Satellite cells are required for muscle regeneration, remodeling, and repair through their activation, proliferation, and differentiation; however, how dietary factors regulate this process remains poorly understood. The L-Type amino acid transporter 1 (LAT1) transports amino acids, such as leucine, into mature myofibers, which then stimulates protein synthesis and anabolic signaling. However, whether LAT1 is expressed on myoblasts and is involved in regulating myogenesis is unknown. The aim of this study was to characterize the expression and functional relevance of LAT1 during different stages of myogenesis and in response to growth and atrophic conditions in vitro. We determined that LAT1 is expressed by C2C12 and human primary myoblasts, and its gene expression is lower during differentiation (p<0.05). Pharmacological inhibition and genetic knockdown of LAT1 impaired myoblast viability, differentiation, and fusion (all p<0.05). LAT1 protein content in C2C12 myoblasts was not significantly altered in response to different leucine concentrations in cell culture media or in two in vitro atrophy models. However, LAT1 content was decreased in myotubes under atrophic conditions in vitro (p<0.05). These findings indicate that LAT1 is stable throughout myogenesis and in response to several in vitro conditions that induce muscle remodeling. Further, amino acid transport through LAT1 is required for normal myogenesis in vitro.

The purpose was to investigate the effects of a 7-day creatine (Cr) loading protocol at the end of four weeks of β-alanine supplementation (BA) on physical performance, blood lactate, cognitive performance, and resting hormonal concentrations compared to BA alone. Twenty male military personnel (age: 21.5 ± 1.5 yrs; height: 1.78 ± 0.05 m; body mass: 78.5 ± 7.0 kg; BMI: 23.7 ± 1.64 kg/m2) were recruited and randomized into two groups: BA + Cr or BA + placebo (PL). Participants in each group (n = 10 per group) were supplemented with 6.4 g/day of BA for 28 days. After the third week, the BA + Cr group participants were also supplemented with Cr (0.3 g/kg/day), while the BA + PL group ingested an isocaloric placebo for 7 days. Before and after supplementation, each participant performed a battery of physical and cognitive tests and provided a venous blood sample to determine resting testosterone, cortisol, and IGF-1. Furthermore, immediately after the last physical test, blood lactate was assessed. There was a significant improvement in physical performance and mathematical processing in the BA + Cr group over time (p < 0.05), while there was no change in the BA + PL group. Vertical jump performance and testosterone were significantly higher in the BA + Cr group compared to BA + PL. These results indicate that Cr loading during the final week of BA supplementation (28 days) enhanced muscular power and appears to be superior for muscular strength and cognitive performance compared to BA supplementation alone.

Background: The aim of this study was to compare the effect of 12 weeks of high intensity interval training (HIIT) and continues training (CT) on SIRT3 protein level, FOXO3 gene expression, and mtDNA oxidative damage in gastrocnemius of female aged rats. Methods and Results: Female wistar rats (18 months, 250-300 g, n=36) were divided into three groups (HIIT, CT, control). Based on aerobic capacity determined using the ramp protocol, HIIT intensity corresponded to 85-90% and CT was 65-70% of VO2max. Rats trained three times per week for 12 weeks. Forty-eight hours after the last training session, rats were sacrificed and gastrocnemius muscle excised. Our results showed that both exercise protocol increased SIRT3 protein content and FOXO3 gene expression compared to control. However, no significant difference was observed between HIIT and CT. In addition, our data showed that MnSOD activity was significantly higher in HIIT compared to both CT and control and CT versus control. Finally, the level of 8-OHdg was significantly lower in HIIT and CT compered to control and there was no significant difference between HIIT and CT. Conclusion: Our results showed that 12 weeks of HIIT and CT increase SIRT3 protein content, improve antioxidant defense of aged female waster rats. Therfore, HIIT is a time efficient protocol for improving some aspects of mitochondrial function.