A new porcine in vivo animal model of disc degeneration: response of anulus fibrosus cells, chondrocyte-like nucleus pulposus cells, and notochordal nucleus pulposus cells to partial nucleotomy.
METHODS
In vivo animal study.


OBJECTIVE
To describe a new porcine disc degeneration model, and to analyze disc remodeling and degeneration after nucleotomy with special view to the different nucleus pulposus (NP) cell types.


BACKGROUND
Thus far, predominantly smaller animals were used for disc degeneration models; however, such small discs were inappropriate to investigate cell implementation therapies. Though notochordal cells (NCs) are important for disc formation and maintenance, differences in the amount of NCs between human and animal discs have often been neglected.


METHODS
Twenty-four Goettingen minipigs underwent partial nucleotomy with a 16G biopsy cannula, to remove approximately 10% of total NP volume. Animals were followed up for 3, or 24 weeks and analyzed by radiographs, MRIs, (immuno)histology, gene expression analysis, and biomechanical testing.


RESULTS
Three weeks after nucleotomy disc height was reduced by 26%, and magnetic resonance imaging signal intensity by 40%. At 24 weeks disc height was decreased by 32%. Increased degenerative changes were found in a histodegeneration score 3 and 24 weeks after nucleotomy, as well as considerable NP scarification after 3 weeks. In controls, cytokeratin-8 immunohistochemistry identified NCs in proximity to chondrocyte-like NP cells at approximately equal ratio. After nucleotomy, NCs were considerably reduced to <10% of total NP cells. Matrix genes were upregulated, except for aggrecan that decreased to 35% of initial values 3 weeks after nucleotomy. Matrix degrading factors (matrix metalloproteinases 13 and 3) were continuously upregulated, whereas transcripts of their inhibitors (tissue inhibitors of matrix metalloproteinase 2 and 3) were downregulated. No significant changes in segmental spinal flexibility or bone density were found after nucleotomy.


CONCLUSIONS
We introduced a new disc degeneration model with relatively large discs that could be used for cell therapeutic approaches. The study gives further information about disc remodeling after nucleotomy and indicates the relevance of an altered cellular composition for the development of disc degeneration.
Omlor
Georg W
GW
Department of Orthopaedic Surgery, University of Heidelberg, Germany.
Nerlich
Andreas G
AG
Wilke
Hans-Joachim
HJ
Pfeiffer
Michael
M
Lorenz
Helga
H
Schaaf-Keim
Markus
M
Bertram
Helge
H
Richter
Wiltrud
W
Carstens
Claus
C
Guehring
Thorsten
T
D053674:Aggrecans / Q000378:metabolism; D000818:Animals; D001696:Biomechanical Phenomena; D019902:Chondrocytes / Q000378:metabolism / Q000473:pathology*; D004195:Disease Models, Animal; D017586:Diskectomy / Q000379:methods*; D007403:Intervertebral Disc / Q000378:metabolism / Q000473:pathology* / Q000601:surgery*; D055959:Intervertebral Disc Degeneration / Q000378:metabolism / Q000473:pathology / Q000601:surgery*; D053533:Keratin-8 / Q000378:metabolism; D008279:Magnetic Resonance Imaging; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D019278:Matrix Metalloproteinase 3 / Q000378:metabolism; D013552:Swine; D013556:Swine, Miniature; D019716:Tissue Inhibitor of Metalloproteinase-2 / Q000378:metabolism; D019717:Tissue Inhibitor of Metalloproteinase-3 / Q000378:metabolism
D053674:Aggrecans; D053533:Keratin-8; D019717:Tissue Inhibitor of Metalloproteinase-3; D019716:Tissue Inhibitor of Metalloproteinase-2; D053509:Matrix Metalloproteinase 13; D019278:Matrix Metalloproteinase 3