title: Disuse-induced preferential loss of the giant protein titin depresses muscle performance via abnormal sarcomeric organization.
abstract: Persistent muscle weakness due to disuse-associated skeletal muscle atrophy limits the quality of life for patients with various diseases and individuals who are confined to bed. Fibers from disused muscle exhibit a marked reduction in active force production, which can exacerbate motor function, coupled with the well-known loss of muscle quantity. Despite recent understanding of the signaling pathways leading to the quantity loss, the molecular mechanisms of the depressed qualitative performance still remain elusive. Here we show that long-term disuse causes preferential loss of the giant sarcomere protein titin, associated with changes in physiologic muscle function. Ca(2+) sensitivity of active force decreased following 6 wk of hindlimb immobilization in the soleus muscle of the rat, accompanied by a shift in the length-active force relationship to the shorter length side. Our analyses revealed marked changes in the disused sarcomere, with shortening of thick and thin filaments responsible for altered length dependence and expansion of interfilament lattice spacing leading to a reduction in Ca(2+) sensitivity. These results provide a novel view that disuse-induced preferential titin loss results in altered muscle function via abnormal sarcomeric organization.
authors.affiliation: Department of Cell Physiology, The Jikei University, Tokyo, Japan. judk@jikei.ac.jp
authors.forename: Jun
authors.initials: J
authors.lastname: Udaka
authors.forename: Shintaro
authors.initials: S
authors.lastname: Ohmori
authors.forename: Takako
authors.initials: T
authors.lastname: Terui
authors.forename: Iwao
authors.initials: I
authors.lastname: Ohtsuki
authors.forename: Shin'ichi
authors.initials: S
authors.lastname: Ishiwata
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kurihara
authors.forename: Norio
authors.initials: N
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D064211:Connectin; D004195:Disease Models, Animal; D019417:Hindlimb Suspension / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism*; D053580:Muscle Strength / Q000502:physiology; D018908:Muscle Weakness / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology*; D020966:Muscular Disorders, Atrophic / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology*; D009218:Myosins / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012518:Sarcomeres / Q000378:metabolism* / Q000473:pathology* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D011494:Protein Kinases; D009218:Myosins