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The aim of the study was to investigate the expression of genes regulating cholesterol efflux in human chondrocytes and to study the effect of an LXR agonist on cholesterol efflux and lipid accumulation in osteoarthritic chondrocytes.

Human cartilage was obtained from 24 patients with primary osteoarthritis (OA) undergoing total knee replacement surgery. Normal cartilage was obtained from 8 individuals undergoing fracture repair surgery, with no history of joint disease. ATP-binding-cassette transporter A1(ABCA1), apolipoprotein A1 (ApoA1), and liver X receptors(LXRα and LXRβ) mRNA expression levels were evaluated using real-time PCR. The effect of the synthetic LXR agonist TO-901317 was studied after treatment of osteoarthritic chondrocytes and subsequent investigation of ABCA1 and ApoA1 mRNA expression levels. Cholesterol efflux was evaluated in osteoarthritic chondrocytes radiolabeled with [1,2(n)-3H] cholesterol after LXR treatment, while intracellular lipid accumulation was studied after Oil-red-O staining. Apoptosis was evaluated using flow cytometry.

ApoA1, ABCA1, LXRα and LXRβ mRNA expressions were significantly lower in osteoarthritic chondrocytes compared to normal. Treatment of osteoarthritic chondrocytes with the LXR agonist TO-901317 significantly increased ApoA1 and ABCA1 mRNA expression levels as well as cholesterol efflux, while it significantly reduced apoptosis. Additionally, osteoarthritic chondrocytes presented intracellular lipids deposits, while no deposits were found after treatment with TO-901317.

Our findings suggest that impaired expression of genes regulating cholesterol efflux may be a critical player in osteoarthritis, while the ability of the LXR agonist to facilitate cholesterol efflux and decrease apoptosis suggests that it may be a target for therapeutic intervention in osteoarthritis.

Correspondence should be addressed to Anastasia C. Tilentzoglou MD, General Secretary of the Board of Directors of HAOST, 20 A. Fleming Str. (N.Filothei), Gr. 15123 Maroussi, Athens Greece. E-mail: info@eexot.gr