The expression and function of microRNAs in chondrogenesis and osteoarthritis

Osteoarthritis year 2013 in review: genetics and genomics

Progress in genetic research has delivered important highlights in the last year. One of the widest impact is the publication of the Encyclopedia of DNA Elements (ENCODE) project showing the impressive complexity of the human genome and providing information useful for all areas of genetics. More specific of osteoarthritis (OA) has been the incorporation of DOT1-like, histone H3 methyltransferase (DOT1L) to the list of 11 OA loci with genome-wide significant association, the demonstration of significant overlap between OA genetics and height or body mass index (BMI) genetics, and the tentative prioritization of HMG-box transcription factor 1 (HBP1) in the 7q22 locus based on functional analysis. In addition, the first large scale analysis of DNA methylation has found modest differences between OA and normal cartilage, but has identified a subgroup of OA patients with a very differentiated phenotype. The role of DNA methylation in regulation of NOS2, SOX9, MMP13 and IL1B has been further clarified. MicroRNA expression studies in turn have shown some replication of differences between OA and control cartilage from previous profiling studies and have identified potential regulators of TGFβ signaling and of IL1β effects. In addition, non-coding RNAs showed promising results as serum biomarkers of cartilage damage. Gene expression microarray studies have found important differences between studies of hip or knee OA that reinforce the idea of joint specificity in OA. Expression differences between articular cartilage and other types of cartilage highlighted the WNT pathway whose regulation is proposed as critical for maintaining the articular cartilage phenotype. Many of these results need confirmation but they signal the exciting progress that is taking place in all areas of OA genetics, indicate questions requiring more study and augur further interesting discoveries.

Differentially expressed microRNAs in chondrocytes from distinct regions of developing human cartilage

There is compelling in vivo evidence from reports on human genetic mutations and transgenic mice that some microRNAs (miRNAs) play an important functional role in regulating skeletal development and growth. A number of published in vitro studies also point toward a role for miRNAs in controlling chondrocyte gene expression and differentiation. However, information on miRNAs that may regulate a specific phase of chondrocyte differentiation (i.e. production of progenitor, differentiated or hypertrophic chondrocytes) is lacking. To attempt to bridge this knowledge gap, we have investigated miRNA expression patterns in human embryonic cartilage tissue. Specifically, a developmental time point was selected, prior to endochondral ossification in the embryonic limb, to permit analysis of three distinct populations of chondrocytes. The location of chondroprogenitor cells, differentiated chondrocytes and hypertrophic chondrocytes in gestational day 54-56 human embryonic limb tissue sections was confirmed both histologically and by specific collagen expression patterns. Laser capture microdissection was utilized to separate the three chondrocyte populations and a miRNA profiling study was carried out using TaqMan® OpenArray® Human MicroRNA Panels (Applied Biosystems®). Here we report on abundantly expressed miRNAs in human embryonic cartilage tissue and, more importantly, we have identified miRNAs that are significantly differentially expressed between precursor, differentiated and hypertrophic chondrocytes by 2-fold or more. Some of the miRNAs identified in this study have been described in other aspects of cartilage or bone biology, while others have not yet been reported in chondrocytes. Finally, a bioinformatics approach was applied to begin to decipher developmental cellular pathways that may be regulated by groups of differentially expressed miRNAs during distinct stages of chondrogenesis. Data obtained from this work will serve as an important resource of information for the field of cartilage biology and will enhance our understanding of miRNA-driven mechanisms regulating cartilage and endochondral bone development, regeneration and repair.

miR-1247 functions by targeting cartilage transcription factor SOX9

microRNAs are a large and essential class of gene regulators that play key roles in development, homeostasis, and disease. They are necessary for normal skeletal development, and their expression is altered in arthritis. However, the specific role of individual microRNAs is only beginning to be unraveled. Using microRNA expression profiling in healthy human articular cartilage cells (chondrocytes), we identified miR-1247 expression as highly correlated with that of the differentiated cell phenotype. Transcribed from the DLK1-DIO3 locus, the function of miR-1247 is completely unknown. In mice its expression level was relatively high in cartilage tissue, and correlated with cartilage-associated microRNA miR-675 across a range of 15 different mouse tissues. To further probe miR-1247 function, overexpression and inhibition studies were performed in isolated human chondrocytes. Modulation of miR-1247 was found to exert profound phenotypic effects altering expression levels of cartilage master regulator transcription factor SOX9. SOX9 is essential for cartilage development and subsequent function throughout life, and mutations in this gene result in severe dwarfism. Putative miR-1247 binding sites were further investigated using luciferase reporter assays, which indicated binding of miR-1247 to a highly conserved region in the coding sequence of SOX9 but not in its 3'-UTR. Interestingly, depletion of SOX9 in human chondrocytes resulted in increased levels of the mature, processed microRNA, suggesting a negative feedback loop between miR-1247 and its target SOX9.

microRNAs and cartilage

microRNAs are small non-coding RNAs that in the last decade have emerged as overarching regulators of gene expression. Their abundance, ability to repress a large number of target genes and overlapping target specificity indicate a complex network of interactions that is still being defined. A number of studies focused on the role of microRNAs in cartilage have identified a small number, including miR-140 and -675 as playing important roles in regulation of cartilage homeostasis and together with the broader description of the activity of microRNAs in other tissues are beginning to define the function of microRNAs in cartilage development and homeostasis.

Molecular mechanisms of the cartilage-specific microRNA-140 in osteoarthritis

Osteoarthritis (OA) is the most widespread chronic degenerative joint disorder, characterized by progressive destruction of articular cartilage, subchondral bone alterations, formation of osteophytes and synovitis. MicroRNAs (miRNAs) are a class of endogenous and non-coding single-strand RNAs with a length of about 22 nucleotides, and many of them are evolutionarily conserved. miRNAs have been implicated in the process of development and pathogenesis of diseases, and tissue-specific miRNA functional studies in mice have revealed both pathogenic and protective functions. miRNA-140 (miR-140) was shown to be specifically expressed in cartilage tissues in developing zebrafish and mouse embryos during the development of both long and flat bones. Recently, miR-140 has been reported in many studies to play significant roles in OA pathogenesis. Although the previous results were not always consistent, the molecular mechanisms of the regulation and dual function of miR-140 in cartilage homeostasis and development have been established in previous studies. Further elucidation of the molecular basis of miR-140 will uncover synergistic inhibitory effects of miR-140 and other factors on OA pathogenesis, and provide a novel means of treating OA disease.

MicroRNA-558 regulates the expression of cyclooxygenase-2 and IL-1β-induced catabolic effects in human articular chondrocytes

OBJECTIVE

Cyclooxygenase-2 (COX-2) is a major prostaglandin E2 (PGE2) synthetic enzyme and is involved in the pathogenesis of chronic inflammation and pain in osteoarthritis (OA). The objective of this study was to directly address whether microRNA (miR)-558 can control the interleukin (IL)-1β-mediated induction of COX-2 and catabolic effects in human articular chondrocytes.

MATERIALS AND METHODS

Total RNA was extracted from the cartilage tissues of normal and OA donors or cultured human articular chondrocytes. The expression of miR-558 was quantified by TaqMan assay. To investigate the repressive effect of miR-558 on COX-2 expression, human chondrocytes and chondrogenic SW1353 cells were transfected with mature miR-558 or an antisense inhibitor (anti-miR-558). The expression of COX-2 protein was determined by Western blot analysis and the involvement of miR-558 in IL-1β-induced catabolic effects was examined by Western blot analysis and enzyme-linked immunosorbent assay (ELISA). Direct interaction between miR-558 and the putative site in the 3'-untranslated region (UTR) of COX-2 messenger RNA (mRNA) was validated by luciferase reporter assay.

RESULTS

Normal human articular cartilage expressed miR-558, and its expression was significantly lower in OA cartilage. Stimulation with IL-1β led to a significant reduction in miR-558 expression in normal and OA chondrocytes. IL-1β-induced activation of MAP kinase (MAPK) and nuclear factor-κB (NF-κB) decreased miR-558 expression and induced COX-2 expression in chondrocytes. The overexpression of miR-558 directly suppressed the luciferase activity of a reporter construct containing the 3'-UTR of human COX-2 mRNA and significantly inhibited IL-1β-induced upregulation of COX-2, while treatment with anti-miR-558 enhanced IL-1β-induced COX-2 expression and reporter activity in chondrocytes. Interestingly, IL-1β-induced activation of NF-κB and expression of matrix metalloproteinase (MMP)-1 and MMP-13 was significantly inhibited by miR-558 overexpression.

CONCLUSION

These findings demonstrated that cartilage homeostasis is influenced by miR-558, which directly targets COX-2 and regulates IL-1β-stimulated catabolic effects in human chondrocytes.

Post-transcriptional dysregulation by miRNAs is implicated in the pathogenesis of gastrointestinal stromal tumor [GIST]

In contrast to adult mutant gastrointestinal stromal tumors [GISTs], pediatric/wild-type GISTs remain poorly understood overall, given their lack of oncogenic activating tyrosine kinase mutations. These GISTs, with a predilection for gastric origin in female patients, show limited response to therapy with tyrosine kinase inhibitors and generally pursue a more indolent course, but still may prove fatal. Defective cellular respiration appears to underpin tumor development in these wild-type cases, which as a group lack expression of succinate dehydrogenase [SDH] B, a surrogate marker for respiratory chain metabolism. Yet, only a small subset of the wild-type tumors show mutations in the genes coding for the SDH subunits [SDHx]. To explore additional pathogenetic mechanisms in these wild-type GISTs, we elected to investigate post-transcriptional regulation of these tumors by conducting microRNA (miRNA) profiling of a mixed cohort of 73 cases including 18 gastric pediatric wild-type, 25 (20 gastric, 4 small bowel and 1 retroperitoneal) adult wild-type GISTs and 30 gastric adult mutant GISTs. By this approach we have identified distinct signatures for GIST subtypes which correlate tightly with clinico-pathological parameters. A cluster of miRNAs on 14q32 show strikingly different expression patterns amongst GISTs, a finding which appears to be explained at least in part by differential allelic methylation of this imprinted region. Small bowel and retroperitoneal wild-type GISTs segregate with adult mutant GISTs and express SDHB, while adult wild-type gastric GISTs are dispersed amongst adult mutant and pediatric wild-type cases, clustering in this situation on the basis of SDHB expression. Interestingly, global methylation analysis has recently similarly demonstrated that these wild-type, SDHB-immunonegative tumors show a distinct pattern compared with KIT and PDGFRA mutant tumors, which as a rule do express SDHB. All cases with Carney triad within our cohort cluster together tightly.

Sox9-regulated miRNA-574-3p inhibits chondrogenic differentiation of mesenchymal stem cells

The aim of this study was to identify new microRNAs (miRNAs) that are modulated during the differentiation of mesenchymal stem cells (MSCs) toward chondrocytes. Using large scale miRNA arrays, we compared the expression of miRNAs in MSCs (day 0) and at early time points (day 0.5 and 3) after chondrogenesis induction. Transfection of premiRNA or antagomiRNA was performed on MSCs before chondrogenesis induction and expression of miRNAs and chondrocyte markers was evaluated at different time points during differentiation by RT-qPCR. Among miRNAs that were modulated during chondrogenesis, we identified miR-574-3p as an early up-regulated miRNA. We found that miR-574-3p up-regulation is mediated via direct binding of Sox9 to its promoter region and demonstrated by reporter assay that retinoid X receptor (RXR)α is one gene specifically targeted by the miRNA. In vitro transfection of MSCs with premiR-574-3p resulted in the inhibition of chondrogenesis demonstrating its role during the commitment of MSCs towards chondrocytes. In vivo, however, both up- and down-regulation of miR-574-3p expression inhibited differentiation toward cartilage and bone in a model of heterotopic ossification. In conclusion, we demonstrated that Sox9-dependent up-regulation of miR-574-3p results in RXRα down-regulation. Manipulating miR-574-3p levels both in vitro and in vivo inhibited chondrogenesis suggesting that miR-574-3p might be required for chondrocyte lineage maintenance but also that of MSC multipotency.

The genetics and functional analysis of primary osteoarthritis susceptibility

Recent genome-wide association scans (GWASs) along with several adequately powered candidate gene studies have yielded a number of risk alleles for osteoarthritis (OA). This number is now sufficiently large to allow conclusions to be drawn regarding the nature of genetic susceptibility, including the fact that the risk alleles have variable effects depending on sex, ethnicity and on the skeletal site of the disease. Several of the alleles that have emerged from the GWASs are within or close to highly plausible candidate genes, including RUNX2 and CHST11. However, the majority of risk alleles do not map to genes previously reported to play a role in musculoskeletal biology, indicating that the GWAS datasets are telling us something new about the OA disease process. Functional studies have so far revealed that effects on gene expression are likely to be one of the main mechanisms through which OA susceptibility is acting. Epigenetic mechanisms such as DNA methylation also influence OA risk, and integration of genetic, transcriptomic and epigenetic data will allow us to use the genetic discoveries for informed development of new OA biological treatments.

Expression of microRNAs during chondrogenesis of human adipose-derived stem cells

OBJECTIVES

MicroRNAs (miRNAs) play an important role in the regulation of chondrogenesis of mesenchymal stem cells, but their expression still remains unknown in human adipose-derived stem cells (hADSCs). In this study the miRNA expression profile during chondrogenic differentiation of hADSC and the potential mechanism whereby miRNAs may affect the process of chondrogenesis are considered.

METHODS

hADSCs were isolated and cultured. The expression of chondrogenic proteins was detected using enzyme-linked immunosorbent assay (ELISA). miRNA expression profiles before and after chondrogenic induction were obtained using miRNA microarray essay and differently expressed miRNAs were primarily verified using quantitative real-time polymerase chain reaction (qRT-PCR). Putative targets of the miRNAs were predicted using online software programs MiRanda, TargetScan and miRBase.

RESULTS

Twelve miRNAs were found to be differentially expressed pre- and post-chondrogenic induction by over a two-fold change, including eight up-regulated miRNAs (miR-193b, miR-199a-3p/hsa-miR-199b-3p, miR-455-3p, miR-210, miR-381, miR-92a, miR-320c, and miR-136), and four down-regulated miRNAs (miR-490-5p, miR-4287, miR-BART8*, and miR-US25-1*). qRT-PCR analysis further confirmed these results. Predicted target genes of the differentially expressed miRNAs were based on the overlap of at least two online prediction algorithms, with the known functions of regulating chondrogenic differentiation, self-renewal, signal transduction and cell cycle control.

CONCLUSIONS

In this study we have identified a group of miRNAs and their target genes, which may play important roles in regulating chondrogenic differentiation of hADSCs. Our results provide the basis for further investigation into the molecular mechanism of chondrogenesis in hADSCs and their differentiation for cartilage engineering.

Macro view of microRNA function in osteoarthritis

Osteoarthritis (OA), the most common musculoskeletal disorder, is complex, multifaceted, and characterized by degradation of articular cartilage and alterations in other joint tissues. Although some pathogenic pathways have been characterized, current knowledge is incomplete and effective approaches to the prevention or treatment of OA are lacking. Understanding novel molecular mechanisms that are involved in the maintenance and destruction of articular cartilage, including extracellular regulators and intracellular signalling mechanisms in joint cells that control cartilage homeostasis, has the potential to identify new therapeutic targets in OA. MicroRNAs control tissue development and homeostasis by fine-tuning gene expression, with expression patterns specific to tissues and developmental stages, and are increasingly implicated in the pathogenesis of complex diseases such as cancer and cardiovascular disorders. The emergent roles of microRNAs in cartilage homeostasis and OA pathogenesis are summarized in this Review, alongside potential clinical applications.

Chondrogenesis, chondrocyte differentiation, and articular cartilage metabolism in health and osteoarthritis

Chondrogenesis occurs as a result of mesenchymal cell condensation and chondroprogenitor cell differentiation. Following chondrogenesis, the chondrocytes remain as resting cells to form the articular cartilage or undergo proliferation, terminal differentiation to chondrocyte hypertrophy, and apoptosis in a process termed endochondral ossification, whereby the hypertrophic cartilage is replaced by bone. Human adult articular cartilage is a complex tissue of matrix proteins that varies from superficial to deep layers and from loaded to unloaded zones. A major challenge to efforts to repair cartilage by stem cell-based and other tissue-engineering strategies is the inability of the resident chondrocytes to lay down a new matrix with the same properties as it had when it was formed during development. Thus, understanding and comparing the mechanisms of cartilage remodeling during development, osteoarthritis (OA), and aging may lead to more effective strategies for preventing cartilage damage and promoting repair. The pivotal proteinase that marks OA progression is matrix metalloproteinase 13 (MMP-13), the major type II collagen-degrading collagenase, which is regulated by both stress and inflammatory signals. We and other investigators have found that there are common mediators of these processes in human OA cartilage. We also observe temporal and spatial expression of these mediators in early through late stages of OA in mouse models and are analyzing the consequences of knockout or transgenic overexpression of critical genes. Since the chondrocytes in adult human cartilage are normally quiescent and maintain the matrix in a low turnover state, understanding how they undergo phenotypic modulation and promote matrix destruction and abnormal repair in OA may to lead to identification of critical targets for therapy to block cartilage damage and promote effective cartilage repair.

Regulation of multiple target genes by miR-1 and miR-206 is pivotal for C2C12 myoblast differentiation

MicroRNAs are short non-coding RNAs involved in post-transcriptional regulation of multiple messenger RNA targets. The miR-1/miR-206 family is expressed during skeletal muscle differentiation and is an integral component of myogenesis. To better understand miR-1/miR-206 function during myoblast differentiation we identified novel target mRNAs by microarray and characterized their function in C2C12 myoblasts. Candidate targets from the screen were experimentally validated together with target genes that were predicted by three different algorithms. Some targets characterised have a known function in skeletal muscle development and/or differentiation and include Meox2, RARB, Fzd7, MAP4K3, CLCN3 and NFAT5, others are potentially novel regulators of myogenesis, such as the chromatin remodelling factors Smarcd2 and Smarcb1 or the anti-apoptotic protein SH3BGRL3. The expression profiles of confirmed target genes were examined during C2C12 cell myogenesis. We found that inhibition of endogenous miR-1 and miR-206 by antimiRs blocked the downregulation of most targets in differentiating cells, thus indicating that microRNA activity and target interaction is required for muscle differentiation. Finally, we show that sustained expression of validated miR-1 and/or miR-206 targets resulted in increased proliferation and inhibition of C2C12 cell myogenesis. In many cases the expression of genes related to non-muscle cell fates, such as chondrogenesis, was activated. This indicates that the concerted downregulation of multiple microRNA targets is not only crucial to the skeletal muscle differentiation program but also serves to prevent alternative cell fate choices.