Skeletal Dysplasias Caused by Sulfation Defects

Advances in post-translational modifications and recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is defined as two or more pregnancy loss, which affects approximately 1-2% of women's fertility. The etiology of RSA has not yet been fully revealed, which poses a great problem for clinical treatment. Post- translational modifications(PTMs) are chemical modifications that play a crucial role in the functional proteome. A considerable number of published studies have shown the relationship between post-translational modifications of various proteins and RSA. The study of PTMs contributes to elucidating the role of modified proteins in the pathogenesis of RSA, as well as the design of more effective diagnostic/prognostic tools and more targeted treatments. Most reviews in the field of RSA have only focused on RNA epigenomics research. The present review reports the latest research developments of PTMs related to RSA, such as glycosylation, phosphorylation, Methylation, Acetylation, Ubiquitination, etc.

Sulfate: a neglected (but potentially highly relevant) anion

Sulfate is an important anion as sulfonation is essential in modulation of several compounds, such as exogens, polysaccharide chains of proteoglycans, cholesterol or cholesterol derivatives and tyrosine residues of several proteins. Sulfonation requires the presence of both the sulfate donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS) and a sulfotransferase. Genetic disorders affecting sulfonation, associated with skeletal abnormalities, impaired neurological development and endocrinopathies, demonstrate the importance of sulfate. Yet sulfate is not measured in clinical practice. This review addresses sulfate metabolism and consequences of sulfonation defects, how to measure sulfate and why we should measure sulfate more often.

Proteoglycan Dysfunction: A Common Link Between Intervertebral Disc Degeneration and Skeletal Dysplasia

Proteoglycans through their sulfated glycosaminoglycans regulate cell-matrix signaling during tissue development, regeneration, and degeneration processes. Large extracellular proteoglycans such as aggrecan, versican, and perlecan are especially important for the structural integrity of the intervertebral disc and cartilage during development. In these tissues, proteoglycans are responsible for hydration, joint flexibility, and the absorption of mechanical loads. Loss or reduction of these molecules can lead to disc degeneration and skeletal dysplasia, evident from loss of disc height or defects in skeletal development respectively. In this review, we discuss the common proteoglycans found in the disc and cartilage and elaborate on various murine models and skeletal dysplasias in humans to highlight how their absence and/or aberrant expression causes accelerated disc degeneration and developmental defects.

Enhanced SLC35B2/SAV1 sulfation axis promotes tumor growth by inhibiting Hippo signaling in HCC

BACKGROUND AND AIMS

Protein tyrosine sulfation (PTS) is a common posttranslational modification that regulates a variety of physiological and pathological processes. However, the role of PTS in cancer remains poorly understood. The goal of this study was to determine whether and how PTS plays a role in HCC progression.

APPROACH AND RESULTS

By mass spectrometry and bioinformatics analysis, we identified SAV1 as a novel substrate of PTS in HCC. Oxidative stress upregulates the transcription of SLC35B2, a Golgi-resident transporter of sulfate donor 3'-phosphoadenosine 5'-phosphosulfate, leading to increased sulfation of SAV1. Sulfation of SAV1 disrupts the formation of the SAV1-MST1 complex, resulting in a decrease of MST1 phosphorylation and subsequent inactivation of Hippo signaling. These molecular events ultimately foster the growth of HCC cells both in vivo and in vitro. Moreover, SLC35B2 is a novel transcription target gene of the Hippo pathway, constituting a positive feedback loop that facilitates HCC progression under oxidative stress.

CONCLUSIONS

Our findings reveal a regulatory mechanism of the SLC35B2/SAV1 sulfation axis in response to oxidative stress, highlighting its potential as a promising therapeutic target for HCC.

Targeting sulfation-dependent mechanoreciprocity between matrix and osteoblasts to mitigate bone loss

Sulfation is a widespread modification of biomolecules that has been incompletely explored to date. Through cross-phenotype meta-analysis of bone mineral density in up to 426,824 genotyped human participants along with phenotypic characterization of multiple mutant mouse lines, we identified a causative role for sulfate transporter solute carrier family 26 member A2 (SLC26A2) deficiency in osteoporosis. Ablation of SLC26A2 in osteoblasts caused severe bone loss and accumulation of immature bone cells and elicited peculiar pericellular matrix (PCM) production characterized by undersulfation coupled with decreased stiffness. These altered chemophysical properties of the PCM disrupted the formation of focal adhesions in osteoblasts. Bulk RNA sequencing and functional assays revealed that the mechanoreciprocal inhibition of focal adhesion kinase (FAK) and Yes1-associated transcriptional regulator (YAP)/WW domain containing transcription regulator 1 (TAZ) signaling impinged osteoblast maturation upon SLC26A2 deficiency. Moreover, pharmacological abrogation of the Hippo kinases and forced wheel-running ameliorated SLC26A2-deficient osteoporosis by promoting YAP/TAZ activity. Analysis of mouse single-cell RNA sequencing data suggested coordination among sulfate metabolism, focal adhesion, and YAP/TAZ activity during osteoblast-to-osteocyte transition. In addition to the SLC26A2-deficient setting, altered FAK and YAP/TAZ signaling was also observed in bone cells of ovariectomized mice and patients with osteoporosis, and pharmacological enforcing of YAP/TAZ activity ameliorated bone loss in ovariectomized mice. Collectively, these data unveil a role for sulfation in the developmental mechanoreciprocity between matrix and osteoblasts, which could be leveraged to prevent bone loss.

History and highlights of the teratological collection in the Narrenturm, Vienna (Austria)

The collection of the Narrenturm in Vienna houses and maintains more than 50,000 objects including approximately 1200 teratological specimens; making it one of the biggest collections of specimens from human origin in Europe. The existence of this magnificent collection-representing an important resource for dysmorphology research, mostly awaiting contemporary diagnoses-is not widely known in the scientific community. Here, we show that the Narrenturm harbors a wealth of specimens with (exceptionally) rare congenital anomalies. These museums can be seen as physical repositories of human malformation, covering hundreds of years of dedicated collecting and preserving, thereby creating unique settings that can be used to expand our knowledge of developmental conditions that have to be preserved for future generations of scientists.

A Chinese case of CHST3-related skeletal dysplasia and a systematic review

PURPOSE

We reported a case with carbohydrate sulfotransferase 3 (CHST3) spondyloepiphyseal dysplasia and made a systematic review of all previously reported cases.

METHODS

A 14.8-year-old boy underwent clinical, radiological, and genetic evaluations. The patients and five age-matched healthy boys accepted high-resolution peripheral quantitative computed tomography evaluation. All CHST3-related skeletal dysplasia cases from PubMed and Embase were collected and summarized. The genotype-phenotype correlation was analyzed.

RESULTS

The proband complained of aggravated joint pain and had a compression fracture of L2 during his second decade. Physical examination showed a height Z score of -4.94, short limbs, and restricted movement of the elbows and knees. X-rays showed carpal epiphyseal dysplasia, enlargement of elbow and knee joints, and subluxation of the left hip. Echocardiography showed abnormal cardiac valves. Compared with the norm, his total and trabecular volumetric bone mineral density (BMD), and the microarchitecture of the trabecular bone had trends to be worse at the distal radius and tibia. Two novel missense variants of c.1343T>G and c.761C>G in CHST3 were inherited from his father and mother, respectively. In the systematic review, short stature, limited joint extension, joint pain, and joint dislocation were the most common characteristics of this disorder. Height Z score and the proportion of hearing impairment had no significant differences between the missense and nonmissense mutations groups.

CONCLUSION

Progressive joint pain and movement restriction are the main characteristics of CHST3-related skeletal dysplasia. BMD and bone microarchitecture of this disorder needs further exploration. There is no apparent genotype-phenotype correlation in this disorder.

Biallelic variants in the SLC13A1 sulfate transporter gene cause hyposulfatemia with a mild spondylo-epi-metaphyseal dysplasia

Sulfate is the fourth most abundant anion in human plasma but is not measured in clinical practice and little is known about the consequences of sulfate deficiency. Nevertheless, sulfation plays an essential role in the modulation of numerous compounds, including proteoglycans and steroids. We report the first patient with a homozygous loss-of-function variant in the SLC13A1 gene, encoding a renal and intestinal sulfate transporter, which is essential for maintaining plasma sulfate levels. The homozygous (Arg12Ter) variant in SLC13A1 was found by exome sequencing performed in a patient with unexplained skeletal dysplasia. The main clinical features were enlargement of joints and spondylo-epi-metaphyseal radiological abnormalities in early childhood, which improved with age. In addition, autistic features were noted. We found profound hyposulfatemia due to complete loss of renal sulfate reabsorption. Cholesterol sulfate was reduced. Intravenous N-acetylcysteine administration temporarily restored plasma sulfate levels. We conclude that loss of the SLC13A1 gene leads to profound hypersulfaturia and hyposulfatemia, which is mainly associated with abnormal skeletal development, possibly predisposing to degenerative bone and joint disease. The diagnosis might be easily missed and more frequent.

Degradomics technologies in matrisome exploration

Consisting of a defined set of extracellular proteins secreted from resident cells and with minor contributions from serum proteins, the extracellular matrix (ECM) is an essential component of all tissues. Maintaining tissue homeostasis, structural support and cellular control through cell-ECM communication, the ECM has come to be viewed as not just a passive structural entity but rather as a dynamic signaling conduit between cells and the extracellular compartment. Proteins and their cleavage products mediate this communication, and aberrant signaling, either directly or indirectly distorting the ECM, results in pathological conditions including cancer, inflammation, fibrosis, and neurodegenerative diseases. Characterization of ECM components, the matrisome, the extracellular environment and their changes in disease is therefore of importance to understand and mitigate by developing novel therapeutics. Liquid chromatography-mass spectrometry (LC-MS) proteomics has been integral to protein and proteome research for decades and long superseded the obsolescent gel-based approaches. A continuous effort has ensured progress with increased sensitivity and throughput as more advanced equipment has been developed hand in hand with specialized enrichment, detection, and identification methods. Part of this effort lies in the field of degradomics, a branch of proteomics focused on discovering novel protease substrates by identification of protease-generated neo-N termini, the N-terminome, and characterizing the responsible protease networks. Various methods to do so have been developed, some specialized for specific tissue types, others for particular proteases, throughput, or ease of use. This review aims to provide an overview of the state-of-the-art proteomics techniques that have successfully been recently utilized to characterize proteolytic cleavages in the ECM and thereby guided new research and understanding of the ECM and matrisome biology.

Fetal phenotypes of Mendelian disorders: A descriptive study from India

OBJECTIVE

Exome sequencing(ES) based diagnosis of Mendelian diseases in the fetus is limited by paucity of phenotypic information. This study reports the comprehensive phenotypes of some fetuses with Mendelian disorders.

METHODS

Next generation technology based sequencing of all coding regions of the genome(Exome sequencing) or targeted gene sequencing using Sanger or next generation platforms was performed in a cohort of deeply phenotyped, cytogenetically normal fetuses with morphological defects. Prenatal ultrasonographic phenotypes and Postmortem details including dysmorphology, histopathology, radiography were ascertained. Novel candidate genes, novel/ unusual findings and unusual genotypes in cases with confirmed Mendelian disorders are described.

RESULTS

Of the 102 fetuses sequenced, 45 (44%) achieved definitive diagnosis of a Mendelian disorder with 50 pathogenic/likely pathogenic variants. The majority (87%) were autosomal recessive, 69% families were consanguineous and 54% variants were novel. Dysmorphic syndromes, skeletal dysplasias and metabolic disorders were the commonest disease categories, ciliopathies and dystroglycanopathies commonest molecular categories. We describe the first fetal description of six monogenic diseases, and nine cases with novel histological findings. Nineteen cases had novel/ unusual findings.

CONCLUSION

This cohort demonstrates how deep fetal phenotypes of some Mendelian disorders can show novel/unusual findings which have important implications for prenatal diagnosis of these conditions. This article is protected by copyright. All rights reserved.

Disease-Related Protein Variants of the Highly Conserved Enzyme PAPSS2 Show Marginal Stability and Aggregation in Cells

Cellular sulfation pathways rely on the activated sulfate 3′-phosphoadenosine-5′-phosphosulfate (PAPS). In humans, PAPS is exclusively provided by the two PAPS synthases PAPSS1 and PAPSS2. Mutations found in the PAPSS2 gene result in severe disease states such as bone dysplasia, androgen excess and polycystic ovary syndrome. The APS kinase domain of PAPSS2 catalyzes the rate-limiting step in PAPS biosynthesis. In this study, we show that clinically described disease mutations located in the naturally fragile APS kinase domain are associated either with its destabilization and aggregation or its deactivation. Our findings provide novel insights into possible molecular mechanisms that could give rise to disease phenotypes associated with sulfation pathway genes.

Heparan Sulfate, Mucopolysaccharidosis IIIB and Sulfur Metabolism Disorders

Mucopolysaccharidosis, type IIIB (MPS IIIB) is a rare disease caused by mutations in the N-alpha-acetylglucosaminidase (NAGLU) gene resulting in decreased or absent enzyme activity. On the cellular level, the disorder is characterized by the massive lysosomal storage of heparan sulfate (HS)—one species of glycosaminoglycans. HS is a sulfur-rich macromolecule, and its accumulation should affect the turnover of total sulfur in cells; according to the studies presented here, it, indeed, does. The lysosomal degradation of HS in cells produces monosaccharides and inorganic sulfate (SO₄²⁻). Sulfate is a product of L-cysteine metabolism, and any disruption of its levels affects the entire L-cysteine catabolism pathway, which was first reported in 2019. It is known that L-cysteine level is elevated in cells with the Naglu^−/− gene mutation and in selected tissues of individuals with MPS IIIB. The level of glutathione and the Naglu^−/− cells’ antioxidant potential are significantly reduced, as well as the activity of 3-mercaptopyruvate sulfurtransferase (MPST, EC 2.8.1.2) and the level of sulfane sulfur-containing compounds. The direct reason is not yet known. This paper attempts to identify some of cause-and-effect correlations that may lead to this condition and identifies research directions that should be explored.

Biallelic variants in SLC35B2 cause a novel chondrodysplasia with hypomyelinating leukodystrophy

Sulfated proteoglycans are essential in skeletal and brain development. Recently, pathogenic variants in genes encoding proteins involved in the proteoglycan biosynthesis have been identified in a range of chondrodysplasia associated with intellectual disability. Nevertheless, several patients remain with unidentified molecular basis. This study aimed to contribute to the deciphering of new molecular bases in patients with chondrodysplasia and neuro-developmental disease. Exome sequencing was performed to identify pathogenic variants in patients presenting with chondrodysplasia and intellectual disability. The pathogenic effects of the potentially causative variants were analyzed by functional studies. We identified homozygous variants (c.1218_1220del and c.1224_1225del) in SLC35B2 in two patients with pre- and postnatal growth retardation, scoliosis, severe motor and intellectual disabilities and hypomyelinating leukodystrophy. By functional analyses, we showed that the variants affect SLC35B2 mRNA expression and protein subcellular localization leading to a functional impairment of the protein. Consistent with those results, we detected proteoglycan sulfation impairment in SLC35B2 patient fibroblasts and serum. Our data support that SLC35B2 functional impairment causes a novel syndromic chondrodysplasia with hypomyelinating leukodystrophy, most likely through a proteoglycan sulfation defect. This is the first time that SLC35B2 variants are associated with bone and brain development in human.

Fetal presentation of chondrodysplasia with joint dislocations, GPAPP type, caused by novel biallelic IMPAD1 variants

Biallelic IMPAD1 pathogenic variants leads to deficiency of GPAPP (Golgi 3-prime phosphoadenosine 5-prime phosphate 3-prime phosphatase) protein and clinically causes chondrodysplasia, which is characterized by short stature with short limbs, craniofacial malformations, cleft palate, hand and foot anomalies, and various radiographic skeletal manifestations. Here we describe prenatal presentation of GPAPP deficiency caused by novel biallelic pathogenic variants, 2 base pair duplication in exon 2 of IMAPD1 gene in a patient of Asian-Indian origin. Further we report on diagnostic clues of prenatal presentation of GPAPP deficiency through ultrasonography, fetal MRI, and postmortem findings. We also provide evidence of pathophysiology of underlying GPAPP deficiency in the form of disorganization and dysplastic chondrocytes and reduced sulfation of glycoproteins through histopathology of cartilage similar to that described in mice IMPAD1 homozygous mutant model.

Phenotypic Characterization of Immortalized Chondrocytes from a Desbuquois Dysplasia Type 1 Mouse Model: A Tool for Studying Defects in Glycosaminoglycan Biosynthesis

The complexity of skeletal pathologies makes use of in vivo models essential to elucidate the pathogenesis of the diseases; nevertheless, chondrocyte and osteoblast cell lines provide relevant information on the underlying disease mechanisms. Due to the limitations of primary chondrocytes, immortalized cells represent a unique tool to overcome this problem since they grow very easily for several passages. However, in the immortalization procedure the cells might lose the original phenotype; thus, these cell lines should be deeply characterized before their use. We immortalized primary chondrocytes from a Cant1 knock-out mouse, an animal model of Desbuquois dysplasia type 1, with a plasmid expressing the SV40 large and small T antigen. This cell line, based on morphological and biochemical parameters, showed preservation of the chondrocyte phenotype. In addition reduced proteoglycan synthesis and oversulfation of glycosaminoglycan chains were demonstrated, as already observed in primary chondrocytes from the Cant1 knock-out mouse. In conclusion, immortalized Cant1 knock-out chondrocytes maintained the disease phenotype observed in primary cells validating the in vitro model and providing an additional tool to further study the proteoglycan biosynthesis defect. The same approach might be extended to other cartilage disorders.

Chondrodysplasias With Multiple Dislocations Caused by Defects in Glycosaminoglycan Synthesis

Chondrodysplasias with multiple dislocations form a group of severe disorders characterized by joint laxity and multiple dislocations, severe short stature of pre- and post-natal onset, hand anomalies, and/or vertebral anomalies. The majority of chondrodysplasias with multiple dislocations have been associated with mutations in genes encoding glycosyltransferases, sulfotransferases, and transporters implicated in the synthesis or sulfation of glycosaminoglycans, long and unbranched polysaccharides composed of repeated disaccharide bond to protein core of proteoglycan. Glycosaminoglycan biosynthesis is a tightly regulated process that occurs mainly in the Golgi and that requires the coordinated action of numerous enzymes and transporters as well as an adequate Golgi environment. Any disturbances of this chain of reactions will lead to the incapacity of a cell to construct correct glycanic chains. This review focuses on genetic and glycobiological studies of chondrodysplasias with multiple dislocations associated with glycosaminoglycan biosynthesis defects and related animal models. Strong comprehension of the molecular mechanisms leading to those disorders, mostly through extensive phenotypic analyses of in vitro and/or in vivo models, is essential for the development of novel biomarkers for clinical screenings and innovative therapeutics for these diseases.

Improvement of the skeletal phenotype in a mouse model of diastrophic dysplasia after postnatal treatment with N-acetylcysteine

Diastrophic dysplasia (DTD) is a recessive chondrodysplasia caused by mutations in the SLC26A2 gene encoding for a sulfate/chloride transporter. When SLC26A2 is impaired intracellular level of sulfate is reduced leading to the synthesis of undersulfated proteoglycans. In normal chondrocytes, the main source of intracellular sulfate is the extracellular uptake through SLC26A2, but a small amount comes from the catabolism of sulfur-containing amino acids and other thiols. Here N-acetylcysteine (NAC), an extensively used drug, is proposed as alternative source of intracellular sulfate in an animal model of DTD (dtd mouse). Mutant and wild type mice were treated twice a day with hypodermic injections of 250 mg NAC/kg body weight for one week after birth. At the end of the treatment, an improvement trend in cartilage proteoglycan sulfation and in the skeletal phenotype of treated dtd mice were observed. Thus, a longer treatment lasted three weeks starting from birth was performed. Treated mutant mice showed a significant increase of cartilage proteoglycan sulfation and a relevant improvement of the skeletal phenotype based on measurements of several bony elements and bone quality by DEXA and micro CT. Moreover, the amelioration of the overall growth plate morphology in treated dtd mice suggested a partial rescue of the endochondral ossification process. Overall, the results prove that NAC is an effective source of intracellular sulfate for dtd mice in the postnatal period. This finding paves the way for a potential pharmacological treatment of DTD patients taking advantage from a drug repositioning strategy.

Bi-allelic Pathogenic Variants in HS2ST1 Cause a Syndrome Characterized by Developmental Delay and Corpus Callosum, Skeletal, and Renal Abnormalities

Heparan sulfate belongs to the group of glycosaminoglycans (GAGs), highly sulfated linear polysaccharides. Heparan sulfate 2-O-sulfotransferase 1 (HS2ST1) is one of several specialized enzymes required for heparan sulfate synthesis and catalyzes the transfer of the sulfate groups to the sugar moiety of heparan sulfate. We report bi-allelic pathogenic variants in HS2ST1 in four individuals from three unrelated families. Affected individuals showed facial dysmorphism with coarse face, upslanted palpebral fissures, broad nasal tip, and wide mouth, developmental delay and/or intellectual disability, corpus callosum agenesis or hypoplasia, flexion contractures, brachydactyly of hands and feet with broad fingertips and toes, and uni- or bilateral renal agenesis in three individuals. HS2ST1 variants cause a reduction in HS2ST1 mRNA and decreased or absent heparan sulfate 2-O-sulfotransferase 1 in two of three fibroblast cell lines derived from affected individuals. The heparan sulfate synthesized by the individual 1 cell line lacks 2-O-sulfated domains but had an increase in N- and 6-O-sulfated domains demonstrating functional impairment of the HS2ST1. As heparan sulfate modulates FGF-mediated signaling, we found a significantly decreased activation of the MAP kinases ERK1/2 in FGF-2-stimulated cell lines of affected individuals that could be restored by addition of heparin, a GAG similar to heparan sulfate. Focal adhesions in FGF-2-stimulated fibroblasts of affected individuals concentrated at the cell periphery. Our data demonstrate that a heparan sulfate synthesis deficit causes a recognizable syndrome and emphasize a role for 2-O-sulfated heparan sulfate in human neuronal, skeletal, and renal development.

Mutations in GRK2 cause Jeune syndrome by impairing Hedgehog and canonical Wnt signaling

Mutations in genes affecting primary cilia cause ciliopathies, a diverse group of disorders often affecting skeletal development. This includes Jeune syndrome or asphyxiating thoracic dystrophy (ATD), an autosomal recessive skeletal disorder. Unraveling the responsible molecular pathology helps illuminate mechanisms responsible for functional primary cilia. We identified two families with ATD caused by loss-of-function mutations in the gene encoding adrenergic receptor kinase 1 (ADRBK1 or GRK2). GRK2 cells from an affected individual homozygous for the p.R158* mutation resulted in loss of GRK2, and disrupted chondrocyte growth and differentiation in the cartilage growth plate. GRK2 null cells displayed normal cilia morphology, yet loss of GRK2 compromised cilia-based signaling of Hedgehog (Hh) pathway. Canonical Wnt signaling was also impaired, manifested as a failure to respond to Wnt ligand due to impaired phosphorylation of the Wnt co-receptor LRP6. We have identified GRK2 as an essential regulator of skeletogenesis and demonstrate how both Hh and Wnt signaling mechanistically contribute to skeletal ciliopathies.