Characterization of Solitalea canadensis α-mannosidase with specific activity towards α1,3-Mannosidic linkages.

A recombinant exo-α-mannosidase from Solitalea canadensis (Sc3Man) has been characterized to exhibit strict specificity for hydrolyzing α1,3-mannosidic linkages located at the non-reducing end of glycans containing α-mannose. Enzymatic characterization revealed that Sc3Man operates optimally at a pH of 5.0 and at a temperature of 37 °C. The enzymatic activity was notably enhanced twofold in the presence of Ca2+ ions, emphasizing its potential dependency on this metal ion, while Cu2+ and Zn2+ ions notably impaired enzyme function. Sc3Man was able to efficiently cleave the terminal α1,3 mannose residue from various high-mannose N-glycan structures and from the model glycoprotein RNase B. This work not only expands the categorical scope of bacterial α-mannosidases, but also offers new insight into the glycan metabolism of S. canadensis, highlighting the enzyme's utility for glycan analysis and potential biotechnological applications.

An iPSC-derived astrocyte model of fragile X syndrome exhibits dysregulated cholesterol homeostasis.

Cholesterol is an essential membrane structural component and steroid hormone precursor, and is involved in numerous signaling processes. Astrocytes regulate brain cholesterol homeostasis and they supply cholesterol to the needs of neurons. ATP-binding cassette transporter A1 (ABCA1) is the main cholesterol efflux transporter in astrocytes. Here we show dysregulated cholesterol homeostasis in astrocytes generated from human induced pluripotent stem cells (iPSCs) derived from males with fragile X syndrome (FXS), which is the most common cause of inherited intellectual disability. ABCA1 levels are reduced in FXS human and mouse astrocytes when compared with controls. Accumulation of cholesterol associates with increased desmosterol and polyunsaturated phospholipids in the lipidome of FXS mouse astrocytes. Abnormal astrocytic responses to cytokine exposure together with altered anti-inflammatory and cytokine profiles of human FXS astrocyte secretome suggest contribution of inflammatory factors to altered cholesterol homeostasis. Our results demonstrate changes of astrocytic lipid metabolism, which can critically regulate membrane properties and affect cholesterol transport in FXS astrocytes, providing target for therapy in FXS.

EphA4 targeting agents protect motor neurons from cell death induced by amyotrophic lateral sclerosis -astrocytes.

Amyotrophic lateral sclerosis (ALS) is a degenerative disease that progressively destroys motor neurons (MNs). Earlier studies identified EphA4, a receptor tyrosine kinase, as a possible disease-modifying gene. The complex interplay between the EphA4 receptor and its ephrin ligands in motor neurons and astrocytes has not yet been fully elucidated and includes a putative pro-apoptotic activity of the unbound receptor compared to ephrin-bound receptor. We recently reported that astrocytes from patients with ALS induce cell death in co-cultured MNs. Here we found that first-generation synthetic EphA4 agonistic agent 123C4, effectively protected MNs when co-cultured with reactive astrocytes from patients with ALS from multiple subgroups (sALS and mutant SOD1). Newer generation and more potent EphA4 agonistic agents 150D4, 150E8, and 150E7 provided effective protection at a lower therapeutic dose. Combined, the data suggest that the development of EphA4 agonistic agents provides potentially a promising therapeutic strategy for patients with ALS.

Functional consequences of postnatal interventions in a mouse model of Fragile X syndrome.

BACKGROUND: Fragile X syndrome (FXS) is a leading genetic cause of autism and intellectual disability with cortical hyperexcitability and sensory hypersensitivity attributed to loss and hypofunction of inhibitory parvalbumin-expressing (PV) cells. Our studies provide novel insights into the role of excitatory neurons in abnormal development of PV cells during a postnatal period of inhibitory circuit refinement. METHODS: To achieve Fragile X mental retardation gene (Fmr1) deletion and re-expression in excitatory neurons during the postnatal day (P)14-P21 period, we generated CreCaMKIIa/Fmr1Flox/y (cOFF) and CreCaMKIIa/Fmr1FloxNeo/y (cON) mice, respectively. Cortical phenotypes were evaluated in adult mice using biochemical, cellular, clinically relevant electroencephalogram (EEG) and behavioral tests. RESULTS: We found that similar to global Fmr1 KO mice, the density of PV-expressing cells, their activation, and sound-evoked gamma synchronization were impaired in cOFF mice, but the phenotypes were improved in cON mice. cOFF mice also showed enhanced cortical gelatinase activity and baseline EEG gamma power, which were reduced in cON mice. In addition, TrkB phosphorylation and PV levels were lower in cOFF mice, which also showed increased locomotor activity and anxiety-like behaviors. Remarkably, when FMRP levels were restored in only excitatory neurons during the P14-P21 period, TrkB phosphorylation and mouse behaviors were also improved. CONCLUSIONS: These results indicate that postnatal deletion or re-expression of FMRP in excitatory neurons is sufficient to elicit or ameliorate structural and functional cortical deficits, and abnormal behaviors in mice, informing future studies about appropriate treatment windows and providing fundamental insights into the cellular mechanisms of cortical circuit dysfunction in FXS.

NMR-Guided Design of Potent and Selective EphA4 Agonistic Ligands.

In this paper, we applied an innovative nuclear magnetic resonance (NMR)-guided screening and ligand design approach, named focused high-throughput screening by NMR (fHTS by NMR), to derive potent, low-molecular-weight ligands capable of mimicking interactions elicited by ephrin ligands on the receptor tyrosine kinase EphA4. The agents bind with nanomolar affinity, trigger receptor activation in cellular assays with motor neurons, and provide remarkable motor neuron protection from amyotrophic lateral sclerosis (ALS) patient-derived astrocytes. Structural studies on the complex between EphA4 ligand-binding domain and a most active agent provide insights into the mechanism of the agents at a molecular level. Together with preliminary in vivo pharmacology studies, the data form a strong foundation for the translation of these agents for the treatment of ALS and potentially other human diseases.

Biochemical characterization of the endo-α-N-acetylgalactosaminidase pool of the human gut symbiont Tyzzerella nexilis.

Three large (2084-, 984-, and 2104-amino acids) endo-α-N-acetylgalactosaminidase candidate genes from the commensal human gut bacterium Tyzzerella nexilis were successfully cloned and subsequently expressed in Escherichia coli. Activity tests of the purified proteins revealed that two of the candidate genes (Tn0153 and Tn2105) were able to hydrolyze the disaccharide unit from Galß1-3GalNAc-α-pNP. The biochemical characterization revealed optimum pH conditions of 4.0 for both enzymes and temperature optima of 50 °C. The addition of 2-mercaptoethanol, Triton X-100 and urea had only minor effects on the activity of the enzymes, and the addition of imidazole and sodium dodecyl sulfate led to a significant reduction of the enzymes' activities. A mutational study identified and confirmed the role of the catalytically significant amino acids. The present study describes the first functional characterization of members of the GH101 family from this human gut symbiont.

Beneficial effects of sound exposure on auditory cortex development in a mouse model of Fragile X Syndrome.

BACKGROUND: Fragile X syndrome (FXS) is the most common genetic cause of autism and intellectual disability. Fragile X mental retardation gene (Fmr1) knock-out (KO) mice display core deficits of FXS, including abnormally increased sound-evoked responses, and show a delayed development of parvalbumin (PV) cells. Here, we present the surprising result that sound exposure during early development reduces correlates of auditory hypersensitivity in Fmr1 KO mice. METHODS: Fmr1 KO and wild-type (WT) mice were raised in a sound-attenuated environment (AE) or sound-exposed (SE) to 14 kHz tones (5 Hz repetition rate) from P9 until P21. At P21-P23, event-related potentials (ERPs), dendritic spine density, PV expression and phosphorylation of tropomyosin receptor kinase B (TrkB) were analyzed in the auditory cortex of AE and SE mice. RESULTS: Enhanced N1 amplitude of ERPs, impaired PV cell development, and increased spine density in layers (L) 2/3 and L5/6 excitatory neurons were observed in AE Fmr1 KO compared to WT mice. In contrast, developmental sound exposure normalized ERP N1 amplitude, density of PV cells and dendritic spines in SE Fmr1 KO mice. Finally, TrkB phosphorylation was reduced in AE Fmr1 KO, but was enhanced in SE Fmr1 KO mice, suggesting that BDNF-TrkB signaling may be regulated by sound exposure to influence PV cell development. CONCLUSIONS: Our results demonstrate that sound exposure, but not attenuation, during early developmental window restores molecular, cellular and functional properties in the auditory cortex of Fmr1 KO mice, and suggest this approach as a potential treatment for sensory phenotypes in FXS.

Engineering of an Episomal Plasmid Suitable for High-Throughput Expression in Pichia pastoris.

AIM AND OBJECTIVE: This study describes the design and evaluation of an expression vector for Pichia pastoris (pPICZαBHF), which is based on the commercial vector construct pPICZαB. MATERIAL AND METHODS: The performance of pPICZαBHF was evaluated with red fluorescent protein as a reporter. Additional His- and Flag-tags on the N-terminal ensured a simplified protein purification procedure. Transformation efficiency, expression level and plasmid maintenance were studied in order to test the functionality and usefulness of the constructed vector. RESULTS: We found that high transformation efficiencies were achieved using pPICZαBHF plasmid for yeast cell transformation in comparison with the commercial vector pPICZαB, which has to be integrated into the Pichia genome. However, expression levels of the recombinant protein were generally lower compared to the commercial construct. Recombinant plasmids were shown to be maintained in cells for approximately five days. CONCLUSION: Although pPICZαBHF may not be suitable for the production of high levels of recombinant protein, the simplicity of this P. pastoris expression system may still be of interest for the expression of proteins involved in cofactor regeneration or the expression of reporter genes. In addition, high transformation efficiency of pPICZαBHF may be beneficial for the applications such as high-throughput screening of mutant gene libraries.

Effects of microvirin monomers and oligomers on hepatitis C virus.

Microvirin (MVN) is a carbohydrate-binding protein which shows high specificity for high-mannose type N-glycan structures. In the present study, we tried to identify whether MVN could bind to high-mannose containing hepatitis C virus (HCV) envelope glycoproteins, which are heavily decorated high-mannose glycans. In addition, recombinantly expressed MVN oligomers in di-, tri- and tetrameric form were evaluated for their viral inhibition. MVN oligomers bound more efficiently to HCV virions, and displayed in comparison with the MVN monomer a higher neutralization potency against HCV infection. The antiviral effect was furthermore affected by the peptide linker sequence connecting the MVN monomers. The results indicate that MVN oligomers such as trimers and tetramers may be used as future neutralization agents against HCV infections.

Potent and Selective EphA4 Agonists for the Treatment of ALS.

Amyotrophic lateral sclerosis (ALS) is a progressive degenerative disease that affects motor neurons. Recent studies identified the receptor tyrosine kinase EphA4 as a disease-modifying gene that is critical for the progression of motor neuron degeneration. We report on the design and characterization of a family of EphA4 targeting agents that bind to its ligand binding domain with nanomolar affinity. The molecules exhibit excellent selectivity and display efficacy in a SOD1 mutant mouse model of ALS. Interestingly, the molecules appear to act as agonists for the receptor in certain surrogate cellular assays. While the exact mechanisms responsible for the therapeutic effect of the new agonists remain to be elucidated, we believe that the described agent represents both an invaluable pharmacological tool to further decipher the role of the EphA4 in ALS and potentially other human diseases, and a significant stepping stone for the development of novel treatments.

Alpha-synuclein activates BV2 microglia dependent on its aggregation state.

Synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA) are defined by the presence of intracellular alpha-synuclein aggregates in neurons and/or oligodendrocytes. In addition, post mortem tissue analysis revealed profound changes in microglial morphology, indicating microglial activation and neuroinflammation. Thus, alpha-synuclein may directly activate microglia, leading to increased production of key pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1ß), which in turn modulates the disease progression. The distinct alpha-synuclein species, which mediates the activation of microglia, is not well defined. We hypothesized that microglial activation depends on a specific aggregation state of alpha-synuclein. Here, we show that primarily human fibrillar alpha-synuclein increased the production and secretion of pro-inflammatory cytokines by microglial BV2 cells compared to monomeric and oligomeric alpha-synuclein. BV2 cells also preferentially phagocytosed fibrillar alpha-synuclein compared to alpha-synuclein monomers and oligomers. Microglial uptake of alpha-synuclein fibrils and the consequent activation were time- and concentration-dependent. Moreover, the degree of fibrillization determined the efficiency of microglial internalization. Taken together, our study highlights the specific crosstalk of distinct alpha-synuclein species with microglial cells.

Human milk oligosaccharides: The role in the fine-tuning of innate immune responses.

In order to secure the health of newborns over the period of immune immaturity during the first months of life, a mother provides her offspring with passive protection: bioactive molecules transferred through the placenta and breast milk. It is well known that human milk contains immunoglobulins (Ig), immune cells and diverse cytokines, which affect newborn directly or indirectly and contribute to the maturation of the immune system. However, in addition to the above-stated molecules, human milk oligosaccharides (HMOs), a complex mixture of free indigestible carbohydrates with multiple functions, play exceptional roles in the functioning of the infants' immune system. These biological molecules have been studied over decades, however, interest in HMOs does not seem to have abated. Although biological activities of oligosaccharides from human milk have been explicitly reviewed, information regarding the role of HMOs in inflammation remains rather fragmented. The purpose of this review is to compile existing knowledge about the role of certain species of HMOs, including fucosylated, galactosylated and sialylated oligosaccharides, and their signaling pathways in immunity and inflammation. The advances in applying this information to the treatment of diseases in infants as well as adults were also reviewed here.

The fucosidase-pool of Emticicia oligotrophica: Biochemical characterization and transfucosylation potential.

Three novel bacterial α-l-fucosidases, which cleave terminal fucosyl residues from glycoconjugates are reported in this work. Originating from the recently discovered bacterium Emticicia oligotrophica, recombinant fucosidase isoforms designated as Eo0918, Eo3066 and Eo3812 were shown to have the highest activity between pH 6.0 and 7.0 and temperature optima between 30 and 45°C. All enzymes catalyzed the hydrolysis of the model substrate pNP-α-l-fucose and revealed significantly different regiospecificities towards fucose-containing oligosaccharides: Eo0918 liberated exclusively α1,6-linked fucose and Eo3812 released only α1,3-fucosyl residues, whereas Eo3066 showed broader substrate promiscuity. The enzymatic activity of Eo0918 and Eo3812 increased upon the addition of Ca(2+), Mn(2+) and Zn(2+) ions, whereas the activity of Eo3066 was significantly decreased in the presence of these metal ions. In addition, Eo0918 also catalyzed the transfer of fucose from pNP-α-l-fucose to the 7-hydroxyl group of 4-methylumbelliferone with up to 15% transglycosylation yield. Facile recombinant expression in E. coli, distinct substrate specificities and the transglycosylation ability of Eo0918 presented herein make these newly discovered fucosidases valuable candidates for bioanalytical and biotechnological applications.

Sequential processing of mannose-containing glycans by two α-mannosidases from Solitalea canadensis.

Two putative α-mannosidase genes isolated from the rather unexplored soil bacterium Solitalea canadensis were cloned and biochemically characterised. Both recombinant enzymes were highly selective in releasing α-linked mannose but no other sugars. The α-mannosidases were designated Sca2/3Man2693 and Sca6Man4191, and showed the following biochemical properties: the temperature optimum for both enzymes was 37 °C, and their pH optima lay at 5.0 and 5.5, respectively. The activity of Sca2/3Man2693 was found to be dependent on Ca(2+) ions, whereas Cu(2+) and Zn(2+) ions almost completely inhibited both α-mannosidases. Specificity screens with various substrates revealed that Sca2/3Man2693 could release both α1-2- and α1-3-linked mannose, whereas Sca6Man4191 only released α1-6-linked mannose. The combined enzymatic action of both recombinant α-mannosidases allowed the sequential degradation of high-mannose-type N-glycans. The facile expression and purification procedures in combination with strict substrate specificities make α-mannosidases from S. canadensis promising candidates for bioanalytical applications.

Biochemical characterisation of the neuraminidase pool of the human gut symbiont Akkermansia muciniphila.

Since the isolation and identification of Akkermansia muciniphila one decade ago, much attention has been drawn to this gut bacterium due to its role in obesity and type 2 diabetes. This report describes the discovery and biochemical characterisation of all four putative neuraminidases annotated in the A. muciniphila genome. Recombinantly expressed candidate genes, which were designated Am0705, Am0707, Am1757 and Am2085, were shown to cover complementary pH ranges between 4.0 and 9.5. Temperature optima of the enzymes lay between 37 and 42 °C. All four enzymes were strongly inhibited by Cu(2+) and Zn(2+), and loss of activity after the addition of EDTA suggests that all neuraminidases, with the exception of Am0707, require divalent metal ions for their catalytic function. Chemoenzymatically synthesised α2,3- and α2,6-linked indoyl-sialosides were utilised to determine the regioselectivity and substrate promiscuity of the neuraminidases towards C5-modifications of sialic acids with N-acetyl-, N-glycolyl-, N-propionyl-, or hydroxyl-groups. The combination of simple purification procedures and good activities of some of the characterised neuraminidases makes them potentially interesting as tools in bioanalytical or industrial applications.

Identification and Characterization of Two Novel Alpha-D-Galactosidases from Pedobacter heparinus.

Two putative α-D-galactosidases (α-GALs) belonging to glycosyl hydrolase family 27, and originating from the rather unexplored bacterial strain Pedobacter heparinus, were cloned and biochemically characterized. The recombinant enzymes designated as PhAGal729 and PhAGal2920 showed comparable biochemical properties: the optimum pH values were determined to be pH 5.0 and 5.5, and temperature optima lay between 30°C and 37°C, respectively. Both α-GALs were not dependent on the presence of divalent metal ions, and the addition of EDTA had no influence on enzymatic activity. The activity of both enzymes substantially increased in the presence of Fe3(+) ions. Both enzymes were inhibited by sodium dodecyl sulfate (SDS) and urea. α-GALs from P. heparinus were highly specific in hydrolyzing glycosides with α-1,2/3/4 or α-1,6-linked galactose to other sugars, whereas other glycosides such as α-linked N-acetylgalactosamine, N-acetylglucosamine or glucose residues were not released. Nevertheless, neither PhAGal729 nor PhAGal2920 were able to remove α-linked galactose epitopes from native human erythrocytes. The facile expression and purification procedures in combination with wide substrate specificities make α-GALs from P. heparinus potential candidates for applications in analytical research, and food- and biotechnology.

Discovery and Biochemical Characterization of UDP-Glucose Dehydrogenase from Granulibacter bethesdensis.

UDP-glucose dehydrogenases (EC 1.1.1.22) are responsible for the conversion of UDP-glucose to UDP-glucuronic acid, a key precursor in the biosynthesis of glycoconjugates. Herein we report the discovery and characterization of a UDPglucose dehydrogenase (GbUGD) from Granulibacter bethesdensis, a bacterium originally isolated from the lymph nodes of patients with chronic granulomatous disease (CGD). The recombinant form of the protein was expressed in high yield and the purified enzyme showed highest activity at 37°C/pH 9.0 and was strongly inhibited by Zn(2+) ions, sodium dodecyl sulfate (SDS) and urea. UDP-xylose, an allosteric feedback inhibitor, reduced significantly the activity of the enzyme. High activities were observed using the co-substrates UDP-glucose and NAD+, whereas no activity could be detected using other nucleotide sugars or NADP(+) as potential alternative substrates. The high activity combined with the simple purification procedure used make GbUGD a valuable new alternative biocatalyst for the synthesis of UDP-glucuronic acid or the development of NAD+ regeneration systems.

Increased tyrosine hydroxylase expression accompanied by glial changes within the non-lesioned hemisphere in the 6-hydroxydopamine model of Parkinson's disease.

PURPOSE: Parkinson's disease (PD) is characterized by striatal synaptic deafferentation followed by dopaminergic cell death in the substantia nigra pars compacta. Not only degenerative, but also regenerative, compensatory changes at distant sites of the primary lesion may occur in PD. The aim of the study was to analyze the temporal pattern of axonal and glial responses over a time course of six weeks post-lesioning. METHODS: For this aim, 6-hydroxydopamine (6-OHDA) was injected unilaterally into the medial forebrain bundle and both lesioned and non-lesioned striata were analyzed. RESULTS: We detected increased tyrosine hydroxylase (TH) immunoreactivity within the non-lesioned striatum six weeks after injection indicative either of increased TH expression or compensatory neuritic changes. An increased number of microglial cells was present in both lesioned and unlesioned striata. There was no obvious change in microglial phenotype or in pro-inflammatory cytokine gene expression within the striatum without any apparent switch into a pro-inflammatory phenotype. No changes were observed in the number of mature oligodendrocytes. CONCLUSIONS: This temporal pattern shows, that the non-lesioned striatum undergoes profound changes, involving increased TH expression accompanied by a glial response. A better understanding of this complex interplay of neuronal as well as glial components not only within the lesioned, but also non-lesioned striatum may help to restore local neural circuits in PD.