Dickkopf-3 enhances the chondroprotective effect of chondrogenic progenitor cells in a rat model of posttraumatic osteoarthritis.

BACKGROUND: Our previous work suggested biological potential alterations in chondrogenic progenitor cells (CPCs) during knee osteoarthritic progression. The Wnt pathway plays a pivotal role in osteoarthritis progression, and Dickkopf-3 (DKK3) is a noncanonical Wnt antagonist. However, it remains unclear whether the DKK3 expression level is involved in the changes of the biological characteristics of CPCs during OA progression. This study aimed to explore the difference of DKK3 expression in osteochondral specimens and corresponding CPCs during osteoarthritis progression. Furthermore, the influence of DKK3 on the in vitro characteristics and in vivo therapeutic efficacy of CPCs was investigated. METHODS: The expression levels of DKK3 in human paired grade 1-2 and grade 3-4 osteoarthritic cartilage and corresponding CPCs were determined via immunohistochemical staining and western blotting, respectively. CPCs were isolated, cultured and characterized for their self-renewal and multidifferentiation abilities. Then, the CPCs were transfected with Lentiviral-DKK3 or siRNA to overexpress or knock down DKK3, respectively. The chondrogenic potential of the CPCs was examined via pellet staining and gene detection. The expression levels of inflammatory factors in different groups of CPCs were examined via qRT‒PCR and ELISA. The activation status of β-catenin in Wnt signalling was investigated via confocal microscopy. The in vivo chondroprotective effects of LV-DKK3 and Si-DKK3-transgenic CPCs were examined in a rat model of posttraumatic osteoarthritis. RESULTS: The DKK3 expression level was significantly increased in Grade 3-4 cartilage compared with Grade 1-2 cartilage. However, the DKK3 expression level was significantly lower in Grade 3-4 CPCs than in Grade 1-2 CPCs. The overexpression of DKK3 significantly increased CPC chondrogenic potential and inhibited the expression of catabolic factors, whereas the knockdown of DKK3 had the opposite effects, decreasing CPC chondrogenic potential and increasing the expression of catabolic factors. Wnt signalling was significantly inhibited by DKK3. The in vivo results suggested that lentivirus-induced LV-dkk3 significantly delayed the progression of experimental OA, whereas lentivirus-mediated Si-DKK3, which aimed to silence endogenous DKK3, accelerated the progression of experimental OA. CONCLUSION: Our results suggest that DKK3 has a chondroprotective effect during osteoarthritis progression and that CPCs may be functional targets. The underlying mechanisms of DKK3 may include enhancing CPC chondrogenic capacity and inhibiting Wnt-mediated expression of catabolic factors and matrix remodelling activities. These findings indicate that DKK3 is a potential therapeutic target for CPC-mediated OA treatment.