Apoptosis and p53 expression in chondrocytes relate to degeneration in articular cartilage of immobilized knee joints.
OBJECTIVE
We have reported that articular cartilage showed early stage degeneration at 7 and 14 days after immobilization, moderate degeneration at 28 days, and severe degeneration at 42 days in rabbits. To test whether apoptosis occurs in association with p53 expression in chondrocytes during the process of articular cartilage degeneration, we investigated the degree of cartilage degeneration, the frequency of apoptotic cells, and the levels of p53 mRNA in rabbits and mice after knee immobilization.


METHODS
Right knees of male Japanese white rabbits were immobilized in full extension with fiberglass casts for up to 42 days. Similarly, right knees of male p53 wild-type [p53 (+/+)] and p53 null [p53 (-/-)] mice were immobilized in full extension with bandage tape for up to 84 days. Apoptotic cells were confirmed by TUNEL staining on the sections of knee joints. Total RNA of articular chondrocytes obtained from Day 0 or immobilized knees was analyzed semiquantitatively by RT-PCR using specific primers for p53.


RESULTS
Articular cartilage degenerated after immobilization of p53 (+/+) mouse knees, but not after immobilization of p53 (-/-) knees. Apoptotic cells were observed in articular cartilage in the femur and tibia of rabbits and p53 (+/+) mice after immobilization. However, only a few apoptotic cells were observed at the same sites in p53 (-/-) mice. In RT-PCR analysis, the levels of p53 mRNA obtained from immobilized groups were significantly higher than those of Day 0 groups in rabbit and p53 (+/+) mouse knees.


CONCLUSIONS
Apoptosis and p53 expression in chondrocytes relate to degeneration in articular cartilage of immobilized knee joints.
Okazaki
Ryuji
R
Department of Radiation Biology and Health, University of Occupational and Environmental Health, Kitakyushu, Japan.
Sakai
Akinori
A
Ootsuyama
Akira
A
Sakata
Takeshi
T
Nakamura
Toshitaka
T
Norimura
Toshiyuki
T
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002358:Cartilage, Articular / Q000473:pathology; D019902:Chondrocytes / Q000473:pathology* / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D007103:Immobilization / Q000009:adverse effects*; D020287:In Situ Nick-End Labeling; D007202:Indicators and Reagents; D007719:Knee Joint / Q000473:pathology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010619:Phenazines; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics*
D007202:Indicators and Reagents; D010619:Phenazines; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; C009195:safranine T