title: Matrix metalloproteinase 12 is an indicator of intervertebral disc degeneration co-expressed with fibrotic markers.
abstract: Recent evidence suggests a role of fibrogenesis in intervertebral disc (IVD) degeneration. We aim to explore if fibrotic genes may serve as IVD degeneration indicators, and if their expression is associated with myofibroblast activity.
  
  
  
  Transcriptional expression of fibrosis markers (COL1A1, COL3A1, FN1, HSP47, MMP12, RASAL1) were analyzed in degenerated (D) and non-degenerated (ND) human nucleus pulposus (NP) and annulus fibrosus (AF) cells, along with traditional (SOX9, ACAN) and newly established degeneration markers (CDH2, KRT19, KRT18, FBLN1, MGP, and COMP). Protein expression was investigated by immunohistochemistry in human IVDs, and in rodent IVDs undergoing natural ageing or puncture-induced degeneration. Co-expression with myofibroblast markers was examined by double staining on human and rat specimens. Disc degeneration severity and extent of fibrosis were determined by histological scoring and picrosirius red staining respectively.
  
  
  
  Human D-NP showed more intensive staining for picrosirius red than ND-NP. Among the genes examined, D-NP showed significantly higher MMP12 expression along with lower KRT19 expression. Protein expression analysis revealed increased MMP12(+) cells in human D-IVD. Histological scoring indicated mild degeneration in the punctured rat discs and discs of ageing mouse. Higher MMP12 positivity was found in peripheral NP and AF of the degenerative rat discs and in NP of the aged mice. In addition, human D-NP and D-AF showed increased α-SMA(+) cells, indicating enhanced myofibroblast activity. MMP12 was found co-expressed with α-SMA, FSP1 and FAP-α in human and rat degenerative IVDs.
  
  
  
  Our study suggests that in addition to a reduced KRT19 expression, an increased expression of MMP12, a profibrotic mediator, is characteristic of disc degenerative changes. Co-expression study indicates an association of the increased MMP12 positivity with myofibroblast activity in degenerated IVDs. Overall, our findings implicate an impact of MMP12 in disc cell homeostasis. The precise role of MMP12 in IVD degeneration warrants further investigation.
authors.affiliation: Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, China; HKU Shenzhen Institute of Research and Innovation, China; Center for Reproduction, Development and Growth, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China; Stem Cell & Regenerative Medicine Consortium, The University of Hong Kong, Hong Kong, China. Electronic address: fengjuan@hku.hk.
authors.forename: F-J
authors.initials: FJ
authors.lastname: Lv
authors.affiliation: Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, China. Electronic address: u3002479@connect.hku.hk.
authors.forename: Y
authors.initials: Y
authors.lastname: Peng
authors.affiliation: Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, China. Electronic address: h0894164@connect.hku.hk.
authors.forename: F L
authors.initials: FL
authors.lastname: Lim
authors.affiliation: Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, China; Stem Cell & Regenerative Medicine Consortium, The University of Hong Kong, Hong Kong, China. Electronic address: hkusunyi@connect.hku.hk.
authors.forename: Y
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Advanced Technology Research Institution of China Science Institution, Shenzhen, China. Electronic address: lvminmin2015@163.com.
authors.forename: M
authors.initials: M
authors.lastname: Lv
authors.affiliation: Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, China. Electronic address: lxzhou@connect.hku.hk.
authors.forename: L
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Gaungdong, China. Electronic address: wangxucheng@gmail.com.
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Spine Surgery, The First Affiliated Hospital, Sun Yat-sen University, Gaungdong, China. Electronic address: zhengzm1@163.com.
authors.forename: Z
authors.initials: Z
authors.lastname: Zheng
authors.affiliation: Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, China; Center for Reproduction, Development and Growth, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China; Stem Cell & Regenerative Medicine Consortium, The University of Hong Kong, Hong Kong, China. Electronic address: ken-cheung@hku.hk.
authors.forename: K M C
authors.initials: KMC
authors.lastname: Cheung
authors.affiliation: Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, China; HKU Shenzhen Institute of Research and Innovation, China; Center for Reproduction, Development and Growth, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China; Stem Cell & Regenerative Medicine Consortium, The University of Hong Kong, Hong Kong, China. Electronic address: vicleung@hku.hk.
authors.forename: V Y L
authors.initials: VYL
authors.lastname: Leung
mesh_terms: D000818:Animals; D015415:Biomarkers; D005355:Fibrosis; D006801:Humans; D007403:Intervertebral Disc; D055959:Intervertebral Disc Degeneration; D053508:Matrix Metalloproteinase 12; D051379:Mice; D000070614:Nucleus Pulposus; D051381:Rats
chemical_list: D015415:Biomarkers; D053508:Matrix Metalloproteinase 12
keywords: Degeneration; Intervertebral disc; MMP12; Matrix metalloproteinase; Myofibroblast; Nucleus pulposus