Involvement of Iba1 in membrane ruffling and phagocytosis of macrophages/microglia

Immunofluorescent spectral analysis reveals the intrathecal cannabinoid agonist, AM1241, produces spinal anti-inflammatory cytokine responses in neuropathic rats exhibiting relief from allodynia

During pathological pain, the actions of the endocannabinoid system, including the cannabinoid 2 receptor (CB(2)R), leads to effective anti-allodynia and modifies a variety of spinal microglial and astrocyte responses. Here, following spinal administration of the CB(2)R compound, AM1241, we examined immunoreactive alterations in markers for activated p38 mitogen-activated protein kinase, interleukin-1β (IL-1β), the anti-inflammatory cytokine, interleukin-10 (IL-10) as well as degradative endocannabinoid enzymes, and markers for altered glial responses in neuropathic rats. In these studies, the dorsal horn of the spinal cord and dorsal root ganglia were examined. AM1241 produced profound anti-allodynia with corresponding immunoreactive levels of p38 mitogen-activated kinase, IL-1β, IL-10, the endocannabinoid enzyme monoacylglycerol lipase, and astrocyte activation markers that were similar to nonneuropathic controls. In contrast, spinal AM1241 did not suppress the increased microglial responses observed in neuropathic rats. The differences in fluorescent markers were determined within discrete anatomical regions by applying spectral analysis methods, which virtually eliminated nonspecific signal during the quantification of specific immunofluorescent intensity. These data reveal expression profiles that support the actions of intrathecal AM1241 control pathological pain through anti-inflammatory mechanisms by modulating critical glial factors, and additionally decrease expression levels of endocannabinoid degradative enzymes.

Microglial activation and TDP-43 pathology correlate with executive dysfunction in amyotrophic lateral sclerosis

While cognitive deficits are increasingly recognized as common symptoms in amyotrophic lateral sclerosis (ALS), the underlying histopathologic basis for this is not known, nor has the relevance of neuroinflammatory mechanisms and microglial activation to cognitive impairment (CI) in ALS been systematically analyzed. Staining for neurodegenerative disease pathology, TDP-43, and microglial activation markers (CD68, Iba1) was performed in 102 autopsy cases of ALS, and neuropathology data were related to clinical and neuropsychological measures. ALS with dementia (ALS-D) and ALS with impaired executive function (ALS-Ex) patients showed significant microglial activation in middle frontal and superior or middle temporal (SMT) gyrus regions, as well as significant neuronal loss and TDP-43 pathology in these regions. Microglial activation and TDP-43 pathology in middle frontal and superior or middle temporal regions were highly correlated with measures of executive impairment, but not with the MMSE. In contrast, only one ALS-D patient showed moderate Alzheimer's disease (AD) pathology. Tau and Aβ pathology increased with age. A lower MMSE score correlated with tau pathology in hippocampus and SMT gyrus, and with Aβ pathology in limbic and most cortical regions. Tau and Aβ pathology did not correlate with executive measures. We conclude that microglial activation and TDP-43 pathology in frontotemporal areas are determinants of FTLD spectrum dementia in ALS and correlate with neuropsychological measures of executive dysfunction. In contrast, AD pathology in ALS is primarily related to increasing age and associated with a poorer performance on the MMSE.

Microglia-inhibiting activity of Parkinson's disease drug amantadine

Amantadine is currently used as an antiviral and an antiparkinsonian drug. Although the drug is known to bind a viral proton channel protein, the mechanism of action in Parkinson's disease (PD) remains to be determined. This study investigated whether the drug has an inhibitory effect on microglial activation and neuroinflammation, which have been implicated in the progression of neurodegenerative processes. Using cultured microglial cells, it was demonstrated that the drug inhibited inflammatory activation of microglia and a signaling pathway that governs the microglial activation. The drug reduced the expression and production of proinflammatory mediators in bacterial lipopolysaccharide-stimulated microglia cells. The microglia-inhibiting activity of amantadine was also demonstrated in a microglia/neuron coculture and animal models of neuroinflammation and Parkinson's disease. Collectively, our results suggest that amantadine may act on microglia in the central nervous system to inhibit their inflammatory activation, thereby attenuating neuroinflammation. These results provide a molecular basis of the glia-targeted mechanism of action for amantadine.

Spinal cord injury, dendritic spine remodeling, and spinal memory mechanisms

Spinal cord injury (SCI) often results in the development of neuropathic pain, which can persist for months and years after injury. Although many aberrant changes to sensory processing contribute to the development of chronic pain, emerging evidence demonstrates that mechanisms similar to those underlying classical learning and memory can contribute to central sensitization, a phenomenon of amplified responsiveness to stimuli in nociceptive dorsal horn neurons. Notably, dendritic spines have emerged as major players in learning and memory, providing a structural substrate for how the nervous system modifies connections to form and store information. Until now, most information regarding dendritic spines has been obtained from studies in the brain. Recent experimental data in the spinal cord, however, demonstrate that Rac1-regulated dendritic spine remodeling occurs on second-order wide dynamic range neurons and accompanies neuropathic pain after SCI. Thus, SCI-induced synaptic potentiation engages a putative spinal memory mechanism. A compelling, novel possibility for pain research is that a synaptic model of long-term memory storage could explain the persistent nature of neuropathic pain. Such a conceptual bridge between pain and memory could guide the development of more effective strategies for treatment of chronic pain after injury to the nervous system.

Microglial activation in a neuroinflammational animal model of schizophrenia--a pilot study

Inflammatory and immunological processes interfering with brain development are discussed as one cause of schizophrenia. Various signs of overactivation of the immune system were often found in this disease. Based on post-mortem analysis showing an increased number of activated microglial cells in patients with schizophrenia, it can be hypothesized that these cells contribute to disease pathogenesis and may actively be involved in gray matter loss observed in such patients. In the present study, PolyI:C incubation of pregnant dams was used as animal model of schizophrenia, and the number and shape of microglia were assessed in the offspring in the early phase of this disease, using fluorescence immunostaining (Iba1). Descendants of mice exposed to PolyI:C at embryonic day 9 showed higher number of microglial cells in the hippocampus and striatum, but not in the frontal cortex at postnatal day 30, which is similarly to adolescence in man, as compared to those exposed to saline. Furthermore, offspring microglia from PolyI:C treated mothers were morphologically characterized by a reduced arborization indicative for a status of higher activation compared to the offspring microglia from vehicle treated mice. This study supports the hypothesis that maternal infection during embryogenesis contributes to microglial activation in the offspring, which may therefore represent a contributing factor to the pathogenesis of schizophrenia and underlines the need for new pharmacological treatment options in this regard.

Early microglia activation in a mouse model of chronic glaucoma

Changes in microglial cell activation and distribution are associated with neuronal decline in the central nervous system (CNS), particularly under pathological conditions. Activated microglia converge on the initial site of axonal degeneration in human glaucoma, yet their part in its pathophysiology remains unresolved. To begin with, it is unknown whether microglia activation precedes or is a late consequence of retinal ganglion cell (RGC) neurodegeneration. Here we address this critical element in DBA/2J (D2) mice, an established model of chronic inherited glaucoma, using as a control the congenic substrain DBA/2J Gpnmb(+/SjJ) (D2G), which is not affected by glaucoma. We analyzed the spatial distribution and timecourse of microglial changes in the retina, as well as within the proximal optic nerve prior to and throughout ages when neurodegeneration has been reported. Exclusively in D2 mice, we detected early microglia clustering in the inner central retina and unmyelinated optic nerve regions, with microglia activation peaking by 3 months of age. Between 5 and 8 months of age, activated microglia persisted and concentrated in the optic disc, but also localized to the retinal periphery. Collectively, our findings suggest microglia activation is an early alteration in the retina and optic nerve in D2 glaucoma, potentially contributing to disease onset or progression. Ultimately, detection of microglial activation may have value in early disease diagnosis, while modulation of microglial responses may alter disease progression.

Temporomandibular joint inflammation activates glial and immune cells in both the trigeminal ganglia and in the spinal trigeminal nucleus

BACKGROUND

Glial cells have been shown to directly participate to the genesis and maintenance of chronic pain in both the sensory ganglia and the central nervous system (CNS). Indeed, glial cell activation has been reported in both the dorsal root ganglia and the spinal cord following injury or inflammation of the sciatic nerve, but no data are currently available in animal models of trigeminal sensitization. Therefore, in the present study, we evaluated glial cell activation in the trigeminal-spinal system following injection of the Complete Freund's Adjuvant (CFA) into the temporomandibular joint, which generates inflammatory pain and trigeminal hypersensitivity.

RESULTS

CFA-injected animals showed ipsilateral mechanical allodynia and temporomandibular joint edema, accompanied in the trigeminal ganglion by a strong increase in the number of GFAP-positive satellite glial cells encircling neurons and by the activation of resident macrophages. Seventy-two hours after CFA injection, activated microglial cells were observed in the ipsilateral trigeminal subnucleus caudalis and in the cervical dorsal horn, with a significant up-regulation of Iba1 immunoreactivity, but no signs of reactive astrogliosis were detected in the same areas. Since the purinergic system has been implicated in the activation of microglial cells during neuropathic pain, we have also evaluated the expression of the microglial-specific P2Y12 receptor subtype. No upregulation of this receptor was detected following induction of TMJ inflammation, suggesting that any possible role of P2Y12 in this paradigm of inflammatory pain does not involve changes in receptor expression.

CONCLUSIONS

Our data indicate that specific glial cell populations become activated in both the trigeminal ganglia and the CNS following induction of temporomandibular joint inflammation, and suggest that they might represent innovative targets for controlling pain during trigeminal nerve sensitization.

Early Involvement of Immune/Inflammatory Response Genes in Retinal Degeneration in DBA/2J Mice

Purpose

The DBA/2J (D2) mouse carries mutations in two of its genes, Tyrp1 and Gpnmb. These alterations result in the development of an immune response in the iris, leading to iris atrophy and pigment dispersion. The development of elevated intraocular pressure (IOP) in this model of glaucoma is considered to be a significant factor leading to the death of retinal ganglion cells (RGCs). Changes in gene expression in the retina have already been correlated with the appearance of elevated IOP in the D2 mouse. The purpose of the present study was to determine if any changes in gene expression occur prior to the development of IOP.

Methods

The IOP was measured monthly using a rebound tonometer in D2 and age-matched C57/BL6 (B6) mice (normal controls). D2 animals with normal IOP at 2 and 4 M were used. In addition, mice at the age of 6–7 M were included to look for any trends in gene expression that might develop during the progression of the disease. Separate RNA samples were prepared from each of three individual retinas for each age, and gene expression profiles were determined with the aid of mouse oligonucleotide arrays (Agilent). A subset of genes was examined with the aid of real-time PCR. Immunocytochemistry was used to visualize changes in the retina for some of the gene-products.

Results

Four hundred and thirteen oligonucleotide probes were differentially expressed in the retinas of 4 M versus 2 M old D2 mice. The most significantly up-regulated genes (181) were associated with immune responses including interferon signaling, the complement system and the antigen presentation pathway, whereas the down-regulated genes (232) were linked to pathways related to cell death and known neurological diseases/disorders. These particular changes were not revealed in the age-matched B6 mice. By 6 M, when IOP started to increase in many of the D2 mice, more robust changes of these same genes were observed. Changes in the levels of selected genes, representative of different functions/pathways, were validated with RT-PCR, and changes in glial responses were visualized in the retina with immunocytochemistry.

Conclusions

The results showed that the expression of genes related to the immune response and acute stress were altered independently of the development of elevated IOP, and indicated early involvement of the immune system in the onset of the disease. The later development of elevated IOP, observed in this animal model, was coincident with continued changes in expression of genes observed at earlier time points. Further studies are warranted to identify the roles of specific genes identified here with respect to the death of the RGCs.

Does elevated intraocular pressure reduce retinal TRKB-mediated survival signaling in experimental glaucoma?

Reduced retrograde transport of neurotrophins (NT) and their receptors has been hypothesized to contribute directly to retinal ganglion cell (RGC) loss in glaucoma. However, strategies of supplementing NT and NT receptors have failed to avert ultimate RGC death in experimental glaucoma. This study examines the response of major components of the NT system and their interacting proteins in a rat glaucoma model. Unilateral chronic intraocular pressure (IOP) elevation was produced by episcleral vein injection of hypertonic saline (N = 99). Retinas were collected and grouped by extent of optic nerve injury. Quantitative reverse transcription PCR, western blot analysis and immunohistochemistry were used to determine mRNA and protein levels and protein localization. Out of three RGC-specific Brn3 proteins (Brn3a, b, and c), only Brn3a was significantly downregulated at the message level to 35 +/- 4% of fellow values with the severest nerve injury. With IOP elevation, no significant alterations were found in retinal mRNA levels for BDNF, NGF, NT-4/5 or NT-3. The abundance of mature retinal BDNF protein was not significantly affected by elevated IOP, while proBDNF protein decreased linearly with increasing injury grade (r(2) = 0.50). In retinas with the severest nerve injury, TrkB and TrkC receptor mRNA levels significantly declined to 67 +/- 9% and 44 +/- 5% of fellow values, respectively. However, the levels of TRKB protein and its phosphorylated form were unchanged. Message level for p75(NTR) was linearly upregulated up to 219 +/- 26% with increasing injury (r(2) = 0.46), but no alteration was detected at protein level. The mRNA expression of p75(NTR) apoptosis adaptor proteins NADE, NRIF, and Lingo1 were significantly downregulated in retinas with the greatest nerve injury. A positive correlation was found between injury extent and message levels for Jun (r(2) = 0.23) as well as Junb (r(2) = 0.27), and RGC labeling of activated JUN protein increased. Atf3 mRNA levels demonstrated a positive linear correlation to the extent of injury (r(2) = 0.53), resulting in a nearly five-fold increase (482 +/- 76%) in eyes with the greatest nerve damage. Among downstream pro-survival signaling components, Erk5 mRNA expression was linearly upregulated (r(2) = 0.32) up to 157 +/- 15% of fellow values in retinas with the severest nerve injury (p < 0.01). A slight positive correlation was found between NF-kappaB message levels and injury extent (r(2) = 0.12). Bcl-xl mRNA levels in the most severely injured retinas were significantly reduced to 83 +/- 7% by elevated IOP exposure. Message levels for Erk1/2, Akt1-3 or Bcl2 appeared unaffected. Elevated IOP did not alter mRNA levels of pro-apoptotic Bim, Bax, or p53. This study demonstrates that elevated IOP exposure does not result in a dramatic decrease in retinal levels of either BDNF or its receptor, TrkB. It shows that the responses of NT pathways to elevated IOP are complex, particularly with regard to the role of p75(NTR) and Atf3. A better understanding of the roles of these proteins in IOP-induced injury is likely to suggest informed strategies for neuroprotection in glaucoma.

DOCK2 is a microglial specific regulator of central nervous system innate immunity found in normal and Alzheimer's disease brain

Neuroinflammation is a hallmark of several neurodegenerative diseases, including Alzheimer's disease (AD). Strong epidemiological and experimental evidence supports the use of nonsteroidal anti-inflammatory drugs to reduce AD risk. However, poor outcome in clinical trials and toxicity in a prevention trial have shifted focus away from these cyclooxygenase (COX) inhibitors to seek additional therapeutic targets in the prostaglandin pathway. Previously, the prostaglandin E2 receptor, EP2, was shown to regulate neuroinflammation and reduce Abeta plaque burden in transgenic mice. Unfortunately, widespread EP2 distribution and a direct effect on COX2 induction make EP2 a less desirable target. In this study, we link dedicator of cytokinesis 2 (DOCK2) to the prostaglandin pathway in the brain. Additionally, we show that DOCK2 regulates microglial innate immunity independent of COX2 induction and that DOCK2+ microglia are associated with human AD pathology. Together, these results suggest DOCK2 as a COX2 expression-independent therapeutic target for neurodegenerative diseases such as AD.

Increased activation of Iba1+ microglia in pediatric epilepsy patients with Rasmussen's encephalitis compared with cortical dysplasia and tuberous sclerosis complex

Microgliosis is prominent in Rasmussen's encephalitis (RE), a disease with severe seizure activity. However, it is unclear if microglial activation is similar with different histopathologic substrates. Iba1-immunolabelled microglial activation was assessed in neocortex from pediatric epilepsy surgery patients with RE (n=8), cortical dysplasia (CD; n=6) and tuberous sclerosis complex (TSC; n=6). Microglial reactivity was increased, in severely affected RE areas (29% labeling) compared with minimally affected areas of RE cases (15%) and cases of TSC (14%) and CD (12%). There was no qualitative association of Iba1 immunolabelling with the presence of CD8(+) cytotoxic T-cells and no statistical association with clinical epilepsy variables, such as seizure duration or frequency. Iba1 appears to be an excellent marker for detecting extensive microglial activation in patients with RE. In addition, this study supports the notion that Iba1-labeled microglial activation is increased in patients with active RE, compared with cases of CD and TSC.

Cannabinoid receptor type 2 activation induces a microglial anti-inflammatory phenotype and reduces migration via MKP induction and ERK dephosphorylation

Background

Cannabinoid receptor type 2 (CBR2) inhibits microglial reactivity through a molecular mechanism yet to be elucidated. We hypothesized that CBR2 activation induces an anti-inflammatory phenotype in microglia by inhibiting extracellular signal-regulated kinase (ERK) pathway, via mitogen-activated protein kinase-phosphatase (MKP) induction. MKPs regulate mitogen activated protein kinases, but their role in the modulation of microglial phenotype is not fully understood.

Results

JWH015 (a CBR2 agonist) increased MKP-1 and MKP-3 expression, which in turn reduced p-ERK1/2 in LPS-stimulated primary microglia. These effects resulted in a significant reduction of tumor necrosis factor-α (TNF) expression and microglial migration. We confirmed the causative link of these findings by using MKP inhibitors. We found that the selective inhibition of MKP-1 by Ro-31-8220 and PSI2106, did not affect p-ERK expression in LPS+JWH015-treated microglia. However, the inhibition of both MKP-1 and MKP-3 by triptolide induced an increase in p-ERK expression and in microglial migration using LPS+JWH015-treated microglia.

Conclusion

Our results uncover a cellular microglial pathway triggered by CBR2 activation. These data suggest that the reduction of pro-inflammatory factors and microglial migration via MKP-3 induction is part of the mechanism of action of CBR2 agonists. These findings may have clinical implications for further drug development.

Sigma receptors suppress multiple aspects of microglial activation

During brain injury, microglia become activated and migrate to areas of degenerating neurons. These microglia release proinflammatory cytokines and reactive oxygen species causing additional neuronal death. Microglia express high levels of sigma receptors, however, the function of these receptors in microglia and how they may affect the activation of these cells remain poorly understood. Using primary rat microglial cultures, it was found that sigma receptor activation suppresses the ability of microglia to rearrange their actin cytoskeleton, migrate, and release cytokines in response to the activators adenosine triphosphate (ATP), monocyte chemoattractant protein 1 (MCP-1), and lipopolysaccharide (LPS). Next, the role of sigma receptors in the regulation of calcium signaling during microglial activation was explored. Calcium fluorometry experiments in vitro show that stimulation of sigma receptors suppressed both transient and sustained intracellular calcium elevations associated with the microglial response to these activators. Further experiments showed that sigma receptors suppress microglial activation by interfering with increases in intracellular calcium. In addition, sigma receptor activation also prevented membrane ruffling in a calcium-independent manner, indicating that sigma receptors regulate the function of microglia via multiple mechanisms.

Imaging macrophages in trehalose with SIMS

Phagocytosis is a major component of the animal immune system where apoptotic cellular material, metabolites, and waste are safely processed. Further, efficient phagocytosis by macrophages is key to maintaining healthy vascular systems and preventing atherosclerosis. Single-cell images of macrophage phagocytosis of red blood cells, RBCs, and polystyrene microspheres have been chemically mapped with TOF-SIMS. We demonstrate here cholesterol and phosphocholine localizations as relative to time and activity.

Exacerbated glial response in the aged mouse hippocampus following controlled cortical impact injury

Old age is associated with enhanced susceptibility to and poor recovery from brain injury. An exacerbated microglial and astrocyte response to brain injury might be involved in poor outcomes observed in the elderly. The present study was therefore designed to quantitate the expression of markers of microglia and astrocyte activation using real-time RT-PCR, immunoblot and immunohistochemical analysis in aging brain in response to brain injury. We examined the hippocampus, a region that undergoes secondary neuron death, in aged (21-24 months) and adult (5-6 months) mice following controlled cortical impact (CCI) injury to the sensorimotor cortex. Basal mRNA expression of CD11b and Iba1, markers of activated microglia, was higher in aged hippocampus as compared to the adult. The mRNA expression of microglial markers increased and reached maximum 3 days post-injury in both adult and aged mice, but was higher in the aged mice at all time points studied, and in the aged mice the return to baseline levels was delayed. Basal mRNA expression of GFAP and S100B, markers of activated astrocytes, was higher in aged mice. Both markers increased and reached maximum 7 days post-injury. The mRNA expression of astrocyte markers returned to near basal levels rapidly after injury in the adult mice, whereas again in the aged mice return to baseline was delayed. Immunochemical analysis using Iba1 and GFAP antibodies indicated accentuated glial responses in the aged hippocampus after injury. The pronounced and prolonged activation of microglia and astrocytes in hippocampus may contribute to worse cognitive outcomes in the elderly following TBI.

Is microglial apoptosis an early pathogenic change in cerebral X-linked adrenoleukodystrophy?

OBJECTIVE

Mutations in the X-linked adrenoleukodystrophy (X-ALD) protein cause accumulation of unbranched saturated very-long-chain fatty acids, particularly in brain and adrenal cortex. In humans, the genetic defect causes progressive inflammatory demyelination in the brain, where very-long-chain fatty acids accumulate within phospholipid fractions such as lysophosphatidylcholine.

METHODS

To address mechanisms of inflammation, we studied microglial activation in human ALD (10 autopsies) and lysophosphatidylcholine (C24:0) injection into the parietal cortex of mice.

RESULTS

Unexpectedly, we found a zone lacking microglia within perilesional white matter, immediately beyond the actively demyelinating lesion edge. Surrounding this zone we observed clusters of activated and apoptotic microglia within subcortical white matter. Lysophosphatidylcholine (C24:0) injection in mice led to widespread microglial activation and apoptosis.

INTERPRETATION

Our data suggest that the distinct mononuclear phagocytic cell response seen in cerebral X-ALD results, at least in part, from aberrant signaling to cognate receptors on microglia. Our findings support a hypothesis that microglial apoptosis in perilesional white matter represents an early stage in lesion evolution and may be an appropriate target for intervention in X-ALD patients with evidence of cerebral demyelination.

Impaired astrocytes and diffuse activation of microglia in the cerebral cortex in simian immunodeficiency virus-infected Macaques without simian immunodeficiency virus encephalitis

Various types of neuronal damage have been reported in acquired immunodeficiency syndrome (AIDS) dementia. We previously demonstrated that inflammation and cortical damage occur independently according to viral tropism in a simian immunodeficiency virus (SIV)-infected macaque model of AIDS dementia. To elucidate the pathogenesis of cortical degeneration, we examined the frontal cortex of SIV-infected macaques and found apoptosis and decreased expression of the excitatory amino acid transporter 2 in astrocytes and diffuse activation of microglia in association with limited neuronal damage. Some activated microglia also expressed excitatory amino acid transporter 2 but not proinflammatory cytokines. No inflammatory changes were seen in the cortex or the white matter, and SIV-infected cells were not detected in or around cortical lesions either by immunohistochemistry or by the polymerase chain reaction detection of SIV genomes of extracted DNA from microdissected tissue samples. These results indicate that an astrocytic abnormality and a compensatory activation of microglia might provide a protective effect against neuronal degeneration in the frontal cortex of SIV-infected macaques without SIV encephalitis.

Tissue-specific reduction in DC-SIGN expression correlates with progression of pathogenic simian immunodeficiency virus infection

Studies were undertaken to determine whether previously described reductions in splenic DC-SIGN expression in simian acquired immune deficiency syndrome (AIDS) are limited to pathogenic simian immunodeficiency virus (SIV) infection. DC-SIGN expression was evaluated by immunohistochemistry in lymphoid tissues from AIDS-susceptible Asian macaque monkeys as compared with AIDS-resistant sooty mangabey monkeys in the presence and absence of SIV infection. The phenotype of DC-SIGN+ cells in susceptible and resistant species was identical and most consistent with macrophage identity. Significantly lower levels of DC-SIGN expression were identified in spleen, mesenteric lymph node, and bone marrow of macaques with AIDS (P<0.05). Reduced levels of splenic DC-SIGN correlated significantly with CD4T cell depletion in long-term pathogenic infection of macaques (P<0.01), whereas SIV-infected mangabeys retained high levels of DC-SIGN expression in spleen despite persistent infection. Reduced expression of DC-SIGN in spleen specifically characterizes pathogenic forms of SIV infection, correlates with disease progression, and may contribute to SIV pathogenesis.

Metastatic cancer cells with macrophage properties: evidence from a new murine tumor model

Metastasis is the process by which cancer cells disseminate from the primary neoplasm and invade surrounding tissue and distant organs, and is the primary cause of morbidity and mortality for cancer patients. Most conventional cancer therapies are ineffective in managing tumor metastasis. This has been due in large part to the absence of in vivo metastatic models that represent the full spectrum of metastatic disease. Here we identify 3 new spontaneously arising tumors in the inbred VM mouse strain, which has a relatively high incidence of CNS tumors. Two of the tumors (VM-M2 and VM-M3) reliably expressed all of the major biological processes of metastasis to include local invasion, intravasation, immune system survival, extravasation and secondary tumor formation involving liver, kidney, spleen, lung and brain. Metastasis was assessed through visual organ inspection, histology, immunohistochemistry and bioluminescence imaging. The metastatic VM tumor cells also expressed multiple properties of macrophages including morphological appearance, surface adhesion, phagocytosis, total lipid composition (glycosphingolipids and phospholipids) and gene expression (CD11b, Iba1, F4/80, CD68, CD45 and CXCR4). The third tumor (VM-NM1) grew rapidly and expressed properties of neural stem/progenitor cells, but was neither invasive nor metastatic. Our data indicate that spontaneous brain tumors can arise from different cell types in VM mice and that metastatic cancer can represent a disease of macrophage-like cells similar to those described in several human metastatic cancers. The new VM tumor model will be useful for defining the biological processes of cancer metastasis and for evaluating potential therapies for tumor management.

Neuroprotective and neurotoxic properties of glial cells in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) affects more than 18 million people worldwide and is characterized by progressive memory deficits, cognitive impairment and personality changes. The main cause of AD is generally attributed to the increased production and accumulation of amyloid-β (Aβ), in association with neurofibrillary tangle (NFT) formation. Increased levels of pro-inflammatory factors such as cytokines and chemokines, and the activation of the complement cascade occurs in the brains of AD patients and contributes to the local inflammatory response triggered by senile plaque. The existence of an inflammatory component in AD is now well known on the basis of epidemiological findings showing a reduced prevalence of the disease upon long-term medication with anti-inflammatory drugs, and evidence from studies of clinical materials that shows an accumulation of activated glial cells, particularly microglia and astrocytes, in the same areas as amyloid plaques. Glial cells maintain brain plasticity and protect the brain for functional recovery from injuries. Dysfunction of glial cells may promote neurodegeneration and, eventually, the retraction of neuronal synapses, which leads to cognitive deficits. The focus of this review is on glial cells and their diversity properties in AD.

Age-related changes in ionized calcium-binding adapter molecule 1 immunoreactivity and protein level in the gerbil hippocampal CA1 region

Microglia are evenly distributed throughout the brain parenchyma. They respond rapidly to a variety of alterations in the microenvironment of the brain and act as sensors for pathological events in the brain. In the present study, we investigated the age-dependent changes in the immunoreactivity and protein level of ionized calcium-binding adapter molecule 1 (Iba-1), a microglial marker, in the CA1 region of the gerbil hippocampus. Iba-1 immunoreactive microglia were detected in the hippocampal CA1 region of the postnatal month 1 (PM 1) group. Iba-1 positive microglia were morphologically inactive between the PM 1 and PM 12 stages. Some Iba-1 immunoreactive microglia were present in the active form in the hippocampal CA1 region of the PM 18 and PM 24 groups. The Iba-1 protein levels in hippocampal CA1 homogenates were decreased in the PM 1 through PM 6 groups and increased in an age-dependent manner thereafter. These results suggest that Iba-1 immunoreactive microglia in the active form were detected in the hippocampal CA1 region in the PM 18 and PM 24 groups. This result may be associated with an age-dependent susceptibility to neurodegenerative diseases associated with the hippocampus.

Allograft inflammatory factor-1/Ionized calcium-binding adapter molecule 1 is specifically expressed by most subpopulations of macrophages and spermatids in testis

Ionized calcium-binding adapter molecule 1 (Iba1) is a 147-amino-acid calcium-binding protein widely in use as a marker for microglia. It has actin-crosslinking activity and is involved in aspects of motility-associated rearrangement of the actin cytoskeleton. The Iba1 gene and protein are identical to allograft inflammatory factor-1 (AIF-1), a protein involved in various aspects of inflammation, which was investigated independently from Iba1. Although regarded to be monocyte/macrophage-specific, expression by germ cells in testis showed that AIF-1/Iba1 is not exclusively expressed by cells of the monocyte/macrophage lineage. Furthermore, AIF-1 was found in cells not belonging to the monocyte/macrophage lineage under pathological conditions. Here, the distribution of AIF-1/Iba1 in the normal mouse has been examined, by immunohistochemistry, to determine whether AIF-1/Iba1 expression is confined to macrophages and spermatids. Spermatids are the only cells not belonging to the monocyte/macrophage lineage found to express AIF-1/Iba1 in the normal mouse, by this method. This study has not demonstrated AIF-1/Iba1 expression in dendritic cells, although this protein might be expressed by subsets of dendritic cells. AIF-1/Iba1 can be regarded a "pan-macrophage marker" because, except for alveolar macrophages, all subpopulations of macrophages examined express AIF-1/Iba1.

UDP acting at P2Y6 receptors is a mediator of microglial phagocytosis

Microglia, brain immune cells, engage in the clearance of dead cells or dangerous debris, which is crucial to the maintenance of brain functions. When a neighbouring cell is injured, microglia move rapidly towards it or extend a process to engulf the injured cell. Because cells release or leak ATP when they are stimulated or injured, extracellular nucleotides are thought to be involved in these events. In fact, ATP triggers a dynamic change in the motility of microglia in vitro and in vivo, a previously unrecognized mechanism underlying microglial chemotaxis; in contrast, microglial phagocytosis has received only limited attention. Here we show that microglia express the metabotropic P2Y6 receptor whose activation by endogenous agonist UDP triggers microglial phagocytosis. UDP facilitated the uptake of microspheres in a P2Y6-receptor-dependent manner, which was mimicked by the leakage of endogenous UDP when hippocampal neurons were damaged by kainic acid in vivo and in vitro. In addition, systemic administration of kainic acid in rats resulted in neuronal cell death in the hippocampal CA1 and CA3 regions, where increases in messenger RNA encoding P2Y6 receptors that colocalized with activated microglia were observed. Thus, the P2Y6 receptor is upregulated when neurons are damaged, and could function as a sensor for phagocytosis by sensing diffusible UDP signals, which is a previously unknown pathophysiological function of P2 receptors in microglia.

Actin-binding proteins coronin-1a and IBA-1 are effective microglial markers for immunohistochemistry

This study identifies the actin-binding protein, coronin-1a, as a novel and effective immunohistochemical marker for microglia in both cell cultures and in formaldehyde-fixed, paraffin-embedded tissue. Antibodies to coronin-1a effectively immunostained microglia in human, monkey, horse, rat, and mouse tissues, even in tissues stored for long periods of time. The identity of coronin-1a-immunoreactive cells as microglia was confirmed using double immunolabeling with cell type-specific markers as well as by morphological features and the distribution of immunoreactive cells. These properties are shared by another actin-binding protein, IBA-1. Unlike IBA-1, coronin-1a immunoreactivity was also detected in lymphocytes and certain other hematopoietic cells. The results indicate that both coronin-1a and IBA-1 are robust markers for microglia that can be used in routinely processed tissue of humans and animals. Because both coronin-1a and IBA-1 are actin-binding proteins that play a role in rearrangement of the membrane cytoskeleton, it suggests that these proteins are critical to dynamic properties of microglia.

Identification of a heat-shock protein Hsp40, DjB1, as an acrosome- and a tail-associated component in rodent spermatozoa

Iba1 is a 17-kDa EF-hand protein highly expressed in the cytoplasm of elongating spermatids in testis. Using Iba1 as a bait, we performed yeast Two-hybrid screening and isolated a heat-shock protein Hsp40, DjB1, from cDNA library of mouse testis. To characterize DjB1 that is encoded by Dnajb1 gene, we carried out immunoblot analyses, in situ hybridization, and immunohistochemistry. Immunoblot analyses showed that DjB1was constitutively expressed in mouse testis and that its expression level was not changed by heat shock. Dnajb1 mRNA was exclusively expressed in spermatocytes and round spermatids in mouse testis, and Dnajb1 protein DjB1 was predominantly expressed in the cytoplasm of spermatocytes, round spermatids, and elongating spermatids. In mature mouse spermatozoa, DjB1 was localized in the middle and the end pieces of flagella as well as in association with the head (acrosomal region). Association of DjB1 with the acrosomal region in sperm head was also observed in rat spermatozoa. These data suggested that DjB1, which was constitutively expressed in postmeiotic spermatogenic cells in testis, was integrated into spermatozoa as at least two components, that is, sperm head and tail of rodent spermatozoa.

X-ray Structures of the Microglia/Macrophage-specific Protein Iba1 from Human and Mouse Demonstrate Novel Molecular Conformation Change Induced by Calcium binding

The ionized calcium-binding adaptor molecule 1 (Iba1) with 147 amino acid residues has been identified as a calcium-binding protein, expressed specifically in microglia/macrophages, and is expected to be a key factor in membrane ruffling, which is a typical feature of activated microglia. We have determined the crystal structure of human Iba1 in a Ca(2+)-free form and mouse Iba1 in a Ca(2+)-bound form, to a resolution of 1.9 A and 2.1 A, respectively. X-ray structures of Iba1 revealed a compact, single-domain protein with two EF-hand motifs, showing similarity in overall topology to partial structures of the classical EF-hand proteins troponin C and calmodulin. In mouse Iba1, the second EF-hand contains a bound Ca(2+), but the first EF-hand does not, which is often the case in S100 proteins, suggesting that Iba1 has S100 protein-like EF-hands. The molecular conformational change induced by Ca(2+)-binding of Iba1 is different from that found in the classical EF-hand proteins and/or S100 proteins, which demonstrates that Iba1 has an unique molecular switching mechanism dependent on Ca(2+)-binding, to interact with target molecules.

Neuronal neprilysin overexpression is associated with attenuation of Aβ-related spatial memory deficit

Converging evidence links abnormally high brain concentrations of amyloid-beta peptides (Abeta) to the pathology of Alzheimer's disease (AD). Lowering brain Abeta levels, therefore, is a therapeutic strategy for the treatment of AD. Neuronal neprilysin upregulation led to increased degradation of Abeta, reduced the formation of Abeta-plaques and the associated cytopathology, but whether overexpression of neprilysin can improve cognition is unknown. We show that neuronal overexpression of neprilysin improved the Morris water maze memory performance in mice with memory deficits resulting from overexpression of the AD-causing mutated human amyloid precursor protein (APP). This improvement was associated with decreased brain levels of Abeta and with unchanged endoproteolytic processing of APP. These results provide the evidence that lowering of brain Abeta levels by increasing its degradation can improve cognitive functions in vivo, and suggest that increasing the activity of neprilysin in brain may be effective in preventing cognitive decline in AD.

Functional role of calcium signals for microglial function

In this review we summarize mechanisms of Ca(2+) signaling in microglial cells and the impact of Ca(2+) signaling and Ca(2+) levels on microglial function. So far, Ca(2+) signaling has been only characterized in cultured microglia and thus these data refer rather to activated microglia as observed in pathology when compared with the resting form found under physiological conditions. Purinergic receptors are the most prominently expressed ligand-gated Ca(2+)-permeable channels in microglia and control several microglial functions such as cytokine release in a Ca(2+)-dependent fashion. A large variety of metabotropic receptors are linked to Ca(2+) release from intracellular stores. Depletion of these intracellular stores triggers a capacitative Ca(2+) entry. While microglia are already in an activated state in culture, they can be further activated, for example, by exposure to bacterial endotoxin. This activation leads to a chronic increase of [Ca(2+)](i) and this Ca(2+) increase is a prerequisite for the release of nitric oxide and cytokines. Moreover, several factors (TNFalpha, IL-1beta, and IFN-gamma) regulate resting [Ca(2+)](i) levels.

Behavior of in vitro cultured ameboid microglial cells migrating on Müller cell end-feet in the quail embryo retina

Ameboid microglial cells migrate tangentially on the vitreal part of quail embryo retinas by crawling on Müller cell end-feet (MCEF) to which they adhere. These microglial cells can be cultured immediately after dissection of the eye and isolation of sheets containing the inner limiting membrane (ILM) covered by a carpet of MCEF (ILM/MCEF sheets), to which the cells remain adhered. Morphological changes of microglial cells cultured on ILM/MCEF sheets for 4 days were characterized in this study. During the first minutes in vitro, lamellipodia-bearing bipolar microglial cells became rounded in shape. From 1 to 24 h in vitro (hiv), microglial cells swept and phagocytosed the MCEF on which they were initially adhered, becoming directly adhered on the ILM. MCEF sweep was dependent on active cell motility, as shown by inhibition of sweep after cytochalasin D treatment. From 24 hiv on, after MCEF phagocytosis, microglial cells became more flattened, increasing the surface area of their adhesion to substrate, and expressed the beta1 subunit of integrins on their membrane. Morphological evidence suggested that microglial cells migrated for short distances on ILM/MCEF sheets, leaving tracks produced by their strong adhesion to the substrate. The simplicity of the isolation method, the immediate availability of cultured microglial cells, and the presence of multiple functional processes (phagocytosis, migration, upregulation of surface molecules, etc.) make cultures of microglial cells on ILM/MCEF sheets a valuable model system for in vitro experimental investigation of microglial cell functions.

Bone marrow CD34+/B220+ progenitors target the inflamed brain and display in vitro differentiation potential toward microglia

Recent evidence indicates that microglial cells may not derive from blood circulating mature monocytes as they express features of myeloid progenitors. Here, we observed that a subpopulation of microglial cells expressed CD34 and B220 antigens during brain development. We thus hypothesized that microglia, or a subset of microglial cells, originate from blood circulating CD34+/B220+ myeloid progenitors, which could target the brain under developmental or neuroinflammatory conditions. Using experimental allergic encephalomyelitis (EAE) as a model of chronic neuroinflammation, we found that a discrete population of CD34+/B220+ cells expands in both blood and brain of diseased animals. In EAE mice, intravenous transfer experiments showed that macrophage-colony stimulating factor (M-CSF) -expanded CD34+ myeloid progenitors target the inflamed central nervous system (CNS) while keeping their immature phenotype. Based on these results, we then assessed whether CD34+/B220+ cells display in vitro differentiation potential toward microglia. For this purpose, CD34+/B220+ cells were sorted from M-CSF-stimulated bone marrow (BM) cultures and exposed to a glial cell conditioned medium. Under these experimental conditions, CD34+/B220+ cells were able to differentiate into microglial-like cells showing the morphological and phenotypic features of native microglia. Overall, our data suggest that under developmental or neuroinflammatory conditions, a subpopulation of microglial cells derive from CNS-invading CD34+/B220+ myeloid progenitors.

Kainate induces rapid redistribution of the actin cytoskeleton in ameboid microglia

Microglia are key mediators of the immune response in the central nervous system (CNS). They are closely related to macrophages and undergo dramatic morphological and functional changes after CNS trauma or excitotoxic lesions. Microglia can be directly stimulated by excitatory neurotransmitters and are known to express many neurotransmitter receptors. The role of these receptors, however, is not clear. This study describes the microglial response to the glutamate receptor agonist kainate (KA) and shows via immunochemistry that the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate receptor subunit GluR1 is present on cultured microglia. In the presence of 100 microM or 1 mM KA, cultured microglia underwent dramatic morphological and cytoskeletal changes as observed by time-lapse photography and quantitative confocal analysis of phalloidin labeling. KA-stimulated microglia showed condensation of cytoplasmic actin filaments, rapid de- and repolymerization, and cytoplasmic redistribution of condensed actin bundles. Rearrangement of actin filaments-thought to be involved in locomotion and phagocytosis and to indicate an increased level of activation (for reviews see Greenberg [ 1995] Trends Cell Biol. 5:93-99; Imai and Kohsaka [ 2002] Glia 40:164-174)-was significantly increased in treated vs. control cultures. Morphological plasticity and membrane ruffling were also seen. These findings suggest direct microglial excitation via glutamate receptor pathways. Thus, neurotransmitter release after brain or spinal cord injury might directly modulate the inflammatory response.

Tumor necrosis factor-alpha and CD40L modulate cell surface morphology and induce aggregation in Ramos Burkitt's lymphoma cells

Interaction of CD40L and its cognate receptor is an essential component of B-lymphocyte signaling, affecting various aspects of B-cell differentiation pathways and immunoglobulin gene expression. However, much less is known about the biological consequences of B-cell signaling through tumor necrosis factor (TNF)-alpha and its cognate receptors TNF-R1 and 2. We used Ramos Burkitt's lymphoma cell line as a model system to study the direct effects of these cytokines on B cells. Treatment of Ramos cells with either TNF-alpha or CD40L, but not with interleukin (IL)- 4, interferon (IFN)-gamma and transforming growth factor (TGF)-beta, resulted in enhanced cell aggregation and enhancement of adherence to glass cover-slips. Scanning electron microscopy showed that Ramos cells have a polarized cell surface morphology and exhibit at least 3 cell surface morphological domains: microvilli, filopodia and ruffled membranes. The cells adhered to the glass matrix through multiple filopodia/podopodia-like cell processes and demonstrated distinct ruffled-like membrane projections on their opposite pole. Induction by TNF-alpha or CD40L, but not with IL-4, IFN-gamma and TGF-beta, resulted in increased number and complexity of both types of membrane projections. TNF-alpha and CD40L upregulated the expression of the adhesion molecule intercellular adhesion molecule-1 and the Fas receptor on Ramos cells, without affecting the expression levels of membrane immunoglobulin M or its secretion rate. Reverse transcriptase-polymerase chain reaction, and flow cytometry demonstrated that Ramos cells expressed TNF-R1 but very little if any TNF-R2, indicating that TNF-alpha exerted its effects on Ramos cells through the former receptor.

Aminoguanidine inhibits caspase-3 and calpain activation without affecting microglial activation following neonatal transient cerebral ischemia

Microglial cells, the resident macrophages of the CNS, can be both beneficial and detrimental to the brain. These cells play a central role as mediators of neuroinflammation associated with many neurodegenerative states, including cerebral ischemia. Because microglial cells are both a major source of inducible nitric oxide synthase (iNOS)/nitric oxide (NO) production locally in the injured brain and are activated by NO-mediated injury, we tested whether iNOS inhibition reduces microglial activation and ischemic injury in a neonatal focal ischemia-reperfusion model. Post-natal day 7 rats were subjected to a 2 h transient middle cerebral artery (MCA) occlusion. Pups with confirmed injury on diffusion-weighted magnetic resonance imaging (MRI) during occlusion were administered 300 mg/kg/dose aminoguanidine (AG) or vehicle at 0, 4 and 18 h after reperfusion, and animals were killed at 24 or 72 h post-reperfusion. The effect of AG on microglial activation as judged by the acquisition of ED1 immunoreactivity and proliferation of ED1-positive cells, on activation of cell death pathways and on injury volume, was determined. The study shows that while AG attenuates caspase 3 and calpain activation in the injured tissue, treatment does not affect the rapidly occurring activation and proliferation of microglia following transient MCA occlusion in the immature rat, or reduce injury size.

Epidermal growth factor-dependent enhancement of axonal regeneration in the pond snail Lymnaea stagnalis: role of phagocyte survival

Peripheral nerve injury triggers complex responses from neuronal as well as from multiple nonneuronal cell types. These responses are coordinated by a wide spectrum of secreted and nonsecreted factors, including growth factors, cytokines, and cell adhesion molecules. These molecules originate from different sources and act both locally at the site of injury as well as centrally at the location of the neuronal cell bodies. One of the signal systems frequently implicated in this process is the epidermal growth factor (EGF) family and its receptors. Expression of members of this family as well as that of EGF-receptors is upregulated in different cell types after peripheral nerve injury. However, the functional significance of this response is unclear. Using a simple invertebrate model system (Lymnaea stagnalis), the present study implicates the EGF/EGF-receptor system in the survival of ionized calcium-binding adaptor molecule 1 (Iba1)-positive phagocytes that reside in the nervous system. We show that inhibiting the EGF-signaling pathway enhances cell death in this type of cell, an effect paralleled by a substantial reduction in axonal regeneration. Therefore, complementing our previous observation that Lymnaea EGF provides trophic support to axotomized neurons, the present results emphasize the significance of nonneuronal actions of EGF receptor ligands in axonal regeneration. Thus, we add a novel perspective to the ongoing discussion on the functional significance of the EGF signaling system in the injury responses of the nervous system.

Active immunization trial in Abeta42-injected P301L tau transgenic mice

Amyloid beta-peptide (Abeta) containing plaques and neurofibrillary tangles (NFT) are the two major histopathological hallmarks of Alzheimer's disease (AD). According to the amyloid cascade hypothesis, deposition of Abeta is an initial and essential step in the pathogenesis of AD, and formation of NFT has been proposed to be caused by increased Abeta levels. Several previous studies revealed that Abeta plaque formation can be reduced or even prevented by active immunization with Abeta preparations or by administration of Abeta-specific antibodies. To assess the role of fibrillar preparations of Abeta42 in NFT formation, we previously performed intracerebral (i.c.) injections of Abeta42 into brains of NFT-forming P301L tau transgenic mice which caused significant increases in NFT numbers. To determine whether these increases in NFT can be blocked or reduced by active immunization, P301L tau mice were immunized with intraperitoneal injections of preaggregated Abeta42. Abeta42-specific titers were monitored and the mice injected i.c. with Abeta42. We found that i.c. injection of Abeta42 caused significant increases in NFT formation. However, this induction was not affected by active immunization despite high serum anti-Abeta42 titer levels and binding of anti-Abeta42 antibodies to the injected Abeta42 aggregates. We conclude that active immunization is not sufficient to prevent the effect of Abeta42 on tau aggregation in our model system. Further studies are required to determine whether modifications of our protocol could affect the Abeta42-mediated induction of NFT formation.

Protein 4.1 G localizes in rodent microglia

Although it was reported that protein 4.1 G, a cytoskeletal protein characterized by its general expression in the body, interacts with some signal transduction molecules in the central nervous system (CNS), its distribution and significance in vivo remained to be elucidated. In the present study, we have identified 4.1 G-positive cells in the rodent CNS, and demonstrated its immunolocalization in the developing mouse CNS. In the rodent CNS, 4.1 G was colocalized with markers for microglia, such as CD45, OX-42 and ionized calcium-binding adapter molecule 1 (Iba1), but not with markers for neuronal or other glial cells. Additionally, colocalization of 4.1 G and A1 adenosine receptor was observed in the mouse cerebrum. In a mixed glial culture, most OX-42-positive microglia were positive for 4.1 G, and 4.1 G isoforms of the same molecular weight as in the rat brain were expressed in cultured microglia, where 4.1 G mRNA was detected by RT-PCR. In the developing mouse cerebral cortex, 4.1 G was detected in immature microglia, which were positive for Iba1. These results indicate that 4.1 G in the CNS is mainly distributed in microglia in vivo. Considering the interactions between 4.1 G and the signal transduction molecules, putative roles have been proposed for 4.1 G in microglial functions in the CNS.

The function of microglia through purinergic receptors: neuropathic pain and cytokine release

Microglia play an important role as immune cells in the central nervous system (CNS). Microglia are activated in threatened physiological homeostasis, including CNS trauma, apoptosis, ischemia, inflammation, and infection. Activated microglia show a stereotypic, progressive series of changes in morphology, gene expression, function, and number and produce and release various chemical mediators, including proinflammatory cytokines that can produce immunological actions and can also act on neurons to alter their function. Recently, a great deal of attention is focusing on the relation between activated microglia through adenosine 5'-triphosphate (ATP) receptors and neuropathic pain. Neuropathic pain is often a consequence of nerve injury through surgery, bone compression, diabetes, or infection. This type of pain can be so severe that even light touching can be intensely painful and it is generally resistant to currently available treatments. There is abundant evidence that extracellular ATP and microglia have an important role in neuropathic pain. The expression of P2X4 receptor, a subtype of ATP receptors, is enhanced in spinal microglia after peripheral nerve injury model, and blocking pharmacologically and suppressing molecularly P2X4 receptors produce a reduction of the neuropathic pain. Several cytokines such as interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) in the dorsal horn are increased after nerve lesion and have been implicated in contributing to nerve-injury pain, presumably by altering synaptic transmission in the CNS, including the spinal cord. Nerve injury also leads to persistent activation of p38 mitogen-activated protein kinase (MAPK) in microglia. An inhibitor of this enzyme reverses mechanical allodynia following spinal nerve ligation (SNL). ATP is able to activate MAPK, leading to the release of bioactive substances, including cytokines, from microglia. Thus, diffusible factors released from activated microglia by the stimulation of purinergic receptors may have an important role in the development of neuropathic pain. Understanding the key roles of ATP receptors, including P2X4 receptors, in the microglia may lead to new strategies for the management of neuropathic pain.

Identification of a multiprotein "motor" complex binding to water channel aquaporin-2

Targeted positioning of water channel aquaporin-2 (AQP2) strictly regulates body water homeostasis. Trafficking of AQP2 to the apical membrane is critical to the reabsorption of water in renal collecting ducts. Recently, we have identified for the first time proteins which directly bind to AQP2: SPA-1, a GTPase-activating protein for Rap1, and cytoskeletal protein actin. Based on these findings, we have speculated the existence of a multiprotein complex which includes AQP2, SPA-1, and actin, for providing the mechanism which generates force and motion in AQP2 trafficking. To clarify the proteins comprising the complex, a large amount of AQP2-associated protein complex was isolated from the extract of rat kidney papilla using immunoaffinity column coupled with anti-AQP2 antibody and was analyzed by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). In addition to SPA-1 and actin, 11 proteins were identified using this method: ionized calcium binding adapter molecule 2, myosin regulatory light chain smooth muscle isoforms 2-A and 2-B, alpha-tropomyosin 5b, annexin A2 and A6, scinderin, gelsolin, alpha-actinin 4, alpha-II spectrin, and myosin heavy chain nonmuscle type A. Our findings show for the first time an AQP2-binding multiprotein "force generator" complex. This multiprotein complex may provide the machinery of driving AQP2 movement.

Reduced cerebral blood flow and N-acetyl aspartate in a murine model of cerebral malaria

Cerebral malaria is an important cause of morbidity and mortality in many parts of the world. It has been suggested that cerebral malaria is associated with reduced perfusion due to the blockage of blood vessels by parasitized erythrocytes; although, no quantitative validation of this has been done. We infected C57BL/6 mice with the ANKA strain of Plasmodium berghei and on day 6 of infection we investigated alterations in brain function using arterial spin labeling MRI and proton MRS. MR images did not demonstrate signs of damage. However, there was a significant reduction in cerebral blood flow (P<0.012) and the ratio of N-acetyl-aspartate (NAA) to creatine (Cr) (P<0.01) relative to non-infected mice. The NAA/Cr ratios were significantly correlated with cerebral perfusion (r=0.87) suggesting a relationship between impaired oxygen delivery and neuronal dysfunction. Pathological examination revealed accumulations of damaged axons providing a correlate for the decreased NAA/Cr ratio in infected mice. This murine model will permit non-invasive studies of neurologic function during malarial infection.

Molecular cloning of rat Spergen-3, a spermatogenic cell-specific gene-3, encoding a novel 75-kDa protein bearing EF-hand motifs

By use of differential display in combination with cDNA cloning approach, we isolated a novel rat gene designated as Spergen-3, which has an open reading frame of 2055-length nucleotides encoding a protein of 685 amino acids. Spergen-3 gene is composed of 15 exons and mapped on chromosome 5q36, and its mouse counterpart, which shares 85.5% identity to rat Spergen-3 at the amino acid level, is mapped on chromosome 4E1. Spergen-3 encodes a 75-kDa soluble protein bearing putative 2 EF-hand motifs, proline-repeat, and a putative nuclear localization signal. Of the 2 EF-hand motifs in Spergen-3, the second one seems to match the consensus sequence. Reverse transcription-polymerase chain reaction analysis showed that the expression of Spergen-3 is developmentally up-regulated and that it is exclusively expressed in testis. In situ hybridization revealed that Spergen-3 mRNA was exclusively expressed in haploid spermatids, but its signal was weak or undetectable in spermatogonia, spermatocytes, and Sertoli cells as well as in interstitial cells. We interpreted these data as a potential role of Spergen-3, a new member of EF-hand family, in differentiation of haploid spermatids in testis.

Tumor Necrosis Factor Reduces Brain Tumor Growth by Enhancing Macrophage Recruitment and Microcyst Formation

Recent findings implicate macrophages and some of their secreted products, especially tumor necrosis factor (TNF), as tumor promoters. Inhibitors of these inflammatory components are currently regarded as potential therapeutic tools to block tumor progression. Here, we show that infiltrating macrophages represented a significant population of nonneoplastic cells within malignant gliomas, in which they were the exclusive producers of TNF. Contrary to the reported pro-oncogenic effects of TNF in other types of solid tumors, glioma-bearing mice deficient in TNF developed larger tumors and had reduced survival compared with their wild-type controls. Histologic examinations revealed that glioma volume was negatively correlated with the number of macrophages and small cavities called microcysts. Overall, our results support the concept that macrophages alter brain tumor development through a TNF-dependent process that culminates in the formation of microcysts. This raises the question of whether anti-inflammatory drugs, such as those commonly administrated to patients with brain cancer, could interfere with antitumor mechanisms.

Characterization of microglia induced from mouse embryonic stem cells and their migration into the brain parenchyma

We derived microglia from mouse embryonic stem cells (ES cells) at very high density. Using the markers Mac1(+)/CD45(low) and Mac1(+)/CD45(high) to define microglia and macrophages, respectively, we show that Mac1(+) cells are induced by GM-CSF stimulation following neuronal differentiation of mouse ES cells using a five-step method. CD45(low) expression was high and CD45(high) expression was low on induced cells. We used a density gradient method to obtain a large amount of microglia-like cells, approximately 90% of Mac1(+) cells. Microglia-like cells expressed MHC class I, class II, CD40, CD80, CD86, and IFN-gammaR. The expression level of these molecules on microglia-like cells was barely enhanced by IFN-gamma. Intravenously transferred GFP(+) microglia derived from GFP(+) ES cells selectively accumulated in brain but not in peripheral tissues such as spleen and lymph node. GFP(+) cells were detected mainly in corpus callosum and hippocampus but were rarely seen in cerebral cortex, where Iba1, another marker of microglia, is primarily expressed. Furthermore, both GFP(+) and Iba1(+) cells exhibited a ramified morphology characteristic of mature microglia. These studies suggest that ES cell-derived microglia-like cells obtained using our protocol are functional and migrate selectively into the brain but not into peripheral tissues after intravenous transplantation.

Recovery of focal brain ischemia-induced behavioral dysfunction by intracerebroventricular injection of microglia

The function of microglia in the brain parenchyma is not fully understood. Occlusion of the middle cerebral artery (MCA) and reperfusion caused behavioral dysfunction with massive neuronal loss in the rat cerebral cortex and striatum. When exogenous microglia were microinjected into the intracerebroventricle (i.c.v.) during MCA occlusion, focal ischemia-induced behavioral dysfunction was significantly inhibited. At that time, many microglia migrated into the ischemic lesion, and microglia-derived neuron-like cells were barely detectable. These results suggest that exogenous microglia protect against focal ischemia-induced neurodegeneration and improve behavioral dysfunction.

Assessment of the Bioactivity of Antibodies against β-Amyloid Peptide in vitro and in vivo

The accumulation of the beta-amyloid peptide (Abeta) is a central event in the pathogenesis of Alzheimer's disease (AD). Abeta removal from the brain by immune therapy shows promising potential for the treatment of patients with AD, although the mechanisms of the antibody action are incompletely understood. In this study we compared the biological activities of antibodies raised against various Abeta fragments for Abeta reduction in vitro and in vivo. Antibodies against Abeta enhanced the uptake of Abeta42 aggregates up to 6-fold by primary microglial cells in vitro. The kinetics of Abeta42 uptake varied considerably among antibodies. Based on the activity to mediate Abeta42 uptake by microglial cells, we identified a bioactive antibody that significantly reduced Abeta42 levels in the brains of transgenic mice with neuronal expression of an AD-related mutated amyloid precursor protein. This effect depended on the epitopes recognized by the antibody. Our data suggest that the ability to facilitate Abeta42 uptake by primary microglia cells in vitro can be used to predict the biological activity of the antibody by passive immunization in vivo. This protocol may prove useful for the rapid validation of the activity of antibodies designed to be used in immune therapy of AD.

Aβ is targeted to the vasculature in a mouse model of hereditary cerebral hemorrhage with amyloidosis

The E693Q mutation in the amyloid beta precursor protein (APP) leads to cerebral amyloid angiopathy (CAA), with recurrent cerebral hemorrhagic strokes and dementia. In contrast to Alzheimer disease (AD), the brains of those affected by hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D) show few parenchymal amyloid plaques. We found that neuronal overexpression of human E693Q APP in mice (APPDutch mice) caused extensive CAA, smooth muscle cell degeneration, hemorrhages and neuroinflammation. In contrast, overexpression of human wild-type APP (APPwt mice) resulted in predominantly parenchymal amyloidosis, similar to that seen in AD. In APPDutch mice and HCHWA-D human brain, the ratio of the amyloid-beta40 peptide (Abeta40) to Abeta42 was significantly higher than that seen in APPwt mice or AD human brain. Genetically shifting the ratio of AbetaDutch40/AbetaDutch42 toward AbetaDutch42 by crossing APPDutch mice with transgenic mice producing mutated presenilin-1 redistributed the amyloid pathology from the vasculature to the parenchyma. The understanding that different Abeta species can drive amyloid pathology in different cerebral compartments has implications for current anti-amyloid therapeutic strategies. This HCHWA-D mouse model is the first to develop robust CAA in the absence of parenchymal amyloid, highlighting the key role of neuronally produced Abeta to vascular amyloid pathology and emphasizing the differing roles of Abeta40 and Abeta42 in vascular and parenchymal amyloid pathology.

Restricted diffusion in the brain of transgenic mice with cerebral amyloidosis

A prominent hallmark of Alzheimer's disease pathology is cerebral amyloidosis. However, it is not clear how extracellular amyloid-beta peptide (A beta) deposition and amyloid formation compromise brain function and lead to dementia. It has been argued that extracellular amyloid deposition is neurotoxic and/or that soluble A beta oligomers impair synaptic function. Amyloid deposits, by contrast, may affect diffusion properties of the brain interstitium with implications for the transport of endogenous signalling molecules during synaptic and/or extrasynaptic transmission. We have used diffusion-weighted magnetic resonance imaging to study diffusion properties in brains of young (6-month-old) and aged (25-month-old) APP23 transgenic mice and control littermates. Our results demonstrate that fibrillar amyloid deposits and associated gliosis in brains of aged APP23 transgenic mice are accompanied by a reduction in the apparent diffusion coefficient. This decrease was most pronounced in neocortical areas with a high percentage of congophilic amyloid and was not significant in the caudate putamen, an area with only modest and diffuse amyloid deposition. These findings suggest that extracellular deposition of fibrillar amyloid and/or associated glial proliferation and hypertrophy cause restrictions to interstitial fluid diffusion. Reduced diffusivity within the interstitial space may alter volume transmission and therefore contribute to the cognitive impairment in Alzheimer's disease.

Diverse microglial motility behaviors during clearance of dead cells in hippocampal slices

We used two-channel three-dimensional time-lapse fluorescence confocal imaging in live rat hippocampal slice cultures (1-7 days in vitro) to determine the motility behaviors of activated microglia as they engage dead and dying cells following traumatic brain tissue injury. Live microglia were labeled with a fluorescently conjugated lectin (IB(4)), and dead neurons were labeled with a membrane-impermeant fluorescent DNA-binding dye (Sytox Orange or To-Pro-3). Tissue injury during the slicing procedure induced neuronal death and microglial activation, but the density of dead cells diminished approximately 10-fold by 7 days in vitro as resident microglia cleared dead cells. In time-lapse movies (4-20 h long), activated microglia exhibited varying levels of motile and locomotory activity. The motility of microglia could change abruptly following contact by other microglia or death of nearby cells. When neighboring cells died, some microglia rapidly moved toward or extended a process to engulf the dead cell, consistent with a chemotactic signaling response. Dead cell nuclei usually were engulfed and carried along by highly motile and locomoting microglia. The mean time to engulfment was approximately 5 times faster for newly deceased cells (33 min) than for extant dead cells (160 min), suggesting that the efficacy of microglial phagocytosis in situ might vary with time after cell death or mode of cell death. These observations demonstrate that activated microglia are heterogeneous with respect to motile activity following traumatic tissue injury and further indicate that cell motility in situ is temporally regulated at the single cell level, possibly by direct cell-cell contact and by diffusible substances emanating from nearby dead cells.

Microglia/macrophage-specific protein Iba1 binds to fimbrin and enhances its actin-bundling activity

Ionized calcium binding adaptor molecule 1 (Iba1) is a microglia/macrophage-specific calcium-binding protein. Iba1 has the actin-bundling activity and participates in membrane ruffling and phagocytosis in activated microglia. In order to understand the Iba1-related intracellular signalling pathway in greater detail, we employed a yeast two-hybrid screen to isolate an Iba1-interacting molecule and identified another actin-bundling protein, L-fimbrin. In response to stimulation, L-fimbrin accumulated and co-localized with Iba1 in membrane ruffles induced by M-CSF-stimulation and phagocytic cups formed by IgG-opsonized beads in microglial cell line MG5. L-fimbrin was shown to associate with Iba1 in cell lysate of COS-7 expressing L-fimbrin and Iba1. By using purified proteins, direct binding of Iba1 to L-fimbrin was demonstrated by immunoprecipitation, glutathione S-transferase pull-down assays and ligand overlay assays. The binding of Iba1 was also found to increase the actin-bundling activity of L-fimbrin. These results indicate that Iba1 forms complexes with L-fimbrin in membrane ruffles and phagocytic cups, and suggest that Iba1 co-operates with L-fimbrin in modulating actin reorganization to facilitate cell migration and phagocytosis by microglia.