Diminished Glial Scar Formation at Hypergravity

Introduction: Disturbed neuronal connectivity is the ultimate cause of disability in individuals with neurological disease including spinal cord injury, head trauma, and stroke. Functional neurological recovery is limited through an unfavorable balance between neuronal regrowth and glia scar formation. The prevalent type of glial cells are astrocytes, providing neurons with growth factors, nutrients and other promoting factors in the extracellular environment. In addition, these cells are predominant in the formation of the so-called glial scar, which not only sterically hinders neuronal re-growth but actively inhibits axonal regeneration processes. Neuronal growth as well as astroglial function and migration require dynamic cytoskeletal protein rearrangements. Because hypergravity stabilizes microtubules while de-stabilizing actin filaments, we hypothesized that experimental hypergravity would shift the balance between neuronal and astroglial growth in vitro. Methods: The exposure of cells to a defined level of hypergravity, preferably in the physiological range that would be tolerable also to human subjects, is the aim of the Multi-Sample Incubator Centrifuge (MuSIC) of the DLR. This centrifuge was designed to create hypergravity environments in a vibration-free manner in controlled incubation setups suitable for living samples. Moreover, observing cellular responses live during exposure to altered environmental stimuli is the key to yield a deeper understanding on underlying mechanisms and time frames, in which cells react and possibly adapt. Thus, we employed the DLR short-arm human centrifuge to install a live-cell imaging microscope system on a swing-out platform onto the centrifuge. Results: The formation of the glial scar requires dynamic cytoskeletal rearrangements, which are induced upon exposure of astrocytes to increased gravitational loads in the physiologically tolerable range of 2g. Under these conditions changes in astrocytic properties can already be observed. Astrocytes fail to spread as under normal conditions and show a reduced cell area. This reduction in cell spreading is not coincidental with a diminished proliferation rate, but correlated to impaired migratory behavior. Impairment in migration behavior is an important mechanism that will have a direct impact on glial scar formation and thus on neuronal regeneration in general.