Brain and muscle arnt-like protein 1 (BMAL1), is a transcription factor known to regulate circadian rhythm. BMAL1 was originally characterized by its high expression in the skeletal muscle. Since the skeletal muscle is the dominant organ system in energy metabolism, the possible functions of BMAL1 in the skeletal muscle include the control of metabolism. Here, we established that its involvement in the regulation of oxidative capacity in the skeletal muscle. Muscle-specific Bmal1 KO mice (MKO mice) displayed several physiological hallmarks for the increase of oxidative capacity. This included increased energy expenditure and oxygen consumption, high running endurance and resistance to obesity with improved metabolic profiles. Also, the phosphorylation status of AMP-activated protein kinase and its downstream signaling substrate acetyl-CoA carboxylase in the MKO mice were substantially higher than those in the Bmal1^flox/flox mice. In addition, biochemical and histological studies confirmed the substantial activation of oxidative fibers in the skeletal muscle of the MKO mice. The mechanism includes the regulation of Cacna1s expression, followed by the activation of calcium—nuclear factor of activated T cells (NFAT) axis. We thus conclude that BMAL1 is a critical regulator of the muscular fatty acid level under nutrition overloading and that the mechanism involves the control of oxidative capacity.

Flavanones, a class of flavonoids, are abundant in fruits, vegetables, and herbs. They are known to have several biological activities, such as anti-inflammatory and anti-cancer activities, but their effects on obesity remain unclear. Obesity is closely associated with adipocyte differentiation and lipid accumulation in adipose tissue. Therefore, in this study, we examined the effects of flavanone derivatives on adipocyte differentiation and lipid accumulation by using 3T3-L1 cells. Among the 15 flavanone derivatives studied, 4′-phenylflavanone (4PF), with a biphenyl structure, significantly inhibited adipocyte differentiation-related lipid accumulation in 3T3-L1 cells; this inhibition of lipid accumulation was dose-dependent. Gene expression analysis showed that 4PF suppressed the expression of adipogenic marker genes. Although the induction of peroxisome proliferator activator γ2 (Pparγ2), a master regulator of adipocyte differentiation, and its target genes during adipocyte differentiation was attenuated in 4PF-treated cells, 4PF did not directly regulate Pparγ2 gene expression and its activation. In contrast, 4PF suppressed mitotic clonal expansion (MCE), which is associated with changes in the expression of proliferation-related genes at the early stages of adipocyte differentiation. Taken together, these results suggest that 4PF inhibits lipid accumulation because it suppresses MCE during adipocyte differentiation. Thus, our findings may help in the development of anti-obesity drugs.

Brain and muscle Arnt-like protein 1 (BMAL1) is a transcription factor that forms heterodimers with circadian locomotor output cycles kaput (CLOCK) and drives transcription from E-box elements, thereby regulating the circadian rhythms of gene expression. The kidney expresses numerous rhythmic genes and exhibits circadian physiological function regulation. Circadian rhythm abnormalities, such as sleep disorders and excessive daytime sleepiness, are particularly frequent in patients with chronic kidney disease (CKD). Furthermore, reduced amplitude and phase disruption in clock gene expression rhythms have been reported in mouse CKD models. These results suggest that circadian disruption is associated with renal pathophysiology. However, the role of BMAL1 in the repair process following acute kidney injury (AKI) remains unclear; therefore, this study aimed to elucidate its role in kidney repair following ischemia–reperfusion injury (IRI). We found that the tamoxifen (TAM)-inducible global Bmal1 knockout (BKO) mouse kidneys exhibited increased lipid accumulation, enhanced fibrosis, and delayed kidney repair post-IRI, and that these abnormalities were associated with reduced Peroxisome proliferator-activated receptor alpha (Pparα) expression. Furthermore, treatment with a PPARα agonist reduced these abnormalities in BKO mice. Collectively, our findings demonstrate that the BMAL1–PPARα axis promotes post-AKI kidney repair.