Investigating the niches of stem and progenitor cells in arthritis

Osteoarthritis (OA) is the commonest joint disease affecting over 9 million people in the UK. It causes progressive breakdown of articular cartilage and associated tissue remodelling, leading to deformities and disability. At present, there is no drug that can slow down or reverse the disease process, and current treatments focus on symptom relief and joint replacement for end-stage disease.

A hallmark of OA is an outgrowth of the thin membrane lining the joint cavity called synovium, which causes joint pain and damage. A key cell sustaining synovial tissue outgrowth via proliferation is the fibroblast. Our recent studies using single-cell transcriptomics on fibroblast populations purified from adult mouse knee joints, either at homeostasis or after injury, have demonstrated that synovial fibroblasts are heterogeneous and contain stem and progenitor cells (SPCs). We showed that these SPCs are located in two niches in the synovium, the lining layer where they are adjacent to the specialised fibroblast-like synoviocytes that produce lubricating factors such as hyaluronic acid, and the sublining tissue where they are in close proximity to blood vessels. We and others also showed that SPCs in synovium can repair cartilage after acute injury, but give rise to osteophytes under conditions of continuous damage such as OA.

We hypothesise that in homeostatic conditions, SPCs function to maintain and repair joint tissues via replacing specialised mature cells lost to turnover or injury, while in OA they give rise to dysfunctional fibroblasts that contribute to disease progression. Understanding the molecular regulation of the SPCs in joint health and disease will allow development of novel drugs to promote maintenance of healthy joints and repair damaged tissues, thereby counteracting the breakdown in early-stage OA.

In this project, the successful candidate will utilise state-of-the-art spatial proteomics, named Method of the Year 2024 by Nature Methods (https://doi.org/10.1038/s41592-024-02565-3). The proteome of SPCs and surrounding cells at the niche sites will be detected using laser-capture microdissection followed by mass spectrometry in synovial tissues from mouse and human joints, either homeostatic or after injury or from OA. Bioinformatics analyses will reveal the identities of the niche cells together with putative signalling pathways that are activated in these different conditions and the molecular interactions across the niche that regulate the SPCs. Mechanistic investigations will be carried out in an in vitro 3D synovial organoid culture system that mimics the in vivo synovial tissue, using e.g. CRISPR-mediated gene silencing and activation.

The successful candidate will employ a wide range of cutting-edge techniques. These will include spatial proteomics and bioinformatics analyses, tissue and cell culture, CRISPR-mediated gene editing, histological sample preparation and analysis, immunohistochemical and immunofluorescence stainings, and light and confocal laser-scanning microscopy. The successful candidate will also perform Fluorescence-Activated Cell Sorting (FACS), proliferation, migration, invasion and differentiation assays.

This PhD will be undertaken in the Rheumatology Research Group Laboratory (Rheumatology Research Group | Institute of Genetics and Cancer | Institute of Genetics and Cancer) based at the Institute of Genetics and Cancer. The Rheumatology Research Group is a partner of the Versus Arthritis Tissue Engineering and Regenerative Therapies Centre.