Role of NF-kappaB transcription factors in antiinflammatory and proinflammatory actions of mechanical signals.
OBJECTIVE
The mechanisms by which chondrocytes convert biomechanical signals into intracellular biochemical events are not well understood. In this study, we sought to determine the intracellular mechanisms of the magnitude-dependent actions of mechanical signals.


METHODS
Chondrocytes isolated from rabbit articular cartilage were grown on flexible membranes. Cells were subjected to cyclic tensile strain (CTS) of various magnitudes in the presence or absence of interleukin-1beta (IL-1beta), which was used as a proinflammatory signal for designated time intervals. The regulation of NF-kappaB was measured by reverse transcriptase-polymerase chain reaction, electrophoretic mobility shift assay, and immunofluorescence.


RESULTS
CTS of low magnitudes (4-8% equibiaxial strain) was a potent inhibitor of IL-1beta-dependent NF-kappaB nuclear translocation. Cytoplasmic retention of NF-kappaB and reduction of its synthesis led to sustained suppression of proinflammatory gene induction. In contrast, proinflammatory signals generated by CTS of high magnitudes (15-18% equibiaxial strain) mimicked the actions of IL-1beta and induced rapid nuclear translocation of NF-kappaB subunits p65 and p50.


CONCLUSIONS
Magnitude-dependent signals of mechanical strain utilize the NF-kappaB transcription factors as common elements to abrogate or aggravate proinflammatory responses. Furthermore, the intracellular events induced by mechanical overload are similar to those that are initiated by proinflammatory cytokines in arthritis.
Agarwal
Sudha
S
Biomechanical and Tissue Engineering Laboratory, Section of Oral Biology, Ohio State University, 305 West 12th Avenue, Columbus, OH 43210, USA. agarwal.61@osu.edu
Deschner
James
J
Long
Ping
P
Verma
Anupam
A
Hofman
Cynthia
C
Evans
Christopher H
CH
Piesco
Nicholas
N
D021581:Active Transport, Cell Nucleus; D000818:Animals; D001168:Arthritis / Q000209:etiology* / Q000517:prevention & control*; D002358:Cartilage, Articular / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism*; D016207:Cytokines / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects; D018836:Inflammation Mediators / Q000378:metabolism; D007375:Interleukin-1 / Q000494:pharmacology; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D015398:Signal Transduction; D013314:Stress, Mechanical; D014157:Transcription Factors / Q000378:metabolism*
D016207:Cytokines; D018836:Inflammation Mediators; D007375:Interleukin-1; D016328:NF-kappa B; D014157:Transcription Factors