Myostatin as a mediator of sarcopenia versus homeostatic regulator of muscle mass: insights using a new mass spectrometry-based assay

Abstract

Background: Myostatin is a protein synthesized and secreted by skeletal muscle that negatively regulates muscle mass. The extent to which circulating myostatin levels change in the context of aging is controversial, largely due to methodological barriers.

Methods: We developed a specific and sensitive liquid chromatography with tandem mass spectrometry (LC-MS/MS) assay to measure concentrations of myostatin and two of its key inhibitors, follistatin-related gene (FLRG) protein and growth and serum protein-1 (GASP-1) in 80 younger (<40 years), 80 older (>65 years), and 80 sarcopenic older women and men.

Results: Older women had 34 % higher circulating concentrations of myostatin than younger women. Per unit of lean mass, both older and sarcopenic older women had >23 % higher myostatin levels than younger women. By contrast, younger men had higher myostatin concentrations than older men with and without sarcopenia. Younger men had approximately twofold higher concentrations of myostatin than younger women; however, older women and sarcopenic older women had significantly higher relative myostatin levels than the corresponding groups of men. In both sexes, sarcopenic older subjects had the highest concentrations of FLRG. Circulating concentrations of myostatin exhibited positive, but not robust, correlations with relative muscle mass in both sexes.

Conclusions: Our data suggest that myostatin may contribute to the higher prevalence of sarcopenia in women but acts as a homeostatic regulator of muscle mass in men. Moreover, this new LC-MS/MS-based approach offers a means to determine the extent to which myostatin serves as a biomarker of muscle health in diverse conditions of muscle loss and deterioration.

Keywords: Aging; Body composition; Myostatin; Sarcopenia; Skeletal muscle mass; Strength.

Fig. 1

Calibration curves for LC-MS/MS measures of myostatin, propeptide, GASP-1, and FLRG. Linear calibration curves for recombinant intact myostatin (a), propeptide (b), GASP-1 (c), and FLRG (d) diluted into bovine serum albumin over a concentration range of 0.031 to 1.00 nM

Fig. 2

Circulating myostatin and propeptide levels by LC-MS/MS in younger and older women and men. Box plots (25–75 percentile) and whiskers (Tukey method) comparing serum concentrations of a myostatin, b myostatin relative to total body lean mass (TBLM), c propeptide, and d propeptide relative to TBLM between younger women (YW), older women (OW), and sarcopenic older women (SOW). Comparisons of circulating concentrations of absolute and relative concentrations of myostatin and propeptide between corresponding groups of men are also illustrated (e-h). *, **, and *** denote p < 0.05, 0.01, and 0.001, respectively, compared to the younger group except when denoted with a bracket

Fig. 3

Circulating FLRG and GASP-1 concentrations by LC-MS/MS in younger and older women and men. Box plots (25–75 percentile) and whiskers (Tukey method) showing comparisons of a FLRG, b GASP-1, c FLRG relative to myostatin, and d GASP-1 relative to myostatin between younger women (YW), older women (OW) and sarcopenic older women (SOW). Comparisons of myostatin inhibitors and their ratios to myostatin between corresponding groups of men are also illustrated (e-h). *, **, and *** denote p < 0.05, 0.01, and 0.001, respectively, compared to the younger group except when denoted with a bracket

Fig. 4

Circulating myostatin and propeptide levels in women compared to men. Box plots (25–75 percentile) and whiskers (Tukey method) showing comparisons of a myostatin, b myostatin relative to total body lean mass (TBLM), c propeptide, and d propeptide relative to TBLM between younger women (YW) and younger men (YM) (top panel), older women (OW) and older men (OM) (middle panel), and sarcopenic OW (SOW) and sarcopenic OM (SOM) (bottom panel). * and *** denote p < 0.05 and 0.001, respectively

Fig. 5

Circulating FLRG and GASP-1 concentrations in women compared to men. Box plots (25–75 percentile) and whiskers (Tukey method) showing comparisons of a FLRG, b GASP-1, c FLRG relative to myostatin, and d GASP-1 relative to myostatin between younger women (YW) and younger men (YM) (top panel), older women (OW) and older men (OM) (middle panel), and sarcopenic OW (SOW) and sarcopenic OM (SOM) (bottom panel). *** denotes p < 0.001