decorin is an example of a proteoglycan which functions as a myokine. kanzleiter et al have established that this myokine is secreted during muscular contraction against resistance, and plays a role in muscle growth. they reported on july 1, 2014: "the small leucine-rich proteoglycan decorin has been described as a myokine for some time. however, its regulation and impact on skeletal muscle (had) not been investigated in detail. in (our recent) study, we report decorin to be differentially expressed and released in response to muscle contraction using different approaches. decorin is released from contracting human myotubes, and circulating decorin levels are increased in response to acute resistance exercise in humans. moreover, decorin expression in skeletal muscle is increased in humans and mice after chronic training. because decorin directly binds myostatin, a potent inhibitor of muscle growth, we investigated a potential function of decorin in the regulation of skeletal muscle growth. in vivo overexpression of decorin in murine skeletal muscle promoted expression of the pro-myogenic factor mighty, which is negatively regulated by myostatin. we also found myod1 and follistatin to be increased in response to decorin overexpression. moreover, muscle-specific ubiquitin ligases atrogin1 and murf1, which are involved in atrophic pathways, were reduced by decorin overexpression. in summary, our findings suggest that decorin secreted from myotubes in response to exercise is involved in the regulation of muscle hypertrophy and hence could play a role in exercise-related restructuring processes of skeletal muscle."