title: The expression of NG2 proteoglycan in the human intervertebral disc.
abstract: METHODS
  Immunohistochemical and biochemical analyses of NG2 proteoglycan in the human intervertebral disc.
  
  
  OBJECTIVE
  To determine if the human intervertebral disc expresses NG2 proteoglycan.
  
  
  BACKGROUND
  In the nervous system, NG2 has been reported to play an important role as an interactive extracellular matrix component and membrane receptor for growth factors. NG2 is also found in non-neuronal tissues, such as cartilage and bone; however, the expression of NG2 within the human intervertebral disc is unknown.
  
  
  METHODS
  NG2 expression in the intervertebral disc was examined through Western blotting, reverse transcriptase polymerase chain reaction, and immunohistochemistry. Confocal microscopy was used to assess the spatial association of NG2 with type VI collagen. To reveal changes in the content of NG2 with disc degeneration, Western blot analysis was used to assess the relative content of NG2 in human intervertebral disc tissues with varying degrees of degeneration.
  
  
  RESULTS
  NG2 was clearly identified in cells from both the anulus fibrosus and nucleus pulposus, and colocalized with both type VI collagen and beta-integrin, located in the inner area of the cell-associated matrix. Throughout the anterior and posterior regions of the disc tissues, most cells were confirmed to be NG2 positive. Cells expressed NG2 messenger ribonucleic acid, and Western blot confirmed the presence of the core protein of the NG2 protein, 250 kDa. A study comparing the different grades of disc degeneration showed that the content of NG2 was elevated in disc tissues in an advanced stage of degeneration compared to tissues in an early stage of degeneration.
  
  
  CONCLUSIONS
  Although the biologic role of NG2 remains to be elucidated, the colocalization of NG2 with type VI collagen in the pericellular area suggests that NG2 may play an important role in cell-matrix interactions. The high level of NG2 expression in advanced degeneration also suggests an important role of NG2 in the loss of disc integrity.
authors.affiliation: Department of Orthopedic Surgery, Rush Medical College at Rush University Medical Center, Chicago, IL, USA.
authors.forename: Koji
authors.initials: K
authors.lastname: Akeda
authors.forename: Howard S
authors.initials: HS
authors.lastname: An
authors.forename: Rajeswari
authors.initials: R
authors.lastname: Pichika
authors.forename: Kalpa
authors.initials: K
authors.lastname: Patel
authors.forename: Carol
authors.initials: C
authors.lastname: Muehleman
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakagawa
authors.forename: Atsumasa
authors.initials: A
authors.lastname: Uchida
authors.forename: Koichi
authors.initials: K
authors.lastname: Masuda
mesh_terms: D000368:Aged; D000941:Antigens / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology; D002478:Cells, Cultured; D005109:Extracellular Matrix / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D007403:Intervertebral Disc / Q000378:metabolism* / Q000473:pathology; D008875:Middle Aged; D011509:Proteoglycans / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D000099216:Chondroitin Sulfate Proteoglycan 4
chemical_list: D000941:Antigens; D011509:Proteoglycans; D000099216:Chondroitin Sulfate Proteoglycan 4