Omega-3 fatty acids induce Ca(2+) mobilization responses in human colon epithelial cell lines endogenously expressing FFA4

AIM: Free fatty acid receptor 4 (FFA4; formerly known as GPR120) is the G protein-coupled receptor (GPCR) for omega-3 polyunsaturated fatty acids. FFA4 has been found to express in the small intestines and colons of mice and humans. In this study we investigate the effects of omega-3 polyunsaturated fatty acids on FFA4 in human colon epithelial cells in vitro. METHODS: HCT116 and HT-29 human colon epithelial cell lines endogenously expressing FFA4 were used. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured in fura 2-AM-loaded cells with fluorescence spectrophotometry. RT-PCR and immunohistochemistry were used to detect FFA4. RESULTS: Ten to 100 μmol/L of omega-3 polyunsaturated fatty acids α-linolenic acid (αLA) or eicosapentaenoic acid (EPA) induced dose-dependent [Ca(2+)](i) increase in HCT116 and HT-29 cells, whereas docosahexaenoic acid (DHA) had no effect. In addition, the omega-6 fatty acids linoleic acid and γ-linoleic acid also dose-dependently increase [Ca(2+)](i), but the mono-unsaturated fatty acid oleic acid and saturated fatty acids such as stearic acid and palmitic acid had no effect. In HCT116 and HT-29 cells, the αLA-induced [Ca(2+)](i) increase was partially inhibited by pretreatment with EGTA, phospholipase C inhibitor edelfosine, cADPR inhibitors 8-bro-cADPR or DAB, and abolished by pretreatment with Ca(2+)ATPase inhibitor thapsigargin, but was not affected by G(i/o) protein inhibitor PTX or IP(3)R inhibitor 2-APB. CONCLUSION: Omega-3 and omega-6 long-chain polyunsaturated fatty acids (C18-20) induce Ca(2+) mobilization responses in human colonic epithelial cells in vitro through activation of FFA4 and PTX-insensitive G(i/o) protein, followed by Ca(2+) release from thapsigargin-sensitive Ca(2+) stores and Ca(2+) influx across the plasma membrane.