MicroRNAs in osteoarthritis and chondrogenesis

• Main Author: Budd, Emma
• Format: Dissertation
• Language: English
• Published: University of Southampton 2016

Loss of chondrocytes along with diminishment of specialised extracellular matrix (ECM) is often the outcome of articular cartilage injury and can progress to the onset of osteoarthritis (OA). OA is typically seen as an age related disease and with the changing world demographic, the fastest growing age category is the elderly population. Cartilage injury, which may result in OA, results in the clinical requirement for replacement of degenerated tissues and with an ageing population the demand for clinical replacement of degenerated tissue is set to dramatically increase posing socio-economic burdens. MicroRNAs are a class of small non-coding single stranded RNA which regulate gene expression post transcriptionally. MicroRNAs could be directly administered to articular cartilage, having direct effect upon resident articular chondrocytes, as a form of treatment for cartilage injury and OA. Exogenous microRNAs could be used in combination with isolated skeletal stem cells and transplanted to defective articular sites to induce articular cartilage regeneration. The identification and function of dysregulated microRNAs in OA and identification of microRNAs which govern chondrogenic differentiation may help the development of novel strategies to enhance cartilage formation and possibly in the treatment of cartilage injury and OA. The work in this thesis has looked to identify if specific microRNAs are dysregulated in OA. Specifically the expression of miR-146b in human OA articular chondrocytes was investigated. MiR-146b shares close sequence homology to miR-146a and was hypothesised to exhibit similar expression in OA chondrocytes and be receptive to IL-1β stimulation. Using TaqMan qPCR, the expression of miR-146b-5p was found to be significantly up-regulated in human articular OA chondrocytes, with a fold change of ~123. Treatment of human chondrocytes with pro-inflammatory IL-1β did not induce miR-146b up-regulation, but did induce miR-146a up-regulation. Specific microRNAs were also hypothesised to be involved with chondrogenic differentiation of human stem cells. Specifically, miR-34a was hypothesised to target specific chondrogenic associated genes in human fetal femur-derived cells and miR-146b was hypothesised to target chondrogenic associated genes in human bone marrow derived skeletal stem cells. Skeletal stem cell chondrogenic differentiation can be conducted in vitro with the use of chemical cues and a three dimensional micromass culture system. Despite the identification that miR-34a was found to be significantly up-regulated during chondrogenic differentiation of fetal femur-derived cells, no effect was observed following modulation of miR-34a levels on the selected predicted mRNA target; TGIF2. MiR-146b was found to be significantly down-regulated during chondrogenic differentiation of human bone marrow derived skeletal stem cells and both SMAD4 and SOX5 were identified as predicted targets of miR-146b. Overexpression of miR-146b resulted in the significant down-regulation of SOX5. SOX5 is required for early chondrogenic differentiation. MiR-146b is suggested to be down-regulated during chondrogenesis to prevent the inhibitory effects upon SOX5 expression. Future studies to modulate anti-chondrogenic miR-146b through stable transfection and future in vivo studies will assess the ability of miR-146b to modulate chondrogenic differentiation in vivo. Identification of miR-146b, which was shown to display dysregulated expression in human OA articular chondrocytes, could be used as a potential therapeutic target in the future, as a potential anti-inflammatory therapeutic. Identification of miR-146b down-regulation during the chondrogenic differentiation of human bone marrow derived skeletal stem cells may enable the potential use of miR-146b modulation in combination with skeletal stem cell therapy to induce articular cartilage regeneration at articular cartilage defect sites, which may prevent to the onset of OA.