Citrullinated human and murine MOG35-55 display distinct biophysical and biochemical behavior

The peptide spanning residues 35 to 55 of the protein myelin oligodendrocyte glycoprotein (MOG) has been studied extensively in its role as a key autoantigen in the neuroinflammatory autoimmune disease multiple sclerosis. Rodents and nonhuman primate species immunized with this peptide develop a neuroinflammatory condition called experimental autoimmune encephalomyelitis, often used as a model for multiple sclerosis. Over the last decade, the role of citrullination of this antigen in the disease onset and progression has come under increased scrutiny. We recently reported on the ability of these citrullinated MOG35-55 peptides to aggregate in an amyloid-like fashion, suggesting a new potential pathogenic mechanism underlying this disease. The immunodominant region of MOG is highly conserved between species, with the only difference between the murine and human protein, a polymorphism on position 42, which is serine in mice and proline for humans. Here, we show that the biophysical and biochemical behavior we previously observed for citrullinated murine MOG35-55 is fundamentally different for human and mouse MOG35-55. The citrullinated human peptides do not show amyloid-like behavior under the conditions where the murine peptides do. Moreover, we tested the ability of these peptides to stimulate lymphocytes derived from MOG immunized marmoset monkeys. While the citrullinated murine peptides did not produce a proliferative response, one of the citrullinated human peptides did. We postulate that this unexpected difference is caused by disparate antigen processing. Taken together, our results suggest that further study on the role of citrullination in MOG-induced experimental autoimmune encephalomyelitis is necessary.

Immunofluorescence studies on the expression of the SARS-CoV-2 receptors in human term placenta

Until September 2021, the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2; COVID-19) pandemic caused over 217 million infections and over 4.5 million deaths. In pregnant women, the risk factors for the need of intensive care treatment are generally the same as in the overall population. Of note, COVID-19-positive women deliver earlier than COVID-19-negative women, and the risk for severe neonatal and perinatal morbidity and mortality is significantly higher. The probability and pathways of vertical transmission of the virus from the pregnant woman to the fetus are highly controversial. Recent data have shown that 54 (13%) of 416 neonates born to COVID-19-positive women were infected. Here, we investigated term placentas collected before the SARS-CoV-2 pandemic and studied the main COVID-19 receptors angiotensin-converting enzyme 2 (ACE2), transmembrane protease serine subtype 2 (TMPRSS2), as well as neuropilin 1 (NRP1). We performed real-time PCR and immunofluorescence on cryosections in combination with markers for syncytiotrophoblast, endothelial cells, macrophages and stromal cells. The PCR studies showed expression of both the truncated delta form of ACE2, which does not bind the COVID-19 spike protein, and the long form. The ACE2 antibody used does not distinguish between the two forms. We did not observe expression of the canonical SARS-CoV-2 entry machinery on syncytio- and cytotrophoblast. ACE2 and TMPRSS2 are co-expressed in a subpopulation of stromal cells, which in part are CD68-positive macrophages. NRP1 is localized to endothelial cells. In sum, the term placenta is not an organ that directly favors vertical transmission of COVID-19; however, microtraumas and placentitis may weaken its barrier function.

Rapidly progressive amyotrophic lateral sclerosis is associated with microglial reactivity and small heat shock protein expression in reactive astrocytes

AIMS

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disease characterized by progressive loss of motor neurons, muscle weakness, spasticity, paralysis and death usually within 2-5 years of onset. Neuroinflammation is a hallmark of ALS pathology characterized by activation of glial cells, which respond by upregulating small heat shock proteins (HSPBs), but the exact underlying pathological mechanisms are still largely unknown. Here, we investigated the association between ALS disease duration, lower motor neuron loss, TARDNA-binding protein 43 (TDP-43) pathology, neuroinflammation and HSPB expression.

METHODS

With immunohistochemistry, we examined HSPB1, HSPB5, HSPB6, HSPB8 and HSP16.2 expression in cervical, thoracic and sacral spinal cord regions in 12 ALS cases, seven with short disease duration (SDD), five with moderate disease duration (MDD), and ten age-matched controls. Expression was quantified using ImageJ to examine HSP expression, motor neuron numbers, microglial and astrocyte density and phosphorylated TDP-43 (pTDP-43+) inclusions.

RESULTS

SDD was associated with elevated HSPB5 and 8 expression in lateral tract astrocytes, while HSP16.2 expression was increased in astrocytes in MDD cases. SDD cases had higher numbers of motor neurons and microglial activation than MDD cases, but similar levels of motor neurons with pTDP-43+ inclusions.

CONCLUSIONS

Increased expression of several HSPBs in lateral column astrocytes suggests that astrocytes play a role in the pathogenesis of ALS. SDD is associated with increased microgliosis, HSPB5 and 8 expression in astrocytes, and only minor changes in motor neuron loss. This suggests that the interaction between motor neurons, microglia and astrocytes determines neuronal fate and functional decline in ALS.

Heat shock proteins are differentially expressed in brain and spinal cord: implications for multiple sclerosis

Multiple sclerosis (MS) is a chronic neurodegenerative disease characterized by demyelination, inflammation and neurodegeneration throughout the central nervous system. Although spinal cord pathology is an important factor contributing to disease progression, few studies have examined MS lesions in the spinal cord and how they differ from brain lesions. In this study we have compared brain and spinal cord white (WM) and grey (GM) matter from MS and control tissues, focusing on small heat shock proteins (HSPB) and HSP16.2. Western blotting was used to examine protein levels of HSPB1, HSPB5, HSPB6, HSPB8 and HSP16.2 in brain and spinal cord from MS and age-matched non-neurological controls. Immunohistochemistry was used to examine expression of the HSPs in MS spinal cord lesions and controls. Expression levels were quantified using ImageJ. Western blotting revealed significantly higher levels of HSPB1, HSPB6 and HSPB8 in MS and control spinal cord compared to brain tissues. No differences in HSPB5 and HSP16.2 protein levels were observed, although HSPB5 protein levels were higher in brain WM versus GM. In MS spinal cord lesions, increased HSPB1 and HSPB5 expression was observed in astrocytes, and increased neuronal expression of HSP16.2 was observed in normal-appearing GM and type 1 GM lesions. The high constitutive expression of several HSPBs in spinal cord and increased expression of HSPBs and HSP16.2 in MS illustrate differences between brain and spinal cord in health and upon demyelination. Regional differences in HSP expression may reflect differences in astrocyte cytoskeleton composition and influence inflammation, possibly affecting the effectiveness of pharmacological agents.

Sex hormone binding globulin deficiency due to a homozygous missense mutation

CONTEXT

SHBG is known as the major sex steroid binding protein in plasma, and it regulates the bioavailability of both T and estradiol levels required for effects on target tissues. We identified a man with an undetectable SHBG concentration in combination with low total T. He presented with a 7-year history of muscle weakness, fatigue, and a low libido.

OBJECTIVES

To determine the cause of the SHBG deficiency, we employed both genetic analysis of the SHBG gene and transgene SHBG expression.

RESULTS

Genetic analysis identified a novel homozygous missense mutation that was predicted to be deleterious for protein function. Transgene expression showed that the mutation resulted in a block in SHBG secretion accompanied by increased expression of the endoplasmic reticulum molecular chaperone HSPA5. The mutation results in accumulation of the mutant SHBG within the cell and failure to secrete the mutant protein. Screening of family members identified one sister who was also deficient for SHBG.

CONCLUSIONS

We have identified a family with a missense mutation within the SHBG gene, which results in a complete deficiency of plasma SHBG in the homozygous state. Although total T level was low in the male patient, it did not interfere with normal gonadal development and spermatogenesis, suggesting a limited role of SHBG in sexual maturation and male physiology.

Polyunsaturated fatty acid supplementation stimulates differentiation of oligodendroglia cells

Dietary polyunsaturated fatty acids (PUFAs) have been postulated as alternative supportive treatment for multiple sclerosis, since they may promote myelin repair. We set out to study the effect of supplementation with n-3 and n-6 PUFAs on OLN-93 oligodendroglia and rat primary oligodendrocyte differentiation in vitro. It appeared that OLN-93 cells actively incorporate and metabolise the supplemented PUFAs in their cell membrane. The effect of PUFAs on OLN-93 differentiation was further assessed by morphological and Western blot evaluation of markers of oligodendroglia differentiation: 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), zonula occludens-1 (ZO-1) and myelin-associated glycoprotein (MAG). Supplementation of the OLN-93 cells with n-3 and n-6 PUFAs increased the degree of differentiation determined by morphological analysis. Moreover, CNP protein expression was significantly increased by gamma-linolenic acid (GLA, 18:3n-6) supplementation. In accordance with the OLN-93 results, studies with rat primary oligodendrocytes, a more advanced model of cell differentiation, showed GLA supplementation to promote oligodendrocyte differentiation. Following GLA supplementation, increased numbers of proteolipid protein (PLP)-positive oligodendrocytes and increased myelin sheet formation was observed during differentiation of primary oligodendrocytes. Moreover, increased CNP, and enhanced PLP and myelin basic protein expression were found after GLA administration. These studies provide support for the dietary supplementation of specific PUFAs to support oligodendrocyte differentiation and function.

Lipid rafts: microenvironments for integrin-growth factor interactions in neural development

The development of a complex multicellular organ such as the nervous system requires precise regulation of cell migration, proliferation and survival. This regulation in turn requires the integration of long-range signals, such as growth factors, with short-range cues that define the precise location and cellular neighbours for any given cell. This short review examines one integrative mechanism, integrin-growth factor receptor interactions, and explores the role of lipid rafts in the molecular mechanisms that underlie the receptor interactions.

Expression of dominant-negative and chimeric subunits reveals an essential role for beta1 integrin during myelination

Myelination represents a remarkable example of cell specialization and cell-cell interaction in development. During this process, axons are wrapped by concentric layers of cell membrane derived either from central nervous system (CNS) oligodendrocytes or peripheral nervous system Schwann cells. In the CNS, oligodendrocytes elaborate a membranous extension with an area of more than 1000 times that of the cell body. The mechanisms regulating this change in cell shape remain poorly understood. Signaling mechanisms regulated by cell surface adhesion receptors of the integrin family represent likely candidates. Integrins link the extracellular environment of the cell with both intracellular signaling molecules and the cytoskeleton and have been shown to regulate the activity of GTPases implicated in the control of cell shape. Our previous work has established that oligodendrocytes and their precursors express a limited repertoire of integrins. One of these, the alpha6beta1 laminin receptor, can interact with laminin-2 substrates to enhance oligodendrocyte myelin membrane formation in cell culture. However, these experiments do not address the important question of integrin function during myelination in vivo, nor do they define the respective roles of the alpha and beta subunits in the signaling pathways involved. Here, we use a dominant-negative approach to provide, for the first time, evidence that beta1 integrin function is required for myelination in vivo and use chimeric integrins to dissect apart the roles of the extracellular and cytoplasmic domains of the alpha6 subunit in the signaling pathways of myelination.

Enzymic and structural studies on Drosophila alcohol dehydrogenase and other short-chain dehydrogenases/reductases

Enzymic and structural studies on Drosophila alcohol dehydrogenases and other short-chain dehydrogenases/reductases (SDRs) are presented. Like alcohol dehydrogenases from other Drosophila species, the enzyme from D. simulans is more active on secondary than on primary alcohols, although ethanol is its only known physiological substrate. Several secondary alcohols were used to determine the kinetic parameters kcat and Km. The results of these experiments indicate that the substrate-binding region of the enzyme allows optimal binding of a short ethyl side-chain in a small binding pocket, and of a propyl or butyl side-chain in large binding pocket, with stereospecificity for R(-) alcohols. At a high concentration of R(-) alcohols substrate activation occurs. The kcat and Km values determined under these conditions are about two-fold, and two orders of magnitude, respectively, higher than those at low substrate concentrations. Sequence alignment of several SDRs of known, and unknown three-dimensional structures, indicate the presence of several conserved residues in addition to those involved in the catalyzed reactions. Structural roles of these conserved residues could be derived from observations made on superpositioned structures of several SDRs with known structures. Several residues are conserved in tetrameric SDRs, but not in dimeric ones. Two halohydrin-halide-lyases show significant homology with SDRs in the catalytic domains of these enzymes, but they do not have the structural features required for binding NAD+. Probably these lyases descend from an SDR, which has lost the capability to bind NAD+, but the enzyme reaction mechanisms may still be similar.

PDGF and FGF-2 signaling in oligodendrocyte progenitor cells: regulation of proliferation and differentiation by multiple intracellular signaling pathways

In this paper we address the linking of platelet-derived growth factor (PDGF) and basic fibroblast growth factor (FGF-2) to intracellular signaling molecules in oligodendrocyte progenitors. It is demonstrated that both growth factors activate downstream targets similar to those shown for protein kinase C (PKC) activation. Yet, neither the arrest of terminal oligodendrocyte differentiation nor the proliferation induced by PDGF or FGF-2 can be antagonized by inhibition of PKC. Rather, p42/p44 mitogen-activated protein kinase (MAPK), p38 MAPK, and pp70 S6 kinase were found to be necessary for the mitogenic activity of PDGF and FGF-2. Paradoxically, these kinases were also necessary for the onset of oligodendrocyte differentiation in control cells. In addition, cAMP-dependent kinase A (PKA) activation inhibited the mitogenic response of oligodendrocyte progenitors to FGF-2. Taken together, the molecular mechanism that controls oligodendrocyte lineage progression is operated by at least two signal pathways, which interfere either with proliferation and/or differentiation of oligodendrocyte progenitors.

Perturbation of myelination by activation of distinct signaling pathways: an in vitro study in a myelinating culture derived from fetal rat brain

An in vitro myelinating mouse-derived model system has been adapted and optimized for fetal rat brain. In these mixed brain cell (MBC) cultures, myelinogenesis was studied by examining the effect of signaling pathways that are involved in the timing of oligodendrocyte differentiation. When PMA, a protein kinase C (PKC) activator, was kept present during development, the early myelin protein, CNP, was expressed in oligodendrocytes as promptly as in control MBC cultures. In contrast, continuous activation of signaling pathways triggered by FGF-2 caused a delay in the expression of CNP. The expression of the late myelin proteins MBP and PLP in oligodendrocytes was impeded by both PMA- and FGF-2-treatment, and, as a consequence, also myelin formation. Surprisingly, the continuous presence of PDGF during development also prevented myelin formation, even though all myelin-specific proteins were significantly expressed. Taken together, the data indicate that this in vitro myelinating culture system represents an excellent system to study signaling events necessary for the onset of myelination. Moreover, the present results demonstrate that oligodendrocyte differentiation in the presence of neurons and astrocytes can be manipulated both by extracellular and intracellular signaling factors. Importantly, differentiation per se is not necessarily culminating into myelination.

Protein kinase C prevents oligodendrocyte differentiation: modulation of actin cytoskeleton and cognate polarized membrane traffic

In a previous study, we showed that activation of protein kinase C (PKC) prevents oligodendrocyte differentiation at the pro-oligodendrocyte stage. The present study was undertaken to identify downstream targets of PKC action in oligodendrocyte progenitor cells. Activation of PKC induced the predominant phosphorylation of an 80-kD protein, identified as myristoylated alanine-rich C-kinase substrate (MARCKS). Upon phosphorylation, MARCKS is translocated from the plasma membrane to the cytosol. Furthermore, PKC activation perturbed the organization of the actin cytoskeleton, causing a redistribution of actin filaments to the submembranous or cortical actin cytoskeleton. As a consequence, transport of a protein traffic marker, the vesicular stomatitis virus glycoprotein, from the trans-Golgi network to the plasma membrane becomes perturbed. The effect of disruption of the actin filament network by cytochalasin D perfectly matched the effect of PKC. These data thus favor the existence of a causal relationship between actin rearrangement and docking and/or fusion of proteins to the plasma membrane. Interestingly, neither in control cells nor in PKC-activated cells did another protein traffic marker, influenza hemagglutinin (HA), reach the cell surface. However, an eminent and specific accumulation of HA just underneath the plasma membrane became apparent upon PKC activation. Yet, this effect could not be simulated by cytochalasin D treatment. Therefore, these observations imply that although MARCKS represents a prominent PKC target site in regulating differentiation, another target involves the differential control of cognate polarized trafficking pathways, which are apparently operating in oligodendrocyte progenitor cells.

Regulation of oligodendrocyte differentiation: protein kinase C activation prevents differentiation of O2A progenitor cells toward oligodendrocytes

Oligodendrocytes differentiate on a specific schedule in vivo in order to myelinate axons at the precise time and at the appropriate position. The current study was undertaken to obtain further insight as to how this timed appearance is regulated intracellularly. We observed that exposure of O2A progenitor cells in culture to phorbol 12-myristate 13-acetate (PMA; an activator of protein kinase C, PKC) inhibited their differentiation to oligodendrocytes by suppressing the expression of specific myelin markers at the O4-stage. To positively identify a role of PKC per se in differentiation, the use of a minimal medium with low serum content turned out to be essential. This was demonstrated by showing that the inhibitory effect of PMA on oligodendrocyte differentiation could be completely abolished by a combined action of insulin, triiodothyronine (T3), hydrocortisone and other components of a chemically defined medium (CDM). Furthermore, the PMA-mediated inhibition of oligodendrocyte differentiation could be partially restored by activation of the cAMP signal transduction pathway. The results indicate that PKC plays a crucial role in the differentiation of O2A progenitor cells toward oligodendrocytes: PKC activation prevents differentiation of O2A progenitor cells, whereas differentiation toward oligodendrocytes is dependent on other signaling compounds which may counteract the PKC signal transduction route.

Production and characterization of monoclonal antibodies against Panulirus interruptus hemocyanin

Since the primary and higher-order structures of hemocyanin from the crustacean arthropod Panulirus interruptus have been elucidated completely, it should be possible to determine which regions of this immunogenic molecule are recognized most often by antibodies. Monoclonal antibodies were raised against subunits a and b of this hemocyanin, and fourteen of them were further characterized. The produced antibodies were of class IgG, subclasses 1 or 2a. Most of them had dissociation constants on the order of magnitude 10(-8)-10(-10), a few had lower affinities. Most clones showed no or negligible cross-reactivity with other crustacean hemocyanins. The reactivity of most other clones diminished with increasing sequence difference between the investigated hemocyanins. However, in a few instances a stronger reactivity with other hemocyanins was observed than with that from Panulirus interruptus. After complete denaturation of the hemocyanin there was no reaction with the monoclonal antibodies, indicating that the latter recognize conformational epitopes. Only one monoclonal antibody reacted with denatured hemocyanin. This antibody was also the only one which reacted with a CNBr digest, which means that it recognizes a sequential epitope. Several antibodies showed a faint reaction on Western blots, indicating the presence of some refolded native structure. Limited proteolysis of the hemocyanin molecule results in the formation of a 18 kDa fragment, representing domain 1, and a 55 kDa fragment representing domains 2 and 3. It was determined on Western blots of the digest on which fragment epitopes for eleven of the monoclonal antibodies were located.

Arg21 is the preferred kexin cleavage site in parathyroid-hormone-related protein

Parathyroid-hormone-related protein (PTHrP) contains several potential sites for proteolytic processing. Although there is considerable evidence for the existence of cleaved products in vivo, little is known about the post-translational processing of PTHrP. We have used purified kexin (Kex2) protease to identify which cleavage sites in recombinant PTHrP(1-141) might be of physiological significance. Cleavage products were identified by N-terminal sequencing. Kex2 preferentially cleaved PTHrP(1-141) carboxy to the triplet arginine site Arg-Arg-Arg21 with a Km of 3.3 +/- 1.7 microM and a kcat of 6 +/- 1.2 s-1. Substitution of alanine for Arg19 resulted in substantially reduced conversion, while no detectable cleavage occurred when alanine was substituted for either Arg20 or Arg21. In contrast, the degree of Kex2 cleavage at Arg21 in PTHrP(1-34) was lower. No detectable cleavage occurred in an unrelated synthetic peptide containing both double and triple arginine sites. Low levels of cleavage also took place carboxy to Lys-Arg97, Lys-Arg105, Arg-Arg106 and Thr-Arg108. Cleavage carboxy to Lys-Arg105, the best of these minor sites, occurred with a Km of 8.4 +/- 2.7 microM and a kcat of 0.8 +/- 0.2 s-1. These studies indicate that the preferred Kex2 cleavage site in PTHrP(1-141) is carboxy to Arg-Arg-Arg21, which effectively destroys its parathyroid-hormone-like biological activity. Cleavage of this site by Kex2-related mammalian convertases in vivo may be an important mechanism for full elaboration of the non-parathyroid-hormone-like paracrine actions of PTHrP in a tissue-specific manner.