Δ6-, Stearoyl CoA-, and Δ5-desaturase enzymes are expressed in β-cells and are altered by increases in exogenous PUFA concentrations

摘要

In the evolution of Type II diabetes, an initial period of hyper-fatty acidemia leads to an insulin secretory defect which triggers overt hyperglycemia and frank diabetes. The mechanism by which elevated free fatty acids contribute to β-cell dysfunction, however, is not clearly understood. We recently reported that arachidonic acid (20:4) or linoleic acid (18:2) supplementations result in increases in abundances of long chain polyunsaturated fatty acids in INS-1 β-cell membrane lipids, suggesting that β-cells express desaturases that catalyze generation of unsaturated fatty acids. As expression of desaturases by β-cells has not yet been addressed, we initiated studies to examine this issue using INS-1 β-cells and find that they express messages for the Δ6-, stearoyl CoA-, and Δ5-desaturase. Supplementation of the INS-1 β-cells with arachidonic acid leads to decreased expression of all three desaturases, presumably in response to the decreased need for endogenous generation of unsaturated fatty acids. In contrast, linoleic acid supplementation promoted minimal changes in the three desaturases. These finding demonstrate for the first time that β-cells express regulatable desaturases. Additionally, reverse transcriptase-polymerase chain reaction analyses reveal expression of the desaturases in native pancreatic islets. It might be speculated that long-term elevations in fatty acids can also adversely influence desaturase activity in β-cells and affect PUFA composition in β-cell membranes contributing to β-cell membrane structural abnormalities and altered secretory function.