Effect of lipid-induced macrophage M1/M2 polarization on lipid metabolism in hepatocytes

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Objective: This study aims to explore the effect of lipid-induced macrophage M1/M2 polarization on lipid metabolism in hepatocytes. Methods: RAW264.7 macrophages were incubated with different kinds of fatty acids including saturated fatty acids-palmitic acid (PA), monounsaturated fatty acids-oleic acid (OA) and polyunsaturated fatty acids-docosahexaenoic acid (DHA), and cell culture supernatants were collected to prepare conditioned medium (CM). Hepatocytes were isolated by in situ perfusion of the liver with collagenase in mice, and a macrophage-hepatocyte CM co-culture system was established. Macrophage M1/M2 phenotype markers were detected by Real-time PCR. Lipid synthesis and decomposition related mRNA and protein expressions in hepatocytes were detected by Real-time PCR and Western Blot. Lipid depositions in hepatocytes were detected by oil red O staining. An analysis of variance was used for comparison of means between multiple groups. Results: Compared with control groups, PA polarized macrophages to a M1 phenotype (expression of TNF-α and IL-6 significantly increased, F≥22.68, P < 0.01), OA polarized macrophages to a M1/M2 mixed phenotype (expression of IL-6, Mrc2 and IL-10 increased F≥4.94, P < 0.05) and DHA polarized macrophages to a M2 phenotype (expression of Mrc2 and IL-10 significantly increased, F≥4.94, P < 0.01). CM-PA significantly increased lipid synthesis related genes, including SREBP1C, ACC1 mRNA expression (F≥5.66, P < 0.01) and FASN, ACC1 protein expression (F≥38.34, P < 0.05) in hepatocytes, and decreased lipid decomposition gene ACOX1 protein expression (F=154.48, P < 0.01). CM-OA affected several lipid metabolism genes expression. CM-DHA significantly increased CPT1A mRNA expression (F = 10.30, P < 0.01) and ACOX1, CPT1A protein expression (F≥47.06, P < 0.05), and decreased SREBP1C, ACC1 protein expression (F≥65.84, P < 0.05) in hepatocytes. Massive lipid droplets were deposited in hepatocytes in CM-PA treated hepatocytes, and a few amount of lipid droplets were deposited in CM-DHA treated hepatocytes. Conclusion: Different fatty acids affect the balance of lipid metabolism in hepatocytes and liver by inducing macrophage M1 / M2 polarization, thus promoting or delaying the progression of non-alcoholic fatty liver disease.