Microenvironmental control of capillary morphogenesis
Using a combination of in vitro and in vivo models, we have discovered that the formation of nascent vasculature is regulated by both the biophysical properties of the ECM and the identity of the supporting stromal cells. Our data suggest that stromal cells of different origins differentially control ECM proteolysis during angiogenic sprouting, and that controlling the rate of ECM breakdown is critical to yield stable, functional vessels. In this project, we are mechanistically investigating how these two critical instructive elements of the local microenvironment (i.e., the stromal cells and the ECM) influence the quantity, functional quality, and stability of new vasculature.
We also utilize engineered hydrogel platforms based on poly(ethylene glycol) (PEG) to understand the influence of the ECM microenvironment on capillary morphogenesis. By fabricating PEG hydrogels with peptide crosslinks differentially susceptible to different proteases, we can tune the degradation kinetics of the ECM and assess the resulting effects on capillary growth and functionality. We have also conjugated PEG to full-length ECM proteins (PEG-collagen, PEG-fibrinogen) to make biosynthetic conjugates that support complex cellular programs in 3D. By altering features of the PEG (weight fraction, number of arms, MW, etc.), we can alter the bulk mechanical properties of the gels while keeping the biological properties unchanged. These gels enable us to address fundamental questions in vitro, and have also shown great promise as morphogenetic guides to direct vascularization in ischemic tissues in vivo.
B.A. Juliar, J.A. Beamish, M.E. Busch, D.S. Cleveland, L. Nimmagadda, and A.J. Putnam. “Cell-mediated matrix stiffening accompanies capillary morphogenesis in ultrasoft amorphous hydrogels.” Biomaterials, 230:119634 (2020).
B.A. Juliar, M.T. Keating, Y.P. Kong, E.L. Botvinick, and A.J. Putnam. “Sprouting angiogenesis induces significant mechanical heterogeneities and ECM stiffening across length scales in fibrin hydrogels.” Biomaterials, 162:99-108 (2018).
M.L. Vigen, J. Ceccarelli, and A.J. Putnam. “Protease-Sensitive PEG Hydrogels Regulate Vascularization In Vitro and In Vivo.” Macromolecular Bioscience, 14(10): 1368-79 (2014).
S.J. Grainger, B. Carrion, J. Ceccarelli, and A.J. Putnam. “Stromal Cell Identity Influences the In Vivo Functionality of Engineered Capillary Networks Formed by Co-Delivery of Endothelial Cells and Stromal Cells.” Tissue Engineering: Part A, 19(9-10):1209-22 (2013).
Video of an endothelial tip cell dynamically probing the fibrillar ECM during capillary morphogenesis in a 3D fibrin gel.
(Credit: Max Kotlarchyk, in collaboration with Elliot Botvinick)