DHA Protects Hepatocytes from Oxidative Injury through GPR120/ERK-Mediated Mitophagy.

Oxidative stress occurs in a variety of clinical liver diseases and causes cellular damage and mitochondrial dysfunction. The clearance of damaged mitochondria by mitophagy may facilitate mitochondrial biogenesis and enhance cell survival. Although the supplementation of docosahexaenoic acid (DHA) has been recognized to relieve the symptoms of various liver diseases, the antioxidant effect of DHA in liver disease is still unclear. The purpose of our research was to investigate the antioxidant effect of DHA in the liver and the possible role of mitophagy in this. In vitro, H2O2-induced injury was caused in AML12 cells. The results showed that DHA repressed the level of reactive oxygen species (ROS) induced by H2O2 and stimulated the cellular antioxidation response. Most notably, DHA restored oxidative stress-impaired autophagic flux and promoted protective autophagy. In addition, PINK/Parkin-mediated mitophagy was activated by DHA in AML12 cells and alleviated mitochondrial dysfunction. The ERK1/2 signaling pathway was inhibited during oxidative stress but reactivated by DHA treatment. It was proven that the expression of ERK1/2 was involved in the regulation of mitophagy by the ERK1/2 inhibitor. We further proved these results in vivo. DHA effectively alleviated the liver oxidative damage caused by CCl4 and enhanced antioxidation capacity; intriguingly, autophagy was also activated. In summary, our data demonstrated that DHA protected hepatocytes from oxidative damage through GPR120/ERK-mediated mitophagy.

Corticosterone-Induced Lipogenesis Activation and Lipophagy Inhibition in Chicken Liver Are Alleviated by Maternal Betaine Supplementation.

Background: We have shown previously that in ovo betaine injection can prevent nonalcoholic fatty liver induced by glucocorticoid exposure in chickens; yet it remains unknown whether feeding betaine to laying hens may exert similar effects in their progeny. Objective: In this study, we fed laying hens a betaine-supplemented diet, and the progeny were later exposed chronically to corticosterone (CORT) to test hepatoprotective effects and further elucidate underlying mechanisms. Methods: Rugao yellow-feathered laying hens (n = 120) were fed a basal (control, C) diet or a 0.5% betaine-supplemented (B) diet for 28 d before their eggs were collected for incubation. At 49 d of age, male chickens selected from each group were daily injected subcutaneously with solvent (15% ethanol; vehicle, VEH) or CORT (4.0 mg/kg body mass) for 7 d to establish a fatty liver model. Chickens in the 4 groups (C-VEH, C-CORT, B-VEH, and B-CORT) were killed at day 57. Plasma and hepatic triglyceride (TG) concentrations, as well as the hepatic expression of genes involved in lipogenesis and lipophagy, were determined. Results: CORT induced a 1.6-fold increase in the plasma TG concentration (P < 0.05) and a 1.8-fold increment in the hepatic TG concentration (P < 0.05), associated with activation of lipogenic genes (70-780%). In contrast, lipophagy and mitochondrial ß-oxidation genes were inhibited by 30-60% (P < 0.05) in CORT-treated chickens. These CORT-induced changes were completely normalized by maternal betaine supplementation or were partially normalized to intermediate values that were significantly different from those in the C-VEH and C-CORT groups. These effects were accompanied by modifications in CpG methylation and glucocorticoid receptor binding to the promoters of major lipogenic and lipophagic genes (P < 0.05). Conclusions: These results indicate that maternal betaine supplementation protects male juvenile chickens from CORT-induced TG accumulation in the liver via epigenetic modulation of lipogenic and lipophagic genes.

Dietary betaine supplementation increases adrenal expression of steroidogenic acute regulatory protein and yolk deposition of corticosterone in laying hens.

Betaine, an important methyl donor, is known to execute epigenetic regulation of gene expression via nutritional reprogramming. Herein, we explore whether feeding a betaine-supplemented diet to laying hens would affect corticosteroid biosynthesis in the adrenal gland and corticosterone deposition in eggs, in correlation with the expression of methyl transfer enzymes and the promoter DNA methylation status of affected genes. Rugao yellow-feathered laying hens at 38 weeks of age were assigned to Control and Betaine groups, fed basal and betaine-supplemented diets, respectively, for four weeks. Betaine supplementation significantly increased (P < 0.05) the average laying rate, while the body weight and egg quality remained unchanged. Plasma concentrations of cholesterol and low-density lipoprotein-cholesterol were also higher (P < 0.05) in the Betaine group. Moreover, eggs in the Betaine group contained higher corticosterone in the yolk, which was associated with up-regulation of steroidogenesis genes in adrenal glands. Steroidogenic acute regulatory protein (StAR), the rate-limiting protein responsible for transporting cholesterol to the inner mitochondrial membrane, was significantly activated (P < 0.05), together with its transcription factors steroidogenic factor-1 (SF-1) and glucocorticoid receptor. Also, betaine supplementation significantly up-regulated (P < 0.05) the adrenal mRNA expression of adenosyl homocysteinase-like 1 and DNA methyltransferases1 and 3a. Bisulfite sequencing analysis revealed significant hypomethylation in several CpG sites within the promoter region of SF-1 gene in the adrenal gland. These results indicate that dietary supplementation of betaine in hens activates adrenal expression of StAR, possibly through epigenetic regulation of SF-1 gene.