MCP-1 Upregulates Amylin Expression in Murine Pancreatic β Cells through ERK/JNK-AP1 and NF-κB Related Signaling Pathways Independent of CCR2

BACKGROUND: Amylin is the most abundant component of islet amyloid implicated in the development of type 2 diabetes. Plasma amylin levels are elevated in individuals with obesity and insulin resistance. Monocyte chemoattractant protein-1 (MCP-1, CCL2) is involved in insulin resistance of obesity and type 2 diabetes. We investigated the effect of MCP-1 on amylin expression and the underlying mechanisms with murine pancreatic β-cell line MIN6 and pancreatic islets. METHODOLOGY/PRINCIPAL FINDINGS: We found that MCP-1 induced amylin expression at transcriptional level and increased proamylin and intermediate forms of amylin at protein level in MIN6 cells and islets. However, MCP-1 had no effect on the expressions of proinsulin 1 and 2, as well as prohormone convertase (PC) 1/3 and PC2, suggesting that MCP-1 specifically induces amylin expression in β-cells. Mechanistic studies showed that although there is no detectable CCR2 mRNA in MIN6 cells and islets, pretreatment of MIN6 cells with pertussis toxin inhibited MCP-1 induced amylin expression, suggesting that alternative Gi-coupled receptor(s) mediates the inductive effect of MCP-1. MCP-1 rapidly induced ERK1/2 and JNK phosphorylation. Inhibitors for MEK1/2 (PD98059), JNK (SP600125) or AP1 (curcumin) significantly inhibited MCP-1-induced amylin mRNA expression. MCP-1 failed to induce amylin expression in pancreatic islets isolated from Fos knockout mice. EMSA showed that JNK and ERK1/2 were involved in MCP-1-induced AP1 activation. These results suggest that MCP-1 induces murine amylin expression through AP1 activation mediated by ERK1/2 or JNK. Further studies showed that treatment of MIN6 cells with NF-κB inhibitor or overexpression of IκBα dominant-negative construct in MIN6 cells significantly inhibited MCP-1-induced amylin expression, suggesting that NF-κB related signaling also participates in MCP-1-induced murine amylin expression. CONCLUSIONS/SIGNIFICANCE: MCP-1 induces amylin expression through ERK1/2/JNK-AP1 and NF-κB related signaling pathways independent of CCR2. Amylin upregulation by MCP-1 may contribute to elevation of plasma amylin in obesity and insulin resistance

Amyloid in the islets of Langerhans: Thoughts and some historical aspects

Deposition of amyloid, derived from the polypeptide hormone islet amyloid polypeptide (IAPP; ‘amylin’) is the single most typical islet alteration in type 2 diabetes. Islet amyloid was described as hyalinization already in 1901, but not until 1986 was it understood that it is a polymerization product of a novel β-cell regulatory product. The subject of this focused review deals with the pathogenesis and importance of the islet amyloid itself, not with the biological effect of the polypeptide. Similar to the situation in Alzheimer's disease, it has been argued that the amyloid may not be of importance since there is no strict correlation between the degree of islet amyloid infiltration and the disease. However, it is hardly discussable that the amyloid is important in subjects where islets have been destroyed by pronounced islet amyloid deposits. Even when there is less islet amyloid the deposits are widely spread, and β-cells show ultrastructural signs of cell membrane destruction. It is suggested that type 2 diabetes is heterogeneous and that in one major subtype aggregation of IAPP into amyloid fibrils is determining the progressive loss of β-cells. Interestingly, development of islet amyloid may be an important event in the loss of β-cell function after islet transplantation into type 1 diabetic subjects

Genetic Associations of Type 2 Diabetes with Islet Amyloid Polypeptide Processing and Degrading Pathways in Asian Populations

10.1371/journal.pone.0062378PLoS ONE86

Intrinsic rectification of ion flux in alamethicin channels: studies with an alamethicin dimer.

Covalent dimers of alamethicin form conducting structures with gating properties that permit measurement of current-voltage (I-V) relationships during the lifetime of a single channel. These I-V curves demonstrate that the alamethicin channel is a rectifier that passes current preferentially, with voltages of the same sign as that of the voltage that induced opening of the channel. The degree of rectification depends on the salt concentration; single-channel I-V relationships become almost linear in 3 M potassium chloride. These properties may be qualitatively understood by using Poisson-Nernst-Planck theory and a modeled structure of the alamethicin pore

Membrane damage by human islet amyloid polypeptide through fibril growth at the membrane

Fibrillar protein deposits (amyloid) in the pancreatic islets of Langerhans are thought to be involved in death of the insulin-producing islet β cells in type 2 diabetes mellitus. It has been suggested that the mechanism of this β cell death involves membrane disruption by human islet amyloid polypeptide (hIAPP), the major constituent of islet amyloid. However, the molecular mechanism of hIAPP-induced membrane disruption is not known. Here, we propose a hypothesis that growth of hIAPP fibrils at the membrane causes membrane damage. We studied the kinetics of hIAPP-induced membrane damage in relation to hIAPP fibril growth and found that the kinetic profile of hIAPP-induced membrane damage is characterized by a lag phase and a sigmoidal transition, which matches the kinetic profile of hIAPP fibril growth. The observation that seeding accelerates membrane damage supports the hypothesis. In addition, variables that are well known to affect hIAPP fibril formation, i.e., the presence of a fibril formation inhibitor, hIAPP concentration, and lipid composition, were found to have the same effect on hIAPP-induced membrane damage. Furthermore, electron microscopy analysis showed that hIAPP fibrils line the surface of distorted phospholipid vesicles, in agreement with the notion that hIAPP fibril growth at the membrane and membrane damage are physically connected. Together, these observations point toward a mechanism in which growth of hIAPP fibrils, rather than a particular hIAPP species, is responsible for the observed membrane damage. This hypothesis provides an additional mechanism next to the previously proposed role of oligomers as the main cytotoxic species of amyloidogenic proteins

Dual amyloid domains promote differential functioning of the chaplin proteins during Streptomyces aerial morphogenesis

The chaplin proteins are functional amyloids found in the filamentous Streptomyces bacteria. These secreted proteins are required for the aerial development of Streptomyces coelicolor, and contribute to an intricate rodlet ultrastructure that decorates the surfaces of aerial hyphae and spores. S. coelicolor encodes eight chaplin proteins. Previous studies have revealed that only three of these proteins (ChpC, ChpE, and ChpH) are necessary for promoting aerial development, and of these three, ChpH is the primary developmental determinant. Here, we show that the model chaplin, ChpH, contains two amyloidogenic domains: one in the N terminus and one in the C terminus of the mature protein. These domains have different polymerization properties as determined using fluorescence spectroscopy, secondary structure analyses, and electron microscopy. We coupled these in vitro assays with in vivo genetic studies to probe the connection between ChpH amyloidogenesis and its biological function. Using mutational analyses, we demonstrated that both N- and C-terminal amyloid domains of ChpH were required for promoting aerial hypha formation, while the N-terminal domain was dispensable for assembly of the rodlet ultrastructure. These results suggest that there is a functional differentiation of the dual amyloid domains in the chaplin proteins