title: Type VI Collagen Regulates Pericellular Matrix Properties, Chondrocyte Swelling, and Mechanotransduction in Mouse Articular Cartilage.
abstract: OBJECTIVE
  Mechanical factors play a critical role in the physiology and pathology of articular cartilage, although the mechanisms of mechanical signal transduction are not fully understood. We undertook this study to test the hypothesis that type VI collagen is necessary for mechanotransduction in articular cartilage by determining the effects of type VI collagen knockout on the activation of the mechano-osmosensitive, calcium-permeable channel TRPV4 (transient receptor potential vanilloid channel 4) as well as on osmotically induced chondrocyte swelling and pericellular matrix (PCM) mechanical properties.
  
  
  METHODS
  Confocal laser scanning microscopy was used to image TRPV4-mediated calcium signaling and osmotically induced cell swelling in intact femora from 2- and 9-month-old wild-type (WT) and type VI collagen-deficient (Col6a1(-/-)) mice. Immunofluorescence-guided atomic force microscopy was used to map PCM mechanical properties based on the presence of perlecan.
  
  
  RESULTS
  Hypo-osmotic stress-induced TRPV4-mediated calcium signaling was increased in Col6a1(-/-) mice relative to WT controls at 2 months. Col6a1(-/-) mice exhibited significantly increased osmotically induced cell swelling and decreased PCM moduli relative to WT controls at both ages.
  
  
  CONCLUSIONS
  In contrast to our original hypothesis, type VI collagen was not required for TRPV4-mediated Ca(2+) signaling; however, knockout of type VI collagen altered the mechanical properties of the PCM, which in turn increased the extent of cell swelling and osmotically induced TRPV4 signaling in an age-dependent manner. These findings emphasize the role of the PCM as a transducer of mechanical and physicochemical signals, and they suggest that alterations in PCM properties, as may occur with aging or osteoarthritis, can influence mechanotransduction via TRPV4 or other ion channels.
authors.affiliation: Duke University Medical Center, Durham, North Carolina.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Zelenski
authors.forename: Holly A
authors.initials: HA
authors.lastname: Leddy
authors.forename: Johannah
authors.initials: J
authors.lastname: Sanchez-Adams
authors.forename: Jinzi
authors.initials: J
authors.lastname: Zhang
authors.forename: Paolo
authors.initials: P
authors.lastname: Bonaldo
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Liedtke
authors.forename: Farshid
authors.initials: F
authors.lastname: Guilak
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism*; D019902:Chondrocytes / Q000378:metabolism*; D024142:Collagen Type VI / Q000235:genetics* / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism*; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism; D040542:Mechanotransduction, Cellular / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D009997:Osmotic Pressure; D050916:TRPV Cation Channels / Q000378:metabolism*
chemical_list: C540085:Col6a1 protein, mouse; D024142:Collagen Type VI; D019812:Heparan Sulfate Proteoglycans; D050916:TRPV Cation Channels; C486576:Trpv4 protein, mouse; C071927:perlecan