Control of Dkk-1 Ameliorates Chondrocyte Apoptosis, Cartilage Destruction, and Subchondral Bone Deterioration in Osteoarthritic Knees

Objective. Perturbation of Wnt signaling components reportedly regulates chondrocyte fate and joint disorders. The Wnt inhibitor Dkk-1 mediates remodeling of various tissue types. We undertook this study to examine whether control of Dkk-1 expression prevents joint deterioration in osteoarthritic (OA) knees. Methods. Anterior cruciate ligament transection and collagenase-induced OA in rat knees was treated with end-capped phosphorothioate Dkk-1 antisense oligonucleotide (Dkk-1-AS). Articular cartilage destruction, cartilage degradation markers, bone mineral density (BMD), and subchondral trabecular bone volume of injured knee joints were measured using Mankin scoring, enzyme-linked immunosorbent assay, dual x-ray absorptiometry, and histomorphometry. Dkk-1-responsive molecule expression and apoptotic cells in knee tissue were detected by quantitative reverse transcriptase-polymerase chain reaction, immunoblotting, and TUNEL staining. Results. Up-regulated Dkk-1 expression was associated with increased Mankin score and with increased serum levels of cartilage oligomeric matrix protein and C-telopeptide of type II collagen (CTX-II) during OA development. Dkk-1-AS treatment alleviated OA-associated increases in Dkk-1 expression, Mankin score, cartilage fibrillation, and serum cartilage degradation markers. Dkk-1-AS also alleviated epiphyseal BMD loss and subchondral bone exposure associated with altered serum levels of osteocalcin and CTX-I. The treatment abrogated chondrocyte/osteoblast apoptosis and subchondral trabecular bone remodeling in OA. Dkk-1 knockdown increased levels of nuclear beta-catenin and phosphorylated Ser(473)-Akt but attenuated expression of inflammatory factors (Toll-like receptor 4 [TLR-4], TLR-9, interleukin-1 beta, and tumor necrosis factor alpha), the apoptosis regulator Bax, matrix metalloproteinase 3, and RANKL in OA knee joints. Conclusion. Interference with the cartilage- and bone-deleterious actions of Dkk-1 provides therapeutic potential for alleviating cartilage destruction and subchondral bone damage in OA knee joints.