Organisms living in temperate regions are sensitive to seasonal variations in the environment; they are known to accumulate energy as fat in their livers during the winter when days are shorter, temperatures are lower, and food is scarce. However, the effect of variations in photoperiod alone on hepatic lipid metabolism has not been well studied. Therefore, in this study, we analyzed lipid metabolism in the liver of medaka, Oryzias latipes, while varying the length of days at constant temperature. Larger amounts of fatty acids accumulated in the liver after 14 days under short‐day conditions than under long‐day conditions. Metabolome analysis showed no accumulation of long‐chain unsaturated fatty acids, but showed a significant accumulation of long‐chain saturated fatty acids. Short‐day conditions induced a reduction in the levels of succinate, fumarate, and malate in the tricarboxylic acid cycle, decreased expression of PPARα, and decreased accumulation of acylcarnitine, which suggested inhibition of lipolysis. In addition, transparent medaka fed on a high‐fat diet under short‐day conditions exhibited greater amounts of fat accumulation and developed fatty liver. The findings of our study will be useful for creating a medaka hepatic steatosis model for future studies of hepatic steatosis‐related diseases.

中文翻译：

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光周期的季节性变化影响青鳉 (Oryzias latipes) 的肝脏代谢

生活在温带地区的生物对环境的季节性变化很敏感；众所周知，在冬季，白天较短、温度较低且食物稀缺时，它们会在肝脏中以脂肪的形式积累能量。然而，光周期变化对肝脏脂质代谢的影响尚未得到很好的研究。因此，在本研究中，我们分析了青鳉肝脏中的脂质代谢，Oryzias latipes，同时在恒温下改变天数。短日照条件下 14 天后肝脏中积累的脂肪酸量比长日照条件下更多。代谢组分析显示没有长链不饱和脂肪酸的积累，但显示长链饱和脂肪酸的显着积累。短日照条件导致三羧酸循环中琥珀酸、富马酸和苹果酸的水平降低，PPARα 的表达降低，酰基肉碱的积累减少，这表明抑制了脂肪分解。此外，在短日条件下以高脂肪饮食喂养的透明青鳉表现出更多的脂肪积累并发展为脂肪肝。