Disruption of BCATm in Mice Leads to Increased Energy Expenditure Associated with the Activation of a Futile Protein Turnover Cycle

Abstract

Leucine is recognized as a nutrient signal; however, the long-term in vivo consequences of leucine signaling and the role of branched-chain amino acid (BCAA) metabolism in this signaling remain unclear. To investigate these questions, we disrupted the BCATm gene, which encodes the enzyme catalyzing the first step in peripheral BCAA metabolism. BCATm(-/-) mice exhibited elevated plasma BCAAs and decreased adiposity and body weight, despite eating more food, along with increased energy expenditure, remarkable improvements in glucose and insulin tolerance, and protection from diet-induced obesity. The increased energy expenditure did not seem to be due to altered locomotor activity, uncoupling proteins, sympathetic activity, or thyroid hormones but was strongly associated with food consumption and an active futile cycle of increased protein degradation and synthesis. These observations suggest that elevated BCAAs and/or loss of BCAA catabolism in peripheral tissues play an important role in regulating insulin sensitivity and energy expenditure.

Dairy protein and leucine alter GLP-1 release and mRNA of genes involved in intestinal lipid metabolism in vitro

“…Total RNA (1 μg) was reverse-transcribed using Superscript II Reverse Transcriptase (Invitrogen, Carlsbad, CA, USA) with oligo-d(T) [12][13][14][15][16][17][18] as primer. After reverse transcription, the same batch of diluted cDNA was subjected to real-time polymerase chain reaction (PCR) to amplify target genes.…”

“…As regulators of protein metabolism, branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) have also been reported to improve glucose and cholesterol metabolism [13,14] and control appetite [15]. A study by Bowen et al [16] suggested that the protein component of dairy appears to be more important for weight loss than calcium in over-weight adults.…”

Voluntary exercise under a food restriction condition decreases blood branched-chain amino acid levels, in addition to improvement of glucose and lipid metabolism, in db mice, animal model of type 2 diabetes

“…In the present study, exercise decreased BCAA in db mice more than food restriction in db mice. In db mice, branched-chain a-keto acids such as isovaleric acid showed lower excretion in urine [32], indicating the slow degradation and transport of BCAA in WAT and SM, which are thought to play a role in BCAA metabolism [26,27,33]. The gene expressions of BCAT2, SLC3A2, and SLC7A5, the responsible genes in BCAA degradation and transport, were not altered under exercise conditions in our models, except BCAT2 in SM (Fig.…”

“…Real-time quantitative PCR was performed using SYBR-green on a TAKARA detection system (TAKARA, Shiga, Japan) under the conditions recommended by the manufacturer. The primary sequences of the genes are shown in supplementary Table 1 [26,27]. The relative level of mRNA was calculated using cycle time (Ct) values, which were normalized against the value of btubulin.…”

Leucine Facilitates Insulin Signaling through a Gαi Protein-dependent Signaling Pathway in Hepatocytes

“…Theoretically, leucine is capable of modulating insulin signaling through the mammalian target of rapamycin (mTOR) 3 and S6K-mediated serine phosphorylations of IRS1/2 (3,21). It is noteworthy that supplementation of leucine can increase insulin sensitivity in obese animals (13,14), and the increased level of branched chain amino acids by knocking out the ratelimiting enzyme that catabolizes branched chain amino acids is associated with increased and not decreased insulin sensitivity (22). The increased insulin sensitivity by branched chain amino acids can be at least partially explained by decreased food intake and elevated energy expenditure (13,14,22).…”