Strain rate-dependent induction of reactive astrogliosis and cell death in three-dimensional neuronal–astrocytic co-cultures

Abstract

A mechanical insult to the brain drastically alters the microenvironment as specific cell types become reactive in an effort to sequester severely damaged tissue. Although injury-induced astrogliosis has been investigated, the relationship between well-defined biomechanical inputs and acute astrogliotic alterations are not well understood. We evaluated the effects of strain rate on cell death and astrogliosis using a three-dimensional (3-D) in vitro model of neurons and astrocytes within a bioactive matrix. At 21 days post-plating, co-cultures were deformed to 0.50 shear strain at strain rates of 1, 10, or 30 s −1 . We found that cell death and astrogliotic profiles varied differentially based on strain rate at two days post-insult. Significant cell death was observed after moderate (10 s −1 ) and high (30 s −1 ) rate deformation, but not after quasi-static (1 s −1 ) loading. The vast majority of cell death occurred in neurons, suggesting these cells are more susceptible to high rate shear strains than astrocytes for the insult parameters used here. Injury-induced astrogliosis was compared to co-cultures treated with transforming growth factor β, which induced robust astrocyte hypertrophy and increased glial fibrillary acidic protein (GFAP) and chondroitinsulfate proteoglycans (CSPGs). Quasi-static loading resulted in increased cell density and CSPG secretion. Moderate rate deformation increased cell density, GFAP reactivity, and hypertrophic process density. High rate deformation resulted in increased GFAP reactivity; however, other astrogliotic alterations were not observed at this time-point. These results demonstrate that the mode and degree of astrogliosis depend on rate of deformation, demonstrating astrogliotic augmentation at sub-lethal injury levels as well as levels inducing cell death.

Alignment of Astrocytes Increases Neuronal Growth in Three-Dimensional Collagen Gels and Is Maintained Following Plastic Compression to Form a Spinal Cord Repair Conduit

“…12,[18][19][20][21][22] Recently, we developed a 3D collagen gel model for studying astroglial biology that has significant advantages over standard 2D models, allowing astrocytes to behave in a way much more reminiscent of their in vivo counterparts. 23 Since 3D culture systems can allow mechanical cues to be isolated from chemical cues, 24 we have adapted our 3D culture model in this study to explore the effect of astrocyte alignment on neurite growth.…”

Study on Impact Resistance of PC12 Cells

“…It was reported a strain rate of larger than 10 (1/s) caused damage to axons (3) (5) (7) , therefore, the strain rate obtained from the impact experiment was large enough to damage the cell. LaPlaca et al (7) gave a load to the cultured cells in which the strain was 50% and the strain rate was 30 (1/s), and observed approximately 20% cell mortality. When mortality of cells in this study was 20%, the strain was 0.2% and the strain rate was 19.02 (1/s).…”

Study on the Mechanism of Traumatic Brain Injury

“…Laplaca et al cultured cells in a gel and generated 3D deformation of the cells by producing a shear deformation of the gel (strain < 50%, strain rate < 30/s). Neuronal cells showed a lower tolerance to this strain than the glial cells (LaPlaca et al, 2005;Cullen et al, 2007).Tamura et al analyzed the difference in strain caused by a tensile test between porcine brain tissue and nerve fiber in the white matter, and reported that the maximum neural fiber strain was ~25% of the level in the surrounding tissue (Tamura et al, 2006). Nakayama et al showed morphological changes of axons and the progress of this damage over time caused by one-dimensional, horizontal oscillations of nerve cells (Nakayama et al, 2001).…”