TNF-α acutely upregulates amylin expression in murine pancreatic beta cells

Abstract

Aims/hypothesis Amylin, a secretory protein mainly produced by pancreatic beta cells, is elevated in the circulation of patients with diseases related to acute and chronic inflammation, including acute pancreatitis, pancreas graft rejection, obesity and insulin resistance. TNF-α is involved in these disorders. We investigated the effect of TNF-α on amylin levels and the underlying mechanisms, using murine pancreatic beta cell line MIN6 and pancreatic islets. Methods Amylin, proinsulin and prohormone convertase 1/3, 2 (Pc1/3, Pc2 [also known as Pcsk1/3 and Pcsk2, respectively]) mRNA levels, and amylin promoter and nuclear factor κB (NF-κB) activation were examined by real-time PCR and luciferase reporter assay, respectively. Amylin protein level and mitogen-activated protein kinase phosphorylation were detected by western blot. Activator protein 1 (AP1) activation was examined by electrophoretic mobility shift assay (EMSA).Results TNF-α acutely induced amylin expression at the transcriptional level and increased proamylin and the intermediate form of amylin in MIN6 cells and islets. However, it had no effect on proinsulin, Pc1/3 and Pc2 expression. Studies with (1) MIN6 cells treated with inhibitors of MEK1/2, c-Jun-N-terminal kinase (JNK) or protein kinase CK PKC ð z Þ, (2) MIN6 cells expressing a c-Jun-dominant negative construct and (3) islets from Fos knockout mice demonstrated that TNF-α induced amylin expression through the PKC z Àextracellular signal-regulated kinase (ERK)/JNK pathways. EMSA showed that PKC z , JNK and ERK1/2 were involved in TNF-α-induced AP1 activation, suggesting that TNF-α induces murine amylin expression through the PKC z ÀERK1=2ÀAP1 and PKC z À JNKÀAP1 pathways. Further studies showed that TNF-α also induced murine amylin expression through the phosphatidylinositol 3 kinase-NF-κB signalling pathway and enhanced human amylin promoter activation through NF-κB and AP1. Conclusions/interpretation TNF-α acutely induces amylin gene expression in beta cells through multiple signalling pathways, possibly contributing to amylin elevation in acute inflammation-related pancreatic disorders.

Acute pancreatitis due to diabetes: The role of hyperglycaemia and insulin resistance

“…Phillips et al [39] and others have reported various mechanisms by which amylin may be involved in the pathogenesis of AP including stimulation of acinar cell secretion [40] and reduction of pancreatic blood flow [41]. Furthermore, it has been recently demonstrated that TNF-a can acutely upregulates amylin expression in murine pancreatic beta cells [42].…”

The role of adipokines in β-cell failure of type 2 diabetes

“…There is a substantial number of reports on direct effects of TNFa inhibiting insulin secretion (for example Kim et al (2008)), and one study (Cai et al 2011b) reported that TNFa induces the expression of amylin from the b-cell. This latter study is of particular relevance in diabetes as the authors also report that there was no concurrent induction of proinsulin expression by TNFa.…”

Clinical islet transplantation

“…Interestingly, IL-1 blockade with the IL-1 receptor antagonist Anakinra was recently shown to inhibit amyloid-associated islet graft injury [36 & ]. The inflammatory cytokine TNF-a also can enhance amylin expression in mouse islets, providing additional evidence that inflammation may promote islet dysfunction through this pathway [45]. Consistent with these findings, a recent study shows that blocking IL-1 and TNF can improve the engraftment of human islets in immune-deficient mice [35 & ].…”