title: Canonical Wnt signaling in the notochordal cell is upregulated in early intervertebral disk degeneration.
abstract: The notochordal cell (NC) of the nucleus pulposus (NP) is considered a potential NP progenitor cell, and early intervertebral disk (IVD) degeneration involves replacement of NCs by chondrocyte-like cells (CLCs). Wnt/β-catenin signaling plays a crucial role in maintaining the notochordal fate during embryogenesis, but is also involved in tissue degeneration and regeneration. The canine species, which can be subdivided into non-chondrodystrophic and chondrodystrophic breeds, is characterized by differential maintenance of the NC: in non-chondrodystrophic dogs, the NC remains the predominant cell type during the majority of life, with IVD degeneration only occurring at old age; conversely, in chondrodystrophic dogs the NC is lost early in life, with concurrent degeneration of all IVDs. This study investigated Wnt/β-catenin signaling in the healthy, NC-rich NP and early degenerated, CLC-rich NP of both breed types by immunohistochemistry of β-catenin and relative gene expression of brachyury and cytokeratin 8 (notochordal markers) and Wnt targets axin2, cyclin D1, and c-myc. Both NCs and CLCs showed nuclear and cytoplasmic β-catenin protein expression and axin2 gene expression, but β-catenin signal intensity and Wnt target gene expression were higher in the CLC-rich NP. Primary NCs in monolayer culture (normoxic conditions) showed Wnt/β-catenin signaling comparable to the in vivo situation, with increased cyclin D1 and c-myc gene expression. In conclusion, Wnt/β-catenin signaling activity in the NC within the NC-rich NP and in culture supports the role of this cell as a potential progenitor cell; increased Wnt/β-catenin signaling activity in early IVD degeneration may be a reflection of its dual role.
authors.affiliation: Department of Clinical Sciences of Companion Animals, Utrecht University, Yalelaan 108, 3508 TD, Utrecht, The Netherlands. l.a.smolders@uu.nl
authors.forename: Lucas A
authors.initials: LA
authors.lastname: Smolders
authors.forename: Björn P
authors.initials: BP
authors.lastname: Meij
authors.forename: Frank M
authors.initials: FM
authors.lastname: Riemers
authors.forename: Ruud
authors.initials: R
authors.lastname: Licht
authors.forename: Richard
authors.initials: R
authors.lastname: Wubbolts
authors.forename: Douwe
authors.initials: D
authors.lastname: Heuvel
authors.forename: Guy C M
authors.initials: GC
authors.lastname: Grinwis
authors.forename: Hans C M
authors.initials: HC
authors.lastname: Vernooij
authors.forename: Herman A W
authors.initials: HA
authors.lastname: Hazewinkel
authors.forename: Louis C
authors.initials: LC
authors.lastname: Penning
authors.forename: Marianna A
authors.initials: MA
authors.lastname: Tryfonidou
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002478:Cells, Cultured; D004285:Dogs; D005326:Fetal Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D007403:Intervertebral Disc / Q000378:metabolism* / Q000473:pathology; D055959:Intervertebral Disc Degeneration / Q000378:metabolism* / Q000473:pathology; D053533:Keratin-8 / Q000235:genetics / Q000378:metabolism; D009672:Notochord / Q000166:cytology* / Q000378:metabolism; D013045:Species Specificity; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D060449:Wnt Signaling Pathway; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism; D000098908:Brachyury Protein
chemical_list: D015415:Biomarkers; D005326:Fetal Proteins; D053533:Keratin-8; D020825:T-Box Domain Proteins; D051153:Wnt Proteins; D051176:beta Catenin; D000098908:Brachyury Protein