Simvastatin attenuates microglial cells and astrocyte activation and decreases interleukin-1beta level after traumatic brain injury

Attenuation of astrogliosis and modulation of endothelial growth factor receptor in lipid rafts by simvastatin after traumatic brain injury

OBJECT

The authors' previous studies have demonstrated that simvastatin treatment promotes neuronal survival and reduces inflammatory cytokine release from astrocytes after traumatic brain injury (TBI) in rats. Since reactive astrocytes produce inflammation mediators, in the current study the authors investigated the effect of simvastatin on astrocyte activation after TBI and its underlying signaling mechanisms.

METHODS

Saline or simvastatin (1 mg/kg) was orally administered to rats starting at Day 1 after TBI and then daily for 14 days. Rats were killed at 1, 3, 7, and 14 days after treatment. Brain sections and tissues were prepared for immunohistochemical staining and Western blot analysis, respectively. Cultured astrocytes were subjected to oxygen-glucose deprivation (OGD) and followed by immunocytochemical staining with glial fibrillary acidic protein/caveolin-1 and Western blot analysis. Lipid rafts were isolated from the cell lysate and Western blotting was carried out to detect the changes in epidermal growth factor receptor (EGFR) expression and phosphorylation in the lipid rafts.

RESULTS

Simvastatin significantly promoted neuronal survival after TBI and attenuated activation of astrocytes. Simvastatin modified the caveolin-1 expression in lipid rafts in astrocyte cell membrane, suppressed the phosphorylation of EGFR in lipid rafts of astrocytes after OGD, and inhibited the OGD-induced interleukin-1 production.

CONCLUSIONS

These data suggest that simvastatin reduces reactive astrogliosis and rescues neuronal cells after TBI. These beneficial effects of simvastatin may be mediated by inhibiting astrocyte activation after TBI through modifying the caveolin-1 expression in lipid rafts and the subsequent modulation of EGFR phosphorylation in lipid rafts.

Local cell proliferation upon enucleation in Direct Retinal Brain Targets in the Visual system of the Adult Mouse

In this study we used incorporation of the DNA synthesis marker 5-bromo-2′-deoxyuridine or BrdU to visualize cell proliferation in the visual system of the adult mouse as a response to monocular enucleation. We detected new BrdU-labeled cells in different subcortical retinal target regions and we established a specific time frame in which this cell proliferation occurred. By performing immunofluorescent double stainings for BrdU and different vascular (glucose transporter type 1, collagen type IV), glial (thymosin β4, glial fibrillary acidic protein) and neuronal (Neuronal Nuclei, doublecortin) markers, we identified these proliferating cells as activated microglia. Additional immunohistochemical stainings for thymosin β4 and glial fibrillary acidic protein also revealed reactive astrocytes in the different retinorecipient nuclei and allowed us to delineate a time frame for microglial and astroglial activation. A PCR array experiment further showed increased levels of cytokines, chemokines, growth factors and enzymes that play an important role in microglial-astroglial communication during the glial activation process in response to the deafferentation.

Cell death mechanisms and modulation in traumatic brain injury

Cell death after traumatic brain injury (TBI) is a major cause of neurological deficits and mortality. Understanding the mechanisms of delayed post-traumatic cell loss may lead to new therapies that improve outcome. Although TBI induces changes in multiple cell types, mechanisms of neuronal cell death have been the predominant focus. Recent work has emphasized the diversity of neuronal death phenotypes, which have generally been defined by either morphological or molecular changes. This diversity has led to confusing and at times contradictory nomenclature. Here we review the historical basis of proposed definitions of neuronal cell death, with the goal of clarifying critical research questions and implications for therapy in TBI. We believe that both morphological and molecular features must be used to clarify post-traumatic cell death and related therapeutic targets. Further, we underscore that the most effective neuroprotective strategies will need to target multiple pathways to reflect the regional and temporal changes underlying diverse neuronal cell death phenotypes.