The embryonic myosin R672C mutation that underlies Freeman-Sheldon syndrome impairs cross-bridge detachment and cycling in adult skeletal muscle.
Distal arthrogryposis is the most common known heritable cause of congenital contractures (e.g. clubfoot) and results from mutations in genes that encode proteins of the contractile complex of skeletal muscle cells. Mutations are most frequently found in MYH3 and are predicted to impair the function of embryonic myosin. We measured the contractile properties of individual skeletal muscle cells and the activation and relaxation kinetics of isolated myofibrils from two adult individuals with an R672C substitution in embryonic myosin and distal arthrogryposis syndrome 2A (DA2A) or Freeman-Sheldon syndrome. In R672C-containing muscle cells, we observed reduced specific force, a prolonged time to relaxation and incomplete relaxation (elevated residual force). In R672C-containing muscle myofibrils, the initial, slower phase of relaxation had a longer duration and slower rate, and time to complete relaxation was greatly prolonged. These observations can be collectively explained by a small subpopulation of myosin cross-bridges with greatly reduced detachment kinetics, resulting in a slower and less complete deactivation of thin filaments at the end of contractions. These findings have important implications for selecting and testing directed therapeutic options for persons with DA2A and perhaps congenital contractures in general.
Department of Bioengineering.
Alice W
AW
Racca
Department of Pediatrics, Seattle Children's Hospital, Seattle, WA 98105, USA.
Anita E
AE
Beck
Department of Pediatrics.
Margaret J
MJ
McMillin
Department of Bioengineering.
F Steven
FS
Korte
Department of Pediatrics, Department of Genome Sciences, Seattle Children's Hospital, Seattle, WA 98105, USA.
Michael J
MJ
Bamshad
Department of Bioengineering, Center for Cardiovascular Biology, University of Washington, Seattle, WA 98195, USA and mregnier@uw.edu.
Michael
M
Regnier
D000293:Adolescent; D000328:Adult; D002118:Calcium / Q000378:metabolism; D016022:Case-Control Studies; D002478:Cells, Cultured; D003394:Craniofacial Dysostosis / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology*; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000235:genetics*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology*; D009154:Mutation; D009210:Myofibrils / Q000235:genetics / Q000378:metabolism; D009218:Myosins / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D055815:Young Adult
D003598:Cytoskeletal Proteins; C510594:MYH3 polypeptide, human; D012333:RNA, Messenger; D009218:Myosins; D002118:Calcium