Regular physical activity is well accepted as a key intervention for reducing the risk of chronic disease, including mobility disability, heart disease, type 2 diabetes, and several cancers (Hawley, 2004; Warburton et al., 2006). Acute sprint exercise is a time-efficient physical activity that improves cardiorespiratory fitness in younger and middle-aged adults (Willoughby et al., 2016), promotes favorable enhancement in insulin sensitivity (Richards et al., 2010), and has beneficial effects on the enhancement of cognitive abilities with increased neuroprotective factors (Kujach et al., 2019). The previous study has shown that acute sprint exercise provides equal to or superior health benefits compared with moderate-intensity continuous training, which will dramatically increase aerobic capacity, insulin sensitivity, and muscle capillarization (Cocks et al., 2016). Different from other exercise manners, acute sprint exercise is characterized by rapid glycogen degradation and large net ATP breakdown in muscle and is accompanied by the increased secretion of hormones such as insulin, catecholamines, and growth factor (Esbjörnsson-Liljedahl et al., 1985; Esbjörnsson et al., 2009). Gene signatures related to a turnover of skeletal muscle mass are upregulated after sprint exercise (Rundqvist et al., 2019). Although the beneficial effects of acute sprint exercise are well documented, the mechanisms behind how acute sprint exercise prevents disease and benefits health are less understood.

Skeletal muscles have the fourth largest number of sex differentially expressed genes across 29 human tissues, with more than 3,000 differentially expressed genes between male and female skeletal muscles at rest (Welle et al., 2008; Lopes-Ramos et al., 2020). Thus, differentially expressed genes may be the most important cause of sex differences in muscle morphology, function, and plasticity (Pointer et al., 2013). According to a previous study, men usually have significantly larger cross-sectional areas than women, especially in type II fibers (Miller et al., 1993). Conversely, women may be more resistant to muscle fatigue due to a higher proportion of type I fibers (Salomoni et al., 2008; Avin et al., 2010). Furthermore, men and women have sex-based differences in response to sprint interval training. It is reported that after six weeks of sprint interval training, insulin sensitivity was increased only in healthy men but not women (Metcalfe et al., 2012). Sprint interval training reduced 24-h blood glucose concentration in men but not women among adults with overweight (Gillen et al., 2014). Glucose transporter 4 (GLUT4), a key regulator of glucose metabolism in muscle, is higher increased in men compared with women in response to sprint interval training. In summary, previous studies indicate that men showed stronger adaptative responses to sprint interval training than women. However, the mechanism underlying sex-based differences in skeletal muscle remodeling and metabolism in response to acute sprint exercise is still unclear. To the best of our knowledge, the difference of global gene expression in skeletal muscle between men and women in response to once acute sprint exercise (three bouts of 30-s sprint exercise with 20-min rest) has not been previously demonstrated.

In this study, we focused on the response to acute sprint exercise, not long-term adaptation exercise training, to increase the understanding of the transcriptomic difference of skeletal muscle in response to acute sprint exercise between men and women. First, we obtained differentially expressed genes in muscle from men and women before and after an acute sprint exercise. Then, we identified hub genes from the protein–protein interaction (PPI) network of DEGs in men and women related to acute sprint exercise. Finally, KEGG and GO enrichment analyses were performed on DEGs and sex-biased genes, respectively. Our study shed light on the understanding of how the health benefits of acute sprint exercise are regulated in men and women. In addition, our results may also indicate the mechanism underlying sex-based differences in skeletal muscle remodeling and metabolism related to acute sprint exercise.

Acute sprint exercise induces numerous adaptations in the body resulting in beneficial effects on health, which may induce fat loss, increase cognitive functions, improve cardiorespiratory fitness, and alleviate metabolic syndrome (Gibala et al., 2006; Vollaard and Metcalfe, 2017; Kujach et al., 2019). Although the effects of sprint exercise-induced adaptations to skeletal muscle have been well-established in various diseases, the difference of global gene expression in skeletal muscle in men and women in response to acute bouts of acute sprint exercise has not been previously demonstrated. In this study, we conducted an analysis of gene expression profiles obtained from muscle biopsies collected from human volunteers before and after acute bouts of acute sprint exercise to discover exercise-related sexually dimorphic genes, which might be part of the mechanism underlying the sex-based differences in skeletal muscle remodeling and metabolism in response to acute sprint exercise.

RNA-seq results show that about 3,000 genes of human in skeletal muscle at rest are identified as differentially expressed genes (Lindholm et al., 2014). However, the sex-specific epigenomic signatures of immediate early genes in response to acute sprint exercise are still unknown. We performed differentially expressed gene analysis to explore the difference in gene expression between men and women in response to acute sprint exercise. A total of 234 genes (192 upregulated and 42 downregulated) in men were identified as differentially expressed genes using bioinformatics analysis, while only 182 differentially expressed genes were identified in women, containing 157 upregulated and 25 downregulated genes. The number of differentially expressed genes in men is dramatically greater than that in women. This result may account for the fact that men have a stronger adaptative response to sprint interval training than women. Cytokine-inducible SH2-containing protein (CISH), known as cytokine-induced STAT inhibitor, is the top upregulated gene in males. A recent study showed that CISH may play an important role in promoting free fatty acid mobilization (Vestergaard et al., 2014; Vendelbo et al., 2015). Our data also suggest that the expression of CISH may be also regulated by sex hormones. After acute sprint exercise, OTUD1 is the top fold-change gene in females. Although previous independent studies showed that OTUD1 was significantly induced by acute sprint exercise, its function related to acute sprint exercise was still unknown (Bolotta et al., 2020). Furthermore, we identified ZNF217 and CLOCK as the top significant enrichment transcription factors in men-biased genes. CLOCK is necessary for the maintenance of the skeletal muscle phenotype and function through regulating MyoD. Skeletal muscles from mice with mutation of Clock and Bmal1 exhibit ∼30% reductions in normalized maximal force (Andrews et al., 2010). Our result is consistent with previous research that CLOCK is a key regulator of muscle fibers, which may be one of the reasons inducing the difference in muscle type between men and women. However, LXR and SOX2 are the top significant enrichment transcription factors in women. LXRβ is the dominant LXR subtype in skeletal muscle regulating lipogenesis and cholesterol efflux (Hessvik et al., 2010). This result indicates that transcription factors induced by acute sprint are different between men and women. Since the biological function of ZNF217 and SOX2 in skeletal muscle is still unclear, we can only speculate that interference of these two factors may play a role in muscle groups of different fiber type composition or metabolism in men or women, respectively.

Our study also showed that men and women shared several GO and KEGG pathways in response to acute sprint exercise. The significantly enriched GO terms for DEGs in men and women can be categorized into several biological functional groups including positive regulation of transcription, cellular response to starvation, and positive regulation of nucleic acid-templated transcription. These results indicate that acute sprint exercise promoted cell proliferation in muscle both in men and women, which is consistent with the previous study (Pearson, 1990; Bazgir et al., 2017; Saito et al., 2020). Moreover, DEGs in men and women significantly enrich a list of KEGG pathways relevant to the MAPK signaling pathway, mTOR signaling pathway, and AGE-RAGE signaling pathway. The AKT/mTOR signaling pathway played an important role in regulating muscle hypertrophy (Bodine et al., 2001). Similar to AKT/mTOR signaling, MAPK also promoted improvements in fuel homeostasis and could prevent skeletal muscle atrophy (Kramer and Goodyear, 1985). What is more, emerging evidence shows that RAGE signaling pathway is critical for skeletal muscle physiology controlling both the activity of muscle precursors during skeletal muscle development and the correct time of muscle regeneration after acute injury (Riuzzi et al., 2018). These data may implicate a mechanism behind muscle growth both in men and women.

Exercise training is associated with profound changes in skeletal muscle, including increased abundance of glucose up-take, activation of AMPK, and mitochondrial biogenesis (Egan and Zierath, 2013). Our results also provide novel insights into the difference in the pathway between men and women in response to acute sprint. Compared with women-biased genes, the enrichment pathways of men-biased genes are mainly about response to starvation or amino acid starvation (GO: cellular response to amino acid starvation). Men always consume more energy than women. Higher enrichment of these pathways may support an increased rate of energy consumption in men. Therefore, men are more urgent to face the “insufficient energy” situation. However, there is a tendency for women to restore the calcium and zinc homeostasis (GO: cellular response to cadmium ion). These results indicate acute sprint may induce a more severe disturbance of ion homeostasis in cellular processes. Moreover, our study also identified novel sex-specific areas, such as cellular response to cadmium ion, that exist in the fine regulatory system of the muscle response to acute sprint exercise at the transcriptional level which merit further exploration. It is well known that gender differences exist in skeletal muscle mass and distribution (Janssen et al., 1985). Females often have less total and lean body mass, a higher body fat percentage, and a smaller muscle fiber cross-sectional area (Staron et al., 1985). KEGG analysis showed that the JAK-STAT signaling pathway is dramatically enriched in the men-biased genes, not in women. The JAK/STAT pathway participates in lipid metabolism in muscle. Activation of the JAK/STAT pathway in skeletal muscle promotes muscle hypertrophy by increasing the proliferation of satellite cells (Moresi et al., 2019). These results indicate that the JAK-STAT pathway may account for gender differences in muscle fiber-type distribution and substrate metabolism in men and women. These findings may also help us to understand how sex differences manifest in gene regulatory networks in muscle.

Sample size significantly affects DEG analysis output in microarray datasets, and more biological samples predict more accurate outcomes (Stretch et al., 2013). The gene expression profile we analyzed is from previously published literature. In the original study, Rundqvist et al. (2019) expressed reservations about the identification of sexually dimorphic changes due to the small sample size. As described in the method, we downloaded the expression profile of muscle from the original dataset including seven males and seven females before and after acute sprint exercise. Then, we identified the differentially expressed genes using the “limma” package. The screening threshold used in this study was FDR<0.05 and |log2 (fold change)| > 0.3. Through this manner, we identified a total of 234 DEGs in men and 182 DEGs in women. We believe that the biological number in our study (7 vs. 7) is sufficient to get the significant DEGs to a certain extent. We also believe that more samples included will increase the statistical power and further improve the conclusion in the future.

This study needs to be improved in the future for the following reasons: first, the protein level of differentially expressed genes remains to be confirmed. Second, further studies are required to understand the role of sex-biased genes in response to acute sprint exercise. Third, even if the health benefits brought by sprint exercise are similar to those of endurance training, it also should be mentioned that acute response to exercise is not always similar to the long-term adaptation exercise training.

In this study, we found sex-biased genes and their related potential key pathways in muscle in response to acute sprint exercise. Thus, these results will shed new light on the mechanism underlying sex-based differences in skeletal muscle remodeling and metabolism related to sprint interval training, which may also illustrate the mechanisms behind how acute sprint exercise prevents disease and benefits health.