| Autor: |
Fajardo VA; Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada.; Centre for Bone and Muscle Health, Brock University, St. Catharines, Ontario, Canada., Watson CJF; Department of Health Sciences, Brock University, St. Catharines, Ontario, Canada., Bott KN; Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada., Moradi F; Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada., Maddalena LA; Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada., Bellissimo CA; Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada., Turner KD; Department of Health Sciences, Brock University, St. Catharines, Ontario, Canada., Peters SJ; Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada.; Centre for Bone and Muscle Health, Brock University, St. Catharines, Ontario, Canada., LeBlanc PJ; Department of Health Sciences, Brock University, St. Catharines, Ontario, Canada.; Centre for Bone and Muscle Health, Brock University, St. Catharines, Ontario, Canada., MacNeil AJ; Department of Health Sciences, Brock University, St. Catharines, Ontario, Canada., Stuart JA; Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada., Tupling AR; Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada. |
| Abstrakt: |
Calcineurin is a Ca 2+ /calmodulin (CaM)-dependent phosphatase that plays a critical role in promoting the slow fiber phenotype and myoblast fusion in skeletal muscle, thereby making calcineurin an attractive cellular target for enhancing fatigue resistance, muscle metabolism, and muscle repair. Neurogranin (Ng) is a CaM-binding protein thought to be expressed solely in brain and neurons, where it inhibits calcineurin signaling by sequestering CaM, thus lowering its cellular availability. Here, we demonstrate for the first time the expression of Ng protein and mRNA in mammalian skeletal muscle. Both protein and mRNA levels are greater in slow-oxidative compared with fast-glycolytic muscles. Coimmunoprecipitation of CaM with Ng in homogenates of C2C12 myotubes, mouse soleus, and human vastus lateralis suggests that these proteins physically interact. To determine whether Ng inhibits calcineurin signaling in muscle, we used Ng siRNA with C2C12 myotubes to reduce Ng protein levels by 60%. As a result of reduced Ng expression, C2C12 myotubes had enhanced CaM-calcineurin binding and calcineurin signaling as indicated by reduced phosphorylation of nuclear factor of activated T cells and increased utrophin mRNA . In addition, calcineurin signaling affects the expression of myogenin and stabilin-2, which are involved in myogenic differentiation and myoblast fusion, respectively. Here, we found that both myogenin and stabilin-2 were significantly elevated by Ng siRNA in C2C12 cells, concomitantly with an increased fusion index. Taken together, these results demonstrate the expression of Ng in mammalian skeletal muscle where it appears to be a novel regulator of calcineurin signaling. |
