Endothelial cell biology
Projects in this area of research seek to identify and characterize the molecular pathways controlling endothelial cell sprouting, arteriovenous differentiation and vessel remodeling. Examples include the analysis of signaling by the Notch pathway (Benedito et al. 2009, Cell; Benedito et al. 2012, Nature), Eph receptor tyrosine kinases and their ephrin ligands (Wang et al. 2010, Nature), and VEGF receptor endocytosis in the growing vasculature (Nakayama et al. 2013, Nat Cell Biol). These projects made use of sophisticated cell type-specific and inducible genetic approaches in mice, which enable functional studies in the embryonic, postnatal and adult endothelium.
We are also strongly interested in the signaling interactions between blood vessels and the surrounding tissues. Tissue-derived signals control the growth and organ-specific specialization of the vasculature. Conversely, vascular cells play key roles in the differentiation of certain organs and therefore we are currently studying the mechanisms mediating this crosstalk.
To gain better insight into the molecular processes regulating arteriovenous differentiation, we have generated artery-specific tamoxifen-inducible transgenic Bmx-CreERT2 mice. This permits the temporally controlled targeting of genes in arteries without affecting their essential function in capillary beds or other tissues. We typically combine genetic experiments in mice with in vitro assays to validate findings and gain additional mechanistic insight.
Biology of pericytes and vascular smooth muscle cells
Despite the important roles of pericytes in the healthy organism and in vascular disease, relatively little is known about the biology of these cells and the relevant signaling pathways. Due to the close relationship between pericytes and vascular smooth muscle cells, several of our projects are investigating both classes of mural cells.
Our previous work has identified important roles of integrin cell cell-matrix receptors and integrin-linked kinase in the adhesion, spreading and contractility of mural cells (Abraham et al. 2008, Circ Res.; Kogata et al. 2009, Genes Dev). Furthermore, we have shown that expression of the Eph receptor ligand ephrin-B2 in pericytes and vascular smooth muscle cells is essential for the normal association of mural cells with blood vessel endothelium (Foo et al. 2006, Cell).
In the embryonic heart, endocardial endothelial cells are a source of pericytes and vascular smooth muscle cells (Chen et al. 2016, Nat Commun.).
To improve the genetic toolkit for loss-of-function and gain-of-function genetic experiments in mural cells, we have generated tamoxifen-inducible Pdgrfb-CreERT2 transgenic mice. This line facilitates experiments investigating the function of certain pathways and the better characterization of mural cells from different organs in healthy and diseased conditions.
Tissue-specific specialization of blood vessels and roles in organ morphogenesis
A third area of research in the laboratory is concerned with the role of vessels in the context of the surrounding tissue. Here, we are studying the vasculature of the mammalian skeletal system, which has been functionally linked to processes as diverse as bone formation and hematopoiesis. While there is a large body of published work on hematopoietic cells, stem cells and their niches, surprisingly little was known about the organization of the vasculature and distribution of key cell types in bone.
With the help of technical improvements concerning tissue processing and imaging in combination with powerful cell type-specific genetic approaches, we have been able to gain much deeper insight into the organization of bone marrow. This has led to the discovery of a new bone marrow subcompartment composed of endothelial, mesenchymal and hematopoietic cells that enables rapid hematopoietic progenitor cell proliferation (Wang et al. 2012, EMBO J).
Our work has also led to the identification of functional specialized capillary and endothelial cell subtypes in bone, which promote osteogenesis and are important for the function of hematopoietic stem cells (Ramasamy et al. 2014, Nature; Kusumbe et al. 2016, Nature). We also found that these capillaries decline during ageing, which might contribute to age-related changes in bone mass and hematopoiesis (Kusumbe et al. 2014, Nature; Kusumbe et al. 2016, Nature).
Transgenic mouse lines
Transgenic mice expressing tamoxifen-inducible CreERT2 recombinase in all endothelial cells (Cdh5-CreERT2) or in the arterial endothelium (Bmx-CreERT2) are now commercially available:
Alternatively, MTAs can be obtained via:
Selected publications on angiogenesis and endothelial biology:
- Yamamoto H, Ehling M, Kato K, Kanai K, van Lessen M, Frye M, Zeuschner D, Nakayama M, Vestweber D, Adams RH. (2015). Integrin β1 controls VE-cadherin localization and blood vessel stability. Nat Commun. Mar 10;6:6429.
- M. Nakayama, A. Nakayama, M. van Lessen, H. Yamamoto, S. Hoffmann, H.C. Drexler, N. Itoh, T. Hirose, G. Breier, D. Vestweber, J.A. Cooper, S. Ohno, K. Kaibuchi, R.H. Adams (2013), Spatial regulation of VEGF receptor endocytosis in angiogenesis. Nat Cell Biol. 2013 Jan 27. doi: 10.1038/ncb2679.
- R. Benedito, S.F. Rocha, M. Woeste, M. Zamykal, F. Radtke, O. Casanovas, A. Duarte, B. Pytowski, R.H. Adams. (2012), Notch-dependent VEGFR3 upregulation allows angiogenesis without VEGF-VEGFR2 signalling. Nature 484:110-4.
- Y. Wang, M. Nakayama, M.E. Pitulescu, T.S. Schmidt, M.L. Bochenek, A. Sakakibara, S. Adams, D. Davy, U. Deutsch, U. Lüthi, A. Barberis, L.E. Benjamin, T. Mäkinen, C.D. Nobes and R.H. Adams (2010), Ephrin-B2 controls VEGF-induced angiogenesis and lymphangiogenesis. Nature 465:483-486.
- R. Benedito, C. Roca, I. Sörensen, S. Adams, A. Gossler, M. Fruttiger, and R.H. Adams (2009), The Notch ligands Dll4 and Jagged1 have opposing effects on angiogenesis. Cell 137:1124-1135.
- C. Roca and R.H. Adams (2007), Regulation of vascular morphogenesis by Notch signaling. Genes Dev. 21:2511-24.
- R.H. Adams and Kari Alitalo (2007), Molecular regulation of angiogenesis and lymphangiogenesis. Nature Rev. Mol. Cell. Biol. 8:464-78.
Selected publications on mural cell biology:
- Nakayama A, Nakayama M, Turner CJ, Höing S, Lepore JJ, Adams RH. (2013). Ephrin-B2 controls PDGFRβ internalization and signaling. Genes Dev. Dec 1;27(23):2576-89.
- N. Kogata, R.M. Tribe, R. Fässler, M. Wa, and R.H. Adams (2009), Integrin-linked kinase controls vascular wall formation by negatively regulating Rho/ROCK-mediated vascular smooth muscle cell contraction. Genes Dev 23:2278-83.
- S. Abraham, N. Kogata, R. Fässler and R.H. Adams (2008), The integrin ß1 subunit controls mural cell adhesion, spreading and blood vessel wall stability. Circ Res. 102:562-570.
- D. Stenzel, E. Nye, M. Nisancioglu, R.H. Adams, Y. Yamaguchi, H. Gerhardt H (2009), Peripheral mural cell recruitment requires cell-autonomous heparan-sulfate. Blood 114:915-24.
- S.S. Foo, C.J. Turner, S. Adams, A. Compagni, D. Aubyn, N. Kogata, P. Lindblom, M. Shani, D. Zicha and R.H. Adams (2006), Ephrin-B2 controls cell motility and adhesion during blood-vessel-wall assembly. Cell 124:161-173.
Selected publications on bone marrow biology:
- A.P. Kusumbe, S.K. Ramasamy, T. Itkin, M. Andoloussi, U.H. Langen, C. Betsholtz, T. Lapidot, R.H. Adams (2016). Age-dependent modulation of vascular niches for haematopoietic stem cells. Nature 532:380-4
- T. Itkin , S. Gur-Cohen, J.A. Spencer, A. Schajnovitz, S.K. Ramasamy, A.P. Kusumbe, G. Ledergor, Y. Jung, I. Milo, M.G. Poulos, A. Kalinkovich, A. Ludin, O. Kollet, G. Shakhar, J.M. Butler, S. Rafii, R.H. Adams, D.T. Scadden, C.P. Lin, T. Lapidot (2016). Distinct bone marrow blood vessels differentially regulate haematopoiesis. Nature. 532:323-8.
- A.P. Kusumbe, S.K. Ramasamy, A. Starsichova, R.H. Adams (2015). Sample preparation for high-resolution 3D confocal imaging of mouse skeletal tissue. Nat Protoc. 10:1904-14.
- S.K. Ramasamy, A.P. Kusumbe, L. Wang, R.H. Adams (2014). Endothelial Notch activity promotes angiogenesis and osteogenesis in bone. Nature 507:376-80.
- A.P. Kusumbe, S.K. Ramasamy, R.H. Adams (2014). Coupling of angiogenesis and osteogenesis by a specific vessel subtype in bone. Nature. Mar 507(7492):323-8.
- L. Wang, R. Benedito, M.G. Bixel, D. Zeuschner, M. Stehling, L. Sävendahl, J.J. Haigh, H. Snippert, H. Clevers, G. Breier, F. Kiefer, R.H. Adams (2012), Identification of a clonally expanding haematopoietic compartment in bone marrow. EMBO J. 32:219-30.