Reactive microgliosis engages distinct responses by microglial subpopulations after minor central nervous system injury

Microglia are bone marrow-derived cells that constitute a facultative macrophage population when activated by trauma or pathology in the CNS. Endogenous CNS-resident microglia as well as exogenous (immigrant) bone marrow-derived cells contribute to reactive microgliosis, raising fundamental questions about the cellular composition, kinetics, and functional characteristics of the reactive microglial cell population. Bone marrow chimeric mice reconstituted with green fluorescent protein-expressing (GFP(+)) donor bone marrow cells were subjected to entorhinal cortex lesion, resulting in selective axonal degeneration and a localized microglial reaction in the hippocampus. Flow cytometric evaluation of individually dissected hippocampi differentiated immigrant GFP(+) microglia from resident GFP(-) microglia (CD11b(+)CD45(dim)) and identified a subset of mainly resident CD11b(+) microglia that was induced to express CD34. The proportion of immigrant GFP(+) microglia (CD11b(+)CD45(dim)) increased signficantly by 3 and 5 days postlesion and reached a maximum of 13% by 7 days. These cells expressed lower CD11b levels than resident microglia, forming a distinct subpopulation on CD11b/CD45 profiles. The proportion of CD34(+)CD11b(+) microglia was significantly increased at 3 days postlesion but had normalized by 5 and 7 days, when the microglial reaction is known to be at its maximum. Our results show that distinct subpopulations of microglia respond to minor CNS injury. The heterogeneity in microglial response may have functional consequences for repair and possibly therapy.     

Neuronal apoptosis does not correlate with dementia in HIV infection but is related to microglial activation and axonal damage

To characterize the distribution of apoptotic neurons and their relationships with the stage of disease, a history of HIV-dementia, and the degree of productive HIV infection, microglial activation and axonal damage, we examined the brains of 40 patients. Samples of frontal and temporal cortex, basal ganglia and brain stem were taken post-mortem from 20 patients with AIDS (including three with HIV-dementia, and eight with cognitive disorders that did not fulfil the criteria for HIV-dementia), 10 HIV-positive asymptomatic cases and 10 seronegative controls. Neuronal apoptosis was demonstrated by in situ end labelling in 18 AIDS cases and two pre-AIDS cases; a single apoptotic neuron was present in the temporal cortex of a control. Semiquantitative evaluation showed that the severity of neuronal apoptosis in the cerebral cortex correlated with the presence of cerebral atrophy, but not with a history of HIV dementia. There was no global quantitative correlation between neuronal apoptosis and HIV encephalitis or microglial activation. However, there was some topographical correlation between these changes. In the basal ganglia, apoptotic neurons were much more abundant in the vicinity of multinucleated giant cells and/or p24 expressing cells. Microglial activation was constantly present in these areas. Axonal damage was identified using beta-amyloid-precursor protein (betaAPP) immunostaining in 17 AIDS and eight pre-AIDS brains. Although no global quantitative correlation could be established between axonal damage and neuronal apoptosis there was an obvious topographic correlation supporting the view that axonal damage, either secondary to local microglial activation or due to the intervention of systemic factors, may also contribute to neuronal apoptosis.     

Central nervous system infarction related to cocaine abuse

BACKGROUND: Cocaine use in the United States has reached epidemic proportions, and increased availability of "crack" since 1983 has noticeably increased the incidence of neurovascular complications. In this report, we examine the relationship between cocaine use and ischemic infarct. SUMMARY OF COMMENT: This study reports 18 cases of ischemic cerebrovascular events, which occurred among 15 men and three women aged 21-47 years who were evaluated in a 2-year period. Clinical presentations include thirteen cases with hemispheric infarcts, two brain stem strokes, two anterior spinal artery infarcts, and one with both hemispheric and cerebellar infarcts. Nine patients smoked crack, four snorted cocaine, and three injected it intravenously. In two cases, the route of administration could not be determined. Two patients died, but the other survived with various degrees of neurological deficit. CONCLUSIONS: Traditional risk factors for strokes were identified in only six patients, suggesting that these factors are not necessary for the occurrence of a cocaine-related infarct. Multiple overlapping mechanisms may be responsible, including vasospasm, sudden onset of hypertension, myocardial infarction with cardiac arrhythmias, increased platelet aggregation, and vasculitis.     

RIM3gamma is a postsynaptic protein in the rat central nervous system

RIMs (Rab3-interacting molecules) are synaptic proteins essential for neural transmission and plasticity. RIM1alpha has been implicated in membrane trafficking and regulation of secretory vesicle exocytosis in eukaryotic cells. Little information is as yet available on RIM3gamma. In the present study, we investigated the cellular expression, subcellular distribution, and possible functions of RIM3gamma in the rat CNS. Rim3gamma cDNA was subcloned and the protein expressed in vitro for the generation and purification of a rabbit anti-RIM3gamma polyclonal antibody. In situ hybridization histochemistry, immunohistochemistry, and immunoelectron microscopy were performed to map expression of the mRNA and protein in the rat CNS. Our results indicated widespread distribution of RIM3gamma in diverse CNS neuronal cell types. The mRNA was found mainly in the cell bodies, whereas the protein immunoreactivity was localized chiefly to neuronal dendrites and to the postsynaptic densities as visualized under the light and electron microscope. This postsynaptic placement of RIM3gamma is distinct from the presynaptic localization of RIM1alpha but may contribute to regulating synaptic transmission and plasticity. The identification of RIM3gamma as a postsynaptic protein has functional implications for CNS synapse functions.     

Central nervous system effects of current and emerging multiple sclerosis-directed immuno-therapies

Objective

To review the direct and indirect effects on the central nervous system (CNS) of systemically administered immuno-modulatory therapies in use or under evaluation for the relapsing forms of multiple sclerosis (MS).

Methods

We summarize data published by our own lab and by others that delineate the effects of such therapies on in vitro neural cell cultures and in animal model-based systems.

Results

The long-approved therapies, interferon β (IFNβ) and glatiramer acetate (GA), do not readily access the CNS. These agents can still indirectly have an effect on disease-related immune regulatory and effector functions within the CNS by modulating the properties of systemic immune cells that migrate to this compartment. Such immune cells could interact with perivascular and innate immune cells that are involved in immune regulation and with cells that are either targets of the disease process (oligodendrocytes, neurons) and/or are involved with repair (progenitor cells). Newer agents reported to favorably impact on relapse frequency in MS include the sphingosine-1-phosphate agonist, fingolimod, and the lipophilic statin, simvastatin. Both agents access the CNS and thus represent examples of agents that could directly impact on disease-relevant injury and repair process within the CNS.

Conclusions

The observations reviewed in this report regarding indirect and direct effects of immuno-modulatory agents on the CNS indicate the need to understand and monitor the neurobiologic effects of such therapies.     

Proteolipid protein cannot replace P0 protein as the major structural protein of peripheral nervous system myelin

The central nervous system (CNS) of terrestrial vertebrates underwent a prominent molecular change when proteolipid protein (PLP) replaced P₀ protein as the most abundant protein of CNS myelin. However, PLP did not replace P₀ in peripheral nervous system (PNS) myelin. To investigate the possible consequences of a PLP to P₀ shift in PNS myelin, we engineered mice to express PLP instead of P₀ in PNS myelin (PLP‐PNS mice). PLP‐PNS mice had severe neurological disabilities and died between 3 and 6 months of age. Schwann cells in sciatic nerves from PLP‐PNS mice sorted axons into one‐to‐one relationships but failed to form myelin internodes. Mice with equal amounts of P₀ and PLP had normal PNS myelination and lifespans similar to wild‐type (WT) mice. When PLP was overexpressed with one copy of the P₀ gene, sciatic nerves were hypomyelinated; mice displayed motor deficits, but had normal lifespans. These data support the hypothesis that while PLP can co‐exist with P₀ in PNS myelin, PLP cannot replace P₀ as the major structural protein of PNS myelin. GLIA 2015;63:66–77     

NOD样受体热蛋白结构域相关蛋白3炎性小体在常见中枢神经系统疾病中作用的研究进展

NOD样受体热蛋白结构域相关蛋白3（NLRP3）炎性小体是一种多蛋白复合物,可导致有活性的胱天蛋白酶1（caspase-1）的形成,以及白细胞介素（IL）-1β、IL-18等炎症因子的成熟和释放。研究表明,NLRP3炎性小体在多种中枢神经系统（CNS）疾病的发病机制中扮演着重要角色。该文围绕NLRP3炎性小体的结构特征、表达分布、激活及作用机制进行综述,并阐述其在常见CNS疾病中发挥的作用,以期为CNS疾病的防治提供新的研究思路。     

Glial cell transplanatation and remyelination of the central nervous system

Glial cell transplantation has proved to be a powerful tool in the study of glial cell biology. The extent of myelination achieved by transplanting myelin-producing cells into the CNS of myelin mutants, or into focal demyelinating lesions has raised hope that such a strategy may have therapeutic applications. Oligodendrocytes or Schwann cells could be used for repair. It is likely that the immature stages of the oligodendrocyte lineage have the best phenotypic characteristics for remyelination when transplanted, either as primary cells or as immortalized cells or cell lines. Prior culturing and growth factor treatment provides opportunities to expand cell populations before transplantation as dissociated cell preparations. Cell lines are attractive candidates for transplantation, but the risk of transformation must be monitored. The application of this technique to human myelin disorders may requier proof that migration, division and stable remyelination of axons by the tranplanted cells can occur in the presence of gliosis and inflammation.     

Optogenetic manipulation of astrocytes from synapses to neuronal networks: A potential therapeutic strategy for neurodegenerative diseases

Astrocytes are the most widespread and heterogeneous glial cells in the central nervous system and key regulators for brain development. They are capable of receiving neurotransmitters produced by synaptic activities and regulating synaptic functions by releasing gliotransmitters as part of the tripartite synapse. In addition to communicating with neurons at synaptic levels, astrocytes can integrate into inhibitory neural networks to interact with neurons in neuronal circuits. Astrocytes are closely related to the pathogenesis and pathological processes of neurodegenerative diseases (NDs). Recently, optogenetics has now been applied to reveal the function of astrocytes in physiology and pathology. Herein, we discuss the possibility whether optogenetics could be used to control the release of gliotransmitters and regulate astrocytic membrane channels. Thus, the capability of modulating the bidirectional interactions between astrocytes and neurons in both synaptic and neuronal networks via optogenetics is evaluated. Furthermore, we discuss that manipulating astrocytes via optogenetics might be an effective way to investigate the potential therapeutic strategy for NDs.     

Microglial responses after phagocytosis: Escherichia coli bioparticles,but not cell debris or amyloid beta,induce matrix metalloproteinase-9 secretion in cultured rat primary microglial cells

Upon infection or brain damage, microglia are activated to play roles in immune responses, including phagocytosis and soluble factor release. However, little is known whether the event of phagocytosis could be a trigger for releasing soluble factors from microglia. In this study, we tested if microglia secrete a neurovascular mediator matrix metalloproteinase-9 (MMP-9) after phagocytosis in vitro. Primary microglial cultures were prepared from neonatal rat brains. Cultured microglia phagocytosed Escherichia coli bioparticles within 2 hr after incubation and started to secrete MMP-9 at around 12 hr after the phagocytosis. A TLR4 inhibitor TAK242 suppressed the E. coli-bioparticle-induced MMP-9 secretion. However, TAK242 did not change the engulfment of E. coli bioparticles in microglial cultures. Because lipopolysaccharides (LPS), the major component of the outer membrane of E. coli, also induced MMP-9 secretion in a dose–response manner and because the response was inhibited by TAK242 treatment, we assumed that the LPS-TLR4 pathway, which was activated by adhering to the substance, but not through the engulfing process of phagocytosis, would play a role in releasing MMP-9 from microglia after E. coli bioparticle treatment. To support the finding that the engulfing step would not be a critical trigger for MMP-9 secretion after the event of phagocytosis in microglia, we confirmed that cell debris and amyloid beta were both captured into microglia via phagocytosis, but neither of them induced MMP-9 secretion from microglia. Taken together, these data demonstrate that microglial response in MMP-9 secretion after phagocytosis differs depending on the types of particles/substances that microglia encountered.     

Do early lesions affect cell death in the central nervous system? A study on the effects of early cerebellar hemispherectomy in rats

Cell death patterns in the lateral and interposed nuclei were compared in control rats and rats in whom a unilateral cerebellar hemispherectomy was performed at day 2 of life. Both groups were studied between days 2 and 20 of life. Pyknotic cells and live neuronal and glial cells were counted from Nissl stained sections. After correction of these values, pyknotic to live cell ratios were calculated. In the lateral nucleus of normal rats, around 14-28 pyknotic cells per 1,000 live cells occurred from day 2 to day 12. Thereafter this value decreased, and from day 16 less than 3 pyknotic/1,000 live cells were observed. In the interposed nuclei, 18-28 pyknotic cells/1,000 live cells occurred at day 2, and from this age onward values gradually decreased. At day 20 values ranged around 1.6/1,000. After unilateral cerebellar hemispherectomy, values in both nuclei began to decrease as early as from day 8. Results from the present study strongly suggest that these cells are prevented from dying because they find an aberrant synaptic target in the ipsilateral red nucleus. Our results demonstrate that early lesions interfere with the regulation of fundamental processes of neuro-ontogeny.     

The relevance of symmetric and asymmetric cell divisions to human central nervous system diseases

During development of the embryonic central nervous system (CNS), large numbers of neurons and glia are generated from the neuroepithelium and its progenitor derivatives as a result of symmetric and asymmetric cell divisions. We describe the biology of symmetric and asymmetric cell divisions in the CNS as gleaned from animal models, and discuss the relevance of these processes to human CNS development and disease.     

Central nervous system lesions in hypomclanosis of Ito: an MRI and pathological study

A severe form of hypomelanosis of Ito is reported, which presented as fetal macrocephaly and neonatal epileptic encephalopathy. Lymphocyte karyotypes were normal. MRI showed an absence of delineation between cortical grey matter and white matter. The prominent neuropathological finding was an abnormal cortical morphogenesis, with the co-existence of cells migrating normally and cells exhibitingarrêt en route or even the complete absence of migration. Intense astrocytic reaction with moderate dystrophie features was prescrit. Juxtaposition of two migration behaviours in the neural cells paralleled the cutaneous findings and reinforced the hypothesis of a genetic chimerism.     

Experimental strategies to promote central nervous system remyelination in multiple sclerosis: Insights gained from the Theiler's virus model system

The Destruction of central nervous system (CNS) myelin, the lipid-rich insulator surrounding axons in the mammalian brain and spinal cord, is the primary pathological finding in multiple sclerosis. Myelin loss can result in a significant clinical deficit, and was originally thought to be permanent, similar to axonal destruction. However, myelin regeneration is now an established phenomenon in both human disease and animal models of CNS demyelination. In this review, the concept of remyelination in demyelinating deseases such as multiple sclerosis is discussed and the usefulness of animal models of CNS demyelination in developing experimental strategies to promote remyelination is examined Special emphasis is given to the Theiler's murine encephalomyelitis model, which has been the primary animal model used to investigate therapies designed specifically to stimulate myelin repair. © 1995 Wiley-Liss, Inc.     

Localization of annexin II in the paranodal regions and Schmidt-Lanterman incisures in the peripheral nervous system

Annexin II (AX II) is a member of the family of calcium-dependent actin- and phospholipid-binding proteins implicated in numerous intracellular functions such as signal transduction, membrane trafficking, and mRNA transport, as well as in the regulation of membrane/cytoskeleton contacts and extracellular functions. AX II is expressed in the central nervous system (CNS) and is upregulated in some pathological conditions. However, expression and localization of this protein in the peripheral nervous system (PNS) is still uncertain. In the present study, we examined the expression and distribution of AX II in the PNS. By western blot analysis, we found that a higher level of AX II was present in sciatic nerve homogenates than in brain homogenates. RT-PCR of total RNA from rat sciatic nerves revealed that AX II was synthesized within the nerves. Immunohistological analysis showed the characteristic distribution of AX II in Schmidt-Lanterman incisures (SLI) as well as in the paranodal regions. Localization of AX II in the PNS was examined in two mutant mouse models, shiverer and cerebroside sulfotransferase knockout mice, both of which show increased numbers of SLI. The paranodal axo-glial junction is also disrupted in the latter. Interestingly, the staining intensities of AX II in these regions were increased markedly in both mutants, suggesting that not only the numbers but also AX II content in each incisure and paranodal loop were affected. From its characteristic distribution and molecular features, AX II may be important for myelin function in the PNS.     

Macrophages and glia participate in the removal of apoptotic neurons from the Drosophila embryonic nervous system

Cell death in the Drosophila embryonic central nervous system (CNS) proceeds by apoptosis, which is revealed ultrastructurally by nuclear condensation, shrinkage of cytoplasmic volume, and preservation of intracellular organelles. Apoptotic cells do not accumulate in the CNS but are continuously removed and engulfed by phagocytic haemocytes. To determine whether embryonic glia can function as phagocytes, we studied serial electron microscopic sections of the Drosophila CNS. Apoptotic cells in the nervous system are engulfed by a variety of glia including midline glia interface (or longitudinal tract) glia, and nerve root glia. However, the majority of apoptotic cells in the CNS are engulfed by subperineurial glia in a fashion similar to the microglia of the vertebrate CNS. A close proximity between macrophages and subperineurial glia suggests that glia may transfer apoptotic profiles to the macrophages. Embryos affected by the maternal-effect mutation Bicaudal-D have no macrophages. In the absence of macrophages, most apoptotic cells are retained at the outer surfaces of the CNS, and subperineurial glia contain an abundance of apoptotic cells. Some apoptotic cells are expelled from the CNS, which suggests that the removal of apoptotic cells can occur in the absence of macrophages. The number of subperineurial glia is unaffected by changes in the rate of neuronal apoptosis. © 1995 Wiley-Liss, Inc.     

NMDA receptors amplify mossy fiber synaptic inputs at frequencies up to at least 750 Hz in cerebellar granule cells

Neuronal integration of high‐frequency signals is important for rapid information processing. Cerebellar mossy fiber axons (MFs) can fire action potentials (APs) at frequencies of more than one kilohertz. However, it is unclear whether and how the postsynaptic cerebellar granule cells (GCs) are able to process these high‐frequency MF inputs. Here, we measured AP firing in GCs during high‐frequency MF stimulation and show that GC firing frequency increased non‐linearly when MF stimulation frequency was increased from 100 to 750 Hz. To investigate the mechanisms enabling such high‐frequency signaling, we analyzed the role of N‐methyl‐d ‐aspartate receptors (NMDARs), which have been implicated in synaptic signaling at lower frequencies. Application of D‐2‐amino‐5‐phosphonopentanoic acid (APV), a potent inhibitor of NMDARs, strongly impaired the GC firing frequency during high‐frequency MF stimulation. APV had no significant effect on single excitatory postsynaptic potentials (EPSPs) or currents (EPSCs) evoked at 1 Hz at resting membrane potentials. However, the time course of EPSCs evoked at 1 Hz at depolarized potentials or following high‐frequency MF stimulation was accelerated by APV. Thus, our results show that NMDAR‐mediated currents amplify high‐frequency MF inputs by prolonging the time courses of synaptic inputs, thereby causing greater synaptic summation of inputs. Hence, NMDARs support the integration of MF synaptic input at frequencies up to at least 750 Hz. Synapse 70:269–276, 2016. © 2016 Wiley Periodicals, Inc.