About the Project
Background and preliminary data:
Hand osteoarthritis (OA) is a highly prevalent, debilitating condition that predominantly affects women around the time of the menopause. Pathogenesis of this condition is poorly understood but some recent insight has come from a genome wide association study (GWAS). In this study, based in an Icelandic population, hypomorphic variants in the gene ALDH1A2 were found to be associated with increased risk of disease 1. This gene encodes retinaldehyde dehydrogenase, a key enzyme in the synthesis of intracellular retinoic acid (RA). It was not associated with increased OA in knee or hip. RA is an interesting target in hand OA as it has been used widely in vitro as a catabolic factor, causing breakdown of the key proteoglycan in cartilage, aggrecan 2. Retinoic acid production and signaling is complex, with different cellular responses determined by which cellular RA binding protein is selected and by which RA receptors are utilized 3.
We examined genes regulated in response to cartilage injury (a primary risk factor for OA development) by microarray and RT-PCR. We found strong regulation of several genes on the RA pathway. These included up-regulation of enzymes promoting RA synthesis (e.g. retinol dehydrogenase 12) (see Table 1) as well as suppression of its key breakdown enzymes, Cyp26 a, b and c. (Figure 1). We are still validating primers for ALDH1A2. Injury leads to the up and down-regulation of a number of homeobox (Hox) target genes (Table 1).
The aims of this project are to:
1. Explore how mechanical injury drives retinoic acid pathways in cartilage.
We have already defined a number of mechanisms by which articular cartilage responds to injury and will test whether these are important in driving RA regulation using pharmacological inhibitors and genetically modified murine tissue according to previously defined protocols 4-7. Studies may be extended to in vivo injury models.
2. Define the specific RA pathways that are induced by injury and compare this response to activation by available RA agonists. The pattern of induction of specific HOX genes will be examined by RT-PCR following injury compared with known agonists of RA. Some of these agents are already in clinical use e.g. isotretinoin (currently used for acne) and others are being used experimentally to prevent ectopic ossification e.g. post trauma 8.
3. Verify whether these genes are regulated in tissues from patients with hand OA.
We have amassed a number of surgical specimens of cartilage from individuals with hand OA (trapeziectomy samples from patients with base of thumb OA) and have been able to extract good quality RNA from them. We will compare expression profiles with large joint OA samples (hip and knee) as well as normal cartilage from cadaveric tissue courtesy of the University of Oxford anatomy department (ethical approval for this is imminent) and from other existing control tissue sources.
4. Towards clinical translation.
This project lends itself well to a potential Experimental Medicine approach as there are many drugs targeting RA signalling already in clinical use. By the end of this studentship we expect to be able to design a pilot drug (repurposing) trial to assess the clinical benefit of RA targeting in hand OA.
Research group:
Vincent: Director of OA Pathogenesis Centre. Currently has 3 students, 2 post docs and 1 technician working in her team. She also manages another 4 technicians associated with the OA Centre (most of whom are post-doctoral scientists). The group works closely with other PIs within the OA Centre (approximately 40-50 individuals in total). For further information: https://oacentre.kennedy.ox.ac.uk
or contact Tonia Vincent directly at [Email Address Removed]
Training experience:
RT-PCR; microarray analysis; cartilage injury assays; in vivo cartilage injury (OA model and focal cartilage defect model); handling human diseased and normal tissue; design of clinical experimental medicine trial.
References
1. Styrkarsdottir, U. et al. Severe osteoarthritis of the hand associates with common variants within the ALDH1A2 gene and with rare variants at 1p31. Nat. Genet. 46, 498–502 (2014).
2. Gendron, C. et al. Proteolytic activities of human ADAMTS-5: comparative studies with ADAMTS-4. J. Biol. Chem. 282, 18294–18306 (2007).
3. Cunningham, T. J. & Duester, G. Mechanisms of retinoic acid signalling and its roles in organ and limb development. Nature Publishing Group 16, 110–123 (2015).
4. Vincent, T., Hermansson, M., Bolton, M., Wait, R. & Saklatvala, J. Basic FGF mediates an immediate response of articular cartilage to mechanical injury. Proc. Natl. Acad. Sci. U.S.A. 99, 8259–8264 (2002).
5. Vincent, T. L. Targeting mechanotransduction pathways in osteoarthritis: a focus on the pericellular matrix. Curr Opin Pharmacol 13, 449–454 (2013).
6. Ismail, H. M. et al. JNK2 controls aggrecan degradation in murine articular cartilage and the development of experimental osteoarthritis. Arthritis & Rheumatology n/a–n/a (2015). doi:10.1002/art.39547
7. Chong, K.-W. et al. Fibroblast Growth Factor 2 Drives Changes in Gene Expression Following Injury to Murine Cartilage In Vitro and In Vivo. Arthritis Rheum. 65, 2346–2355 (2013).
8. Shimono, K. et al. Potent inhibition of heterotopic ossification by nuclear retinoic acid receptor-γ agonists. Nat. Med. 17, 454–460 (2011).