title: Mechanical loading by fluid shear stress of myotube glycocalyx stimulates growth factor expression and nitric oxide production.
abstract: Skeletal muscle fibers have the ability to increase their size in response to a mechanical overload. Finite element modeling data suggest that mechanically loaded muscles in vivo may experience not only tensile strain but also shear stress. However, whether shear stress affects biological pathways involved in muscle fiber size adaptation in response to mechanical loading is unknown. Therefore, our aim was twofold: (1) to determine whether shear stress affects growth factor expression and nitric oxide (NO) production by myotubes, and (2) to explore the mechanism by which shear stress may affect myotubes in vitro. C2C12 myotubes were subjected to a laminar pulsating fluid flow (PFF; mean shear stress 0.4, 0.7 or 1.4 Pa, 1 Hz) or subjected to uni-axial cyclic strain (CS; 15 % strain, 1 Hz) for 1 h. NO production during 1-h PFF or CS treatment was quantified using Griess reagent. The glycocalyx was degraded using hyaluronidase, and stretch-activated ion channels (SACs) were blocked using GdCl3. Gene expression was analyzed immediately after 1-h PFF (1.4 Pa, 1 Hz) and at 6 h post-PFF treatment. PFF increased IGF-I Ea, MGF, VEGF, IL-6, and COX-2 mRNA, but decreased myostatin mRNA expression. Shear stress enhanced NO production in a dose-dependent manner, while CS induced no quantifiable increase in NO production. Glycocalyx degradation and blocking of SACs ablated the shear stress-stimulated NO production. In conclusion, shear stress activates signaling pathways involved in muscle fiber size adaptation in myotubes, likely via membrane-bound mechanoreceptors. These results suggest that shear stress exerted on myofiber extracellular matrix plays an important role in mechanotransduction in muscle.
authors.affiliation: Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, MOVE Research Institute Amsterdam, Gustav Mahlerlaan 3004, 1081 LA, Amsterdam, The Netherlands.
authors.forename: Petra
authors.initials: P
authors.lastname: Juffer
authors.forename: Astrid D
authors.initials: AD
authors.lastname: Bakker
authors.forename: Jenneke
authors.initials: J
authors.lastname: Klein-Nulend
authors.forename: Richard T
authors.initials: RT
authors.lastname: Jaspers
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D005786:Gene Expression Regulation; D019276:Glycocalyx / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics*; D007473:Ion Channels / Q000378:metabolism; D040542:Mechanotransduction, Cellular; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000166:cytology* / Q000378:metabolism; D009569:Nitric Oxide / Q000096:biosynthesis*; D012508:Sarcolemma / Q000378:metabolism; D033081:Shear Strength; D013314:Stress, Mechanical
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D007473:Ion Channels; D009569:Nitric Oxide; D002118:Calcium