Testosterone rescues differentiation and hypertrophy in artificially aged skeletal muscle myoblasts

Authors: Deane, C., Hughes, D., Sculthorpe, N. and Sharples, A.

Conference: International Conference of Strength Training

Dates: 24-28 October 2012


INTRODUCTION Resistance exercise acutely elevates endogenous levels of circulating testosterone (Ratamess et al.2005), eliciting an anabolic effect, and leading to increases in muscle strength and fibre hypertrophy(Ahtiainen et al. 2011). However, with age, there is a gradual decline in serum testosterone levels,which correlates to wasting of skeletal muscle (sarcopenia) (Morales et al, 2010). Sarcopenia contributes to a reduction in muscle size, strength and lower regenerative potential (Serra et al. 2012).

The molecular mechanisms by which testosterone (T) contributes to skeletal muscle growth and regeneration remain poorly understood. Therefore, we investigated the effects of T on its ability to restore differentiation in skeletal muscle cells that had undergone multiple population doublings(MPD) and exhibit a degenerative ageing phenotype and reduced differentiation vs. parental controls (CON) (Sharples et al. 2011).

METHODS Monolayer cultures, of mouse C2C12 skeletal muscle cells with no population doublings (CON) were compared with cells that had undergone multiple population doublings (MPD (58 doublings)). Cells were exposed to a standard low serum conditions and treatment consisted of a vehicle control (DMSO)or testosterone treatment (100 nM) for 72 hrs and 7 days (early and late muscle differentiation respectively). For both time points, morphological analyses were performed to determine myotube width (μm) and myonuclear accretion as indices of myotube hypertrophy. Changes in gene expression for myogenin (marker of differentiation) and myostatin (negative regulator of hypertrophy) were also conducted. The experiment was performed in triplicate.

RESULTS Myotube width in CON cells increased from 17.32 ± 2.56 μm to 21.02±1.89μm (p<0.05) after T exposure. MPD cells also improved their myotube width after T treatment from 14.58±2.66μm to 18.29±3.08μm (p<0.05). Indeed, MPD cells responded with a similar increase (+25%) in myotube width to CON cells (+21%) suggesting a similar ability to respond to the exogenous T administration.

With 7 days exposure, T treatment increased the percentage of myotubes expressing 5+ nuclei in both CON cells (+30%) and MPD cells (+30%). After 72 hrs, myogenin mRNA expression significantly increased in both cell types when T was administered compared to non-treated controls (p<0.05). The expression of myostatin mRNA after 7 days was significantly reduced in MPD T-treated cells(p<0.05), yet remained unchanged in the CON cells.

DISCUSSION The present study supports testosterone’s role in myogenic differentiation but more importantly,shows the capacity to rescue differentiation in artificially aged/degenerative skeletal muscle myoblasts. The administration of T, may further enhance hypertrophy through the inhibition of myostatin (Braga et al. 2012), as observed in the current study after 7 days exposure. Interestingly, the extent of the increases in myotube width with a T-stimulus were similar in magnitude between CON and MPD, highlighting that perhaps between “young” and “old”, the regenerative potential in skeletal muscle cells may remain the same.

CONCLUSIONS This study provides initial data to further elucidate the mechanism of action of T in muscle wasting with age.

Source: Manual

Preferred by: Colleen Deane