The Effect of Matrix Density on the Regulation of 3-D Capillary Morphogenesis
Cyrus M. Ghajar 1, Xiaofang Chen 1, Joseph W. Harris 1, Vinod Suresh 1, Chris C.W. Hughes 1, Noo Li Jeon 1, Andrew J. Putnam 1 and Steven C. George 1*
1 University of California, Irvine
* To whom correspondence should be addressed. E-mail: scgeorge{at}uci.edu.
Submitted on August 30, 2007
Revised on September 28, 2007
Accepted on 12 October 2007
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Abstract |
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The means by which extracellular matrix (ECM) density regulates 3-D capillary morphogenesis is unclear. To study this phenomenon, we utilized a fibrin-based in vitro assay in which a fibroblast monolayer is plated atop a fibrin gel ~2.5 mm away from endothelial cell-coated beads within the matrix. Increasing fibrin density from 2.5 to 10 mg/ml resulted in a three-fold reduction in capillary network formation. However, distributing fibroblasts throughout the matrix completely eliminated this inhibitory effect, resulting in robustly vascularized matrices suitable for in vivo applications, as functional anastomoses formed between the implanted tissues and host vasculature when implanted in immune-compromised mice. Dense matrices did not stimulate fibroblast-mediated matrix remodeling: differentiation into myofibroblasts, matrix production and protease secretion were not enhanced by the dense condition. Instead, quantifying diffusivity of FITC-dextran (MW of 10, 40, 70, and 150 kDa) through fibrin revealed a 2- to 3-fold decrease within the 10 mg/ml matrices. Thus, distributing a pro-angiogenic source (fibroblasts) throughout the matrix stimulates capillary network formation by overcoming this diffusion restriction as a result of significantly reduced diffusion distances. While roles for matrix stiffness and ligand binding density have previously been identified, our results emphasize the importance of diffusion restrictions in limiting capillary morphogenesis.
Key Words:
Angiogenesis, Capillary Morphogenesis, Diffusion, Extracellular Matrix Density, Stromal Cells
