Fetuin A—A Major Player in Lipid-Induced Islet Dysfunction and ß-Cell Apoptosis

Abstract

Fetuin-A is a glycoprotein that is secreted from both liver and adipose tissue. Circulating Fetuin-A (FetA) is elevated in type 2 diabetes and causes impaired insulin sensitivity. Few recent findings suggested that FetA is responsible for palmitate induced inflammatory injury to the β-cell via TLR4 pathway. Yet it is unknown whether FetA is associated with β-cell death and reduction of functional islet mass that causes dearth of circulatory insulin in chronic hyperlipidemic condition. To validate this hypothesis MIN6 cells (mice insulinoma cells) were treated with various concentrations of palmitate and /or FetA for 48h and subjected to MTT assay and flowcytometry analysis. The results depicted higher mortality of cells (30-40%) with increasing dose of palmitate (0.25-0.75 mM) and/ or FetA (5-20 mM). Palmitate-FetA treated cells demonstrated substantial reduction in the cell proliferative markers (Akt, cyclin D1) while higher expression of apoptotic markers (Bax, caspase 3 and PARP). Silencing of NF-kB or TLR4 in MIN6 cells restore cell viability on palmitate-FetA treatment indicating significance of TLR4-NF-kB axis in β-cell mortality. Our recent findings demonstrated FetA secretion from MIN6 cells on stimulation of palmitate. Silencing of fetA in MIN6 cells, reduced cell mortality with improved GSIS (1.5 fold). Treatment of MIN6 cells or mice islets with cytokines, such as IL-1β and TNF-α, results β-cell apoptosis mimicking the inflamed conditions of the islets. Co-culture experiments of MIN6 cells with adipocytes or macrophages in presence of palmitate showed elevated levels of cytokines (IL-1β, IL6, TNF-α) in the media and significant number of apoptotic MIN6 cells (20-30%). In vivo analysis of islets structure and function in high fat diet (HFD) fed mice model for a period of 20 weeks demonstrated atrophied islets and accumulation of macrophages. Our present investigation therefore indicated FetA to be a major player in lipid induced pancreatic-β cell death and dysfunction in type 2 diabetes. Disclosure R. Kundu: None. A. Mukhuty: None.