# Sex Differences in Human Myogenesis Following Testosterone Exposure

## TL;DR

This study explores how testosterone affects muscle cell growth and metabolism differently in male and female cells.

## Contribution

The study identifies sex-specific molecular pathways activated by testosterone in human skeletal muscle cells.

## Key findings

- Testosterone activates the MAPK pathway in 46XX cells and the PI3K/AKT pathway in 46XY cells.
- Testosterone increases MYF6, IGF-I, and CXCL1 in 46XX cells but GM-CSF and CXCL1 in 46XY cells.
- Sex differences in myokine release and metabolic pathway activation were observed after testosterone exposure.

## Abstract

Sex steroids refer to several hormones such as testosterone, estrogen, and derivatives thereof, which are released mainly by the gonads (testes and ovaries), influencing the formation of primary and secondary sexual characteristics. However, these hormones can also influence the activity of other tissues; in particular, skeletal muscle is one of the main tissue targets of testosterone action. However, the cellular effects of these molecules are different in male and female tissues, although the molecular processes involved in these differences are not fully understood. The aim of this study is to elucidate some of the molecular processes involved in muscle growth and metabolism that may be different in male and female skeletal muscle cells. The importance of characterizing these processes is fundamental to improving clinical approaches and making gender medicine more specific.

Previous research has demonstrated sex-specific differences in muscle cells regarding sex hormone release and steroidogenic enzyme expression after testosterone exposure. The present study aims to elucidate sex-related differences in intracellular processes involved in myogenesis and regeneration. Neonatal 46XX and 46XY human primary skeletal muscle cells were treated with increasing doses of testosterone (0.5, 2, 5, 10, 32, and 100 nM) for 24 h. The molecular pathways involved in muscle metabolism and growth, as well as the release of myokines involved in satellite cell activation, were analyzed using western blot, real-time PCR, and a Luminex assay. The unpaired Student’s t-test and one-way ANOVA for repeated measures were used to determine significant variations within and between groups. An increase in the expression and release of MYF6, IGF-I, IGF-II, and CXCL1, as well as a decrease in GM-CSF, IL-9, and IL-12, was observed in 46XX cells. Conversely, testosterone up-regulated GM-CSF and CXCL1 in 46XY cells but did not affect the release of the other myokines. Preferential activation of the MAPK pathway was observed in 46XX cells, while the PI3K/AKT pathway was preferentially activated in 46XY cells. In conclusion, our findings demonstrate differential responses to androgen exposure in 46XX and 46XY cells, resulting in the activation of muscle cell growth and energy metabolic pathways in a sex-specific manner.