Search

Objectives: To collate the genes experimentally modulated in animal models of osteoarthritis (OA) and compare these data with OA transcriptomics data to identify potential therapeutic targets.Methods: PubMed searches were conducted to identify publications describing gene modulations in animal models. Analysed gene expression data were retrieved from the SkeletalVis database of analysed skeletal microarray and RNA-Seq expression data. A network diffusion approach was used to predict new genes associated with OA joint damage.Results: A total of 459 genes were identified as having been modulated in animal models of OA, with ageing and post-traumatic (surgical) models the most prominent. Ninety-eight of the 143 genes (69%) genetically modulated more than once had a consistent effect on OA joint damage severity. Several discrepancies between different studies were identified, providing lessons on interpretation of these data. We used the data collected along with OA gene expression data to expand existing annotations and prioritise the most promising therapeutic targets, which we validated using the latest reported associations. We constructed an online database OATargets to allow researchers to explore the collated data and integrate it with existing OA and skeletal gene expression data.Conclusions: We present a comprehensive survey and online resource for understanding gene regulation of animal model OA pathogenesis. [ABSTRACT FROM AUTHOR]

Key points: microRNAs (miRs) are small non‐coding molecules that regulate post‐transcriptional target gene expression.miRs are involved in regulating cellular activities in response to mechanical loading in all physiological systems, although it is largely unknown whether this response differs with increasing magnitudes of load.miR‐221, miR‐222, miR‐21‐5p and miR‐27a‐5p were significantly increased in ex vivo cartilage explants subjected to increasing load magnitude and in in vivo joint cartilage exposed to abnormal loading.TIMP3 and CPEB3 are putative miR targets in chondrocytesIdentification of mechanically regulated miRs that have potential to impact on tissue homeostasis provides a mechanism by which load‐induced tissue behaviour is regulated, in both health and pathology, in all physiological systems. MicroRNAs (miRs) are small non‐coding molecules that regulate post‐transcriptional target gene expression and are involved in mechano‐regulation of cellular activities in all physiological systems. It is unknown whether such epigenetic mechanisms are regulated in response to increasing magnitudes of load. The present study investigated mechano‐regulation of miRs in articular cartilage subjected to 'physiological' and 'non‐physiological' compressive loads in vitro as a model system and validated findings in an in vivo model of abnormal joint loading. Bovine full‐depth articular cartilage explants were loaded to 2.5 MPa (physiological) or 7 MPa (non‐physiological) (1 Hz, 15 min) and mechanically‐regulated miRs identified using next generation sequencing and verified using a quantitative PCR. Downstream targets were verified using miR‐specific mimics or inhibitors in conjunction with 3′‐UTR luciferase activity assays. A subset of miRs were mechanically‐regulated in ex vivo cartilage explants and in vivo joint cartilage. miR‐221, miR‐222, miR‐21‐5p and miR‐27a‐5p were increased and miR‐483 levels decreased with increasing load magnitude. Tissue inhibitor of metalloproteinase 3 (TIMP3) and cytoplasmic polyadenylation element binding protein 3 (CPEB3) were identified as putative downstream targets. Our data confirm miR‐221 and ‐222 mechano‐regulation and demonstrates novel mechano‐regulation of miR‐21‐5p and miR‐27a‐5p in ex vivo and in vivo cartilage loading models. TIMP3 and CPEB3 are putative miR targets in chondrocytes. Identification of specific miRs that are regulated by increasing load magnitude, as well as their potential to impact on tissue homeostasis, has direct relevance to other mechano‐sensitive physiological systems and provides a mechanism by which load‐induced tissue behaviour is regulated, in both health and pathology. Key points: microRNAs (miRs) are small non‐coding molecules that regulate post‐transcriptional target gene expression.miRs are involved in regulating cellular activities in response to mechanical loading in all physiological systems, although it is largely unknown whether this response differs with increasing magnitudes of load.miR‐221, miR‐222, miR‐21‐5p and miR‐27a‐5p were significantly increased in ex vivo cartilage explants subjected to increasing load magnitude and in in vivo joint cartilage exposed to abnormal loading.TIMP3 and CPEB3 are putative miR targets in chondrocytesIdentification of mechanically regulated miRs that have potential to impact on tissue homeostasis provides a mechanism by which load‐induced tissue behaviour is regulated, in both health and pathology, in all physiological systems. [ABSTRACT FROM AUTHOR]

A wide range of specific microRNAs have been shown to have either positive or negative effects on osteoblast differentiation and function, with consequent changes in postnatal bone mass. A number of specific targets have been identified. We previously used CrispR-Cas9 to make a miR-455 null mouse, characterizing a behavioral phenotype with age. The current study identifies a bone phenotype, starting in younger animals. At 3 weeks of age, the miR-455 null mice (both male and female) display increased length of both long bones and vertebrae and, while this difference diminishes across 1 year, it remains significant. Increased bone formation in vivo is mirrored by an increase in osteogenesis from bone marrow-derived stem cells in vitro. This is accompanied by a decrease in osteoclastogenesis and osteoclast function. MicroCT analyses show increased trabecular bone and less porosity/decreased separation in the miR-455 null mouse, suggesting a more dense and stronger bone at 3 weeks of age; these differences normalize by 1 year. Gain-of-function and loss-of-function datasets show that FGF18 expression is regulated by miR-455 and FGF18 was validated as a direct target of miR-455. The regulation of FGF18 by miR-455 is a likely mediator of its effect on bone., Competing Interests: None declared., (© The Author(s) 2025. Published by Oxford University Press on behalf of the American Society for Bone and Mineral Research.)

The epigenome, including the methylation of cytosine bases at CG dinucleotides, is intrinsically linked to transcriptional regulation. The tight regulation of gene expression during skeletal development is essential, with ~1/500 individuals born with skeletal abnormalities. Furthermore, increasing evidence is emerging to link age-associated complex genetic musculoskeletal diseases, including osteoarthritis (OA), to developmental factors including joint shape. Multiple studies have shown a functional role for DNA methylation in the genetic mechanisms of OA risk using articular cartilage samples taken from aged patients. Despite this, our knowledge of temporal changes to the methylome during human cartilage development has been limited. We quantified DNA methylation at ~700,000 individual CpGs across the epigenome of developing human articular cartilage in 72 samples ranging from 7-21 post-conception weeks, a time period that includes cavitation of the developing knee joint. We identified significant changes in 8% of all CpGs, and >9400 developmental differentially methylated regions (dDMRs). The largest hypermethylated dDMRs mapped to transcriptional regulators of early skeletal patterning including MEIS1 and IRX1 . Conversely, the largest hypomethylated dDMRs mapped to genes encoding extracellular matrix proteins including SPON2 and TNXB and were enriched in chondrocyte enhancers. Significant correlations were identified between the expression of these genes and methylation within the hypomethylated dDMRs. We further identified 811 CpGs at which significant dimorphism was present between the male and female samples, with the majority (68%) being hypermethylated in female samples. Following imputation, we captured the genotype of these samples at >5 million variants and performed epigenome-wide methylation quantitative trait locus (mQTL) analysis. Colocalization analysis identified 26 loci at which genetic variants exhibited shared impacts upon methylation and OA genetic risk. This included loci which have been previously reported to harbour OA-mQTLs (including GDF5 and ALDH1A2 ), yet the majority (73%) were novel (including those mapping to CHST3, FGF1 and TEAD1 ). To our knowledge, this is the first extensive study of DNA methylation across human articular cartilage development. We identify considerable methylomic plasticity within the development of knee cartilage and report active epigenomic mediators of OA risk operating in prenatal joint tissues., Competing Interests: Declaration of Interests LM has received speaker and consultancy fees from Illumina. We have no other conflicting interest to declare.

MicroRNAs are small double-stranded RNAs, which negatively regulate gene expression and have been shown to have key roles in both chondrocyte development and cartilage homeostasis with age. Deletion of all microRNAs in chondrocytes leads to skeletal growth defects in mice, whilst deletion of specific microRNAs, e.g. miR-140, leads to premature articular cartilage degradation and increased susceptibility to posttraumatic osteoarthritis. Studies comparing microRNA expression in normal human articular cartilage compared to osteoarthritic cartilage show differential expression, but varying sample groups make interpretation difficult. MicroRNAs have been proposed as circulating biomarkers of osteoarthritis, but again, this differs amongst patient cohorts. Many micro-RNAs have been shown to have roles in chondrocyte phenotype via signalling pathways, apoptosis, autophagy and senescence. Modulating microRNAs in the joint has been shown to reduce osteoarthritis in animal models and translating this to man as a novel therapeutic strategy will be key.