Abstract
Glycogen synthase kinase 3 (GSK3) slows myogenic differentiation and myoblast fusion partly by inhibiting the Wnt/β-catenin signaling pathway. Lithium, a common medication for bipolar disorder, inhibits GSK3 via Mg+ competition and increased Ser21 (GSK3α) or Ser9 (GSK3β) phosphorylation, leading to enhanced myoblast fusion and myogenic differentiation. However, previous studies demonstrating the effect of lithium on GSK3 have used concentrations up to 10 mM, which greatly exceeds concentrations measured in the serum of patients being treated for bipolar disorder (0.5–1.2 mM). Here, we determined whether a low-therapeutic (0.5 mM) dose of lithium could promote myoblast fusion and myogenic differentiation in C2C12 cells. C2C12 myotubes differentiated for three days in media containing 0.5 mM lithium chloride (LiCl) had significantly higher GSK3β (ser9) and GSK3α (ser21) phosphorylation compared with control myotubes differentiated in the same media without LiCl (+2–2.5 fold, p < 0.05), a result associated with an increase in total β-catenin. To further demonstrate that 0.5 mM LiCl inhibited GSK3 activity, we also developed a novel GSK3-specific activity assay. Using this enzyme-linked spectrophotometric assay, we showed that 0.5 mM LiCl-treated myotubes had significantly reduced GSK3 activity (−86%, p < 0.001). Correspondingly, 0.5 mM LiCl treated myotubes had a higher myoblast fusion index compared with control (p < 0.001) and significantly higher levels of markers of myogenesis (myogenin, +3-fold, p < 0.001) and myogenic differentiation (myosin heavy chain, +10-fold, p < 0.001). These results indicate that a low-therapeutic dose of LiCl is sufficient to promote myoblast fusion and myogenic differentiation in muscle cells, which has implications for the treatment of several myopathic conditions.
Highlights
Disease or age related declines in muscle mass and/or function is associated with falls, fractures, frailty, poor quality of life, and disability [1,2,3,4], all while being a significant predictor of all-cause mortality [5]
Once the myoblasts were at 80% confluence, the growth medium was replaced with differentiation medium (DMEM supplemented with 1% adult horse serum, 1% penicillin/streptomycin, 2% non-essential amino acids) that was either supplemented with 0.5 mM lithium chloride (LiCl group) or not
LiCl treatment led to a significant increase in phosphorylated GSK3β and GSK3α with no change in total Glycogen synthase kinase 3 (GSK3) content compared to non-treated cells, which led to an overall increase in the ratio of phosphorylated to total GSK3
Summary
Disease or age related declines in muscle mass and/or function is associated with falls, fractures, frailty, poor quality of life, and disability [1,2,3,4], all while being a significant predictor of all-cause mortality [5]. Strategies to maintain skeletal muscle mass throughout the lifespan could lead to significant benefits to overall health. Skeletal muscle is a dynamic and plastic tissue responding to internal (e.g., biochemical) and/or external (e.g., biophysical) stimuli, and an increase in strength and/or size (e.g., hypertrophy) can result from nutritional supplementation and exercise training [6,7,8]. Myonuclear accretion, which is accomplished through myoblast fusion [9], appears to be critical for muscle hypertrophy [10,11], as described in the myonuclear domain theory [12,13]. Myoblast fusion enables repair of damaged muscle [14], which is important for recovery from exercise or injury as well as for constant muscle degenerating diseases, such as muscular dystrophy [15,16].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
