EGFR activation triggers cellular hypertrophy and lysosomal disease in NAGLU-depleted cardiomyoblasts, mimicking the hallmarks of mucopolysaccharidosis IIIB.
ABSTRACT: Mucopolysaccharidosis (MPS) IIIB is an inherited lysosomal storage disease caused by the deficiency of the enzyme ?-N-acetylglucosaminidase (NAGLU) required for heparan sulfate (HS) degradation. The defective lysosomal clearance of undigested HS results in dysfunction of multiple tissues and organs. We recently demonstrated that the murine model of MPS IIIB develops cardiac disease, valvular abnormalities, and ultimately heart failure. To address the molecular mechanisms governing cardiac dysfunctions in MPS IIIB, we generated a model of the disease by silencing NAGLU gene expression in H9C2 rat cardiomyoblasts. NAGLU-depleted H9C2 exhibited accumulation of abnormal lysosomes and a hypertrophic phenotype. Furthermore, we found the specific activation of the epidermal growth factor receptor (EGFR), and increased phosphorylation levels of extracellular signal-regulated kinases (ERKs) in NAGLU-depleted H9C2. The inhibition of either EGFR or ERKs, using the selective inhibitors AG1478 and PD98059, resulted in the reduction of both lysosomal aberration and hypertrophy in NAGLU-depleted H9C2. We also found increased phosphorylation of c-Src and a reduction of the hypertrophic response in NAGLU-depleted H9C2 transfected with a dominant-negative c-Src. However, c-Src phosphorylation remained unaffected by AG1478 treatment, posing c-Src upstream EGFR activation. Finally, heparin-binding EGF-like growth factor (HB-EGF) protein was found overexpressed in our MPS IIIB cellular model, and its silencing reduced the hypertrophic response. These results indicate that both c-Src and HB-EGF contribute to the hypertrophic phenotype of NAGLU-depleted cardiomyoblasts by synergistically activating EGFR and subsequent signaling, thus suggesting that EGFR pathway inhibition could represent an effective therapeutic approach for MPS IIIB cardiac disease.
Project description:Sanfilippo syndrome type B, or mucopolysaccharidosis IIIB (MPS IIIB), is a rare autosomal recessive lysosomal storage disease caused by a deficiency of ?-N-acetylglucosaminidase (NAGLU). Deficiency in NAGLU disrupts the lysosomal turnover of heparan sulfate (HS), which results in the abnormal accumulation of partially degraded HS in cells and tissues. BMN 250 (NAGLU-insulin-like growth factor 2 [IGF2]) is a recombinant fusion protein developed as an investigational enzyme replacement therapy for MPS IIIB. The IGF2 peptide on BMN 250 promotes enhanced targeting of the enzyme to lysosomes through its interaction with the mannose 6-phosphate receptor. The focus of these studies was to further characterize the ability of NAGLU-IGF2 to clear accumulated HS compared to unmodified NAGLU in primary cellular models of MPS IIIB. Here, we establish distinct primary cell models of MPS IIIB with HS accumulation. These cellular models revealed distinct NAGLU uptake characteristics that depend on the duration of exposure. We found that with sustained exposure, NAGLU uptake and HS clearance occurred independent of known lysosomal targeting signals. In contrast, under conditions of limited exposure duration, NAGLU-IGF2 was taken up more rapidly than the unmodified NAGLU into MPS IIIB primary fibroblasts, astrocytes, and cortical neurons, where it efficiently degraded accumulated HS. These studies illustrate the importance of using physiologically relevant conditions in the evaluation of enzyme replacement therapies in cellular models.
Project description:Mucopolysaccharidosis type IIIB (MPS IIIB) is a rare genetic disorder caused by loss-of-function mutations in the <i>NAGLU</i> gene. Pigs are an ideal large animal model for human diseases; however, a porcine model of MPS IIIB has not been reported. We have previously generated a heterozygous <i>NAGLU</i>-deficient (<i>NAGLU</i> <sup>+/-</sup>) Large White boar via a transgenic approach. Here we characterized phenotypes of the F<sub>1</sub> offspring of this founder to establish a pig model for MPS IIIB. qRT-PCR revealed that the <i>NAGLU</i> expression level was significantly decreased in a variety of tissues in <i>NAGLU</i> <sup>+/-</sup> pigs. ELISA assays showed obvious deficiency of NAGLU and higher (<i>P</i><0.05) glycosaminoglycan levels in multiple tissues from <i>NAGLU</i> <sup>+/-</sup> pigs. <i>NAGLU</i> <sup>+/-</sup> pigs grew at a significantly (<i>P</i><0.05) slower rate than control animals (<i>NAGLU</i> <sup>+/+</sup>). Death, mostly sudden death, occurred at all ages in <i>NAGLU</i> <sup>+/-</sup> pigs, most of which died within two years. Necropsy findings included pleural adhesions, lung shrinkage and abnormalities in the pericardium and mild hepatomegaly in <i>NAGLU</i> <sup>+/-</sup> pigs. Notable pathological changes were observed in the sections of brain, liver, spleen and kidney from <i>NAGLU</i> <sup>+/-</sup> pigs. Brain atrophy, ventriculomegaly, cerebellar atrophy and abnormalities in the intracerebral capsule, parietal lobes and the thalamus were also evident in <i>NAGLU</i> <sup>+/-</sup> pigs. Together, <i>NAGLU</i> <sup>+/-</sup> pigs show typical symptoms of human MPS IIIB patients and thus represent a novel large animal model for the disease.This article has an associated First Person interview with the first author of the paper.
Project description:BACKGROUND:Mucopolysaccharidosis type IIIB (MPS IIIB) is a rare genetic disorder in which the deficiency of the lysosomal enzyme N-acetyl-α-glucosaminidase (NAGLU) results in the accumulation of heparan sulfate (HS), leading to progressive neurocognitive deterioration. In MPS IIIB a wide spectrum of disease severity is seen. Due to a large allelic heterogeneity, establishing genotype-phenotype correlations is difficult. However, reliable prediction of the natural course of the disease is needed, in particular for the assessment of the efficacy of potential therapies. METHODS:To identify markers that correlate with disease severity, all Dutch patients diagnosed with MPS IIIB were characterised as either rapid (RP; classical, severe phenotype) or slow progressors (SP; non-classical, less severe phenotype), based on clinical data. NAGLU activity and HS levels were measured in patients' fibroblasts after culturing at different temperatures. RESULTS:A small, though significant difference in NAGLU activity was measured between RP and SP patients after culturing at 37 °C (p < 0.01). Culturing at 30 °C resulted in more pronounced and significantly higher NAGLU activity levels in SP patients (p < 0.001) with a NAGLU activity of 0.58 nmol.mg-1.hr-1 calculated to be the optimal cut-off value to distinguish between the groups (sensitivity and specificity 100 %). A lower capacity of patients' fibroblasts to increase NAGLU activity at 30 °C could significantly predict for the loss of several disease specific functions. CONCLUSION:NAGLU activity in fibroblasts cultured at 30 °C can be used to discriminate between RP and SP MPS IIIB patients and the capacity of cells to increase NAGLU activity at lower temperatures correlates with disease symptoms.
Project description:Mucopolysaccharidosis III (MPS III) has four forms (A-D) that result from buildup of an improperly degraded glycosaminoglycan in lysosomes. MPS IIIB is attributable to the decreased activity of a lysosomal alpha-N-acetylglucosaminidase (NAGLU). Here, we describe the structure, catalytic mechanism, and inhibition of CpGH89 from Clostridium perfringens, a close bacterial homolog of NAGLU. The structure enables the generation of a homology model of NAGLU, an enzyme that has resisted structural studies despite having been studied for >20 years. This model reveals which mutations giving rise to MPS IIIB map to the active site and which map to regions distant from the active site. The identification of potent inhibitors of CpGH89 and the structures of these inhibitors in complex with the enzyme suggest small-molecule candidates for use as chemical chaperones. These studies therefore illuminate the genetic basis of MPS IIIB, provide a clear biochemical rationale for the necessary sequential action of heparan-degrading enzymes, and open the door to the design and optimization of chemical chaperones for treating MPS IIIB.
Project description:Mucopolysaccharidosis IIIB (MPS IIIB) is an inherited metabolic disease due to deficiency of ?-N-Acetylglucosaminidase (NAGLU) enzyme with subsequent storage of undegraded heparan sulfate (HS). The main clinical manifestations of the disease are profound intellectual disability and neurodegeneration. A label-free quantitative proteomic approach was applied to compare the proteome profile of brains from MPS IIIB and control mice to identify altered neuropathological pathways of MPS IIIB. Proteins were identified through a bottom up analysis and 130 were significantly under-represented and 74 over-represented in MPS IIIB mouse brains compared to wild type (WT). Multiple bioinformatic analyses allowed to identify three major clusters of the differentially abundant proteins: proteins involved in cytoskeletal regulation, synaptic vesicle trafficking, and energy metabolism. The proteome profile of NAGLU-/- mouse brain could pave the way for further studies aimed at identifying novel therapeutic targets for the MPS IIIB. Data are available via ProteomeXchange with the identifier PXD017363.
Project description:Mucopolysaccharidosis type IIIB (MPS IIIB; or Sanfilippo syndrome type B) is a lysosomal disease, due to glycosaminoglycan storage caused by mutations on the alpha-N-acetylglucosaminidase (NAGLU) gene. The disease is characterized by neurological dysfunction but relatively mild somatic manifestations. No effective treatment is available for affected patients. In the present study, we evaluated the role of a lentiviral vector as the transducing agent of NAGLU cDNA in MPS IIIB fibroblasts. The vector expressed high transduction efficiency and high levels of enzymic activity, 20-fold above normal levels, persisting for at least 2 months. PCR experiments confirmed the integration of the viral vector into the target genome. The NAGLU activity restored by virus infection was sufficient to normalize glycosaminoglycan accumulation, which is directly responsible for the disease phenotype. Metabolic labelling experiments on transduced fibroblasts exhibited, in the medium and in cellular lysates, polypeptide forms of 84 and 80 kDa respectively related to the precursor and mature forms of the enzyme. The enzyme secreted by transduced MPS IIIB fibroblasts was endocytosed in deficient cells by the mannose 6-phosphate system. Thus we show that lentiviral vectors may provide a therapeutic approach for the treatment of MPS IIIB disease.
Project description:The greatest challenge in developing therapies for mucopolysaccharidosis (MPS) IIIB is to achieve efficient central nervous system (CNS) delivery across the blood-brain barrier (BBB). In this study, we used the novel ability of adeno-associated virus serotype 9 (AAV9) to cross the BBB from the vasculature to achieve long-term global CNS, and widespread somatic restoration of ?-N-acetylglucosaminidase (NAGLU) activity. A single intravenous (IV) injection of rAAV9-CMV-hNAGLU, without extraneous treatment to disrupt the BBB, restored NAGLU activity to normal or above normal levels in adult MPS IIIB mice, leading to the correction of lysosomal storage pathology in the CNS and periphery, and correction of astrocytosis and neurodegeneration. The IV delivered rAAV9 vector also transduced abundant neurons in the myenteric and submucosal plexus, suggesting peripheral nervous system (PNS) targeting. While CNS entry did not depend on osmotic disruption of the BBB, it was significantly enhanced by pretreatment with an IV infusion of mannitol. Most important, we demonstrate that a single systemic rAAV9-NAGLU gene delivery provides long-term (>18 months) neurological benefits in MPS IIIB mice, resulting in significant improvement in behavioral performance, and extension of survival. These data suggest promising clinical potential using the trans-BBB neurotropic rAAV9 vector for treating MPS IIIB and other neurogenetic diseases.
Project description:Mucopolysaccharidosis (MPS) IIIB is a lysosomal disease due to the deficiency of the enzyme ?-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, ?-smooth muscle actin, ?-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.
Project description:Mucopolysaccharidosis type III (MPS III) is a rare genetic disorder caused by lysosomal storage of heparan sulfate. MPS IIIB results from a deficiency in the enzyme alpha-N-acetyl-D-glucosaminidase (NAGLU). Affected patients begin showing behavioral changes, progressive profound mental retardation, and severe disability from the age of 2 to 6 years. We report a patient with MPS IIIB with a long-term follow-up duration. He showed normal development until 3 years. Subsequently, he presented behavioral changes, sleep disturbance, and progressive motor dysfunction. He had been hospitalized owing to recurrent pneumonia and epilepsy with severe cognitive dysfunction. The patient had compound heterozygous c.1444C>T (p.R482W) and c.1675G>T (p.D559Y) variants of NAGLU. Considering that individuals with MPS IIIB have less prominent facial features and skeletal changes, evaluation of long-term clinical course is important for diagnosis. Although no effective therapies for MPS IIIB have been developed yet, early and accurate diagnosis can provide important information for family planning in families at risk of the disorder.
Project description:Sanfilippo syndrome type B or mucopolysaccharidosis type IIIB (MPS IIIB) is one of a group of lysosomal storage disorders that are characterised by the inability to breakdown heparan sulphate. In MPS IIIB, there is a deficiency in the enzyme alpha-N-acetylglucosaminidase (NAGLU) and early clinical symptoms include aggressive behaviour and hyperactivity followed by progressive mental retardation. The disease is autosomal recessive and the gene for NAGLU, which is situated on chromosome 17q21, is approximately 8.5 kb in length and contains six exons. Primers were designed to amplify the entire coding region and intron/exon boundaries of the NAGLU gene in 10 fragments. The PCR products were analysed for sequence changes using SSCP analysis and fluorescent DNA sequencing technology. Sixteen different putative mutations were detected in DNA from 14 MPS IIIB patients, 12 of which have not been found previously. The mutations include four deletions (219-237del19, 334-358del25, 1335delC, 2099delA), two insertions (1447-1448insT, 1932-1933insGCTAC), two nonsense mutations (R297X, R626X), and eight missense mutations (F48C, Y140C, R234C, W268R, P521L, R565W, L591P, E705K). In this study, the Y140C, R297X, and R626X mutations were all found in more than one patient and together accounted for 25% of mutant alleles.