Background/Purpose: In osteoarthritis (OA), chondrocytes display marked changes in their gene expression profile. Some of these are thought to be protective [e.g. increased synthesis of extracellular matrix (ECM) components] and some harmful (e.g. secretion of proteolytic enzymes and proinflammatory factors). Glucocorticoids (GCs) can counteract many of those harmful changes. Accordingly, intra-articular GC injections are widely used as a symptomatic treatment for OA. However, there are also concerns about their potentially harmful effects, and their comprehensive effect on chondrocyte phenotype remains poorly understood. We studied the effects of GCs on gene expression in OA chondrocytes with genome wide expression analysis based on next generation sequencing (NGS).

Methods: Chondrocytes were isolated from cartilage obtained from ten OA patients undergoing knee replacement surgery. The cells were cultured with or without the GC dexamethasone for 24 h. Total mRNA was isolated and sequenced with Illumina HiSeq2500 at the Institute for Molecular Medicine Finland. Functional analysis was performed against the GO (Gene Ontology) database. We also separately investigated the 54 genes linked to OA in recent genome-wide association (GWAS) studies (Loughlin 2015, Wang et al. 2016), as well as those 19 genes previously found to be differentially expressed in OA affected vs. preserved cartilage in a genome wide expression analysis (the RAAK study, Ramos et al. 2014).

Results: In dexamethasone-treated chondrocytes, 896 genes were down- and 685 upregulated in a statistically significant manner with a fold change of more than 2.0. Several genes associated with lipid and glucose metabolism as well as those involved in inflammation were among the most strongly affected genes. In the GO analysis, genes involved in ECM organization, cell proliferation and adhesion, and both collagen catabolism and anabolism were enriched among the significantly affected genes. Of note was the downregulation of several matrix degrading enzymes (e.g. MMP1, MMP13 and ADAMTS1) and pro-inflammatory factors (e.g. COX-2, MCP-1 and TNFSFS15) but also cartilage-specific collagens (including COL2A1, COL9A1 and COL11A1). Conversely, several anti-inflammatory (e.g. DUSP1, DUSP4) and antioxidative (e.g. KLF9, FOXO3) genes were upregulated. Notably, 11 (COL11A1, FILIP1L, VEGFA, DIO2, COX-2, IGFBP3, VDR, ADAM12, ASPN, GDF5 and IL16) of the 54 genes linked to OA in GWAS studies were significantly affected by dexamethasone. Of these, IL16 was up- and all others downregulated. Also, two (NGF and COL9A1) of the 19 genes identified to be upregulated in OA vs. normal cartilage in the RAAK study were downregulated by dexamethasone.

Conclusion: The results indicate that GCs regulate the expression of a wide range of genes in OA chondrocytes. In addition to clear anti-inflammatory and anticatabolic effects, CGs affect lipid and glucose metabolism in chondrocytes, an observation that might be particularly important in the metabolic phenotype of OA. Further studies are needed to confirm the long-term net effects of these wide-range changes in chondrocyte pathophysiology, as they are induced by a widely used pharmacological treatment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/widespread-regulation-of-gene-expression-by-glucocorticoids-in-chondrocytes-from-oa-patients-as-determined-by-ngs-based-genome-wide-expression-analysis/