Progressive resistance‐loaded voluntary wheel running increases hypertrophy and differentially affects muscle protein synthesis, ribosome biogenesis, and proteolytic markers in rat muscle

Abstract

Funding informationDiscretionary laboratory funds from JMW were provided to MDR as a subcontract to complete perform rat training studies. Laboratory start-up funds were also used by MDR to perform RNA and Western blotting analyses. SummaryWe examined if 6 weeks of progressive resistance-loaded voluntary wheel running in rats induced plantaris, soleus, and/or gastrocnemius hypertrophy and/or affected markers of translational efficiency, ribosome biogenesis, and markers of proteolysis. For 6 weeks, 8 male Sprague-Dawley rats (~9-10 weeks of age, ~300-325 g) rats were assigned to the progressive resistance-loaded voluntary wheel running model (EX), and ten rats were not trained (SED). For EX rats, the wheel-loading paradigm was as follows -days 1-7: free-wheel resistance, days 8-15: wheel resistance set to 20%-25% body mass, days 16-24: 40% body mass, days 25-32: 60% body mass, days 33-42: 40% body mass. Following the intervention, muscles were analysed for markers of translational efficiency, ribosome biogenesis, and muscle proteolysis. Raw gastrocnemius mass (+13%, p < .01), relative (body mass-corrected) gastrocnemius mass (+16%, p < .001), raw plantaris mass (+13%, p < .05), and relative plantaris mass (+15%, p < .01) were greater in EX vs. SED rats. In spite of gastrocnemius hypertrophy, EX animals presented a 54% decrease in basal muscle protein synthesis levels (p < .01), a 125% increase in pan 4EBP1 levels (p < .001) and a 31% decrease in pan eIF4E levels (p < .05).However, in relation to SED animals, EX animals presented a 70% increase in gastrocnemius c-Myc protein levels (p < .05). Most markers of translational efficiency and ribosome biogenesis were not altered in the plantaris or soleus muscles of EX vs. SED animals. Gastrocnemius F-box protein 32 and poly-ubiquinated protein levels were approximately 150% and 200% greater in SED vs. EX rats (p < .001). These data suggest that the employed resistance training model increases hind limb muscle hypertrophy, and this may be mainly facilitated through reductions in skeletal muscle proteolysis, rather than alterations in ribosome biogenesis or translational efficiency. K E Y W O R D Sproteolysis, resisted wheel running, ribosome biogenesis, skeletal muscle hypertrophy, translational efficiency 318 | MOBLEY Et aL. | INTRODUCTIONThere is a current research emphasis on how hypertrophic overload or exercise models in rodents and humans affect markers of translational efficiency and/or ribosome biogenesis. Briefly, ribosomes catalyse muscle protein synthesis (MPS) in muscle fibres, and ribosome biogenesis involves the formation of new ribosomes through the coordinated expression of ribosomal RNA (rRNA) and ribosomal proteins as well as the intricate process of rRNA processing, ribosome assembly and ribosome export (Chaillou, Kirby, & McCarthy, 2014). Acute resistance exercise bouts increase MPS in humans and rodents (Kubica, Bolster, Farrell, Kimball, & Jefferson, 2005;Phillips, Tipton, Aarsland, Wolf, & Wolfe, 1997). Likewise, acute resistance exercise bouts in...

Physiological Differences Between Low Versus High Skeletal Muscle Hypertrophic Responders to Resistance Exercise Training: Current Perspectives and Future Research Directions

“…In rats, recent evidence suggests the degree of synergist ablation-induced plantaris hypertrophy parallels proportional increases in ribosome content ( Nakada et al, 2016 ). Our laboratory ( Mobley et al, 2016 , 2018b ; Roberts et al, 2016 ) and others ( West et al, 2016 ; Brook et al, 2017 ) have also reported that acute and chronic resistance exercise training models in rats increase indices of ribosome biogenesis and ribosome content, respectively.…”

“…While mTORC1 is the hub that regulates MPS, there are multiple systems that regulate skeletal muscle proteolysis including ( Pasiakos and Carbone, 2014 ; Tipton et al, 2018 ): (a) the calcium-dependent calpain system which liberates myofibrillar proteins from sarcomeric Z-lines, (b) the autophagy-lysosomal system which degrades cellular organelles as well as myofibrillar proteins, (c) the caspase system which cleaves myofibrillar proteins into smaller fragments, and (d) the ubiquitin-proteasome system (UPS) which uses E1/E2/E3 enzymes to poly-ubiquinate myofibril fragments and degrade these proteins into individual amino acids via the 26S proteasome. Proteolysis rates are likely influenced by a combination of these systems, and several human and rodent studies have reported biomarkers in each system are dynamically altered in response to acute and chronic resistance exercise training ( Louis et al, 2007 ; Kerksick et al, 2010 , 2013 ; Dalbo et al, 2013 ; Kwon et al, 2015 ; Stefanetti et al, 2015 ; Mobley et al, 2018b ). Interestingly, rodent and in vitro studies have also demonstrated that inhibiting autophagy and UPS reduces skeletal muscle mass ( Masiero and Sandri, 2010 ) and promotes myotube atrophy ( Chandler et al, 2017 ), respectively, which suggests proteolytic mechanisms are seemingly obligatory for muscle mass maintenance.…”

Voluntary Resistance Running as a Model to Induce mTOR Activation in Mouse Skeletal Muscle

“…Numerous studies showed increased muscle mass after resistance running in mice. It has been reported that muscle mass is increased in the PLT (Legerlotz et al, 2008; Holland et al, 2016; Mobley et al, 2018), SOL (Konhilas et al, 2005; Legerlotz et al, 2008; Call et al, 2010; White et al, 2016), GAS (Mobley et al, 2018), m. quadriceps (Soffe et al, 2016), and TRI (Call et al, 2010) after long term (>4 weeks) resistance running. Our findings provide evidence of a potential molecular basis for the above findings as we report increased mTORC1 activation after one night of resistance running in the aforementioned muscles.…”

“…Therefore, as mouse handling and stress is minimal, the running wheel is considered an excellent model of physiological training with similar muscular adaptations as other well-accepted models such as synergistic ablation and electrical stimulation. Indeed, many groups have shown that voluntary resistance running leads to muscular hypertrophy in rodents (Legerlotz et al, 2008; Call et al, 2010; White et al, 2016; Mobley et al, 2018).…”

Voluntary running influences the efficacy of fluoxetine in a model of postpartum depression

“…Notably, another possible explanation is that exercise increased overall cardiovascular and muscular fitness or reduced adipose tissue, rendering exercise dams more adept than sedentary dams in active coping behavior in FST2. Although these factors have not been explicitly studied in forced swim test, voluntary running in rats is beneficial for cardiovascular and skeletal muscle health (Pósa et al, 2015;Mobley et al, 2017) which may ultimately contribute to forced swim test performance. However, using body mass as a covariate still resulted in the main effect of exercise to reduce immobility in the FLX.…”