title: First insights into human acetabular labrum cell metabolism.
abstract: OBJECTIVE
  Hip labrum pathology has only begun to emerge as a significant source of groin pain in the last decade since the development of hip arthroscopy. Few data are available on the anatomy, histology and function of this structure. Moreover, no metabolic data exist at cellular level. The aim of this study was to characterize extracellular matrix (ECM) genes and pro-inflammatory mediators expressed by these cells.
  
  
  METHODS
  Isolated human acetabular labrum cells were cultured in alginate beads for 10 days and additionally stimulated with interleukin (IL)-1 for 24 h. Gene expression levels and secretion of different ECM genes, enzymes and cytokines were examined by quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA) to assess the metabolic characteristics of labrum cells. Articular chondrocytes and meniscus cells served as controls.
  
  
  RESULTS
  Labrum cells expressed high levels of COL1A1 and low levels of COL2A1, aggrecan and SOX-9 compared to chondrocytes. However, COL2A1 was more expressed by labrum cells than by meniscus cells. The expression of matrix metalloproteinase (MMP)-1/-2/-9, ADAMTS-4 and IL-6 was significantly higher in labrum cells than in chondrocytes. IL-1 suppressed the ECM gene expression levels of labrum cells, but increased the expression levels and release of MMP-1/-3/-9/-13 and ADAMTS-4 and IL-6 by these cells. Remarkably, MMP-9 was only significantly upregulated in acetabular labrum cells.
  
  
  CONCLUSIONS
  The findings in this study demonstrated that the acetabular labrum is populated with unique highly active fibrochondrocyte-like cells. These cells are capable of expressing and releasing pro-inflammatory enzymes and cytokines and react to a pro-inflammatory stimulus. In this way, they contribute obviously to disturbed tissue function in hip labrum pathology.
authors.affiliation: Laboratory of Connective Tissue Biology, Department of Rheumatology, Ghent University, Ghent, Belgium. Aad.Dhollander@Ugent.be
authors.forename: A A M
authors.initials: AA
authors.lastname: Dhollander
authors.forename: S
authors.initials: S
authors.lastname: Lambrecht
authors.forename: P C M
authors.initials: PC
authors.lastname: Verdonk
authors.forename: E A
authors.initials: EA
authors.lastname: Audenaert
authors.forename: K F
authors.initials: KF
authors.lastname: Almqvist
authors.forename: C
authors.initials: C
authors.lastname: Pattyn
authors.forename: R
authors.initials: R
authors.lastname: Verdonk
authors.forename: D
authors.initials: D
authors.lastname: Elewaut
authors.forename: G
authors.initials: G
authors.lastname: Verbruggen
mesh_terms: D000077:Acetabulum / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D000368:Aged; D000369:Aged, 80 and over; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism; D048430:Cell Shape / Q000187:drug effects; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism; D005109:Extracellular Matrix / Q000187:drug effects / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000096:biosynthesis / Q000235:genetics; D005260:Female; D020869:Gene Expression Profiling / Q000379:methods; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D007375:Interleukin-1 / Q000494:pharmacology; D008297:Male; D008592:Menisci, Tibial / Q000166:cytology / Q000378:metabolism; D008875:Middle Aged
chemical_list: D016326:Extracellular Matrix Proteins; D018836:Inflammation Mediators; D007375:Interleukin-1