Biomedical subjects

Ingo Bechmann

Publications and source records attributed to Ingo Bechmann.

33 records · Page 2Linked to original sources

PubMed2004

Inflammatory response after neurosurgery.

Investigation into the inflammatory response in the central nervous system (CNS) is a rapidly growing field, and a vast amount of information on this topic has accumulated over the past two decades. Inflammation is a particularly interesting issue in the (traditionally non-regenerating) CNS, owing to its dual role in worsening or improving regeneration and functional outcome in certain circumstances. This paper reviews the current literature on the interactions between the immune system and the CNS in physiological and pathological states. The first part will provide an overview of the cellular and molecular components of CNS inflammation, this being followed by a discussion of the concept of systemic immunodepression after neurotrauma and neurosurgery. Finally, the delicate balance of immune responses in the CNS, with an emphasis on the beneficial effects of inflammation and possible therapeutic options, will be discussed.

Animals↗

PubMed2004

Production of neuroprotective NGF in astrocyte-T helper cell cocultures is upregulated following antigen recognition.

Astrocytic production of nerve growth factor (NGF) is increased during inflammation of the central nervous system (CNS). Here we show that cell-cell interaction between primary murine astrocytes and myelin basic protein (MBP)-specific T cell receptor (TCR) transgenic Th1 and Th2 cells significantly increased production of NGF. This upregulation was found to be dependent on antigen recognition. Neutralization of cytokines produced in cocultures did not affect NGF production. This novel finding suggests a neuroprotective role of astrocytes during T cell-mediated inflammation in the CNS.

Animals↗

PubMed2004

RDP58, a novel immunomodulatory peptide, ameliorates clinical signs of disease in the Lewis rat model of acute experimental autoimmune encephalomyelitis.

The therapeutic value of a novel immunomodulatory peptide, RDP58, was investigated in the acute experimental autoimmune encephalomyelitis (EAE) model of Multiple Sclerosis (MS). RDP58 is a 10-amino acid peptide with two major activities: (i) inhibition of inflammatory TH1 cytokines such as TNFalpha, IFNgamma, and IL12 and (ii) up-regulation of heme oxygenase-1 (HO-1) expression. Experiments in which EAE-induced Lewis rats exhibit an acute monophasic episode of disease demonstrated that a single intracerebroventricular injection of RDP58 is effective in preventing clinical signs of disease. The therapeutic effect on disease activity was observed at all pre-onset administration times and at all doses tested. Consistent with disease activity in vivo, RDP58-treated animals had reduced cellular infiltration within the spinal cord along with decreased TNFalpha expression levels. The data in this proof of concept study support the premise that RDP58, as a platform molecule, may be a promising new therapeutic intervention in autoimmune and inflammatory diseases.

Animals↗

PubMed2004

Entorhinal cortex lesion in the mouse induces transsynaptic death of perforant path target neurons.

Entorhinal cortex lesion (ECL) is a well described model of anterograde axonal degeneration, subsequent sprouting and reactive synaptogenesis in the hippocampus. Here, we show that such lesions induce transsynaptic degeneration of the target cells of the lesions pathway in the dentate gyrus. Peaking between 24 and 36 hours post-lesion, dying neurons were labeled with DeOlmos silver-staining and antisera against activated caspase 3 (CCP32), a downstream inductor of programmed cell death. Within caspase 3-positive neurons, fragmented nuclei were co-localized using Hoechst 33342 staining. Chromatin condensation and nuclear fragmentation were also evident in semithin sections and at the ultrastructural level, where virtually all caspase 3-positive neurons showed these hallmarks of apoptosis. There is a well-described upregulation of the apoptosis-inducing CD95/L system within the CNS after trauma, yet a comparison of caspase 3-staining patterns between CD95 (Ipr)- and CD95L (gld)-deficient with non-deficient mice (C57/bl6) provided no evidence for CD95L-mediated neuronal cell death in this setting. However, inhibition of NMDA receptors with MK-801 completely suppressed caspase 3 activation, pointing to glutamate neurotoxicity as the upstream inducer of the observed cell death. Thus, these data show that axonal injury in the CNS does not only damage the axotomized neurons themselves, but can also lethally affect their target cells, apparently by activating glutamate-mediated intracellular pathways of programmed cell death.

Animals↗

PubMed2003

Bone marrow-derived cells expressing green fluorescent protein under the control of the glial fibrillary acidic protein promoter do not differentiate into astrocytes in vitro and in vivo.

Differentiation of bone marrow (BM) cells into astroglia expressing the glial fibrillary acidic protein (GFAP) has been reported in vitro and after intracerebral or systemic BM transplantation. In contrast, recent data suggest that astrocytic differentiation does not occur from BM-derived cells in vivo. Using transgenic mice that express the enhanced green fluorescent protein (GFP) under the control of the human glial fibrillary acidic protein (GFAP) promoter, we investigated the potential of adult murine BM-derived cells to differentiate into macroglia. In the brains of GFAP-GFP transgenic mice, astrocytes were brightly fluorescent from the expression of GFP. When BM from these animals was transplanted into lethally irradiated wild-type animals, the transgene was detected in the reconstituted hematopoietic system, but no GFP expression was found in the nervous system. In contrast, GFAP-GFP neuroectodermal anlage grafted into adult wild-type striatum gave rise to GFP-expressing astrocytes. Because cerebral ischemia has been suggested to promote the differentiation of BM-derived cells into astrocytes, BM chimeric mice were subjected to focal cerebral ischemia. No GFP-positive cells were found in the ischemic or contralateral hemispheres of these brains. Even after direct injection of GFAP-GFP transgenic BM cells into wild-type striatum, no GFP-expressing astroglia were detected. To test the hypothesis that the in vitro environment might be more permissible for astroglial differentiation, we cultured BM from mice that constitutively express GFP, BM cells expressing GFP from a retroviral vector, and BM from GFAP-GFP transgenic mice on astrocytes and on organotypic hippocampal slices. In all experimental paradigms, BM-derived cells were found to differentiate into ramified microglia but not into GFAP-expressing astrocytes.

Animals↗

PubMed2003

Modification of microglia function protects from lesion-induced neuronal alterations and promotes sprouting in the hippocampus.

Primary neuronal destruction in the central nervous system triggers rapid changes in glial morphology and function, after which activated glial cells contribute to secondary neuronal changes. Here we show that, after entorhinal cortex lesion, activation of microglia, but not other glial cells, leads to massive secondary dendritic changes of deafferentiated hippocampal neurons. Blocking of microglial activation in vivo reduced this secondary neuronal damage and enhanced regenerative axonal sprouting. In contrast, abolishing astrocytes or oligodendroglia did not result in specific neuronal changes. Furthermore, primary damage leads to an interleukin 1beta up-regulation, which is attenuated by the immuno-modulator transforming growth factor beta1, whereas tumor necrosis factor alpha is not affected. Modification of microglial activity following denervation of the hippocampus protects neurons from secondary dendritic alterations and therefore enables their reinnervation. These data render activated microglia a putative therapeutic target during the course of axonal degeneration.

Animals↗

PubMed2003

IDO (indolamine 2,3-dioxygenase) expression and function in the CNS.

From an immunological perspective the placenta is an allograft and therefore requires a special immune suppressive status termed immune privilege. Other organs of the body, which possess poor regenerative capacity share this special status, e.g. the brain, the eye and the gonads. The biological function of immune privilege in all these tissues is to protect them from inflammation-mediated injury. The mechanism maintaining immune privilege are poorly understood and are apparently site-specific. In the placenta, inhibition of IDO leads to spontaneous abortion, showing the crucial role of this enzyme for the maintenance of immune privilege. By catabolizing extracellular tryptophan IDO inhibits local T cell proliferation thereby preventing placental rejection. Here, we show that this mechanism can also be active in suppressing inflammatory responses in the CNS, where inflammations must be tightly regulated to prevent the loss of irreplaceable neurons. Employing RT-PCR and Western blot analysis we could show that, upon activation with the pro-inflammatory cytokine interferon-gamma, astrocytes and microglia are capable of expressing IDO in vitro and in vivo. To test the functional capacity of IDO in the CNS, we performed blockade experiments using actively induced experimental autoimmune encephalomyelitis (EAE), a T cell-mediated autoimmune disease which correlates to the human disease multiple sclerosis (MS). Inhibition of IDO activity by daily subcutaneous administration of the specific IDO inhibitor 1-methyl-DL-tryptophan during EAE significantly exacerbates EAE, shown by comparing clinical disease scores. Thus, local expression of IDO during inflammation is apparently a self-protection mechanism which limits antigen-specific immune responses in the CNS.

Animals↗

PubMed2002

Widespread hypoxia-inducible expression of HIF-2alpha in distinct cell populations of different organs.

Cellular responses to oxygen are increasingly recognized as critical in normal development and physiology, and are implicated in pathological processes. Many of these responses are mediated by the transcription factors HIF-1 and HIF-2. Their regulation occurs through oxygen-dependent proteolysis of the alpha subunits HIF-1alpha and HIF-2alpha, respectively. Both are stabilized in cell lines exposed to hypoxia, and recently HIF-1alpha was reported to be widely expressed in vivo. In contrast, regulation and sites of HIF-2alpha expression in vivo are unknown, although a specific role in endothelium was suggested. We therefore analyzed HIF-2alpha expression in control and hypoxic rats. Although HIF-2alpha was not detectable under baseline conditions, marked hypoxic induction occurred in all organs investigated, including brain, heart, lung, kidney, liver, pancreas, and intestine. Time course and amplitude of induction varied between organs. Immunohistochemistry revealed nuclear accumulation in distinct cell populations of each tissue, which were exclusively non-parenchymal in some organs (kidney, pancreas, and brain), predominantly parenchymal in others (liver and intestine) or equally distributed (myocardium). These data indicate that HIF-2 plays an important role in the transcriptional response to hypoxia in vivo, which is not confined to the vasculature and is complementary to rather than redundant with HIF-1.

Animals↗

PubMed2002

Brain mitochondrial uncoupling protein 2 (UCP2): a protective stress signal in neuronal injury.

Mitochondrial uncoupling proteins (UCPs) can dissociate oxidative phosphorylation from respiration, and they appear to be critical for energy balance. One of these proteins, UCP2, is also expressed in neurons of subcortical brain regions of healthy subjects. Here, we report on the protective role of UCP2 in brain injury by revealing its early induction after lesions and its inverse relationship with activation of an apoptotic signal, caspase 3, in wild-type and UCP2 overexpressing transgenic mice.

Animals↗

PubMed2002

Uncoupling protein 2 (UCP2) lowers alcohol sensitivity and pain threshold.

Abuse of ethanol is a major risk factor in medicine, in part because of its widespread effect on the activity of the central nervous system, including behavior, pain, and temperature sensation. Uncoupling protein 2 (UCP2) is a mitochondrial protonophore that regulates cellular energy homeostasis. Its expression in mitochondria of axons and axon terminals of basal forebrain areas suggests that UCP2 may be involved in the regulation of complex neuronal responses to ethanol. We employed a paradigm in which acute exposure to ethanol induces tolerance and altered pain and temperature sensation. In UCP2 overexpressing mice, sensitivity to ethanol was decreased compared to that of wild-type animals, while UCP2 knockouts had increased ethanol sensitivity. In addition, UCP2 expression was inversely correlated with the impairment of pain and temperature sensation induced by ethanol. Taken together, these results indicate that UCP2, a mitochondrial uncoupling protein previously associated with peripheral energy expenditure, is involved in the mediation of acute ethanol exposure on the central nervous system. Enhancement of UCP2 activation after acute alcohol consumption might decrease the time of recovery from intoxication, whereas UCP2 inhibition might decrease the tolerance to ethanol.

Alcohol Drinking↗

PubMed2002

Pore membrane and/or filament interacting like protein 1 (POMFIL1) is predominantly expressed in the nervous system and encodes different protein isoforms.

We have isolated and characterized a novel differentially spliced gene predominantly expressed in the nervous system, which encodes protein isoforms with significant homology to the alpha-actinin protein superfamily, the Caenorhabditis elegans UNC-53 protein and weak homology to the nuclear membrane protein POM121. Similar to POM121 the primary structures show a hydrophobic region that is likely to form one or more adjacent transmembrane segment(s). Indirect immunofluorescence with antibodies against a synthetic peptide gave staining of the nucleus. Target experiments with EGFP (enhanced green fluorescent protein)-fusion proteins confirmed the nuclear localization. Two further members of this gene family could be isolated. All three pore membrane and/or filament interacting like (POMFIL) genes are differentially expressed in neuronal tumor cell lines. In 40% of tested primary neuroblastomas expression of POMFIL1 is strongly reduced and after brain injury POMFIL1 protein expression is upregulated, indicating that POMFIL1 is involved in the process of neuron growth and regeneration, as well as in neural tumorigenesis.

Alternative Splicing↗

PubMed2002

Lack of tumor necrosis factor-related apoptosis-inducing ligand but presence of its receptors in the human brain.

Apoptosis mediated by members of the tumor necrosis factor (TNF)-nerve growth factor superfamily plays a crucial role in the interaction of the nervous and the immune system. On the one hand, it is involved in the defense mechanisms of the brain, the immune privilege. On the other hand, it is involved in the induction of glial-neuronal cell death in neuroinflammatory diseases. Here, we show that in contrast to the other known death ligands, TNF-related apoptosis-inducing ligand (TRAIL) is not constitutively expressed in the human brain, whereas both apoptosis-mediating and apoptosis-blocking TRAIL receptors are found on neurons, astrocytes, and oligodendrocytes. Thus, the brain differs from other immune-privileged organs, such as the placenta, with the TRAIL receptor-TRAIL system not being part of the immune privilege of the brain. Conversely, this death receptor-ligand system might well play an important role in T cell-mediated autoimmune diseases of the CNS such as multiple sclerosis.

Antibody Specificity↗

PubMed2002

Astrocyte-induced T cell elimination is CD95 ligand dependent.

The brain has an intrinsic capacity to remove infiltrating T cells by inducing apoptosis. However, the pathways and cellular components driving this process are still under debate. Astrocytes seem to play an important role because they colocalize with apoptotic lymphocytes in vivo and induce apoptosis of transformed T cells in vitro. Since we previously demonstrated the expression of the death ligand CD95L (APO-1L/FasL) on astrocytes in the brain, we wanted to know whether nontransformed astrocytes induce cell death in nontransformed T cells, reflecting the in vivo situation and, if so, whether CD95/CD95 ligand interaction is important. T cell apoptosis measured by Annexin V binding and DNA fragmentation was significantly lower using CD95 ligand-deficient (gld) astrocytes compared to nondeficient controls. Moreover, neutralizing anti-CD95 ligand antibody reduced astrocyte-induced T cell apoptosis. Thus, adult astrocytes are capable of inducing the apoptotic death of T cells by involving the CD95/CD95 ligand pathway without undergoing cell death in vitro. Since astrocytic end-feet contribute to the formation of the blood-brain barrier, this depletion mechanism may play an important role as the first line of defense in the brain.

Animals↗

PubMed2002

Neuroprotection by T-cells depends on their subtype and activation state.

This study analyzes how the antigen specificity, the subtype, and the activation state of T cells modulate their recently discovered neuroprotective potential. We assessed the prevention from neuronal damage in organotypic entorhinal-hippocampal slice cultures after co-culture with Th1 and Th2 cells either specific for myelin basic protein (MBP) or ovalbumin (OVA). We found that MBP-specific Th2 cells were the most effective in preventing central nervous system (CNS) tissue from secondary injury. This neuroprotective T cell effect appears to be mediated by soluble factors. After stimulation with phorbol myristate acetate and ionomycin, all T cells were most effective in preventing neuronal death. Our data show that the T cell subtype and activation state are important features in determining the neuroprotective potential of these cells.

Animals↗

PubMed2002

Comparison of neuronal density and subfield sizes in the hippocampus of CD95L-deficient (gld), CD95-deficient (lpr) and nondeficient mice.

During brain development, the majority of neurons undergo programmed cell death. It is now clear that caspases are involved in this process of selective induction of neuronal apoptosis, yet the signals for this caspase activation remain undefined. As an upstream activator of these enzymes, the death receptor CD95 (Fas, APO1) was recently shown on neurons in the cornu ammonis (CA)2 and CA3 hippocampal subfields of early postnatal mice and rats. In vitro, cortical neuroblast cells are susceptible to CD95 ligand (CD95L, FasL, APO-1 L)-induced apoptosis. It was therefore suggested that the CD95/CD95L system is involved in neuronal apoptosis during hippocampal development. We therefore performed a blinded study comparing field size and neuronal density in the hippocampi of p20 CD95-deficient (lpr), CD95L-deficient (gld) and C57 mice. Whereas field sizes did not differ significantly between these strains, paired Mann-Whitney analyses revealed an increased number of neurons in the CA2 regions of CD95-deficient mice (P = 0.008), and minor, yet at 1% nonsignificant, differences between gld, lpr and C57 strains in the CA1 and CA3 regions. However, joint comparison of the three strains using the Kruskal-Wallis test rendered all differences insignificant. We conclude that the CD95/CD95L system is either not involved, or can be replaced by alternate mechanisms in the control of neuronal populations during hippocampal development.

Animals↗