In vivo remodeling of intervertebral discs in response to short- and long-term dynamic compression.
This study evaluated how dynamic compression induced changes in gene expression, tissue composition, and structural properties of the intervertebral disc using a rat tail model. We hypothesized that daily exposure to dynamic compression for short durations would result in anabolic remodeling with increased matrix protein expression and proteoglycan content, and that increased daily load exposure time and experiment duration would retain these changes but also accumulate changes representative of mild degeneration. Sprague-Dawley rats (n = 100) were instrumented with an Ilizarov-type device and divided into three dynamic compression (2 week-1.5 h/day, 2 week-8 h/day, 8 week-8 h/day at 1 MPa and 1 Hz) and two sham (2 week, 8 week) groups. Dynamic compression resulted in anabolic remodeling with increased matrix mRNA expression, minimal changes in catabolic genes or disc structure and stiffness, and increased glysosaminoglycans (GAG) content in the nucleus pulposus. Some accumulation of mild degeneration with 8 week-8 h included loss of annulus fibrosus GAG and disc height although 8-week shams also had loss of disc height, water content, and minor structural alterations. We conclude that dynamic compression is consistent with a notion of "healthy" loading that is able to maintain or promote matrix biosynthesis without substantially disrupting disc structural integrity. A slow accumulation of changes similar to human disc degeneration occurred when dynamic compression was applied for excessive durations, but this degenerative shift was mild when compared to static compression, bending, or other interventions that create greater structural disruption.
Wuertz
Karin
K
School of Engineering, University of Vermont, Burlington, Vermont 05405, USA.
Godburn
Karolyn
K
MacLean
Jeffrey J
JJ
Barbir
Ana
A
Donnelly
Justin Stinnett
JS
Roughley
Peter J
PJ
Alini
Mauro
M
Iatridis
James C
JC
D053674:Aggrecans / Q000235:genetics; D000818:Animals; D001696:Biomechanical Phenomena; D024042:Collagen Type I / Q000235:genetics; D024043:Collagen Type II / Q000235:genetics; D019245:Compressive Strength / Q000502:physiology*; D004195:Disease Models, Animal; D005109:Extracellular Matrix / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D006025:Glycosaminoglycans / Q000378:metabolism; D018889:Ilizarov Technique; D007403:Intervertebral Disc / Q000166:cytology* / Q000502:physiology*; D007405:Intervertebral Disc Displacement / Q000473:pathology* / Q000503:physiopathology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000235:genetics; D019717:Tissue Inhibitor of Metalloproteinase-3 / Q000235:genetics; D014867:Water / Q000378:metabolism; D016474:Weight-Bearing / Q000502:physiology
C508321:Acan protein, rat; D053674:Aggrecans; D024042:Collagen Type I; D024043:Collagen Type II; D006025:Glycosaminoglycans; D012333:RNA, Messenger; D019715:Tissue Inhibitor of Metalloproteinase-1; D019717:Tissue Inhibitor of Metalloproteinase-3; D014867:Water