High-Fat Diet Elevates Liver Docosahexaenoic Acid Possibly through Over-Expression of Very Long-Chain Fatty Acid Elongase 2 in C57BL/6J Mice

The liver is the main site of lipid metabolism and vitamin A storage. Dietary factors are known to affect liver function, thereby leading to metabolic abnormalities. Here, we assessed the impact of long-term feeding of a high-fat diet on hepatic vitamin A status and lipid metabolism. For this purpose, 14 male and 14 female 35-day-old mice (strain C57BL/6J) were each divided into 2 groups of 7 animals and fed either a stock diet or a high-fat (HF) diet for 26 weeks. In addition to increased body weight/weight gain, the HF diet induced hypertriglyceridemia in both (p < 0.01). However, liver triglyceride levels were comparable among groups, which could be partly explained by unaltered expression of various lipogenic pathway proteins such as sterol regulatory element binding protein 1 (SREBP1), fatty acid synthase (FAS), microsomal triglyceride transfer protein (MTTP), and glycerol 3-phosphate acyl transferase (GPAT). On the other hand, hepatic retinol stores increased significantly in both sexes, whereas males displayed elevated circulatory retinol levels. Notably, long-term feeding of a HF diet elevated n-3 polyunsaturated fatty acid (PUFA) and docosahexaenoic acid (DHA, C22:6) levels in the liver (p ≤ 0.001), which is in line with the over-expression of very long-chain fatty acid elongase 2 (ELOVL2) protein in both sexes of mice (p < 0.01). In conclusion, very long-term feeding of a HF diet increased hepatic retinol stores and induced hypertriglyceridemia. However, it had no effect on hepatic triglyceride accumulation, possibly due to increased DHA levels arising from the ELOVL2-mediated elongation pathway.