title: Transcription factor Mohawk and the pathogenesis of human anterior cruciate ligament degradation.
abstract: OBJECTIVE
  To investigate the expression and function of Mohawk (MKX) in human adult anterior cruciate ligament (ACL) tissue and ligament cells from normal and osteoarthritis (OA)-affected knees.
  
  
  METHODS
  Knee joints were obtained at autopsy (within 24-48 hours postmortem) from 13 donors with normal knees (mean ± SD age 36.9 ± 11.0 years), 16 donors with knee OA (age 79.7 ± 11.4 years), and 8 aging donors without knee OA (age 76.9 ± 12.9 years). All cartilage surfaces were graded macroscopically. MKX expression was analyzed by immunohistochemistry and quantitative polymerase chain reaction. ACL-derived cells were used to study regulation of MKX expression by interleukin-1β (IL-1β). MKX was knocked down with small interfering RNA (siRNA) to analyze the function of MKX in extracellular matrix (ECM) production and differentiation in ACL-derived cells.
  
  
  RESULTS
  The expression of MKX was significantly decreased in ACL-derived cells from OA knees compared with normal knees. Consistent with this finding, immunohistochemistry analysis showed that MKX-positive cells were significantly reduced in ACL tissue from OA donors, in particular in cells located in disorientated fibers. In ACL-derived cells, IL-1β strongly suppressed MKX expression and reduced expression of the ligament ECM genes COL1A1 and TNXB. In contrast, SOX9, a chondrocyte master transcription factor, was up-regulated by IL-1β treatment. Importantly, knockdown of MKX expression with siRNA up-regulated SOX9 expression in ACL-derived cells, whereas the expression of COL1A1 and TNXB was reduced.
  
  
  CONCLUSIONS
  Reduced expression of MKX is a feature of degenerated ACL in OA-affected joints, and this may be mediated in part by IL-1β. MKX appears necessary to maintain the tissue-specific cellular differentiation status and ECM production in adult human tendons and ligaments.
authors.affiliation: The Scripps Research Institute, La Jolla, CA 92037, USA. asahara@scripps.edu
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakahara
authors.forename: Akihiko
authors.initials: A
authors.lastname: Hasegawa
authors.forename: Koji
authors.initials: K
authors.lastname: Otabe
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Ayabe
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Matsukawa
authors.forename: Naoko
authors.initials: N
authors.lastname: Onizuka
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Ito
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Ozaki
authors.forename: Martin K
authors.initials: MK
authors.lastname: Lotz
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Asahara
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016118:Anterior Cruciate Ligament / Q000378:metabolism* / Q000473:pathology; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D019902:Chondrocytes / Q000378:metabolism / Q000473:pathology; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology*; D020868:Gene Silencing; D018398:Homeodomain Proteins / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000378:metabolism* / Q000473:pathology; D034741:RNA, Small Interfering / Q000235:genetics; D055758:SOX9 Transcription Factor / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018398:Homeodomain Proteins; D034741:RNA, Small Interfering; D055758:SOX9 Transcription Factor; D014157:Transcription Factors; C093504:SCX protein, human; C527932:SOX9 protein, human