Dietary fat plays an important role in higher brain functions. We aimed to assess the short and long term intake of three different types of dietary fat (soybean oil, lard, and fish oil) on anxiety-like and depression-like behavior in mice. For the short term intake assessment, a behavioral test battery for anxiety and depression was carried out for a 3-day feeding period. For the long term intake assessment, a behavioral test battery began after the 4-week feeding period. During the short term intake, the time spent in the open arms of the elevated plus-maze was the longest in the fish oil fed group, followed by the soybean oil and lard-fed groups. The elevated plus-maze is a common animal model to assess anxiety, in which an increased time spent in the open arms indicates an anxiolytic effect. The difference between the fish oil-fed group and lard-fed group was statistically significant (p < 0.01), but there was no significant difference between the soybean oil-fed group and the other two groups. Similar results were observed after a 4-week feeding period. On the other hand, there was no significant difference among the three groups in behavior tests to evaluate depression. Thus, the dietary fat types appeared to influence anxiety but not depression in mice, both in short term (3 days) and long term (4 weeks) feeding.

Recent evidence demonstrated that chronic intake of quercetin attenuated hepatic fat accumulation in various animal models of obesity and diabetes. However, whether quercetin has the ability to enhance energy metabolism in hepatocytes and its exact mechanisms have yet to be identified. In the present study, we investigated whether quercetin directly enhanced the energy metabolism of cultured hepatocytes by focusing on lipophagy, involving selective autophagic degradation of lipid droplets. As an indicator of mitochondrial respiration, oxygen consumption was measured following 12-h treatment with quercetin or its related flavonoids, isorhamnetin and rutin (10 μM) using an extracellular flux analyzer. Treatment of alpha mouse liver 12 (AML12) hepatocytes with quercetin enhanced mitochondrial respiration, but isorhamnetin and rutin did not. Results of a palmitate-bovine serum albumin fatty acid oxidation assay showed that quercetin significantly increased the oxygen consumption of AML12 hepatocytes, suggesting enhanced fatty acid β-oxidation. However, as expression levels of mitochondrial oxidative phosphorylation proteins were unaltered by quercetin, we explored whether lipophagy contributed to enhanced fatty acid β-oxidation. Increased colocalization of lipid droplets and lysosomes confirmed that quercetin promoted lipophagy in AML12 hepatocytes. Furthermore, pharmacological inhibition of the autophagy–lysosomal pathway abolished the enhancement of fatty acid β-oxidation induced by quercetin in AML12 hepatocytes, suggesting that the enhancement of lipophagy by quercetin contributed to increased fatty acid β-oxidation. Finally, we showed that quercetin could activate AMPK signaling, which regulates autophagy even under nutrient-sufficient conditions. Our findings indicate that quercetin enhanced energy metabolism by a potentially novel mechanism involving promotion of lipophagy to produce the substrate for fatty acid β-oxidation in mitochondria through activation of AMPK signaling. Our results suggest the possibility that nutrient-induced lipophagy might contributes to the reduction of fat in hepatocytes.

Apobec2 is a member of the activation‐induced deaminase/apolipoprotein B mRNA editing enzyme catalytic polypeptide cytidine deaminase family expressed in differentiated skeletal and cardiac muscle. We previously reported that Apobec2 deficiency in mice leads to a shift in muscle fiber type, myopathy, and diminished muscle mass. However, the mechanisms of myopathy caused by Apobec2 deficiency and its physiologic functions are unclear. Here we show that, although Apobec2 localizes to the sarcomeric Z‐lines in mouse tissue and cultured myotubes, the sarcomeric structure is not affected in Apobec2‐deficient muscle. In contrast, electron microscopy reveals enlarged mitochondria and mitochondria engulfed by autophagic vacuoles, suggesting that Apobec2 deficiency causes mitochondrial defects leading to increased mitophagy in skeletal muscle. Indeed, Apobec2 deficiency results in increased reactive oxygen species generation and depolarized mitochondria, leading to mitophagy as a defensive response. Furthermore, the exercise capacity of Apobec2 ^−/− mice is impaired, implying Apobec2 deficiency results in ongoing muscle dysfunction. The presence of rimmed vacuoles in myofibers from 10‐mo‐old mice suggests that the chronic muscle damage impairs normal autophagy. We conclude that Apobec2 deficiency causes mitochondrial defects that increase muscle mitophagy, leading to myopathy and atrophy. Our findings demonstrate that Apobec2 is required for mitochondrial homeostasis to maintain normal skeletal muscle function.—Sato, Y., Ohtsubo, H., Nihei, N., Kaneko, T., Sato, Y., Adachi, S.‐I., Kondo, S., Nakamura, M., Mizunoya, W., Iida, H., Tatsumi, R., Rada, C., Yoshizawa, F. Apobec2 deficiency causes mitochondrial defects and mitophagy in skeletal muscle. FASEB J. 32,1428‐1439 (2018). www.fasebj.org

Skeletal muscle is divided into type 1 and type 2 fibers. Type 1 fibers are rich in mitochondria, have high oxidative metabolism, and are resistant to fatigue. Muscle-specific overexpression of peroxisome proliferator-activated receptor (PPAR)δ drastically increases the number of type 1 fibers. We focused on oleic acid, an omega-9 monounsaturated fatty acid, as a factor that activates PPARδ. In this study, we examined the effects of oleic acid on the muscle fiber type of C2C12 myotubes and its relationship with PPARδ. Our results showed that oleic acid treatment increased the levels of myosin heavy chain (MyHC)1, a known type 1 fiber marker, as well as mitochondrial mass and maximum respiration in C2C12 cells. To confirm the relationship between PPARδ activation and oleic acid-induced MyHC1 increase, we examined the effects of oleic acid in PPARδ knockdown C2C12 myoblasts. We found that oleic acid supplementation increased the mRNA expression of MyHC1 in PPARδ-knockdown C2C12 cells. Our data suggest that oleic acid increases type 1 fiber levels in C2C12 myotubes in a PPARδ-independent manner.