Background Progression of osteoarthritis (OA) produces loss of articular cartilage that may culminate in pain, loss of joint function, and disability. Therefore, identification of new biomarkers that predict patients at risk for joint destruction in OA is important. As systemic changes including persistent fundamental differences in skeletal metabolism in OA subjects occur prior to disease development, whole blood analyses could mirror such systemic turnover. Hence, identification of the genes, which are expressed coordinately in the peripheral blood mononuclear cells (PBMCs) and articular cartilage, is essential.
Objectives To identify genes, which expression correlates in the PBMCs and knee articular cartilage in the end-stage OA patients.
Methods We examined the whole blood in 27 healthy volunteers and 28 end-stage OA patients undergoing joint replacement surgery, and knee articular cartilages from the same 28 end-stage OA patients and 26 healthy subjects. p70-S6K, p21, and caspase 3 protein levels were quantified by ELISA. Total RNA isolated from whole blood and articular cartilage was used in expression studies for the genes related to cell growth and proliferation (mammalian target of rapamycin, mTOR), autophagy (ULK1), regulation of cell cycle progression (p21), apoptosis (caspase 3), cartilage extracellular matrix degradation (metalloproteinase (MMP)9; cathepsin K), lipid turnover (fatty acid synthase, FASN), and inflammation (interleukin (IL)-1β). These were performed with quantitative Real-time RT-PCR.
Results The end-stage OA patients have shown significant upregulation of all the examined genes in the PBMCs compared to that in healthy controls. p70-S6K, p21, and caspase 3 protein concentrations measured in PBMCs were also significantly higher in OA patients. Gene expression in OA articular cartilage has shown significant upregulation of mTOR, MMP9, cathepsin K, and FASN versus that in healthy controls. However, ULK1 and p21 genes were downregulated, while no significant change in caspase 3 and IL-1β gene expression was noted in OA cartilage specimens. Plotting of gene expression in PBMCs of the end-stage OA patients versus that in their articular cartilages has revealed positive correlation for mTOR (r=0.687; p=0.01), cathepsin K (r=0.564; p=0.04), and FASN (r=0.890; p=0.03).
Conclusions Significant upregulation and positive correlation of mTOR, cathepsin K, and FASN gene expression in PBMCs and articular cartilages might indicate their presumable co-regulation in both tissues in the end-stage OA. Therefore, mTOR, cathepsin K, and FASN upregulation in the blood could serve an early marker of the knee articular chondrocyte metabolic alterations associated with the disease.
Acknowledgments This study was funded by Russian Foundation for Basic Research (project no. 09-04-01158-a and 12-04-00038-a to EVT).
Disclosure of Interest None Declared