osteoarthritis presents as a change in the chondrocyte phenotype and an imbalance between anabolic and catabolic processes. Age affects its onset and progression. Small nucleolar RNAs (SnoRNAs) direct chemical modification of RNA substrates to fine-tune spliceosomal and rRNA function, accommodating changing requirements for splicing and protein synthesis during health and disease. Articular cartilage from young, old and OA knees was used in a microarray study to identify alterations in snoRNA expression. Changes in snoRNAs in osteoarthritis-like conditions were studied in chondrocytes using interleukin-1 and osteoarthritic synovial fluid. SNORD26 and SNORD96A knockdown and overexpression were undertaken using antisense oligonucleotides and overexpression plasmids. We identified panels of snoRNAs differentially expressed due to ageing (including SNORD96A, SNORD44) and osteoarthritis (including SNORD26 and SNORD116). In vitro experiments using osteoarthritis-like conditions affected snoRNA expression. Knockdown or overexpression of SNORD26 or SNORD96A resulted in changes in chondrogenic, hypertrophic, rRNA and osteoarthritis related gene expression. We demonstrate that snoRnA expression changes in cartilage ageing, and osteoarthritis and in osteoarthritis-like conditions, and when the expression of these snoRNAs is altered this affects chondrogenic and hypertrophic gene expression. Thus, we propose an additional dimension in the molecular mechanisms underlying cartilage ageing and osteoarthritis through the dysregulation of snoRNAs.

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

Purpose. Pulmonary sarcoidosis is associated with dysregulated expression of intracellular miRNAs. There is however only little information on extracellular miRNAs and their association with the disease course in sarcoidosis. We therefore assessed serum miRNAs in sarcoidosis classified according to the presence of Löfgren's syndrome (LS) as a hallmark of good prognosis in contrast to more advanced disease course. Methods. RT-PCR was used to assess 35 miRNAs in 13 healthy controls and 24 sarcoidosis patients (12 with X-ray (CXR) stage ≤ 1 and LS and 12 with insidious onset and CXR stage ≥ 3). Results. Compared to controls, we consistently observed dysregulated expressions of miR-146, miR-16, miR-425-5p, and miR-93-5p in both sarcoidosis groups irrespective of disease course. Specifically, patients without LS had dysregulated expressions of miR-150-5p, miR-1, and miR-212 compared to controls. Patients with LS had dysregulated expressions of miR-21-5p and miR-340-5p compared to controls. Bioinformatics predicted consistently “Pathways in cancer” to be modulated by both altered profiles in patients with/without LS. Three miRNAs (miR-21-5p, miR-340-5p, and miR-212-3p) differed between our patients with LS and those without LS; their cumulative effect may modulate “TGF-β signalling pathway.” Conclusions. Further study should focus on possible applications of serum miRNAs for diagnostics follow-up and for prognosis.

ABSTRACTObjectivesOsteoarthritis (OA) presents as a change in the chondrocyte phenotype and an imbalance between anabolic and catabolic processes. Age affects its onset and progression. Small nucleolar RNAs (SnoRNAs) direct chemical modification of RNA substrates to fine-tune spliceosomal and rRNA function, accommodating changing requirements for splicing and protein synthesis during health and disease. This study was undertaken to examine how changes in snoRNAs expression may have a role in OA.MethodsArticular cartilage from young, old and OA knees was used in a microarray study to identify alterations in snoRNA expression. Changes in expression of snoRNAs in OA-like conditions were studied in chondrocytes using interleukin-1 and OA synovial fluid. SNORD26 and SNORD96A knockdown and overexpression were undertaken using antisense oligonucleotides and overexpression plasmids.ResultsWe identified panels of snoRNAs differentially expressed due to ageing (including SNORD96A, SNORD44) and OA (including SNORD26 and SNORD116) and findings were validated in an independent cohort. In vitro experiments using OA-like conditions affected snoRNA expression. Knockdown or overexpression of SNORD26 or SNORD96A resulted in changes in chondrogenic, hypertrophic, rRNA and osteoarthritis related gene expression.ConclusionWe demonstrate that snoRNA expression changes in cartilage ageing, and OA and in OA-like conditions, and when the expression of these snoRNAs is altered this affects chondrogenic and hypertrophic gene expression. Thus, we propose an additional dimension in the molecular mechanisms underlying cartilage ageing and OA through the dysregulation of snoRNAs.

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