Neutral proteinases secreted by macrophages degrade basic protein: a possible mechanism of inflammatory demyelination

Willis Lecture: Biomarkers for Inflammatory White Matter Injury in Binswanger Disease Provide Pathways to Precision Medicine

Binswanger disease is the small vessel form of vascular cognitive impairment and dementia. Deposition of Alzheimer disease proteins can begin in midlife and progress slowly, whereas aging of the vasculature also can begin in midlife, continuing to progress into old age, making mixed dementia the most common type of dementia. Biomarkers facilitate the early diagnosis of dementias. It is possible to diagnose mixed dementia before autopsy with biomarkers for vascular disease derived from diffusor tensor images on magnetic resonance imaging and Alzheimer disease proteins, Aβ (amyloid β), and phosphorylated tau, in cerebrospinal fluid or in brain with positron emission tomography. The presence of vascular disease accelerates cognitive decline. Both misfolded proteins and vascular disease promote inflammation, which can be detected in cerebrospinal fluid by the presence of MMPs (matrix metalloproteinases), angiogenic growth factors, and cytokines. MMPs disrupt the blood-brain barrier and break down myelin, producing Binswanger disease's 2 main pathological features. Advances in detecting biomarkers in plasma will provide early detection of dementia and aided by machine learning and artificial intelligence, will enhance diagnosis and form the basis for early treatments.

The differentially expressed proteins related to clinical viral encephalitis revealed by proteomics

To screen out the prospective biomarkers of viral encephalitis (VE), analyze the biological process and signaling pathways involved by differentially expressed proteins (DEPs). A total of 11 cerebrospinal fluid (CSF) samples with VE and 5 with non-nervous system infection were used to perform label-free proteomic techniques. Then, the bioinformatic analysis of DEPs was applied by Interproscan software. Moreover, 73 CSF samples in the VE group and 53 in the control group were used to verify the changes of some DEPs by enzyme-linked immunosorbent assay (ELISA). Thirty-nine DEPs were identified, including 18 upregulated DEPs and 21 downregulated DEPs. DEPs were mainly enriched in cell adhesion molecules by Kyoto Encyclopedia of Genes and Genomes analysis pathway analysis. The DEPs related to axon tissue were obviously downregulated and the most significant downregulated proteins were neurexin 3, neurofascin, and neuroligin 2 (NLGN2). Moreover, the protein expression of NLGN2 in the VE group was significantly higher than that in the control group by ELISA. The correlation analysis of NLGN2 in the VE group revealed that there was a weak positive correlation with CSF protein and a weak negative correlation with CSF chloride. The clinical VE may be closely related to NLGN2 and the cell adhesion molecule pathway.

A silver lining of neuroinflammation: Beneficial effects on myelination

Myelin accelerates action potential conduction velocity and provides essential energy support for axons. Unfortunately, myelin and myelinating cells are often vulnerable to injury or disease, resulting in myelin damage, which in turn can lead to axon dysfunction, overt pathology and neurological impairment. Inflammation is a common component of trauma and disease in both the CNS and PNS and therefore an active inflammatory response is often considered deleterious to myelin health. While inflammation can certainly damage myelin, inflammatory processes also can positively affect oligodendrocyte lineage progression, myelin debris clearance, oligodendrocyte metabolism and myelin repair. In the periphery, inflammatory cascades can also augment myelin repair, including processes initiated by infiltrating immune cells as well as by local Schwann cells. In this review, various aspects of inflammation beneficial to myelin repair are discussed and should be considered when designing or implementing anti-inflammatory therapies for CNS and PNS injury involving myelinating cells.

The multiple sclerosis degradome: enzymatic cascades in development and progression of central nervous system inflammatory disease

An array of studies implicate different classes of protease and their endogenous inhibitors in multiple sclerosis (MS) pathogenesis based on expression patterns in MS lesions, sera, and/or cerebrospinal fluid (CSF). Growing evidence exists regarding their mechanistic roles in inflammatory and neurodegenerative aspects of this disease. Proteolytic events participate in demyelination, axon injury, apoptosis, and development of the inflammatory response including immune cell activation and extravasation, cytokine and chemokine activation/inactivation, complement activation, and epitope spreading. The potential significance of proteolytic activity to MS therefore relates not only to their potential use as important biomarkers of disease activity, but additionally as prospective therapeutic targets. Experimental data indicate that understanding the net physiological consequence of altered protease levels in MS development and progression necessitates understanding protease activity in the context of substrates, endogenous inhibitors, and proteolytic cascade interactions, which together make up the MS degradome. This review will focus on evidence regarding the potential physiologic role of those protease families already identified as markers of disease activity in MS; that is, the metallo-, serine, and cysteine proteases.

Cerebral microvessel responses to focal ischemia

Cerebral microvessels have a unique ultrastructure form, which allows for the close relationship of the endothelium and blood elements to the neurons they serve, via intervening astrocytes. To focal ischemia, the cerebral microvasculature rapidly displays multiple dynamic responses. Immediate events include breakdown of the primary endothelial cell permeability barrier, with transudation of plasma, expression of endothelial cell-leukocyte adhesion receptors, loss of endothelial cell and astrocyte integrin receptors, loss of their matrix ligands, expression of members of several matrix-degrading protease families, and the appearance of receptors associated with angiogenesis and neovascularization. These events occur pari passu with neuron injury. Alterations in the microvessel matrix after the onset of ischemia also suggest links to changes in nonvascular cell viability. Microvascular obstruction within the ischemic territory occurs after occlusion and reperfusion of the feeding arteries ("focal no-reflow" phenomenon). This can result from extrinsic compression and intravascular events, including leukocyte(-platelet) adhesion, platelet-fibrin interactions, and activation of coagulation. All of these events occur in microvessels heterogeneously distributed within the ischemic core. The panorama of acute microvessel responses to focal cerebral ischemia provide opportunities to understand interrelationships between neurons and their microvascular supply and changes that underlie a number of central nervous system neurodegenerative disorders.

Rapid differential endogenous plasminogen activator expression after acute middle cerebral artery occlusion

BACKGROUND AND PURPOSE

During focal cerebral ischemia, the microvascular matrix (ECM), which participates in microvascular integrity, is degraded and lost when neurons are injured. Loss of microvascular basal lamina antigens coincides with rapid expression of select matrix metalloproteinases (MMPs). Plasminogen activators (PAs) may also play a role in ECM degradation by the generation of plasmin or by MMP activation.

METHODS

The endogenous expressions of tissue-type plasminogen activator (tPA), urokinase (uPA), and PA inhibitor-1 (PAI-1) were quantified in 10-microm frozen sections from ischemic and matched nonischemic basal ganglia and in the plasma of 34 male healthy nonhuman primates before and after middle cerebral artery occlusion (MCA:O).

RESULTS

Within the ischemic basal ganglia, tissue uPA activity and antigen increased significantly within 1 hour after MCA:O (2P<0.005). tPA activity transiently decreased 2 hours after MCA:O (2P=0.01) in concert with an increase in PAI-1 antigen (2P=0.001) but otherwise did not change. The transient decrease in free tPA antigen was marked by an increase in the tPA-PAI-1 complex (2P<0.001). No significant relations to neuronal injury or intracerebral hemorrhage were discerned.

CONCLUSIONS

The rapid increase in endogenous PA activity is mainly due to significant increases in uPA, but not tPA, within the ischemic basal ganglia after MCA:O. This increase and an increase in PAI-1 coincided with latent MMP-2 generation and microvascular ECM degeneration but not neuronal injury.

Ischemic neuronal injury is ameliorated by astrocyte activation

BACKGROUND

The motivation of this study was to more precisely define the in vivo role of astrocytes in forebrain ischemia. Controversy exists in the literature as to whether they protect or injure neurons in this setting.

METHODS

Astrocytes in the rat hippocampus were disabled with stereotactic administration of a gliotoxin, ethidium bromide, 3 days prior to induction of forebrain ischemia. The extent of neuronal injury in this group was compared to a control category receiving intrahippocampal saline only.

RESULTS

Saline-injected animals demonstrated decreased hippocampal CA1 sector injury, and increased gliosis on the side of the injection compared to the contralateral side (P < 0.01) or ethidium bromide-treated animals (P < 0.05).

CONCLUSIONS

The results suggest that activated astrocytes are protective to neurons subjected to an ischemic insult. This may result from their ability to elaborate neurotrophic factors, buffer potassium and metabolize a variety of neurotransmitters.

Morphometric analysis of blood vessels in chronic experimental spinal cord injury: hypervascularity and recovery of function

A model of spinal cord trauma in guinea pigs, based on compression to a set thickness, was described previously. Compression injuries of the lower thoracic cord were produced in 11 anesthetized, adult guinea pigs, and the outcome monitored, using successive behavioral tests and morphometry of the lesion at 2-3 months. This report describes changes in the vascularity of the spinal cord, based on light microscopic analysis of 1 micron plastic transverse sections through the center of the lesion. Mean blood vessel density in these lesions was approximately twice that found in equivalent regions of normal, uninjured spinal cords, and hypervascularity of the white matter extended at least four spinal cord segments cranially and caudally from the lesion center. Capillary diameter distribution was significantly shifted to larger values and large perivascular spaces surrounded most capillaries and pre- and post-capillary vessels. Extent of hypervascularity was not correlated with the overall severity of the injury, but there was a significant positive correlation between the density of blood vessels in the outer 400 microns of the white matter and secondary loss of neurological function below the lesion, seen between one day and eight weeks after injury. This suggests that hypervascularization of the lesion is related to secondary pathological mechanisms in spinal cord injury, possibly inflammatory responses, that are relatively independent of the primary mechanical injury but more closely connected with loss and recovery of function.

Proteinase induced demyelination. An electrophysiological and histological study

The physiological and histological changes following injection of 10 microliter of proteinase K into the rat tibial nerve have been compared with those induced by proteinase K and specific inhibitor phenylmethylsulphonyl fluoride (PMSF) and also by rabbit experimental allergic neuritis (EAN) serum. Proteinase K and PMSF produced no significant change. Proteinase K alone resulted in progressive conduction block which was complete by about 8 h, and a slowing of motor conduction across the injection site. These changes were very similar to those induced by EAN serum. Histological examination showed early intramyelinic oedema and swelling of Schwann cell cytoplasm, followed by vesicular degeneration of myelin and removal by macrophages. At day 6 the demyelination was most prominent in a perivascular distribution. These changes share many similar features to those seen in EAN and are consistent with the postulate that the final common pathway for myelin destruction in the demyelinating diseases involves proteinases released by macrophages.

Vestibular neuronitis--serum and CSF virus antibody titer

The cerebrospinal fluid (CSF) findings of patients with vestibular neuronitis were virologically evaluated and discussed in contrast to those of herpes zoster. CSF samples obtained from seven patients with vestibular neuronitis, aged 28 to 55 years, were examined. The results were as follows: The CSF protein level in the vestibular neuronitis showed the peculiar change; i.e. its level was normal at the onset period of vertigo, but it rose to abnormal levels mostly in the period of two weeks, while the cell count remained normal throughout all phases of our study. Herpes simplex virus (HSV) type 1 IgG antibody titers measured by indirect immunofluorescent antibody technique (IF) in paired sera rose in one of the seven cases of vestibular neuronitis, but the antibody titers of the same virus in the CSF were not detected. HSV type 1 IgG antibody titers measured by IF in the CSF were detected in two of seven cases of vestibular neuronitis, but not significant. The ratio of EB virus (EBV) capsid antigen IgG antibody titers in CSF to that in serum ranged from 1:160 to 1:80 in vestibular neuronitis. There was no direct available evidence that vestibular neuronitis caused a break in blood-CSF barrier, an increase in IgG synthesis in the central nervous system or active infection with HSV, varicella zoster virus (VZV), or EBV. In this paper, we summarized the recent information on studies of the CSF and a latent herpes virus infection in order to give perspective to the pathogenesis of vestibular neuronitis.

Cleavage of rabbit myelin basic protein by plasmin: isolation and identification of the major products

Rabbit myelin basic protein (BP) was subjected to partial cleavage with plasmin, and 15 cleavage products were isolated by a combination of gel filtration and ion-exchange chromatography. Their identification was achieved by amino acid analysis and tryptic peptide mapping, supplemented in some instances by carboxy-terminal analyses with carboxypeptidases A, B, and Y and amino-terminal analyses with dipeptidyl aminopeptidase I. The results showed that major plasmic cleavage sites included the Lys89-Asn90, Lys133-Ser134, and Lys153-Leu154 bonds. Cleavages also occurred at the Arg31-His32, Lys53-Arg54, and Arg25-His26 bonds, but these appeared to be less extensive. A large number of additional peptides were produced in relatively low yield. The smaller of these were isolated from heterogeneous fractions by high-voltage electrophoresis-TLC. Amino acid analysis of these peptides showed that minor cleavage sites included the Arg9-His10, Lys13-Tyr14, Lys103-Gly104, Lys137-Gly138, Lys140-Gly141, and Arg160-Ser161 bonds. In spite of a lower selectivity toward peptide bonds in BP as compared with pepsin, cathepsin D, and thrombin, plasmin has the advantage over the former proteinases in that it does not cleave at or near the Phe44-Phe45 bond. Instead it cleaves at the Arg31-His32 and Lys53-Arg54 bonds, thus preserving the entire hydrophobic sequence Ile-Leu-Asp-Ser-Ile-Gly-Arg-Phe-Phe as well as short sequences to either side.

Ethidium bromide induced demyelination in the spinal cord of the cat

Small volumes of ethidium bromide were injected into the dorsal column of the spinal cord of cats. Oligodendrocytes and astrocytes showed morphological evidence of intoxication by ethidium bromide from 2 days after injection. However, apart from around the point of injection and the needle tract, demyelination did not occur until between 8 and 14 days. Both oligodendrocytes and astrocytes were absent from the demyelinated area at 14 days and all but a small number of demyelinated axons were remyelinated by Schwann cells. These cells first appeared in the lesion at 10 days, but axon association and myelination did not occur until 16 days. This model of experimental demyelination indicates once again that Schwann cell invasion of demyelinated areas in the CNS occurs if both oligodendrocytes and astrocytes are destroyed. None of the lesions in the present investigation were in continuity with root entry zones, indicating that this location is not a prerequisite for Schwann cell invasion of the CNS.

A theory of virus-induced demyelination in the Landry-Guillain-Barré syndrome

The Landry-Guillain-Barré syndrome (LGBS) is a demyelinating disorder of the peripheral nervous system frequently preceded by infection with common viruses. Most prevalent among these agents are herpesviruses, particularly Epstein-Barr virus (EBV) and cytomegalovirus (CMV). The specific role played by antecedent viral infection in the pathogenesis of the LGBS remains obscure. In this regard, recent studies of Marek's disease (MD) neuropathy, an avian herpesvirus-induced experimental model for the LGBS, may provide insight. The autoimmune pattern of demyelination seen in MD neuropathy is histopathologically indistinguishable from that seen in the LGBS. In this paper, a comprehensive theory is discussed regarding the pathogenetic mechanisms that may be operative in the LGBS.

Degradation of basic protein and Wolfgram protein in central nervous system by soluble enzymes of human peripheral polymorphonuclear leucocytes

The present communication describes the ability of soluble enzymes (SE) of peripheral polymorphonuclear leucocytes of control and multiple sclerosis (MS) patients to degrade major myelin proteins of MS and control myelin. MS and control SE degraded in situ both Wolfgram protein (WP) and basic protein (BP) of isolated myelin. No differences were found between the action of control and MS patients SE on myelin. However, significantly less degradation of BP and WP in control myelin compared to that in MS myelin was found. Only 30% of SE samples (both control and MS) degraded significant amounts of proteolipid protein in myelin. It is postulated that SE associated demyelination in MS may be a factor contributing to the demyelinating process.

Marek's disease: a natural model for the Landry-Guillain-Barré syndrome

The early lesions of Marek's disease in chickens are indistinguishable from those of the Landry-Guillain-Barré syndrome in human beings. Because of these similarities, and since the etiological agent (a herpesvirus) is known, Marek's disease can be meaningfully exploited as a model of the Landry-Guillain-Barré syndrome. Recent work in our laboratories has shown that the agent establishes latent infections in neuronal supporting cells and that affected birds mount cellular and humoral immunological reactions to peripheral nerve and myelin. Based on these findings, a working hypothesis for the pathogenesis of the disease is presented.

Neutral protease activity in lymphocytes of Lewis rats with acute experimental allergic encephalomyelitis

Lymphocytes from popliteal and inguinal lymph nodes of Lewis rats with acute EAE as a result of injection of lyophilized guinea pig myelin in Freund's complete adjuvant exerted strong proteolytic activity at neutral pH toward myelin basic protein. After injection of myelin the level of proteolytic activity remained about the same as that in lymphocytes from Freund's adjuvant-injected controls until about day 10 after injection, just before the onset of paralytic symptoms; then the proteolytic activity increased to approximately double its former level. Myelin basic protein was hydrolyzed by whole lymphocytes, but more activity was unmasked by homogenization. Similar results were also obtained using lymphocytes from thymus of EAE and control animals. Lymphocytes with high levels of proteolytic activity were not absorbed by glass wool, did not stain with neutral red, nor did they phagocytose antibody-coated sheep red blood cells. Thymus and lymph node lymphocytes cleaved myelin basic protein to three major peptides and a fourth minor peptide, while spleen lymphocytes hydrolyzed basic protein at only one point resulting in two peptides whose molecular weights added up to that of myelin basic protein. The protease activity was inhibited by 5 X 10(-3) M p-chloromercuribenzoate and by phenylmethyl sulfonyl fluoride, TPCK, and soybean trypsin inhibitor, therefore the enzymatic activity probably depends on a serine residue and a sulfhydryl group. The bulk of the enzymatic activity is mostly membrane bound with the highest specific activity and total activity contained in a lysosomal-mitochondrial fraction. In view of the infiltration of lymphocytes into the brain substance in acute EAE, it is suggested that these cells may contribute to the destruction of myelin which is usually attributed to the monocyte or macrophage.

Multiple sclerosis: immunochemical studies on the demyelinating serum factor

Sera from patients with multiple sclerosis (MS) frequently produce demyelination of central nervous system tissue cultures. The nature of the factors responsible for demyelination is not as yet clearly established. However, several authors previously reported, in in vivo and in vitro models, demyelinating activity in IgG fractions isolated from sera and cerebrospinal fluid of MS patients14,42,48. We found the demyelinating activity of MS sera to be extremely labile to conventional biochemical treatments. Therefore, we isolated IgG from MS sera by absorption with staphylococcal protein A. Protein A binds specifically IgG1. IgG2 and IgG4. With this method we were able to remove most of the IgG, leaving only a small percentage, most probably IgG3, in the sera. Isolated IgG fractions from several sera of MS patients in the presence of human complement actively demyelinated central nervous system tissue cultures. Although a small, but significant, decrease in demyelinating activity could be observed in most of the sera absorbed in most of the sera absorbed with protein A, the majority of the demyelinating activity could not be removed by this treatment. From these studies, it appears that at least the majority of demyelinating activity in MS sera is not associated with IgG1, IgG2 or IgG4. If IgG is responsible for demyelination, IgG3 will most likely be the active factor.