Toll-like receptor agonist induced changes in clonal rat BRIN-BD11 β-cell insulin secretion and signal transduction

Abstract

Evidence for involvement of toll-like receptors (TLRs) (e.g. TLR4 and TLR2, whose agonists include lipopolysaccharides (LPS) and saturated fatty acids) in altered patterns of signalling in adipose, liver and muscle from animal models of insulin resistance and obesity has been published. We have now extended this area of research and have determined the effects of LPS on cell viability, insulin secretion, insulin signalling and metabolism in a clonal b-cell line. BRIN-BD11 b-cells were treated for 24 h with increasing concentrations of LPS. Chronic (24 h) and acute (20 min) insulin secretion, insulin content and parameters of cell metabolism and insulin signalling were determined. Incubation of BRIN-BD11 cells for 24 h in the presence of increasing concentrations of the TLR4 ligand LPS significantly decreased chronic (24 h) insulin secretion from 1 . 09G0 . 19 to 0 . 76G0 . 18 mg insulin/mg protein in the presence of 100 ng/ml LPS (P!0 . 05). There was no change in acute (20 min) stimulated insulin secretion or insulin content. Cell metabolism was not changed. Insulin receptor-b (IRb) expression levels were increased significantly from 1G0 . 52 to 8 . 6G1 . 83 units (P!0 . 01), whereas calcineurin activity and Akt phosphorylation were significantly (P!0 . 01 and P!0 . 05 respectively) reduced in response to 24 h incubation in the presence of LPS. There was no change in IR substrate-1 protein expression or phosphorylation after 24 h. Further incubation for 24 h in the absence of LPS resulted in the recovery of chronic insulin secretion. The negative b-cell effects of LPS may contribute to hyperglycaemia in vivo.

Innate immunity in diabetes and diabetic nephropathy

“…The agonists for TLR2 and TLR4, such as lipopolysaccharides (LPS) and saturated free fatty acids, are involved in manipulating the signaling events via NFκB-p65 nuclear translocation and proinflammatory cytokine production that have been shown to occur in adipose, liver, muscle and pancreatic β cells of animal models of insulin resistance and obesity 55,75 . The inflammatory pathway mediated by IL6 and TNF is mainly induced by the activation of TLR2 and TLR4, as demonstrated in adipose tissues from adolescents with metabolic syndrome 76 .…”

“…Lack of Tlr4 in mice fed a HFD resulted in protection against obesity 67 , insulin resistance, 68 and inflammation in adipose tissues 69,70 , liver, skeletal muscle 71 , and vasculature 72 . Specific deletion of Tlr4 in haematopoietic cells ameliorated insulin resistance in hepatic and adipose tissue 73 and mice with a specific loss of Tlr4 in hepatocytes exhibited improved glucose tolerance, enhanced insulin sensitivity, and ameliorated hepatic steatosis 74 .The agonists for TLR2 and TLR4, such as lipopolysaccharides (LPS) and saturated free fatty acids, are involved in manipulating the signaling events via NFκB-p65 nuclear translocation and proinflammatory cytokine production that have been shown to occur in adipose, liver, muscle and pancreatic β cells of animal models of insulin resistance and obesity 55,75 . The inflammatory pathway mediated by IL6 and TNF is mainly induced by the activation of TLR2 and TLR4, as demonstrated in adipose tissues from adolescents with metabolic syndrome 76 .…”

Involvement of the TLR4 (Toll-like receptor4) signaling pathway in palmitate-induced INS-1 beta cell death

“…In fact, saturated FFAs are known to be potent activators of TLR2 and TLR4, whereas unsaturated FFAs do not stimulate these pathways [24,25]. Vives-Pi et al reported on expression of both TLR2 and TLR4 in islet beta cells; thus, beta cells were sensitive to TLR ligand lipopolysaccharide (LPS) [26]. In particular, suppression of insulin secretion in clonal beta cells by treatment with LPS demonstrated existence of a TLR signaling pathway in beta cells and suggested its negative role in beta cell function [27].…”

Biotin uptake by mouse and human pancreatic beta cells/islets: a regulated, lipopolysaccharide-sensitive carrier-mediated process

“…Indeed there is an increase in the level of LPS in the circulation of those subjects and a low-grade endotoxemia, which are believed to play a role in the onset of the metabolic disorders (1). Pancreatic beta cells express significant levels of TLR4 which make them sensitive to the effect of LPS (10,14,40). Circulating LPS binding to TLR4 leads to activation of the nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-B), p38 mitogen-activated protein kinases (p38 MAPK), activator protein 1 (AP-1), and interferon-inducible inflammatory gene expression (1,14).…”

“…Pancreatic beta cells express significant levels of TLR4 which make them sensitive to the effect of LPS (10,14,40). Circulating LPS binding to TLR4 leads to activation of the nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-B), p38 mitogen-activated protein kinases (p38 MAPK), activator protein 1 (AP-1), and interferon-inducible inflammatory gene expression (1,14). We observed that chronic exposure of pancreatic beta-TC-6 cells to LPS lead to a significant inhibition in biotin uptake.…”