Inducible knockout of CHUK/IKK\u03b1 in adult chondrocytes reduces progression of cartilage degradation in a surgical model of osteoarthritis

Kirsty L Culley,Cecilia L Dragomir,Jun Chang,Tyler Khilnani,Jordan D Green,Samantha G Lessard,Miguel Otero,Kenneth B Marcu,Mary B Goldring,Justin Quinn,Elisabeth B Wondimu

doi:10.1038/s41598-019-45334-5

Kirsty L Culley, Cecilia L Dragomir + Show 9 more

Open Access

https://doi.org/10.1038/s41598-019-45334-5

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Abstract

CHUK/IKKα contributes to collagenase-driven extracellular matrix remodeling and chondrocyte hypertrophic differentiation in vitro, in a kinase-independent manner. These processes contribute to osteoarthritis (OA), where chondrocytes experience a phenotypic shift towards hypertrophy concomitant with abnormal matrix remodeling. Here we investigated the contribution of IKKα to OA in vivo. To this end, we induced specific IKKα knockout in adult chondrocytes in AcanCreERT2/+; IKKαf/f mice treated with tamoxifen (cKO). Vehicle-treated littermates were used as wild type controls (WT). At 12 weeks of age, WT and cKO mice were subjected to the destabilization of medial meniscus (DMM) model of post-traumatic OA. The cKO mice showed reduced cartilage degradation and collagenase activity and fewer hypertrophy-like features at 12 weeks after DMM. Interestingly, in spite of the protection from structural articular cartilage damage, the postnatal growth plates of IKKα cKO mice after DMM displayed abnormal architecture and composition associated with increased chondrocyte apoptosis, which were not as evident in the articular chondrocytes of the same animals. Together, our results provide evidence of a novel in vivo functional role for IKKα in cartilage degradation in post-traumatic OA, and also suggest intrinsic, cell-autonomous effects of IKKα in chondrocytes that control chondrocyte phenotype and impact on cell survival, matrix homeostasis, and remodeling.

Highlights

Articular chondrocytes are terminally differentiated, quiescent cells that display stable phenotypes functionally characterized by a slow matrix turnover, with a fine-tuned balance between anabolic and catabolic actions, which are responsible for maintaining the structural and functional integrity of articular cartilage[1]
We show that IKKα has cell-intrinsic roles in adult articular and growth plate chondrocytes in vivo, which impact on cell survival, phenotypic stability, and matrix homeostasis and remodeling
Previous studies showed that global IKKα-deficient mice display skin abnormalities concomitant with defective limb morphogenesis and perinatal lethality[27,28,29]; and to study the role of IKKα in OA articular chondrocytes in vivo, we generated mice with inducible aggrecan-driven cartilage-specific IKKα knockout, where IKKα knockout can be induced in adult chondrocytes

Summary

Introduction

Articular chondrocytes are terminally differentiated, quiescent cells that display stable phenotypes functionally characterized by a slow matrix turnover, with a fine-tuned balance between anabolic and catabolic actions, which are responsible for maintaining the structural and functional integrity of articular cartilage[1]. To assess whether the cartilage protection observed in cKO mice post-DMM correlated with decreased collagenase activity in vivo, we performed immunohistochemical analyses in WT and cKO cartilage sections using the C1, 2C antibody, which detects collagenase-specific cleavage epitopes in type II collagen[6]. In keeping with our in vitro observations, type X collagen immunostaining was reduced in the cKO cartilage samples at 12 weeks post-DMM (Fig. 3C,D), suggesting that hypertrophy-like differentiation was impaired in the absence of IKKα in vivo.

Results

Conclusion