Mechanism of glycosaminoglycan-mediated bone and joint disease: implications for the mucopolysaccharidoses and other connective tissue diseases

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.

Enzyme replacement therapy for mucopolysaccharidosis VI: Growth and pubertal development in patients treated with recombinant human N-acetylgalactosamine 4-sulfatase

BACKGROUND AND METHODS: Growth failure is characteristic of untreated mucopolysaccharidosis type VI (MPS VI: Maroteaux-Lamy syndrome). Growth was studied in fifty-six MPS VI patients (5 to 29 years old) prior to and for up to 240 weeks of weekly infusions of recombinant human arylsulfatase B (rhASB) at 1 mg/kg during Phase 1/2, Phase 2, Phase 3 or Phase 3 Extension clinical trials. Height, weight, and Tanner stage data were collected. Pooled data were analyzed to determine mean height increase by treatment week, growth impacts of pubertal status, baseline urinary GAG, and age at treatment initiation. Growth rate for approximately 2 years prior to and following treatment initiation was analyzed using longitudinal modeling. RESULTS: Mean height increased by 2.9 cm after 48 weeks and 4.3 cm after 96 weeks on enzyme replacement therapy (ERT). Growth on ERT was not correlated with baseline urinary GAG. Patients under 16 years of age showed greatest increases in height on treatment. Model results based on pooled data showed significant improvement in growth rate during 96 weeks of ERT when compared to the equivalent pretreatment time period. Delayed pubertal onset or progression was noted in 10 patients entering the clinical trials; all of whom showed progression of at least one Tanner stage during 2 years on ERT, and 6 of whom (60%) completed puberty. CONCLUSION: Analysis of mean height by treatment week and longitudinal modeling demonstrate significant increase in height and growth rate in MPS VI patients receiving long-term ERT. This impact was greatest in patients aged below 16 years. Height increase may result from bone growth and/or reduction in joint contractures. Bone growth and resolution of delayed puberty may be related to improvements in general health, bone cell health, nutrition, endocrine gland function and reduced inflammation.

Bone density assessment in patients with mucopolysaccharidosis: A preliminary report from patients with MPS II and VI

Enzyme replacement therapy has been successful in alleviating morbidity and improving endurance in Mucopolysaccharidosis (MPS) type I, II, and VI, however little attention has been paid to the effects on bone mineralization. Brief case reports in MPS type III and IV suggest that bone mineral density (BMD) is diminished, but did not account for patient size. In this report, BMD was evaluated by quantitative computed tomography and by dual-energy x-ray absorptiometry (DXA) in separate studies involving 10 patients with MPS type VI (7 Female; 7.0 to 21.0 y) and 4 male patients with MPS II (8.1 to 35.5 y). Vitamin D intake met the current RDA (200 IU) for most, though 25-OH vitamin D was insufficient (< 30 ng/mL) in 87.5% of patients tested. Ht Z-score was low -5.8 +/- 3.6, with height deficits greatest in MPS VI. Spine and whole body BMD Z-scores by DXA were considered normal for chronological age in all MPS II, and after correction for Ht Z-score, in all but one subject with MPS VI. These results suggest that vitamin D insufficiency is quite common in MPS. BMD by DXA is within normal range for most, particularly after correction for short stature. A review of bone health assessment is provided as well as a discussion of these results.

Involvement of the Toll-like receptor 4 pathway and use of TNF-alpha antagonists for treatment of the mucopolysaccharidoses

Enzyme replacement therapy is currently available for three of the mucopolysaccharidoses (MPSs) but has limited effects on the skeletal lesions. We investigated the involvement of the Toll-like receptor 4 (TLR4) signaling pathway in the pathogenesis of MPS bone and joint disease, and the use of the anti-TNF-alpha drug, Remicade (Centocor, Inc.), for treatment. TLR4 KO (TLR4(lps-/-)) mice were interbred with MPS VII mice to produce double-KO (DKO) animals. The DKO mice had longer and thinner faces and longer femora as revealed by micro-computed tomography analysis compared with MPS VII mice. Histological analyses also revealed more organized and thinner growth plates. The serum levels of TNF-alpha were normalized in the DKO animals, and the levels of phosphorylated STAT1 and STAT3 in articular chondrocytes were corrected. These findings led us to evaluate the effects of Remicade in MPS VI rats. When initiated at 1 month of age, i.v. treatment prevented the elevation of TNF-alpha, receptor activator of NF-kappaB, and other inflammatory molecules not only in the blood but in articular chondrocytes and fibroblast-like synoviocytes (FLSs). Treatment of 6-month-old animals also reduced the levels of these molecules to normal. The number of apoptotic articular chondrocytes in MPS VI rats was similarly reduced, with less infiltration of synovial tissue into the underlying bone. These studies revealed the important role of TLR4 signaling in MPS bone and joint disease and suggest that targeting TNF-alpha may have positive therapeutic effects.

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.

Musculoskeletal manifestations of lysosomal storage disorders

Lysosomal storage disorders (LSDs), a heterogeneous group of inborn metabolic disorders, are far more common than most doctors presume. Although patients with a severe LSD subtype are often readily diagnosed, the more attenuated subtypes are frequently missed or diagnosis is significantly delayed. The presenting manifestations often involve the bones and/or joints and therefore these patients are frequently under specialist care by (paediatric) rheumatologists, receiving inadequate treatment. Since effective disease-specific treatments, including enzyme replacement therapy and stem cell transplantation, have become available for certain LSDs and timely initiation of these treatments is necessary to prevent the development of severe, disabling and irreversible manifestations, early diagnosis has become essential. The challenge is to raise awareness for better recognition of the presenting signs and symptoms of LSDs by all doctors who may encounter these patients, including rheumatologists.

Joint contractures in the absence of inflammation may indicate mucopolysaccharidosis

BACKGROUND

Undiagnosed patients with the attenuated form of mucopolysaccharidosis (MPS) type I often have joint symptoms in childhood that prompt referral to a rheumatologist. A survey conducted by Genzyme Corporation of 60 European and Canadian rheumatologists and pediatric rheumatologists demonstrated that < 20% recognized signs and symptoms of MPS I or could identify appropriate diagnosis tests. These results prompted formation of an international working group of rheumatologists, pediatric rheumatologists, and experts on MPS I to formulate a rheumatology-based diagnostic algorithm. The resulting algorithm applies to all MPS disorders with musculoskeletal manifestations.Bone and joint manifestations are prominent among most patients with MPS disorders. These life-threatening lysosomal storage diseases are caused by deficient activity of specific enzymes involved in the degradation of glycosaminoglycans. Patients with attenuated MPS disease often experience diagnostic delays. Enzyme replacement therapy is now commercially available for MPS I (laronidase), MPS II (idursulfase), and MPS VI (galsulfase).

PRESENTATION OF THE HYPOTHESIS

Evolving joint pain and joint contractures in the absence of inflammation should always raise the suspicion of an MPS disorder. All such patients should undergo urinary glycosaminoglycan (uGAG) analysis (not spot tests for screening) in a reputable laboratory. Elevated uGAG levels and/or an abnormal uGAG pattern confirms an MPS disorder and specific enzyme testing will determine the MPS type. If uGAG analysis is unavailable and the patient exhibits any other common sign or symptom of an MPS disorder, such as corneal clouding, history of hernia surgery, frequent respiratory and/or ear, nose and throat infections; carpal tunnel syndrome, or heart murmur, proceed directly to enzymatic testing. Refer patients with confirmed MPS to a geneticist or metabolic specialist for further evaluation and treatment.

TESTING OF THE HYPOTHESIS

We propose that rheumatologists, pediatric rheumatologists, and orthopedists consider our diagnostic algorithm when evaluating patients with joint pain and joint contractures.

IMPLICATIONS OF THE HYPOTHESIS

Children and young adults can suffer for years and sometimes even decades with unrecognized MPS. Rheumatologists may facilitate early diagnosis of MPS based on the presenting signs and symptoms, followed by appropriate testing. Early diagnosis helps ensure prompt and appropriate treatment for these progressive and debilitating diseases.

Phenotype and genotype in mucolipidoses II and III alpha/beta: a study of 61 probands

BACKGROUND

Mucolipidoses II and III alpha/beta (ML II and ML III) are lysosomal disorders in which the essential mannose 6-phosphate recognition marker is not synthesised on to lysosomal hydrolases and other glycoproteins. The disorders are caused by mutations in GNPTAB, which encodes two of three subunits of the heterohexameric enzyme, N-acetylglucosamine-1-phosphotransferase.

OBJECTIVES

Clinical, biochemical and molecular findings in 61 probands (63 patients) are presented to provide a broad perspective of these mucolipidoses.

METHODS

GNPTAB was sequenced in all probands and/or parents. The activity of several lysosomal enzymes was measured in plasma, and GlcNAc-1-phosphotransferase was assayed in leucocytes. Thirty-six patients were studied in detail, allowing extensive clinical data to be abstracted.

RESULTS

ML II correlates with near-total absence of phosphotransferase activity resulting from homozygosity or compound heterozygosity for frameshift or nonsense mutations. Craniofacial and orthopaedic manifestations are evident at birth, skeletal findings become more obvious within the first year, and growth is severely impaired. Speech, ambulation and cognitive function are impaired. ML III retains a low level of phosphotransferase activity because of at least one missense or splice site mutation. The phenotype is milder, with minimal delays in milestones, the appearance of facial coarsening by early school age, and slowing of growth after the age of 4 years.

CONCLUSIONS

Fifty-one pathogenic changes in GNPTAB are presented, including 42 novel mutations. Ample clinical information improves criteria for delineation of ML II and ML III. Phenotype-genotype correlations suggested in more general terms in earlier reports on smaller groups of patients are specified and extended.

Mechanism of shortened bones in mucopolysaccharidosis VII

Mucopolysaccharidosis VII (MPS VII) is a lysosomal storage disease in which deficiency in beta-glucuronidase results in glycosaminoglycan (GAG) accumulation in and around cells, causing shortened long bones through mechanisms that remain largely unclear. We demonstrate here that MPS VII mice accumulate massive amounts of the GAG chondroitin-4-sulfate (C4S) in their growth plates, the cartilaginous region near the ends of long bones responsible for growth. MPS VII mice also have only 60% of the normal number of chondrocytes in the growth plate and 55% of normal chondrocyte proliferation at 3weeks of age. We hypothesized that this reduction in proliferation was due to C4S-mediated overactivation of fibroblast growth factor receptor 3 (FGFR3). However, MPS VII mice that were FGFR3-deficient still had shortened bones, suggesting that FGFR3 is not required for the bone defect. Further study revealed that MPS VII growth plates had reduced tyrosine phosphorylation of STAT3, a pro-proliferative transcription factor. This was accompanied by a decrease in expression of leukemia inhibitory factor (LIF) and other interleukin 6 family cytokines, and a reduction in phosphorylated tyrosine kinase 2 (TYK2), Janus kinase 1 (JAK1), and JAK2, known activators of STAT3 phosphorylation. Intriguingly, loss of function mutations in LIF and its receptor leads to shortened bones. This suggests that accumulation of C4S in the growth plate leads to reduced expression of LIF and reduced STAT3 tyrosine phosphorylation, which results in reduced chondrocyte proliferation and ultimately shortened bones.

Abnormal autophagy, ubiquitination, inflammation and apoptosis are dependent upon lysosomal storage and are useful biomarkers of mucopolysaccharidosis VI

Background

Lysosomal storage diseases are characterized by intracellular accumulation of metabolites within lysosomes. Recent evidence suggests that lysosomal storage impairs autophagy resulting in accumulation of polyubiquitinated proteins and dysfunctional mitochondria, ultimately leading to apoptosis. We studied the relationship between lysosome storage and impairment of different intracellular pathways and organelle function in mucopolysaccharidosis VI, which is characterized by accumulation of dermatan sulfate and signs of visceral and skeletal but not cerebral involvement.

Results

We show lysosomal storage, impaired autophagy, accumulation of polyubiquitinated proteins, and mitochondrial dysfunction in fibroblasts from mucopolysaccharidosis VI patients. We observe similar anomalies, along with inflammation and cell death, in association with dermatan sulfate storage in the visceral organs of mucopolysaccharidosis VI rats, but not in their central nervous system where dermatan sulfate storage is absent. Importantly, we show that prevention of dermatan sulfate storage in the mucopolysaccharidosis VI rat visceral organs by gene transfer results in correction of abnormal autophagy, inflammation, and apoptosis, suggesting that dermatan sulfate accumulation impairs lysosomal ability to receive and degrade molecules and organelles from the autophagic pathway, thus leading to cell toxicity.

Conclusion

These results indicate that the non-lysosomal degradation pathways we found activated in mucopolysaccharidosis VI can be both targets of new experimental therapies and biomarkers for follow-up of existing treatments.

Gene therapy for lysosomal storage diseases (LSDs) in large animal models

Lysosomal storage diseases (LSDs) are inherited metabolic disorders caused by deficient activity of a single lysosomal enzyme or other defects resulting in deficient catabolism of large substrates in lysosomes. There are more than 40 forms of inherited LSDs known to occur in humans, with an aggregate incidence estimated at 1 in 7,000 live births. Clinical signs result from the inability of lysosomes to degrade large substrates; because most lysosomal enzymes are ubiquitously expressed, a deficiency in a single enzyme can affect multiple organ systems. Thus LSDs are associated with high morbidity and mortality and represent a significant burden on patients, their families, the health care system, and society. Because lysosomal enzymes are trafficked by a mannose 6-phosphate receptor mechanism, normal enzyme provided to deficient cells can be localized to the lysosome to reduce and prevent storage. However, many LSDs remain untreatable, and gene therapy holds the promise for effective therapy. Other therapies for some LSDs do exist, or are under evaluation, including heterologous bone marrow or cord blood transplantation (BMT), enzyme replacement therapy (ERT), and substrate reduction therapy (SRT), but these treatments are associated with significant concerns, including high morbidity and mortality (BMT), limited positive outcomes (BMT), incomplete response to therapy (BMT, ERT, and SRT), life-long therapy (ERT, SRT), and cost (BMT, ERT, SRT). Gene therapy represents a potential alternative, albeit with its own attendant concerns, including levels and persistence of expression and insertional mutagenesis resulting in neoplasia. Naturally occurring animal homologues of LSDs have been described in all common domestic animals (and in some that are less common) and these animal models play a critical role in evaluating the efficacy and safety of therapy.

Systemic correction of storage disease in MPS I NOD/SCID mice using the sleeping beauty transposon system

The Sleeping Beauty (SB) transposon system is a nonviral vector that directs transgene integration into vertebrate genomes. We hydrodynamically delivered SB transposon plasmids encoding human alpha-L-iduronidase (hIDUA) at two DNA doses, with and without an SB transposase gene, to NOD.129(B6)-Prkdc(scid) IDUA(tm1Clk)/J mice. In transposon-treated, nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice with mucopolysaccharidosis type I (MPS I), plasma IDUA persisted for 18 weeks at levels up to several hundred-fold wild-type (WT) activity, depending on DNA dose and gender. IDUA activity was present in all examined somatic organs, as well as in the brain, and correlated with both glycosaminoglycan (GAG) reduction in these organs and level of expression in the liver, the target of transposon delivery. IDUA activity was higher in the treated males than in females. In females, omission of transposase source resulted in significantly lower IDUA levels and incomplete GAG reduction in some organs, confirming the positive effect of transposition on long-term IDUA expression and correction of the disease. The SB transposon system proved efficacious in correcting several clinical manifestations of MPS I in mice, including thickening of the zygomatic arch, hepatomegaly, and accumulation of foamy macrophages in bone marrow and synovium, implying potential effectiveness of this approach in treatment of human MPS I.

Musculoskeletal complications encountered in the lysosomal storage disorders

The lysosomal storage disorders are a heterogeneous group of inherited metabolic diseases resulting from defects in the degradation or transport of several distinct by-products of cellular turnover. The various subtypes are characterized by multi-systemic involvement; the wide range in patient ages at symptom onset is only partly explained by the underlying mutation(s). Neurodegenerative features and musculoskeletal complications are often seen in the most severe variants, and are features of the disease that have the most significant impact on patients' physical and functional well-being. Until recently, the care of affected individuals relied mainly on palliative or supportive measures. The introduction of therapies directed at correcting the primary defect (i.e., deficient enzyme activity) in several of these disorders has led to modification of the phenotype and natural history or disease course; however, clinical problems arising from brain and bone involvement remain major sources of morbidity. Factors that might influence therapeutic outcome include pre-existing pathology at the time of treatment initiation, drug access to tissues sites of pathology, and - in the case of enzyme therapy - antibody formation. Increasing understanding of the pathogenesis or relevant mechanism(s) of diseases is providing insights into additional therapeutic targets, enabling the potential for optimized patient outcomes with the use of adjunctive or supplemental agents. Physical and occupational therapy remain critical components of a comprehensive approach to patient care.

Lysosomal disorders: from storage to cellular damage

Lysosomal storage diseases represent a group of about 50 genetic disorders caused by deficiencies of lysosomal and non-lysosomal proteins. Patients accumulate compounds which are normally degraded in the lysosome. In many diseases this accumulation affects various organs leading to severe symptoms and premature death. The revelation of the mechanism by which stored compounds affect cellular function is the basis for understanding pathophysiology underlying lysosomal storage diseases. In the past years it has become clear that storage compounds interfere with various processes on the cellular level. The spectrum covers e.g. receptor activation by non-physiologic ligands, modulation of receptor response and intracellular effectors of signal transduction cascades, impairment of autophagy, and others. Importantly, many of these processes are associated with accumulation of storage material in non-lysosomal compartments. Here we summarize current knowledge on the effects that storage material can elicit on the cellular level.

Radiographic evaluation of bones and joints in mucopolysaccharidosis I and VII dogs after neonatal gene therapy

Mucopolysaccharidosis I (MPS I) and MPS VII are due to deficient activity of the glycosaminoglycan-degrading lysosomal enzymes alpha-L-iduronidase and beta-glucuronidase, respectively, and result in abnormal bones and joints. Here, the severity of skeletal disease in MPS I and MPS VII dogs and the effects of neonatal gene therapy were evaluated. For untreated MPS VII dogs, the lengths of the second cervical vertebrae (C2) and the femur were only 56% and 84% of normal, respectively, and bone dysplasia and articular erosions, and joint subluxation were severe. Previously, we reported that neonatal intravenous injection of a retroviral vector (RV) with the appropriate gene resulted in expression in liver and blood cells, and high serum enzyme activity. In this study, we demonstrate that C2 and femurs of RV-treated MPS VII dogs were longer at 82% and 101% of normal, respectively, and there were partial improvements of qualitative abnormalities. For untreated MPS I dogs, the lengths of C2 and femurs (91% and 96% of normal, respectively) were not significantly different from normal dogs. Qualitative changes in MPS I bones and joints were generally modest and were partially improved with RV treatment, although cervical spine disease was severe and was difficult to correct with gene therapy in both models. The greater severity of skeletal disease in MPS VII than in MPS I dogs may reflect accumulation of chondroitin sulfate in cartilage in MPS VII, or could relate to the specific mutations. Neonatal RV-mediated gene therapy ameliorates, but does not prevent, skeletal disease in MPS I and MPS VII dogs.