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Impaired Proteasomal Function in Human Osteoarthritic Chondrocytes Can Contribute to Decreased Levels of SOX 9 and Aggrecan
Author(s) -
Serrano Ramon L.,
Chen LiangYu,
Lotz Martin K.,
LiuBryan Ru,
Terkeltaub Robert
Publication year - 2018
Publication title -
arthritis and rheumatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.106
H-Index - 314
eISSN - 2326-5205
pISSN - 2326-5191
DOI - 10.1002/art.40456
Subject(s) - proteasome , aggrecan , microbiology and biotechnology , chondrocyte , small interfering rna , autophagy , proteostasis , ubiquitin , chemistry , gene knockdown , biology , cartilage , osteoarthritis , transfection , biochemistry , medicine , pathology , anatomy , apoptosis , alternative medicine , gene , articular cartilage
Objective Osteoarthritis ( OA ) chondrocytes exhibit impairment of autophagy, one arm of the proteostasis network that coordinates proteome and organelle quality control and degradation. Deficient proteostasis impacts differentiation and viability, and inflammatory processes in aging and disease. The present study was undertaken to assess ubiquitin proteasome system proteasomal function in OA chondrocytes. Methods We evaluated human knee cartilage by immunohistochemistry, and assessed proteasomal function, levels of proteasomal core subunits and chaperones, and autophagy in cultured chondrocytes. Assays included Western blotting, quantitative reverse transcription–polymerase chain reaction, proteasomal protease activity assessment, and cell immunofluorescence analysis. Results Human knee OA cartilage exhibited polyubiquitin accumulation, with increased ubiquitin K48‐linked polyubiquitinated proteins in situ, suggesting proteasomal impairment. Cultured OA chondrocytes demonstrated accumulation of K48 polyubiquitinated proteins, significantly reduced 20S proteasome core protease activity, and decreased levels of phosphorylated FOXO 4 and proteasome 26S subunit, non‐ATPase 11 ( PSMD 11), a FOXO 4‐inducible promoter of proteasomal activation. Levels of proteasome subunit β type 3 ( PSMB 3), PSMB 5, PSMB 6, and proteasome assembly chaperone 1 were not decreased in OA chondrocytes. In normal chondrocytes, PSMD 11 small interfering RNA knockdown stimulated certain autophagy machinery elements, increased extracellular nitric oxide ( NO ) levels, and reduced chondrocytic master transcription factor SOX 9 protein and messenger RNA ( mRNA ) and aggrecan ( AGC 1 ) mRNA . PSMD 11 gain‐of‐ function by transfection increased proteasomal function, increased levels of SOX 9‐induced AGC 1 mRNA , stimulated elements of the autophagic machinery, and inhibited extracellular levels of interleukin‐1–induced NO and matrix metalloproteinase 13 in OA chondrocytes. Conclusion Deficient PSMD 11, associated with reduced phosphorylated FOXO 4, promotes impaired proteasomal function in OA chondrocytes, dysregulation of chondrocytic homeostasis, and decreased levels of SOX 9 mRNA , SOX 9 protein, and AGC 1 mRNA . Chondrocyte proteasomal impairment may be a therapeutic target for OA.