Introduction The pathogenesis of OA is not fully characterised, but is thought to be due to perturbation of chondrocytes homeostasis including an impairment in the autophagy process particularly during ageing. Among the anti-ageing factors, Klotho has been shown to regulate autophagy in a variety of cell types, and Klotho polymorphisms have been associated with higher risks of OA.

Objectives The aim of this project was to investigate the role of Klotho in OA.

Methods The expression of Klotho and autophagy markers (LC3b and Beclin-1) and OA onset were evaluated in ageing C57BL/6 mice as an age-related spontaneous model of OA. The cartilage integrity, autophagy and apoptosis status in Klotho-deficient mice knee joints were also analysed. In parallel, to investigate the relationship between Klotho and autophagy, immature murine articular chondrocytes (iMACs) were stimulated with increasing doses of soluble recombinant Klotho. The effect of Klotho on autophagy was also evaluated in a pathological context, i.e. following IL1-β stimulation (10 ng/ml) for 24 hours. Bax/Bcl-2 ratio, a marker of the intrinsic apoptotic pathway, was also evaluated in IL1-β-treated chondrocytes.

Results In the knee joints of mice from escalating ages, the expression of Klotho correlated with LC3b and Beclin-1 expression and gradually decreased with age while OA features appear. Articular cartilage of KL-/- mice revealed an increase in the OARSI score, associated with increased chondrocyte death and LC3b expression, as well as caspase 3 and TUNEL expression. In IL1-β-treated chondrocytes, the autophagy markers and Bax/Bcl-2 ratio were overexpressed, while the addition of Klotho counteracted this effect.

Conclusions In summary, we described an early articular cartilage degradation in the absence of Klotho, suggesting a potential protective role of Klotho in OA development. The increase in autophagic process in Klotho mutant mice associated with the decrease in autophagy and Klotho expression with age clearly indicate intimate relationships between these two players. In vitro experiments suggested that Klotho may not have a direct effect on autophagy but rather through reducing apoptosis induced by pro-inflammatory cytokines such as IL1-β. Our study revealed the close relationship between the anti-ageing Klotho protein and chondrocyte death in articular cartilage, unveiling Klotho as a potential target to enhance chondrocyte survival.

Disclosure of interest None declared