Compression stiffening of brain and its effect on mechanosensing by glioma cells

Katarzyna Pogoda,Cezary Marcinkiewicz,Michael Weaver,Richard Kim,Likang Chin,Rebecca G Wells,Paul A Janmey,Penelope C Georges,Robert Bucki,Fitzroy J Byfield

doi:10.1088/1367-2630/16/7/075002

Abstract

Many cell types, including neurons, astrocytes and other cells of the central nervous system, respond to changes in the extracellular matrix or substrate viscoelasticity, and increased tissue stiffness is a hallmark of several disease states, including fibrosis and some types of cancers. Whether the malignant tissue in brain, an organ that lacks the protein-based filamentous extracellular matrix of other organs, exhibits the same macroscopic stiffening characteristic of breast, colon, pancreatic and other tumors is not known. In this study we show that glioma cells, like normal astrocytes, respond strongly in vitro to substrate stiffness in the range of 100 to 2000 Pa, but that macroscopic (mm to cm) tissue samples isolated from human glioma tumors have elastic moduli in the order of 200 Pa that are indistinguishable from those of normal brain. However, both normal brain and glioma tissues increase their shear elastic moduli under modest uniaxial compression, and glioma tissue stiffens more strongly under compression than normal brain. These findings suggest that local tissue stiffness has the potential to alter glial cell function, and that stiffness changes in brain tumors might arise not from increased deposition or crosslinking of the collagen-rich extracellular matrix, but from pressure gradients that form within the tumors in vivo.

Highlights

A common feature of many solid tumors and other diseased tissues is that they are stiffer than the normal tissue in which they arise [1,2,3,4] and often have increased interstitial fluid pressures [5, 6] and solid tissue stress [7, 8]
When glioma cells are cultured on polyacrylamide gels of elastic modulus similar to that of the normal brain or on gels that are 50 times stiffer, they adhere and survive on both substrates coated with either collagen 1 or laminin, but their morphology and area are strongly dependent on substrate stiffness
The dependence of LN229 cell adherent area on substrate stiffness is quantified in Figure 1B, which shows a monotonic dependence of area on substrate shear modulus over the range from 300 to 14,000 Pa, which spans the stiffness range reported by most studies of brain viscoelasticity over a range of frequencies, strains, and brain region 14

Summary

Introduction

A common feature of many solid tumors and other diseased tissues is that they are stiffer than the normal tissue in which they arise [1,2,3,4] and often have increased interstitial fluid pressures [5, 6] and solid tissue stress [7, 8]. Usually quantified as an increase in shear storage or Young's modulus, arises from multiple mechanisms including increased or chemically altered extracellular matrix production, increased matrix crosslinking due to upregulation of lysyl oxidases, and increased intercellular tensions driven by abnormal activation of acto-myosin that produces increased internal stress within the strain-stiffening matrix. We suggest that compression stiffening, which might occur with the increased vascularization and interstitial pressure gradients that are characteristic of glioma and other tumors, effectively stiffens the environment of glioma cells and that in situ, the elastic resistance these cells sense might be sufficient to trigger the same responses that are activated in vitro by increased substrate stiffness

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