. TNFα tissue concentration is also increased in MUSCLE-MP homogenates of diabetic duodenum, while decreased in MUC-SUBMUC-SP samples of diabetic ileum and colon. These findings support that type 1 diabetes has region-specific and intestinal layer-dependent effects on TNFα expression, contributing to the regional damage of myenteric neurons and their intestinal milieu.

Gut region-specific TNFR expression: TNFR2 is more affected than TNFR1 in duodenal myenteric ganglia of diabetic rats

“…Furthermore, tissue levels of different TNFRs and their proportion also remained unchanged in the MUSCLE-MP homogenates from these segments. Since the myenteric and mucosal/submucosal TNFα expression has been shown to decrease in the distal gut regions of diabetic rats[ 10 ] presumably as a result of heme oxygenase induction[ 6 , 35 ], we suppose that the crucial mechanism involved in diabetic loss of myenteric neurons[ 12 ] and environmental damage[ 5 , 7 ] in the colon and ileum is not the result of TNFα-TNFRs signaling. Therefore, further investigation is necessary regarding the impact of other cytokines in diabetic enteric neuropathy.…”

“…This suggests that the TNFα-TNFR2 signaling is more affected by the diabetic state in the duodenum. Recently, regionally distinct TNFα production has been demonstrated in myenteric ganglia of different gut segments and intestinal layer-dependent differences in TNFα levels have been revealed in type 1 diabetic rats[ 10 ]. A significantly increased TNFα expression has been observed only in the duodenal ganglia of diabetics[ 10 ].…”

“…Recently, regionally distinct TNFα production has been demonstrated in myenteric ganglia of different gut segments and intestinal layer-dependent differences in TNFα levels have been revealed in type 1 diabetic rats[ 10 ]. A significantly increased TNFα expression has been observed only in the duodenal ganglia of diabetics[ 10 ]. TNFR2-deficient mice have decreased sensitivity to TNFα or greater resistance to TNFα-induced cell death[ 41 ], therefore decreased TNFR2 levels may protect neurons.…”

“…The rats were divided randomly into three groups: streptozotocin (STZ)-induced diabetics (diabetics; n = 17), insulin-treated STZ-induced diabetics (insulin-treated diabetics; n = 15) and sex- and age-matched controls ( n = 15). Hyperglycemia was induced as described previously[ 7 , 10 , 12 ]. The animals were considered diabetic if the non-fasting blood glucose concentration was higher than 18 mmol/L.…”

“…The variety of ligands and receptors that belong to tumor necrosis factor (TNF) superfamily is characterized by a conserved TNF homology domain at the C-terminal[ 19 ]. Tumor necrosis factor alpha (TNFα) is mainly expressed by immune cells and macrophages[ 20 ], however, it is also produced by central and enteric neurons[ 10 , 21 , 22 ]. TNFα can bind to two functionally distinct transmembrane receptors, TNFR1 and TNFR2.…”