Cell Growth in Response to Mechanical Stiffness is Affected by Neuron- Astroglia Interactions

Cell adhesion and morphology are affected by the mechanical properties of the extracellular matrix. Using polyacrylamide gels as cell substrates, the cellular response to substrate compliance was investigated in pure neuronal, pure astroglial, or mixed co-cultures. Substrates used spanned a large range of stiffnesses including that of brain tissue. In both pure and mixed cultures, immature (vimentin+) astroglia adhered best to stiffest gels. Mature (GFAP+) astrocyte ad- hesion peaked on intermediate stiffness, while pure GFAP+ astroglial adhesion displayed no intermediate preference and increased with stiffness. Neurite length was constant with stiffness; however, primary dendrite number was lowest on in- termediate gels. Pure neuronal cultures were more adherent to hard gels, while mixed cultures had no stiffness preference. Furthermore, we investigated the role of stiffness in the modulation of the neurotoxic effect of glutamate. Exposure to two glutamate concentrations (500 and 1000 � M) of cultured spinal cord neurons induced cell death. The damage elicited by 500 � m glutamate to neurons in a mixed culture of spinal cord cells is most severe on soft 300 Pa gels. The neurotoxic ef- fect of glutamate on neurons cultured on hard gels where astrocytes are present was strongly attenuated compared with that observed on soft gels, where there is a relatively low number of astrocytes. Our data suggest that mechanical stiffness of the substrate affects the response of both neurons and astroglia, and this response is varied by interaction between the two cell types.