ERK1/2 signaling induces skeletal muscle slow fiber-type switching and reduces muscular dystrophy disease severity
Justin G. Boyer, Vikram Prasad, Taejeong Song, Donghoon Lee, Xing Fu, Kelly M. Grimes, Michelle A. Sargent, Sakthivel Sadayappan, Jeffery D. Molkentin
Justin G. Boyer, Vikram Prasad, Taejeong Song, Donghoon Lee, Xing Fu, Kelly M. Grimes, Michelle A. Sargent, Sakthivel Sadayappan, Jeffery D. Molkentin
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Research Article Muscle biology

ERK1/2 signaling induces skeletal muscle slow fiber-type switching and reduces muscular dystrophy disease severity

Abstract

MAPK signaling consists of an array of successively acting kinases. ERK1 and -2 (ERK1/2) are major components of the greater MAPK cascade that transduce growth factor signaling at the cell membrane. Here, we investigated ERK1/2 signaling in skeletal muscle homeostasis and disease. Using mouse genetics, we observed that the muscle-specific expression of a constitutively active MEK1 mutant promotes greater ERK1/2 signaling that mediates fiber-type switching to a slow, oxidative phenotype with type I myosin heavy chain expression. Using a conditional and temporally regulated Cre strategy, as well as Mapk1 (ERK2) and Mapk3 (ERK1) genetically targeted mice, MEK1-ERK2 signaling was shown to underlie this fast-to-slow fiber-type switching in adult skeletal muscle as well as during development. Physiologic assessment of these activated MEK1-ERK1/2 mice showed enhanced metabolic activity and oxygen consumption with greater muscle fatigue resistance. In addition, induction of MEK1-ERK1/2 signaling increased dystrophin and utrophin protein expression in a mouse model of limb-girdle muscle dystrophy and protected myofibers from damage. In summary, sustained MEK1-ERK1/2 activity in skeletal muscle produces a fast-to-slow fiber-type switch that protects from muscular dystrophy, suggesting a therapeutic approach to enhance the metabolic effectiveness of muscle and protect from dystrophic disease.

Authors

Justin G. Boyer, Vikram Prasad, Taejeong Song, Donghoon Lee, Xing Fu, Kelly M. Grimes, Michelle A. Sargent, Sakthivel Sadayappan, Jeffery D. Molkentin

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Figure 6

MEK1-ERK1/2 signaling protects myofibers from muscular dystrophy.

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MEK1-ERK1/2 signaling protects myofibers from muscular dystrophy. (A) We...
(A) Western blot for total MEK1/2, ERK1/2 and δ-sarcoglycan (δ-SGC) protein levels from muscle protein lysates of mice from the indicated genotypes at 3 months of age. n = 3 for all groups. GAPDH is shown as loading control. (B) Representative image of the hindlimb muscles from 3-month-old mice of the indicated genotypes. (C) Quantification of myofibers with centrally located nuclei in histological sections of the quad from 3-month-old mice of indicated genotypes; n = 5 per group. Significance was determined using a 2-tailed Student’s t test. *P < 0.05. Average values are presented as a percentage from all fibers analyzed, error bars represent SEM. (D) Fiber size distribution quantified from the quad of mice of the indicated genotypes at 3 months of age. The mean (±SEM) percentage value relative to all fibers analyzed was graphed, n = 4 per group. Significance was determined using a 2-tailed Student’s t test. *P < 0.05. (E) Quantification of interstitial fibrosis assessed by picrosirius red staining of quad muscle histological sections from 3-month-old mice of the indicated genotypes. n = 5 per group. Significance was determined using a 2-tailed Student’s t test. *P < 0.05. (F) Average time spent running on a treadmill with 3-month-old mice of the indicated genotypes. n = 3 (Rosa26-MEK1 Sgcd–/–) and n = 5 (Rosa26-MEK1Myl1–cre Sgcd–/–). Significance was determined using a 2-tailed Student’s t test. *P < 0.05. (G) Representative immunohistochemical images showing myofibers stained with immunoglobulin M (IgM) antibody (green) and with laminin antibody (red) to delineate the myofibers. Images from the quad are shown from the indicated genotypes of mice at 3 months of age. Scale bars: 100 μm. (H) IgM positive myofibers quantification from histological sections as shown in G. Data are presented as the mean number of IgM positive fibers for a given area. Error bars represent SEM; n = 5 per group. Significance was determined using a 2-tailed Student’s t test. *P < 0.05. (I) Western blot for utrophin A (Utrn) and dystrophin (Dystro) using gastroc protein lysate from 3-month-old mice of the indicated genotypes. Results from 3 different mice are shown. Coomassie (Coom) staining was used to show equal loading. (J) Western blot analysis for calcineurin A (CnA) and Utrn using gastroc muscle of mice of the indicated genotypes at 6 months of age. Equal loading was assessed using Coom stain. Results from 3 separate mice are shown.