Matrix stiffening promotes a tumor vasculature phenotype

Abstract

Tumor microvasculature tends to be malformed, more permeable, and more tortuous than vessels in healthy tissue, effects that have been largely attributed to up-regulated VEGF expression. However, tumor tissue tends to stiffen during solid tumor progression, and tissue stiffness is known to alter cell behaviors including proliferation, migration, and cell-cell adhesion, which are all requisite for angiogenesis. Using in vitro, in vivo, and ex ovo models, we investigated the effects of matrix stiffness on vessel growth and integrity during angiogenesis. Our data indicate that angiogenic outgrowth, invasion, and neovessel branching increase with matrix cross-linking. These effects are caused by increased matrix stiffness independent of matrix density, because increased matrix density results in decreased angiogenesis. Notably, matrix stiffness up-regulates matrix metalloproteinase (MMP) activity, and inhibiting MMPs significantly reduces angiogenic outgrowth in stiffer crosslinked gels. To investigate the functional significance of altered endothelial cell behavior in response to matrix stiffness, we measured endothelial cell barrier function on substrates mimicking the stiffness of healthy and tumor tissue. Our data indicate that barrier function is impaired and the localization of vascular endothelial cadherin is altered as function of matrix stiffness. These results demonstrate that matrix stiffness, separately from matrix density, can alter vascular growth and integrity, mimicking the changes that exist in tumor vasculature. These data suggest that therapeutically targeting tumor stiffness or the endothelial cell response to tumor stiffening may help restore vessel structure, minimize metastasis, and aid in drug delivery.tumor stiffness | endothelial cells | vascular permeability | glycation | extracellular matrix T he ingrowth of newly sprouted blood vessels is necessary for solid tumor growth, and tumor vasculature is typically malformed, leakier, and more tortuous than the vasculature of normal tissues (1-3). Generally, aberrant tumor vasculature is considered to be caused by up-regulated VEGF expression resulting in chaotic vascular growth and failure to establish mature, well-regulated networks (4, 5). Here, we propose a different hypothesis, namely that extracellular matrix (ECM) mechanical properties also contribute to the aberrant vascular phenotype seen in tumors.Solid tumor tissue is typically stiffer than native, healthy tissue (1, 6). Increased ECM stiffness within tumors is caused primarily by both increased collagen deposition and increased cross-linking within the tumor stroma (7). Increased ECM density and crosslinking are associated with poor prognosis in a number of cancers (8, 9). Many studies have investigated the role of matrix density on angiogenesis and, in both collagen and fibrin matrices, have shown that angiogenesis decreases with increasing matrix concentration (10-13). Increased matrix density appears to act as a physical barrier that restricts cell migration, and cells rely on matr...

Quantitative assessment of cell contractility using polarized light microscopy

“…Accordingly, we observed a lower QPOL signal in tumor sections from mice treated with BAPN compared to the untreated control (Figure E). These results are consistent with the reduced stiffness and contractility of tumor tissue observed in BAPN treated mice . Of particular relevance, the quantification of the retardance revealed that we could distinguish between soft and stiff tumors (Figure F).…”

“…Type I collagen was isolated from rat‐tail tendons and extracted in 0.1% sterile acetic acid at 4°C as described previously . Stiffness of the collagen scaffolds was controlled either by changing the collagen density or by increasing collagen crosslinking through non‐enzymatic glycation.…”

Matrix stiffness enhances VEGFR-2 internalization, signaling, and proliferation in endothelial cells

“…Briefly, the ratio of acrylamide (40% w/v; Bio-Rad, Hercules, CA) and bis-acrylamide (2% w/v; Bio-Rad) was varied to tune gel stiffness from 1 to 10 kPa to mimic vascular and tumorous tissue as described previously [22,26,39]. Gels were coated with either 0.1 mg/ml collagen type I (BD Biosciences, San Jose, CA) or fibronectin (Thermo Fisher Scientific, Waltham, MA).…”

Engineering and physical sciences in oncology: challenges and opportunities

“…Enhanced ECM density and rigidity facilitates liver and breast cancer detection via , and may indicate risk factors for tumour progression and therapeutic response 53,54 . ECM changes alter mechanotransduction 55,56 and promote malignant behaviour by disrupting epithelial morphogenesis 57 , growth factor secretion and signalling 58 , invasive phenotype 59,60 and stem cell differentiation 61 , as well as angiogenesis and vessel permeability 62 . As such, efforts have focused on characterizing altered ECM and how it contributes to tumour progression, with the goal of normalizing ECM for therapy 3,63 (FIG.…”