Basic nutritional investigationWhey protein modifies gene expression related to protein metabolism affecting muscle weight in resistance-exercised rats
Introduction
Regular resistance exercise (RE), such as weightlifting, in combination with adequate protein consumption, efficiently stimulates muscle growth, which results from a cumulative increase in muscle protein synthesis, a decrease in muscle protein degradation, or a combination of the two. The rate of protein synthesis is mediated by the activation of a cellular network of signaling pathways involving the mammalian target of rapamycin (mTOR), a central serine/threonine kinase that integrates several different upstream and downstream signals that regulate mRNA translation [1], [2]. Muscle protein degradation is mediated primarily (80%–90%) by the ubiquitin proteasome system (UPS) [3], which includes the following three components that participate in ubiquitin transfer reactions: Ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin ligases (E3). E3 ligases, particularly muscle atrophy F-box (MAFbx) and muscle-specific RING finger-1 (MuRF-1), are key enzymes mediating muscle protein loss and are overexpressed in numerous catabolic conditions [4], [5].
The phosphorylation of mTOR can be enhanced by amino acids and proteins, especially those with high leucine content [2], [6]. Therefore, whey protein (WP) deserves special attention because it is present in a variety of sports supplements, and several benefits of WP for athletes have been reported [7], [8]. WP induces mTOR phosphorylation to a greater extent than other protein sources, such as soy, in treadmill-exercised rats [9] and prolongs mTOR signaling in response to RE in humans [10]. However, the effects of RE in combination with WP ingestion on mTOR gene expression are not well known.
Conflicting data have been reported on the effects of RE on the E3 ligases, MAFbx, and MuRF-1. Overexpression of E3 ligases mRNA was observed after a single RE session [11], [12], whereas other studies reported different effects of chronic RE on MuRF-1 and MAFbx mRNA expression [3], [13]. Additionally, the effects of combined RE and WP ingestion on MAFbx and MuRF-1 mRNA expression are less clear. We hypothesize that RE in combination with WP ingestion might alter the gene expression of proteins related to muscle protein synthesis and/or degradation in rats and thus affect muscle weight gain.
Therefore, this study aimed to evaluate the mRNA expression of mTOR, MAFbx, and MuRF-1 in rats subjected to a RE protocol for 8 wk. Additionally, we evaluated the effects of WP on RE-induced gene expression and how these adaptations affect body and muscle weight gain.
Section snippets
Animals and groups
Thirty-two male Fischer rats (60 d old) weighing approximately 110 g were used in the experiment. The animals were housed individually in galvanized wire metabolic cages in a room with controlled temperature (23 ± 1°C), relative humidity (55 ± 10%), and a 12-h light/dark cycle. The animals received care in accordance with the guidelines of the Canadian Council on Animal Care. Rats were randomly distributed into four experimental groups (n = 8/group) as follows: Control sedentary (CS) control
Body weight gain and muscle weights
Body weight gain and gastrocnemius and EDL muscle weights were similar in all groups except for CE rats, which exhibited the lowest values. Although WE rats exhibited body and muscle weights similar to those of the CS and WS rats, these values were higher than those observed in CE rats (Table 3).
Food intake and feeding efficiency
During the experiment, food intake was slightly lower in exercised rats compared with sedentary rats and was not modified by WP ingestion. Additionally, WP ingestion promoted better feeding efficiency (
Discussion
The present study evaluated the influence of RE alone or in combination with WP ingestion on the gene expression of proteins related to muscle protein synthesis (mTOR) and degradation (MuRF-1 and MAFbx) and aimed to determine how these adaptations affect body and muscle weight gain in rats. WP ingestion prevented the reduction of mTOR mRNA expression induced by RE and significantly reduced the expression of MAFbx mRNA in sedentary and resistance-exercised rats. As a result, rats exhibited
Conclusion
In this study, we demonstrated that WE rats exhibited higher body and muscle weights gains compared with CE rats after 8 wk. The reduction of MAFbx mRNA transcription induced by WP ingestion and the interaction between RE and WP in mTOR mRNA expression contributed significantly to these differences.
Acknowledgments
The authors acknowledge Probiotica Produtos Naturais Ltda (São Paulo, Brazil) for donating the whey protein and for providing its aminogram.
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This study was supported by the Federal University of Ouro Preto (UFOP, Minas Gerais, Brazil), the Fundação de Amparo à Pesquisa de Minas Gerais (FAPEMIG, Minas Gerais Research Support Foundation), and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, National Council for Scientific and Technological Development).
FKH was responsible for generation, collection, assembly, analysis, and interpretation of the data; drafting of the manuscript. CLdeBM was responsible for analysis and interpretation of the data. LXN was responsible for generation, collection, assembly, and analysis of the data. RCdosS was responsible for drafting and revision of the manuscript. MLP was responsible for study conception and design; data interpretation; and manuscript revision. MES was responsible for study conception and design; generation, collection, assembly, analysis, and interpretation of the data; and manuscript revision. All authors approved the final version of the manuscript.
The authors report no conflicts of interest.