Professor Kielty's laboratory has two interconnected research themes: how the cell-matrix interface regulates extracellular matrix assembly and function, and how it regulates growth factor receptor signals in mesenchymal stem (progenitor) cells. The extracellular matrix is a complex multi-component structural microenvironment that is laid down by cells, and in turn supports cells and regulates their survival, migration, proliferation and behaviour. The matrix also stores growth factors which, upon release, activate cell receptors which signal intracellular to alter cell activity. We are studying vascular extracellular matrix (elastic fibres) and growth factor receptors.
Assembly, Structure and Function of Fibrillin Microfibrils and Elastic Fibres
Extracellular matrix assembly studies focus on elastic fibres. The template for elastin deposition is fibrillin microfibrils, whose essential contribution to tissue integrity is highlighted by linkage of fibrillin mutations to Marfan syndrome which has severe cardiovascular, skeletal and ocular abnormalities. Microfibrils endow connective tissues with long-range elastic recoil, and microfibrillar structures include zonular fibres which hold the lens in dynamic suspension and oxytalan fibres which dispense elasticity to skin. Elastin is deposited on pre-formed microfibrils, in association with fibulins-4 and -5 and the crosslinking enzyme lysyl oxidase.
We are using recombinant elastic fibre molecules in combination with microscopy and in vitro binding studies to determine how elastic fibre molecules assemble, electron microscopy approaches to map tropoelastin binding sites on microfibrils, and biophysical approaches (analytical ultracentrifugation, laser light scattering) to study the process of multimerisation. We have developed a comprehensive mass spectrometry database of the molecular interactions of elastic fibres, including secondary associations mediated by heparan suphate. The roles of cell surface receptors in this process are being determined using knock-down and over-expression studies, in combination with biochemical approaches, confocal microscopy and real-time imaging. The effects of disease-causing mutations on elastic fibre assembly and function are also being addressed.
Adult Mesenchymal Stem cells in Vascular tissue engineering
Our stem cell interests arose from adult mesenchymal stem cell (MSC) applications in vascular tissue engineering. We showed that vascular endothelial growth factor (VEGF) signals through platelet-derived growth factor PDGF) receptrs in MSCs, thereby regulating their migration, proliferation and tube-forming potential in culture (Ball et al., 2007, J Cell Biol. 177:489-500). We have shown that PDGF receptors crosstalk with both integrins and neuropilin receptors expressed on MSCs, how this crosstalk regulates MSC phenotype, and the structural and signalling basis of growth factor ligand binding to PDGF receptors. This research has important implications for regulating neovascularisation. Using quantitative proteomic and glycomic approaches, we are defining the MSC cell-matrix interface and it regulates MSCs (collaborative studies with Profs Ann Canfield and Tony Whetton and Dr Cathy Merry).