Integrin α1β1 participates in chondrocyte transduction of osmotic stress.
OBJECTIVE
The goal of this study was to determine the role of the collagen binding receptor integrin α1β1 in regulating osmotically induced [Ca(2+)]i transients in chondrocytes.


METHODS
The [Ca(2+)]i transient response of chondrocytes to osmotic stress was measured using real-time confocal microscopy. Chondrocytes from wildtype and integrin α1-null mice were imaged ex vivo (in the cartilage of intact murine femora) and in vitro (isolated from the matrix, attached to glass coverslips). Immunocytochemistry was performed to detect the presence of the osmosensor, transient receptor potential vanilloid-4 (TRPV4), and the agonist GSK1016790A (GSK101) was used to test for its functionality on chondrocytes from wildtype and integrin α1-null mice.


RESULTS
Deletion of the integrin α1 subunit inhibited the ability of chondrocytes to respond to a hypo-osmotic stress with [Ca(2+)]i transients ex vivo and in vitro. The percentage of chondrocytes responding ex vivo was smaller than in vitro and of the cells that responded, more single [Ca(2+)]i transients were observed ex vivo compared to in vitro. Immunocytochemistry confirmed the presence of TRPV4 on wildtype and integrin α1-null chondrocytes, however application of GSK101 revealed that TRPV4 could be activated on wildtype but not integrin α1-null chondrocytes. Integrin α1β1 is a key participant in chondrocyte transduction of a hypo-osmotic stress. Furthermore, the mechanism by which integrin α1β1 influences osmotransduction is independent of matrix binding, but likely dependent on the chondrocyte osmosensor TRPV4.
Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada. Electronic address: cljablon@ucalgary.ca.
Christina L
CL
Jablonski
Faculty of Science, University of Victoria, Victoria, BC, Canada. Electronic address: samferg@uvic.ca.
Samuel
S
Ferguson
Department of Medicine, Vanderbilt University, Nashville, TN, USA; Department of Medicine, Veterans Affairs Hospital, Nashville, TN, USA. Electronic address: ambra.pozzi@vanderbilt.edu.
Ambra
A
Pozzi
Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada; Department of Surgery, Faculty of Medicine, University of Calgary, Calgary, AB, Canada. Electronic address: alclark@kin.ucalgary.ca.
Andrea L
AL
Clark
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D007150:Immunohistochemistry; D039222:Integrin alpha1beta1 / Q000235:genetics / Q000378:metabolism*; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D009997:Osmotic Pressure / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology; D050916:TRPV Cation Channels / Q000819:agonists / Q000378:metabolism
D039222:Integrin alpha1beta1; C530602:N-(1-((4-(2-(((2,4-dichlorophenyl)sulfonyl)amino)-3-hydroxypropanoyl)-1-piperazinyl)carbonyl)-3-methylbutyl)-1-benzothiophene-2-carboxamide; D013449:Sulfonamides; D050916:TRPV Cation Channels; C486576:Trpv4 protein, mouse; D007930:Leucine; D002118:Calcium
Chondrocytes; Integrin α1β1; Intracellular calcium transients; Osmolarity; TRPV4