Title: Unlocking the Joint Morphogenetic Code in Mesenchymal Stem Cells from Human Synovium
Funder: Versus Arthritis

Abstract: This discovery project aims to identify the epigenetic code and associated gene expression profile underpinning the joint-morphogenetic ability of mesenchymal stromal/stem cells (MSCs), with the ultimate goal to preserve, or reinstate, this ability in adult MSCs to safeguard joints from damage, arthritis or ageing. Our work has identified the synovium as an important MSC niche, and has shown in mice that a sub-population of synovial MSCs deriving from the Gdf5-expressing embryonic joint interzone has properties that make them ideally suited for joint maintenance and repair throughout life. In parallel, we have made the exciting discovery that adult human synovial MSCs, culture-expanded and adenovirally modified to overexpress Bmp7, can give rise to a new joint-like organ upon nude mouse intramuscular injection. Since the epigenetic status of cells determines their gene-expression landscape and functional abilities, we hypothesise that the joint-morphogenetic ability of synovial MSCs is laid down during embryonic joint development as an epigenetic code that is preserved in adult life. MSCs descending from the joint interzone, present in synovium, would carry this code, while MSCs with distinct ontogeny, in periosteum and bone marrow, would not. We speculate that an efficient tissue regenerative capacity, necessary for joint homeostasis, is dependent on this code, with loss of the code through ageing or disease resulting in inefficient stem cell-mediated tissue regeneration/repair. To discover this epigenetic code, we will 1) identify the human MSC populations that display joint-morphogenetic ability; 2) perform epigenetic and gene-expression analyses; 3) methodologically validate differentially expressed genes and methylated loci. We will employ our unique in vivo model of ectopic joint formation to investigate whether the joint-morphogenetic ability is specific to human MSCs from synovium by comparing them with MSCs from bone marrow and periosteum. In mouse, we will use our Gdf5-Cre;Tom;Pdgfra-H2BGFP transgenic model to purify the Gdf5-lineage MSCs (marked by tdTomato), which maintain and repair joints in adulthood, and the remaining synovial MSC lineage(s) marked by Pdgfra-promoter-driven expression of H2B-GFP. We will carry out genome-wide DNA methylation and RNA-sequencing analyses, comparing for human the MSC populations with/without joint-morphogenetic ability, and for mouse the Gdf5-lineage MSCs with the remaining Pdgfra+ MSCs. Cells isolated from developing joints of human and mouse embryos will be included for reference as holders of the code. Unique and common DNA-methylation signatures will be identified and mapped against gene expression profiles. The analyses will be conducted separately in human and mouse cells, and differentially expressed genes and methylated loci that are common to human and mouse will be taken forward. Gene-ontology analysis will determine the nature of differentially methylated loci and related transcript networks. Identified differentially methylated loci will be methodologically validated using pyrosequencing, while differentially expressed genes will be validated by quantitative RT-PCR and immunostaining on tissue sections. This work will lead to the identification of epigenetic and gene-expression signatures associated with the joint-morphogenetic ability of MSC populations that can be exploited for therapeutic approaches aimed at preserving or reinstating the joint morphogenetic code in MSCs to maintain healthy joints and prevent or cure early osteoarthritis.


Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING
Health categories: MUSCULOSKELETAL