Identification of regulatory angiocrine signalling networks from the bone marrow vascular niche in osteoarthritis
In the skeletal system, blood vessels play a central role in the maintenance of microenvironments required for regulating bone and blood cell formation (1-4). Apart from supplying oxygen and nutrients, blood vessels provide a number of tissue-specific inductive paracrine signals (so-called angiocrine signals/factors) to generate, define and shape the tissue-specific niche microenvironments. During skeletal development blood vessel growth (angiogenesis) and bone formation (osteogenesis) are tightly coupled; particularly a specialized capillary subtype that mediates osteogenesis and angiogenesis in bone, and ageing is associated with the decline of these specialized capillaries (1). Therefore, blood vessels and particularly their endothelial cells are of key importance in maintaining skeletal health. Further, it has been speculated that several ageing-related diseases such as osteoporosis and osteoarthritis are associated with dysregulation of the vasculature. In osteoarthritis (OA), neo-vascularisation and innervatation of the (normally avascular and aneural) articular cartilage occurs and this is associated with the development of painful disease (5). Vascular alterations also occur during the formation of the osteophyte, a bony outgrowth on the margin of the joint. These likely arise from chondrocytes derived from the periosteum through the process of endochondral ossification. During cartilage loss in OA these osteophytes are thought to stabilize the osteoarthritic joint, thereby decreasing further structural alterations and progression. Despite the obvious importance of the bone vasculature in bone changes in OA, endothelial cells and their angiocrine signaling, which directly contribute towards abnormal bone growth and altered bone perfusion remain largely unknown.
- Characterize the endothelial cells and associated mesenchymal stem progenitor cells that directly contribute to bone changes in OA. A well-validated model of OA induced by surgical joint destabilization will be used. Chondrophyte (immature osteophyte) formation is apparent within the first week after destabilization with ossification occurring by 2 weeks. Painful behaviour, which may be associated with neo-innervation of the cartilage, occurs late after destabilization (around 12 weeks). The role of the endothelial cells in these processes will be explored using endothelial-specific genetically modified mouse models, validated previously by Kusumbe. High resolution 3-D imaging of thick bone sections (developed by Kusumbe) will be used to visualize, identify and characterize the endothelial cells and associated perivascular mesenchymal stem progenitor cells (6).
- Elucidate the angiocrine signalling networks that modulate abnormal bone growth, and bone perfusion in OA. Molecular studies will be performed to identify key angiocrine signals. Transcriptional profiling of endothelial cells from normal and diseased samples will be performed and a list of candidate genes that are differentially regulated will be selected by performing qPCR, IHC and in situ hybridization in bone samples from mouse models. Finally, the functionality of important selected genes/signals will be validated using endothelial-specific inducible genetic mouse models.
This interdisciplinary project on the frontiers of bone, cartilage and vascular biology will not only provide the first insights into the angiocrine signalling networks in regulating the osteophyte formation and disease progression, but will also test whether manipulation of the endothelium and its angiocrine signalling provide therapeutic benefits towards clinical management of this disease.
Training and career Opportunities
In addition to variety of cell and molecular biology techniques, this interdisplinary project on the frontiers of cartilage, bone and vascular biology will utilize multiple cutting-edge technologies including high-resolution 3-D bone imaging, RNA seq and sophisticated cell-specific inducible mouse genetics in combination with surgical mouse models for OA.
In the third and fourth year of the fellowship, student can have the opportunity to participate and contribute to the other ongoing projects (on vascular and bone biology) in the laboratory of Dr. Anjali Kusumbe.
In addition to the lab meetings, seminar programme and journal clubs, student will attend national and international scientific conferences where he/she will be expected to present the research findings.
Transferable or generic skills and career development
The student will receive training on writing papers, giving presentations, time and project management. Student will have the opportunity to attend career seminars and workshops. Dr. Anjali Kusumbe will supervise the project and will monitor the overall progress. Prof. Tonia Vincent (Director, Centre for OA Pathogenesis) will co-supervise and will provide helpful advice and mentoring. The student will have access to other training opportunities, seminars, journal club, annual review meeting and biennial international meetings through the OA Centre.
- Kusumbe AP, Ramasamy SK, Adams RH (2014) Coupling of angiogenesis and osteogenesis by a specific vessel subtype in bone. Nature 507: 323-328
- Ramasamy SK, Kusumbe AP, Wang L, Adams RH (2014) Endothelial Notch activity promotes angiogenesis and osteogenesis in bone. Nature 507: 376-380.
- Kusumbe AP, Ramasamy SK, Itkin T, Mae M, Langen U, Betsholtz C, Lapidot T, Adams RH (2016). Age-dependent modulation of vascular niches for haematopoetic stem cells. Nature 532: 380-384
- Itkin T, Gur-Cohen S, Spencer JA, Schajnovitz A, Ramasamy SK, Kusumbe AP, Ledergor G, Jung Y, Milo I, Poulos MG, Kalinkovich A, Ludin A, Golan K, Khatib E, Kumari A, Kollet O, Shakhar G, Butler JM, Rafii S, Adams RH, Scadden DT, Lin CP, Lapidot T (2016) Distinct bone marrow blood vessels differentially regulate hematopoiesis. Nature 532: 323-328
- Walsh DA, McWilliams DF, Turley MJ, Dixon MR, Fransès RE, Mapp PI, Wilson D (2010) Angiogenesis and nerve growth factor at the osteochondral junction in rheumatoid arthritis and osteoarthritis. Rheumatology (Oxford). 2010 49(10):1852-61
- Kusumbe AP, Ramasamy SK, A Starsichova, Adams RH (2015) Sample preparation for high-resolution 3D confocal imaging of mouse skeletal tissue. Nature Protocols 10: 1904-1914