Fluid Shear Stress Regulates the Invasive Potential of Glioma Cells via Modulation of Migratory Activity and Matrix Metalloproteinase Expression

Abstract

BackgroundGlioma cells are exposed to elevated interstitial fluid flow during the onset of angiogenesis, at the tumor periphery while invading normal parenchyma, within white matter tracts, and during vascular normalization therapy. Glioma cell lines that have been exposed to fluid flow forces in vivo have much lower invasive potentials than in vitro cell motility assays without flow would indicate.Methodology/Principal FindingsA 3D Modified Boyden chamber (Darcy flow through collagen/cell suspension) model was designed to mimic the fluid dynamic microenvironment to study the effects of fluid shear stress on the migratory activity of glioma cells. Novel methods for gel compaction and isolation of chemotactic migration from flow stimulation were utilized for three glioma cell lines: U87, CNS-1, and U251. All physiologic levels of fluid shear stress suppressed the migratory activity of U87 and CNS-1 cell lines. U251 motility remained unaltered within the 3D interstitial flow model. Matrix Metalloproteinase (MMP) inhibition experiments and assays demonstrated that the glioma cells depended on MMP activity to invade, and suppression in motility correlated with downregulation of MMP-1 and MMP-2 levels. This was confirmed by RT-PCR and with the aid of MMP-1 and MMP-2 shRNA constructs.Conclusions/SignificanceFluid shear stress in the tumor microenvironment may explain reduced glioma invasion through modulation of cell motility and MMP levels. The flow-induced migration trends were consistent with reported invasive potentials of implanted gliomas. The models developed for this study imply that flow-modulated motility involves mechanotransduction of fluid shear stress affecting MMP activation and expression. These models should be useful for the continued study of interstitial flow effects on processes that affect tumor progression.

Interstitial Flow in a 3D Microenvironment Increases Glioma Invasion by a CXCR4-Dependent Mechanism

“…Interstitial flow has been implicated in modulating several cell functions including transport function in the lymphatic endothelium (33), fibroblast alignment, migration, and TGF-b activation (34). A recent report examined the effect of shear flow on glioma cells and found that invasion decreased (35). However, this study primed the cells with acute flow followed by exposure to stable chemokine gradients and was interested in only the cells migrating after this flow period (under static conditions).…”

Migration dynamics of breast cancer cells in a tunable 3D interstitial flow chamber

“…Interstitial flow is driven by hydrostatic and osmotic pressure gradients that exist between arterioles, the interstitial space, lymphatic capillaries, and post-capillary venules, 15 and fluid flow between the blood to the lymphatics can be dramatically increased under pathological conditions such as inflammation and cancer. 14,16,17 Interstitial flow has been hypothesized to affect cell migration in a number of different ways, including matrix stiffening and local strain gradient induction, [18][19][20][21] flow-upregulated proteolysis by migrating cells, 3,22 stress-mediated cytokine activation, 23 and autologous chemotaxis. [23][24][25] In the latter mechanism, autologously secreted (or activated) chemokine forms local pericellular diffusion gradients skewed by fluid convection, and the cells subsequently ''chemotact'' up the flow-directed gradient; this requires that the migrating cell expresses both the chemokine to which it is chemotactically sensitive as well as its receptor, such as CCL19/ CCR7 by dendritic cells 26 and some types of invasive tumor cells.…”

“…3E, left). 22,24 To do this, we first carried out experiments with two different average flow velocities (limited by technical considerations), 0.4 and 4 mm s…”

Modeling Tumor Microenvironments In Vitro

“…At the same time, in vitro models cannot recapitulate every aspect of the tumor microenvironment, and thus care must be taken to identify their limitations and assumptions. For example, while a threedimensional (3D) culture of tumor cells in a collagen gel under interstitial flow might be used to explore direct effects of interstitial flow on tumor cell invasion [23][24][25], it ignores other factors present at an invasive edge of the tumor such as the architecture and composition of the ECM (which is highly heterogeneous), the diversity of cell types present in the tumor stroma and their physiological interactions, and gradients of oxygen, pH, metabolites, and nutrient that are formed from the tumor mass. As such, one can only infer from such studies the direct effects of interstitial flow on uniformly distributed tumor cells within a homogeneous collagen ECM (which itself is important), but not necessarily translate those findings directly to the tumor invasive edge, since one does not know the relative importance of interstitial flow versus the other factors that were excluded from the in vitro model.…”