Kenji Matsutani

The order of concurrent endurance and resistance exercise modifies mTOR signaling and protein synthesis in rat skeletal muscle

Concurrent training, a combination of endurance (EE) and resistance exercise (RE) performed in succession, may compromise the muscle hypertrophic adaptations induced by RE alone. However, little is known about the molecular signaling interactions underlying the changes in skeletal muscle adaptation during concurrent training. Here, we used an animal model to investigate whether EE before or after RE affects the molecular signaling associated with muscle protein synthesis, specifically the interaction between RE-induced mammalian target of rapamycin complex 1 (mTORC1) signaling and EE-induced AMP-activated protein kinase (AMPK) signaling. Male Sprague-Dawley rats were divided into five groups: an EE group (treadmill, 25 m/min, 60 min), an RE group (maximum isometric contraction via percutaneous electrical stimulation for 3 × 10 s, 5 sets), an EE before RE group, an EE after RE group, and a nonexercise control group. Phosphorylation of p70S6K, a marker of mTORC1 activity, was significantly increased 3 h after RE in both the EE before RE and EE after RE groups, but the increase was smaller in latter. Furthermore, protein synthesis was greatly increased 6 h after RE in the EE before RE group. Increases in the phosphorylation of AMPK and Raptor were observed only in the EE after RE group. Akt and mTOR phosphorylation were increased in both groups, with no between-group differences. Our results suggest that the last bout of exercise dictates the molecular responses and that mTORC1 signaling induced by any prior bout of RE may be downregulated by a subsequent bout of EE.

Resistance training restores muscle sex steroid hormone steroidogenesis in older men

Skeletal muscle can synthesize testosterone and 5α‐dihydrotestosterone (DHT) from dehydro‐epiandrosterone (DHEA) via steroidogenic enzymes in vitro, but hormone levels and steroidogenic enzyme expression decline with aging. Resistance exercise has been shown to increase in plasma sex steroid hormone levels. However, it remains unclear whether resistance training can restore impaired steroidogenic enzyme expressions in older individuals. Six young and 13 older men were recruited, and muscle biopsies were taken from the vastus lateralis at basal state. The same group of older subjects underwent resistance training involving knee extension and flexion exercises for 12 wk, and post‐training biopsies were performed 4–5 d after the last exercise session. Muscular sex steroid hormone levels and sex steroidgenesis‐related enzyme expressions were significantly lower in older subjects than younger ones at baseline, but 12 wk of resistance training significantly restored hormone levels (DHEA: 432±26 at baseline, 682±31 pg/μg protein, DHT: 6.2±0.9 at baseline, 9.8±1.4 pg/μg protein). Furthermore, the steroidogenesis‐related enzymes such as 3β‐hydroxysteroid dehydrogenase (HSD), 17β‐HSD, and 5α‐reductase expressions were significantly restored by resistance training. We conclude progressive resistance training restores age‐related declines in sex steroidogenic enzyme and muscle sex steroid hormone levels in older men.—Sato, K., Iemitsu, M., Matsutani, K., Kurihara, T., Hamaoka, T., Fujita, S. Resistance training restores muscle sex steroid hormone steroidogenesis in older men. FASEB J. 28, 1891–1897 (2014). www.fasebj.org

Serum C1q as a novel biomarker of sarcopenia in older adults

Aging‐induced elevation in C1q secretion activates the Wnt signaling pathway in muscles, leading to the development of muscle fibrosis. However, the association between serum C1q level and muscle mass and strength remains unclear in humans. The aim of the study was to elucidate whether serum C1q level is associated with aging‐ and resistance training‐induced changes in muscle mass and strength. First, in a cross‐sectional study, we investigated the association between serum C1q level and muscle mass and strength in 131 healthy subjects, aged 20‐81 yr. Second, in an intervention study, we examined the association between the effects of serum C1q level and muscle mass and strength on 12 wk resistance training in 11 healthy older adults (60‐81 yr). In the cross‐sectional study, serum C1q level increased with aging and was negatively correlated with muscle mass and strength. Furthermore, 12 wk resistance training in older adults reduced the age‐associated elevation in serum C1q levels. The training effect of serum C1q level significantly correlated with the change in the cross‐sectional area of the thigh (r = – 0.703; P < 0.01). Serum C1q level may reflect loss of muscle mass; therefore, C1q may be a novel biomarker of sarcopenia.—Watanabe, S., Sato, K., Hasegawa, N., Kurihara, T., Matsutani, K., Sanada, K., Hamaoka, T., Fujita, S., Iemitsu, M., Serum C1q as a novel biomarker of sarcopenia in older adults. FASEB J. 29, 1003–1010 (2015). www.fasebj.org