title: Hypoxia: a critical regulator of early human tendinopathy.
abstract: OBJECTIVE
  To seek evidence for the role of hypoxia in early human tendinopathy, and thereafter to explore mechanisms whereby tissue hypoxia may regulate apoptosis, inflammatory mediator expression and matrix regulation in human tenocytes.
  
  
  METHODS
  Fifteen torn supraspinatus tendon (established pathology) and matched intact subscapularis tendon (representing 'early pathology') biopsies were collected from patients undergoing arthroscopic shoulder surgery. Control samples of the subscapularis tendon were collected from 10 patients undergoing arthroscopic stabilisation surgery. Markers of hypoxia were quantified by immunohistochemical methods. Human tendon-derived primary cells were derived from hamstring tendon tissue obtained during hamstring tendon anterior cruciate ligament reconstruction. The impact of hypoxia upon tenocyte biology ex vivo was measured using quantitative real-time PCR, multiplex cytokine assays, apoptotic proteomic profiling, immunohistochemistry and annexin V fluorescence-activated cell sorter staining.
  
  
  RESULTS
  Increased expression of hypoxia-inducible factor 1α, Bcl-2 and clusterin was detected in subscapularis tendon samples compared with both matched torn samples and non-matched control samples (p<0.01). Hypoxic tenocytes exhibited increased production of proinflammatory cytokines (p<0.001), altered matrix regulation (p<0.01) with increased production of collagen type III operating through a mitogen-activated protein kinase-dependent pathway. Finally, hypoxia increased the expression of several mediators of apoptosis and thereby promoted tenocyte apoptosis.
  
  
  CONCLUSIONS
  Hypoxia promotes the expression of proinflammatory cytokines, key apoptotic mediators and drives matrix component synthesis towards a collagen type III profile by human tenocytes. The authors propose hypoxic cell injury as a critical pathophysiological mechanism in early tendinopathy offering novel therapeutic opportunities in the management of tendon disorders.
authors.affiliation: Institute of Infection, Immunity and Inflammation, College of Medicine, Veterinary and Life Sciences, University of Glasgow, UK. neal.millar@glasgow.ac.uk
authors.forename: Neal L
authors.initials: NL
authors.lastname: Millar
authors.forename: James H
authors.initials: JH
authors.lastname: Reilly
authors.forename: Shauna C
authors.initials: SC
authors.lastname: Kerr
authors.forename: Abigail L
authors.initials: AL
authors.lastname: Campbell
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Little
authors.forename: William J
authors.initials: WJ
authors.lastname: Leach
authors.forename: Brian P
authors.initials: BP
authors.lastname: Rooney
authors.forename: George A C
authors.initials: GA
authors.lastname: Murrell
authors.forename: Iain B
authors.initials: IB
authors.lastname: McInnes
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001182:Arthroscopy; D015687:Cell Hypoxia / Q000502:physiology*; D002478:Cells, Cultured; D003094:Collagen / Q000096:biosynthesis / Q000378:metabolism; D016207:Cytokines / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D008875:Middle Aged; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D017006:Rotator Cuff / Q000187:drug effects / Q000473:pathology / Q000601:surgery; D000070636:Rotator Cuff Injuries; D012785:Shoulder Joint / Q000601:surgery; D052256:Tendinopathy / Q000378:metabolism / Q000473:pathology*; D055815:Young Adult; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors
chemical_list: D016207:Cytokines; D004791:Enzyme Inhibitors; D018836:Inflammation Mediators; D003094:Collagen; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases