Characterization of mature vs aged rabbit articular cartilage: analysis of cell density, apoptosis-related gene expression and mechanisms controlling chondrocyte apoptosis.
OBJECTIVE
The prevalence of osteoarthritis (OA) is increased in aged individuals and a direct correlation between chondrocyte apoptosis and cartilage degradation secondary to OA has been demonstrated. To address the question of whether age predisposes articular cartilage to apoptosis, the objective of the present study was to characterize and compare in aged and mature non-OA rabbit articular cartilage, cell density and expression levels of specific genes associated with apoptosis. Mechanistic studies on the inhibition of induced apoptosis were also carried out.


METHODS
Grade I (non-OA) femoral condyles and tibial plateaus from mature and aged rabbits were taken for assessment of viable cell density (VCD) and mRNA (reverse transcription-polymerase chain reaction) expression levels of the pro-apoptotic genes, Fas, Fas ligand (FasL), caspase-8, inducible nitric oxide synthase (iNOS) and p53. In vitro insulin-like growth factor (IGF-1)-mediated inhibition of nitric oxide (NO)-induced apoptosis was also examined using sodium nitroprusside (SNP) as NO donor.


RESULTS
VCD was decreased 50-70% in aged articular cartilage relative to mature cartilage. mRNA expression levels of Fas, FasL, caspase-8 and p53 were higher in aged cartilage than in mature cartilage. iNOS expression was unchanged. IGF-1-mediated inhibition of NO-induced apoptosis was dose-dependent and reversed with addition of phosphatidylinositol-3 kinase inhibitor.


CONCLUSIONS
This controlled animal model study demonstrates that age predisposes articular cartilage to changes in VCD and expression levels of specific pro-apoptotic genes. It is significant that these findings were demonstrated on cartilage that showed no prior signs of OA; it is also possible that such changes are a prelude to the age-related development of OA.
Todd Allen
R
R
Department of Orthopaedic Surgery, University of California San Diego, La Jolla, CA 92093-0630, USA.
Robertson
Catherine M
CM
Harwood
Frederick L
FL
Sasho
Takahisa
T
Williams
Seth K
SK
Pomerleau
Adam C
AC
Amiel
David
D
D000375:Aging / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D002358:Cartilage, Articular / Q000502:physiology*; D053181:Caspase 8; D020169:Caspases / Q000235:genetics; D002452:Cell Count; D019902:Chondrocytes / Q000502:physiology*; D053222:Fas Ligand Protein; D015870:Gene Expression / Q000502:physiology*; D006614:Hindlimb; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D008562:Membrane Glycoproteins / Q000235:genetics; D019001:Nitric Oxide Synthase / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D016159:Tumor Suppressor Protein p53 / Q000235:genetics
D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D007334:Insulin-Like Growth Factor I; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D053181:Caspase 8; D020169:Caspases