title: Myostatin regulates fiber-type composition of skeletal muscle by regulating MEF2 and MyoD gene expression.
abstract: Myostatin (Mstn) is a secreted growth factor belonging to the tranforming growth factor (TGF)-beta superfamily. Inactivation of murine Mstn by gene targeting, or natural mutation of bovine or human Mstn, induces the double muscling (DM) phenotype. In DM cattle, Mstn deficiency increases fast glycolytic (type IIB) fiber formation in the biceps femoris (BF) muscle. Using Mstn null ((-/-)) mice, we suggest a possible mechanism behind Mstn-mediated fiber-type diversity. Histological analysis revealed increased type IIB fibers with a concomitant decrease in type IIA and type I fibers in the Mstn(-/-) tibialis anterior and BF muscle. Functional electrical stimulation of Mstn(-/-) BF revealed increased fatigue susceptibility, supporting increased type IIB fiber content. Given the role of myocyte enhancer factor 2 (MEF2) in oxidative type I fiber formation, MEF2 levels in Mstn(-/-) tissue were quantified. Results revealed reduced MEF2C protein in Mstn(-/-) muscle and myoblast nuclear extracts. Reduced MEF2-DNA complex was also observed in electrophoretic mobility-shift assay using Mstn(-/-) nuclear extracts. Furthermore, reduced expression of MEF2 downstream target genes MLC1F and calcineurin were found in Mstn(-/-) muscle. Conversely, Mstn addition was sufficient to directly upregulate MLC promoter-enhancer activity in cultured myoblasts. Since high MyoD levels are seen in fast fibers, we analyzed MyoD levels in the muscle. In contrast to MEF2C, MyoD levels were increased in Mstn(-/-) muscle. Together, these results suggest that while Mstn positively regulates MEF2C levels, it negatively regulates MyoD expression in muscle. We propose that Mstn could regulate fiber-type composition by regulating the expression of MEF2C and MyoD during myogenesis.
authors.affiliation: AgResearch, Functional Muscle Genomics, Hamilton, New Zealand.
authors.forename: Alex
authors.initials: A
authors.lastname: Hennebry
authors.forename: Carole
authors.initials: C
authors.lastname: Berry
authors.forename: Victoria
authors.initials: V
authors.lastname: Siriett
authors.forename: Paul
authors.initials: P
authors.lastname: O'Callaghan
authors.forename: Linda
authors.initials: L
authors.lastname: Chau
authors.forename: Trevor
authors.initials: T
authors.lastname: Watson
authors.forename: Mridula
authors.initials: M
authors.lastname: Sharma
authors.forename: Ravi
authors.initials: R
authors.lastname: Kambadur
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000235:genetics; D002417:Cattle; D002460:Cell Line; D004558:Electric Stimulation; D005786:Gene Expression Regulation; D064326:MEF2 Transcription Factors; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D017570:MyoD Protein / Q000235:genetics* / Q000378:metabolism; D018006:Myogenic Regulatory Factors / Q000235:genetics* / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics; D018994:Myosin Light Chains / Q000235:genetics; D055435:Myostatin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D064326:MEF2 Transcription Factors; C578041:Mef2c protein, mouse; C525912:Mstn protein, mouse; C484588:Myl1 protein, mouse; D017570:MyoD Protein; C057363:MyoD1 myogenic differentiation protein; D018006:Myogenic Regulatory Factors; D018994:Myosin Light Chains; D055435:Myostatin; D012333:RNA, Messenger; D019703:Calcineurin; D018995:Myosin Heavy Chains