Growth plate pathology in feline mucopolysaccharidosis VI

Modeling cartilage pathology in mucopolysaccharidosis VI using iPSCs reveals early dysregulation of chondrogenic and metabolic gene expression

Mucopolysaccharidosis type VI (MPS VI) is a metabolic disorder caused by disease-associated variants in the Arylsulfatase B (ARSB) gene, resulting in ARSB enzyme deficiency, lysosomal glycosaminoglycan accumulation, and cartilage and bone pathology. The molecular response to MPS VI that results in cartilage pathology in human patients is largely unknown. Here, we generated a disease model to study the early stages of cartilage pathology in MPS VI. We generated iPSCs from four patients and isogenic controls by inserting the ARSB cDNA in the AAVS1 safe harbor locus using CRISPR/Cas9. Using an optimized chondrogenic differentiation protocol, we found Periodic acid-Schiff positive inclusions in hiPSC-derived chondrogenic cells with MPS VI. Genome-wide mRNA expression analysis showed that hiPSC-derived chondrogenic cells with MPS VI downregulated expression of genes involved in TGF-β/BMP signalling, and upregulated expression of inhibitors of the Wnt/β-catenin signalling pathway. Expression of genes involved in apoptosis and growth was upregulated, while expression of genes involved in glycosaminoglycan metabolism was dysregulated in hiPSC-derived chondrogenic cells with MPS VI. These results suggest that human ARSB deficiency in MPS VI causes changes in the transcriptional program underlying the early stages of chondrogenic differentiation and metabolism.

Mucopolysaccharidosis VI in a European Shorthair cat: Neurological presentation, computed tomography findings and genetic investigation

The present case report describes the clinical signs of a 10-month-old, intact female, Domestic Shorthair cat presented with a history of chronic progressive difficulty to walk with the four limbs. The physical and neurological examinations revealed skeletal deformities, corneal opacity and a severe spastic non-ambulatory tetraparesis. Complete blood count and biochemistry profiles were unremarkable. Diffuse bone rarefaction, hyperostosis and an apparent fusion of the vertebral bodies were observed on spinal radiographs. A non-contrast computed tomography (CT) exam of the whole body of the patient was performed. Based on the medical history, clinical findings, laboratory analysis, spinal radiographs and CT findings, a lysosomal storage disorder was suspected. Genetic testing for mucopolysaccharidosis VI and VII revealed a genetic mutation, ARSB variant L476P, confirming the diagnosis of mucopolysaccharidosis type VI.

Hip disease in Mucopolysaccharidoses and Mucolipidoses: A review of mechanisms, interventions and future perspectives

The hips are frequently involved in inheritable diseases which affect the bones. The clinical and radiological presentation of these diseases may be very similar to common hip disorders as developmental dysplasia of the hip, osteoarthritis and avascular necrosis, so the diagnosis may be easily overlooked and treatment may be suboptimal. Mucopolysaccharidosis (MPS) and Mucolipidosis (ML II and III) are lysosomal storage disorders with multisystemic involvement. Characteristic skeletal abnormalities, known as dysostosis multiplex, are common in MPS and ML and originate from intra-lysosomal storage of glycosaminoglycans in cells of the cartilage, bones and ligaments. The hip joint is severely affected in MPS and ML. Hip pathology results in limitations in mobility and pain from young age, and negatively affects quality of life. In order to better understand the underlying process that causes hip disease in MPS and ML, this review first describes the normal physiological (embryonic) hip joint development, including the interplay between the acetabulum and the femoral head. In the second part the factors contributing to altered hip morphology and function in MPS and ML are discussed, such as abnormal development of the pelvic- and femoral bones (which results in altered biomechanical forces) and inflammation. In the last part of this review therapeutic options and future perspectives are addressed.

Failures of Endochondral Ossification in the Mucopolysaccharidoses

PURPOSE OF REVIEW

The mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage disorders characterized by abnormal accumulation of glycosaminoglycans (GAGs) in cells and tissues. MPS patients frequently exhibit failures of endochondral ossification during postnatal growth leading to skeletal deformity and short stature. In this review, we outline the current understanding of the cellular and molecular mechanisms underlying failures of endochondral ossification in MPS and discuss associated treatment challenges and opportunities.

RECENT FINDINGS

Studies in MPS patients and animal models have demonstrated that skeletal cells and tissues exhibit significantly elevated GAG storage from early in postnatal life and that this is associated with impaired cartilage-to-bone conversion in primary and secondary ossification centers, and growth plate dysfunction. Recent studies have begun to elucidate the underlying cellular and molecular mechanisms, including impaired chondrocyte proliferation and hypertrophy, diminished growth factor signaling, disrupted cell cycle progression, impaired autophagy, and increased cell stress and apoptosis. Current treatments such as hematopoietic stem cell transplantation and enzyme replacement therapy fail to normalize endochondral ossification in MPS. Emerging treatments including gene therapy and small molecule-based approaches hold significant promise in this regard. Failures of endochondral ossification contribute to skeletal deformity and short stature in MPS patients, increasing mortality and reducing quality of life. Early intervention is crucial for effective treatment, and there is a critical need for new approaches that normalize endochondral ossification by directly targeting affected cells and signaling pathways.

Growth Plate Pathology in the Mucopolysaccharidosis Type VI Rat Model-An Experimental and Computational Approach

BACKGROUND

Mucopolysaccharidoses (MPS) are a group of inherited metabolic diseases caused by impaired function or absence of lysosomal enzymes involved in degradation of glycosaminoglycans. Clinically, MPS are skeletal dysplasias, characterized by cartilage abnormalities and disturbances in the process of endochondral ossification. Histologic abnormalities of growth cartilage have been reported at advanced stages of the disease, but information regarding growth plate pathology progression either in humans or in animal models, as well as its pathophysiology, is limited.

METHODS

Histological analyses of distal femur growth plates of wild type (WT) and mucopolysaccharidosis type VI (MPS VI) rats at different stages of development were performed, including quantitative data. Experimental findings were then analyzed in a theoretical scenario.

RESULTS

Histological evaluation showed a progressive loss of histological architecture within the growth plate. Furthermore, in silico simulation suggest the abnormal cell distribution in the tissue may lead to alterations in biochemical gradients, which may be one of the factors contributing to the growth plate abnormalities observed, highlighting aspects that must be the focus of future experimental works.

CONCLUSION

The results presented shed some light on the progression of growth plate alterations observed in MPS VI and evidence the potentiality of combined theoretical and experimental approaches to better understand pathological scenarios, which is a necessary step to improve the search for novel therapeutic approaches.

Cell cycle progression is disrupted in murine MPS VII growth plate leading to reduced chondrocyte proliferation and transition to hypertrophy

Endochondral bone growth is abnormal in 6 of the 11 types of mucopolysaccharidoses (MPS) disorders; resulting in short stature, reduced size of the thoracic cavity and compromised manual dexterity. Current therapies for MPS have had a limited effect on bone growth and to improve these therapies or develop adjunct approaches requires an understanding of the underlying basis of abnormal bone growth in MPS. The MPS VII mouse model replicates the reduction in long bone and vertebral length observed in human MPS. Using this model we have shown that the growth plate is elongated but contains fewer chondrocytes in the proliferative and hypertrophic zones. Endochondral bone growth is in part regulated by entry and exit from the cell cycle by growth plate chondrocytes. More MPS VII chondrocytes were positive for Ki67, a marker for active phases of the cell cycle, suggesting that more MPS VII chondrocytes were in the cell cycle. The number of cells positive for phosphorylated histone H3 was significantly reduced in MPS VII chondrocytes, suggesting fewer MPS VII chondrocytes progressed to mitotic division. While MPS VII HZ chondrocytes continued to express cyclin D1 and more cells were positive for E2F1 and phos pRb than normal, fewer MPS VII HZ chondrocytes were positive for p57^kip2 a marker of terminal differentiation, suggesting fewer MPS VII chondrocytes were able to exit the cell cycle. In addition, multiple markers typical of PZ to HZ transition were not downregulated in MPS VII, in particular Sox9, Pthrpr and Wnt5a. These findings are consistent with MPS VII growth plates elongating at a slower rate than normal due to a delay in progression through the cell cycle, in particular the transition between G1 and S phases, leading to both reduced cell division and transition to the hypertrophic phenotype.

Surgical Management of Progressive Thoracolumbar Kyphosis in Mucopolysaccharidosis: Is a Posterior-only Approach Safe and Effective?

BACKGROUND

According to the current literature, the recommended surgical treatment is circumferential spinal fusion, including both anterior and posterior procedures, for progressive thoracolumbar kyphosis in mucopolysaccharidosis (MPS). The purpose of this study was to report our experience with the posterior-only approach and instrumented fusion for MPS kyphosis.

METHODS

Six consecutive patients with MPS and thoracolumbar junctional kyphosis managed with the posterior-only approach were included. Demographic data, the type of MPS, medical comorbidities, and accompanying clinical manifestations were recorded. Measurements recorded on radiographs for the study included the presence of any coronal-plane deformity, fusion levels, changes in the local kyphosis angle (LKA), proximal and distal junctional kyphosis angles, and the apical vertebral wedge angle.

RESULTS

The average age at the time of surgery was 6.6 (range, 4 to 12) years. The average follow-up duration was 52.6 (range, 44 to 64) months. The mean preoperative LKA of 63.1±15.8 (range, 48 to 92) degrees decreased to a mean of 16.6±8.4 (range, 5 to 30) degrees immediately after surgery. At the latest follow-up, the mean LKA was 19.6±8.8 (range, 8 to 34) degrees. Apical vertebral listhesis was reduced in all patients with surgical correction. The average apical vertebral wedge angle of 15 (range, 11 to 19) degrees at the early postoperative period decreased to 4.6 (range, 2 to 7) degrees at the latest follow-up. Adjacent-segment problems occurred in 2 patients. There were no neurological complications or implant failures in any of the patients.

CONCLUSIONS

Posterior-only corrective techniques and instrumented fusion with pedicle screws for progressive thoracolumbar junctional kyphosis in MPS patients are safe and effective methods. Its results are comparable to those achieved with conventional circumferential fusion. However, patients should be monitored closely for adjacent-segment problems.

LEVEL OF EVIDENCE

Level IV-retrospective case series.

The effect of galsulfase enzyme replacement therapy on the growth of patients with mucopolysaccharidosis VI (Maroteaux-Lamy syndrome)

Mucopolysaccharidosis (MPS) VI is an autosomal recessive lysosomal storage disorder arising from deficient activity of N-acetylgalactosamine-4-sulfatase (arylsulfatase B) and subsequent intracellular accumulation of the glycosaminoglycans (GAGs) dermatan sulfate and chondroitin-4-sulfate. Manifestations are multi-systemic and include skeletal abnormalities such as dysostosis multiplex and short stature. Reference height-for-age growth charts for treatment-naïve MPS VI patients have been published for both the slowly and rapidly progressing populations. Categorization of disease progression for these charts was based on urinary GAG (uGAG) level; high (>200μg/mg creatinine) levels identified subjects as rapidly progressing. Height data for 141 patients who began galsulfase treatment by the age of 18years were collected and stratified by baseline uGAG level and age at ERT initiation in 3-year increments. The reference MPS VI growth charts were used to calculate change in Z-score from pre-treatment baseline to last follow-up. Among patients with high baseline uGAG levels, galsulfase ERT was associated with an increase in Z-score for those beginning treatment at 0-3, >3-6, >6-9, >9-12, and >12-15years of age (p<0.05). Increases in Z-score were not detected for patients who began treatment between 15 and 18years of age, nor for patients with low (≤200μg/mg creatinine) baseline uGAG levels, regardless of age at treatment initiation. The largest positive deviation from untreated reference populations was seen in the high uGAG excretion groups who began treatment by 6years of age, suggesting an age- and severity-dependent impact of galsulfase ERT on growth.

Mucopolysaccharidosis VI in cats - clarification regarding genetic testing

The release of new DNA-based diagnostic tools has increased tremendously in companion animals. Over 70 different DNA variants are now known for the cat, including DNA variants in disease-associated genes and genes causing aesthetically interesting traits. The impact genetic tests have on animal breeding and health management is significant because of the ability to control the breeding of domestic cats, especially breed cats. If used properly, genetic testing can prevent the production of diseased animals, causing the reduction of the frequency of the causal variant in the population, and, potentially, the eventual eradication of the disease. However, testing of some identified DNA variants may be unwarranted and cause undo strife within the cat breeding community and unnecessary reduction of gene pools and availability of breeding animals. Testing for mucopolysaccharidosis Type VI (MPS VI) in cats, specifically the genetic testing of the L476P (c.1427T>C) and the D520N (c.1558G>A) variants in arylsulfatase B (ARSB), has come under scrutiny. No health problems are associated with the D520N (c.1558G>A) variant, however, breeders that obtain positive results for this variant are speculating as to possible correlation with health concerns. Birman cats already have a markedly reduced gene pool and have a high frequency of the MPS VI D520N variant. Further reduction of the gene pool by eliminating cats that are heterozygous or homozygous for only the MPS VI D520N variant could lead to more inbreeding depression effects on the breed population. Herein is debated the genetic testing of the MPS VI D520N variant in cats. Surveys from different laboratories suggest the L476P (c.1427T>C) disease-associated variant should be monitored in the cat breed populations, particularly breeds with Siamese derivations and outcrosses. However, the D520N has no evidence of association with disease in cats and testing is not recommended in the absence of L476P genotyping. Selection against the D520N is not warranted in cat populations. More rigorous guidelines may be required to support the genetic testing of DNA variants in all animal species.

Characterization of the MPS I-H knock-in mouse reveals increased femoral biomechanical integrity with compromised material strength and altered bone geometry

Mucopolysaccharidosis type I (MPS I), is an autosomal recessive lysosomal storage disorder caused by a deficiency in the α-L-iduronidase enzyme, resulting in decreased enzymatic activity and accumulation of glycosaminoglycans. The disorder phenotypically manifests with increased urine glycosaminoglycan excretion, facial dysmorphology, neuropathology, cardiac manifestations, and bone deformities. While the development of new treatment strategies have shown promise in attenuating many symptoms associated with the disorder, the bone phenotype remains unresponsive. The aim of this study was to investigate and further characterize the skeletal manifestations of the Idua-W392X knock-in mouse model, which carries a nonsense mutation corresponding to the IDUA-W402X mutation found in Hurler syndrome (MPS I-H) patients. μCT analysis of the microarchitecture demonstrated increased cortical thickness, trabecular number, and trabecular connectivity along with decreased trabecular separation in the tibiae of female homozygous Idua-W392X knock-in (IDUA^−/−) mice, and increased cortical thickness in male IDUA^−/− tibiae. Cortical density, as determined by μCT, and bone mineral density distribution, as determined by quantitative backscattered microscopy, were equivalent in IDUA^−/− and wildtype (Wt) bone. However, tibial porosity was increased in IDUA^−/− cortical bone. Raman spectroscopy results indicated that tibiae from female IDUA^−/− had decreased phosphate to matrix ratios and increased carbonate to phosphate ratios compared to Wt female tibiae, whereas these ratios remained equivalent in male IDUA^−/− and Wt tibiae. Femora demonstrated altered geometry and upon torsional loading to failure analysis, female IDUA^−/− mouse femora exhibited increased torsional ultimate strength, with a decrease in material strength relative to Wt littermates. Taken together, these findings suggest that the IDUA^−/− mutation results in increased bone torsional strength by altering the overall bone geometry and the microarchitecture which may be a compensatory response to increased porosity, reduced bone tensile strength and altered physiochemical composition.

Growth Charts for Individuals with Mucopolysaccharidosis VI (Maroteaux-Lamy Syndrome)

BACKGROUND

The skeletal phenotype of mucopolysaccharidosis VI (MPS VI) is characterized by short stature and growth failure.

OBJECTIVE

The purpose of this study was to construct reference growth curves for MPS VI patients with rapidly and slowly progressive disease.

METHODS

We pooled cross-sectional and longitudinal height for age data from galsulfase (Naglazyme(®), BioMarin Pharmaceutical Inc.), treatment naïve patients (n = 269) who participated in various MPS VI studies, including galsulfase clinical trials and their extension programs, the MPS VI clinical surveillance program (CSP), and the MPS VI survey and resurvey studies, to construct growth charts for the MPS VI population. There were 229 patients included in this study, of which data from 207 patients ≤25 years of age with 513 height measurements were used for constructing reference growth curves.

RESULTS

Height for age growth curves for the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles were constructed for patients with rapidly and slowly progressing disease defined by the pre-enzyme replacement therapy (ERT) uGAG levels of > or ≤200 μg/mg creatinine. The mean (SD) pre-ERT uGAG levels were 481.0 (218.6) and 97.8 (56.3) μg/mg creatinine for the patients ≤25 years of age with rapidly (n = 131) and slowly (n = 76) progressing MPS VI disease, respectively. The median growth curves for patients with ≤ and >200 μg/mg creatinine were above and below the median (50th percentile) growth curve for the entire MPS VI population.

CONCLUSION

MPS VI growth charts have been developed to assist in the clinical management of MPS VI patients.

Intra-articular enzyme replacement therapy with rhIDUA is safe, well-tolerated, and reduces articular GAG storage in the canine model of mucopolysaccharidosis type I

BACKGROUND

Treatment with intravenous enzyme replacement therapy and hematopoietic stem cell transplantation for mucopolysaccharidosis (MPS) type I does not address joint disease, resulting in persistent orthopedic complications and impaired quality of life. A proof-of-concept study was conducted to determine the safety, tolerability, and efficacy of intra-articular recombinant human iduronidase (IA-rhIDUA) enzyme replacement therapy in the canine MPS I model.

METHODS

Four MPS I dogs underwent monthly rhIDUA injections (0.58 mg/joint) into the right elbow and knee for 6 months. Contralateral elbows and knees concurrently received normal saline. No intravenous rhIDUA therapy was administered. Monthly blood counts, chemistries, anti-rhIDUA antibody titers, and synovial fluid cell counts were measured. Lysosomal storage of synoviocytes and chondrocytes, synovial macrophages and plasma cells were scored at baseline and 1 month following the final injection.

RESULTS

All injections were well-tolerated without adverse reactions. One animal required prednisone for spinal cord compression. There were no clinically significant abnormalities in blood counts or chemistries. Circulating anti-rhIDUA antibody titers gradually increased in all dogs except the prednisone-treated dog; plasma cells, which were absent in all baseline synovial specimens, were predominantly found in synovium of rhIDUA-treated joints at study-end. Lysosomal storage in synoviocytes and chondrocytes following 6 months of IA-rhIDUA demonstrated significant reduction compared to tissues at baseline, and saline-treated tissues at study-end. Mean joint synovial GAG levels in IA-rhIDUA joints were 8.62 ± 5.86 μg/mg dry weight and 21.6 ± 10.4 μg/mg dry weight in control joints (60% reduction). Cartilage heparan sulfate was also reduced in the IA-rhIDUA joints (113 ± 39.5 ng/g wet weight) compared to saline-treated joints (142 ± 56.4 ng/g wet weight). Synovial macrophage infiltration, which was present in all joints at baseline, was abolished in rhIDUA-treated joints only.

CONCLUSIONS

Intra-articular rhIDUA is well-tolerated and safe in the canine MPS I animal model. Qualitative and quantitative assessments indicate that IA-rhIDUA successfully reduces tissue and cellular GAG storage in synovium and articular cartilage, including cartilage deep to the articular surface, and eliminates inflammatory macrophages from synovial tissue.

CLINICAL RELEVANCE

The MPS I canine IA-rhIDUA results suggest that clinical studies should be performed to determine if IA-rhIDUA is a viable approach to ameliorating refractory orthopedic disease in human MPS I.

Effect of recombinant human growth hormone on changes in height, bone mineral density, and body composition over 1-2 years in children with Hurler or Hunter syndrome

Patients with Hurler or Hunter syndrome typically have moderate to severe growth deficiencies despite therapy with allogeneic hematopoietic stem cell transplantation and/or enzyme replacement therapy. It is unknown whether treatment with recombinant human growth hormone (hGH) can improve growth in these children. The objectives of this study were to determine the effects of hGH on growth, bone mineral density (BMD), and body composition in children with Hurler or Hunter syndrome enrolled in a longitudinal observational study. The difference in annual change in outcomes between hGH treated and untreated subjects was estimated by longitudinal regression models that adjusted for age, Tanner stage, and sex where appropriate. We report on 23 participants who completed at least 2 annual study visits (10 [43%] treated with hGH): Hurler syndrome (n=13) average age of 9.8 ± 3.1 years (range 5.3-13.6 years; 54% female) and Hunter syndrome (n=10) average age of 12.0 ± 2.7 years (range 7.0-17.0 years; 0% female). As a group, children with Hurler or Hunter syndrome treated with hGH had no difference in annual change in height (growth velocity) compared to those untreated with hGH. Growth velocity in hGH treated individuals ranged from -0.4 to 8.1cm/year and from 0.3 to 6.6 cm/year in the untreated individuals. Among children with Hunter syndrome, 100% (N=4) of those treated but only 50% of those untreated with hGH had an annual increase in height standard deviation score (SDS). Of the individuals treated with hGH, those with GHD had a trend towards higher annualized growth velocity compared to those without GHD (6.5 ± 1.9 cm/year vs. 3.5 ± 2.1cm/year; p=.050). Children treated with hGH had greater annual gains in BMD and lean body mass. In conclusion, although as a group we found no significant difference in growth between individuals treated versus not treated with hGH, individual response was highly variable and we are unable to predict who will respond to treatment. Thus, a trial of hGH may be appropriate in children with Hurler or Hunter syndrome, severe short stature, and growth failure. However, efficacy of hGH therapy should be evaluated after 1 year and discontinued if there is no increase in growth velocity or height SDS. Finally, the long-term benefits of changes in body composition with hGH treatment in this population are unknown.

Osteoimmunology in mucopolysaccharidoses type I, II, VI and VII. Immunological regulation of the osteoarticular system in the course of metabolic inflammation

BACKGROUND

Mucopolysaccharidoses (MPSs) are rare genetic diseases caused by a deficient activity of one of the lysosomal enzymes involved in the glycosaminoglycan (GAG) breakdown pathway. These metabolic blocks lead to the accumulation of GAGs in various organs and tissues, resulting in a multisystemic clinical picture. The pathological GAG accumulation begins a cascade of interrelated responses: metabolic, inflammatory and immunological with systemic effects. Metabolic inflammation, secondary to GAG storage, is a significant cause of osteoarticular symptoms in MPS disorders.

OBJECTIVE AND METHOD

The aim of this review is to present recent progress in the understanding of the role of inflammatory and immune processes in the pathophysiology of osteoarticular symptoms in MPS disorders and potential therapeutic interventions based on published reports in MPS patients and studies in animal models.

RESULTS AND CONCLUSIONS

The immune and skeletal systems have a number of shared regulatory molecules and many relationships between bone disorders and aberrant immune responses in MPS can be explained by osteoimmunology. The treatment options currently available are not sufficiently effective in the prevention, inhibition and treatment of osteoarticular symptoms in MPS disease. A lot can be learnt from interactions between skeletal and immune systems in autoimmune diseases such as rheumatoid arthritis (RA) and similarities between RA and MPS point to the possibility of using the experience with RA in the treatment of MPS in the future. The use of different anti-inflammatory drugs requires further study, but it seems to be an important direction for new therapeutic options for MPS patients.

Effects of enzyme replacement therapy on growth in patients with mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II; Hunter syndrome) is an X-linked, recessive, lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase. It has multisystemic involvement, with manifestations in the brain, upper respiratory tract, heart, abdomen, joints and bones. Bone involvement leads to decreased growth velocity and short stature in nearly all patients. A therapeutic option for patients with MPS II is enzyme replacement therapy (ERT) with idursulfase (Elaprase®). We compared annual growth rates before and during ERT in 18 patients from Mainz, Germany, and Manchester, UK. Group 1 included nine patients who started ERT before 10 years of age; group 2 contained nine patients aged more than 10 years at the start of ERT. All patients had received weekly or biweekly ERT or placebo for 1 year, followed by ERT for more than 3 years. For patients in group 1, the mean (± SD) height increase was 14.6 ± 5.5 cm during 3 years of ERT. Only one patient in this group (who was below the 3rd percentile when starting ERT) deviated from the normal growth curve over this time. Patients in group 2 had a mean height increase of 8.1 ± 1.7 cm after 3 years of ERT compared with an increase of 1 cm in the year before ERT. ERT seems to have a positive influence on growth in patients with MPS II. Most benefit is seen in patients beginning ERT before the age of 10 years. This supports the recommendation that ERT should be started as early as possible in patients with MPS II.

Long-term amelioration of feline Mucopolysaccharidosis VI after AAV-mediated liver gene transfer

Mucopolysaccharidosis VI (MPS VI) is caused by deficient arylsulfatase B (ARSB) activity resulting in lysosomal storage of glycosaminoglycans (GAGs). MPS VI is characterized by dysostosis multiplex, organomegaly, corneal clouding, and heart valve thickening. Gene transfer to a factory organ like liver may provide a lifetime source of secreted ARSB. We show that intravascular administration of adeno-associated viral vectors (AAV) 2/8-TBG-felineARSB in MPS VI cats resulted in ARSB expression up to 1 year, the last time point of the study. In newborn cats, normal circulating ARSB activity was achieved following delivery of high vector doses (6 × 10(13) genome copies (gc)/kg) whereas delivery of AAV2/8 vector doses as low as 2 × 10(12) gc/kg resulted in higher than normal serum ARSB levels in juvenile MPS VI cats. In MPS VI cats showing high serum ARSB levels, independent of the age at treatment, we observed: (i) clearance of GAG storage, (ii) improvement of long bone length, (iii) reduction of heart valve thickness, and (iv) improvement in spontaneous mobility. Thus, AAV2/ 8-mediated liver gene transfer represents a promising therapeutic strategy for MPS VI patients.

Different serum enzyme levels are required to rescue the various systemic features of the mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are lysosomal storage disorders characterized by progressive accumulation of glycosaminoglycans (GAGs) in various tissues. Enzyme replacement therapy (ERT) for several MPSs is available to date. However, the efficacy of ERT is limited, in particular in compartments such as bone, cartilage, the brain, and the eyes. We selected a rodent model of an MPS, with no central nervous system storage, to study the impact, on systemic features of the disease, of various stable levels of exogenous enzymes produced by adeno-associated viral vector (AAV)-mediated liver gene transfer. Low levels (6% of normal) of circulating enzyme were enough to reduce storage and inflammation in the visceral organs and to ameliorate skull abnormalities; intermediate levels (11% of normal) were required to reduce urinary GAG excretion; and high levels (>or=50% of normal) rescued abnormalities of the long bones and motor activity. These data will be instrumental to design appropriate clinical protocols based on either enzyme or gene replacement therapy for MPS and to predict their impact on the pathological features of MPS.

Chondroitin sulfate and growth factor signaling in the skeleton: Possible links to MPS VI

Mucopolysaccharidosis type VI (MPS VI), also called Maroteaux-Lamy syndrome, is an autosomal recessive lysosomal storage disorder caused by deficiency of a specific enzyme required for glycosaminoglycan catabolism. Deficiency in the N-acetylgalactosamine-4-sulfatase (4S) enzyme, also called arylsulfatase B (ARSB), may have profound skeletal consequences. In MPS VI, partially degraded glycosaminoglycans (GAGs) such as dermatan sulfate and chondroitin sulfate accumulate within lysosomes. Through mechanisms that remain unclear, the abnormal GAG metabolism impacts several aspects of cellular function, particularly in the growth plate. This article explores the hypothesis that accrued partially degraded GAGs may contribute to deregulation of signaling pathways that normally orchestrate skeletal development, with a focus on members of the transforming growth factor-β (TGF-β) family. Understanding the molecular mechanisms disrupted by MPS VI may yield insight to improve the efficacy of MPS VI therapies, including bone marrow transplantation and enzyme replacement therapies.

Anthropometric data of 14 patients with mucopolysaccharidosis I: retrospective analysis and efficacy of recombinant human alpha-L-iduronidase (laronidase)

OBJECTIVES

Our goal was to evaluate growth patterns in terms of body height, weight, head and chest circumference in patients with mucopolysaccharidosis type I (MPS I) without treatment and after enzyme replacement therapy (ERT) with alpha-l-iduronidase (laronidase).

PATIENTS AND METHODS

Anthropometric features of 14 patients with MPS I were followed from birth until the introduction of ERT (group 1-1st year of life, group 2 3rd year of life), after 52-260 weeks of ERT and periodically during treatment. The data since birth until beginning of treatment was obtained by retrospective review of patients' charts. Patients received intravenous laronidase at 100 U/kg (0.58 mg/kg) weekly for 52-260 weeks.

RESULTS

Patients from group 1 (n=7) and group 2 (n=7) had similar characteristics at the time of birth but showed significant difference when compared with healthy population. Growth patterns were associated significantly with the MPS I at birth. After 96-260 weeks of ERT, patients receiving laronidase (group 1) compared with group 2 did not show statistically significant improvement.

CONCLUSIONS

Anthropometric features of patients with MPS I significantly differ from the healthy population. Children with MPS I grew considerably slower, and differences between healthy and affected children increased with age. In studied patients with MPS I, laronidase did not appear to alter the growth patterns.

Growth patterns and the use of growth hormone in the mucopolysaccharidoses

Short stature is characteristic of patients with mucopolysaccharidosis (MPS) diseases. For children with skeletal dysplasias, such as MPS, it is important to know the natural history of growth. An understanding of the natural growth pattern in each MPS disease provides a measurement to which treatments can be compared, as well as data which can help families and providers make individualized decisions about growth promoting treatments. Multiple advancements have been made in the treatment of MPS with both hematopoietic cell transplantation (HCT) and enzyme replacement therapy (ERT). The long term benefit of these treatments on growth is unknown. This article will review the published data on growth in children with MPS, and describe preliminary data on the use of human growth hormone (hGH) in children with MPS.

Potential role of cathepsin K in the pathophysiology of mucopolysaccharidoses

Cathepsin K, a papain-like cysteine protease, is highly expressed in osteoclasts and plays a critical role in bone resorption. Dysfunction of the enzyme leads to various skeletal abnormalities. The recent knowledge that the collagenolytic activity of cathepsin K depends on interactions with bone and cartilage-resident glycosaminoglycans (GAGs) may shed some light on diseases such as mucopolysaccharidoses (MPSs). MPSs are a group of lysosomal storage diseases characterized by the accumulation of GAGs in tissues including bone. Typical pathological features of these diseases include skeletal abnormalities such as dysostosis multiplex, short stature, and multiple irregularities in bone development. We describe how further investigation of the cathepsin K/GAG complexes could provide valuable insights into the bone pathology associated with MPS diseases. In this review, we discuss the inhibition of osteoclast function through altered activity of cathepsin K by GAGs and offer insight into a mechanism for the bone pathology seen in MPS patients.

Glycosaminoglycan-mediated loss of cathepsin K collagenolytic activity in MPS I contributes to osteoclast and growth plate abnormalities

Mucopolysaccharidoses are a group of lysosomal storage diseases characterized by the build-up of glycosaminoglycans (GAGs) and severe skeletal abnormalities. As GAGs can regulate the collagenolytic activity of the major osteoclastic protease cathepsin K, we investigated the presence and activity of cathepsin K and its co-localization with GAGs in mucopolysaccharidosis (MPS) type I bone. The most dramatic difference between MPS I and wild-type mice was an increase in the amount of cartilage in the growth plates in MPS I bones. Though the number of cathepsin K-expressing osteoclasts was increased in MPS I mice, these mice revealed a significant reduction in cathepsin K-mediated cartilage degradation. As excess heparan and dermatan sulfates inhibit type II collagen degradation by cathepsin K and the spatial overlap between cathepsin K and heparan sulfate strongly increased in MPS I mice, the build up of subepiphyseal cartilage is speculated to be a direct consequence of cathepsin K inhibition by MPS I-associated GAGs. Moreover, isolated MPS I and Ctsk(-/-) osteoclasts displayed fewer actin rings and formed fewer resorption pits on dentine disks, as compared with wild-type cells. These results suggest that the accumulation of GAGs in murine MPS I bone has an inhibitory effect on cathepsin K activity, resulting in impaired osteoclast activity and decreased cartilage resorption, which may contribute to the bone pathology seen in MPS diseases.

Nutrition-induced catch-up growth at the growth plate

The effect of 40% food restriction (FR) and replenishment on the growth hormone (GH) and insulin-like growth factor-I (IGF-I) axis in the epiphyseal growth plate (EGP) was examined in a mouse model. Changes in RNA and protein levels were evaluated with real time PCR and immunohistochemistry, respectively, and serum levels of IGF-I and leptin were measured with radioimmunoassay. Dramatic changes in weight, tibial length and EGP height were observed following 10 days of 40% FR. The protein levels of IGF-I receptor (IGF-IR) and GH receptor (GHR), which were reduced during FR, increased during catch-up growth without an apparent change in the level of their RNA. The levels of type II and X collagens were unchanged. Serum IGF-I and leptin levels were reduced during FR and increased during catch-up growth. Following 40% FR, there was a significant decrease in the level of GHR and IGF-IR in the EGP which may explain the reduced effect of GH treatment in malnourished animals and children.

Management guidelines for mucopolysaccharidosis VI

Mucopolysaccharidosis VI (Maroteaux-Lamy syndrome) is a lysosomal storage disease that is characterized by systemic clinical manifestations and significant functional impairment. Diagnosis and management are often challenging because of the considerable variability in symptom presentation and rate of progression. The optimal standard of care should be based on evidence from randomized, controlled trials, meta-analyses, systematic reviews, and expert opinion. In support of this goal, comprehensive management guidelines have been drafted by an international group of experts in the management of patients with mucopolysaccharidosis VI. The guidelines provide a detailed outline of disease manifestations by body system, recommendations for regular assessments, and an overview of current treatment options.

Joint and bone disease in mucopolysaccharidoses VI and VII: identification of new therapeutic targets and biomarkers using animal models

The mucopolysaccharidoses (MPS) are inherited metabolic disorders resulting from the defective catabolism of glycosaminoglycans. In this report, we find that the stimulation of MPS connective tissue cells by the inflammatory cytokines causes enhanced secretion of several matrix-degrading metalloproteinases (MMPs). In addition, expression of tissue inhibitor of metalloproteinase-1 was elevated, consistent with the enhanced MMP activity. These findings were not restricted to one particular MPS disorder or species, and are consistent with previous observations in animal models with chemically induced arthritis. Bromodeoxyuridine incorporation studies also revealed that MPS chondrocytes proliferated up to 5-fold faster than normal chondrocytes, and released elevated levels of transforming growth factor-beta, presumably to counteract the marked chondrocyte apoptosis and matrix degradation associated with MMP expression. Despite this compensatory mechanism, studies of endochondral ossification revealed a reduction in chondro-differentiation in the growth plates. Thus, although MPS chondrocytes grew faster, most of the newly formed cells were immature and could not mineralize into bone. Our studies suggest that altered MMP expression, most likely stimulated by inflammatory cytokines and nitric oxide, is an important feature of the MPS disorders. These data also identify several proinflammatory cytokines, nitric oxide, and MMPs as novel therapeutic targets and/or biomarkers of MPS joint and bone disease. This information should aid in the evaluation of existing therapies for these disorders, such as enzyme replacement therapy and bone marrow transplantation, and may lead to the development of new therapeutic approaches.

Improvement of skeletal lesions in mice with mucopolysaccharidosis type VII by neonatal adenoviral gene transfer

Neonatal gene transfer using adenovirus vectors expressing human beta-glucuronidase (AxCAhGUS) resulted in pathological improvement in multiple visceral organs of mice with mucopolysaccharidosis type VII (MPSVII). However, the therapeutic effect on skeletal deformities and growth retardation, the major clinical symptoms in MPSVII, was not fully investigated by biochemical and histopathological analyses. In this study, we injected AxCAhGUS into a murine model of MPSVII (B6/MPSVII) within 24 h of birth and evaluated the therapeutic effects on skeletal deformities and growth retardation. High levels of beta-glucuronidase (GUSB) activity (approximately threefold higher than normal GUSB activity) were observed in the articular cartilage of the mice 30 days after the treatment. Histopathological study in the knee joints showed elimination of vacuole cells in the articular cartilage and growth plate. Subchondral bone near the articular surface was almost normal in the treated MPSVII mice. Long-term observation (for 140 days after treatment) indicated that characteristic phenotypes such as flattened face, hunched stature, and shortening of bone length in the treated mice were almost normal. These results demonstrate that a single injection of adenovirus vector into neonatal MPSVII mice is sufficient for long-term normalization of skeletal deformities and effective in pathological correction of the articular cartilage and growth plate.

Articular chondrocytes from animals with a dermatan sulfate storage disease undergo a high rate of apoptosis and release nitric oxide and inflammatory cytokines: a possible mechanism underlying degenerative joint disease in the mucopolysaccharidoses

Mucopolysaccharidosis (MPS) Type VI (Maroteaux-Lamy Disease) is the lysosomal storage disease characterized by deficient arylsulfatase B activity and the resultant accumulation of dermatan sulfate-containing glycosaminoglycans (GAGs). A major feature of this and other MPS disorders is abnormal cartilage and bone development leading to short stature, dysostosis multiplex, and degenerative joint disease. To investigate the underlying cause(s) of degenerative joint disease in the MPS disorders, articular cartilage and cultured articular chondrocytes were examined from rats and cats with MPS VI. An age-progressive increase in the number of apoptotic chondrocytes was identified in the MPS animals by terminal transferase nick-end translation (TUNEL) staining and by immunohistochemical staining with anti-poly (ADP-ribose) polymerase (PARP) antibodies. Articular chondrocytes grown from these animals also released more nitric oxide (NO) and tumor necrosis factor alpha (TNF-alpha) into the culture media than did control chondrocytes. Notably, dermatan sulfate, the GAG that accumulates in MPS VI cells, induced NO release from normal chondrocytes, suggesting that GAG accumulation was responsible, in part, for the enhanced cell death in the MPS cells. Coculture of normal chondrocytes with MPS VI cells reduced the amount of NO release, presumably because of the release of arylsulfatase B by the normal cells and reuptake by the mutant cells. As a result of the enhanced chondrocyte death, marked proteoglycan and collagen depletion was observed in the MPS articular cartilage matrix. These results demonstrate that MPS VI articular chondrocytes undergo cell death at a higher rate than normal cells, because of either increased levels of dermatan sulfate and/or the presence of inflammatory cytokines in the MPS joints. In turn, this leads to abnormal cartilage matrix homeostasis in the MPS individuals, which further exacerbates the joint deformities characteristic of these disorders.

Murine MPS I: insights into the pathogenesis of Hurler syndrome

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disease resulting from deficiency of the lysosomal enzyme alpha-L-iduronidase. A murine model which shows complete deficiency in alpha-L-iduronidase activity has been developed and shows phenotypic features similar to severe MPS I in humans. Here we report on the long-term clinical, biochemical, and pathological course of MPS I in mice with emphasis on the skeletal and central nervous system (CNS) manifestations. Affected mice show a progressive clinical course with the development of coarse features, altered growth characteristics and a shortened life span. Progressive lysosomal accumulation is seen in all tissues. Skeletal manifestations represent the earliest clinical finding in MPS I mice with histologic analysis of growth plate and cortical bone revealing evidence that significant early pathology is present. Analysis of the CNS has revealed the novel finding of progressive neuronal loss within the cerebellum. In addition, brain tissue from MPS I mice shows increased levels of GM2 and GM3 gangliosides. This murine model clearly shows phenotypic and pathologic features which mimic those seen in severe human MPS I and should be an invaluable tool for the study of the pathogenesis of generalized storage disorders.

Effect of enzyme replacement therapy on bone formation in a feline model of mucopolysaccharidosis type VI

A range of skeletal abnormalities are evident in mucopolysaccharidosis type VI (MPS VI, Maroteaux-Lamy syndrome) including short stature and dysostosis multiplex, resulting from a deficiency in the lysosomal hydrolase N-acetylgalactosamine-4-sulphatase (4S). In this article, bone pathology was assessed in a feline model of MPS VI to evaluate the efficacy of enzyme replacement therapy (ERT) as a treatment modality for this genetic disorder. Osteopenia is clearly evident in MPS VI animals, with bone mineral volume (BV/TV) falling well below that of normal animals (4.39% vs. 20.11%, respectively). Trabecular bone architecture was also affected in MPS VI with fewer, thinner, and more widely spaced trabeculae apparent. Bone formation rate (BFR/BS) was also lower in MPS VI animals than controls (0.0011 mm3/mm2 per day vs. 0.008 mm3/mm2 per day, respectively). Vertebral and tibial bone length in MPS VI animals progressively fell behind normal values with increasing age, as did cortical bone thickness. Vertebral body shape was also altered. ERT with recombinant human 4S (rh4S) resulted in a vertebral BV/TV of 8.23% in animals treated with an intravenous enzyme dose of 1 mg/kg and a BV/TV of 14.33% in animals treated with a dose of 5 mg/kg. BFR/BS also increased to 0.0034 mm3/mm2 per day in animals treated with enzyme doses of either 1.0 or 5.0 mg/kg rh4S. All other affected histomorphometric parameters also improved with ERT to a level intermediate between MPS VI untreated animals and normals. However, individual animals treated with 0.2 mg/kg rh4S intravenously or 1.0 mg/kg rh4S administered subcutaneously did not exhibit an improvement over untreated MPS VI animals. Vertebral and tibial bone lengths, tibial cortical bone thickness, and vertebral body shape also responded to ERT, with a trend away from the untreated group. Thus, ERT had a positive effect on bone development in MPS VI animals that was dependent upon the dose of enzyme administered and the route of administration.