Consecutive bouts of electrical stimulation-induced contractions alter ribosome biogenesis in rat skeletal muscle

Abstract

Ribosome biogenesis has been implicated in resistance exercise training (RET)-induced skeletal muscle hypertrophy. However, it is unclear how increasing bouts of RET affects ribosome content and biogenesis. This was investigated in the present study using simulated RET where rat skeletal muscle is subjected to increasing bouts of electrical stimulation. Sprague-Dawley rats were randomly assigned to the following seven groups: sedentary for 5 days (SED) or 6 wk (SED_6w), resistance-exercise trained with 1 bout (1B), 2 bouts (2B), 3 bouts (3B), 6 bouts (6B), and 18 bouts (18B). RET was simulated on the right gastrocnemius muscle by transcutaneous electric stimulation under isoflurane anesthesia, and a RET bout was given 3 times a week. Rats in 1B, 2B, and 3B groups showed increased 45S precursor (pre-) rRNA and 18S+28S rRNA content per muscle weight and elevated mRNA levels of c- myc and upstream binding factor (UBF). Increases in phosphorylated UBF and total cyclin D1 protein level were observed 48 h after RET; the former increased as a function of RET duration. In 3B, 6B, and 18B groups, the 18S+28S rRNA content per muscle weight was kept unchanged, and 45S pre-rRNA, cyclin D1, and phosphorylated UBF levels in 18B were lower than those in 3B. These results suggest that RET activates ribosome biogenesis and increases ribosome content through modulation of UBF and cyclin D1 activity at its early phase. Additional bouts of RET may not lead to a further increase in ribosome content per muscle weight through possibly the attenuation of transcription process. NEW & NOTEWORTHY Ribosome biogenesis has been implicated in resistance exercise training-induced skeletal muscle hypertrophy. However, it remains unclear how this is influenced by the volume of repeated bouts of resistance exercise training. Using resistance exercise training model with rat skeletal muscle, we provide evidence that ribosome biogenesis is stimulated by the initial few bouts of resistance exercise training with no additional effect of further increase in the exercise bout.

Effect of resistance training on rat skeletal muscle during severe food restriction

“…Thus, activity of p70S6K might only be upregulated in the C group. In a recent study, three sessions of RE were reported to significantly increase the expression of rpS6 by 50% in the exercised leg compared to that in the sedentary leg, 18 which agrees with our results in the C group. However, in the FR group, the expression of total rpS6 did not increase with the three sessions of RE.…”

The effect of repeated bouts of electrical stimulation‐induced muscle contractions on proteolytic signaling in rat skeletal muscle

“…The RE protocol was carried out as previously described (Kotani et al, 2019). Briefly, with rats under 3.5%–4.0% isoflurane deep sedation, we shaved the hair on the right leg of each rat off, and then the rat was secured by its right foot on a footplate in the prone posture.…”

“…The voltage (~30 V) and stimulation frequency (100 Hz) were adjusted to evoke maximal isometric contraction (Ogasawara et al, 2014). The frequency of RE bouts was every other day (48 h between bouts) in the 2B and 3B groups because previous studies showed that this frequency induces muscle hypertrophy in greater than or equal to12B (Kotani et al, 2019; Ogasawara et al, 2014, 2016).…”

“…Western blot analysis was performed as reported previously (Kotani et al, 2019). Briefly, frozen muscle samples were homogenized in a RIPA buffer with a protease and phosphatase inhibitor cocktail (catalog no.…”

“…Our group created a rat RE model with electrical stimulation‐induced muscle contraction and reported that repeated bouts of RE of every other day or three times a week induce muscle hypertrophy (Kotani et al, 2019; Ogasawara et al, 2013, 2014). Using this RE model with rat skeletal muscle, we examined the effects of repeated RE bouts on the acute proteolytic signaling responses involved in both the autophagy–lysosome and ubiquitin–proteasome systems to obtain an insight into the proteolytic response with repeated bouts of RE.…”