title: Inhibition of CDK9 prevents mechanical injury-induced inflammation, apoptosis and matrix degradation in cartilage explants.
abstract: Joint injury often leads to post-traumatic osteoarthritis (PTOA). Acute injury responses to trauma induce production of pro-inflammatory cytokines and catabolic enzymes, which promote chondrocyte apoptosis and degrade cartilage to potentiate PTOA development. Recent studies show that the rate-limiting step for transcriptional activation of injury response genes is controlled by cyclin-dependent kinase 9 (CDK9), and thus it is an attractive target for limiting the injury response. Here, we determined the effects of CDK9 inhibition in suppressing the injury response in mechanically-injured cartilage explants. Bovine cartilage explants were injured by a single compressive load of 30 % strain at 100 %/s, and then treated with the CDK9 inhibitor Flavopiridol. To assess acute injury responses, we measured the mRNA expression of pro-inflammatory cytokines, catabolic enzymes, and apoptotic genes by RT-PCR, and chondrocyte viability and apoptosis by TUNEL staining. For long-term outcome, cartilage matrix degradation was assessed by soluble glycosaminoglycan release, and by determining the mechanical properties with instantaneous and relaxation moduli. Our data showed CDK9 inhibitor markedly reduced injury-induced inflammatory cytokine and catabolic gene expression. CDK9 inhibitor also attenuated chondrocyte apoptosis and reduced cartilage matrix degradation. Lastly, the mechanical properties of the injured explants were preserved by CDK9 inhibitor. Our results provide a temporal profile connecting the chain of events from mechanical impact, acute injury responses, to the subsequent induction of chondrocyte apoptosis and cartilage matrix deterioration. Thus, CDK9 is a potential disease-modifying agent for injury response after knee trauma to prevent or delay PTOA development.
authors: Department of Orthopaedic Surgery, Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou, 310016 PR China; University of California Davis, Department of Orthopaedic Surgery, Lawrence J. Ellison Musculoskeletal Research Center, Research Building 1 Suite 2000, 4635 Second Avenue, Sacramento, CA 95817, USA.
authors: Z
authors: Z
authors: Hu
authors: J H N
authors: JH
authors: Yik
authors: D D
authors: DD
authors: Cissell
authors: P V
authors: PV
authors: Michelier
authors: K A
authors: KA
authors: Athanasiou
authors: D R
authors: DR
authors: Haudenschild
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D002417:Cattle; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D042863:Cyclin-Dependent Kinase 9 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D005109:Extracellular Matrix / Q000187:drug effects / Q000378:metabolism*; D007249:Inflammation / Q000235:genetics / Q000473:pathology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013314:Stress, Mechanical
chemical_list: D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D042863:Cyclin-Dependent Kinase 9