Enzyme replacement therapy in mice lacking arylsulfatase B targets bone-remodeling cells, but not chondrocytes

Skeletal phenotype amelioration in mucopolysaccharidosis VI requires intervention at the earliest stages of postnatal development

Mucopolysaccharidosis VI (MPS VI) is a rare lysosomal disease arising from impaired function of the enzyme arylsulfatase B (ARSB). This impairment causes aberrant accumulation of dermatan sulfate, a glycosaminoglycan (GAG) abundant in cartilage. While clinical severity varies along with age at first symptom manifestation, MPS VI usually presents early and strongly affects the skeleton. Current enzyme replacement therapy (ERT) does not provide effective treatment for the skeletal manifestations of MPS VI. This lack of efficacy may be due to an inability of ERT to reach affected cells or to the irreversibility of the disease. To address the question of reversibility of skeletal phenotypes, we generated a conditional by inversion (COIN) mouse model of MPS VI, ArsbCOIN/COIN, wherein Arsb is initially null and can be restored to WT using Cre. We restored Arsb at different times during postnatal development, using a tamoxifen-dependent global Cre driver. By restoring Arsb at P7, P21, and P56-P70, we determined that skeletal phenotypes can be fully rescued if Arsb restoration occurs at P7, while only achieving partial rescue at P21 and no significant rescue at P56-P70. This work has highlighted the importance of early intervention in patients with MPS VI to maximize therapeutic impact.

Identification of potential non-invasive biomarkers in diastrophic dysplasia

Diastrophic dysplasia (DTD) is a recessive chondrodysplasia caused by pathogenic variants in the SLC26A2 gene encoding for a cell membrane sulfate/chloride antiporter crucial for sulfate uptake and glycosaminoglycan (GAG) sulfation. Research on a DTD animal model has suggested possible pharmacological treatment approaches. In view of future clinical trials, the identification of non-invasive biomarkers is crucial to assess the efficacy of treatments. Urinary GAG composition has been analyzed in several metabolic disorders including mucopolysaccharidoses. Moreover, the N-terminal fragment of collagen X, known as collagen X marker (CXM), is considered a real-time marker of endochondral ossification and growth velocity and was studied in individuals with achondroplasia and osteogenesis imperfecta. In this work, urinary GAG sulfation and blood CXM levels were investigated as potential biomarkers for individuals affected by DTD. Chondroitin sulfate disaccharide analysis was performed on GAGs isolated from urine by HPLC after GAG digestion with chondroitinase ABC and ACII, while CXM was assessed in dried blood spots. Results from DTD patients were compared with an age-matched control population. Undersulfation of urinary GAGs was observed in DTD patients with some relationship to the clinical severity and underlying SLC26A2 variants. Lower than normal CXM levels were observed in most patients, even if the marker did not show a clear pattern in our small patient cohort because CXM values are highly dependent on age, gender and growth velocity. In summary, both non-invasive biomarkers are promising assays targeting various aspects of the disorder including overall metabolism of sulfated GAGs and endochondral ossification.

Particle-induced osteolysis is mediated by endoplasmic reticulum stress-associated osteoblast apoptosis

Osteoblast dysfunction plays a crucial role in periprosthetic osteolysis and aseptic loosening, and endoplasmic reticulum (ER) stress is recognized as an important causal factor of wear particle-induced osteolysis. However, the influence of ER stress on osteoblast activity during osteolysis and its underlying mechanisms remain elusive. This study aims to investigate whether ER stress is involved in the detrimental effects of wear particles on osteoblasts. Through our investigation, we observed elevated expression levels of ER stress and apoptosis markers in particle-stimulated bone specimens and osteoblasts. To probe further, we employed the ER stress inhibitor, 4-PBA, to treat particle-stimulated osteoblasts. The results revealed that 4-PBA effectively alleviated particle-induced osteoblast apoptosis and mitigated osteogenic reduction. Furthermore, our study revealed that wear particle-induced ER stress in osteoblasts coincided with mitochondrial damage, calcium overload, and oxidative stress, all of which were effectively alleviated by 4-PBA treatment. Encouragingly, 4-PBA administration also improved bone formation and attenuated osteolysis in a mouse calvarial model. In conclusion, our results demonstrate that ER stress plays a crucial role in mediating wear particle-induced osteoblast apoptosis and impaired osteogenic function. These findings underscore the critical involvement of ER stress in wear particle-induced osteolysis and highlight ER stress as a potential therapeutic target for ameliorating wear particle-induced osteogenic reduction and bone destruction.

TMCO3, a Putative K+ :Proton Antiporter at the Golgi Apparatus, Is Important for Longitudinal Growth in Mice and Humans

Isolated short stature, defined as short stature without any other abnormalities, is a common heterogeneous condition in children. Exome sequencing identified the homozygous nonsense variant c.1832G>A/p.(Trp611*) in TMCO3 in two sisters with isolated short stature. Radiological studies, biochemical measurements, assessment of the skeletal status, and three-dimensional bone microarchitecture revealed no relevant skeletal and bone abnormalities in both sisters. The homozygous TMCO3 variant segregated with short stature in the family. TMCO3 transcript levels were reduced by ~50% in leukocyte-derived RNA of both sisters compared with controls, likely due to nonsense-mediated mRNA decay. In primary urinary cells of heterozygous family members, we detected significantly reduced TMCO3 protein levels. TMCO3 is functionally uncharacterized. We ectopically expressed wild-type TMCO3 in HeLa and ATDC5 chondrogenic cells and detected TMCO3 predominantly at the Golgi apparatus, whereas the TMCO3W611* mutant did not reach the Golgi. Coordinated co-expression of TMCO3W611* -HA and EGFP in HeLa cells confirmed intrinsic instability and/or degradation of the mutant. Tmco3 is expressed in all relevant mouse skeletal cell types. Highest abundance of Tmco3 was found in chondrocytes of the prehypertrophic zone in mouse and minipig growth plates where it co-localizes with a Golgi marker. Knockdown of Tmco3 in differentiated ATDC5 cells caused reduced and increased expression of Pthlh and Ihh, respectively. Measurement of long bones in Tmco3tm1b(KOMP)Wtsi knockout mice revealed significant shortening of forelimbs and hindlimbs. TMCO3 is a potential member of the monovalent cation:proton antiporter 2 (CPA2) family. By in silico tools and homology modeling, TMCO3 is predicted to have an N-terminal secretory signal peptide, forms a dimer localized to the membrane, and is organized in a dimerization and a core domain. The core domain contains the CPA2 motif essential for K+ binding and selectivity. Collectively, our data demonstrate that loss of TMCO3 causes growth defects in both humans and mice. © 2023 American Society for Bone and Mineral Research (ASBMR).

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.

ALPK1 Accelerates the Pathogenesis of Osteoarthritis by Activating NLRP3 Signaling

Alpha-kinase 1 (ALPK1), a member of the alpha-kinase family, has been shown to be involved in mediating inflammatory responses and is strongly associated with gout; however, its modulatory role in osteoarthritis (OA) remains unclear. Here, we uncovered elevation of ALPK1 in degraded cartilage of destabilized medial meniscus (DMM) and collagenase-induced osteoarthritis (CIOA), two different mouse OA models induced by mechanical stress or synovitis. Intraarticular administration of recombinant human ALPK1 (rhALPK1) in vivo exacerbated OA pathogenesis in both DMM and CIOA mice, whereas ALPK1 knockout reversed this process. In vitro study demonstrated that ALPK1 aggravates metabolic disturbances in chondrocytes by enhancing the production of NOD-like receptor protein 3 (NLRP3), an inflammasome sensors driving interlukin-1β (IL-1β)-mediated inflammatory conditions. Furthermore, the selective inhibition of nuclear factor-κB (NF-κB) or NLRP3 indicates that NLRP3 is a downstream signaling governed by NF-κB in ALPK1-activated chondrocytes. Collectively, these results establish ALPK1 as a novel catabolic regulator of OA pathogenesis, and targeting this signaling may be a promising treatment strategy for OA. © 2022 American Society for Bone and Mineral Research (ASBMR).

Early enzyme replacement therapy prevents dental and craniofacial abnormalities in a mouse model of mucopolysaccharidosis type VI

Mucopolysaccharidosis VI (MPS VI) is a hereditary lysosomal storage disease caused by the absence of the enzyme arylsulfatase B (ARSB). Craniofacial defects are common in MPS VI patients and manifest as abnormalities of the facial bones, teeth, and temporomandibular joints. Although enzyme replacement therapy (ERT) is the treatment of choice for MPS VI, the effects on the craniofacial and dental structures are still poorly understood. In this study, we used an Arsb-deficient mouse model (Arsbm/m) that mimics MPS VI to investigate the effects of ERT on dental and craniofacial structures and compared these results with clinical and radiological observations from three MPS VI patients. Using micro-computed tomography, we found that the craniofacial phenotype of the Arsbm/m mice was characterized by bone exostoses at the insertion points of the masseter muscles and an overall increased volume of the jaw bone. An early start of ERT (at 4 weeks of age for 20 weeks) resulted in a moderate improvement of these jaw anomalies, while a late start of ERT (at 12 weeks of age for 12 weeks) showed no effect on the craniofacial skeleton. While teeth typically developed in Arsbm/m mice, we observed a pronounced loss of tooth-bearing alveolar bone. This alveolar bone loss, which has not been described before in MPS VI, was also observed in one of the MPS VI patients. Interestingly, only an early start of ERT led to a complete normalization of the alveolar bone in Arsbm/m mice. The temporomandibular joints in Arsbm/m mice were deformed and had a porous articular surface. Histological analysis revealed a loss of physiological cartilage layering, which was also reflected in an altered proteoglycan content in the cartilage of Arsbm/m mice. These abnormalities could only be partially corrected by an early start of ERT. In conclusion, our results show that an early start of ERT in Arsbm/m mice achieves the best therapeutic effects for tooth, bone, and temporomandibular joint development. As the MPS VI mouse model in this study resembles the clinical findings in MPS VI patients, our results suggest enzyme replacement therapy should be started as early as possible.

Mammalian Sulfatases: Biochemistry, Disease Manifestation, and Therapy

Sulfatases are enzymes that catalyze the removal of sulfate from biological substances, an essential process for the homeostasis of the body. They are commonly activated by the unusual amino acid formylglycine, which is formed from cysteine at the catalytic center, mediated by a formylglycine-generating enzyme as a post-translational modification. Sulfatases are expressed in various cellular compartments such as the lysosome, the endoplasmic reticulum, and the Golgi apparatus. The substrates of mammalian sulfatases are sulfolipids, glycosaminoglycans, and steroid hormones. These enzymes maintain neuronal function in both the central and the peripheral nervous system, chondrogenesis and cartilage in the connective tissue, detoxification from xenobiotics and pharmacological compounds in the liver, steroid hormone inactivation in the placenta, and the proper regulation of skin humidification. Human sulfatases comprise 17 genes, 10 of which are involved in congenital disorders, including lysosomal storage disorders, while the function of the remaining seven is still unclear. As for the genes responsible for pathogenesis, therapeutic strategies have been developed. Enzyme replacement therapy with recombinant enzyme agents and gene therapy with therapeutic transgenes delivered by viral vectors are administered to patients. In this review, the biochemical substrates, disease manifestation, and therapy for sulfatases are summarized.

A homozygous hypomorphic BNIP1 variant causes an increase in autophagosomes and reduced autophagic flux and results in a spondylo-epiphyseal dysplasia

BNIP1 (BCL2 interacting protein 1) is a soluble N-ethylmaleimide-sensitive factor-attachment protein receptor involved in ER membrane fusion. We identified the homozygous BNIP1 intronic variant c.84+3A>T in the apparently unrelated patients 1 and 2 with disproportionate short stature. Radiographs showed abnormalities affecting both the axial and appendicular skeleton and spondylo-epiphyseal dysplasia. We detected ~80% aberrantly spliced BNIP1 pre-mRNAs, reduced BNIP1 mRNA level to ~80%, and BNIP1 protein level reduction by ~50% in patient 1 compared to control fibroblasts. The BNIP1 ortholog in drosophila, Sec. 20, regulates autophagy and lysosomal degradation. We assessed lysosome positioning and identified a decrease in lysosomes in the perinuclear region and an increase in the cell periphery in patient 1 cells. Immunofluorescence microscopy and immunoblotting demonstrated an increase in LC3B-positive structures and LC3B-II levels, respectively, in patient 1 fibroblasts under steady-state condition. Treatment of serum-starved fibroblasts with or without bafilomycin A1 identified significantly decreased autophagic flux in patient 1 cells. Our data suggest a block at the terminal stage of autolysosome formation and/or clearance in patient fibroblasts. BNIP1 together with RAB33B and VPS16, disease genes for Smith-McCort dysplasia 2 and a multisystem disorder with short stature, respectively, highlight the importance of autophagy in skeletal development. This article is protected by copyright. All rights reserved.

MPS VI associated ocular phenotypes in an MPS VI murine model and the therapeutic effects of odiparcil treatment

Maroteaux - Lamy syndrome (mucopolysaccharidosis type VI, MPS VI) is a lysosomal storage disease resulting from insufficient enzymatic activity for degradation of the specific glycosaminoglycans (GAG) chondroitin sulphate (CS) and dermatan sulphate (DS). Among the most pronounced MPS VI clinical manifestations caused by cellular accumulation of excess CS and DS are eye disorders, in particular those that affect the cornea. Ocular manifestations are not treated by the current standard of care, enzyme replacement therapy (ERT), leaving patients with a significant unmet need. Using in vitro and in vivo models, we previously demonstrated the potential of the β-D-xyloside, odiparcil, as an oral GAG clearance therapy for MPS VI. Here, we characterized the eye phenotypes in MPS VI arylsulfatase B deficient mice (Arsb^-) and studied the effects of odiparcil treatment in early and established disease models. Severe levels of opacification and GAG accumulation were detected in the eyes of MPS VI Arsb^- mice. Histological examination of MPS VI Arsb^- eyes showed an aggregate of corneal phenotypes, including reduction in the corneal epithelium thickness and number of epithelial cell layers, and morphological malformations in the stroma. In addition, colloidal iron staining showed specifically GAG accumulation in the cornea. Orally administered odiparcil markedly reduced GAG accumulation in the eyes of MPS VI Arsb^- mice in both disease models and restored the corneal morphology (epithelial layers and stromal structure). In the early disease model of MPS VI, odiparcil partially reduced corneal opacity area, but did not affect opacity area in the established model. Analysis of GAG types accumulating in the MPS VI Arsb^- eyes demonstrated major contribution of DS and CS, with some increase in heparan sulphate (HS) as well and all were reduced with odiparcil treatment. Taken together, we further reveal the potential of odiparcil to be an effective therapy for eye phenotypes associated with MPS VI disease.

Clinical Development of Cell Therapies to Halt Lysosomal Storage Diseases: Results and Lessons Learned

Although cross-correction was discovered more than 50 years ago, and held the promise of drastically improving disease management, still no cure exists for lysosomal storage diseases (LSDs). Cell therapies hold the potential to halt disease progression: either a subset of autologous cells can be ex vivo/ in vivo transfected with the functional gene or allogenic wild type stem cells can be transplanted. However, majority of cell-based attempts have been ineffective, due to the difficulties in reversing neuronal symptomatology, in finding appropriate gene transfection approaches, in inducing immune tolerance, reducing the risk of graft versus host disease (GVHD) when allogenic cells are used and that of immune response when engineered viruses are administered, coupled with a limited secretion and uptake of some enzymes. In the last decade, due to advances in our understanding of lysosomal biology and mechanisms of cross-correction, coupled with progresses in gene therapy, ongoing pre-clinical and clinical investigations have remarkably increased. Even gene editing approaches are currently under clinical experimentation. This review proposes to critically discuss and compare trends and advances in cell-based and gene therapy for LSDs. Systemic gene delivery and transplantation of allogenic stem cells will be initially discussed, whereas proposed brain targeting methods will be then critically outlined.

Lysosome function in glomerular health and disease

The lysosome represents an important regulatory platform within numerous vesicle trafficking pathways including the endocytic, phagocytic, and autophagic pathways. Its ability to fuse with endosomes, phagosomes, and autophagosomes enables the lysosome to break down a wide range of both endogenous and exogenous cargo, including macromolecules, certain pathogens, and old or damaged organelles. Due to its center position in an intricate network of trafficking events, the lysosome has emerged as a central signaling node for sensing and orchestrating the cells metabolism and immune response, for inter-organelle and inter-cellular signaling and in membrane repair. This review highlights the current knowledge of general lysosome function and discusses these findings in their implication for renal glomerular cell types in health and disease including the involvement of glomerular cells in lysosomal storage diseases and the role of lysosomes in nongenetic glomerular injuries.

Imbalanced cellular metabolism compromises cartilage homeostasis and joint function in a mouse model of mucolipidosis type III gamma

Mucolipidosis type III (MLIII) gamma is a rare inherited lysosomal storage disorder caused by mutations in GNPTG encoding the γ-subunit of GlcNAc-1-phosphotransferase, the key enzyme ensuring proper intracellular location of multiple lysosomal enzymes. Patients with MLIII gamma typically present with osteoarthritis and joint stiffness, suggesting cartilage involvement. Using Gnptg knockout (Gnptgko ) mice as a model of the human disease, we showed that missorting of a number of lysosomal enzymes is associated with intracellular accumulation of chondroitin sulfate in Gnptgko chondrocytes and their impaired differentiation, as well as with altered microstructure of the cartilage extracellular matrix (ECM). We also demonstrated distinct functional and structural properties of the Achilles tendons isolated from Gnptgko and Gnptab knock-in (Gnptabki ) mice, the latter displaying a more severe phenotype resembling mucolipidosis type II (MLII) in humans. Together with comparative analyses of joint mobility in MLII and MLIII patients, these findings provide a basis for better understanding of the molecular reasons leading to joint pathology in these patients. Our data suggest that lack of GlcNAc-1-phosphotransferase activity due to defects in the γ-subunit causes structural changes within the ECM of connective and mechanosensitive tissues, such as cartilage and tendon, and eventually results in functional joint abnormalities typically observed in MLIII gamma patients. This idea was supported by a deficit of the limb motor function in Gnptgko mice challenged on a rotarod under fatigue-associated conditions, suggesting that the impaired motor performance of Gnptgko mice was caused by fatigue and/or pain at the joint.This article has an associated First Person interview with the first author of the paper.

Odiparcil, a potential glycosaminoglycans clearance therapy in mucopolysaccharidosis VI-Evidence from in vitro and in vivo models

Mucopolysaccharidoses are a class of lysosomal storage diseases, characterized by enzymatic deficiency in the degradation of specific glycosaminoglycans (GAG). Pathological accumulation of excess GAG leads to multiple clinical symptoms with systemic character, most severely affecting bones, muscles and connective tissues. Current therapies include periodic intravenous infusion of supplementary recombinant enzyme (Enzyme Replacement Therapy–ERT) or bone marrow transplantation. However, ERT has limited efficacy due to poor penetration in some organs and tissues. Here, we investigated the potential of the β-D-xyloside derivative odiparcil as an oral GAG clearance therapy for Maroteaux–Lamy syndrome (Mucopolysaccharidosis type VI, MPS VI). In vitro, in bovine aortic endothelial cells, odiparcil stimulated the secretion of sulphated GAG into culture media, mainly of chondroitin sulphate (CS) /dermatan sulphate (DS) type. Efficacy of odiparcil in reducing intracellular GAG content was investigated in skin fibroblasts from MPS VI patients where odiparcil was shown to reduce efficiently the accumulation of intracellular CS with an EC₅₀ in the range of 1 μM. In vivo, in wild type rats, after oral administrations, odiparcil was well distributed, achieving μM concentrations in MPS VI disease-relevant tissues and organs (bone, cartilage, heart and cornea). In MPS VI Arylsulphatase B deficient mice (Arsb^-), after chronic oral administration, odiparcil consistently stimulated the urinary excretion of sulphated GAG throughout the treatment period and significantly reduced tissue GAG accumulation in liver and kidney. Furthermore, odiparcil diminished the pathological cartilage thickening observed in trachea and femoral growth plates of MPS VI mice. The therapeutic efficacy of odiparcil was similar in models of early (treatment starting in juvenile, 4 weeks old mice) or established disease (treatment starting in adult, 3 months old mice). Our data demonstrate that odiparcil effectively diverts the synthesis of cellular glycosaminoglycans into secreted soluble species and this effect can be used for reducing cellular and tissue GAG accumulation in MPS VI models. Therefore, our data reveal the potential of odiparcil as an oral GAG clearance therapy for MPS VI patients.