title: Collagen crosslinking and cell density have distinct effects on fibroblast-mediated contraction of collagen gels.
abstract: OBJECTIVE
  Fibroblasts are actively and dynamically involved in wound healing (dermal regeneration, wound contraction, and scar contracture) and fibrosis. Fibroblast-seeded collagen gels provide an in vitro model for these processes. Over time, fibroblasts will contract the gels, but the mechanisms are not completely understood. This research investigated the influence of cell density and collagen crosslinking on the contraction of fibroblast-populated gels by varying seeding density and blocking the catalyzing enzyme lysyl oxidase, respectively.
  
  
  METHODS
  Collagen gels were seeded with fibroblasts at either 3 x 104 or 1 x 105 cells/mL and incubated with or without the lathyrogen beta-aminoproprionitrile (BAPN) for 8 days. In all, four experimental groups were analyzed: low cell density control, high cell density control, low density plus BAPN, and high density plus BAPN. Digital images were taken daily and gel area was calculated.
  
  
  RESULTS
  Contraction was dependent on cell concentration, with higher density gels being contracted to a greater extent. BAPN had no effect until after day 2 when it inhibited (high density) or almost completely blocked (low density) the gel contraction. BAPN also reduced total long-term contraction.
  
  
  CONCLUSIONS
  The results demonstrated a bimodal nature to fibroblast-mediated gel contraction: a cell density-dependent component, most likely mediated through cellular forces, and a delayed collagen crosslinking component that could be blocked by BAPN. In the long-term, similar contraction rates among the four experimental groups, particularly between the two BAPN groups, implies that the collagen crosslinking effect is discrete and independent of cell density.
authors.affiliation: Department of Pediatric General and Thoracic Surgery, Children's Hospital of Philadelphia and University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Redden
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Doolin
mesh_terms: D000629:Aminopropionitrile / Q000494:pharmacology; D002452:Cell Count; D003094:Collagen / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology* / Q000502:physiology*; D005782:Gels; D006801:Humans; D013997:Time Factors
chemical_list: D005782:Gels; D000629:Aminopropionitrile; D003094:Collagen