Distribution and Function of the Bestrophin-1 (Best1) Channel in the Brain

Bestrophin-1 (Best1) is a calcium-activated anion channel identified from retinal pigment epithelium where human mutations are associated with Best's macular degeneration. Best1 is known to be expressed in a variety of tissues including the brain, and is thought to be involved in many physiological processes. This review focuses on the current state of knowledge on aspects of expression and function of Best1 in the brain. Best1 protein is observed in cortical and hippocampal astrocytes, in cerebellar Bergmann glia and lamellar astrocytes, in thalamic reticular neurons, in meninges and in the epithelial cells of the choroid plexus. The most prominent feature of Best1 is its significant permeability to glutamate and GABA in addition to chloride ions because glutamate and GABA are important transmitters in the brain. Under physiological conditions, both Best1-mediated glutamate release and tonic GABA release from astrocytes modulate neuronal excitability, synaptic transmission and synaptic plasticity. Under pathological conditions such as neuroinflammation and neurodegeneration, reactive astrocytes phenotypically switch from GABA-negative to GABA-producing and redistribute Best1 from the perisynaptic microdomains to the soma and processes to tonically release GABA via Best1. This implicates that tonic GABA release from reactive astrocyte via redistributed Best1 is a common phenomenon that occur in various pathological conditions with astrogliosis such as traumatic brain injury, neuroinflammation, neurodegeneration, and hypoxic and ischemic insults. These properties of Best1, including the permeation and release of glutamate and GABA and its redistribution in reactive astrocytes, promise us exciting discoveries of novel brain functions to be uncovered in the future.

Functional Characterization of Resting and Adenovirus-Induced Reactive Astrocytes in Three-Dimensional Culture

Brain is a rich environment where neurons and glia interact with neighboring cells as well as extracellular matrix in three-dimensional (3D) space. Astrocytes, which are the most abundant cells in the mammalian brain, reside in 3D space and extend highly branched processes that form microdomains and contact synapses. It has been suggested that astrocytes cultured in 3D might be maintained in a less reactive state as compared to those growing in a traditional, two-dimensional (2D) monolayer culture. However, the functional characterization of the astrocytes in 3D culture has been lacking. Here we cocultured neurons and astrocytes in 3D and examined the morphological, molecular biological, and electrophysiological properties of the 3D-cultured hippocampal astrocytes. In our 3D neuron-astrocyte coculture, astrocytes showed a typical morphology of a small soma with many branches and exhibited a unique membrane property of passive conductance, more closely resembling their native in vivo counterparts. Moreover, we also induced reactive astrocytosis in culture by infecting with high-titer adenovirus to mimic pathophysiological conditions in vivo. Adenoviral infection induced morphological changes in astrocytes, increased passive conductance, and increased GABA content as well as tonic GABA release, which are characteristics of reactive gliosis. Together, our study presents a powerful in vitro model resembling both physiological and pathophysiological conditions in vivo, and thereby provides a versatile experimental tool for studying various neurological diseases that accompany reactive astrocytes.

Neuropathological characters of delayed cortical infarcts after transient unilateral brain ischemia in Mongolian gerbils / 中华神经科杂志

Objective To investigate the distribution of eosinphililic neurons ( ENs),reactive astrocytes ( RAs),and infarction after transient cerebal ischemia,and the time profile of pathomorphological changes.Methods Unilateral forebrain ischemia was induced in Mongolian gerbils by two 10 minutes unilateral common carotid artery occlusions with a 5 hours interval.Laser Doppler flowmetry was used to detect intra-ischemic anterior cortex blood flow.Animals were sacrificed at 24 hours,4 days,2 weeks,4 weeks,16 weeks and the brain were prepared for pathomorphological assay.Results Intra-ischemic laser Doppler flowmetry show significant ischemia during carotid artery occlusion:22.1％ ± 9.5％,26.3％ ± 4.9％,37.5％ ± 3.5％,F =67.219,P ＜ 0.01 ; the decrease was significantly greater in the anterior cortex.ENs appeared in middle and deep layers at 24 hours postischemia,and ENs area extend to all layers of cortex by 4 days.Large areas of high EN density ( ≥80/mm2) evolved to infarcts between 4 days and 4 weeks.Posterior cortex evolved to low EN area ( ＜ 80/mm2) without transformation into infarcts.RAs were consistently distributed in areas with ENs,and RA areas with high EN density were largely transformed into infarcts between 4 days and 4 weeks. Delayed astrocytic death took place in the RA areas with high EN density.Conclusion Density of ENs is an important indicator of delayed astrocytic death and infarction in postischemic tissue.