title: mTOR regulates peripheral nerve response to tensile strain.
abstract: While excessive tensile strain can be detrimental to nerve function, strain can be a positive regulator of neuronal outgrowth. We used an in vivo rat model of sciatic nerve strain to investigate signaling mechanisms underlying peripheral nerve response to deformation. Nerves were deformed by 11% and did not demonstrate deficits in compound action potential latency or amplitude during or after 6 h of strain. As revealed by Western blotting, application of strain resulted in significant upregulation of mammalian target of rapamycin (mTOR) and S6 signaling in nerves, increased myelin basic protein (MBP) and β-actin levels, and increased phosphorylation of neurofilament subunit H (NF-H) compared with unstrained (sham) contralateral nerves (P< 0.05 for all comparisons, paired two-tailedt-test). Strain did not alter neuron-specific β3-tubulin or overall nerve tubulin levels compared with unstrained controls. Systemic rapamycin treatment, thought to selectively target mTOR complex 1 (mTORC1), suppressed mTOR/S6 signaling, reduced levels of MBP and overall tubulin, and decreased NF-H phosphorylation in nerves strained for 6 h, revealing a role for mTOR in increasing MBP expression and NF-H phosphorylation, and maintaining tubulin levels. Consistent with stretch-induced increases in MBP, immunolabeling revealed increased S6 signaling in Schwann cells of stretched nerves compared with unstretched nerves. In addition, application of strain to cultured adult dorsal root ganglion neurons showed an increase in axonal protein synthesis based on a puromycin incorporation assay, suggesting that neuronal translational pathways also respond to strain. This work has important implications for understanding mechanisms underlying nerve response to strain during development and regeneration.NEW & NOTEWORTHYPeripheral nerves experience tensile strain (stretch) during development and movement. Excessive strain impairs neuronal function, but moderate strains are accommodated by nerves and can promote neuronal growth; mechanisms underlying these phenomena are not well understood. We demonstrated that levels of several structural proteins increase following physiological levels of nerve strain and that expression of a subset of these proteins is regulated by mTOR. Our work has important implications for understanding nerve development and strain-based regenerative strategies.
authors.affiliation: Fischell Department of Bioengineering, University of Maryland, College Park, Maryland.
authors.forename: James M
authors.initials: JM
authors.lastname: Love
authors.affiliation: Department of Bioengineering, University of California-San Diego, La Jolla, California.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Bober
authors.affiliation: Department of Orthopaedic Surgery, University of California-San Diego, La Jolla, California.|Veterans Affairs San Diego Healthcare System, San Diego, California; and.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Orozco
authors.affiliation: Department of Orthopaedic Surgery, University of California-San Diego, La Jolla, California.
authors.forename: Amanda T
authors.initials: AT
authors.lastname: White
authors.affiliation: Department of Orthopaedic Surgery, University of California-San Diego, La Jolla, California.|Veterans Affairs San Diego Healthcare System, San Diego, California; and.
authors.forename: Shannon N
authors.initials: SN
authors.lastname: Bremner
authors.affiliation: Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Richard M
authors.identifier: 0000-0002-9899-5071
authors.initials: RM
authors.lastname: Lovering
authors.affiliation: Department of Orthopaedic Surgery, University of California-San Diego, La Jolla, California.
authors.forename: Simon
authors.initials: S
authors.lastname: Schenk
authors.affiliation: Department of Bioengineering, University of California-San Diego, La Jolla, California; sbshah@ucsd.edu.|Department of Orthopaedic Surgery, University of California-San Diego, La Jolla, California.|Veterans Affairs San Diego Healthcare System, San Diego, California; and.
authors.forename: Sameer B
authors.initials: SB
authors.lastname: Shah
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D000076222:Mechanistic Target of Rapamycin Complex 1 / Q000378:metabolism*; D040542:Mechanotransduction, Cellular; D004676:Myelin Basic Protein / Q000378:metabolism; D010525:Peripheral Nerves / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012583:Schwann Cells / Q000378:metabolism / Q000502:physiology; D013718:Tensile Strength; D014404:Tubulin / Q000378:metabolism
chemical_list: D000199:Actins; D004676:Myelin Basic Protein; D014404:Tubulin; D000076222:Mechanistic Target of Rapamycin Complex 1
keywords: cytoskeleton; mTOR; myelin; neurofilament; peripheral nerve; rapamycin; strain