Molecular basis of endothelial cell morphogenesis in three-dimensional extracellular matrices

Angiogenesis, the growth of new blood vessels from existing ones, is an important, yet not fully understood, process and is involved in diseases such as rheumatoid arthritis, diabetic retinopathy and solid tumour growth. Central to the process of angiogenesis are endothelial cells (EC), which line all blood vessels, and are capable of forming new capillaries by migration, proliferation and lumen formation. We construct a cell-based mathematical model of an experiment (Vernon, R.B. and Sage, E.H. (1999) “A novel, quantitative model for study of endothelial cell migration and sprout formation within three-dimensional collagen matrices”,Microvasc. Res.57, 118–133) carried out to assess the response of EC to various diffusible angiogenic factors, which is a crucial part of angiogenesis. The model for cell movement is based on the theory of reinforced random walks and includes both chemotaxis and chemokinesis. Three-dimensional simulations are run and the results correlate well with the experimental data. The experiment cannot easily distinguish between chemotactic and chemokinetic effects of the angiogenic factors. We, therefore, also run two-dimensional simulations of a hypothetical experiment, with a point source of angiogenic factor. This enables directed (gradient-driven) EC migration to be investigated independently of undirected (diffusion-driven) migration.

Download Full-text

Matrix metalloproteinase-1 and -9 activation by plasmin regulates a novel endothelial cell-mediated mechanism of collagen gel contraction and capillary tube regression in three-dimensional collagen matrices

Journal of Cell Science ◽

10.1242/jcs.114.5.917 ◽

2001 ◽

Vol 114 (5) ◽

pp. 917-930 ◽

Cited By ~ 2

Author(s):

G.E. Davis ◽

K.A. Pintar ◽

Allen, R. Salazar ◽

S.A. Maxwell

Keyword(s):

Extracellular Matrix ◽

Endothelial Cells ◽

Endothelial Cell ◽

Three Dimensional ◽

Collagen Gel ◽

Plasminogen Activators ◽

Collagen Matrices ◽

Collagen Gel Contraction ◽

Blocking Antibodies ◽

Pai 1

Here, we describe a new function for plasmin and matrix metalloproteinases (MMPs), which is to regulate the regression of capillary tubes in three-dimensional extracellular matrix environments. Using a well-described capillary morphogenesis system in three-dimensional collagen matrices, a new model of capillary regression has been established by adding plasminogen to the culture medium. Plasminogen is converted to plasmin by endothelial cell plasminogen activators which then induces matrix metalloproteinase-dependent collagen gel contraction and capillary regression. Plasminogen addition results in activation of MMP-1 and MMP-9, which then results in collagen proteolysis followed by capillary regression. The endothelial cells undergo apoptosis following gel contraction as detected by flow cytometric analysis as well as by detectable caspase-3 cleavage and caspase-dependent cleavage of the actin cytoskeletal regulatory protein, gelsolin. In addition, directly correlating with the contraction response, tyrosine phosphorylation of p130cas, an adapter protein in the focal adhesion complex, is observed followed by disappearance of the protein. Proteinase inhibitors that block MMPs (TIMP-1 or TIMP-2), plasminogen activators (PAI-1) or plasmin (aprotinin) completely block the gel contraction and regression process. In addition, chemical inhibitors of MMPs that block capillary regression also block MMP-1 and MMP-9 activation suggesting that a key element in this regression response is the molecular control of MMP activation by endothelial cells. Blocking antibodies directed to MMP-1 or MMP-9 interfere with capillary regression while blocking antibodies directed to PAI-1 accelerate capillary regression suggesting that endogenous synthesis of PAI-1 negatively regulates this process. These data present a novel system to study a new mechanism that may regulate regression of capillary tubes, namely, plasmin and MMP-mediated degradation of extracellular matrix.

Download Full-text