Juvenile mucopolysaccharidosis plus disease caused by a missense mutation in VPS33A

A rare and fatal disease resembling mucopolysaccharidosis in infants, is caused by impaired intracellular endocytic trafficking due to deficiency of core components of the intracellular membrane-tethering protein complexes, HOPS, and CORVET. Whole exome sequencing identified a novel VPS33A mutation in a patient suffering from a variant form of mucopolysaccharidosis. Electron and confocal microscopy, immunoblotting, and glycosphingolipid trafficking experiments were undertaken to investigate the effects of the mutant VPS33A in patient-derived skin fibroblasts. We describe an attenuated juvenile form of VPS33A-related syndrome-mucopolysaccharidosis plus in a man who is homozygous for a hitherto unknown missense mutation (NM_022916.4: c.599 G>C; NP_075067.2:p. Arg200Pro) in a conserved region of the VPS33A gene. Urinary glycosaminoglycan (GAG) analysis revealed increased heparan, dermatan sulphates, and hyaluronic acid. We showed decreased abundance of VPS33A in patient derived fibroblasts and provided evidence that the p.Arg200Pro mutation leads to destablization of the protein and proteasomal degradation. As in the infantile form of mucopolysaccharidosis plus, the endocytic compartment in the fibroblasts also expanded-a phenomenon accompanied by increased endolysosomal acidification and impaired intracellular glycosphingolipid trafficking. Experimental treatment of the patient's cultured fibroblasts with the proteasome inhibitor, bortezomib, or exposure to an inhibitor of glucosylceramide synthesis, eliglustat, improved glycosphingolipid trafficking. To our knowledge this is the first report of an attenuated juvenile form of VPS33A insufficiency characterized by appreciable residual endosomal-lysosomal trafficking and a milder mucopolysaccharidosis plus than the disease in infants. Our findings expand the proof of concept of redeploying clinically approved drugs for therapeutic exploitation in patients with juvenile as well as infantile forms of mucopolysaccharidosis plus disease.

The lysosomal disease caused by mutant VPS33A

A rare lysosomal disease resembling a mucopolysaccharidosis with unusual systemic features, including renal disease and platelet dysfunction, caused by the defect in a conserved region of the VPS33A gene on human chromosome 12q24.31, occurs in Yakuts-a nomadic Turkic ethnic group of Southern Siberia. VPS33A is a core component of the class C core vacuole/endosome tethering (CORVET) and the homotypic fusion and protein sorting (HOPS) complexes, which have essential functions in the endocytic pathway. Here we show that cultured fibroblasts from patients with this disorder have morphological changes: vacuolation with disordered endosomal/lysosomal compartments and-common to sphingolipid diseases-abnormal endocytic trafficking of lactosylceramide. Urine glycosaminoglycan studies revealed a pathological excess of sialylated conjugates as well as dermatan and heparan sulphate. Lipidomic screening showed elevated β-D-galactosylsphingosine with unimpaired activity of cognate lysosomal hydrolases. The 3D crystal structure of human VPS33A predicts that replacement of arginine 498 by tryptophan will de-stabilize VPS33A folding. We observed that the missense mutation reduced the abundance of full-length VPS33A and other components of the HOPS and CORVET complexes. Treatment of HeLa cells stably expressing the mutant VPS33A with a proteasome inhibitor rescued the mutant protein from degradation. We propose that the disease is due to diminished intracellular abundance of intact VPS33A. Exposure of patient-derived fibroblasts to the clinically approved proteasome inhibitor, bortezomib, or inhibition of glucosylceramide synthesis with eliglustat, partially corrected the impaired lactosylceramide trafficking defect and immediately suggest therapeutic avenues to explore in this fatal orphan disease.

Glucosylated cholesterol in mammalian cells and tissues: formation and degradation by multiple cellular β-glucosidases

The membrane lipid glucosylceramide (GlcCer) is continuously formed and degraded. Cells express two GlcCer-degrading β-glucosidases, glucocerebrosidase (GBA) and GBA2, located in and outside the lysosome, respectively. Here we demonstrate that through transglucosylation both GBA and GBA2 are able to catalyze in vitro the transfer of glucosyl-moieties from GlcCer to cholesterol, and vice versa. Furthermore, the natural occurrence of 1-O-cholesteryl-β-D-glucopyranoside (GlcChol) in mouse tissues and human plasma is demonstrated using LC-MS/MS and ¹³C₆-labeled GlcChol as internal standard. In cells, the inhibition of GBA increases GlcChol, whereas inhibition of GBA2 decreases glucosylated sterol. Similarly, in GBA2-deficient mice, GlcChol is reduced. Depletion of GlcCer by inhibition of GlcCer synthase decreases GlcChol in cells and likewise in plasma of inhibitor-treated Gaucher disease patients. In tissues of mice with Niemann-Pick type C disease, a condition characterized by intralysosomal accumulation of cholesterol, marked elevations in GlcChol occur as well. When lysosomal accumulation of cholesterol is induced in cultured cells, GlcChol is formed via lysosomal GBA. This illustrates that reversible transglucosylation reactions are highly dependent on local availability of suitable acceptors. In conclusion, mammalian tissues contain GlcChol formed by transglucosylation through β-glucosidases using GlcCer as donor. Our findings reveal a novel metabolic function for GlcCer.

Inhibition of UDP-glucosylceramide synthase in mice prevents Gaucher disease-associated B-cell malignancy

Clonal B-cell proliferation is a frequent manifestation of Gaucher disease - a sphingolipidosis associated with a high risk of multiple myeloma and non-Hodgkin lymphoma. Gaucher disease is caused by genetic deficiency of acid β-glucosidase, the natural substrates of which (β-d-glucosylceramide and β-d-glucosylsphingosine) accumulate, principally in macrophages. Mice with inducible deficiency of β-glucosidase [Gba(tm1Karl/tm1Karl)Tg(MX1-cre)1Cgn/0] serve as an authentic model of human Gaucher disease; we have recently reported clonal B-cell proliferation accompanied by monoclonal serum paraproteins and cognate tumours in these animals. To explore the relationship between B-cell malignancy and the biochemical defect, we treated Gaucher mice with eliglustat tartrate (GENZ 112638), a potent and selective inhibitor of the first committed step in glycosphingolipid biosynthesis. Twenty-two Gaucher mice received 300 mg/kg of GENZ 112638 daily for 3-10 months from 6 weeks of age. Plasma concentrations of β-d-glucosylceramide and the unacylated glycosphingolipid, β-d-glucosylsphingosine, declined. After administration of GENZ 112638 to Gaucher mice for 3-10 months, serum paraproteins were not detected and there was a striking reduction in the malignant lymphoproliferation: neither lymphomas nor plasmacytomas were found in animals that had received the investigational agent. In contrast, 14 out of 60 Gaucher mice without GENZ 112638 treatment developed these tumours; monoclonal paraproteins were detected in plasma from 18 of the 44 age-matched mice with Gaucher disease that had not received GENZ 112638. Long-term inhibition of glycosphingolipid biosynthesis suppresses the development of spontaneous B-cell lymphoma and myeloma in Gaucher mice.

B cell lymphoma and myeloma in murine Gaucher's disease

Multiple myeloma and B cell lymphoma are leading causes of death in Gaucher's disease but the nature of the stimulus driving the often noted clonal expansion of immunoglobulin-secreting B cells and cognate lymphoid malignancy is unknown. We investigated the long-term development of B cell malignancies in an authentic model of non-neuronopathic Gaucher's disease in mice: selective deficiency of β-glucocerebrosidase in haematopoietic cells [Gba(tm1Karl/tm1Karl)Tg(Mx1-cre)1Cgn/0, with excision of exons 9-11 of the murine GBA1 gene, is induced by poly[I:C]. Mice with Gaucher's disease showed visceral storage of β-glucosylceramide and greatly elevated plasma β-glucosylsphingosine [median 57.9 (range 19.8-159) nm; n = 39] compared with control mice from the same strain [median 0.56 (range 0.04-1.38) nm; n = 29] (p < 0.0001). Sporadic fatal B cell lymphomas developed in 11 of 21 GD mice (6-24 months) but only two of eight control animals developed tumours by age 24 months. Unexpectedly, most mice with overt lymphoma had absent or few Gaucher cells but local inflammatory macrophages were present. Eleven of 39 of Gaucher mice developed monoclonal gammopathy, but in the control group only one animal of 25 had clonal immunoglobulin abnormalities. Seven of 10 of the B cell lymphomas were found to secrete a monoclonal paraprotein and the lymphomas stained intensely for pan-B cell markers; reactive T lymphocytes were also present in tumour tissue. In the Gaucher mouse strain, it was notable that, as in patients with this disease, CD138(+) plasma cells frequently surrounded splenic macrophages engorged with glycosphingolipid. Our strain of mice, with inducible deficiency of β-glucocerebrosidase in haematopoietic cells and a high frequency of sporadic lethal B cell malignancies, faithfully recapitulates human Gaucher's disease: it serves as a tractable model to investigate the putative role of bioactive sphingolipids in the control of B cell proliferation and the pathogenesis of myelomatosis-the most prevalent human cancer associated with this disorder.

Biomarkers for osteonecrosis in Gaucher disease

INTRODUCTION

The search for surrogate biomarkers of osteonecrosis, a disabling complication of Gaucher disease, has intensified in the last decade. Biomarkers that predict osteonecrosis and monitor the effectiveness of therapies would improve clinical practice and enrich the molecular exploration of this disorder.

AREAS COVERED

Here we discuss advances in biomarker research with special reference to those biomarkers associated with Gaucher disease and investigated in the context of enzyme therapy. Much progress has been made in the diversification of treatment for the condition and several biomarker molecules, which may ultimately improve risk assessment for osteonecrosis, have been identified.

EXPERT OPINION

The discovery of prospective biomarkers of osteonecrosis such as CCL18/PARC, CXCL8/IL-8, CCL5/RANTES, CCL3/MIP-1α, CCL4/MIP-1β, particularly during recurrent episodes occurring despite enzyme treatment, has the potential radically to change practices in the management of Gaucher disease and should improve therapeutic monitoring and prognostic evaluation. Ultimately, exploration of this field will provide the basis for a refined mechanistic understanding of pathogenesis.

[Use of pH-sensitive immobilized monoclonal antibodies for optimization of immunoenzyme sandwich technique of detection of HBsAg of hepatitis B virus]

AIM

To develop highly sensitive sandwich technique for identification of surface hepatitis B virus antigen (HBsAg) in serum and analyse of possible improvement of solid phase for immunoenzyme sandwich technique of HBsAg identification through variation of pH-dependent sorption of monoclonal antibodies on the surface of immune plates.

MATERIALS AND METHODS

Calibration curves for identification of HBsAg in sandwich techniques using 36 possible binary combinations of monoclonal antibodies of our panel (including high affinity antibodies to HBsAg produced by 6 hybridomas) were compared. Immobilization of antibodies on solid phase (by passive sorption) was performed at different pH values (2.8, 7.5, and 9.5).

RESULTS

Analysis of panel of antibodies to HBsAg produced by 6 hybridomas revealed pH-dependent monoclonal antibodies (18C8), which immobilization at low pH values together with detecting antibodies F4F3 allowed to greatly improve sensitivity of the sandwich technique. Minimal credibly detectable concentration of HBsAg in sera of persons infected with hepatitis B virus was 0.013 - 0.017 ng/ml. Validation of sandwich technique was performed on certified panel of serum samples with various concentrations of HBsAg (different serotypes).

CONCLUSION

Highly sensitive sandwich technique for detection of HBsAg was developed. It was shown that analysis of panel of monoclonal antibodies on pH-dependence could be used as simple methodical approach for optimization of immunoenzyme sandwich techniques for detection of different antigens.

[Platelet serotonergic parameters and clinical symptoms of psychosis in patients with episodic progressive schizophrenia]

A sample included 59 patients, 38 males and 21 females, mean age (M+/-SD) 33,4+/-10,2 years, age-at-onset 26+/-9,5 years, illness duration 7,8+/-6,1 years, with episodic progressive schizophrenia (ICD-10: schizophrenia, paranoid type, F20.0) with continuous course at the stage of exacerbation. Clinical symptoms were assessed using the PANSS. Platelet 5-HT content, 3H-serotonin uptake (Vmax), 3H-imipramine receptor density (Bmax), high- and low molecular weight human serotonin platelet transporter protein immunoreactivity (HMW-SERT and LMW-SERT values) were measured. The most frequent psychotic symptoms were delusions, conceptual disorganization and hallucinations, with the majority of patients experiencing from one to three symptoms. A significant increase of platelet 5-HT content and 3H-imipramine receptor density (Bmax) was found in male patients. In the male group, delusions, conceptual disorganization and hallucinations as well as PANSS psychotic cluster scores were correlated positively with 5-HT content and negatively with HMW-SERT and LMW-SERT values. Possible reasons of the differences in correlations of platelet 5-HT serotonin and serotonin transporter values with psychotic symptoms are discussed. The results are additional evidence for the involvement of serotonergic dysfunction in the pathogenesis of schizophrenic psychoses. They confirm the usefulness of testing of platelet 5-HT content and SERT immunoreactivity as biological markers of schizophrenic psychoses, in particular for male patents.

Western blot analysis of human and rat serotonin transporter in platelets and brain using site-specific antibodies: evidence that transporter undergoes endoproteolytic cleavage

BACKGROUND

Serotonin transporter (SERT) is important target molecule for many antidepressive drugs and substances of abuse and is implicated in psychiatric disorders. We performed immunoblotting analysis of human and rat SERT in platelets and brain using the panel of eight site-specific SERT monoclonal and polyclonal antibodies (mAbs and pAbs).

METHODS

SDS-PAGE/Western blotting was conducted using peroxidase-labeled DEAE and affinity purified SERT antibodies under conditions preventing SERT post-extraction degradation.

RESULTS

Immunoreactive polypeptides of 14, 22, 32, 35, 37, 56, 68, and approximately 150-200 kDa were revealed in human platelet extracts using N-terminal and C-terminal SERT antibodies. In rat brain, C-terminal mAbs detected 68, 56, and 37 kDa proteins, in postmortem human brain predominated 35-37 kDa proteins. The immunoreactivity was abolished after antibody preadsorption with antigens. N-terminal pAbs recognized the 68 kDa protein, affinity purified on C-terminal mAbs, confirming its identity as full-size human SERT (the predicted size approximately 70.5 kDa).

CONCLUSIONS

The explanation of the results of immunoblotting most likely is a site-specific SERT endoproteolytic cleavage and a marked difference in glycosylation rather than nonspecific protein degradation, cross-reactivity with other epitopes or SERT alternative splicing.

Analysis of Serotonin Transporter in Human Platelets by Immunoblotting Using Site-Specific Antibodies

We have produced a panel of site-specific antibodies recognizing different regions of the human serotonin transporter (SERT). This panel included: 1) monoclonal antibodies 23C5 (mAbs 23C5) to the C-terminal region (amino acid residues 597-630); 2) polyclonal antibodies (pAbs) to the N-terminal region (amino acid residues 69-83); 3) pAbs to the region (amino acid residues 86-100) in the beginning of the first transmembrane domain (TMD). The antibodies were produced using recombinant proteins and synthetic peptides (containing certain sequences of SERT) as antigens. These antibodies were purified by affinity chromatography, conjugated to horseradish peroxidase (HRP), and used for immunoblotting analysis of SERT in extracts of human platelets. Sodium dodecyl sulfate extracts were prepared under conditions preventing non-specific proteolytic degradation of the proteins. In platelet extracts, all antibodies were able to detect the 67 kD protein, apparently corresponding to full-length SERT molecule (its theoretical mass is about 70 kD). These antibodies also detected several polypeptides of smaller size (56, 37, 35, 32, 22, and 14 kD), apparently corresponding to N-terminal, C-terminal, and non-terminal SERT fragments. Specificity of immunostaining was confirmed by preincubation of HRP-labeled anti-SERT antibodies with excess of corresponding antigen, which resulted in disappearance of protein band staining. It is suggested that SERT undergoes a programmed proteolytic cleavage (processing) resulting in formation of several SERT-derived polypeptides of smaller size. It is possible that one of the cleaved SERT species is required for serotonin transport activity. Possible sites for specific proteolysis may be located in the region near TMD1 and in the intracellular loop between TMD4 and TMD5.

[Serum levels of lipid peroxidation products as markers of dyslipidemia disorders]

The content of triglycerides (TG), total cholesterol (TC) and the level of 5 categories of lipid-peroxidation (LP) products were investigated in blood serum of 27 patients with atherogenic dislipidemic disorders. Multiple regression analysis was made for the dependence of the concentrations of TG and TC on a level of the LP circulating products. It was found that the parameters of the LP products' content in blood serum can be used to calculate the TG and TC concentrations, i.e. they are a system of indirect markers of a pronouncement degree of dislipidemic disorders.

[Antigenic polymorphism in circulating leukocytes as an indirect indicator of severity of dyslipidemic disorders]

Examinations of 19 patients with dislipedemias (types IIA, IIB, III and IV) led to establishing the interrelations between the indices of the antigenic composition of circulating blood leukocytes, the total leukocyte count, the circulating neutrophil count and a severity of dislipidemia disorders (according to the parameters of the atherogenic coefficient and the beta-LP content). It was found that the assessment of polymorphism of circulating leukocytes could be used as an indirect evaluation of a severity of dislipidemia disorders.

[Body mass index and blood lipid peroxides as interrelated markers of neutrophils function and immunoglobulins level]

Complex anthropometric and laboratory investigation of 30 healthy men produced evidence that body mass index and the lipoperoxidation product contents in blood sera may be regarded as associated indirect markers of neutrophiles' functional status and immunoglobulinemia.

Analysis of bispecific monoclonal antibody binding to immobilized antigens using an optical biosensor

The interaction between two different monoclonal antibodies (Mabs) and their corresponding bispecific antibodies (Babs) with immobilized antigens was investigated using an optical biosensor (IAsys). The analyzed panel of affinity-purified antibodies included two parental Mabs (one of which was specific to human IgG (hIgG), and another one to horseradish peroxidase (HRP)), as well as Babs derived thereof (anti-hIgG/HRP). Babs resulting from the fusion of parental hybridomas bear two antigen-binding sites toward two different antigens and thus may interact with immobilized antigen through only one antigen-binding site (monovalently). Using an IAsys biosensor this study shows that the bivalent binding of Mabs predominates over the monovalent binding with immobilized HRP, whereas anti-hIgG parental Mabs were bound monovalently to the immobilized hIgG. The observed equilibrium association constant (K(ass)) values obtained in our last work [1] by solid-phase radioimmunoassay are consistent with those constants obtained by IAsys. The K(ass) of anti-HRP Mabs was about 50 times higher than that of anti-HRP shoulder of Babs. The dissociation rate constant (k(diss)) for anti-HRP shoulder of Babs was 21 times higher than k(diss) for anti-HRP Mabs. The comparison of the kinetic parameters for bivalent anti-HRP Mabs and Babs derived from anti-Mb/HRP and anti-hIgG/HRP, allowed to calculate that 95% of bound anti-HRP Mabs are bivalently linked with immobilized HRP, whereas only 5% of bound anti-HRP Mabs are monovalently linked. In general, the data obtained indicate that Babs bearing an enzyme-binding site may not be efficiently used instead of traditional antibody-enzyme conjugates in the case of binding of bivalent Mabs.

[Levels and molecular heterogeneity of serotonin transporter protein in platelets of patients with different mental diseases: a comparative analysis with the use of monoclonal and polyclonal antibodies]

Polyclonal (PAb) and monoclonal (MAb) antibodies to CT2-epitope of the C-terminal fragment of serotonin transporter (SERT) protein were used to study the levels and molecular heterogeneity of platelet SERT in healthy donors and patients with affective (AD) and somatoform (SD) disorders, schizoaffective disorder (SAD) and schizophrenia. SERT was found to exist as high molecular wight (HMW) and low molecular weight (LMW) forms separated after electrophoresis. The levels of HMW and LMW forms of SERT were significantly, decreased in mentally ill patients as compared to healthy individuals. Unlike PAb, horse radish peroxidase (HRP)-conjugated MAbs were more sensitive and specific to SERT and could detect the LMW form of SERT as a duplet protein form with MW about 40 and 43 kDa. The MAb to CT2 C-terminal fragment of SERT conjugated with HRP is considered to be a new valuable tool for further investigation of SERT expression, properties, and posttranslation modification in the controls and in patients with different psychopathology.

Analysis of the binding of bispecific monoclonal antibodies with immobilized antigens (human IgG and horseradish peroxidase) using a resonant mirror biosensor

The interaction between two monoclonal antibodies (mAbs) and their corresponding bispecific antibody (bAb) with immobilized antigens has been examined using a resonant mirror biosensor (IAsys). BAbs were produced by cell fusion. The analysed panel of affinity-purified antibodies included two parental mAbs, one specific to human IgG (hIgG), and another specific to horseradish peroxidase (HRP), and a bAb derived thereof (anti-hIgG/HRP). The real-time analysis showed the drastic differences in the avidity of bivalent anti-HRP mAbs and anti-HRP shoulder of bAbs. Thus, the observed equilibrium association constant (K(ass)) of anti-HRP mAbs was about 50 times higher that of anti-HRP shoulder of bAbs. The ratio of association rate constants (k(ass)) of mAbs and bAbs was about two, due to the statistical factor of two binding sites per bivalent antibody molecule. However, the dissociation rate constant (k(diss)) of anti-HRP shoulder of bAbs was 21 times higher k(diss) of anti-HRP mAbs. The comparison with the theoretical model shows that these observations are consistent only with a situation in which bivalent binding of mAbs with immobilized HRP predominates over monovalent binding. On the contrary, the second parental mAb (anti-hIgG) did not show the increase in avidity due to bivalent binding, compared to the anti-hIgG shoulder of bAbs, suggesting that this mAb was bound monovalently to immobilized hIgG. The K(ass) values determined by solid-phase radioimmunoassay (RIA) yielded figures almost overlapping with those obtained by IAsys. The results of the comparison of bAbs and mAbs are discussed from the viewpoint of the use of bAbs in heterogeneous systems. On the other hand, these data demonstrate that real-time analysis of antibody binding parameters in IAsys biosensor is valuable for the selection of mAbs and bAbs with desired features, for different fields of application.

The comparison of the ability of monoclonal antibodies directed to different proteins (human IgG, human myoglobin and HRP) and bispecific antibodies derived thereof to bind antigens immobilized on a surface of a solid phase

BACKGROUND

Bindings of mouse monoclonal antibodies (mAbs) and affinity purified bispecific antibodies (bAbs), derived thereof, to antigens adsorbed on immunoplates have been compared, using ELISA and RIA methods.

METHODS

The analysed panel of antibodies included mAbs specific to human myoglobin (Mb), human IgG (hIgG) and horseradish peroxidase (HRP) and biologically produced bAbs with double specificity to Mb and HRP, and to hIgG and HRP.

RESULTS

The degree of difference between different mAbs and corresponding bAbs varied markedly from antibody to antibody, depending on whether the parental mAbs could bind immobilized antigens bivalently. The observed equilibrium binding constant (K(obs)) for anti-HRP mAbs was 21-38 times higher that of anti-HRP site of bAbs (anti-hIgG/HRP or anti-Mb/HRP, respectively), due to bivalent binding of mAbs. Anti-Mb mAbs also bound bivalently with immobilized Mb. On the contrary, anti-hIgG mAbs bound monovalently with immobilized hIgG in the same conditions. The avidity of anti-Mb/HRP bAbs increased, if both antigens were simultaneously adsorbed on a solid phase.

CONCLUSIONS

The obtained data indicate that the use of bAbs in heterogeneous immunoassays instead of traditional mAb-enzyme conjugates hardly can provide the significant gain in assay performance if parental mAbs bind bivalently.

[Cell cultivation on polyimide film to obtain preparations for light optical and electron microscopic research]

Upon cultivation of the brain tissue and skin-muscle tissues of human embryos, a polyimide film was used as a lining. The optimal conditions of the preliminary processing of the lining (sterilization, washing) are described. An easy separation of the polyimide film from the media (in the process of tissue treatment for electron microscope studies) facilitates the use of the material for light and electron microscopy without damaging the culture.