title: Paraspinal Muscle Passive Stiffness Remodels in Direct Response to Spine Stiffness: A Study Using the ENT1-Deficient Mouse.
abstract: METHODS
  Basic science study of the relationship between the structural properties of the spine and its surrounding musculature.
  
  
  OBJECTIVE
  To determine whether an increase in spine stiffness causes an inverse compensatory change in the passive stiffness of the adjacent paraspinal muscles.
  
  
  BACKGROUND
  Intervertebral disc degeneration causes an increase in multifidus passive stiffness; this was hypothesized to compensate for a decrease in spine stiffness associated with disc degeneration. Mice lacking equilibrative nucleoside transporter 1 (ENT1) develop progressive ectopic calcification of the fibrous connective tissues of the spine, which affects the lumbar spine by 6 months of age and likely creates a mechanically stiffer spine.
  
  
  METHODS
  Experiments were conducted on four groups of mice (n = 8 mice/group): wild-type (WT) and ENT1 knockout (KO) at 2 or 8 months of age. Lumbar spines were removed and tested in cyclic axial compression to determine neutral zone length and stiffness. Single muscle fibers and bundles of fibers were isolated from lumbar multifidus and erector spinae, as well as tibialis anterior (a non-spine-related control) and tested to determine elastic modulus (passive stiffness).
  
  
  RESULTS
  At 2 months of age, neither spine nor muscle stiffness was different between KO and WT. At 8 months of age, compared with WT the lumbar spines of ENT1 KO mice had a stiffer and shorter neutral zone, and the paraspinal muscle fibers were less stiff; however, fiber bundles were not different. In addition, tibialis anterior was not different between KO and WT.
  
  
  CONCLUSIONS
  This work has confirmed that calcification of spinal connective tissues in the ENT1 KO mouse results in a stiffened spine, whereas the concurrent decrease in muscle fiber elastic modulus in the adjacent paraspinal muscles suggests a direct compensatory relationship between the stiffness of the spine and the muscles that are attached to it.
  
  
  METHODS
  N/A.
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Kelsey Y
authors.initials: KY
authors.lastname: Gsell
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Derek P
authors.initials: DP
authors.lastname: Zwambag
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Bone and Joint Institute, University of Western Ontario, London, Ontario, Canada.
authors.forename: Dale E
authors.initials: DE
authors.lastname: Fournier
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Bone and Joint Institute, University of Western Ontario, London, Ontario, Canada.
authors.forename: Cheryle A
authors.initials: CA
authors.lastname: Séguin
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Stephen H M
authors.initials: SHM
authors.lastname: Brown
mesh_terms: D000818:Animals; D002114:Calcinosis / Q000000981:diagnostic imaging / Q000378:metabolism*; D055119:Elastic Modulus / Q000502:physiology; D033721:Equilibrative Nucleoside Transporter 1 / Q000378:metabolism*; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging / Q000378:metabolism; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000473:pathology; D064170:Paraspinal Muscles / Q000000981:diagnostic imaging / Q000378:metabolism*
chemical_list: D033721:Equilibrative Nucleoside Transporter 1; C498476:SLC29A1 protein, mouse