Does skeletal muscle have a memory of testosterone?

Abstract

Recent evidence has shown that skeletal muscle tissue exhibits a memory of a range of stimuli, enhancing the response to the stimuli if it has been previously encountered. Some evidence suggests such a muscle memory exists for the anabolic hormone testosterone, with potential implications for both therapeutic interventions and anti-doping policies. The aim of this study was to examine whether an early-life exposure to testosterone could mitigate the age-related decline in skeletal muscle cell physiology, and whether it could enhance the response to a later exercise-like stimuli. To achieve this, C2C12 cells were used to make three sub-populations of cells, cultured into 3D-bioengineered fibrin muscle-constructs: control cells (CC) which were cells at a low passage number, population doubled cells (PD) that had undergone 30 population doublings relative to CC, and population doubled + testosterone cells (PDT) that were first treated with testosterone before undergoing 30 population doublings relative to CC. These cell populations were cultured for 8 days, before being subjected to an acute bout of mechanical stretch as the later anabolic stimulus. The population doublings proved effective in inducing an aged phenotype, with reductions in myotube number, area, and nuclei per myotube. The early testosterone could not mitigate these changes, but did lead to larger myonuclear domain sizes compared to both CC and PD cells alone. Basal gene expression of several genes related to growth, differentiation, and NAD+ metabolism was reduced by the population doublings, with the early testosterone administration unable to alleviate this effect. The mechanical stretch was unable to induce a gene expression response previously associated with exercise mimicking stimuli, therefore a potential enhanced response to stretch caused by an earlier testosterone encounter could not be directly examined. Despite this, the gene NR4A2 demonstrated increased expression in response to mechanical stress only in cells that had encountered an earlier testosterone treatment, and was therefore identified as a potential memory gene that should be further examined. In conclusion, whether skeletal muscle has a memory of testosterone remains unknown. However, an encounter with testosterone did increase the myonuclear domain size in myotubes long after its initial exposure.