Objective The zinc-ZIP8-MTF1 axis induces metallothionein (MT) expression and is a catabolic regulator of experimental osteoarthritis (OA) in mice. The main aim of the current study was to explore the roles and underlying molecular mechanisms of MTs in OA pathogenesis.
Methods Experimental OA in mice was induced by destabilisation of the medial meniscus or intra-articular injection of adenovirus carrying a target gene (Ad-Zip8, Ad-Mtf1, Ad-Epas1, Ad-Nampt, Ad-Mt1 or Ad-Mt2) into wild type, Zip8fl/fl; Col2a1-Cre, Mtf1fl/fl; Col2a1-Cre and Mt1/Mt2 double knockout mice. Primary cultured mouse chondrocytes were infected with Ad-Mt1 or Ad-Mt2, and gene expression profiles analysed via microarray and reverse transcription-PCR. Proteins in human and mouse OA cartilage were identified via immunostaining. Chondrocyte apoptosis in OA cartilage was determined using terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end labelling (TUNEL).
Results MTs were highly expressed in human and mouse OA cartilage. Hypoxia-inducible factor 2α, nicotinamide phosphoribosyltransferase and several proinflammatory cytokine pathways, as well as the zinc-ZIP8-MTF1 axis were identified as upstream regulators of MT expression. Genetic deletion of Mt1 and Mt2 enhanced cartilage destruction through increasing chondrocyte apoptosis. Unexpectedly, aberrant overexpression of MT2, but not MT1, induced upregulation of matrix-degrading enzymes and downregulation of matrix molecules through nuclear factor-kappa B (NF-κB) and activator protein-1 (AP-1) activation, ultimately leading to OA.
Conclusions MTs play an antiapoptotic role in post-traumatic OA. However, aberrant and chronic upregulation of MT2 triggers an imbalance between chondrocyte anabolism and catabolism, consequently accelerating OA development. Our findings collectively highlight pleiotropic roles of MTs as regulators of chondrocyte apoptosis as well as catabolic and anabolic pathways during OA pathogenesis.
This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Statistics from Altmetric.com
Handling editor Tore K Kvien
Contributors YW: Study design, data acquisition, data analysis and interpretation, manuscript preparation and approval; YS, C-HC, YC, and C-WH: data acquisition, analysis and interpretation, and manuscript approval; J-HK and J-SC: funding acquisition, study design, data interpretation, manuscript preparation and approval. J-HK and J-SC take responsibility for the integrity of this work.
Funding This work was supported by grants from the National Research Foundation of Korea (2007-0056157 and 2013R1A2A1A01009713), the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (H114C3484), and the Silver Health Bio Research Center of Gwangju Institute of Science and Technology to J-SC. J-HK was supported by grants from the National Research Foundation of Korea (2015M3A9E6028674) and the National R&D Program for Cancer Control (1520070) funded by the Ministry of Health & Welfare. YW was supported by a Global PhD Fellowship Program through the National Research Foundation of Korea funded by the Ministry of Education (2014H1A2A1017835).
Competing interests None declared.
Patient consent Obtained.
Ethics approval The Institutional Review Board of the Wonkwang University Hospital approved the use of human materials. All animal experiments were approved by the Gwangju Institute of Science and Technology Animal Care and Use Committee.
Provenance and peer review Not commissioned; externally peer reviewed.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.