Effects of short-term glucocorticoid treatment on changes in cartilage matrix degradation and chondrocyte gene expression induced by mechanical injury and inflammatory cytokines

Abstract

IntroductionTraumatic joint injury damages cartilage and causes adjacent joint tissues to release inflammatory cytokines, increasing the risk of developing osteoarthritis. The main objective of this study was to determine whether the combined catabolic effects of mechanical injury, tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6)/soluble IL-6 receptor (sIL-6R) on cartilage could be abolished by short-term treatment with glucocorticoids such as dexamethasone.MethodsIn an initial dexamethasone-dose-response study, bovine cartilage explants were treated with TNFα and increasing concentrations of dexamethasone. Bovine and human cartilage explants were then subjected to individual and combined treatments with TNFα, IL-6/sIL-6R and injury in the presence or absence of dexamethasone. Treatment effects were assessed by measuring glycosaminoglycans (GAG) release to the medium and synthesis of proteoglycans. Additional experiments tested whether pre-exposure of cartilage to dexamethasone could prevent GAG loss and inhibition of biosynthesis induced by cytokines, and whether post-treatment with dexamethasone could diminish the effects of pre-established cytokine insult. Messenger ribonucleic acid (mRNA) levels for genes involved in cartilage homeostasis (proteases, matrix molecules, cytokines, growth and transcription factors) were measured in explants subjected to combined treatments with injury, TNFα and dexamethasone. To investigate mechanisms associated with dexamethasone regulation of chondrocyte metabolic response, glucocorticoid receptor (GR) antagonist (RU486) and proprotein convertase inhibitor (RVKR-CMK) were used.ResultsDexamethasone dose-dependently inhibited GAG loss and the reduction in biosynthesis caused by TNFα. The combination of mechanical injury, TNFα and IL-6/sIL-6R caused the most severe GAG loss; dexamethasone reduced this GAG loss to control levels in bovine and human cartilage. Additionally, dexamethasone pre-treatment or post-treatment of bovine explants lowered GAG loss and increased proteoglycan synthesis in cartilage explants exposed to TNFα. Dexamethasone did not down-regulate aggrecanase mRNA levels. Post-transcriptional regulation by dexamethasone of other genes associated with responses to injury and cytokines was noted. GR antagonist reversed the effect of dexamethasone on sulfate incorporation. RVKR-CMK significantly reduced GAG loss caused by TNFα + IL-6 + injury.ConclusionsShort-term glucocorticoid treatment effectively abolished the catabolic effects exerted by the combination of pro-inflammatory cytokines and mechanical injury: dexamethasone prevented proteoglycan degradation and restored biosynthesis. Dexamethasone appears to regulate the catabolic response of chondrocytes post-transcriptionally, since the abundance of transcripts encoding aggrecanases was still elevated in the presence of dexamethasone.

Melanocortin peptides protect chondrocytes from mechanically induced cartilage injury

“…It is well described that elevated levels of pro-inflammatory cytokines provoke resident chondrocytes to initiate pathological expression and secretion of inflammatory mediators [18,32] and cartilagedegrading proteases [34,74]. In addition, excess stimulation of chondrocytes with proinflammatory cytokines such as TNF- and IL-1 induces apoptosis via activation of caspase-driven pathways [64,75].…”

“…Abnormal mechanical forces appear to 'awaken' adult A c c e p t e d M a n u s c r i p t 14 chondrocytes from a state of low metabolic activity and stimulate the production of a large number of pro-inflammatory molecules including TNF-, IL-1β [18,32] We have previously proposed that melanocortin peptides display potent chondroprotective, anti-apoptotic and anti-inflammatory effects through their ability to inhibit TNF--induced chondrocyte apoptosis and inflammation [64]. However, in spite of the potential of melanocortin peptides to limit inflammation, few studies have looked at their chondroprotective properties.…”

“…Mechanical loading within physiological limits is an essential stimulus for chondrocytes to produce extra-cellular matrix (ECM), capable of withstanding normal levels of stress and is responsible for triggering the synthesis, exportation and degradation of ECM components -collagen and proteoglycans [14]. However, when the joint/cartilage experiences mechanical stresses above the normal physiological range and/or frequency, such as in impact trauma, this results in significant chondrocyte death attributed to mechanical necrosis [15] and apoptotic processes [16,17] that could trigger the development of OA [18].…”

“…Abnormal mechanical forces cause adult chondrocytes to initiate production of a large number of pro-inflammatory mediators including the cytokines TNF- and IL-1β [18,32], which in combination with reactive oxygen species and lipid-derived…”

Development of in vitro joint tissue co-culture models for evaluating transport and biological crosstalk

“…The single versus continuous dose has previously been modeled using dexamethasone (DEX), a corticosteroid often used in the treatment of arthritic diseases due to its anti-inflammatory and immunosuppressant effects [37,68]. Bovine cartilage explants were given 1 ng/mL IL-1α and dosed with 100 nM DEX in either a single or continuous pattern [37].…”