The structure of human GALNS reveals the molecular basis for mucopolysaccharidosis IV A

Diminished GALNS activity in induced pluripotent stem cells of mucopolysaccharidosis IVA caused by compound p.S162Y and p.C165F mutation

BACKGROUND

Mucopolysaccharidosis (MPS) IVA is a lysosomal storage disorder caused by mutations in the gene encoding the galactosamine (N-acetyl)-6-sulfatase (GALNS) enzyme. Children with MPS IVA usually develop pectus carinatum, genu valgum and multiple skeletal abnormalities.

AIM

To establish a patient-derived induced pluripotent stem cell (iPSC) disease model to investigate the effects of two GALNS missense mutations.

METHODS

The medical history and clinical manifestations of a patient with MPS IVA were first inspected. The effects of the identified GALNS mutations were predicted through bioinformatic analysis. iPSCs were then generated by using Sendai virus to introduce Yamanaka reprogramming factors to urinary cells isolated from the patient. The pluripotency, karyotypic integrity, genetic mutations and differentiation ability of the iPSCs were tested. The effects of the GALNS mutations were further experimentally characterized using patient-derived cells.

RESULTS

The patient exhibited a typical MPS IVA phenotype. Enzyme replacement therapy could not correct her skeletal abnormalities. GALNS c.485C>A (p.S162Y) and c.494G>T (p.C165F) mutations, inherited from her father and mother, respectively, were identified in the patient. These two mutations were predicted to disturb the hydrophobic core of the GALNS catalytic domain. Patient-derived iPSCs were successfully generated, and further characterization indicated that the two missense mutations significantly diminished GALNS activity without affecting its amount at both the RNA and protein levels.

CONCLUSIONS

We established a novel clinically relevant MPS IVA disease model that will be useful not only for investigating the pathogenic mechanisms of MPS IVA variants but also for drug screening and preclinical evaluation of novel therapies.

Structural and Functional Integration of Tissue-Nonspecific Alkaline Phosphatase Within the Alkaline Phosphatase Superfamily: Evolutionary Insights and Functional Implications

Phosphatases are enzymes that catalyze the hydrolysis of phosphate esters. They play critical roles in diverse biological processes such as extracellular nucleotide homeostasis, transport of molecules across membranes, intracellular signaling pathways, or vertebrate mineralization. Among them, tissue-nonspecific alkaline phosphatase (TNAP) is today increasingly studied, due to its ubiquitous expression and its ability to dephosphorylate a very broad range of substrates and participate in several different biological functions. For instance, TNAP hydrolyzes inorganic pyrophosphate (PPi) to allow skeletal and dental mineralization. Additionally, TNAP hydrolyzes pyridoxal phosphate to allow cellular pyridoxal uptake, and stimulate vitamin B6-dependent reactions. Furthermore, TNAP has been identified as a key enzyme in non-shivering adaptive thermogenesis, by dephosphorylating phosphocreatine in the mitochondrial creatine futile cycle. This latter recent discovery and others suggest that the list of substrates and functions of TNAP may be much longer than previously thought. In the present review, we sought to examine TNAP within the alkaline phosphatase (AP) superfamily, comparing its sequence, structure, and evolutionary trajectory. The AP superfamily, characterized by a conserved central folding motif of a mixed beta-sheet flanked by alpha-helices, includes six subfamilies: AP, arylsulfatases (ARS), ectonucleotide pyrophosphatases/phosphodiesterases (ENPP), phosphoglycerate mutases (PGM), phosphonoacetate hydrolases, and phosphopentomutases. Interestingly, TNAP and several ENPP family members appear to participate in the same metabolic pathways and functions. For instance, extra-skeletal mineralization in vertebrates is inhibited by ENPP1-mediated ATP hydrolysis into the mineralization inhibitor PPi, which is hydrolyzed by TNAP expressed in the skeleton. Better understanding how TNAP and other AP family members differ structurally will be very useful to clarify their complementary functions. Structurally, TNAP shares the conserved catalytic core with other AP superfamily members but has unique features affecting substrate specificity and activity. The review also aims to highlight the importance of oligomerization in enzyme stability and function, and the role of conserved metal ion coordination, particularly magnesium, in APs. By exploring the structural and functional diversity within the AP superfamily, and discussing to which extent its members exert redundant, complementary, or specific functions, this review illuminates the evolutionary pressures shaping these enzymes and their broad physiological roles, offering insights into TNAP's multifunctionality and its implications for health and disease.

Phenotype-Genotype Correlation in Morquio A Syndrome: Protocol for a Meta-Analysis

BACKGROUND

Mucopolysaccharidosis type IVA (MPS IVA), also known as Morquio A syndrome, is a rare lysosomal storage disease characterized by autosomal recessive inheritance of mutations in the N-acetylgalactosamine-6-sulfatase (GALNS) gene. This leads to a deficiency of the GALNS enzyme, causing the accumulation of glycosaminoglycans in tissues. Morquio A syndrome primarily affects the skeletal system and joints but can also impact various organs, resulting in symptoms such as hearing and vision loss, respiratory issues, spinal cord compression, heart diseases, and hepatomegaly. The genotype-phenotype relationship is diverse, with studies highlighting variants associated with classic, nonclassic, or intermediate phenotypes. Understanding these genetic factors is crucial for predicting disease prognosis and tailoring effective treatment strategies for individuals with Morquio A syndrome.

OBJECTIVE

The aim of this meta-analysis is to comprehend the relationship between the severity of the phenotype and the genotype of patients with MPS IVA, considering factors such as the type of variant and its location in the different domains of the protein.

METHODS

This meta-analysis will include articles featuring participants of all genders and age groups who have a molecular diagnosis of MPS IVA and a description of the phenotype. Literature published in English, Spanish, and Portuguese will be considered. Exclusion criteria will encompass studies lacking full-text availability and those involving patients with an MPS IVA diagnosis but without phenotype information. The databases to be searched include PubMed, MEDLINE, ScienceDirect, and Scopus. The screening of literature, paper selection, and data extraction will involve 2 independent reviewers, who will conduct the process blindly. In the event of disagreements between the 2 reviewers at any stage, resolution will be sought through discussion or with the involvement of an additional reviewer. The final selection of manuscripts will be based on consensus. The results of the review will be presented using descriptive statistics, and the information will be organized in either diagrammatic or tabular formats, following the guidelines provided by the Joanna Briggs Institute. Genotype-phenotype relationships will be analyzed using IBM SPSS Statistics, using chi-square tests, Fisher exact tests, and regression analysis to interpret the data.

RESULTS

A literature search conducted in January 2024 produced 760 results. The review is expected to be completed by the end of 2024.

CONCLUSIONS

This meta-analysis will gather and analyze information on the phenotype-genotype relationship in patients diagnosed with MPS IVA. The data collection and resulting analyses will make a substantial contribution to understanding the underlying mechanism of the disease, enabling the prediction of the syndrome's progression and severity.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/56649.

Novel human recombinant N-acetylgalactosamine-6-sulfate sulfatase produced in a glyco-engineered Escherichia coli strain

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disease caused by mutations in the gene encoding the lysosomal enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS), resulting in the accumulation of keratan sulfate (KS) and chondroitin-6-sulfate (C6S). Previously, it was reported the production of an active human recombinant GALNS (rGALNS) in E. coli BL21(DE3). However, this recombinant enzyme was not taken up by HEK293 cells or MPS IVA skin fibroblasts. Here, we leveraged a glyco-engineered E. coli strain to produce a recombinant human GALNS bearing the eukaryotic trimannosyl core N-glycan, Man3GlcNAc2 (rGALNSoptGly). The N-glycosylated GALNS was produced at 100 mL and 1.65 L scales, purified and characterized with respect to pH stability, enzyme kinetic parameters, cell uptake, and KS clearance. The results showed that the addition of trimannosyl core N-glycans enhanced both protein stability and substrate affinity. rGALNSoptGly was capture through a mannose receptor-mediated process. This enzyme was delivered to the lysosome, where it reduced KS storage in human MPS IVA fibroblasts. This study demonstrates the potential of a glyco-engineered E. coli for producing a fully functional GALNS enzyme. It may offer an economic approach for the biosynthesis of a therapeutic glycoprotein that could prove useful for MPS IVA treatment. This strategy could be extended to other lysosomal enzymes that rely on the presence of mannose N-glycans for cell uptake.

The deleterious variants of N-acetylgalactosamine-6-sulfatase (GalN6S) enzyme trigger Morquio a syndrome by disrupting protein foldings

Lysosomal enzymes degrade cellular macromolecules, while their inactivation causes human hereditary metabolic disorders. Mucopolysaccharidosis IVA (MPS IVA; Moquio A syndrome) is one of the lysosomal storage disorders caused by a defective Galactosamine-6-sulfatase (GalN6S) enzyme. In several populations, disease incidence is elevated due to missense mutations brought on by non-synonymous allelic variation in the GalN6S enzyme. Here, we studied the effect of non-synonymous single nucleotide polymorphism (nsSNPs) on the structural dynamics of the GalN6S enzyme and its binding with N-acetylgalactosamine (GalNAc) using all-atom molecular dynamics simulation and an essential dynamics approach. Consequently, in this study, we have identified three functionally disruptive mutations in domain-I and domain-II, that is, S80L, R90W, and S162F, which presumably contribute to post-translational modifications. The study delineated that both domains work cooperatively, and alteration in domain II (S80L, R90W) leads to conformational changes in the catalytic site in domain-I, while mutation S162F mainly provokes higher residual flexibility of domain II. These results show that these mutations impair the hydrophobic core, implying that Morquio A syndrome is caused by misfolding of the GalN6S enzyme. The results also show the instability of the GalN6S-GalNAc complex upon substitution. Overall, the structural dynamics resulting from point mutations give the molecular rationale for Moquio A syndrome and, more importantly, the Mucopolysaccharidoses (MPS) family of diseases, re-establishing MPS IVA as a protein-folding disease.Communicated by Ramaswamy H. Sarma.

Gold nanoparticles decorated with monosaccharides and sulfated ligands as potential modulators of the lysosomal enzyme N-acetylgalactosamine-6-sulfatase (GALNS)

N-Acetylgalactosamine-6-sulfatase (GALNS) is an enzyme whose deficiency is related to the lysosomal storage disease Morquio A. For the development of effective therapeutic approaches against this disease, the design of suitable enzyme enhancers (i.e. pharmacological chaperones) is fundamental. The natural substrates of GALNS are the glycosaminoglycans keratan sulfate and chondroitin 6-sulfate, which mainly display repeating units of sulfated carbohydrates. With a biomimetic approach, gold nanoparticles (AuNPs) decorated with simple monosaccharides, sulfated ligands (homoligand AuNPs), or both monosaccharides and sulfated ligands (mixed-ligand AuNPs) were designed here as multivalent inhibitors of GALNS. Among the homoligand AuNPs, the most effective inhibitors of GALNS activity are the β-D-galactoside-coated AuNPs. In the case of mixed-ligand AuNPs, β-D-galactosides/sulfated ligands do not show better inhibition than the β-D-galactoside-coated AuNPs. However, a synergistic effect is observed for α-D-mannosides in a mixed-ligand coating with sulfated ligands that reduced IC50 by one order of magnitude with respect to the homoligand α-D-mannoside-coated AuNPs. SAXS experiments corroborated the association of GALNS with β-D-galactoside AuNPs. These AuNPs are able to restore the enzyme activity by almost 2-fold after thermal denaturation, indicating a potential chaperoning activity towards GALNS. This information could be exploited for future development of nanomedicines for Morquio A. The recent implications of GALNS in cancer and neuropathic pain make these kinds of multivalent bionanomaterials of great interest towards multiple therapies.

Mucopolysaccharidosis IVA: Current Disease Models and Drawbacks

Mucopolysaccharidosis IVA (MPS IVA) is a rare disorder caused by mutations in the N-acetylgalactosamine-6-sulfate-sulfatase (GALNS) encoding gene. GALNS leads to the lysosomal degradation of the glycosaminoglyccreasans keratan sulfate and chondroitin 6-sulfate. Impaired GALNS enzymes result in skeletal and non-skeletal complications in patients. For years, the MPS IVA pathogenesis and the assessment of promising drugs have been evaluated using in vitro (primarily fibroblasts) and in vivo (mainly mouse) models. Even though value information has been raised from those studies, these models have several limitations. For instance, chondrocytes have been well recognized as primary cells affected in MPS IVA and responsible for displaying bone development impairment in MPS IVA patients; nonetheless, only a few investigations have used those cells to evaluate basic and applied concepts. Likewise, current animal models are extensively represented by mice lacking GALNS expression; however, it is well known that MPS IVA mice do not recapitulate the skeletal dysplasia observed in humans, making some comparisons difficult. This manuscript reviews the current in vitro and in vivo MPS IVA models and their drawbacks.

Molecular Trojan Horses for treating lysosomal storage diseases

Lysosomal storage diseases (LSDs) are caused by monogenic mutations in genes encoding for proteins related to the lysosomal function. Lysosome plays critical roles in molecule degradation and cell signaling through interplay with many other cell organelles, such as mitochondria, endoplasmic reticulum, and peroxisomes. Even though several strategies (i.e., protein replacement and gene therapy) have been attempted for LSDs with promising results, there are still some challenges when hard-to-treat tissues such as bone (i.e., cartilages, ligaments, meniscus, etc.), the central nervous system (mostly neurons), and the eye (i.e., cornea, retina) are affected. Consistently, searching for novel strategies to reach those tissues remains a priority. Molecular Trojan Horses have been well-recognized as a potential alternative in several pathological scenarios for drug delivery, including LSDs. Even though molecular Trojan Horses refer to genetically engineered proteins to overcome the blood-brain barrier, such strategy can be extended to strategies able to transport and deliver drugs to specific tissues or cells using cell-penetrating peptides, monoclonal antibodies, vesicles, extracellular vesicles, and patient-derived cells. Only some of those platforms have been attempted in LSDs. In this paper, we review the most recent efforts to develop molecular Trojan Horses and discuss how this strategy could be implemented to enhance the current efficacy of strategies such as protein replacement and gene therapy in the context of LSDs.

Genotype and Phenotype Characterization of Patients with Mucopolysaccharidosis IV-A in Chile

Introduction

Morquio syndrome or mucopolysaccharidosis type IV-A (MPS IV-A) is an autosomal recessive disease caused by biallelic variants in the GALNS gene, encoding the lysosomal enzyme GalN6S, responsible for glycosaminoglycan keratan sulfate and chondroitin-6-sulfate degradation. Studies have shown that the degree of evolutionary and chemical divergence of missense variants in GalN6S when compared to ancestral amino acids is associated with the severity of the syndrome, suggesting a genotype-phenotype correlation. There is little information on Latin American patients with MPS IV-A that replicate these findings. This study aimed to characterize the phenotype and genotype from patients with MPS IV-A, who are under Enzyme Replacement Therapy at the Children's Neuropsychiatry Service of the Hospital Clínico San Borja Arriarán, Santiago, Chile, and to determine if there is any association between genotype and phenotype with those findings.

Methods

Information was collected from medical charts, all patients went through a GalN6S enzymatic activity measurement in leukocytes from peripheral blood, and the GALNS gene was sequenced for all cases.

Results

12 patients with MPS IV-A were recruited, all patients presented multisystem involvement, mostly skeletal, and 75% of cases underwent surgical interventions, and cervical arthrodesis was the most frequent procedure. In regards of the genotype, the two most frequent variants were c.319+2T>C (n = 10, 41.66%) and p.(Arg386Cys) (n = 8, 33.33%), the first one was previously described in 2018 in a patient from Chile [Bochernitsan et al., 2018].

Conclusion

This is the first time that a genotype-phenotype correlation has been studied by analyzing the variants effect on the molecular structure of human GalN6S and the evolutionary conservation degree of affected residues in a cohort of patients in Chile. Albeit our work could not find statistically significant associations, we may infer that the evolutionary conservations of affected amino acids and the effect of variants on enzyme structure may play a main role. Further analyzes should consider a meta-analysis of published cases with genotype data and larger samples and include other variables that could provide more information. Finally, our data strongly suggest that variant c.319+2T>C could have a founder effect in Chilean patients with MPS IV-A.

Identification of galactosamine-(N-acetyl)-6-sulfatase (GALNS) as a novel therapeutic target in progression of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a commonly diagnosed malignancy in southern China and southeast Asia. Previous studies have identified galactosamine-(N-acetyl)-6-sulfatase (GALNS) as a potential biomarker for multiple cancers. However, it is unknown whether GALNS plays a role in NPC development, and the underlying mechanisms remain unclear. In this study, we found that GALNS is overexpressed in NPC cell lines and tissues compared to the normal nasopharyngeal counterparts. Knocking down GALNS expression in the NPC cells significantly decreased their proliferation in vitro, and inhibited xenograft growth in a mouse model. Mechanistically, the anti-proliferative effect of GALNS silencing was the result of autophagy induction via the inhibition of PI3K-AKT-mTOR signaling pathway. Taken together, GALNS drives the progression of NPC via PI3K-AKT-mTOR signaling-mediated autophagy, and is therefore a promising therapeutic target.

Primary Processes of Free Radical Formation in Pharmaceutical Formulations of Therapeutic Proteins

Oxidation represents a major pathway for the chemical degradation of pharmaceutical formulations. Few specific details are available on the mechanisms that trigger oxidation reactions in these formulations, specifically with respect to the formation of free radicals. Hence, these mechanisms must be formulated based on information on impurities and stress factors resulting from manufacturing, transportation and storage. In more detail, this article focusses on autoxidation, metal-catalyzed oxidation, photo-degradation and radicals generated from cavitation as a result of mechanical stress. Emphasis is placed on probable rather than theoretically possible pathways.

Blood RNA alternative splicing events as diagnostic biomarkers for infectious disease

Assays detecting blood transcriptome changes are studied for infectious disease diagnosis. Blood-based RNA alternative splicing (AS) events, which have not been well characterized in pathogen infection, have potential normalization and assay platform stability advantages over gene expression for diagnosis. Here, we present a computational framework for developing AS diagnostic biomarkers. Leveraging a large prospective cohort of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and whole-blood RNA sequencing (RNA-seq) data, we identify a major functional AS program switch upon viral infection. Using an independent cohort, we demonstrate the improved accuracy of AS biomarkers for SARS-CoV-2 diagnosis compared with six reported transcriptome signatures. We then optimize a subset of AS-based biomarkers to develop microfluidic PCR diagnostic assays. This assay achieves nearly perfect test accuracy (61/62 = 98.4%) using a naive principal component classifier, significantly more accurate than a gene expression PCR assay in the same cohort. Therefore, our RNA splicing computational framework enables a promising avenue for host-response diagnosis of infection.

Efficient CRISPR/Cas9 nickase-mediated genome editing in an in vitro model of mucopolysaccharidosis IVA

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disorder (LSD) caused by mutations in gene encoding for GALNS enzyme. Lack of GALNS activity leads to the accumulation of glycosaminoglycans (GAGs) keratan sulfate and chondroitin 6-sulfate. Although enzyme replacement therapy has been approved since 2014 for MPS IVA, still there is an unmet medical need to have improved therapies for this disorder. CRISPR/Cas9-based gene therapy has been tested for several LSDs with encouraging findings, but to date it has not been assayed on MPS IVA. In this work, we validated for the first time the use of CRISPR/Cas9, using a Cas9 nickase, for the knock-in of an expression cassette containing GALNS cDNA in an in vitro model of MPS IVA. The results showed the successful homologous recombination of the expression cassette into the AAVS1 locus, as well as a long-term increase in GALNS activity reaching up to 40% of wild-type levels. We also observed normalization of lysosomal mass, total GAGs, and oxidative stress, which are some of the major findings regarding the pathophysiological events in MPS IVA. These results represent a proof-of-concept of the use of CRISPR/Cas9 nickase strategy for the development of a novel therapeutic alternative for MPS IVA.

CRISPR/nCas9-Based Genome Editing on GM2 Gangliosidoses Fibroblasts via Non-Viral Vectors

The gangliosidoses GM2 are a group of pathologies mainly affecting the central nervous system due to the impaired GM2 ganglioside degradation inside the lysosome. Under physiological conditions, GM2 ganglioside is catabolized by the β-hexosaminidase A in a GM2 activator protein-dependent mechanism. In contrast, uncharged substrates such as globosides and some glycosaminoglycans can be hydrolyzed by the β-hexosaminidase B. Monogenic mutations on HEXA, HEXB, or GM2A genes arise in the Tay–Sachs (TSD), Sandhoff (SD), and AB variant diseases, respectively. In this work, we validated a CRISPR/Cas9-based gene editing strategy that relies on a Cas9 nickase (nCas9) as a potential approach for treating GM2 gangliosidoses using in vitro models for TSD and SD. The nCas9 contains a mutation in the catalytic RuvC domain but maintains the active HNH domain, which reduces potential off-target effects. Liposomes (LPs)- and novel magnetoliposomes (MLPs)-based vectors were used to deliver the CRISPR/nCas9 system. When LPs were used as a vector, positive outcomes were observed for the β-hexosaminidase activity, glycosaminoglycans levels, lysosome mass, and oxidative stress. In the case of MLPs, a high cytocompatibility and transfection ratio was observed, with a slight increase in the β-hexosaminidase activity and significant oxidative stress recovery in both TSD and SD cells. These results show the remarkable potential of CRISPR/nCas9 as a new alternative for treating GM2 gangliosidoses, as well as the superior performance of non-viral vectors in enhancing the potency of this therapeutic approach.

Delivery and assessment of a CRISPR/nCas9-based genome editing system on in vitro models of mucopolysaccharidoses IVA assisted by magnetite-based nanoparticles

Mucopolysaccharidosis IV A (MPS IVA) is a lysosomal disorder caused by mutations in the GALNS gene. Consequently, the glycosaminoglycans (GAGs) keratan sulfate and chondroitin 6-sulfate accumulate in the lysosomal lumen. Although enzyme replacement therapy has shown essential advantages for the patients, several challenges remain to overcome, such as the limited impact on the bone lesion and recovery of oxidative profile. Recently, we validated a CRISPR/nCas9-based gene therapy with promising results in an in vitro MPS IVA model. In this study, we have expanded the use of this CRISPR/nCas9 system to several MPS IVA fibroblasts carrying different GALNS mutations. Considering the latent need to develop more safety vectors for gene therapy, we co-delivered the CRISPR/nCas9 system with a novel non-viral vector based on magnetoliposomes (MLPs). We found that the CRISPR/nCas9 treatment led to an increase in enzyme activity between 5 and 88% of wild-type levels, as well as a reduction in GAGs accumulation, lysosomal mass, and mitochondrial-dependent oxidative stress, in a mutation-dependent manner. Noteworthy, MLPs allowed to obtain similar results to those observed with the conventional transfection agent lipofectamine. Overall, these results confirmed the potential of CRISPR/nCas9 as a genome editing tool for treating MPS IVA. We also demonstrated the potential use of MLPs as a novel delivery system for CRISPR/nCas9-based therapies.

RNA analysis of the GALNS transcript reveals novel pathogenic mechanisms associated with Morquio syndrome A

Morquio syndrome A (Mucopolysaccharidosis IVA, MPS IVA) is an autosomal recessive lysosomal storage disorder caused by deficiency of N-acetyl-galactosamine-6-sulfatase (GALNS) which catabolizes the glycosaminoglycans (GAG), keratan sulfate and chondroitin-6-sulfate. Homozygous or compound heterozygous pathogenic variants in the GALNS result in the deficiency of the enzyme and consequent GAG accumulations. DNA sequence and copy number analysis of the GALNS coding region fails to identify biallelic causative pathogenic variants in up to 15% of patients with Morquio syndrome A. RNA transcript analysis was performed to identify pathogenic alterations in two unrelated families with Morquio syndrome A in whom a single heterozygous or no pathogenic alteration was detected by standard analysis of the GALNS gene. RNA sequencing and quantitative expression analysis identified the overabundance of an aberrant GALNS transcript isoform and a reduction of the clinically relevant isoform (NM_000512.4) in the Morquio syndrome A patients from both families. The aberrant isoform (ENST00000568613.1) was produced by alternative splicing and contained intronic sequence that was likely a cryptic exon predicted to result in a reading frame shift and generation of a premature termination codon. These findings indicated that the aberrant splicing is likely the novel molecular defect in our patients. RNA transcript analysis could be useful to identify pathogenic alterations and increase the yield of molecular diagnosis in patients with Morquio syndrome A whose genetic variants are not found by standard sequencing or gene dosage analysis.

Investigation of GALNS variants and genotype-phenotype correlations in a large cohort of patients with mucopolysaccharidosis type IVA

Mucopolysaccharidosis type IVA (MPS IVA) is a rare autosomal recessive disorder resulting from the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) caused by pathogenic variants in the GALNS gene. A systematic analysis for genotype-phenotype correlation is essential due to hundreds of variants generating different levels of residual GALNS activity and causing a wide degree of clinical manifestation effects. Here, we retrospectively analyzed clinical and genetic data of 108 unrelated patients with MPS IVA to investigate the variants spectrum of GALNS and assess their clinical effects. In this cohort, 82 patients were classified as severe, 14 as intermediate, and 12 as mild. One hundred and one GALNS variants were identified, of which 47 were novel. Most patients with at least one GALNS null variant were classified as severe phenotype (92%, 33/36). Missense variants mapped to different residues of GALNS protein resulted in different phenotypes in patients with MPS IVA. Ninety-two percent of patients with two missense variants mapped to buried residues were classified as severe (92%, 24/26), while at least one missense variant mapped to surface residues was identified in patients with biallelic missense variants presenting intermediate MPS IVA (78%, 7/9) and presenting mild MPS IVA (86%, 6/7). Our study contributes to a better understanding of the molecular spectrum of GALNS variants and their clinical implications. Based on the data herein reported, we generated a systematic flowchart correlating the GALNS variants to assist in phenotype prediction and classification of patients with MPS IVA.

Autophagy in the Neuronal Ceroid Lipofuscinoses (Batten Disease)

The neuronal ceroid lipofuscinoses (NCLs), also referred to as Batten disease, are a family of neurodegenerative diseases that affect all age groups and ethnicities around the globe. At least a dozen NCL subtypes have been identified that are each linked to a mutation in a distinct ceroid lipofuscinosis neuronal (CLN) gene. Mutations in CLN genes cause the accumulation of autofluorescent lipoprotein aggregates, called ceroid lipofuscin, in neurons and other cell types outside the central nervous system. The mechanisms regulating the accumulation of this material are not entirely known. The CLN genes encode cytosolic, lysosomal, and integral membrane proteins that are associated with a variety of cellular processes, and accumulated evidence suggests they participate in shared or convergent biological pathways. Research across a variety of non-mammalian and mammalian model systems clearly supports an effect of CLN gene mutations on autophagy, suggesting that autophagy plays an essential role in the development and progression of the NCLs. In this review, we summarize research linking the autophagy pathway to the NCLs to guide future work that further elucidates the contribution of altered autophagy to NCL pathology.

Identification and Action Patterns of Two Chondroitin Sulfate Sulfatases From a Marine Bacterium Photobacterium sp. QA16

Chondroitin sulfate (CS)/dermatan sulfate (DS) is a kind of sulfated polyanionic, linear polysaccharide belonging to glycosaminoglycan. CS/DS sulfatases, which specifically hydrolyze sulfate groups from CS/DS oligo-/polysaccharides, are potential tools for structural and functional studies of CD/DS. However, only a few sulfatases have been reported and characterized in detail to date. In this study, two CS/DS sulfatases, PB_3262 and PB_3285, were identified from the marine bacterium Photobacterium sp. QA16 and their action patterns were studied in detail. PB_3262 was characterized as a novel 4-O-endosulfatase that can effectively and specifically hydrolyze the 4-O-sulfate group of disaccharide GlcUAβ1–3GalNAc(4-O-sulfate) but not GlcUAβ1–3GalNAc(4,6-O-sulfate) and IdoUAα1–3GalNAc(4-O-sulfate) in CS/DS oligo-/polysaccharides, which is very different from the identified 4-O-endosulfatases in the substrate profile. In contrast, PB_3285 specifically hydrolyzes the 6-O-sulfate groups of GalNAc(6-O-sulfate) residues located at the reducing ends of the CS chains and is the first recombinantly expressed 6-O-exosulfatase to effectively act on CS oligosaccharides.

Molecular characterization of a large cohort of Mucopolysaccharidosis patients: Iran Mucopolysaccharidosis RE-diagnosis Study (IMPRESsion)

Mucopolysaccharidoses (MPSs) are rare, heterogeneous inborn errors of metabolism (IEM) diagnosed through a combination of clinical, biochemical, and genetic investigations. The aim of this study was molecular characterization of the largest cohort of Iranian MPS patients (302 patients from 289 unrelated families), along with tracking their ethnicity and geographical origins. 185/289 patients were studied using an IEM-targeted NGS panel followed by complementary Sanger sequencing, which led to the diagnosis of 154 MPS patients and 5 non-MPS IEMs (diagnostic yield: 85.9%). Furthermore, 106/289 patients who were referred with positive findings went through re-analysis and confirmatory tests which confirmed MPS diagnosis in 104. Among the total of 258 MPS patients, 225 were homozygous, 90 harbored novel variants, and 9 had copy number variations. MPS IV was the most common type (34.8%) followed by MPS I (22.7%) and MPS VI (22.5%). Geographical origin analysis unveiled a pattern of distribution for frequent variants in ARSB (c.430G>A, c.962T>C [p.Leu321Pro], c.281C>A [p.Ser94*]), GALNS (c.319G>A [p.Ala107Thr], c.860C>T [p.Ser287Leu], c.1042A>G [p.Thr348Ala]), and IDUA (c.1A>C [p.Met1Leu], c.1598C>G [p.Pro533Arg], c.1562_1563insC [p.Gly522Argfs*50]). Our extensive patient cohort reveals the genetic and geographic landscape of MPS in Iran, which provides insight into genetic epidemiology of MPS and can facilitate a more cost-effective, time-efficient diagnostic approach based on the region-specific variants. This article is protected by copyright. All rights reserved.

Structural analysis of the sulfatase AmAS from Akkermansia muciniphila

Akkermansia muciniphila, an anaerobic Gram-negative bacterium, is a major intestinal commensal bacterium that can modulate the host immune response. It colonizes the mucosal layer and produces nutrients for the gut mucosa and other commensal bacteria. It is believed that mucin desulfation is the rate-limiting step in the mucin-degradation process, and bacterial sulfatases that carry out mucin desulfation have been well studied. However, little is known about the structural characteristics of A. muciniphila sulfatases. Here, the crystal structure of the premature form of the A. muciniphila sulfatase AmAS was determined. Structural analysis combined with docking experiments defined the critical active-site residues that are responsible for catalysis. The loop regions I–V were proposed to be essential for substrate binding. Structure-based sequence alignment and structural superposition allow further elucidation of how different subclasses of formylglycine-dependent sulfatases (FGly sulfatases) adopt the same catalytic mechanism but exhibit diverse substrate specificities. These results advance the understanding of the substrate-recognition mechanisms of A. muciniphila FGly-type sulfatases. Structural variations around the active sites account for the different substrate-binding properties. These results will enhance the understanding of the roles of bacterial sulfatases in the metabolism of glycans and host–microbe interactions in the human gut environment.

A novel thermostable prokaryotic fucoidan active sulfatase PsFucS1 with an unusual quaternary hexameric structure

Fucoidans are sulfated, fucose-rich marine polysaccharides primarily found in cell walls of brown seaweeds (macroalgae). Fucoidans are known to possess beneficial bioactivities depending on their structure and sulfation degree. Here, we report the first functional characterization and the first crystal structure of a prokaryotic sulfatase, PsFucS1, belonging to sulfatase subfamily S1_13, able to release sulfate from fucoidan oligosaccharides. PsFucS1 was identified in the genome of a Pseudoalteromonas sp. isolated from sea cucumber gut. PsFucS1 (57 kDa) is Ca²⁺ dependent and has an unusually high optimal temperature (68 °C) and thermostability. Further, the PsFucS1 displays a unique quaternary hexameric structure comprising a tight trimeric dimer complex. The structural data imply that this hexamer formation results from an uncommon interaction of each PsFucS1 monomer that is oriented perpendicular to the common dimer interface (~ 1500 Ų) that can be found in analogous sulfatases. The uncommon interaction involves interfacing (1246 Ų) through a bundle of α-helices in the N-terminal domain to form a trimeric ring structure. The high thermostability may be related to this unusual quaternary hexameric structure formation that is suggested to represent a novel protein thermostabilization mechanism.

Nationwide Newborn Screening Program for Mucopolysaccharidoses in Taiwan and an Update of the "Gold Standard" Criteria Required to Make a Confirmatory Diagnosis

Mucopolysaccharidoses (MPSs) are a group of lysosomal storage diseases (LSDs) caused by an inherited gene defect. MPS patients can remain undetected unless the initial signs or symptoms have been identified. Newborn screening (NBS) programs for MPSs have been implemented in Taiwan since 2015, and more than 48.5% of confirmed cases of MPS have since been referred from these NBS programs. The purpose of this study was to report the current status of NBS for MPSs in Taiwan and update the gold standard criteria required to make a confirmative diagnosis of MPS, which requires the presence of the following three laboratory findings: (1) elevation of individual urinary glycosaminoglycan (GAG)-derived disaccharides detected by MS/MS-based assay; (2) deficient activity of a particular leukocyte enzyme by fluorometric assay; and (3) verification of heterogeneous or homogeneous variants by Sanger sequencing or next generation sequencing. Up to 30 April 2021, 599,962 newborn babies have been screened through the NBS programs for MPS type I, II, VI, and IVA, and a total of 255 infants have been referred to MacKay Memorial Hospital for a confirmatory diagnosis. Of these infants, four cases were confirmed to have MPS I, nine cases MPS II, and three cases MPS IVA, with prevalence rates of 0.67, 2.92, and 4.13 per 100,000 live births, respectively. Intensive long-term regular physical and laboratory examinations for asymptomatic infants with confirmed MPS or with highly suspected MPS can enhance the ability to administer ERT in a timely fashion.

Identification of incompletely penetrant variants and interallelic interactions in autosomal recessive disorders by a population-genetic approach

We aimed to identify incompletely penetrant (IP) variants and interallelic interactions in autosomal recessive disorders by a population-genetic approach. Genotype and clinical data were collected from 9038 patients of European origin with ASL, ATP7B, CAPN3, CFTR, CTNS, DHCR7, GAA, GALNS, GALT, IDUA, MUT, NPHS1, NPHS2, PAH, PKHD1, PMM2, or SLC26A4-related disorders. We calculated the relative allele frequency of each pathogenic variant (n = 1936) to the loss-of-function (LOF) variants of the corresponding gene in the patient ( A C p t V / A C p t L O F ) and the general population ( AC gnomAD V / AC gnomAD LOF ) and estimated the penetrance of each variant by calculating their ratio: ( A C p t V / A C p t L O F ) ( A C g n o m A D V / A C g n o m A D L O F ) (V/LOF ratio). We classified all variants as null or hypomorphic based on the associated clinical phenotype. We found 25 variants, 29% of the frequent 85 variants, to be underrepresented in the patient population (V/LOF ratio <30% with p < 7.22 × 10^-5 ), including 22 novel ones in the ASL, CAPN3, CFTR, GAA, GALNS, PAH, and PKHD1 genes. In contrast to the completely penetrant variants (CP), the majority of the IP variants were hypomorphic (IP: 16/18, 88%; CP: 177/933, 19.0%; p = 5.12 × 10^-10 ). Among them, only the NPHS2 R229Q variant was subject to interallelic interactions. The proposed algorithm identifies frequent IP variants and estimates their penetrance and interallelic interactions in large patient cohorts.

Enzyme replacement combinational therapy: effective treatments for mucopolysaccharidoses

INTRODUCTION

Mucopolysaccharidoses (MPS), as a group of inherited lysosomal storage disorders (LSDs), are clinically heterogeneous and characterized by multi-systemic manifestations, such as skeletal abnormalities and neurological dysfunctions. The currently used enzyme replacement therapy (ERT) might be associated with several limitations including the low biodistribution of the enzymes into the main targets, immunological responses against foreign enzymes, and the high cost of the treatment procedure. Therefore, a suitable combination approach can be considered for the successful treatment of each type of MPS.

AREAS COVERED

In this review, we provide comprehensive insights into the ERT-based combination therapies of MPS by reviewing the published literature on PubMed and Scopus. We also discuss the recent advancements in the treatment of MPS and bring up the hopes and hurdles in the futuristic treatment strategies.

EXPERT OPINION

Given the complex pathophysiology of MPS and its involvement in different tissues, the ERT of MPS in combination with stem cell therapy or gene therapy is deemed to provide a personalized precision treatment modality with the highest therapeutic responses and minimal side effects. By the same token, new combinational approaches need to be evaluated by using drugs that target alternative and secondary pathological pathways.

Evaluation of HIV-1 derived lentiviral vectors as transductors of Mucopolysaccharidosis type IV a fibroblasts

Mucopolysaccharidosis type IVA (MPS IVA) is a lysosomal storage disease produced by the deficiency of the N-acetylgalactosamine-6-sulfate sulfatase (GALNS) enzyme, leading to glycosaminoglycans (GAGs) accumulation. Since currently available treatments remain limited and unspecific, novel therapeutic approaches are essential for the disease treatment. In an attempt to reduce treatment limitations, gene therapy rises as a more effective and specific alternative. We present in this study the delivery assessment of GALNS and sulfatase-modifying factor 1 (SUMF1) genes via HIV-1 derived lentiviral vectors into fibroblasts from MPS IVA patients. After transduction, we determined GALNS enzymatic activity, lysosomal mass change, and autophagy pathway impairment. Additionally, we computationally assessed the effect of mutations over the enzyme-substrate interaction and phenotypic effects. The results showed that the co-transduction of MPS IVA fibroblasts with GALNS and SUMF1 cDNAs led to a significant increase in GALNS enzyme activity and a reduction of lysosomal mass. We show that patient-specific differences in cellular response are directly associated with the set of mutations on each patient. Lastly, we present new evidence supporting autophagy impairment in MPS IVA due to the presence and changes in autophagy proteins in treated MPS IVA fibroblasts. Our results offer new evidence that demonstrate the potential of lentiviral vectors as a strategy to correct GALNS deficiency.

Clinical outcomes in elderly patients with Morquio a syndrome receiving enzyme replacement therapy - experience in a Colombian center

INTRODUCTION

Mucopolysaccharidosis type IV A (MPS IVA) or Morquio A syndrome is an autosomal recessive lysosomal storage disease caused by GALNS gene mutations that lead to a deficiency of the N-acetylgalactosamine-6-sulfate sulfatase enzyme and the accumulation of two glycosaminoglycans in cell lysosomes, namely, chondroitin and keratan sulfate.

OBJECTIVE

To present two female patients with Morquio A syndrome in their late adult years (over 50 years of age) with a classical phenotype, treated with enzyme replacement therapy; and to present a summary of the natural history and the characteristics of the disease, and the benefit of comprehensive management.

MATERIALS AND METHODS

Descriptive clinical study before and after the treatment with enzyme replacement therapy as part of the comprehensive management of MPS IVA.

RESULTS

Enzyme replacement therapy with elosulfase alfa was effective, with an adequate safety profile in these two patients, showing evidence of sustained improvement in terms of endurance and gait patterns.

CONCLUSION

We present two cases of MPS IVA, with longer survival than reported previously in classical phenotypes associated with this disease condition. There is a paucity of reports of similar cases in the literature. We believe that the clinical heterogeneity of the disease manifesting with the classical phenotype, together with comprehensive management, have played a role in the survival of these two patients. Therapy with elosulfase alfa as part of comprehensive management has been crucial; we suspect a clinical response and infer a better quality of life and reduced burden for the caregiver, supporting its use in older patients.

Oral immunotherapy tolerizes mice to enzyme replacement therapy for Morquio A syndrome

Immune response to therapeutic enzymes poses a detriment to patient safety and treatment outcome. Enzyme replacement therapy (ERT) is a standard therapeutic option for some types of mucopolysaccharidoses, including Morquio A syndrome caused by N-acetylgalactosamine-6-sulfate sulfatase (GALNS) deficiency. Current protocols tolerize patients using cytotoxic immunosuppressives, which can cause adverse effects. Here we show development of tolerance in Morquio A mice via oral delivery of peptide or GALNS for 10 days prior to ERT. Our results show that using an immunodominant peptide (I10) or the complete GALNS enzyme to orally induce tolerance to GALNS prior to ERT resulted in several improvements to ERT in mice: (a) decreased splenocyte proliferation after in vitro GALNS stimulation, (b) modulation of the cytokine secretion profile, (c) decrease in GALNS-specific IgG or IgE in plasma, (d) decreased GAG storage in liver, and (e) fewer circulating immune complexes in plasma. This model could be extrapolated to other lysosomal storage disorders in which immune response hinders ERT.

Lysosomal sulfatases: a growing family

Sulfatases constitute a family of enzymes that specifically act in the hydrolytic degradation of sulfated metabolites by removing sulfate monoesters from various substrates, particularly glycolipids and glycosaminoglycans. A common essential feature of all known eukaryotic sulfatases is the posttranslational modification of a critical cysteine residue in their active site by oxidation to formylglycine (FGly), which is mediated by the FGly-generating enzyme in the endoplasmic reticulum and is indispensable for catalytic activity. The majority of the so far described sulfatases localize intracellularly to lysosomes, where they act in different catabolic pathways. Mutations in genes coding for lysosomal sulfatases lead to an accumulation of the sulfated substrates in lysosomes, resulting in impaired cellular function and multisystemic disorders presenting as lysosomal storage diseases, which also cover the mucopolysaccharidoses and metachromatic leukodystrophy. Bioinformatics analysis of the eukaryotic genomes revealed, besides the well described and long known disease-associated sulfatases, additional genes coding for putative enzymes with sulfatases activity, including arylsulfatase G as well as the arylsulfatases H, I, J and K, respectively. In this article, we review current knowledge about lysosomal sulfatases with a special focus on the just recently characterized family members arylsulfatase G and arylsulfatase K.

Structural Insights into Endobiotic Reactivation by Human Gut Microbiome-Encoded Sulfatases

Phase II drug metabolism inactivates xenobiotics and endobiotics through the addition of either a glucuronic acid or sulfate moiety prior to excretion, often via the gastrointestinal tract. While the human gut microbial β-glucuronidase enzymes that reactivate glucuronide conjugates in the intestines are becoming well characterized and even controlled by targeted inhibitors, the sulfatases encoded by the human gut microbiome have not been comprehensively examined. Gut microbial sulfatases are poised to reactivate xenobiotics and endobiotics, which are then capable of undergoing enterohepatic recirculation or exerting local effects on the gut epithelium. Here, using protein structure-guided methods, we identify 728 distinct microbiome-encoded sulfatase proteins from the 4.8 million unique proteins present in the Human Microbiome Project Stool Sample database and 1766 gut microbial sulfatases from the 9.9 million sequences in the Integrated Gene Catalogue. We purify a representative set of these sulfatases, elucidate crystal structures, and pinpoint unique structural motifs essential to endobiotic sulfate processing. Gut microbial sulfatases differentially process sulfated forms of the neurotransmitters serotonin and dopamine, and the hormones melatonin, estrone, dehydroepiandrosterone, and thyroxine in a manner dependent both on variabilities in active site architecture and on markedly distinct oligomeric states. Taken together, these data provide initial insights into the structural and functional diversity of gut microbial sulfatases, providing a path toward defining the roles these enzymes play in health and disease.

Bromocriptine as a Novel Pharmacological Chaperone for Mucopolysaccharidosis IV A

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disease caused by mutations in the gene encoding for the enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS), leading to lysosomal accumulation of keratan sulfate (KS) and chondroitin-6-sulfate. In this study, we identified and characterized bromocriptine (BC) as a novel PC for MPS IVA. BC was identified through virtual screening and predicted to be docked within the active cavity of GALNS in a similar conformation to that observed for KS. BC interacted with similar residues to those predicted for natural GALNS substrates. In vitro inhibitory assay showed that BC at 50 μM reduced GALNS activity up to 30%. However, the activity of hrGALNS produced in HEK293 cells was increased up to 1.48-fold. BC increased GALNS activity and reduced lysosomal mass in MPS IVA fibroblasts in a mutation-dependent manner. Overall, these results show the potential of BC as a novel PC for MPS IVA and contribute to the consolidation of PCs as a potential therapy for this disease.

Abnormally increased carotid intima media-thickness and elasticity in patients with Morquio A disease

Background

Cardiovascular disease frequently causes morbidity and mortality in mucopolysaccharidoses (MPS); however, cardiovascular anatomy and dysfunction in MPS IVA (Morquio A disease) is not well described. Consequently, the study aimed to compare carotid artery structure and elasticity of MPS IVA patients with other MPS patients and healthy control subjects, and quantitate frequency of MPS IVA cardiac structural and functional abnormalities.

Methods

Prospective, multi-center echocardiogram and carotid ultrasound evaluations of 12 Morquio A patients were compared with other MPS and healthy control subjects. Average differences between groups were adjusted for age, sex, and height with robust variance estimation for confidence intervals and P-values.

Results

Morquio A patients demonstrated significantly higher (P < 0.001) adjusted carotid intima-media thickness (cIMT), mean (SD) of 0.56 mm (0.03) compared to control subjects, 0.44 mm (0.04). The Morquio A cohort had significantly greater adjusted carotid elasticity (carotid cross-sectional compliance + 43%, P < 0.001; carotid incremental elastic modulus − 33%, P = 0.003) than control subjects and other MPS patients. Aortic root dilatation was noted in 56% of the Morquio A cohort, which also had highly prevalent mitral (73%) and aortic (82%) valve thickening, though hemodynamically significant valve dysfunction was less frequent (9%).

Conclusions

Increased carotid elasticity in Morquio A patients is an unexpected contrast to the reduced elasticity observed in other MPS. These Morquio A cIMT findings corroborate MPS IVA arterial post-mortem reports and are consistent with cIMT of other MPS. Aortic root dilatation in Morquio A indicates arterial elastin dysfunction, but their carotid hyperelasticity indicates other vascular intima/media components, such as proteoglycans, may also influence artery function. Studying MPS I and IVA model systems may uniquely illuminate the function of glycosaminoglycan-bearing proteoglycans in arterial health.

A perspective on research, diagnosis, and management of lysosomal storage disorders in Colombia

Lysosomal storage diseases (LSDs) are a group of about 50 inborn errors of metabolism characterized by the lysosomal accumulation of partially or non-degraded molecules due to mutations in proteins involved in the degradation of macromolecules, transport, lysosomal biogenesis or modulators of lysosomal environment. Significant advances have been achieved in the diagnosis, management, and treatment of LSDs patients. In terms of approved therapies, these include enzyme replacement therapy (ERT), substrate reduction therapy, hematopoietic stem cell transplantation, and pharmacological chaperone therapy. In this review, we summarize the Colombian experience in LSDs thorough the evidence published. We identified 113 articles published between 1995 and 2019 that included Colombian researchers or physicians, and which were mainly focused in Mucopolysaccharidoses, Pompe disease, Gaucher disease, Fabry disease, and Tay-Sachs and Sandhoff diseases. Most of these articles focused on basic research, clinical cases, and mutation reports. Noteworthy, implementation of the enzyme assay in dried blood samples, led to a 5-fold increase in the identification of LSD patients, suggesting that these disorders still remain undiagnosed in the country. We consider that the information presented in this review will contribute to the knowledge of a broad spectrum of LSDs in Colombia and will also contribute to the development of public policies and the identification of research opportunities.

Biodegradable polyethylene glycol hydrogels for sustained release and enhanced stability of rhGALNS enzyme

Mucopolysaccharidosis IVA (Morquio A disease) is a genetic disorder caused by deficiency of N-acetylgalactosamine-6-sulfate-sulfatase (GALNS), leading to accumulation of keratan sulfate and chondroitin-6-sulfate in lysosomes. Many patients become wheelchair-dependent as teens, and their life span is 20-30 years. Currently, enzyme replacement therapy (ERT) is the treatment of choice. Although it alleviates some symptoms, replacing GALNS enzyme poses several challenges including very fast clearance from circulation and instability at 37 °C. These constraints affect frequency and cost of enzyme infusion and ability to reach all tissues. In this study, we developed injectable and biodegradable polyethylene glycol (PEG) hydrogels, loaded with recombinant human GALNS (rhGALNS) to improve enzyme stability and bioavailability, and to sustain release. We established the enzyme's release profile via bulk release experiments and determined diffusivity using fluorescence correlation spectroscopy. We observed that PEG hydrogels preserved enzyme activity during sustained release for 7 days. In the hydrogel, rhGALNS diffused almost four times slower than in buffer. We further confirmed that the enzyme was active when released from the hydrogels, by measuring its uptake in patient fibroblasts. The developed hydrogel delivery device could overcome current limits of rhGALNS replacement and improve quality of life for Morquio A patients. Encapsulated GALNS enzyme in a polyethylene glycol hydrogel improves GALNS stability by preserving its activity, and provides sustained release for a period of at least 7 days.

A Developmental Switch Generating Phenotypic Plasticity Is Part of a Conserved Multi-gene Locus

Switching between alternative complex phenotypes is often regulated by "supergenes," polymorphic clusters of linked genes such as in butterfly mimicry. In contrast, phenotypic plasticity results in alternative complex phenotypes controlled by environmental influences rather than polymorphisms. Here, we show that the developmental switch gene regulating predatory versus non-predatory mouth-form plasticity in the nematode Pristionchus pacificus is part of a multi-gene locus containing two sulfatases and two α-N-acetylglucosaminidases (nag). We provide functional characterization of all four genes, using CRISPR-Cas9-based reverse genetics, and show that nag genes and the previously identified eud-1/sulfatase have opposing influences. Members of the multi-gene locus show non-overlapping neuronal expression and epistatic relationships. The locus architecture is conserved in the entire genus Pristionchus. Interestingly, divergence between paralogs is counteracted by gene conversion, as inferred from phylogenies and genotypes of CRISPR-Cas9-induced mutants. Thus, we found that physical linkage accompanies regulatory linkage between switch genes controlling plasticity in P. pacificus.

Identification of Ezetimibe and Pranlukast as Pharmacological Chaperones for the Treatment of the Rare Disease Mucopolysaccharidosis Type IVA

Mucopolysaccharidosis type IVA (MPS IVA) is a rare disease caused by mutations in the gene encoding the lysosomal enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS). We report here two GALNS pharmacological chaperones, ezetimibe and pranlukast, identified by molecular docking-based virtual screening. These compounds bound to the active cavity of GALNS and increased its thermal stability as well as the production of recombinant GALNS in bacteria, yeast, and HEK293 cells. MPS IVA fibroblasts treated with these chaperones exhibited increases in GALNS protein and enzyme activity and reduced the size of enlarged lysosomes. Abnormalities in autophagy markers p62 and LC3B-II were alleviated by ezetimibe and pranlukast. Combined treatment of recombinant GALNS with ezetimibe or pranlukast produced an additive effect. Altogether, the results demonstrate that ezetimibe and pranlukast can increase the yield of recombinant GALNS and be used as a monotherapy or combination therapy to improve the therapeutic efficacy of MPS IVA enzyme replacement therapy.

Clinical, biochemical and genetic profiles of patients with mucopolysaccharidosis type IVA (Morquio A syndrome) in Malaysia: the first national natural history cohort study

BACKGROUND

Mucopolysaccharidosis IVA (MPS IVA) is an autosomal recessive lysosomal storage disease due to N-acetylgalactosamine-6-sulfatase (GALNS) deficiency. It results in accumulation of the glycosaminoglycans, keratan sulfate and chondroitin-6-sulfate, leading to skeletal and other systemic impairments. Data on MPS IVA in Asian populations are scarce.

METHODS

This is a multicentre descriptive case series of 21 patients comprising all MPS IVA patients in Malaysia. Mutational analysis was performed by PCR and Sanger sequencing of the GALNS gene in 17 patients.

RESULTS

The patients (15 females and 6 males) had a mean age (± SD) of 15.5 (± 8.1) years. Mean age at symptom onset was 2.6 (± 2.1) years and at confirmed diagnosis was 6.9 (± 4.5) years. The study cohort included patients from all the main ethnic groups in Malaysia - 57% Malay, 29% Chinese and 14% Indian. Common presenting symptoms included pectus carinatum (57%) and genu valgum (43%). Eight patients (38%) had undergone surgery, most commonly knee surgeries (29%) and cervical spine decompression (24%). Patients had limited endurance with lower mean walking distances with increasing age. GALNS gene analysis identified 18 distinct mutations comprising 13 missense, three nonsense, one small deletion and one splice site mutation. Of these, eight were novel mutations (Tyr133Ser, Glu158Valfs*12, Gly168*, Gly168Val, Trp184*, Leu271Pro, Glu320Lys, Leu508Pro). Mutations in exons 1, 5 and 9 accounted for 51% of the mutant alleles identified.

CONCLUSIONS

All the MPS IVA patients in this study had clinical impairments. A better understanding of the natural history and the clinical and genetic spectrum of MPS IVA in this population may assist early diagnosis, improve management and permit timely genetic counselling and prenatal diagnosis.

Comparative Study of Two Chondroitin Sulfate/Dermatan Sulfate 4-O-Sulfatases With High Identity

Chondroitin sulfate/dermatan sulfate (CS/DS) sulfatases are potential tools for structural and functional studies of CD/DS chains. In our previous study, a CS/DS 4-O-endosulfatase (endoVB4SF) was identified from a marine bacterium (Wang et al., 2015). Herein, another CS/DS 4-O-sulfatase (exoPB4SF) was identified from a Photobacterium sp. ExoPB4SF shares an 83% identity with endoVB4SF but showed strict exolytic activity. Comparative studies were performed for both enzymes on the basis of biochemical features, substrate-degrading patterns and three-dimensional structures. exoPB4SF exhibited a wider temperature and pH adaptability and better thermostability than endoVB4SF. Furthermore, exoPB4SF is a strict exolytic sulfatase that only releases the sulfate group from the GalNAc residue located at the reducing end, whereas endoVB4SF preferentially removed sulfate esters from the reducing end toward the non-reducing end though its directional degradation property was not strict. In addition, the structure of endoVB4SF was determined by X-ray crystallography at 1.95 Å. It adopts a globular conformation with two monomers per asymmetric unit. The exoPB4SF structure was constructed by homology modeling. Molecular docking results showed that although the residues around the catalytic center are conserved, the residues at the active site of endoVB4SF adopted a more favorable conformation for the binding of long CS/DS chains than those of exoPB4SF, which may explain why the two highly homogenous sulfatases possessed different action patterns. The results of this study provide insight into the structure-function relationship of CS/DS endo- and exosulfatases for the first time.

Identification and Signature Sequences of Bacterial Δ4,5Hexuronate-2-O-Sulfatases

Glycosaminoglycan (GAG) sulfatases, which catalyze the hydrolysis of sulfate esters from GAGs, belong to a large and conserved sulfatase family. Bacterial GAG sulfatases are essential in the process of sulfur cycling and are useful for the structural analysis of GAGs. Only a few GAG-specific sulfatases have been studied in detail and reported to date. Herein, the GAG-degrading Photobacterium sp. FC615 was isolated from marine sediment, and a novel Δ^4,5hexuronate-2-O-sulfatase (PB2SF) was identified from this bacterium. PB2SF specifically removed 2-O-sulfate from the unsaturated hexuronate residue located at the non-reducing end of GAG oligosaccharides produced by GAG lyases. A structural model of PB2SF was constructed through a homology-modeling method. Six conserved amino acids around the active site were chosen for further analysis using site-directed mutagenesis. N113A, K141A, K141H, H143A, H143K, H205A, and H205K mutants exhibited only feeble activity, while the H310A, H310K, and D52A mutants were totally inactive, indicating that these conserved residues, particularly Asp52 and His310, were essential in the catalytic mechanism. Furthermore, bioinformatic analysis revealed that GAG sulfatases with specific degradative properties clustered together in the neighbor-joining phylogenetic tree. Based on this finding, 60 Δ^4,5hexuronate-2-O-sulfatases were predicted in the NCBI protein database, and one with relatively low identity to PB2SF was characterized to confirm our prediction. Moreover, the signature sequences of bacterial Δ^4,5hexuronate-2-O-sulfatases were identified. With the reported signature motifs, the sulfatase sequence of the Δ^4,5hexuronate-2-O-sulfatase family could be simply identified before cloning. Taken together, the results of this study should aid in the identification and further application of novel GAG sulfatases.

Transition-State Interactions in a Promiscuous Enzyme: Sulfate and Phosphate Monoester Hydrolysis by Pseudomonas aeruginosa Arylsulfatase

Pseudomonas aeruginosa arylsulfatase (PAS) hydrolyzes sulfate and, promiscuously, phosphate monoesters. Enzyme-catalyzed sulfate transfer is crucial to a wide variety of biological processes, but detailed studies of the mechanistic contributions to its catalysis are lacking. We present linear free energy relationships (LFERs) and kinetic isotope effects (KIEs) of PAS and analyses of active site mutants that suggest a key role for leaving group (LG) stabilization. In LFERs PASWT has a much less negative Brønsted coefficient (βleaving groupobs-Enz = -0.33) than the uncatalyzed reaction (βleaving groupobs = -1.81). This situation is diminished when cationic active site groups are exchanged for alanine. The considerable degree of bond breaking during the transition state (TS) is evidenced by an 18Obridge KIE of 1.0088. LFER and KIE data for several active site mutants point to leaving group stabilization by active site K375, in cooperation with H211. 15N KIEs and the increased sensitivity to leaving group ability of the sulfatase activity in neat D2O (Δβleaving groupH-D = +0.06) suggest that the mechanism for S-Obridge bond fission shifts, with decreasing leaving group ability, from charge compensation via Lewis acid interactions toward direct proton donation. 18Ononbridge KIEs indicate that the TS for PAS-catalyzed sulfate monoester hydrolysis has a significantly more associative character compared to the uncatalyzed reaction, while PAS-catalyzed phosphate monoester hydrolysis does not show this shift. This difference in enzyme-catalyzed TSs appears to be the major factor favoring specificity toward sulfate over phosphate esters by this promiscuous hydrolase, since other features are either too similar (uncatalyzed TS) or inherently favor phosphate (charge).

Mutation analysis and pathogenicity identification of Mucopolysaccharidosis type IVA in 8 south China families

BACKGROUND

Mucopolysaccharidosis type IVA (MPS IVA) is a rare autosomal recessive lysosomal storage disorder caused by GALNS gene mutation. The aim of our study is to detect pathogenic variants for patients suspected of MPS IVA and set the base for subsequent prenatal diagnosis and preimplantation genetic diagnosis.

METHODS

In our study, 9 MPS IVA patients from south China families were investigated. Urine glycosaminoglycans (GAG_S) screening was used as an initial method. For patients with abnormal result, all 14 exons and intron-exon junctions of the GALNS gene were sequenced after amplification from genomic DNA. The pathogenicity of novel mutations were analyzed with molecular genetics, bioinformatics and structure modeling in light of clinical manifestations and biochemical results.

RESULTS

Among 12 mutations detected, direct sequencing found 3 novel mutations (c.686A>C, p.Y229S; c.1498G>T, p.G500C; c.278T>C, p.I93T). The pathogenicity of these novel mutations was illustrated by correlating clinical symptoms with pedigree analysis and bioinformatics analysis.

CONCLUSION

The detection and variant analysis are essential for accurate diagnosis of MPS IVA patients. Our results enrich GALNS gene mutation spectrum of Chinese population. This information has important clinical value for molecular diagnosis and genetic counseling of patients with this disease.

Utilizing ExAC to assess the hidden contribution of variants of unknown significance to Sanfilippo Type B incidence

Given the large and expanding quantity of publicly available sequencing data, it should be possible to extract incidence information for monogenic diseases from allele frequencies, provided one knows which mutations are causal. We tested this idea on a rare, monogenic, lysosomal storage disorder, Sanfilippo Type B (Mucopolysaccharidosis type IIIB). Sanfilippo Type B is caused by mutations in the gene encoding α-N-acetylglucosaminidase (NAGLU). There were 189 NAGLU missense variants found in the ExAC dataset that comprises roughly 60,000 individual exomes. Only 24 of the 189 missense variants were known to be pathogenic; the remaining 165 variants were of unknown significance (VUS), and their potential contribution to disease is unknown. To address this problem, we measured enzymatic activities of 164 NAGLU missense VUS in the ExAC dataset and developed a statistical framework for estimating disease incidence with associated confidence intervals. We found that 25% of VUS decreased the activity of NAGLU to levels consistent with Sanfilippo Type B pathogenic alleles. We found that a substantial fraction of Sanfilippo Type B incidence (67%) could be accounted for by novel mutations not previously identified in patients, illustrating the utility of combining functional activity data for VUS with population-wide allele frequency data in estimating disease incidence.

Decline in arylsulfatase B expression increases EGFR expression by inhibiting the protein-tyrosine phosphatase SHP2 and activating JNK in prostate cells

Epidermal growth factor receptor (EGFR) has a crucial role in cell differentiation and proliferation and cancer, and its expression appears to be up-regulated when arylsulfatase B (ARSB or GalNAc-4-sulfatase) is reduced. ARSB removes 4-sulfate groups from the nonreducing end of dermatan sulfate and chondroitin 4-sulfate (C4S), and its decreased expression has previously been reported to inhibit the activity of the ubiquitous protein-tyrosine phosphatase, nonreceptor type 11 (SHP2 or PTPN11). However, the mechanism by which decline in ARSB leads to decline in SHP2 activity is unclear. Here, we show that SHP2 binds preferentially C4S, rather than chondroitin 6-sulfate, and confirm that SHP2 activity declines when ARSB is silenced. The reduction in ARSB activity, and the resultant increase in C4S, increased the expression of EGFR (Her1/ErbB1) in human prostate stem and epithelial cells. The increased expression of EGFR occurred after 1) the decline in SHP2 activity, 2) enhanced c-Jun N-terminal kinase (JNK) activity, 3) increased nuclear DNA binding by c-Jun and c-Fos, and 4) EGFR promoter activation. In response to exogenous EGF, there was increased bromodeoxyuridine incorporation, consistent with enhanced cell proliferation. These findings indicated that ARSB and chondroitin 4-sulfation affect the activation of an important dual phosphorylation threonine-tyrosine kinase and the mRNA expression of a critical tyrosine kinase receptor in prostate cells. Restoration of ARSB activity with the associated reduction in C4S may provide a new therapeutic approach for managing malignancies in which EGFR-mediated tyrosine kinase signaling pathways are active.

Determination of genotypic and clinical characteristics of Colombian patients with mucopolysaccharidosis IVA

Background

As mucopolysaccharidosis IVA (MPS IVA) is the most frequent MPS in Colombia, this paper aims to describe its clinical and mutational characteristics in 32 diagnosed patients included in this study.

Methods

Genotyping was completed by amplification and Sanger sequencing of the GALNS gene. The SWISS-model platform was used for bioinformatic analysis, and mutant proteins were generated by homology from the wild-type GALNS code 4FDI template from the Protein Data Bank (PDB) database. Docking was performed using the GalNAc6S ligand (PubChem CID: 193456) by AutoDock Vina 1.0 and visualized in PyMOL and LigPlot+.

Results

Eleven variants were identified, and one new pathogenic variant was described in the heterozygous state, which is consistent with genotype c. 319 G> T or p.Ala107Ser. The pathogenic variant c.901G>T or p.Gly301Cys was the most frequent mutation with 51.6% of alleles. Docking revealed affinity energy of −5.9 Kcal/mol between wild-type GALNS and the G6S ligand. Some changes were evidenced at the intermolecular interaction level, and affinity energy for each mutant decreased.

Conclusion

Clinical variables and genotypic analysis were similar to those reported for other world populations. Genotypic data showed greater allelic heterogeneity than those previously reported. Bioinformatics tools showed differences in the binding interactions of mutant proteins with the G6S ligand, in regard the wild-type GALNS.

The Molecular Basis of Polysaccharide Sulfatase Activity and a Nomenclature for Catalytic Subsites in this Class of Enzyme

Sulfatases play a biologically important role by cleaving sulfate groups from molecules. They can be identified on the basis of signature sequences within their primary structures, and the largest family, S1, has predictable features that contribute specifically to the recognition and catalytic removal of sulfate groups. However, despite advances in the prediction and understanding of S1 sulfatases, a major question regards the molecular determinants that drive substrate recognition beyond the targeted sulfate group. Here, through analysis of an endo-4S-ι-carrageenan sulfatase (PsS1_19A) from Pseudoalteromonas sp. PS47, particularly X-ray crystal structures in complex with intact substrates, we show that specific recognition of the substrate leaving group components, in this case carbohydrate, provides the enzyme with specificity for its substrate. On the basis of these results we propose a catalytic subsite nomenclature that we anticipate will form a general foundation for understanding and describing the molecular basis of substrate recognition by sulfatases.