Leucine imparts cardioprotective effects by enhancing mTOR activity and mitochondrial fusion in a myocardial ischemia/reperfusion injury murine model

Background: Coronary artery disease is a leading cause of morbidity and mortality among patients with diabetes. Previously, we demonstrated that branched-chain amino acids (BCAAs) showed cardioprotective effects against cardiac ischemia/reperfusion (I/R) injury. A recent study suggested that leucine (Leu), a BCAA, is a key amino acid involved in mammalian target of rapamycin (mTOR) activity and mitochondrial function. However, whether Leu has cardioprotective effects on diabetic hearts is unclear. In this study, we examined the preconditioning effect of Leu treatment on high-fat diet (HFD)-induced obese mouse which simulate prediabetic heart. Methods: In vivo mice models of I/R injury were divided into the following groups: control, mTOR+/−, and high-fat diet (HFD)-induced obese groups. Mice were randomly administered with Leu, the mTOR inhibitor rapamycin (Rap), or Leu with Rap. Isolated rat cardiomyocytes were subjected to simulated I/R injury. Biochemical and mitochondrial functional assays were performed to evaluate the changes in mTOR activity and mitochondrial dynamics caused by Leu treatment. Results: Leu-treated mice showed a significant reduction in infarct size when compared with the control group (34.8% ± 3.8% vs. 43.1% ± 2.4%, n = 7, p < 0.05), whereas Rap-treated mice did not show the protective effects of Leu. This preconditioning effect of Leu was attenuated in mTOR+/− mice. Additionally, Leu increased the percentage of fused mitochondria and the mitochondrial volume, and decreased the number of mitochondria per cell in isolated cardiomyocytes. In HFD-induced obese mice, Leu treatment significantly reduced infarct size (41.0% ± 1.1% vs. 51.0% ± 1.4%, n = 7, p < 0.05), which was not induced by ischemic preconditioning, and this effect was inhibited by Rap. Furthermore, we observed enhanced mTOR protein expression and mitochondrial fusion with decreased reactive oxygen species production with Leu treatment in HFD-induced obese mice, but not in mTOR+/− mice. Conclusions: Leu treatment improved the damage caused by myocardial I/R injury by promoting mTOR activity and mitochondrial fusion on prediabetic hearts in mice

DNA Methylation Suppresses Leptin Expression in Adipocytes

Leptin is a key regulator of energy intake and expenditure. This peptide hormone is expressed in mouse white adipose tissue, but hardly expressed in 3T3-L1 adipocytes. Using bisulfite sequencing, we found that CpG islands in the leptin promoter are highly methylated in 3T3-L1cells. 5-azacytidine, an inhibitor of DNA methyltransferase, markedly increased leptin expression as pre-adipocytes matured into adipocytes. Remarkably, leptin expression was stimulated by insulin in adipocytes derived from precursor cells exposed to 5-azacytidine, but suppressed by thiazolidinedione and dexamethasone. In contrast, adipocytes derived from untreated precursor cells were unresponsive to both 5-azacytidine and hormonal stimuli, although lipid accumulation was sufficient to boost leptin expression in the absence of demethylation. Taken together, the results suggest that leptin expression in 3T3-L1 cells requires DNA demethylation prior to adipogenesis, transcriptional activation during adipogenesis, and lipid accumulation after adipogenesis

グレリンの脳室内投与はラットにおいて回転カゴ運動を減少させる

There is an increasing interest in elucidating the molecular mechanisms by which voluntary exercise is regulated. In this study, we examined how the central nervous system regulates exercise. We used SPORTS rats, which were established in our laboratory as a highly voluntary murine exercise model. SPORTS rats showed lower levels of serum ghrelin compared with those of the parental line of Wistar rats. Intrac-erebroventricular and intraperitoneal injection of ghrelin decreased wheel-running activity in SPORTS rats. In addition, daily injection of the ghrelin inhibitor JMV3002 into the lateral ventricles of Wistar rats increased wheel-running activity. Co-administration of obestatin inhibited ghrelin-induced increases in food intake but did not inhibit ghrelin-induced suppression of voluntary exercise in rats. Growth hormone secretagogue receptor (GHSR) in the hypothalamus and hippocampus of SPORTS rats was not difference that in control rats. We created an arcuate nucleus destruction model by administering monosodium glutamate (MSG) to neonatal SPORTS rats. Injection of ghrelin into MSG-treated rats decreased voluntary exercise but did not increase food intake, suggesting that wheel-running activity is not controlled by the arcuate nucleus neurons that regulate feeding. These results provide new insights into the mechanism by which ghrelin regulates voluntary activity independent of arcuate nucleus neurons