The Murine Model of Mucopolysaccharidosis IIIB Develops Cardiopathies over Time Leading to Heart Failure.

Mucopolysaccharidosis (MPS) IIIB is a lysosomal disease due to the deficiency of the enzyme α-N-acetylglucosaminidase (NAGLU) required for heparan sulfate (HS) degradation. The disease is characterized by mild somatic features and severe neurological disorders. Very little is known on the cardiac dysfunctions in MPS IIIB. In this study, we used the murine model of MPS IIIB (NAGLU knockout mice, NAGLU(-/-)) in order to investigate the cardiac involvement in the disease. Echocardiographic analysis showed a marked increase in left ventricular (LV) mass, reduced cardiac function and valvular defects in NAGLU(-/-) mice as compared to wild-type (WT) littermates. The NAGLU(-/-) mice exhibited a significant increase in aortic and mitral annulus dimension with a progressive elongation and thickening of anterior mitral valve leaflet. A severe mitral regurgitation with reduction in mitral inflow E-wave-to-A-wave ratio was observed in 32-week-old NAGLU(-/-) mice. Compared to WT mice, NAGLU(-/-) mice exhibited a significantly lower survival with increased mortality observed in particular after 25 weeks of age. Histopathological analysis revealed a significant increase of myocardial fiber vacuolization, accumulation of HS in the myocardial vacuoles, recruitment of inflammatory cells and collagen deposition within the myocardium, and an increase of LV fibrosis in NAGLU(-/-) mice compared to WT mice. Biochemical analysis of heart samples from affected mice showed increased expression levels of cardiac failure hallmarks such as calcium/calmodulin-dependent protein kinase II, connexin43, α-smooth muscle actin, α-actinin, atrial and brain natriuretic peptides, and myosin heavy polypeptide 7. Furthermore, heart samples from NAGLU(-/-) mice showed enhanced expression of the lysosome-associated membrane protein-2 (LAMP2), and the autophagic markers Beclin1 and LC3 isoform II (LC3-II). Overall, our findings demonstrate that NAGLU(-/-) mice develop heart disease, valvular abnormalities and cardiac failure associated with an impaired lysosomal autophagic flux.

Mucopolysaccharidosis type II in a female patient with a reciprocal X;9 translocation and skewed X chromosome inactivation.

Mucopolysaccharidosis type II (MPS II or Hunter syndrome) is a rare X-linked disorder caused by deficient activity of the lysosomal enzyme, iduronate-2-sulfatase (IDS). Phenotypic expression of MPS II in female patients rarely occurs and may be the result of (i) structural abnormalities of the X chromosome, (ii) homozygosity for disease-causing mutations, or (iii) skewed X-chromosome inactivation, in which the normal IDS allele is preferentially inactivated and the abnormal IDS allele is active. We report here on a female patient with clinical MPS II manifestations, deficiency of IDS enzyme activity and a de novo balanced reciprocal X;9 translocation. As our patient has a skewed XCI pattern, but neither genomic IDS mutations nor abnormal IDS transcripts were detected, we speculate about the possible role of the chromosomal rearrangement in reducing the IDS translation efficiency.

Bisphosphonate Treatment in a Patient Affected by MPS IVA with Osteoporotic Phenotype.

Morquio A syndrome (Mucopolysaccharidosis type IVA) (MPS IVA) is a rare inherited metabolic disorder characterized by the defective degradation of keratan sulfate and chondroitin-6-sulfate. Classically, MPS IVA patients present with severe multisystemic involvement and have a short life expectancy. Attenuated forms with clinical features limited to minor skeletal abnormalities and short stature have also been described, sometimes associated to an early-onset osteoporotic phenotype. No treatment with allogenic bone marrow transplantation or gene therapy is currently available for Morquio A syndrome, and enzyme replacement therapy is under evaluation. We report a case of MPS IVA, who manifested tardily attenuated phenotype and significant bone mass reduction, which was treated with a bisphosphonate (BPN), resulting in an improvement of X-ray skeletal aspects and functional bone performance. We suggest that the use of bisphosphonates may be an interesting supportive therapeutic option for Morquio A patients with osteoporotic phenotype, but further studies involving more patients are necessary to confirm our findings.

A novel GLA mutation in a Fabry family with glucose-6-phosphate dehydrogenase deficiency.

Fabry disease is an X-linked lysosomal disease caused by mutations of the alpha-galactosidase A (GLA) gene at chromosome subband Xq22.1. To date, more than 600 genetic mutations have been identified to determine the nature and frequency of the molecular lesions causing the classical and milder variant phenotypes and for precise carrier detection. We report here a Fabry family (mother, son and daughter) where the alpha-galactosidase A defect was associated with a glucose-6-phosphate dehydrogenase (G6PD) deficiency. Mutation analysis revealed for the GLA gene the presence of a new mutation, i.e., a small deletion (c.452delA) on exon 3 and for the G6PD gene the presence of 2 mutations, p.V68M (G6PD Asahi, G6PD A+) and p.N126D (G6PD A+) on exon 3 and exon 4, respectively.

Unfolded protein response is not activated in the mucopolysaccharidoses but protein disulfide isomerase 5 is deregulated.

Mucopolysaccharidoses (MPSs) are lysosomal storage diseases (LSDs) caused by defects in lysosomal enzymes involved in the catabolism of glycosaminoglycans. The pathogenesis of these disorders is still not completely known, although inflammation and oxidative stress appear to be common mechanisms, as in all LSDs. Recently, it was hypothesized that endoplasmic reticulum (ER) stress followed by an unfolded protein response (UPR) could be another common pathogenetic mechanism in LSDs. The aim of the present study was to verify if the UPR was elicited in the mucopolysaccharidoses and if the mechanism was MPS type- and mutation-dependent. To this end, we analyzed the UPR in vitro, in fibroblasts from patients with different types of mucopolysaccharidoses (MPS I, II, IIIA, IIIB, IVA) and in vivo, in the murine MPS IIIB model. In both cases we found no changes in mRNA levels of several UPR-related genes, such as the spliced or unspliced form of Xbp-1, Bip, Chop, Edem1, Edem2, Edem3. Therefore, we report here that the unfolded protein response of the ER is not triggered either in vitro or in vivo; accordingly, cytotoxicity assays indicated that affected fibroblasts are no more sensitive to apoptosis induction than normal cells. However, our results show that in most of the analyzed MPS fibroblasts the expression of a poorly known protein belonging to the family of the protein disulfide isomerases, namely Pdia5, is upregulated; here we discuss if its upregulation could be an early event of ER stress possibly related to the severity of the damage induced in the mutant proteins.

Activation of stress kinases in the brain of mucopolysaccharidosis IIIB mice.

The accumulation of heparan sulfate (HS) in lysosomes is the primary consequence of the enzyme defect (α-N-acetylglucosaminidase) in mucopolysaccharidosis type IIIB. This accumulation triggers a cascade of pathological events that progressively leads to CNS pathology. Here we examined the activation of the three major stress kinases in the neuronal tissue of a murine model of the disease. ERK1/2 was significantly higher in the cortex of 1-2-month-old affected animals compared with wild-type (Wt) littermates. Similarly, ERK1/2 was stimulated in neurons cultured from MPS IIIB mice. SAPK/JNK was also found to be activated in the cortex of 1-2-month-old affected animals compared with Wt subjects, and the same was found for cultured neurons. In contrast, the active form of p38MAPK was lower in the cortex of 1-month-old MPS IIIB mice compared with Wt animals, but no significant difference was found between the two p38MAPK analyzed in normal and affected neurons cultured in vitro. These data indicate the possible involvement of MAPK dysregulation in the early stage of MPS IIIB brain disease.

Gene therapy augments the efficacy of hematopoietic cell transplantation and fully corrects mucopolysaccharidosis type I phenotype in the mouse model.

Type I mucopolysaccharidosis (MPS I) is a lysosomal storage disorder caused by the deficiency of α-L-iduronidase, which results in glycosaminoglycan accumulation in tissues. Clinical manifestations include skeletal dysplasia, joint stiffness, visual and auditory defects, cardiac insufficiency, hepatosplenomegaly, and mental retardation (the last being present exclusively in the severe Hurler variant). The available treatments, enzyme-replacement therapy and hematopoietic stem cell (HSC) transplantation, can ameliorate most disease manifestations, but their outcome on skeletal and brain disease could be further improved. We demonstrate here that HSC gene therapy, based on lentiviral vectors, completely corrects disease manifestations in the mouse model. Of note, the therapeutic benefit provided by gene therapy on critical MPS I manifestations, such as neurologic and skeletal disease, greatly exceeds that exerted by HSC transplantation, the standard of care treatment for Hurler patients. Interestingly, therapeutic efficacy of HSC gene therapy is strictly dependent on the achievement of supranormal enzyme activity in the hematopoietic system of transplanted mice, which allows enzyme delivery to the brain and skeleton for disease correction. Overall, our data provide evidence of an efficacious treatment for MPS I Hurler patients, warranting future development toward clinical testing.

Large deletion involving exon 5 of the arylsulfatase B gene caused apparent homozygosity in a mucopolysaccharidosis type VI patient.

Apparent homozygosity for the mutation p.R315X present on exon 5 of the arylsulfatase B (ARSB) gene in a mucopolysaccharidosis type VI patient was solved in this study by further testing for a second mutation. Patient cDNA analysis revealed that the entire exon 5 of the ARSB gene was lacking; this new mutation was identified as c.899-1142del. As the genomic DNA sequencing excluded the presence of splicing mutations, polymerase chain reaction analysis was performed for polymorphisms listed in the NCBI SNP database for the ARSB gene. This allowed the mutation at the genomic DNA level to be identified as g.99367-102002del; this gross deletion, involving the entire exon 5 of the gene and parts of introns 4 and 5 led to a frameshift starting at amino acid 300 and resulting in a protein with 39% amino acids different from the normal enzyme. We stress that extensive DNA analysis needs to be performed in case of apparent homozygosity to avoid potential errors in genetic counseling.

Serum MIP-1 alpha level: a biomarker for the follow-up of lentiviral therapy in mucopolysaccharidosis IIIB mice.

Mucopolysaccharidosis (MPS) IIIB is an inherited lysosomal storage disorder caused by deficiency of alpha-N-acetylglucosaminidase (NAGLU). The disease is characterized by mild somatic features and severe neurological involvement, with high mortality rates. Although some therapeutic approaches have been applied to the murine model of the disease, no effective therapy is available. Moreover, assessing therapeutic efficacy is challenged by the lack of markers to for progression and severity. In this study, we examined the effect of brain-directed lentiviral (LV) gene therapy on serum levels of macrophage inflammatory protein 1 alpha (MIP-1alpha) and brain-derived neurotrophic factor (BDNF) proteins in the murine model of MPS IIIB to identify novel serum biomarkers. The cytokine MIP-1alpha was elevated in MPS IIIB mouse serum, and following gene therapy, it was reduced to normal levels. For neurotrophin BDNF, the difference in serum levels between MPS IIIB and normal mice was not statistically significant; after LV gene therapy, an increase in protein was found in treated mice, although the values were not statistically significant. Our studies suggest MIP-1alpha as the first serum biomarker that could be used to monitor disease progression and treatment for MPS IIIB disease.

Intracranial gene delivery of LV-NAGLU vector corrects neuropathology in murine MPS IIIB.

Mucopolysacccharidosis (MPS) IIIB is an inherited lysosomal storage disorder caused by the deficiency of alpha-N-acetylglucosaminidase (NAGLU). The disease is characterized by mild somatic features and severe neurological involvement with high mortality. Although several therapeutic approaches have been applied to the murine model of the disease, no effective therapy is available for patients. In this study, we used the lentiviral-NAGLU vector to deliver the functional human NAGLU gene into the brain of young adult MPS IIIB mice. We report the restoration of active enzyme with a sustained expression throughout a large portion of the brain, and a significantly improved behavioral performance of treated animals. Moreover, we analyzed the effect of therapy on the expression profile of some genes related to neurotrophic signaling molecules and inflammatory cytokines previously found altered in MPS IIIB mice. At 1 month from treatment, the level of cerebellin 1 (Cbln1) was decreased while the brain-derived neurotrophic factor (Bdnf) expression was increased, both reaching normal values. At 6 months from treatment a significant reduction in the expression of all the inflammation- and oxidative stress-related genes was observed, as well as the maintenance of the correction of the Bdnf gene expression. These results indicate that NAGLU delivery from intracerebral sources has the capacity to alleviate most disease manifestations in MPS IIIB mice; furthermore, Bdnf might be a response-to-therapy biomarker for MPS IIIB.

Mucopolysaccharidosis IIIB: oxidative damage and cytotoxic cell involvement in the neuronal pathogenesis.

Sanfilippo B syndrome (Mucopolysaccharidosis IIIB, MPS IIIB) is a lysosomal storage disease due to mutations in the gene encoding alpha-N-acetylglucosaminidase and is characterized by a severe neurological disorder. Although several studies have been reported for the murine model of the disease, the molecular basis and the sequence of events leading to neurodegeneration remain to be clarified. We previously suggested the possible involvement of the reactive oxygen species in the disease pathogenesis. In the present paper we extended the analysis of oxidative stress by evaluating the production of superoxide ions throughout the CNS and by evaluating the effect of the stress on the cellular macromolecules. These approaches applied to one-month-old, three-month-old and six-month-old mice revealed that oxidative stress is present in the affected cerebrum and cerebellum tissues from one month from birth, and that it results primarily in protein oxidation, both in the cerebrum and cerebellum, with lipid peroxidation, and especially DNA oxidation, appearing milder and restricted essentially to the cerebellum. We also identified additional genes possibly associated with the neuropathology of MPS IIIB disease. Real time RT-PCR analysis revealed an altered expression of the Sod1, Ret, Bmp4, Tgfb, Gzmb and Prf1 genes. Since Gzmb and Prf1 are proteins secreted by NK/cytotoxic T-cells, these data suggest the involvement of cytotoxic cells in the neuronal pathogenesis. Extending our previous study, findings reported in the present paper show that oxidative stress and all the analyzed stress-related pathological changes occur very early in the disease course, most likely before one month of age.

Molecular markers for the follow-up of enzyme-replacement therapy in mucopolysaccharidosis type VI disease.

MPS VI (mucopolysaccharidosis type VI) is a lysosomal storage disease in which deficient activity of the enzyme N-acetylgalactosamine 4-sulfatase [ASB (arylsulfatase B)] impairs the stepwise degradation of the GAG (glycosaminoglycan) dermatan sulfate. Clinical studies of ERT (enzyme replacement therapy) by using rhASB (recombinant human ASB) have been reported with promising results. The release of GAG into the urine is currently used as a biomarker of disease, reflecting in some cases disease severity and in all cases therapeutic responsiveness. Using RNA studies in four Italian patients undergoing ERT, we observed that TNFalpha (tumour necrosis factor alpha) might be a biomarker for MPS VI responsive to therapy. In addition to its role as a potential biomarker, TNFalpha expression could provide insights into the possible pathophysiological mechanisms underlying the mucopolysaccharidoses.

Mutational analysis of the HGSNAT gene in Italian patients with mucopolysaccharidosis IIIC (Sanfilippo C syndrome). Mutation in brief #959. Online.

Mucopolysaccharidosis (MPS) describes any inherited lysosomal storage disorder resulting from an inability to catabolize glycosaminoglycans. MPS III (or Sanfilippo syndrome) is an autosomal recessive disease caused by a failure to degrade heparan sulphate. There are four subtypes of MPS III, each categorized by a deficiency in a specific enzyme involved in the heparan sulphate degradation pathway. The genes mutated in three of these (MPS IIIA, MPS IIIB, and MPS IIID) have been cloned for some time. However, only very recently has the gene for MPS IIIC (heparin acetyl CoA: alpha-glucosaminide N-acetyltransferase, or HGSNAT) been identified. Its product (previously termed transmembrane protein 76, or TMEM76) has little sequence similarity to other proteins of known function, although it is well conserved among all species. In this study, a group of MPS IIIC patients, who are mainly of Italian origin, have been clinically characterized. Furthermore, mutational analysis of the HGSNAT gene in these patients resulted in the identification of nine alleles, of which eight are novel. Three splice-site mutations, three frameshift deletions resulting in premature stop codons, one nonsense mutation, and two missense mutations were identified. The latter are of particular interest as they are located in regions which are predicted to be of functional significance. This research will aid in determining the molecular basis of HGSNAT protein function, and the mechanisms underlying MPS IIIC.

Cytokines, neurotrophins, and oxidative stress in brain disease from mucopolysaccharidosis IIIB.

Mucopolysaccharidosis IIIB (MPS IIIB; Sanfilippo syndrome type B) is characterized by profound neurological deterioration. Because a murine model of MPS IIIB disease is available, we focused on analysis of gene expression in the brain and cerebellum of 7-month-old MPS IIIB mice by pathway-specific filter microarrays designed to probe apoptotic-related, neurotrophic signalling molecules and inflammatory cytokines and receptors. Moreover, we extended the analysis with real-time PCR performed at 1, 3, 7 months after birth. Bdnf was down-regulated in the brain but up-regulated in the cerebellum at 7 months of age, both at RNA and at protein levels. Cbln1 presented a threefold increase in the oldest brains while remaining unaltered in the cerebellum. Ccl3, Casp11, gp91(phox), p67(phox), and p47(phox) showed an increased expression in both brain and cerebellum at each examined time point. Ccl3, in particular, exhibited in both organs and at all times tested approximately a tenfold increase in its expression. Insofar as p47(phox), p67(phox), and gp91(phox) are all components of the phagocyte NADPH oxidase, our results suggest the possible involvement of the reactive oxygen species in the genesis of neurodegeneration in MPS IIIB disease.

Differences in methylation patterns in the methylation boundary region of IDS gene in Hunter syndrome patients: implications for CpG hot spot mutations.

Hunter syndrome, an X-linked disorder, results from deficiency of iduronate-2-sulfatase (IDS). Around 40% of independent point mutations at IDS were found at CpG sites as transitional events. The 15 CpG sites in the coding sequences of exons 1 and 2, which are normally hypomethylated, account for very few of transitional mutations. By contrast, the CpG sites in the coding sequences of exon 3, though also normally hypomethylated, account for much higher fraction of transitional mutations. To better understand relationship between methylation status and CpG transitional mutations in this region, the methylation patterns of 11 Hunter patients with transitional mutations at CpG sites were investigated using bisulfite genomic sequencing. The patient cohort mutation spectrum is composed of one mutation in exon 1 (one patient) and three different mutations in exon 3 (10 patients). We confirmed that in normal males, cytosines at the CpG sites from the promoter region to a portion of intron 3 were hypomethylated. However, specific CpG sites in this area were more highly methylated in patients. The patients with p.R8X (exon 1), p.P86L (exon 3), and p.R88H (exon 3) mutations had a hypermethylated condition in exon 2 to intron 3 but retained hypomethylation in exon 1. The same trend was found in four patients with p.A85T (exon 3), although the degree of hypermethylation was less. These findings suggest methylation patterns in the beginning of IDS genomic region are polymorphic in humans and that hypermethylation in this region in some individuals predisposes them to CpG mutations resulting in Hunter syndrome.

Sulphatase activities are regulated by the interaction of sulphatase-modifying factor 1 with SUMF2.

Sulphatases undergo a unique post-translational modification that converts a highly conserved cysteine located within their active site into formylglycine. This modification is necessary for the catalytic activities of the sulphatases, and it is generated by the protein product of sulphatase-modifying factor 1 (SUMF1), the gene mutated in multiple sulphatase deficiency (MSD). A paralogous gene, SUMF2, was discovered through its sequence similarity to SUMF1. We present evidence that SUMF2 colocalizes with SUMF1 within the endoplasmic reticulum and that the two proteins form heterodimers. SUMF1 and SUMF2 also form homodimers. In addition, SUMF2 is able to associate with the sulphatases with and without SUMF1. We have previously shown that co-transfection of SUMF1 with the sulphatase complementary DNAs greatly enhances the activities of the overexpressed sulphatases. Here, we show that SUMF2 inhibits the enhancing effects of SUMF1 on sulphatases, suggesting that the SUMF1-SUMF2 interaction represents a further level of control of these sulphatase activities.

Gene therapy for a mucopolysaccharidosis type I murine model with lentiviral-IDUA vector.

Mucopolysaccharidosis type I is a lysosomal disease due to mutations in the IDUA gene, resulting in deficiency of alpha-L-iduronidase and accumulation of glycosaminoglycans (GAGs). Bone marrow transplantation and enzyme replacement are two therapies considered only moderately successful for affected patients, making the development of novel treatments necessary. We have previously shown the efficacy of lentivirus-mediated gene transfer to correct patient fibroblasts in vitro. Here we tested lentiviral-IDUA vector gene therapy in vivo on a murine MPS I model. Eight- to 10 week-old mice were injected with increasing lentiviral doses via the tail vein and analyzed 1 month after treatment. A single injection of lentiviral-IDUA vector resulted in transgene expression in several murine tissues, with the highest level reached in liver and spleen. Expression of 1% normal activity was sufficient in treated animals to normalize the GAG level in urine, liver, and spleen and was able to reduce the GAG level in kidney, heart, and lung. Polymerase chain reaction assays showed integration of the viral genome only in liver and spleen of treated animals, suggesting that the correction of the pathology in other tissues was due to secretion into the plasma by liver and spleen and uptake of corrective enzyme by distant tissues. Long-term (6 months) analysis showed the presence of enzyme-specific antibodies and the loss of enzyme activity and vector sequence in the target tissue, suggesting that the transgene-specific immune response interfered with long-term therapeutic correction and led to clearance of transduced cells. In conclusion, our results show the promising potential and the limitations of lentiviral-IDUA vector-mediated gene therapy in an in vivo model.

Treatment of the mouse model of mucopolysaccharidosis type IIIB with lentiviral-NAGLU vector.

The Sanfilippo syndrome type B (mucopolysaccharidosis IIIB) is an autosomal recessive disorder due to mutations in the gene encoding NAGLU (alpha-N-acetylglucosaminidase), one of the enzymes required for the degradation of the GAG (glycosaminoglycan) heparan sulphate. No therapy exists for affected patients. We have shown previously the efficacy of lentiviral-NAGLU-mediated gene transfer in correcting in vitro the defect on fibroblasts of patients. In the present study, we tested the therapy in vivo on a knockout mouse model using intravenous injections. Mice (8-10 weeks old) were injected with one of the lentiviral doses through the tail vein and analysed 1 month after treatment. A single injection of lentiviral-NAGLU vector resulted in transgene expression in liver, spleen, lung and heart of treated mice, with the highest level reached in liver and spleen. Expression of 1% normal NAGLU activity in liver resulted in a 77% decrease in the GAG content; more remarkably, an expression of 0.16% normal activity in lung was capable of decreasing the GAG level by 29%. Long-term (6 months) follow up of the gene therapy revealed that the viral genome integration persisted in the target tissues, although the real-time PCR analysis showed a decrease in the vector DNA content with time. Interestingly, the decrease in GAG levels was maintained in liver, spleen, lung and heart of treated mice. These results show the promising potential and the limitations of lentiviral-NAGLU vector to deliver the human NAGLU gene in vivo.