Induced inactivation of Wnt16 in young adult mice has no impact on osteoarthritis development.

Osteoarthritis (OA) is a common disorder and a major cause of disability in the elderly population. WNT16 has been suggested to play important roles in joint formation, bone homeostasis and OA development, but the mechanism of action is not clear. Transgenic mice lacking Wnt16 expression (Wnt16-/-) have a more severe experimental OA than control mice. In addition, Wnt16-/- mice have a reduced cortical thickness and develop spontaneous fractures. Herein, we have used Cre-Wnt16flox/flox mice in which Wnt16 can be conditionally ablated at any age through tamoxifen-inducible Cre-mediated recombination. Wnt16 deletion was induced in 7-week-old mice to study if the Cre-Wnt16flox/flox mice have a more severe OA phenotype after destabilizing the medial meniscus (DMM surgery) than littermate controls with normal Wnt16 expression (Wnt16flox/flox). WNT16 deletion was confirmed in articular cartilage and cortical bone in Cre-Wnt16flox/flox mice, shown by immunohistochemistry and reduced cortical bone area compared to Wnt16flox/flox mice. After DMM surgery, there was no difference in OA severity in the articular cartilage in the knee joint between the Cre-Wnt16flox/flox and Wnt16flox/flox mice in neither female nor male mice. In addition, there was no difference in osteophyte size in the DMM-operated tibia between the genotypes. In conclusion, inactivation of Wnt16 in adult mice do not result in a more severe OA phenotype after DMM surgery. Thus, presence of WNT16 in adult mice does not have an impact on experimental OA development. Taken together, our results from Cre-Wnt16flox/flox mice and previous results from Wnt16-/- mice suggest that WNT16 is crucial during synovial joint establishment leading to limited joint degradation also later in life, after onset of OA. This may be important when developing new therapeutics for OA treatment.