Characterization of the Lipid Droplet Proteome of a Clonal Insulin-producing β-Cell Line (INS-1 832/13)

Lipids are known to play a crucial role both in the normal control of insulin release and in the deterioration of beta-cell function, as observed in type 2 diabetes. Despite this established dual role of lipids, little is known about lipid storage and handling in beta-cells. Here, we isolated lipid droplets from oleate-incubated INS-1 832/13 cells and characterized the lipid droplet proteome. In a total of four rounds of droplet isolation and proteomic analysis by HPLC-MS/MS, we identified 96 proteins that were specific to droplets. The proteins fall into six categories based on function or previously observed localization: metabolism, endoplasmic reticulum/ribosomes, mitochondria, vesicle formation and transport, signaling, and miscellaneous. The protein profile reinforces the emerging picture of the lipid droplet as an active and dynamic organelle involved in lipid homeostasis and intracellular trafficking. Proteins belonging to the category mitochondria were highly represented, suggesting that the beta-cell mitochondria and lipid droplets form a metabolic unit of potential relevance for insulin secretion.