title: Acetylation reduces SOX9 nuclear entry and ACAN gene transactivation in human chondrocytes.
abstract: Changes in the content of aggrecan, an essential proteoglycan of articular cartilage, have been implicated in the pathophysiology of osteoarthritis (OA), a prevalent age-related, degenerative joint disease. Here, we examined the effect of SOX9 acetylation on ACAN transactivation in the context of osteoarthritis. Primary chondrocytes freshly isolated from degenerated OA cartilage displayed lower levels of ACAN mRNA and higher levels of acetylated SOX9 compared with cells from intact regions of OA cartilage. Degenerated OA cartilage presented chondrocyte clusters bearing diffused immunostaining for SOX9 compared with intact cartilage regions. Primary human chondrocytes freshly isolated from OA knee joints were cultured in monolayer or in three-dimensional alginate microbeads (3D). SOX9 was hypo-acetylated in 3D cultures and displayed enhanced binding to a -10 kb ACAN enhancer, a result consistent with higher ACAN mRNA levels than in monolayer cultures. It also co-immunoprecipitated with SIRT1, a major deacetylase responsible for SOX9 deacetylation. Finally, immunofluorescence assays revealed increased nuclear localization of SOX9 in primary chondrocytes treated with the NAD SIRT1 cofactor, than in cells treated with a SIRT1 inhibitor. Inhibition of importin β by importazole maintained SOX9 in the cytoplasm, even in the presence of NAD. Based on these data, we conclude that deacetylation promotes SOX9 nuclear translocation and hence its ability to activate ACAN.
authors.affiliation: Laboratory of Cartilage Biology, Institute of Dental Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Michal
authors.initials: M
authors.lastname: Bar Oz
authors.affiliation: Laboratory of Cartilage Biology, Institute of Dental Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Ashok
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Laboratory of Cartilage Biology, Institute of Dental Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Jinan
authors.initials: J
authors.lastname: Elayyan
authors.affiliation: Laboratory of Cartilage Biology, Institute of Dental Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Eli
authors.initials: E
authors.lastname: Reich
authors.affiliation: Laboratory of Cartilage Biology, Institute of Dental Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Milana
authors.initials: M
authors.lastname: Binyamin
authors.affiliation: Joint Replacement and Reconstructive Surgery Unit, Orthopaedic Surgery Complex, Hadassah Mount Scopus Hospital, Jerusalem, Israel.
authors.forename: Leonid
authors.initials: L
authors.lastname: Kandel
authors.affiliation: Joint Replacement and Reconstructive Surgery Unit, Orthopaedic Surgery Complex, Hadassah Mount Scopus Hospital, Jerusalem, Israel.
authors.forename: Meir
authors.initials: M
authors.lastname: Liebergall
authors.affiliation: Laboratory for Experimental Orthopaedics, Department of Orthopaedic Surgery, University Hospital Giessen & Marburg GmbH, Gießen, Germany.
authors.forename: Juergen
authors.initials: J
authors.lastname: Steinmeyer
authors.affiliation: Cleveland Clinic Lerner Research Institute, Cleveland, OH, USA.
authors.forename: Veronique
authors.initials: V
authors.lastname: Lefebvre
authors.affiliation: Laboratory of Cartilage Biology, Institute of Dental Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Mona
authors.initials: M
authors.lastname: Dvir-Ginzberg
mesh_terms: D000107:Acetylation; D000368:Aged; D053674:Aggrecans / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism / Q000473:pathology; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D004742:Enhancer Elements, Genetic / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008954:Models, Biological; D011485:Protein Binding; D055550:Protein Stability; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D055758:SOX9 Transcription Factor / Q000378:metabolism*; D056564:Sirtuin 1 / Q000378:metabolism; D013314:Stress, Mechanical; D015533:Transcriptional Activation / Q000235:genetics*; D014162:Transfection; D016474:Weight-Bearing
chemical_list: C508319:ACAN protein, human; D053674:Aggrecans; D012333:RNA, Messenger; D055758:SOX9 Transcription Factor; D056564:Sirtuin 1
keywords: Aging; SIRT1; SOX9; acetylation; aggrecan; cartilage; nucleus; osteoarthritis