2',3'-Cyclic nucleotide 3'-phosphodiesterase: a novel RNA-binding protein that inhibits protein synthesis

Spatial omics reveals molecular changes in focal cortical dysplasia type II

Focal cortical dysplasia (FCD) represents a group of diverse localized cortical lesions that are highly epileptogenic and occur due to abnormal brain development caused by genetic mutations, involving the mammalian target of rapamycin (mTOR). These somatic mutations lead to mosaicism in the affected brain, posing challenges to unravel the direct and indirect functional consequences of these mutations. To comprehensively characterize the impact of mTOR mutations on the brain, we employed here a multimodal approach in a preclinical mouse model of FCD type II (Rheb), focusing on spatial omics techniques to define the proteomic and lipidomic changes. Mass Spectrometry Imaging (MSI) combined with fluorescence imaging and label free proteomics, revealed insight into the brain's lipidome and proteome within the FCD type II affected region in the mouse model. MSI visualized disrupted neuronal migration and differential lipid distribution including a reduction in sulfatides in the FCD type II-affected region, which play a role in brain myelination. MSI-guided laser capture microdissection (LMD) was conducted on FCD type II and control regions, followed by label free proteomics, revealing changes in myelination pathways by oligodendrocytes. Surgical resections of FCD type IIb and postmortem human cortex were analyzed by bulk transcriptomics to unravel the interplay between genetic mutations and molecular changes in FCD type II. Our comparative analysis of protein pathways and enriched Gene Ontology pathways related to myelination in the FCD type II-affected mouse model and human FCD type IIb transcriptomics highlights the animal model's translational value. This dual approach, including mouse model proteomics and human transcriptomics strengthens our understanding of the functional consequences arising from somatic mutations in FCD type II, as well as the identification of pathways that may be used as therapeutic strategies in the future.

Nanobodies against the myelin enzyme CNPase as tools for structural and functional studies

2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is an abundant constituent of central nervous system non-compact myelin, frequently used as a marker antigen for myelinating cells. The catalytic activity of CNPase, the 3'-hydrolysis of 2',3'-cyclic nucleotides, is well characterised in vitro, but the in vivo function of CNPase remains unclear. CNPase interacts with the actin cytoskeleton to counteract the developmental closure of cytoplasmic channels that travel through compact myelin; its enzymatic activity may be involved in adenosine metabolism and RNA degradation. We developed a set of high-affinity nanobodies recognizing the phosphodiesterase domain of CNPase, and the crystal structures of each complex show that the five nanobodies have distinct epitopes. One of the nanobodies bound deep into the CNPase active site and acted as an inhibitor. Moreover, the nanobodies were characterised in imaging applications and as intrabodies, expressed in mammalian cells, such as primary oligodendrocytes. Fluorescently labelled nanobodies functioned in imaging of teased nerve fibers and whole brain tissue sections, as well as super-resolution microscopy. These anti-CNPase nanobodies provide new tools for structural and functional biology of myelination, including high-resolution imaging of nerve tissue.

Psychosocial stress and cannabinoid drugs affect acetylation of α-tubulin (K40) and gene expression in the prefrontal cortex of adult mice

The dynamics of neuronal microtubules are essential for brain plasticity. Vesicular transport and synaptic transmission, additionally, requires acetylation of α-tubulin, and aberrant tubulin acetylation and neurobiological deficits are associated. Prolonged exposure to a stressor or consumption of drugs of abuse, like marihuana, lead to neurological changes and psychotic disorders. Here, we studied the effect of psychosocial stress and the administration of cannabinoid receptor type 1 drugs on α-tubulin acetylation in different brain regions of mice. We found significantly decreased tubulin acetylation in the prefrontal cortex in stressed mice. The impact of cannabinoid drugs on stress-induced microtubule disturbance was investigated by administration of the cannabinoid receptor agonist WIN55,212–2 and/or antagonist rimonabant. In both, control and stressed mice, the administration of WIN55,212–2 slightly increased the tubulin acetylation in the prefrontal cortex whereas administration of rimonabant acted antagonistically indicating a cannabinoid receptor type 1 mediated effect. The analysis of gene expression in the prefrontal cortex showed a consistent expression of ApoE attributable to either psychosocial stress or administration of the cannabinoid agonist. Additionally, ApoE expression inversely correlated with acetylated tubulin levels when comparing controls and stressed mice treated with WIN55,212–2 whereas rimonabant treatment showed the opposite.

Lysosomal storage disease associated with a CNP sequence variant in Dalmatian dogs

A progressive neurological disorder was identified in purebred Dalmatian dogs. The disease is characterized by anxiety, pacing and circling, hypersensitivity, cognitive decline, sleep disturbance, loss of coordination, loss of control over urination and defecation, and visual impairment. Neurological signs first became apparent when the dogs were approximately 18 months of age and progressed slowly. Two affected littermates were euthanized at approximately 7 years, 5 months and 8 years, 2 months of age due to the severity of neurological impairment. The mother of the affected dogs and four other relatives exhibited milder, later-onset neurological signs. Pronounced accumulations of autofluorescent intracellular inclusions were found in cerebral cortex, cerebellum, optic nerve, and cardiac muscle of the affected dogs. These inclusions co-localized with immunolabeling of the lysosomal marker protein LAMP2 and bound antibodies to mitochondrial ATPase subunit c, indicating that the dogs suffered from a lysosomal storage disease with similarities to the neuronal ceroid lipofuscinoses. Ultrastructural analysis indicated that the storage bodies were surrounded by a single-layer membrane, but the storage granules were distinct from those reported for other lysosomal storage diseases. Whole genome sequences, generated with DNA from the two euthanized Dalmatians, both contained a rare, homozygous single-base deletion and reading-frame shift in CNP which encodes the enzyme CNPase (EC 3.1.4.37). The late-onset disease was exhibited by five of seven related Dalmatians that were heterozygous for the deletion allele and over 8 years of age, whereas none of 16 age-matched reference-allele homozygotes developed neurologic signs. No CNPase antigen could be detected with immunohistochemical labeling in tissues from the dogs with the earlier-onset disorder. Similar to the later-onset Dalmatians, autofluorescent storage granules were apparent in brain and cardiac tissue from transgenic mice that were nullizygous for Cnp. Based on the clinical signs, the histopathological, immunohistochemical, ultrastructural, and molecular-genetic findings, and the finding that nullizygous Cnp mice accumulate autofluorescent storage granules, we propose that the earlier-onset Dalmatian disorder is a novel lysosomal storage disease that results from a loss-of-function mutation in CNP and that shares features characteristic of the neuronal ceroid lipofuscinoses. That the later-onset disorder occurred only in dogs heterozygous for the CNP deletion variant suggests that this disorder is a result of the variant allele's presence.

Cellular Effects of 2',3'-Cyclic Nucleotide Monophosphates in Gram-Negative Bacteria

Organismal adaptations to environmental stimuli are governed by intracellular signaling molecules such as nucleotide second messengers. Recent studies have identified functional roles for the noncanonical 2',3'-cyclic nucleotide monophosphates (2',3'-cNMPs) in both eukaryotes and prokaryotes. In Escherichia coli, 2',3'-cNMPs are produced by RNase I-catalyzed RNA degradation, and these cyclic nucleotides modulate biofilm formation through unknown mechanisms. The present work dissects cellular processes in E. coli and Salmonella enterica serovar Typhimurium that are modulated by 2',3'-cNMPs through the development of cell-permeable 2',3'-cNMP analogs and a 2',3'-cyclic nucleotide phosphodiesterase. Utilization of these chemical and enzymatic tools, in conjunction with phenotypic and transcriptomic investigations, identified pathways regulated by 2',3'-cNMPs, including flagellar motility and biofilm formation, and by oligoribonucleotides with 3'-terminal 2',3'-cyclic phosphates, including responses to cellular stress. Furthermore, interrogation of metabolomic and organismal databases has identified 2',3'-cNMPs in numerous organisms and homologs of the E. coli metabolic proteins that are involved in key eukaryotic pathways. Thus, the present work provides key insights into the roles of these understudied facets of nucleotide metabolism and signaling in prokaryotic physiology and suggest broad roles for 2',3'-cNMPs among bacteria and eukaryotes. IMPORTANCE Bacteria adapt to environmental challenges by producing intracellular signaling molecules that control downstream pathways and alter cellular processes for survival. Nucleotide second messengers serve to transduce extracellular signals and regulate a wide array of intracellular pathways. Recently, 2',3'-cyclic nucleotide monophosphates (2',3'-cNMPs) were identified as contributing to the regulation of cellular pathways in eukaryotes and prokaryotes. In this study, we define previously unknown cell processes that are affected by fluctuating 2',3'-cNMP levels or RNA oligomers with 2',3'-cyclic phosphate termini in E. coli and Salmonella Typhimurium, providing a framework for studying novel signaling networks in prokaryotes. Furthermore, we utilize metabolomics databases to identify additional prokaryotic and eukaryotic species that generate 2',3'-cNMPs as a resource for future studies.

Capsule Network for Predicting RNA-Protein Binding Preferences Using Hybrid Feature

RNA-Protein binding is involved in many different biological processes. With the progress of technology, more and more data are available for research. Based on these data, many prediction methods have been proposed to predict RNA-Protein binding preference. Some of these methods use only RNA sequence features for prediction, and some methods use multiple features for prediction. But, the performance of these methods is not satisfactory. In this study, we propose an improved capsule network to predict RNA-protein binding preferences, which can use both RNA sequence features and structure features. Experimental results show that our proposed method iCapsule performs better than three baseline methods in this field. We used both RNA sequence features and structure features in the model, so we tested the effect of primary capsule layer changes on model performance. In addition, we also studied the impact of model structure on model performance by performing our proposed method with different number of convolution layers and different kernel sizes.

The Functions of Mitochondrial 2',3'-Cyclic Nucleotide-3'-Phosphodiesterase and Prospects for Its Future

2′,3′-cyclic nucleotide-3′-phosphodiesterase (CNPase) is a myelin-associated enzyme that catalyzes the phosphodiester hydrolysis of 2’,3’-cyclic nucleotides to 2’-nucleotides. However, its presence is also found in unmyelinated cells and other cellular structures. Understanding of its specific physiological functions, particularly in unmyelinated cells, is still incomplete. This review concentrates on the role of mitochondrial CNPase (mtCNPase), independent of myelin. mtCNPase is able to regulate the functioning of the mitochondrial permeability transition pore (mPTP), and thus is involved in the mechanisms of cell death, both apoptosis and necrosis. Its participation in the development of various diseases and pathological conditions, such as aging, heart disease and alcohol dependence, is also reviewed. As such, mtCNPase can be considered as a potential target for the development of therapeutic strategies in the treatment of mitochondria-related diseases.

MsrA Suppresses Inflammatory Activation of Microglia and Oxidative Stress to Prevent Demyelination via Inhibition of the NOX2-MAPKs/NF-κB Signaling Pathway

Introduction

Demyelination causes neurological deficits involving visual, motor, sensory symptoms. Deregulation of several enzymes has been identified in demyelination, which holds potential for the development of treatment strategies for demyelination. However, the specific effect of methionine sulfoxide reductase A (MsrA) on demyelination remains unclear. Hence, this study aims to explore the effect of MsrA on oxidative stress and inflammatory response of microglia in demyelination.

Methods

Initially, we established a mouse model with demyelination induced by cuprizone and a cell model provoked by lipopolysaccharide (LPS). The expression of MsrA in wild-type (WT) and MsrA-knockout (MsrA^-/-) mice were determined by RT-qPCR and Western blot analysis. In order to further explore the function of MsrA on inflammatory response, and oxidative stress in demyelination, we detected the expression of microglia marker Iba1, inflammatory factors TNF-α and IL-1β and intracellular reactive oxygen species (ROS), superoxide dismutase (SOD) activity, as well as expression of the NOX2-MAPKs/NF-κB signaling pathway-related genes in MsrA^-/- mice and LPS-induced microglia following different treatments.

Results

MsrA expression was downregulated in MsrA^-/- mice. MsrA silencing was shown to produce severely injured motor coordination, increased expressions of Iba1, TNF-α, IL-1β, ROS and NOX2, and extent of ERK, p38, IκBα, and p65 phosphorylation, but reduced SOD activity. Conjointly, our study suggests that Tat-MsrA fusion protein can prevent the cellular inflammatory response and subsequent demyelination through negative regulation of the NOX2-MAPKs/NF-κB signaling pathway.

Conclusion

Our data provide a profound insight on the role of endogenous antioxidative defense systems such as MsrA in controlling microglial function.

Flexible Players within the Sheaths: The Intrinsically Disordered Proteins of Myelin in Health and Disease

Myelin ensheathes selected axonal segments within the nervous system, resulting primarily in nerve impulse acceleration, as well as mechanical and trophic support for neurons. In the central and peripheral nervous systems, various proteins that contribute to the formation and stability of myelin are present, which also harbor pathophysiological roles in myelin disease. Many myelin proteins have common attributes, including small size, hydrophobic segments, multifunctionality, longevity, and regions of intrinsic disorder. With recent advances in protein biophysical characterization and bioinformatics, it has become evident that intrinsically disordered proteins (IDPs) are abundant in myelin, and their flexible nature enables multifunctionality. Here, we review known myelin IDPs, their conservation, molecular characteristics and functions, and their disease relevance, along with open questions and speculations. We place emphasis on classifying the molecular details of IDPs in myelin, and we correlate these with their various functions, including susceptibility to post-translational modifications, function in protein–protein and protein–membrane interactions, as well as their role as extended entropic chains. We discuss how myelin pathology can relate to IDPs and which molecular factors are potentially involved.

Region-Resolved Quantitative Proteome Profiling Reveals Molecular Dynamics Associated With Chronic Pain in the PNS and Spinal Cord

To obtain a thorough understanding of chronic pain, large-scale molecular mapping of the pain axis at the protein level is necessary, but has not yet been achieved. We applied quantitative proteome profiling to build a comprehensive protein compendium of three regions of the pain neuraxis in mice: the sciatic nerve (SN), the dorsal root ganglia (DRG), and the spinal cord (SC). Furthermore, extensive bioinformatics analysis enabled us to reveal unique protein subsets which are specifically enriched in the peripheral nervous system (PNS) and SC. The immense value of these datasets for the scientific community is highlighted by validation experiments, where we monitored protein network dynamics during neuropathic pain. Here, we resolved profound region-specific differences and distinct changes of PNS-enriched proteins under pathological conditions. Overall, we provide a unique and validated systems biology proteome resource (summarized in our online database painproteome.em.mpg.de), which facilitates mechanistic insights into somatosensory biology and chronic pain—a prerequisite for the identification of novel therapeutic targets.

RNase I regulates Escherichia coli 2',3'-cyclic nucleotide monophosphate levels and biofilm formation

Regulation of nucleotide and nucleoside concentrations is critical for faithful DNA replication, transcription, and translation in all organisms, and has been linked to bacterial biofilm formation. Unusual 2',3'-cyclic nucleotide monophosphates (2',3'-cNMPs) recently were quantified in mammalian systems, and previous reports have linked these nucleotides to cellular stress and damage in eukaryotes, suggesting an intriguing connection with nucleotide/nucleoside pools and/or cyclic nucleotide signaling. This work reports the first quantification of 2',3'-cNMPs in Escherichia coli and demonstrates that 2',3'-cNMP levels in E. coli are generated specifically from RNase I-catalyzed RNA degradation, presumably as part of a previously unidentified nucleotide salvage pathway. Furthermore, RNase I and 2',3'-cNMP levels are demonstrated to play an important role in controlling biofilm formation. This work identifies a physiological role for cytoplasmic RNase I and constitutes the first progress toward elucidating the biological functions of bacterial 2',3'-cNMPs.

Structural similarities and functional differences clarify evolutionary relationships between tRNA healing enzymes and the myelin enzyme CNPase

BACKGROUND

Eukaryotic tRNA splicing is an essential process in the transformation of a primary tRNA transcript into a mature functional tRNA molecule. 5'-phosphate ligation involves two steps: a healing reaction catalyzed by polynucleotide kinase (PNK) in association with cyclic phosphodiesterase (CPDase), and a sealing reaction catalyzed by an RNA ligase. The enzymes that catalyze tRNA healing in yeast and higher eukaryotes are homologous to the members of the 2H phosphoesterase superfamily, in particular to the vertebrate myelin enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase).

RESULTS

We employed different biophysical and biochemical methods to elucidate the overall structural and functional features of the tRNA healing enzymes yeast Trl1 PNK/CPDase and lancelet PNK/CPDase and compared them with vertebrate CNPase. The yeast and the lancelet enzymes have cyclic phosphodiesterase and polynucleotide kinase activity, while vertebrate CNPase lacks PNK activity. In addition, we also show that the healing enzymes are structurally similar to the vertebrate CNPase by applying synchrotron radiation circular dichroism spectroscopy and small-angle X-ray scattering.

CONCLUSIONS

We provide a structural analysis of the tRNA healing enzyme PNK and CPDase domains together. Our results support evolution of vertebrate CNPase from tRNA healing enzymes with a loss of function at its N-terminal PNK-like domain.

Antibody-Mediated Oligodendrocyte Remyelination Promotes Axon Health in Progressive Demyelinating Disease

Demyelination underlies early neurological symptoms in multiple sclerosis (MS); however, axonal damage is considered critical for permanent chronic deficits. The precise mechanisms by which axonal injury occurs in MS are unclear; one hypothesis is the absence or failure of remyelination, suggesting that promoting remyelination may protect axons from death. This report provides direct evidence that promoting oligodendrocyte remyelination protects axons and maintains transport function. Persistent Theiler's virus infection of Swiss Jim Lambert (SJL)/J mice was used as a model of MS to assess the effects of remyelination on axonal injury following demyelination in the spinal cord. Remyelination was induced using an oligodendrocyte/myelin-specific recombinant human monoclonal IgM, rHIgM22. The antibody is endowed with strong anti-apoptotic and pro-proliferative effects on oligodendrocyte progenitor cells. We used (1)H-magnetic resonance spectroscopy (MRS) at the brainstem to measure N-acetyl-aspartate (NAA) as a surrogate of neuronal health and spinal cord integrity. We found increased brainstem NAA concentrations at 5 weeks post-treatment with rHIgM22, which remained stable out to 10 weeks. Detailed spinal cord morphology studies revealed enhanced remyelination in the rHIgM22-treated group but not in the isotype control antibody- or saline-treated groups. Importantly, we found rHIgM22-mediated remyelination protected small- and medium-caliber mid-thoracic spinal cord axons from damage despite similar demyelination and inflammation across all experimental groups. The most direct confirmation of remyelination-mediated protection of descending neurons was an improvement in retrograde transport. Treatment with rHIgM22 significantly increased the number of retrograde-labeled neurons in the brainstem, indicating that preserved axons are functionally competent. This is direct validation that remyelination preserves spinal cord axons and protects functional axon integrity.

The Cannabinoid CB1/CB2 Agonist WIN55212.2 Promotes Oligodendrocyte Differentiation In Vitro and Neuroprotection During the Cuprizone-Induced Central Nervous System Demyelination

Aim and methods

Different types of insults to the CNS lead to axon demyelination. Remyelination occurs when the CNS attempts to recover from myelin loss and requires the activation of oligodendrocyte precursor cells. With the rationale that CB1 receptor is expressed in oligodendrocytes and marijuana consumption alters CNS myelination, we study the effects of the cannabinoid agonist WIN55212.2 in (1) an in vitro model of oligodendrocyte differentiation and (2) the cuprizone model for demyelination.

Results

The synthetic cannabinoid agonist WIN55212.2 at 1 μM increased the myelin basic protein mRNA and protein expression in vitro. During cuprizone‐induced acute demyelination, the administration of 0.5 mg/kg WIN55212.2 confers more myelinated axons, increased the expression of retinoid X receptor alpha, and declined nogo receptor expression. Controversially, 1 mg/kg of the drug increased the number of demyelinated axons and reduced the expression of nerve growth factor inducible, calreticulin and myelin‐related genes coupling specifically with a decrease in 2′,3′‐cyclic nucleotide 3′ phosphodiesterase expression.

Conclusion

The cannabinoid agonist WIN55212.2 promotes oligodendrocyte differentiation in vitro. Moreover, 0.5 mg/kg of the drug confers neuroprotection during cuprizone‐induced demyelination, while 1 mg/kg aggravates the demyelination process.

Determinants of ligand binding and catalytic activity in the myelin enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase

2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is an enzyme highly abundant in the central nervous system myelin of terrestrial vertebrates. The catalytic domain of CNPase belongs to the 2H phosphoesterase superfamily and catalyzes the hydrolysis of nucleoside 2',3'-cyclic monophosphates to nucleoside 2'-monophosphates. The detailed reaction mechanism and the essential catalytic amino acids involved have been described earlier, but the roles of many amino acids in the vicinity of the active site have remained unknown. Here, several CNPase catalytic domain mutants were studied using enzyme kinetics assays, thermal stability experiments, and X-ray crystallography. Additionally, the crystal structure of a perdeuterated CNPase catalytic domain was refined at atomic resolution to obtain a detailed view of the active site and the catalytic mechanism. The results specify determinants of ligand binding and novel essential residues required for CNPase catalysis. For example, the aromatic side chains of Phe235 and Tyr168 are crucial for substrate binding, and Arg307 may affect active site electrostatics and regulate loop dynamics. The β5-α7 loop, unique for CNPase in the 2H phosphoesterase family, appears to have various functions in the CNPase reaction mechanism, from coordinating the nucleophilic water molecule to providing a binding pocket for the product and being involved in product release.

Structural and functional evolution of 2',3'-cyclic nucleotide 3'-phosphodiesterase

2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is an abundant membrane-associated enzyme within the vertebrate myelin sheath. While the physiological function of CNPase still remains to be characterized in detail, it is known - in addition to its in vitro enzymatic activity - to interact with other proteins, small molecules, and membrane surfaces. From an evolutionary point of view, it can be deduced that CNPase is not restricted to myelin-forming cells or vertebrate tissues. Its evolution has involved gene fusion, addition of other small segments with distinct functions, such as membrane attachment, and possibly loss of function at the polynucleotide kinase-like domain. Currently, it is unclear whether the enzymatic function of the conserved phosphodiesterase domain in vertebrate myelin has a physiological role, or if CNPase could actually function - like many other classical myelin proteins - in a more structural role. This article is part of a Special Issue entitled SI: Myelin Evolution.

Interaction of myelin basic protein and 2',3'-cyclic nucleotide phosphodiesterase with mitochondria

The content and distribution of myelin basic protein (MBP) isoforms (17 and 21.5 kDa) as well as 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase) were determined in mitochondrial fractions (myelin fraction, synaptic and nonsynaptic mitochondria) obtained after separation of brain mitochondria by Percoll density gradient. All the fractions could accumulate calcium, maintain membrane potential, and initiate the opening of the permeability transition pore (mPTP) in response to calcium overloading. Native mitochondria and structural contacts between membranes of myelin and mitochondria were found in the myelin fraction associated with brain mitochondria. Using Western blot, it was shown that addition of myelin fraction associated with brain mitochondria to the suspension of liver mitochondria can lead to binding of CNPase and MBP, present in the fraction with liver mitochondria under the conditions of both closed and opened mPTP. However, induction of mPTP opening in liver mitochondria was prevented in the presence of myelin fraction associated with brain mitochondria (Ca2+ release rate was decreased 1.5-fold, calcium retention time was doubled, and swelling amplitude was 2.8-fold reduced). These results indicate possible protective properties of MBP and CNPase.

The myelin membrane-associated enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase: on a highway to structure and function

The membrane-anchored myelin enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) was discovered in the early 1960s and has since then troubled scientists with its peculiar catalytic activity and high expression levels in the central nervous system. Despite decades of research, the actual physiological relevance of CNPase has only recently begun to unravel. In addition to a role in myelination, CNPase is also involved in local adenosine production in traumatic brain injury and possibly has a regulatory function in mitochondrial membrane permeabilization. Although research focusing on the CNPase phosphodiesterase activity has been helpful, several open questions concerning the protein function in vivo remain unanswered. This review is focused on past research on CNPase, especially in the fields of structural biology and enzymology, and outlines the current understanding regarding the biochemical and physiological significance of CNPase, providing ideas and directions for future research.

2',3'-cyclic nucleotide 3'-phosphodiesterases inhibit hepatitis B virus replication

2’,3’-cyclic nucleotide 3’-phosphodiesterase (CNP) is a member of the interferon-stimulated genes, which includes isoforms CNP1 and CNP2. CNP1 is locally expressed in the myelin sheath but CNP2 is additionally expressed at low levels outside the nervous system. CNPs regulate multiple cellular functions and suppress protein production by association with polyadenylation of mRNA. Polyadenylation of Hepatitis B virus (HBV) RNAs is crucial for HBV replication. Whether CNPs interact with polyadenylation signal of HBV RNAs and interfere HBV replication is unknown. In this study, we evaluated expressions of CNP isoforms in hepatoma cell lines and their effects on HBV replication. We found that CNP2 is moderately expressed and gently responded to interferon treatment in HepG2, but not in Huh7 cells. The CNP1 and CNP2 potently inhibited HBV production by blocking viral proteins synthesis and reducing viral RNAs, respectively. In chronic hepatitis B patients, CNP was expressed in most of HBV-infected hepatocytes of liver specimens. Knockdown of CNP expression moderately improved viral production in the HepG2.2.15 cells treated with IFN-α. In conclusion, CNP might be a mediator of interferon-induced response against HBV.

Reversible and rapid transfer-RNA deactivation as a mechanism of translational repression in stress

Stress-induced changes of gene expression are crucial for survival of eukaryotic cells. Regulation at the level of translation provides the necessary plasticity for immediate changes of cellular activities and protein levels. In this study, we demonstrate that exposure to oxidative stress results in a quick repression of translation by deactivation of the aminoacyl-ends of all transfer-RNA (tRNA). An oxidative-stress activated nuclease, angiogenin, cleaves first within the conserved single-stranded 3'-CCA termini of all tRNAs, thereby blocking their use in translation. This CCA deactivation is reversible and quickly repairable by the CCA-adding enzyme [ATP(CTP):tRNA nucleotidyltransferase]. Through this mechanism the eukaryotic cell dynamically represses and reactivates translation at low metabolic costs.

Oligodendroglia: metabolic supporters of axons

Axons are specialized extensions of neurons that are critical for the organization of the nervous system. To maintain function in axons that often extend some distance from the cell body, specialized mechanisms of energy delivery are likely to be necessary. Over the past decade, greater understanding of human demyelinating diseases and the development of animal models have suggested that oligodendroglia are critical for maintaining the function of axons. In this review, we discuss evidence for the vulnerability of neurons to energy deprivation, the importance of oligodendrocytes for axon function and survival, and recent data suggesting that transfer of energy metabolites from oligodendroglia to axons through monocarboxylate transporter 1 (MCT1) may be critical for the survival of axons. This pathway has important implications both for the basic biology of the nervous system and for human neurological disease. New insights into the role of oligodendroglial biology provide an exciting opportunity for revisions in nervous system biology, understanding myelin-based disorders, and therapeutics development.

Crystallographic analysis of the reaction cycle of 2',3'-cyclic nucleotide 3'-phosphodiesterase, a unique member of the 2H phosphoesterase family

2H phosphoesterases catalyze reactions on nucleotide substrates and contain two conserved histidine residues in the active site. Very limited information is currently available on the details of the active site and substrate/product binding during the catalytic cycle of these enzymes. We performed a comprehensive X-ray crystallographic study of mouse 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNPase), a membrane-associated enzyme present at high levels in the tetrapod myelin sheath. We determined crystal structures of the CNPase phosphodiesterase domain complexed with substrate, product, and phosphorothioate analogues. The data provide detailed information on the CNPase reaction mechanism, including substrate binding mode and coordination of the nucleophilic water molecule. Linked to the reaction, an open/close motion of the β5–α7 loop is observed. The role of the N terminus of helix α7—unique for CNPase in the 2H family—during the reaction indicates that 2H phosphoesterases differ in their respective reaction mechanisms despite the conserved catalytic residues. Furthermore, based on small-angle X-ray scattering, we present a model for the full-length enzyme, indicating that the two domains of CNPase form an elongated molecule. Finally, based on our structural data and a comprehensive bioinformatics study, we discuss the conservation of CNPase in various organisms.

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A detailed structural analysis of the CNPase catalytic cycle was carried out.

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Complexes with substrates, products, and analogues highlight roles for a nearby helix and loop in the reaction mechanism.

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The full-length CNPase adopts an elongated conformation in solution.

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CNPase is a unique member of the 2H family, and the results will help understand its physiological significance.

Delayed myelination in a mouse model of fragile X syndrome

Fragile X Syndrome is the most common inherited cause of autism. Fragile X mental retardation protein (FMRP), which is absent in fragile X, is an mRNA binding protein that regulates the translation of hundreds of different mRNA transcripts. In the adult brain, FMRP is expressed primarily in the neurons; however, it is also expressed in developing glial cells, where its function is not well understood. Here, we show that fragile X (Fmr1) knockout mice display abnormalities in the myelination of cerebellar axons as early as the first postnatal week, corresponding roughly to the equivalent time in human brain development when symptoms of the syndrome first become apparent (1-3 years of age). At postnatal day (PND) 7, diffusion tensor magnetic resonance imaging showed reduced volume of the Fmr1 cerebellum compared with wild-type mice, concomitant with an 80-85% reduction in the expression of myelin basic protein, fewer myelinated axons and reduced thickness of myelin sheaths, as measured by electron microscopy. Both the expression of the proteoglycan NG2 and the number of PDGFRα+/NG2+ oligodendrocyte precursor cells were reduced in the Fmr1 cerebellum at PND 7. Although myelin proteins were still depressed at PND 15, they regained wild-type levels by PND 30. These findings suggest that impaired maturation or function of oligodendrocyte precursor cells induces delayed myelination in the Fmr1 mouse brain. Our results bolster an emerging recognition that white matter abnormalities in early postnatal brain development represent an underlying neurological deficit in Fragile X syndrome.

Prolonged myelination in human neocortical evolution

Nerve myelination facilitates saltatory action potential conduction and exhibits spatiotemporal variation during development associated with the acquisition of behavioral and cognitive maturity. Although human cognitive development is unique, it is not known whether the ontogenetic progression of myelination in the human neocortex is evolutionarily exceptional. In this study, we quantified myelinated axon fiber length density and the expression of myelin-related proteins throughout postnatal life in the somatosensory (areas 3b/3a/1/2), motor (area 4), frontopolar (prefrontal area 10), and visual (areas 17/18) neocortex of chimpanzees (N = 20) and humans (N = 33). Our examination revealed that neocortical myelination is developmentally protracted in humans compared with chimpanzees. In chimpanzees, the density of myelinated axons increased steadily until adult-like levels were achieved at approximately the time of sexual maturity. In contrast, humans displayed slower myelination during childhood, characterized by a delayed period of maturation that extended beyond late adolescence. This comparative research contributes evidence crucial to understanding the evolution of human cognition and behavior, which arises from the unfolding of nervous system development within the context of an enriched cultural environment. Perturbations of normal developmental processes and the decreased expression of myelin-related molecules have been related to psychiatric disorders such as schizophrenia. Thus, these species differences suggest that the human-specific shift in the timing of cortical maturation during adolescence may have implications for vulnerability to certain psychiatric disorders.

A myelin gene causative of a catatonia-depression syndrome upon aging

Severe mental illnesses have been linked to white matter abnormalities, documented by postmortem studies. However, cause and effect have remained difficult to distinguish. CNP (2',3'-cyclic nucleotide 3'-phosphodiesterase) is among the oligodendrocyte/myelin-associated genes most robustly reduced on mRNA and protein level in brains of schizophrenic, bipolar or major depressive patients. This suggests that CNP reduction might be critical for a more general disease process and not restricted to a single diagnostic category. We show here that reduced expression of CNP is the primary cause of a distinct behavioural phenotype, seen only upon aging as an additional 'pro-inflammatory hit'. This phenotype is strikingly similar in Cnp heterozygous mice and patients with mental disease carrying the AA genotype at CNP SNP rs2070106. The characteristic features in both species with their partial CNP 'loss-of-function' genotype are best described as 'catatonia-depression' syndrome. As a consequence of perturbed CNP expression, mice show secondary low-grade inflammation/neurodegeneration. Analogously, in man, diffusion tensor imaging points to axonal loss in the frontal corpus callosum. To conclude, subtle white matter abnormalities inducing neurodegenerative changes can cause/amplify psychiatric diseases.

Differential expression of 2',3'-cyclic-nucleotide 3'-phosphodiesterase and neural lineage markers correlate with glioblastoma xenograft infiltration and patient survival

PURPOSE

Glioblastoma multiforme (GBM) is a poorly treated human brain cancer with few established clinically useful molecular prognostic markers. We characterized glioblastoma stem-like cells (GSC) according to developmental neural lineage markers and correlated their expression with patient survival.

EXPERIMENTAL DESIGN

Immunoblot array of neural lineage markers classified five independently isolated human GSC lines into three classes exhibiting differential expression of oligodendrocyte progenitor cells (OPC), astrocyte progenitor cells (APC), and neural progenitor cells (NPC) markers. Immunodeficient mice were orthotopically implanted with each cell line to evaluate tumor infiltration and recipient survival. 2',3'-Cyclic-nucleotide 3'-phosphodiesterase (CNP) antigenic expression was used to evaluate a clinically annotated GBM tissue microarray with 115 specimens.

RESULTS

We report that molecular classification of patient-derived GSCs using neural lineage markers show association with differential xenograft invasiveness, and also show significant correlation to survival in both the mouse model and human patients. Orthotopic implantation into immunodeficient mice showed Ki-67 proliferative index independent xenograft infiltration: class I GSCs (OPC and NPC positive) established focal lesions, class II GSCs (NPC positive) formed minimally invasive lesions, and class III GSCs (APC positive) established highly infiltrative lesions. The OPC marker, CNP also exhibited high expression in focal xenografts versus low expression in invasive xenografts. Differential CNP expression correlated with mouse model survival, and CNP immunoassay of a large GBM tissue microarray also showed significant differential patient survival.

CONCLUSIONS

GSC classification with developmental neural lineage markers revealed CNP as a novel and potentially useful clinical prognosis marker, and suggests clinical importance for patient-specific GSC analysis.

Myelin 2',3'-cyclic nucleotide 3'-phosphodiesterase: active-site ligand binding and molecular conformation

The 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is a highly abundant membrane-associated enzyme in the myelin sheath of the vertebrate nervous system. CNPase is a member of the 2H phosphoesterase family and catalyzes the formation of 2'-nucleotide products from 2',3'-cyclic substrates; however, its physiological substrate and function remain unknown. It is likely that CNPase participates in RNA metabolism in the myelinating cell. We solved crystal structures of the phosphodiesterase domain of mouse CNPase, showing the binding mode of nucleotide ligands in the active site. The binding mode of the product 2'-AMP provides a detailed view of the reaction mechanism. Comparisons of CNPase crystal structures highlight flexible loops, which could play roles in substrate recognition; large differences in the active-site vicinity are observed when comparing more distant members of the 2H family. We also studied the full-length CNPase, showing its N-terminal domain is involved in RNA binding and dimerization. Our results provide a detailed picture of the CNPase active site during its catalytic cycle, and suggest a specific function for the previously uncharacterized N-terminal domain.

Tubulin potentiates the interaction of the metalloendopeptidase nardilysin with the neuronal scaffold protein p42IP4/centaurin-α1 (ADAP1)

We found colocalization of the neuronal protein p42(IP4) (centaurin-α1; ArfGAP with dual pleckstrin homology domain [ADAP1]), the metalloendopeptidase nardilysin (NRD; involved in axonal maturation and myelination) and tubulin in the cytosol and at the plasma membrane of SH-SY5Y neuroblastoma cells. To examine the importance of tubulin for the interaction of NRD with p42(IP4), we treated cells with nocodazole, which interferes with tubulin polymerization. Nocodazole did not affect the colocalization of p42(IP4) and tubulin but caused a clear redistribution of the proteins in cells, so that the colocalization of p42(IP4), tubulin and NRD was visible exclusively in multiple foci. To reveal the mechanism of the interaction between NRD, p42(IP4) and tubulin observed in neuronal cells, we performed Far-Western blotting, a technique that directly detects protein-protein interactions on Western blots. This technique demonstrated that tubulin enhanced the binding of NRD to functionally renatured p42(IP4). The mutation of a highly conserved cysteine residue in NRD to alanine abolished the potentiation by tubulin. NRD lacking the characteristic acidic domain was able to bind p42(IP4) but addition of tubulin did not significantly potentiate the binding of this deletion mutant to p42(IP4). A function-abolishing mutation of the Zn(2+)-binding motif of NRD did not affect the potentiation by tubulin. Thus, the capacity of tubulin to enhance the interaction between p42(IP4) and NRD together with the known interaction of p42(IP4) with F-actin support the novel notion that p42(IP4) plays a possible role as a linker between the two networks, actin and tubulin, in neural cells.

Resilient emotionality and molecular compensation in mice lacking the oligodendrocyte-specific gene Cnp1

Altered oligodendrocyte structure and function is implicated in major psychiatric illnesses, including low cell number and reduced oligodendrocyte-specific gene expression in major depressive disorder (MDD). These features are also observed in the unpredictable chronic mild stress (UCMS) rodent model of the illness, suggesting that they are consequential to environmental precipitants; however, whether oligodendrocyte changes contribute causally to low emotionality is unknown. Focusing on 2'-3'-cyclic nucleotide 3'-phosphodiesterase (Cnp1), a crucial component of axoglial communication dysregulated in the amygdala of MDD subjects and UCMS-exposed mice, we show that altered oligodendrocyte integrity can have an unexpected functional role in affect regulation. Mice lacking Cnp1 (knockout, KO) displayed decreased anxiety- and depressive-like symptoms (i.e., low emotionality) compared with wild-type animals, a phenotypic difference that increased with age (3-9 months). This phenotype was accompanied by increased motor activity, but was evident before neurodegenerative-associated motor coordination deficits (≤ 9-12 months). Notably, Cnp1(KO) mice were less vulnerable to developing a depressive-like syndrome after either UCMS or chronic corticosterone exposure. Cnp1(KO) mice also displayed reduced fear expression during extinction, despite normal amygdala c-Fos induction after acute stress, together implicating dysfunction of an amygdala-related neural network, and consistent with proposed mechanisms for stress resiliency. However, the Cnp1(KO) behavioral phenotype was also accompanied by massive upregulation of oligodendrocyte- and immune-related genes in the basolateral amygdala, suggesting an attempt at functional compensation. Together, we demonstrate that the lack of oligodendrocyte-specific Cnp1 leads to resilient emotionality. However, combined with substantial molecular changes and late-onset neurodegeneration, these results suggest the low Cnp1 seen in MDD may cause unsustainable and maladaptive molecular compensations contributing to the disease pathophysiology.

Myelination and support of axonal integrity by glia

The myelination of axons by glial cells was the last major step in the evolution of cells in the vertebrate nervous system, and white-matter tracts are key to the architecture of the mammalian brain. Cell biology and mouse genetics have provided insight into axon-glia signalling and the molecular architecture of the myelin sheath. Glial cells that myelinate axons were found to have a dual role by also supporting the long-term integrity of those axons. This function may be independent of myelin itself. Myelin abnormalities cause a number of neurological diseases, and may also contribute to complex neuropsychiatric disorders.

Blood pressure treatment in acute ischemic stroke: a review of studies and recommendations

PURPOSE OF REVIEW

Elevated blood pressure (BP) is frequent in patients with acute ischemic stroke. Pathophysiological data support its usefulness to maintain adequate perfusion of the ischemic penumba. This review article aims to summarize the available evidence from clinical studies that examined the prognostic role of BP during the acute phase of ischemic stroke and intervention studies that assessed the efficacy of active BP alteration.

RECENT FINDINGS

We found 34 observational studies (33,470 patients), with results being inconsistent among the studies; most studies reported a negative association between increased levels of BP and clinical outcome, whereas a few studies showed clinical improvement with higher BP levels, clinical deterioration with decreased BP, or no association at all. Similarly, the conclusions drawn by the 18 intervention studies included in this review (1637 patients) were also heterogeneous. Very recent clinical data suggest a possible beneficial effect of early treatment with some antihypertensives on late clinical outcome.

SUMMARY

Observational and interventional studies of management of acute poststroke hypertension yield conflicting results. We discuss different explanations that may account for this and discuss the current guidelines and pathophysiological considerations for the management of acute poststroke hypertension.

The multiple roles of myelin protein genes during the development of the oligodendrocyte

It has become clear that the products of several of the earliest identified myelin protein genes perform functions that extend beyond the myelin sheath. Interestingly, these myelin proteins, which comprise proteolipid protein, 2′,3′-cyclic nucleotide 3′-phosphodiesterase and the classic and golli MBPs (myelin basic proteins), play important roles during different stages of oligodendroglial development. These non-myelin-related functions are varied and include roles in the regulation of process outgrowth, migration, RNA transport, oligodendrocyte survival and ion channel modulation. However, despite the wide variety of cellular functions performed by the different myelin genes, the route by which they achieve these many functions seems to converge upon a common mechanism involving Ca²⁺ regulation, cytoskeletal rearrangements and signal transduction. In the present review, the newly emerging functions of these myelin proteins will be described, and these will then be discussed in the context of their contribution to oligodendroglial development.

Expression, purification, and initial characterization of different domains of recombinant mouse 2',3'-cyclic nucleotide 3'-phosphodiesterase, an enigmatic enzyme from the myelin sheath

Background

2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is an enigmatic enzyme specifically expressed at high levels in the vertebrate myelin sheath, whose function and physiological substrates are unknown. The protein consists of two domains: an uncharacterized N-terminal domain with little homology to other proteins, and a C-terminal phosphodiesterase domain.

Findings

In order to be able to fully characterize CNPase structurally and functionally, we have set up expression systems for different domains of CNPase, using a total of 18 different expression constructs. CNPase was expressed in E. coli with a TEV-cleavable His-tag. Enzymatic activity assays indicated that the purified proteins were active and correctly folded. The folding of both the full-length protein, as well as the N- and C-terminal domains, was also studied by synchrotron CD spectroscopy. A thermal shift assay was used to optimize buffer compositions to be used during purification and storage. The assay also indicated that CNPase was most stable at a pH of 5.5, and could be significantly stabilized by high salt concentrations.

Conclusions

We have been able to express and purify recombinantly several different domains of CNPase, including the isolated N-terminal domain, which is folded mainly into a β-sheet structure. The expression system can be used as an efficient tool to elucidate the role of CNPase in the myelin sheath.

Early ultrastructural defects of axons and axon-glia junctions in mice lacking expression of Cnp1

Most axons in the central nervous system (CNS) are surrounded by a multilayered myelin sheath that promotes fast, saltatory conduction of electrical impulses. By insulating the axon, myelin also shields the axoplasm from the extracellular milieu. In the CNS, oligodendrocytes provide support for the long-term maintenance of myelinated axons, independent of the myelin sheath. Here, we use electron microscopy and morphometric analyses to examine the evolution of axonal and oligodendroglial changes in mice deficient in 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) and in mice deficient in both CNP and proteolipid protein (PLP/DM20). We show that CNP is necessary for the formation of a normal inner tongue process of oligodendrocytes that myelinate small diameter axons. We also show that axonal degeneration in Cnp1 null mice is present very early in postnatal life. Importantly, compact myelin formed by transplanted Cnp1 null oligodendrocytes induces the same degenerative changes in shiverer axons that normally are dysmyelinated but structurally intact. Mice deficient in both CNP and PLP develop a more severe axonal phenotype than either single mutant, indicating that the two oligodendroglial proteins serve distinct functions in supporting the myelinated axon. These observations support a model in which the trophic functions of oligodendrocytes serve to offset the physical shielding of axons by myelin membranes.

Ca2+-dependent permeability transition regulation in rat brain mitochondria by 2',3'-cyclic nucleotides and 2',3'-cyclic nucleotide 3'-phosphodiesterase

Recent evidence indicates that 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), a marker enzyme of myelin and oligodendrocytes, is also present in neural and nonneural mitochondria. However, its role in mitochondria is still completely unclear. We found CNP in rat brain mitochondria and studied the effects of CNP substrates, 2',3'-cyclic nucleotides, on functional parameters of rat brain mitochondria. 2',3'-cAMP and 2',3'-cNADP stimulated Ca(2+) overload-induced Ca(2+) release from mitochondrial matrix. This Ca(2+) release under threshold Ca(2+) load correlated with membrane potential dissipation and mitochondrial swelling. The effects of 2',3'-cyclic nucleotides were suppressed by cyclosporin A, a potent inhibitor of permeability transition (PT). PT development is a key stage in initiation of apoptotic mitochondria-induced cell death. 2',3'-cAMP effects were observed on the functions of rat brain mitochondria only when PT was developed. This demonstrates involvement of 2',3'-cAMP in PT regulation in rat brain mitochondria. We also discovered that, under PT development, the specific enzymatic activity of CNP was reduced. Thus we hypothesize that suppression of CNP activity under threshold Ca(2+) load leads to elevation of 2',3'-cAMP levels that, in turn, promote PT development in rat brain mitochondria. Similar effects of 2',3'-cyclic nucleotides were observed in rat liver mitochondria. Involvement of CNP in PT regulation was confirmed in experiments using mitochondria from CNP-knockdown oligodendrocytes (OLN93 cells). CNP reduction in these mitochondria correlated with lowering the threshold for Ca(2+) overload-induced Ca(2+) release. Thus our results reveal a new function for CNP and 2',3'-cAMP in mitochondria, being a regulator/promotor of mitochondrial PT.