Protection of Cartilage from Cytokines – published in A&R

Congratulations to our team for getting this story published in the top rheumatology journal!

We take a new approach to protect cartilage from inflammatory cytokines by targeting a critical transcriptional checkpoint common to all primary response genes.

Abstract (pubmed link)
Objective. CDK9 controls the activation of primary inflammatory response genes. We determined whether CDK9 inhibition protects cartilage from the catabolic effects of pro-inflammatory cytokines. Methods. Human chondrocytes were challenged with different pro-inflammatory stimuli (IL-1?, lipopolysaccharides, and TNF?), in the presence or absence of the CDK9 inhibitor Flavopiridol, or siRNA. The mRNA expression of inflammatory mediators, catabolic, and anabolic genes were determined by real-time PCR. Cartilage explants were incubated with IL-1?, with or without Flavopiridol, for 6 days. Cartilage matrix degradation was assessed by the release of glycosaminoglycan (GAG) and cleaved Type II collagen (Col2a) peptides. Results. CDK9 inhibition by Flavopiridol, or knockdown by siRNA, effectively suppressed iNOS mRNA induction by all three pro-inflammatory stimuli. Results from NFkB-targets PCR array showed that Flavopiridol suppressed the induction of a broad range of inflammatory mediator genes (59 out of 67 tested) by IL-1?. CDK9 inhibition also suppressed induction of catabolic genes MMP 1, 3, 9, 13, and ADAMTS4, 5; but did not affect the basal expression of anabolic genes such as Col2a, aggrecan, and COMP, and housekeeping genes. Flavopiridol had no apparent short-term cytotoxicity as assessed by glucose-6-phosphate dehydrogenase activity. Finally, in IL-1?-treated cartilage explants, Flavopiridol reduced the release of matrix degradation products GAG and cleaved Col2a peptides, but did not affect long-term chondrocyte viability. Conclusion. CDK9 activity is required for the primary inflammatory response in chondrocytes. Flavopiridol suppresses the induction of inflammatory mediators and catabolic genes to protect cartilage from the deleterious effects of pro-inflammatory cytokines, without impacting cell viability and functions.