Signal transduction pathways that regulate muscle growth

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Essays Biochem. 2008;44:99-108.

Signal transduction pathways that regulate muscle growth.

Wackerhage H, Ratkevicius A.

Institute of Medical Sciences, Foresterhill, University of Aberdeen,

Aberdeen AB25 2ZD, Scotland, UK.

Progressive high-resistance exercise with 8-12 repetitions per set to

near failure for beginners and 1-12 repetitions for athletes will

increase muscle protein synthesis for up to 72 h; approx. 20 g of

protein, especially when ingested directly after exercise, will

promote high growth by elevating protein synthesis above breakdown.

Muscle growth is regulated by signal transduction pathways that sense

and compute local and systemic signals and regulate various cellular

functions. The main signalling mechanisms are the phosphorylation of

serine, threonine and tyrosine residues by kinases and their

dephosphorylation by phosphatases.

Muscle growth is stimulated by the mTOR (mammalian target of

rapamycin) system, which senses (i) IGF-1 (insulin-like growth factor

1)/MGF (mechano-growth factor)/insulin and/or (ii) mechanical

signals, (iii) amino acids and (iv) the energetic state of the

muscle, and regulates protein synthesis accordingly. The action of

the mTOR system is opposed by myostatin-Smad signalling which

inhibits muscle growth via gene transcription.