Enhancement of intervertebral disc cell senescence by WNT/β-catenin signaling-induced matrix metalloproteinase expression.
OBJECTIVE
To determine whether intervertebral disc (IVD) cells express β-catenin and to assess the role of the WNT/β-catenin signaling pathway in cellular senescence and aggrecan synthesis.


METHODS
The expression of β-catenin messenger RNA (mRNA) and protein in rat IVD cells was assessed by using several real-time reverse transcription-polymerase chain reaction, Western blot, immunohistochemical, and immunofluorescence analyses. The effect of WNT/β-catenin on nucleus pulposus (NP) cells was examined by transfection experiments, an MTT assay, senescence-associated β-galactosidase staining, a cell cycle analysis, and a transforming growth factor (TGFβ)/bone morphogenetic protein (BMP) pathway-focused microarray analysis.


RESULTS
We found that β-catenin mRNA and protein were expressed in discs in vivo and that rat NP cells exhibited increased β-catenin mRNA and protein upon stimulation with lithium chloride, a known activator of WNT signaling. LiCl treatment inhibited the proliferation of NP cells in a time- and dose-dependent manner. In addition, there was an increased level of cellular senescence in LiCl-treated cells. Long-term treatment with LiCl induced cell cycle arrest and promoted subsequent apoptosis in NP cells. Activation of WNT/β-catenin signaling also regulated the expression of aggrecan. We also demonstrated that WNT/β-catenin signaling induced the expression of matrix metalloproteinases (MMPs) and TGFβ in NP cells.


CONCLUSIONS
The activation of WNT/β-catenin signaling promotes cellular senescence and may modulate MMP and TGFβ signaling in NP cells. We hypothesize that the activation of WNT/β-catenin signaling may lead to an increased breakdown of the matrix, thereby promoting IVD degeneration.
Tokai University School of Medicine, Isehara, Japan. a.hiyama@tokai-u.jp
Akihiko
A
Hiyama
Daisuke
D
Sakai
Makarand V
MV
Risbud
Masahiro
M
Tanaka
Fumiyuki
F
Arai
Koichiro
K
Abe
Joji
J
Mochida
D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D005260:Female; D007403:Intervertebral Disc / Q000166:cytology / Q000502:physiology*; D055959:Intervertebral Disc Degeneration / Q000378:metabolism*; D008159:Lumbar Vertebrae / Q000166:cytology / Q000502:physiology*; D020782:Matrix Metalloproteinases / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism*
D051153:Wnt Proteins; D051176:beta Catenin; D020782:Matrix Metalloproteinases