Calcium signaling in astrocytes couples changes in brain activity to regional alterations in cerebral blood flow (CBF) by eliciting vasoconstriction or vasodilation of adjacent arterioles1-7. However, the mechanism for how these disparate astrocyte influences provide appropriate changes in cerebral vascular tone within a cellular environment that has dynamic metabolic requirements remains unclear. The regulation of CBF has recently been shown to be tightly coupled to the lactate/pyruvate ratio and thus the NADH/NAD+ ratio in animals8 and humans9,10. We tested the impact of metabolic changes on the regulation of cerebral blood vessel diameter by astrocytes, by manipulating tissue oxygenation which changes dynamically with brain activity11-14. Using two-photon Ca2+ imaging and uncaging as well as intrinsic nicotinamide adenine dinucleotide (NADH) imaging of single cells as a measure of redox state, we show that the ability of astrocytes to induce vasodilations over vasoconstrictions critically relies on the metabolic state of the tissue. When O2 availability is lowered and astrocyte [Ca2+]i is elevated, astrocyte glycolysis and lactate release are maximized. Extracellular lactate contributes to prostaglandin E2 (PGE2) accumulation by hindering its transporter-mediated uptake, subsequently causing vasodilation. These data reveal the role of metabolic substrates in regulating CBF and provide a mechanism for differential astrocyte control over cerebrovascular diameter during different states of brain activation.

Microglia are morphologically dynamic cells that rapidly extend their processes in response to various stimuli including extracellular ATP. In this study, we tested the hypothesis that stimulation of neuronal NMDARs trigger ATP release leading to communication with microglia. We used acute mouse hippocampal brain slices and two-photon laser scanning microscopy to study microglial dynamics and developed a novel protocol for fixation and immunolabeling of microglia processes. Similar to direct topical ATP application in vivo, short multiple applications of NMDA triggered transient microglia process outgrowth that was reversible and repeatable indicating that this was not due to excitotoxic damage. Stimulation of NMDAR was required as NMDAR antagonists, but not blockers of AMPA/kainate receptors or voltage-gated sodium channels, prevented microglial outgrowth. We report that ATP release, secondary to NMDAR activation, was the key mediator of this neuron-microglia communication as both blocking purinergic receptors and inhibiting hydrolysis of ATP to prevent locally generated gradients abolished outgrowth. Pharmacological and genetic analyses showed that the NMDA-triggered microglia process extension was independent of Pannexin 1, the ATP releasing channels, ATP release from astrocytes via connexins, and nitric oxide generation. Finally, using whole-cell patch clamping we demonstrate that activation of dendritic NMDAR on single neurons is sufficient to trigger microglia process outgrowth. Our results suggest that dendritic neuronal NMDAR activation triggers ATP release via a Pannexin 1-independent manner that induces outgrowth of microglia processes. This represents a novel uncharacterized form of neuron-microglial communication mediated by ATP.

SUMMARY Astrocytes are proposed to participate in brain energy metabolism by supplying substrates to neurons from their glycogen stores and from glycolysis. However, the molecules involved in metabolic sensing and the molecular pathways responsible for metabolic coupling between different cell types in the brain are not fully understood. Here we show that a recently cloned bicarbonate (HCO3−) sensor, soluble adenylyl cyclase (sAC), is highly expressed in astrocytes and becomes activated in response to HCO3− entry via the electrogenic NaHCO3 cotransporter (NBC). Activated sAC increases intracellular cAMP levels, causing glycogen breakdown, enhanced glycolysis, and the release of lactate into the extracellular space, which is subsequently taken up by neurons for use as an energy substrate. This process is recruited over a broad physiological range of [K+]ext and also during aglycemic episodes, helping to maintain synaptic function. These data reveal a molecular pathway in astrocytes that is responsible for brain metabolic coupling to neurons.

Cytotoxic brain edema triggered by neuronal swelling is the chief cause of mortality following brain trauma and cerebral infarct. Using fluorescence lifetime imaging to analyze contributions of intracellular ionic changes in brain slices, we find that intense Na(+) entry triggers a secondary increase in intracellular Cl(-) that is required for neuronal swelling and death. Pharmacological and siRNA-mediated knockdown screening identified the ion exchanger SLC26A11 unexpectedly acting as a voltage-gated Cl(-) channel that is activated upon neuronal depolarization to membrane potentials lower than -20 mV. Blockade of SLC26A11 activity attenuates both neuronal swelling and cell death. Therefore cytotoxic neuronal edema occurs when sufficient Na(+) influx and depolarization is followed by Cl(-) entry via SLC26A11. The resultant NaCl accumulation causes subsequent neuronal swelling leading to neuronal death. These findings shed light on unique elements of volume control in excitable cells and lay the ground for the development of specific treatments for brain edema.

We have generated stable, immortalized cell lines of human NSCs from primary human fetal telencephalon cultures via a retroviral vector encoding v-myc. HB1.F3, one of the human NSC lines, expresses a normal human karyotype of 46, XX, and nestin, a cell type-specific marker for NSCs. F3 has the ability to proliferate continuously and differentiate into cells of neuronal and glial lineage. The HB1.F3 human NSC line was used for cell therapy in a mouse model of intracerebral hemorrhage (ICH) stroke. Experimental ICH was induced in adult mice by intrastriatal administration of bacterial collagenase; 1 week after surgery, the rats were randomly divided into two groups so as to receive intracerebrally either human NSCs labeled with ␤-galactosidase (n ‫؍‬ 31) or phosphate-buffered saline (PBS) (n ‫؍‬ 30). STEM CELLS 2007;25: 1204 -1212

Erythropoietin (EPO) is a hematopoietic growth factor that stimulates proliferation and differentiation of erythroid precursor cells and is also known to exert neurotrophic activity in the central nervous system (CNS). However, little is known about expression of EPO and EPO receptor (EPOR) in human CNS tissues. In the present study, we investigated the effects of proinflammatory cytokines on EPO and EPOR expression in highly purified cultures of human neurons, astrocytes, microglia, and oligodendrocytes using reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). EPO mRNA was demonstrated only in human astrocytes, while EPOR expression was found in human neurons, astrocytes, and microglia. Neither EPO nor EPOR expression was found in oligodendrocytes. In human astrocytes, EPO mRNA and secreted EPO protein levels were downregulated after exposure to proinflammatory cytokines (IL-1beta, IL-6, or TNF-alpha). In human neurons, TNF-alpha treatment markedly increased EPOR expression. These results suggest that proinflammatory cytokines regulate expression of EPO and EPOR in human neurons, astrocytes, and microglia and further facilitate interactions among different cell types in the human CNS.

Complement receptor 3 (CR3) activation in microglia is involved in neuroinflammation-related brain disorders and pruning of neuronal synapses. Hypoxia, often observed together with neuroinflammation in brain trauma, stroke, and neurodegenerative diseases, is thought to exacerbate inflammatory responses and synergistically enhance brain damage. Here we show that when hypoxia and an inflammatory stimulus (lipopolysaccharide [LPS]) are combined, they act synergistically to trigger long-term synaptic depression (LTD) that requires microglial CR3, activation of nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase), and GluA2-mediated A-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) internalization. Microglial CR3-triggered LTD is independent of N-methyl-D-aspartate receptors (NMDARs), metabotropic glutamate receptors (mGluRs), or patterned synaptic activity. This type of LTD may contribute to memory impairments and synaptic disruptions in neuroinflammation-related brain disorders.

The expression of the purinergic receptor subtype P2X(7)R, a nonselective cationic channel activated by high levels of adenosine triphosphate (ATP), has been studied in adult microglia obtained from Alzheimer disease (AD) and nondemented (ND) brains, in fetal human microglia exposed to Abeta(1-42) peptide and in vivo in Abeta(1-42)-injected rat hippocampus. Semiquantitative reverse transcriptase-polymerase chain reaction showed enhanced expression (increase of 70%) of P2X(7)R in AD microglia compared with ND cells (analysis of 6 AD and 8 ND cases). Immunohistochemical analysis showed prominent P2X(7)R expression in association with Abeta plaques and localized to HLA-DR-immunoreactive microglia. In cultured fetal human microglia, cells exposed to Abeta(1-42) (5 microM for 18 hours) had significantly elevated levels of P2X(7)R (by 106%) compared with untreated cells. Amplitudes of Ca(2+) responses in these cells, induced by the selective P2X(7)R agonist BzATP, were increased by 145% with Abeta(1-42) pretreatment relative to control (no peptide pretreatment) and were largely blocked if the P2X(7)R inhibitor-oxidized ATP (oxATP) was added with peptide in pretreatment solution. In vivo, double immunostaining analysis showed considerable P2X(7)R colocalized with microglia after injection of Abeta(1-42) (1 nmol) into rat hippocampus. The overall results suggest roles of P2X(7)R in mediating microglial purinergic inflammatory responses in AD brain.