Palmitic acid enhances electronegative LDL-induced production of IL-1β by increasing potassium efflux in macrophages

• Main Authors: Ting-Yu Chang, 張庭瑜
• Other Authors: 呂紹俊
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/r7v2b2

碩士 === 國立臺灣大學 === 生物化學暨分子生物學研究所 === 106 === Recently, prevalence of obesity is increasing worldwide because of changing of diet preference. And obesity is a major risk factor for metabolic diseases, which usually progresses to type 2 diabetes mellitus and cardiovascular diseases; such as atherosclerosis, myocardial infarction. Inflammation is associated with these diseases, and macrophages are the predominant contributor of inflammation. Moreover, electronegative LDL (LDL(-)), free fatty acids and interleukin-1β (IL-1β) are increased significantly in the blood of these patients. Production of IL-1β requires two signals. Firstly, the priming signal is to activate NF-κB signaling. NF-κB as a transcription factor that promotes pro-IL-1β and NLRP3 expression. Secondly, the activating signal is to activate NLRP3 inflammasome and caspase-1. Then activated caspase-1 proteolytically cleaves pro-IL-1β into mature IL-1β. Our previous study showed that LDL(-) could induce NF-κB activation in macrophage, and weakly promote caspase-1 activation. Evidence has shown that palmitic acid could promote NLRP3 inflammasome/caspase-1 activation. Thus, in this study we investigated whether there is an interaction between LDL(-) and palmitic acid in inducing IL-1β production in macrophages. LDL(-) was isolated from the plasma of the rabbits fed with high-fat/cholesterol diet. THP-1 macrophages were treated with LDL(-) and BSA bound saturated or unsaturated free fatty acids, then the levels of IL-1β in culture medium were analyzed by ELISA. The results show that palmitate, a saturated fatty acid, alone is unable to induce NF-κB activation and IL-1β production in macrophages. However, palmitate enhances LDL(-)-induced IL-1β production. Palmitate did not further activate NF-κB or increase the levels of pro-IL-1β mRNA and protein when treated with LDL(-). Our data also show that palmitate did not further increase LDL(-)-induced increase of LOX-1, a scavenger receptor for LDL(-). These results suggest that palmitate enhances LDL(-)-induced IL- 1β production was not through activation of signal one (NF-κB signaling) or increase levels of LOX-1. Cells treated with LDL(-) under a potassium free medium, and the level of IL-1β in the medium is close to that of LDL(-) and palmitate co-treated cells. Treated potassium channel blockers significantly lower LDL(-) and palmitate-induced levels of IL-1β. The results suggest that palmitate enhances LDL(-)-induced IL-1βproduction is likely through increase potassium efflux. In conclusion, our study show that palmitate enhances LDL(-)-induced IL-1β production, the results is physiological relevant since the concentrations of LDL(-) and palmitate used in this study are under physiological ranges in plasma of patients with AMI and diabetes. However, we do not know which potassium channel is activated by palmitate. The mechanism underlie deserved further investigation.