Microglia-derived elastase produces a low-molecular-weight plasminogen that enhances neurite outgrowth in rat neocortical explant cultures

The Nuclear Translocation of Heme Oxygenase-1 in Human Diseases

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in the degradation of heme to generate carbon monoxide (CO), free iron and biliverdin, which could then be converted to bilirubin by biliverdin reductase. HO-1 exhibits cytoprotective effects of anti-apoptosis, anti-oxidation, and anti-inflammation via these byproducts generated during the above process. In the last few years, despite the canonical function of HO-1 and possible biological significance of its byproducts, a noncanonical function, through which HO-1 exhibits functions in diseases independent of its enzyme activity, also has been reported. In this review, the noncanonical functions of HO-1 and its translocation in other subcellular compartments are summarized. More importantly, we emphasize the critical role of HO-1 nuclear translocation in human diseases. Intriguingly, this translocation was linked to tumorigenesis and tumor progression in lung, prostate, head, and neck squamous cell carcinomas and chronic myeloid leukemia. Given the importance of HO-1 nuclear translocation in human diseases, nuclear HO-1 as a novel target might be attractive for the prevention and treatment of human diseases.

Physiological Interactions between Microglia and Neural Stem Cells in the Adult Subependymal Niche

Microglia are the prototypical innate immune cells of the central nervous system. They constitute a unique type of tissue-resident mononuclear phagocytes which act as glial cells. Elegant experiments in the last few years have revealed the origin, extraordinary molecular diversity, and phenotypic plasticity of these cells and how their potential relates to both immune and non-immune actions in the normal and diseased brain. Microglial cells originate in the yolk sac and colonize the brain during embryogenesis, playing a role in neural development and later in adult brain function. Neurogenesis continues after birth in discrete areas of the mammalian brain sustained by the postnatal persistence of neural stem cells in specific neurogenic niches. Recent data indicate that microglial cells are distinct cellular elements of these neurogenic niches where they regulate different aspects of stem cell biology. Interestingly, microglial and neural stem cells are specified very early in fetal development and persist as self-renewing populations throughout life, suggesting potential life-long interactions between them. We aim at reviewing these interactions in one neurogenic niche, the subependymal zone.

Monocytic elastase-mediated apolipoprotein-E degradation: Potential involvement of microglial elastase-like proteases in apolipoprotein-E proteolysis in brains with Alzheimers disease

Impaired clearance of soluble Aβ (amyloid-β) promotes Aβ aggregation in brains with Alzheimer's disease (AD), while apolipoprotein-E (ApoE) in microglia mediates Aβ clearance. We studied the protease responsible for ApoE(4) degradation in human peripheral monocyte extracts, which are from the same lineage as microglia. We detected the hydrolytic activity for ApoE(4) in high-salt extracts with 2 M NaCl and found that the activity was inhibited by a serine protease inhibitor and an elastase-specific inhibitor, but not by other protease inhibitors. The extracts exhibited higher activity for the elastase substrate, and we followed the activity with ion-exchange and gel-filtration chromatography. Through silver staining, we partially purified a protein of 28 kDa, which was clarified as elastase by liquid chromatography-tandem mass spectrometry. These observations suggest that elastase is the key protease for ApoE(4) degradation. We also detected ApoE(4) hydrolytic activity in high-salt extracts in mouse microglial (BV-2) cell lysates, and showed that the ApoE(4) fragments by the BV-2 extracts differed from the fragments by the monocyte extracts. Though the ApoE(4) degradation by the extracts was not inhibited with elastase-specific inhibitors, it was inhibited by an elastase-specific monoclonal antibody, suggesting that elastase-like proteases in microglia differ from those of monocytes. Immunohistochemistry revealed that both elastase and ApoE were expressed in the senile plaques of brains with AD. In vitro studies also disclosed the localization of elastase in the microglial cell line, BV-2. Our results suggest that elastase-like proteases in the microglial cells surrounding Aβ plaques are responsible for ApoE degradation in the brain.

Factors affecting clot lysis rates in patients with spontaneous intraventricular hemorrhage

BACKGROUND AND PURPOSE

In the treatment of severe intraventricular hemorrhage (IVH), thrombolytic use and clot size are known to influence clot lysis rates. We evaluated the effect of other variables on IVH clot lysis rates among patients treated with recombinant tissue-type plasminogen activator or placebo.

METHODS

One hundred patients with IVH and intracerebral hemorrhage volume <30 mL requiring emergency external ventricular drainage from 2 multicenter trials were treated with intraventricular administration of recombinant tissue-type plasminogen activator (n=78; 53 males, 25 females) or placebo (n=22; 7 males, 15 females). IVH volume was quantified daily by head CT. A segmented linear regression using an optimized spline knot for each patient was fit. Random effects linear regression was used to estimate the effect of prespecified patient characteristics on clot lysis rates over the first 6 days.

RESULTS

Stability IVH volumes were larger in males (N=60; 54 ± 5 mL) than females (N=40; 36 ± 5 mL; P=0.01). Intraventricular thrombolytic treatment was associated with an increase in clot lysis rate of 14.6% of stability IVH volume/day before the spline knot compared with the placebo group (P<0.001). After adjustment for thrombolytic, higher baseline serum plasminogen and lower baseline platelet count were independently associated with an increase in clot lysis of 1.28%/day per 10-g/dL increase (P<0.001) and 0.70% /day per 10×10(3)/uL decrease (P<0.001) before the knot, respectively.

CONCLUSIONS

Although thrombolysis remains the major determinant of IVH clot lysis rate, higher baseline serum plasminogen and lower platelet count also predict faster clot lysis. Further studies are needed to confirm whether plasminogen availability and thrombus structure impact IVH clot removal. Clinical Trial Registration- URL: http://clinicaltrials.gov. Unique identifier: NCT00650858.

Role of purinergic receptors in CNS function and neuroprotection

The purinergic receptor family contains some of the most abundant receptors in living organisms. A growing body of evidence indicates that extracellular nucleotides play important roles in the regulation of neuronal and glial functions in the nervous system through purinergic receptors. Nucleotides are released from or leaked through nonexcitable cells and neurons during normal physiological and pathophysiological conditions. Ionotropic P2X and metabotropic P2Y purinergic receptors are expressed in the central nervous system (CNS), participate in the synaptic processes, and mediate intercellular communications between neuron and gila and between glia and other glia. Glial cells in the CNS are classified into astrocytes, oligodendrocytes, and microglia. Astrocytes express many types of purinergic receptors, which are integral to their activation. Astrocytes release adenosine triphosphate (ATP) as a "gliotransmitter" that allows communication with neurons, the vascular walls of capillaries, oligodendrocytes, and microglia. Oligodendrocytes are myelin-forming cells that construct insulating layers of myelin sheets around axons, and using purinergic receptor signaling for their development and for myelination. Microglia also express many types of purinergic receptors and are known to function as immunocompetent cells in the CNS. ATP and other nucleotides work as "warning molecules" especially by activating microglia in pathophysiological conditions. Studies on purinergic signaling could facilitate the development of novel therapeutic strategies for disorder of the CNS.

In vitro proliferation of axotomized rat facial nucleus-derived activated microglia in an autocrine fashion

Transection of rat adult facial nerve leads to an increase in the number of activated microglia in the facial nucleus (FN), with a peak in proliferation 3 days after transection. To investigate the characteristics of these activated microglia, we isolated the cells with high purity from axotomized FN (axFN) 3 days after transection according to the previously reported procedure for explant culture. The isolated microglia exhibited immunocytochemical properties similar to those in vivo, and their numbers increased approximately five- to sevenfold over a period of 10 days without the addition of any mitogens, suggesting that self-reproduction was occurring. Actually, the microglia actively incorporated bromodeoxyuridine (BrdU) and strongly expressed an S-phase-specific protein marker, proliferating cell nuclear antigen (PCNA). To examine the mechanism underlying this proliferation, the expression of the mitogens and specific receptors of the microglia were analyzed in conditioned medium (CM) and cells. Macrophage-colony stimulating factor (M-CSF) and granulocyte macrophage-CSF (GM-CSF) were detected in the CM as well as in the cells. Their specific receptor proteins, c-Fms and GMCSFRalpha, were also detected in the cell homogenate. These proliferating microglia were not found to produce deleterious factors for neurons. In summary, the microglia isolated from the axFN were found to be proliferative in an autocrine fashion and to have some cellular properties in common with those observed in vivo.

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.

Microglia in health and disease

Microglia, one of three glial cell types in the central nervous system (CNS), play an important role as resident immunocompetent and phagocytic cells in the CNS in the event of injury and disease. It was del Rio Hortega in 1927 who determined that microglia belong a distinct glial cell type apart from astrocytes and oligodendrocytes, and since 1970s there has been wide recognition that microglia are immune effectors in the CNS that respond to pathological conditions and participate in initiation and progression of neurological disorders including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and acquired immune deficiency syndrome dementia complex by releasing potentially cytotoxic molecules such as proinflammatory cytokines, reactive oxygen intermediates, proteinases and complement proteins. There is also evidence to suggest that microglia are capable of secreting neurotrophic or neuron survival factors upon activation via inflammation or injury. It is thus timely to review current status of knowledge on biology and immunology of microglia, and consider new directions of investigation on microglia in health and disease.

Microglia and astrocytes may participate in the shaping of visual callosal projections during postnatal development

In the adult cat, axons running through the corpus callosum interconnect the border between the visual cortical areas 17 and 18 (A17 and A18) of both hemispheres. This specific pattern emerges during postnatal development, under normal viewing conditions (NR), from the elimination of initially exuberant callosal projections. In contrast, if the postnatal visual experience is monocular from birth (MD), juvenile callosal projections are stabilised throughout A17 and A18. The present study aimed at using such a model in vivo to find indications of a contribution of glial cells in the shaping of projections in the developing CNS through interactions with neurones, both in normal and pathological conditions. As a first stage, the distribution and the morphology of microglial cells and astrocytes were investigated from 2 weeks to adulthood. Microglial cells, stained with isolectin-B4, were clustered in the white matter below A17 and A18. Until one month, these clustered cells displayed an ameboid morphology in NR group, while they were more ramified in MD animals. Their phenotype thus depends on the postnatal visual experience, which indicates that microglial cells may interact with axons of visual neurones. It also suggests that they may differentially contribute to the elimination and the stabilisation of juvenile exuberant callosal fibres in NR and MD animals respectively. Beyond one month, microglial cells were very ramified in both experimental groups. Astrocytes were labelled with a GFAP-antibody. The distributions of connexins 43 (Cx43) and 30 (Cx30), the main proteic components of gap junction channels in astrocytes, were also investigated using specific antibodies. Both in NR and MD groups, until 1 month, GFAP-positive astrocytes and Cx43 were mainly localised within the subcortical white matter. Then GFAP, Cx43 and Cx30 stainings progressively appeared within the cortex, throughout A17 and A18 but with a differential laminar expression according to the age. Thus, the distributions of both astrocytes and connexins changed with age; however, the monocular occlusion had no visible effect. This suggests that astrocytes may contribute to the postnatal development of neuronal projections to the primary visual cortex, including visual callosal projections.

Ceramide-enhanced urokinase-type plasminogen activator (uPA) release is mediated by protein kinase C in cultured microglia

As described previously, a relatively high dose of neurotrophins increased the release of urokinase-type plasminogen activator (uPA) from cultured microglia. This biological response is suggested to be caused by ceramide, which is a metabolite of nerve growth factor low-affinity receptor (NGFRp75)-associated sphingomyelin turnover. Therefore, in the present study, we examined the effect of ceramide on the release of uPA from cultured microglia. Treatment of the cells with permeable C8-ceramide (D-erythro-Sphingosine, N-octanoyl-) enhanced uPA release in a dose-dependent manner. This effect of C8-ceramide was mimicked by treatment with bacterial sphingomyelinase. A pharmacological study using a specific PKC activator, phorbol-12-myristate-13-acetate, and a protein kinase C (PKC) inhibitor, bisindolylmaleimide, showed that PKC activation is required in order to release uPA from ceramide-stimulated microglia as well as from nonstimulated microglia. Further study using a specific conventional PKC (cPKC) activator, 1-oleoyl-2-acetyl-sn-glycerol (OAG), and a specific cPKC inhibitor, Gö 6976, suggested that PKC-delta and/or -epsilon is involved in uPA release. As opposed to the apoptotic pathway, however, no activation of c-Jun N-terminal kinase and nuclear factor kappa B was observed in C8-ceramide-stimulated microglia. The findings suggest that uPA release from microglia is regulated by a mechanism in which PKC-delta and/or -epsilon are activated and further signals are transduced subsequently.

Tissue plasminogen activator gene expression in multiple sclerosis brain tissue

Recent studies have implicated tissue-type plasminogen activator (tPA) in neurodegeneration. We studied multiple sclerosis (MS) brain tissue for tPA gene and protein expression in comparison with reference tissue, by in situ hybridisation and immunohistochemistry. MS is characterised by demyelination in the central nervous system. In this study, neuronal cell bodies in MS brain showed high expression of tPA mRNA and protein, while in reference brains, staining for protein and mRNA expression were very low in neurons and mostly restricted to blood vessel walls. In MS, there was an additional staining of mononuclear cells within perivascular cuffs and foamy macrophages within demyelinating plaques. In view of evidence that the final process of demyelination in MS is thought to be enzyme-mediated, our work suggests the involvement of tPA and by inference plasmin, in the demyelinating process. Blocking tPA or plasmin activity may be a potentially beneficial therapeutic approach in MS.

Neurotrophins regulate the function of cultured microglia

Although the physiological role of neurotrophins in neuronal development and survival has been extensively investigated, their role in glial cell physiology remains to be elucidated. In the present study, we investigated the effects of neurotrophins on cultured microglia from newborn rat brain. All of the neurotrophins tested nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4), increased the secretion of plasminogen and urokinase type-plasminogen activator and specific activity of acid phosphatase, but suppressed the release of constitutively-produced and lipopolysaccharide-stimulated nitric oxide (NO) from microglia. The reverse transcription-polymerase chain reaction, immunocytochemical staining, and Western blotting revealed that cultured microglia express Trk A, B, and C, and low-affinity NGF receptor, LNGFRp75. Neurotrophin was found to phosphorylate Trk A and B, and the neurotrophin-induced enhancement of plasminogen-secretion was suppressed by protein kinase inhibitor, K252a. Furthermore, neurotrophins caused an activation of transcription factor, NF-kappaB. These results indicate that the neurotrophin family regulate the function of microglia through Trk and/or LNGFRp75-mediated signal transduction.

Molecular cloning of a novel brain-specific serine protease with a kringle-like structure and three scavenger receptor cysteine-rich motifs

In order to find serine proteases specifically expressed in brain, we designed degenerate mixed primers for consensus sequences of serine protease domains. By PCR utilizing the primers, we have cloned a novel sequence from reverse transcripts of total RNA of mouse brain and used it as a probe to screen a mouse brain cDNA library. Overlapping cDNAs encoding a precursor of a novel brain specific serine protease (BSSP-3) were cloned. DNA insert of the longest clone consisted of 2614-bp with an entire open reading frame encoding a secretory/membrane-anchored precursor protein consisting of 761 amino acids (AA) which may be processed to yield an active enzyme of 245 AA. As found in known serine proteases, BSSP-3 enzyme domain contained a catalytic triad which consists of AA residues essential for the enzyme activity. In the upstream region of the enzyme domain that resides at C-terminus of the precursor protein, there are, from N-terminus to downstream, a sequence similar to a kringle structure and three repetitive ones highly similar to the scavenger receptor cysteine-rich (SRCR) motifs. Northern blot analysis demonstrated that mBSSP-3 mRNA was specifically expressed in the mouse brain, lung and kidney. We concluded that a novel brain serine protease, BSSP-3, is a new member of kringle and SRCR superfamilies.

The amino-terminal region of amyloid precursor protein is responsible for neurite outgrowth in rat neocortical explant culture

We have previously shown that secreted forms of beta-amyloid precursor protein (APP(s)s) promote neurite outgrowth in embryonic rat neocortical explant culture. To determine the region of APP(s) responsible for its biological activity, we produced both amino- and carboxyl-terminal regions of APP(s) using a yeast expression system. The purified fragment corresponding to the amino-terminal region (NAPP) enhanced neurite outgrowth of neocortical explants, but the carboxyl-terminal region fragment did not. The neurite-promoting activity of full length APP(s) and NAPP was blocked by the antibody, 22C11, specific for the amino-terminal region, and the 16-mer peptide of epitope for 22C11 also enhanced neurite outgrowth. However, the 17-mer peptide which contains RERMS sequence did not enhance the neurite outgrowth, but promoted the survival of neocortical neurons in dissociated culture. These findings suggested that the amino-terminal region is responsible for the neurite-promoting activity of APP(s)s.

mRNAs encoding urokinase-type plasminogen activator and plasminogen activator inhibitor-1 are elevated in the mouse brain following kainate-mediated excitation

Urokinase-type plasminogen activator (uPA) is an inducible extracellular serine protease implicated in fibrinolysis and in tissue remodeling. Recently, we have localized uPA mRNA strictly in limbic structures and the parietal cortex of the adult mouse brain. Here, we tested whether the systemic treatment of mice with kainic acid (KA), an amino acid inducing limbic seizures, could elevate in the brain mRNAs encoding uPA and its specific inhibitor, plasminogen activator inhibitor-1 (PAI-1), a major antifibrinolytic agent. Brain sections encompassing the hippocampus were tested through in situ hybridization using radiolabeled riboprobes specific for the two mRNA species. The results showed that KA greatly enhanced both mRNA species in sites of limbic structures and cortex. However, in the hypothalamus and brain blood vessels only PAI-1 mRNA was elevated. Those were also the only two locations where PAI-1 mRNA was detected in the non-treated control brain, although at a low level. For both mRNAs, KA enhancement was first evident 2-4 h after treatment, and it was most prolonged in the hippocampal area, where prominent hybridization signals persisted for three days. Here, both mRNAs were initially elevated in the hilar region of the dentate gyrus and in the molecular and oriens layers; however, PAI-1 mRNA became evident throughout the area, while uPA mRNA became especially pronounced in the CA3/CA4 subfield. In the cortex both mRNA types were induced, but only uPA mRNA was elevated in the retrosplenial cortex, and also in the subiculum. In the amygdaloid complex, uPA mRNA was restricted to the basolateral nucleus, whereas PAI-1 mRNA was seen throughout the structure, however, excluding this nucleus. These data show that seizure activity enhances the expression of uPA and PAI-1 genes in the brain; the patterns of enhancement suggest that the protease and its inhibitor may act in brain plasticity in synchrony, however, also independently of each other. Furthermore, the results suggest that by elevating PAI-1 mRNA in brain blood vessels, limbic seizures generate a risk for stroke.

Neurotrophic effect of hepatocyte growth factor on central nervous system neurons in vitro

Although the expression of hepatocyte growth factor (HGF) and its receptor, proto-oncogene c-met, has been demonstrated in the central nervous system (CNS), the function of HGF in the CNS was not fully understood. In the present studies, we determined the effects of HGF on neuronal development in neocortical explant and mesencephalic neurons obtained from embryonic rat brain. HGF clearly enhanced neurite outgrowth in neocortical explants. In the mesencephalic culture, the number of tyrosine hydroxylase (TH)-positive neurons was significantly higher in the HGF-treated wells and the neurites of the TH-positive neurons appear to be more developed. Moreover, the dopamine uptake into mesencephalic neurons was also enhanced by HGF treatment, indicating that HGF promotes the survival and/or maturation of mesencephalic dopaminergic neurons. In both neocortical explants and mesencephalic neurons, c-met autophosphorylation was induced by HGF and MAP kinase activation was also detected in the neocortical explant. Furthermore, Western blot analysis of the cultured CNS cells revealed that HGF was expressed mainly in microglia. These results suggest that HGF from microglia has neurotrophic activity on the CNS neurons and plays significant roles in the development of the CNS.

Low levels of plasminogen in cerebrospinal fluid after intraventricular haemorrhage: a limiting factor for clot lysis?

The aim of this study was to measure plasminogen in the cerebrospinal fluid (CSF) of control neonates with no infection or haemorrhage and in infants who had suffered intraventricular haemorrhage (IVH). A chromogenic substrate method was used. The 16 reference infants had a median CSF plasminogen level of 0.74% of that of normal adult plasma (range 0.17-1.1%). The 11 infants with IVH had a median CSF plasminogen level of 0.55% of normal adult plasma (range 0-4.4%). Six of the IVH infants went on to develop permanent hydrocephalus despite the use of intraventricular plasminogen activators. Endogenous fibrinolysis and the potential for fibrinolytic treatment in the CSF may be limited by low concentrations of plasminogen, and administration of recombinant plasminogen may assist attempts to clear intraventricular blood clots.