Studying estrogen effects in an in vitro-model of traumatic brain injury (TBI)

In traumatic brain injury (TBI), mechanical forces trigger a series of detrimental processes in the affected brain, which eventually result in substantial neuronal death. TBI has thus become a leading cause of death and disability worldwide. Here we utilized organotypic hippocampal slice cultures from mice to simulate mild diffuse TBI, the most common type, in vitro. We specifically used this model to examine the potential of 17β-estradiol (E2), which is considered to be neuroprotective, to influence injury-induced events, such as astrocyte and microglia activation, and to reduce cell death, if applied acutely after TBI. We found that established consequences of mechanical brain injury are replicated in the model, as increased apoptosis was observed 8 h and PI-uptake was significantly enhanced 24 h after in vitro TBI in CA1 pyramidal layer. GFAP expression was not overall increased, but correlated with cell death, indicating a confined activation of astrocytes associated with cell injury. Similarly, no general increase of microglia was detected, but activated microglia was observed in the vicinity of dying cells. Notably, application of E2 (20 nM) increased GFAP expression after 48 h, but did not significantly reduce cell death at any of the studied time points. We conclude that the presented in vitro TBI model is generally suited to study processes triggered by diffuse mechanical forces acting on brain tissue. Our data further support a stimulating effect of E2 on GFAP expression in astrocytes, but they do not confirm a neuroprotective role of E2 in the early phase of TBI.