Although pathways controlling ribosome activity have been described to regulate chondrocyte homeostasis in osteoarthritis, ribosome biogenesis in osteoarthritis is unexplored. We hypothesized that U3 snoRNA, a non-coding RNA involved in ribosomal RNA maturation, is critical for chondrocyte protein translation capacity in osteoarthritis. U3 snoRNA was one of a number of snoRNAs with decreased expression in osteoarthritic cartilage and osteoarthritic chondrocytes. OA synovial fluid impacted U3 snoRNA expression by affecting U3 snoRNA gene promoter activity, while BMP7 was able to increase its expression. Altering U3 snoRNA expression resulted in changes in chondrocyte phenotype. Interference with U3 snoRNA expression led to reduction of rRNA levels and translational capacity, whilst induced expression of U3 snoRNA was accompanied by increased 18S and 28S rRNA levels and elevated protein translation. Whole proteome analysis revealed a global impact of reduced U3 snoRNA expression on protein translational processes and inflammatory pathways. For the first time we demonstrate implications of a snoRNA in osteoarthritis chondrocyte biology and investigated its role in the chondrocyte differentiation status, rRNA levels and protein translational capacity. Osteoarthritis (OA) is a chronic debilitating joint disease that is strongly associated with ageing 1,2. OA involves pathological cellular processes in all joint structures and affects articular cartilage integrity, leading to dysfunctional joint articulation 2. During OA development and progression, the articular chondrocyte's phenotype changes 3-5 and presents with disturbed cellular homeostasis characterized by abnormal expression of (pre-) hypertrophic-[RUNX2 (runt-related transcription factor 2); COL10A1 (type X collagen)], catabolic-[ALPL (alkaline phosphatase); MMP13 (matrix metallopeptidase 13) and ADAMTS5 (a disintegrin and metalloproteinase with thrombospondin motifs 5) and inflammatory (COX2 (cyclooxygenase 2) and IL-6 (interleukin 6)] genes, while chondrogenic gene expression [SOX9 (SRY-box transcription factor 9); COL2A1 (type 2 collagen); ACAN (aggrecan) and NKX3-2 (NK3 homeobox 2)] is attenuated 3,4. The biomolecular processes that catalyze disturbances in the articular chondrocyte phenotype leading to OA are poorly understood, and it is expected that a comprehensive understanding of the avenues leading to disruption of articular chondrocyte homeostasis will provide important clues for future treatments. Chondrocytes are specialized secretory cells, enabling the synthesis and maintenance of the protein-rich cartilage extracellular matrix (ECM). Disturbances in chondrocyte protein translation in cartilage development and OA are connected to mTOR (mammalian target of rapamycin) activity 6 , endoplasmic reticulum stress 7 , unfolded protein response and apoptosis 8. These responses change the downstream translational activity of the

There continues to be a year on year increase in publications researching miRs in OA (expressed as a percentage of the total publications), with a doubling over the last 4 years. An overview on the last year's progress within the fields of epigenetics and genomics with respect to OA will be given.

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Objective: For many proteins from osteoarthritic synovial fluid, their intra-articular tissue of origin remains unknown. In this study we performed comparative proteomics to identify osteoarthritis-specific and joint tissue-dependent secreted proteins that may serve as candidates for osteoarthritis biomarker development on a tissue-specific basis. Design: Protein secretomes of cartilage, synovium, Hoffa's fat pad and meniscus from knee osteoarthritis patients were determined using liquid chromatography tandem mass spectrometry, followed by labelfree quantification. Validation of tissue-dependent protein species was conducted by ELISA on independent samples. Differential proteomes of osteoarthritic and non-osteoarthritic knee synovial fluids were obtained via similar proteomics approach, followed by ELISA validation. Results: Proteomics revealed 64 proteins highly secreted from cartilage, 94 from synovium, 37 from Hoffa's fat pad and 21 from meniscus. Proteomic analyses of osteoarthritic vs non-osteoarthritic knee synovial fluid revealed 70 proteins with a relatively higher abundance and 264 proteins with a relatively lower abundance in osteoarthritic synovial fluid. Of the 70 higher abundance proteins, 23 were amongst the most highly expressed in the secretomes of a specific intra-articular tissue measured. Tissuedependent release was validated for SLPI, C8, CLU, FN1, RARRES2, MATN3, MMP3 and TNC. Abundance in synovial fluid of tissue-dependent proteins was validated for IGF2, AHSG, FN1, CFB, KNG and C8. Conclusions: We identified proteins with a tissue-dependent release from intra-articular human knee OA tissues. A number of these proteins also had an osteoarthritis-specific abundance in knee synovial fluid. These proteins may serve as novel candidates for osteoarthritis biomarker development on a tissuespecific basis.

Inflammation is a double-edged sword with both detrimental and beneficial consequences. Understanding of the mechanisms of crosstalk between the inflammatory milieu and human adult mesenchymal stem cells is an important basis for clinical efforts. Here, we investigate changes in the transcriptional response of human adipose-derived stem cells to physiologically relevant levels of IL-2 (IL-2 priming) upon replicative senescence. Our data suggest that replicative senescence might dramatically impede human mesenchymal stem cell (MSC) function via global transcriptional deregulation in response to IL-2. We uncovered a novel senescence-associated transcriptional signature in human adipose-derived MSCs hADSCs after exposure to pro-inflammatory environment: significant enhancement of the expression of the genes encoding potent growth factors and cytokines with anti-inflammatory and migration-promoting properties, as well as genes encoding angiogenic and anti-apoptotic promoting factors, all of which could participate in the establishment of a unique microenvironment. We observed transcriptional up-regulation of critical components of the nitric oxide synthase pathway (iNOS) in hADSCs upon replicative senescence suggesting, that senescent stem cells can acquire metastasis-promoting properties via stem cell-mediated immunosuppression. Our study highlights the importance of age as a factor when designing cell-based or pharmacological therapies for older patients and predicts measurable biomarkers characteristic of an environment that is conducive to cancer cells invasiveness and metastasis.