title: Top-Down Targeted Proteomics Reveals Decrease in Myosin Regulatory Light-Chain Phosphorylation That Contributes to Sarcopenic Muscle Dysfunction.
abstract: Sarcopenia, the loss of skeletal muscle mass and function with advancing age, is a significant cause of disability and loss of independence in the elderly and thus, represents a formidable challenge for the aging population. Nevertheless, the molecular mechanism(s) underlying sarcopenia-associated muscle dysfunction remain poorly understood. In this study, we employed an integrated approach combining top-down targeted proteomics with mechanical measurements to dissect the molecular mechanism(s) in age-related muscle dysfunction. Top-down targeted proteomic analysis uncovered a progressive age-related decline in the phosphorylation of myosin regulatory light chain (RLC), a critical protein involved in the modulation of muscle contractility, in the skeletal muscle of aging rats. Top-down tandem mass spectrometry analysis identified a previously unreported bis-phosphorylated proteoform of fast skeletal RLC and localized the sites of decreasing phosphorylation to Ser14/15. Of these sites, Ser14 phosphorylation represents a previously unidentified site of phosphorylation in RLC from fast-twitch skeletal muscle. Subsequent mechanical analysis of single fast-twitch fibers isolated from the muscles of rats of different ages revealed that the observed decline in RLC phosphorylation can account for age-related decreases in the contractile properties of sarcopenic fast-twitch muscles. These results strongly support a role for decreasing RLC phosphorylation in sarcopenia-associated muscle dysfunction and suggest that therapeutic modulation of RLC phosphorylation may represent a new avenue for the treatment of sarcopenia.
authors.affiliation: Department of Cell and Regenerative Biology, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|Molecular and Cellular Pharmacology Training Program, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.
authors.forename: Zachery R
authors.initials: ZR
authors.lastname: Gregorich
authors.affiliation: Department of Cell and Regenerative Biology, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.
authors.forename: Ying
authors.initials: Y
authors.lastname: Peng
authors.affiliation: Department of Cell and Regenerative Biology, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|Molecular and Cellular Pharmacology Training Program, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.
authors.forename: Wenxuan
authors.initials: W
authors.lastname: Cai
authors.affiliation: Department of Cell and Regenerative Biology, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Yutong
authors.initials: Y
authors.lastname: Jin
authors.affiliation: Department of Cell and Regenerative Biology, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|Institutes of Biomedical Sciences, Fudan University , Shanghai 200032, P. R. China.
authors.forename: Liming
authors.initials: L
authors.lastname: Wei
authors.affiliation: Department of Cell and Regenerative Biology, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Chen
authors.affiliation: Department of Kinesiology, University of Wisconsin-Madison , 2000 Observatory Drive, Madison, Wisconsin 53705, United States.
authors.forename: Susan H
authors.initials: SH
authors.lastname: McKiernan
authors.affiliation: Departments of Agriculture, Food, and Nutritional Sciences, University of Alberta-Edmonton , Edmonton, Alberta, Canada.
authors.forename: Judd M
authors.initials: JM
authors.lastname: Aiken
authors.affiliation: Department of Cell and Regenerative Biology, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|Human Proteomics Program, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|UW Cardiovascular Research Center, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Moss
authors.affiliation: Department of Kinesiology, University of Wisconsin-Madison , 2000 Observatory Drive, Madison, Wisconsin 53705, United States.|UW Cardiovascular Research Center, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.
authors.forename: Gary M
authors.initials: GM
authors.lastname: Diffee
authors.affiliation: Department of Cell and Regenerative Biology, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|Molecular and Cellular Pharmacology Training Program, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.|Human Proteomics Program, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.|UW Cardiovascular Research Center, University of Wisconsin-Madison , 1111 Highland Avenue, Madison, Wisconsin 53705, United States.
authors.forename: Ying
authors.initials: Y
authors.lastname: Ge
mesh_terms: D000375:Aging; D000818:Animals; D009119:Muscle Contraction; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018482:Muscle, Skeletal / Q000503:physiopathology; D018994:Myosin Light Chains / Q000378:metabolism*; D010766:Phosphorylation; D040901:Proteomics / Q000379:methods*; D051381:Rats; D055948:Sarcopenia / Q000209:etiology; D053719:Tandem Mass Spectrometry
chemical_list: D018994:Myosin Light Chains
keywords: aging; myofilament; sarcopenia; targeted proteomics; top-down mass spectrometry