Identification of newly synthetized proteins by mass spectrometry to understand palmitate-induced early cellular changes in pancreatic islets.

Obesity and lipid metabolism dysregulation are often associated with insulin resistance, and can lead to type 2 diabetes. However, mechanisms linking insulin resistance, high levels of plasma free fatty acids (FFA) and beta cell failure remain unclear. The aim of this work was to search for proteins whose synthesis was modified by a short exposure to FFA. This could help in the future to identify molecular mechanisms underlying islet dysfunction in presence of FFA. Therefore, we assessed by mass spectrometry protein synthesis of freshly isolated rat islets after palmitate short-exposure. Quantitative proteome and secretome analyses were performed by combining metabolic incorporation of azidohomoalanine (AHA) and pulse labeling with stable isotope labeling by amino acids in cell culture (SILAC). We showed that pancreatic islets, in response to 4 h exposure to palmitate, increased the synthesis of ribosomal proteins and proteins of the cytoskeleton, and increased their secretion of proteins involved in insulin synthesis and insulin secretion, as well as insulin itself. Firstly, these results show that protein quantification analysis by LC-MS/MS is a useful method to investigate cellular modifications induced by FFA on pancreatic islets. Also, these results show that short exposure to palmitate increases the expression of ribosomal proteins and proteins involved in insulin secretion, and it remains to be determined if these effects are responsible or linked to the harmful effect of palmitate on beta cells.