Brown adipose tissue (BAT) plays an important role in body fat accumulation and the regulation of energy expenditure. Since the role of miRNAs in the pathogenesis of obesity and related metabolic diseases is contentious, we analyzed exosomal miRNAs in serum of healthy subjects with special references to BAT activity and body fat level. Forty male volunteers aged 20–30 years were recruited. Their BAT activity was assessed by fluorodeoxyglucose positron emission tomography and computed tomography after 2 h of cold exposure and expressed as a maximal standardized uptake value (SUVmax). Exosomal miRNA levels was analyzed using microarray and real-time PCR analyses. The miR-122-5p level in the high BAT activity group (SUV ≧ 3) was 53% lower than in the low BAT activity group (SUVmax <3). Pearson’s correlation analysis revealed that the serum miR-122-5p level correlated negatively with BAT activity and the serum HDL-cholesterol, and it correlated positively with age, BMI, body fat mass, and total cholesterol and triglyceride serum levels. Multivariate regression analysis revealed that BAT activity was associated with the serum miR-122-5p level independently of the other parameters. These results reveal the serum exosomal miR-122-5p level is negatively associated with BAT activity independently of obesity.

Branched-chain amino acids (BCAAs: leucine, isoleucine, and valine) are nutritionally indispensable (essential) amino acids for humans. We acquire these amino acids mainly as food proteins, in which the BCAAs account for ~20% of the amino acids. The ingested BCAAs are used for protein synthesis in the body. The daily requirement for BCAAs in adults is estimated to be 85 mg/kg body weight (BW) (39, 20, and 26 mg/ kg BW for Leu, Ile, and Val, respectively) using methods such as indicator amino acid oxidation and 24-hour balance studies (1). The primary physiological function of BCAAs is as the building blocks of proteins; however, recent studies have contributed to the mounting evidence for other physiological functions. In this review, we summarize the current findings on the physiological functions of BCAAs, including those from our own studies. Regulation of BCAA CatabolismThe main BCAA catabolic pathway occurs within mitochondria. The first 2 steps of the pathway are common to the 3 BCAAs and are especially important for the regulation of BCAA catabolism (2) (Fig. 1). The first step of the pathway is the reversible transamination of BCAAs catalyzed by branched-chain aminotransferase (BCAT) to produce corresponding branched-chain a-ketoacids (BCKAs). The second step involves the oxidative decarboxylation of BCKAs catalyzed by the BCKA dehydrogenase (BCKDH) complex to produce corresponding CoA esters. Since this reaction is irreversible, it is a rate-limiting step in BCAA catabolism. Furthermore, the BCKDH complex is subject to covalent modification; BCKDH kinase (BDK) is responsible for inactivation of the complex by phosphorylation and BCKDH phosphatase reactivates the complex by dephosphorylation (2). Therefore, the enzyme activity of the BCKDH complex can be quickly changed in response to alterations in physiological conditions. Aberrations of the enzymes involved in the first two steps of BCAA catabolism have a great impact on the circulating concentrations of BCAAs; a defect in the mitochondrial BCAT (BCAT2) gene of mice resulted in a markedly high level of plasma BCAAs (3), and BDK-knockout (KO) mice, in which the BCKDH complex in all tissues was almost fully activated, showed significantly low concentrations of plasma BCAAs (4). Regulation of Protein Metabolism by LeucineThe mammalian target of rapamycin complex 1 (mTORC1) is a serine-threonine protein kinase that controls translation initiation and is responsive to cellular levels of free amino acids (5). mTORC1 phosphorylates and activates the protein kinase p70S6K1, which subsequently phosphorylates eukaryotic initiation factor 4B (eIF4B) and programmed cell death 4 (PDCD4), and phosphorylates eIF4E-binding protein 1 (eIF4E-BP1), thereby permitting eIF4E to associate with eIF4G to form eIF4F. Thus, mTORC1 stimulates the joining of mRNA to the 43S preinitiation complex and has a global effect on protein synthesis. Furthermore, mTORC1 regulates cellular proteolysis by inhibiting the formation of autophagosomes (6). It is also known that leucine strongly...

Brown adipose tissue (BAT) contributes to non-shivering thermogenesis and plays an important role in body temperature control. The contribution of BAT thermogenesis to body temperature control in a non-cold environment was evaluated using developing hamsters. Immunostaining for uncoupling protein 1 (UCP1), a mitochondrial protein responsible for BAT thermogenesis, indicated that interscapular fat tissue had matured as BAT at day 14. When pups were placed on a thermal plate kept at 23°C, the body surface temperature decreased in day 7- and 10-day-old pups but was maintained at least for 15 min in 14-day-old pups, indicating that hamsters are unable to maintain their body temperature until around day 14 even in a non-cold environment. Body temperature maintenance was also evaluated in UCP1-deficient mice. BAT analysis showed that the UCP1 protein level in Ucp1+/− Hetero mice was 61.3 ± 1.4% of that in wild-type (WT) mice and was undetected in Ucp1−/− knockout (KO) mice. When 12-day-old pups were place on a thermal plate at 23°C, body surface temperature was maintained for at least 15 min in WT and Hetero mice but gradually dropped by 2.4 ± 0.2°C in 15 min in KO mice. It is concluded that BAT thermogenesis is indispensable for body temperature maintenance in pups of hamsters and mice, even in the non-cold circumstances. The early life poikilothermy and the later acquirement of homeothermy in hamsters may be because of the postnatal development of BAT.

Despite decades-long existence of the Philippine stingless bee industry, the biological activity of propolis from this native bee species (Tetragonula biroi Friese) remains poorly understood and sparingly investigated. Herein, we examined the potential anti-inflammatory efficacy of Philippine stingless bee propolis using the lambda (λ)-carrageenan-induced mice model of hind paw edema. Thirty (30), sixweek-old, male ICR mice were randomly assigned into three treatment groups (n=10/group) as follows: distilled water group, diclofenac sodium group (10 mg/kg), and propolis group (100mg/kg). All treatment were administered an hour prior to the injection of the phlogistic agent. As observed at 3 hours post-injection, λ-carrageenan remarkably evoked the classical signs of hind paw edema exemplified grossly by swelling and hyperemia. The ameliorative effect of propolis became apparent at the onset of 6 hours post-injection with a statistically significant finding evident at the 24hour period. This gross attenuation histologically correlated to a considerable and specific reduction of the dermal edema, which mirrored those of the diclofenac sodium group. Furthermore, both propolis and diclofenac sodium significantly attenuated the λ-carrageenan-induced increase in the protein expression levels of the pro-inflammatory cytokine TNF-α depicting more than twofold decrement relative to the distilled water group. Altogether, these suggest that Philippine stingless bee propolis also exhibited a promising in vivo anti-inflammatory property, which can be partly mediated through the inhibition of TNF-α.

The main catabolic pathway of branched‐chain amino acids (BCAAs: leucine, isoleucine, and valine) is located in mitochondria. The rate‐limiting step of the catabolism in muscle tissues is catalyzed by BCKDH complex, which is located at the second step in the pathway. The activity of BCKDH complex is regulated by covalent modification, and BCKDH kinase (BDK) is responsible for inactivation of the complex by phosphorylation. In the present study, we produced muscle‐specific BDK knockout (BDK‐mKO) mice. The muscle BCAA concentrations were less than half in BDK‐mKO mice than in control mice. We assessed the endurance capacity of BDK‐mKO mice and control mice at 12 weeks of age (under untrained conditions) and at 21 weeks of age after 9 weeks training by measuring the distance of running to exhaustion using treadmill with 10% grade. The running speed in the test was initial 15 m/min for 4 min and then increased at the rate of 1 m/min every 4 min. The training was performed 5 days/week by running for 60 min/day at the speed of 15 m/min in the initial 4 weeks and 18 m/min in the following 5 weeks. The endurance capacity in control mice was 633 ± 109 m (mean ± SE, n=8) before training and 1,529 ± 165 m after training, and that in BDK‐mKO mice was 1,020 ± 45 m and 1,004 ± 110 m, respectively. These results indicate that BDK‐mKO mice, in contrast to control mice, did not adapt to the endurance training, suggesting that BCAAs play an important role in adaptation to exercise training.