Neuroinflammatory processes in the amyotrophic latera sclerosis brain : study of hSOD1 G93A rat model

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting lower and upper motor neurons. The disease shows fast progression and short lifetime following the disease onset. Several mechanisms contributing to ALS pathogenesis have been proposed, but the cause of disease remains unclear. The aim of this study was to characterize changes in the upper CNS regions of the hSOD1G93A rat model and to try to clarify disease mechanisms. Foci of neurodegeneration and neuroinflammation were localized in the brain of hSOD1G93A rat using magnetic resonance imaging. The same method was applied for in vivo monitoring of T-lymphocytes infiltration using specifically designed antibodies conjugated with ultrasmall superparamagnetic iron oxide particles. It was shown that CD4+ T-lymphocytes were infiltrated into the brain tissue around lateral ventricles while CD8+ T-lymphocytes were infiltrated into the brainstem of the hSOD1G93A rat. Using Gd-DTPA contrast, it has been shown that the blood-brain barrier was compromised in the brain regions invaded with T-cells. Activated microglia and reactive astrocytes were observed in the brainstem of the hSOD1G93A rat. In addition, reactive microglia was shown in the brain tissue around lateral ventricles and in the hippocampus. Processes of activated microglia were in contact with neuronal somata indicating possible interaction. Western blot results showed increased aquaporin-4 (AQP4) and reduced inwardly rectifying potassium channel (Kir4.1) expression in the brainstem and cortex of the hSOD1G93A rat. Immunohistochemistry on the frozen brain slices showed increased AQP4 and decreased Ki4.1 immunoreactivity in the nc. facialis, nc. trigeminus and motor cortex of the hSOD1G93A rat. Increased AQP4 and decreased Kir4.1 immunoreactivity were retained in cortical ALS astrocytes in culture. Examination of the functional properties of Kir channels revealed a decreased current density and diminished specific membrane conductance in ALS astrocytes in culture. Addition of 1 mM CsCl or 100 μM BaCl2 to the extracellular solution revealed significantly lower Cs+-sensitive and Ba2+-sensitive Kir currents in ALS. In this study we localized and characterized neurodegenerative nad neuroinflammatory changes in the brain of hSOD1G93A rat, confirmed the blood-brain barrier compromise and observed changes in the astrocytic proteins involved in the maintenance of the blood-brain barrier. Obtained data may contribute to further understandi