Juvenile-onset glycogen storage disease type II with novel mutations in acid alpha-glucosidase gene.

The authors describe two novel mutations of the acid alpha-glucosidase gene, P361L and R437C, which define the juvenile-onset glycogen storage disease type II (GSDII) in a 16-year-old Chinese patient. The asymptomatic 13-year-old brother of the proband is also a compound heterozygote of the two mutations. These results confirm that intrafamilial phenotypic variation of juvenile-onset GSDII is ethnically diverse and suggest the contribution of other genes to the phenotypic variability of GSDII.

Correction of glycogen storage disease type II by enzyme replacement with a recombinant human acid maltase produced by over-expression in a CHO-DHFR(neg) cell line.

Inherited genetic deficiency of lysosomal acid alpha glucosidase or acid maltase (GAA) results in the autosomal recessive glycogen storage disease type II (GSD II). To investigate whether we could generate a functional recombinant human GAA (rhGAA) for enzyme replacement therapy, we subcloned the cDNAs for human GAA and mouse dihydrofolate reductase (DHFR) into DHFR(neg) Chinese hamster ovary cells and established a stable cotransformant that expressed rhGAA. We cultured the recombinant cells in media with progressively increasing concentrations of methotrexate and found that human GAA enzyme activity increased to over 2,000 IU per gram protein. Importantly, the human GAA enzyme activity correlated to equivalent amounts of human GAA protein by rocketimmunoelectrophoresis. We confirmed that the human GAA enzyme activity corresponded to an amplification in human GAA mRNA by Northern analysis and human GAA cDNA copy number by Southern analysis. Exposing the rhGAA to human GSDII fibroblast cells or patient's lymphocytes or monocytes resulted in uptake of the rhGAA and reversal of the enzymatic defect. Mannose-6-phosphate in the media blocked uptake. GAA -/- mice were treated with the rhGAA at 1 mg/kg, which resulted in heterozygous levels of GAA in tissues, most notably skeletal muscle, heart and diaphragm after two infusions. More importantly, after multiple infusions, hind, and fore-limb muscle weakness was reversed. This rhGAA would be ideal for enzyme replacement therapy in GSD II.

Identification of two subtypes of infantile acid maltase deficiency.

Infantile patients with acid maltase deficiency have severe hypertrophic cardiomyopathy, left ventricular outflow obstruction, and generalized muscle weakness and die before 1 year of age. We identified 12 infants with acid maltase deficiency who had a similar clinical presentation but less severe cardiomyopathy and absence of left ventricular outflow obstruction, and 9 of 12 had longer survival with assisted ventilation and supplemental intubation.

The gene for lysosomal protein CD63 is normal in patients with Hermansky-Pudlak syndrome.

Hermansky-Pudlak syndrome (HPS) is one of the few genetic disorders associated with severe pulmonary fibrosis. Fifty percent of affected patients die as a result of respiratory insufficiency. Fibrosis is thought to be caused by the accumulation of ceroid, an insoluble fluorescent lipoprotein, both extracellularly and in the lysosomes of alveolar macrophages. In addition to pulmonary fibrosis, HPS is characterized by oculocutaneous albinism and a reduction in the number of platelet dense bodies. CD63 is a protein that was described originally in platelet lysosomes. It localizes to the membranes of melanosomes and platelet dense bodies. CD63 is decreased dramatically in the lysosomes and dense bodies of patients with HPS. We theorized that CD63, a membrane protein common to lysosomes, melanosomes, and platelet dense bodies, may play a role in HPS. We sought to characterize the gene coding for this protein in HPS lymphoid cell lines. The coding region for CD63 was sequenced in control and HPS cell lines. Messenger RNA from HPS and normal cell lines was examined by Northern analysis. Genomic DNA from the same cell lines was examined by Southern analysis and polymerase chain reaction (PCR). CD63 protein in lymphoid cell lines and peripheral blood monocytes was compared by Western analysis. We found no mutations in the coding region of CD63 in an HPS cell line. We also found no diminution in the quantity of CD63 RNA by Northern analysis and no gross defects in the structural gene by PCR and Southern analysis, suggesting that the CD63 structural gene, promoter, and untranslated regions were normal. Western analysis showed that the 43-kDa protein was present in control and HPS lymphoid cell lines and peripheral blood monocytes in equivalent amounts. Although CD63 is an attractive candidate for the primary defect of HPS, the disease is probably not caused by a mutation in the CD63 gene.

Nicotine enhances expression of the neutrophil elastase gene and protein in a human myeloblast/promyelocyte cell line.

The pathogenesis of emphysema is considered to be an imbalance of protease and antiprotease activity in the lower respiratory tract leading to uninhibited degradation of lung interstitium by elastolytic enzymes. An increased amount of the serine protease neutrophil elastase (NE) is though to play a major role in this degradation. Because the expression of NE is limited to neutrophil precursors in the bone marrow, we hypothesized that nicotine, which is readily absorbed from lung and distributed to tissue, including bone marrow, would increase expression of the NE gene and protein. HL-60 cells, a myeloblast/promyelocyte cell line, were cultured in the presence or absence of 0.06 and 0.8 microM nicotine for 5 d. Both concentrations of nicotine caused a 2.4- to 3.3-fold increase, respectively, in NE gene expression over unstimulated cells, and NE protein increased 4.8- to 3.4-fold over unstimulated cells, respectively, similar to our positive control DMSO. Nicotine did not induce upregulation of the NE gene by initiating cell differentiation. Both low and high nicotine concentrations upregulate the NE gene in HL-60 cells leading to increased NE protein concentration per cell suggesting a pathophysiologic mechanism for emphysema.

A model of mRNA splicing in adult lysosomal storage disease (glycogenosis type II).

Glycogenosis type II is a recessively inherited disorder caused by mutations in the acid maltase (GAA) gene. Clinically, three different phenotypes are recognized: Infantile, juvenile and adult forms. A majority of compound heterozygous adult-onset patients carry a t-13g mutation in intron 1 associated with splicing out the first coding exon (exon 2). We have studied the mechanism of this mutation in a model system with wild-type and mutant minigenes expressed in a GAA deficient cell line. We have demonstrated that the mutation does not prevent normal splicing; low levels of correctly spliced mRNA are generated with the mutant construct. The data explain why the mutation is restricted to a milder, adult-onset phenotype. We also demonstrate that splicing out of exon 2 occurs with the wild-type construct, and thus represents alternative splicing which takes place in normal cells. Three splice variants (SV1, SV2 and SV3) are made with both the mutant and the wild-type constructs. Furthermore, as shown by RNAse protection assay, these mRNA variants are less abundant with the mutant construct. Thus, a major effect of the mutation appears to be a low splicing efficiency, since the total amount of all the transcripts generated from the mutant construct is reduced compared with the wild type. The removal of approximately 90% of the intron 1 (2.6 kb) sequence resulted in a dramatic increase in the levels of correctly spliced mRNA, indicating that the intron may contain a powerful transcriptional repressor.

Acid alpha-glucosidase deficiency: identification and expression of a missense mutation (S529V) in a Japanese adult phenotype.

We report a missense mutation in an adult Japanese patient with acid alpha-glucosidase (GAA) deficiency. A TC to GT transition at nucleotides 1585-1586, was identified. This transition resulted in an amino acid substitution of Ser-529 to Val (S529V) in exon 11. We also have demonstrated that the S529V mutation abolishes the catalytic activity of the enzyme. Our data suggest that this mutation is the cause of the clinical manifestation known as adult-onset GAA deficiency. The missense mutation described here is a new mutation, and the first identified in Japanese patients with GAA deficiency.

Evidence of molecular heterogeneity for generalised glycogenosis between and within breeds of cattle.

Northern analyses revealed normal levels of acidic alpha-glucosidase mRNA in cultured fibroblasts from a Shorthorn calf affected with glycogenosis but a gross deficiency in an affected Brahman calf. Analyses of acidic alpha-glucosidase activity, relative to that of other lysosomal enzymes, in blood mononuclear cells revealed greater variation within and between Brahman herds than Shorthorn herds. A Msp1 restriction fragment length polymorphism associated with glycogenosis in Brahmans was not found in Shorthorns. These results are considered in relation to molecular heterogeneity for AAG deficiency in cattle and its implications for disease control programs.

Isolation of the gene for the beta subunit of RNA polymerase from rifampicin-resistant Mycobacterium tuberculosis and identification of new mutations.

Tuberculosis (TB) is one of the most important infections worldwide, with an estimated incidence of 10 million active cases per year. Rifampicin is a key component of the first-line therapy used in the treatment of tuberculosis. In Escherichia coli and Mycobacterium leprae, rifampicin has been shown to inhibit the beta subunit of RNA polymerase. The gene (rpoB) encoding this enzyme has been described in both species. We report the isolation of the homologous functional rifampicin resistance gene from M. tuberculosis. A library was constructed with 15 to 25 kb BamHI-digested DNA fragments from a rifampicin-resistant M. tuberculosis clinical isolate that was ligated into an E. coli-mycobacterial shuttle plasmid. Southern analysis of BamHI-digested DNA from 200 recombinant plasmids was performed and filters were hybridized to a 411 bp fragment of the beta subunit of RNA polymerase from M. tuberculosis. Only DNA from one plasmid (#86) hybridized, which suggested that the gene is found as a single copy per genome. This plasmid was able to transfer rifampicin resistance to sensitive M. smegmatis and thus codes for a functional genetic unit. Sequence analysis in the expected "hotspot" region in eight rifampicin-resistant M. tuberculosis strains (including one multidrug-resistant strain) revealed two novel mutations as well as others previously described.

Mycobacterium tuberculosis alters expression of adhesion molecules on monocytic cells.

The host response to Mycobacterium tuberculosis is characterized by interactions between mononuclear cells, with recruitment and fusion of these cells culminating in granuloma formation. In addition, the host response to M. tuberculosis requires CD4+ T-cell reactivity, mediated by antigen-independent as well as antigen-dependent mechanisms. Thus, we hypothesized that cell adhesion molecules such as intercellular adhesion molecule 1 (ICAM-1; CD54) would participate in the response to infection with M. tuberculosis. Exposure of THP-1 cells derived from a monocyte/macrophage cell line to M. tuberculosis (1:1 bacterium/cell ratio) elicited a sustained increase (660% +/- 49% above resting level) in the expression of ICAM-1 that continued for at least 72 h. Neither the expression of vascular cell adhesion molecule 1 (VCAM-1; CD106) nor that of the integrins lymphocyte function-associated antigen 1 (LFA-1; CD11a/CD18) or CR3 (CD11b/CD18) was increased to a similar extent at corresponding time points. The increase in ICAM-1 protein expression was accompanied by an increase in steady-state mRNA (Northern [RNA] analysis). Neutralizing monoclonal antibodies directed against tumor necrosis factor alpha but not interleukin 1 alpha or interleukin 1 beta substantially abrogated the response to M. tuberculosis consistent with a paracrine or autocrine response. Continuous upregulation of the expression of ICAM-1 on mononuclear phagocytes induced by M. tuberculosis may mediate the recruitment of monocytes and enhance the antigen presentation of M. tuberculosis, thus permitting the generation and maintenance of the host response.

Recombinant human acid alpha-glucosidase generated in bacteria: antigenic, but enzymatically inactive.

Genetic deficiency of acid alpha-glucosidase (GAA) results in glycogen storage disease type II. To investigate whether we could generate a functional recombinant human GAA protein for future enzyme replacement therapy, we subcloned the GAA cDNA into the bacterial expression plasmid pMaI and analyzed the recombinant protein produced. This nonglycosylated recombinant human GAA was found to be antigenic by reacting with polyclonal rabbit antibody to human placental GAA using ELISA and Western techniques. However, the protein was not enzymatically active, suggesting that glycosylation may play a role in enzymatic function.

A mechanism for the antiinflammatory effects of corticosteroids: the glucocorticoid receptor regulates leukocyte adhesion to endothelial cells and expression of endothelial-leukocyte adhesion molecule 1 and intercellular adhesion molecule 1.

Corticosteroids are the preeminent antiinflammatory agents although the molecular mechanisms that impart their efficacy have not been defined. The endothelium plays a critical role in inflammation by directing circulating leukocytes into extravascular tissues by expressing adhesive molecules for leukocytes [e.g., endothelial-leukocyte adhesion molecule 1 (ELAM-1) and intercellular adhesion molecule 1 (ICAM-1)]. We therefore determined whether corticosteroids suppress inflammation by inhibiting endothelial expression of adhesion molecules for neutrophils (polymorphonuclear leukocytes). Preincubation of endothelial cells with endotoxin [lipopolysaccharide (LPS), 1 microgram/ml] led to a 4-fold increase in subsequent adherence of polymorphonuclear leukocytes (P < 0.0001, n = 10) to endothelial cells, an increase that was markedly attenuated when endothelial cells were treated with dexamethasone (IC50 < 1 nM, P < 0.0001, n = 6 or 7) during preincubation with LPS. Moreover, the steroid receptor agonist cortisol (10 microM), but not its inactive metabolite tetrahydrocortisol (10 microM), diminished LPS-induced endothelial cell adhesiveness. Further evidence that the action of dexamethasone was mediated through ligation of corticosteroid receptors [human glucocorticoid receptors (hGRs)] was provided by experiments utilizing the steroid antagonist RU-486. RU-486 (10 microM), which prevents translocation of ligated hGR to the nucleus by inhibiting dissociation of hGR from heat shock protein 90, completely aborted the effect of dexamethasone on adhesiveness of endothelial cells (P < 0.0005, n = 3). Treatment of endothelial cells with LPS (1 microgram/ml) stimulated transcription of ELAM-1, as shown by Northern blot analysis, and expression of membrane-associated ELAM-1 and ICAM-1, as shown by quantitative immunofluorescence (both P < 0.001, n = 9). Dexamethasone markedly inhibited LPS-stimulated accumulation of mRNA for ELAM-1 and expression of ELAM-1 and ICAM-1 (IC50 < 10 nM, both P < 0.001, n = 4-9); inhibition of expression by dexamethasone was reversed by RU-486 (both P < 0.005, n = 4-6). As in the adhesion studies, cortisol but not tetrahydrocortisol inhibited expression of ELAM-1 and ICAM-1 (both P < 0.005, n = 3 or 4). In contrast, sodium salicylate (1 mM) inhibited neither adhesion nor expression of these adhesion molecules. These studies suggest that antagonism by dexamethasone of endotoxin-induced inflammation is a specific instance of the general biological principle that the glucocorticoid receptor is a hormone-dependent regulator of transcription.

Developmental expression of glycogenolytic enzymes in rabbit tissues: possible relationship to fetal lung maturation.

Glycogen can be degraded in mammalian tissues by one of three isozymes of glycogen phosphorylase, termed muscle (M), liver (L) and brain (B) after the tissues in which they are preferentially expressed in adult animals, or by members of the family of alpha-glucosidases. In the current study, we have examined the developmental expression of these enzymes and their respective mRNAs in rabbit tissues, with particular emphasis on the developing lung, a tissue in which glycogen serves as an important source of carbon for surfactant phospholipid biosynthesis. Native gel activity assays and RNA blot hybridization analysis revealed that the B isoform of glycogen phosphorylase predominates in fetal and adult lung tissues, accompanied by a low level of expression of the M isoform. Total B and M phosphorylase activities increased during fetal lung development, with a peak at day 28 of gestation, then decreased to the adult level at term. This peak in activity coincided with the peak period of glycogen degradation in developing lung. While the increase in M isozyme activity was correlated with an increase in the level of its mRNA, B isoform mRNA showed no significant alteration during development, suggesting that the increase in B isoform activity is determined by a posttranscriptional mechanism. Analysis of phosphorylase mRNA levels in developing liver, skeletal muscle, brain and heart revealed a diverse expression pattern. The L isozyme mRNA was predominant at all time points in liver, the M isozyme was predominant at all time points in muscle, the B isozyme was predominant at all time points in brain, and heart contained a mixture of B and M mRNA in roughly equal ratios at all time points. Thus, our studies of phosphorylase mRNA in the rabbit provide no evidence for general predominance of the B isozyme in fetal tissues, or for isozyme 'switching' from the B to the L or M forms during development, as has been suggested by others. In addition to the increase in phosphorylase activity, acid, but not neutral alpha-glucosidase activity was found to increase significantly during fetal lung development, again with a peak at day 28 of gestation. Interestingly, RNA blot hybridization analysis with a probe for lysosomal alpha-glucosidase revealed no change in the level of expression of its 4 kb transcript in developing lung. Instead, we observed induction of a structurally related mRNA of 7.4 kb that peaked at day 28 of gestation. Hybridization with a sucrase/isomaltase-specific oligonucleotide excluded the possibility that the 7.4 kb transcript encodes this protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of a missense mutation in an adult-onset patient with glycogenosis type II expressing only one allele.

The lysosomal enzyme acid alpha glucosidase (GAA) or acid maltase is deficient in glycogen storage disease type II. We sought to determine the molecular basis for the disease in an adult-onset patient, unusual for very low enzyme activity similar to that seen with the infantile-onset form and with a previously reported defect in phosphorylation. We constructed cDNA and genomic DNA libraries from the patient's cell line (GM 1935) and determined the nucleotide sequence of the coding region. There were three base-pair substitutions in one allele (C1935 to A; G2446 to A and C2780 to T), all predicting amino acid changes (Asp-645 to Glu; Val-816 to Ile and Thr-927 to Ile). To determine which of the three base-pair substitutions resulted in loss of enzyme activity, we next utilized primer-directed mutagenesis and transient gene expression in an SV40-immortalized GAA-deficient fibroblast cell line. Only the construct containing the G2446 to A mutation (Val-816 to Ile) lost GAA enzyme activity, while the other two substitutions (including the Thr-927 to Ile change that predicts a loss of a potential site for N-linked glycosylation and mannose phosphorylation) each resulted in enzyme activity equal to the control. Analysis of RFLPs in genomic DNA, as well as sequence analysis for the three base-pair alterations, indicated that the patient was a genetic compound. We next digested PCR-amplified cDNA (reverse-transcribed from RNA) with Aat II to detect the base-pair 1935 substitution and found that virtually all of the mRNA was derived from the allele with the three base-pair substitutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a missense mutation in one allele of a patient with Pompe disease, and use of endonuclease digestion of PCR-amplified RNA to demonstrate lack of mRNA expression from the second allele.

Infantile-onset glycogen storage disease type II, or Pompe disease, results from a genetic deficiency of the lysosomal enzyme acid alpha glucosidase (GAA). Sequencing of the cDNA from a cell line (GM 244) derived from a patient with Pompe disease demonstrated a T953-to-C transition that predicted a methionine-to-threonine substitution at codon 318. The basepair substitution resulted in loss of restriction-endonuclease sites for NcoI and StyI. Analysis of genomic DNA revealed both a normal and an abnormal NcoI fragment, indicating that the patient was a genetic compound. NcoI and StyI digestion of cDNA, amplified by PCR from reverse-transcribed RNA, demonstrated that greater than 95% of the GAA mRNA in GM 244 was derived from the allele carrying the missense mutation. The missense mutation was uncommon, since it was not detected in 37 additional GAA-deficient chromosomes, as determined by digestion of genomic DNA with NcoI and hybridization. The amino acid substitution predicts a new potential site for N-linked glycosylation, as well as major changes in secondary structure of the protein. We could confirm that the mutation was responsible for the enzyme deficiency by demonstrating that a hybrid minigene containing the mutation did not express GAA enzyme activity after transient gene expression. We have therefore now provided the first identification of a single-basepair missense mutation in a patient with Pompe disease and furthermore have demonstrated that the patient is a genetic compound with the second allele barely expressing mRNA.

Isolation and partial characterization of the structural gene for human acid alpha glucosidase.

Genetic deficiency of acid alpha glucosidase (GAA) results in glycogen storage disease type II. To study the disease at the molecular level, we have previously isolated and sequenced the cDNA (3.6 kb) for human GAA. We have now isolated the structural gene, mapped and determined the position and size of the exons containing the entire cDNA, and determined the sequence of the intron-exon junctions. The structural gene is approximately 28 kb and contains 20 exons. The first exon has only 5' untranslated sequence and is separated by an approximately 2.7-kb intron from the second exon that contains the initiation ATG. The second as well as the last exon are quite large (578 and 607 bp) with the remainder of the exons ranging from 85-187 bp. Additionally, two new restriction fragment length (RFLPs) for Xba I and Stu I are described at the GAA locus, one of which is most 5' of the eight RFLPs we have previously described.

Identification of the promoter region and gene expression for human acid alpha glucosidase.

Genetic deficiency of acid alpha glucosidase (GAA) results in glycogen storage disease type II. A cDNA containing the complete coding region was constructed and cloned into the expression vector pSV2 and was transiently transfected into an SV40 immortalized GAA deficient human fibroblast cell line which has undetectable levels of GAA enzyme activity and does not express GAA mRNA. Transfected cells had 4.9% of normal human fibroblast enzyme activity. Additionally a 5' 1.8 kb genomic fragment was ligated to the 5' end of the GAA cDNA construct and cloned into pUC19. Transient and stable transfection also resulted in expressed GAA enzyme activity in deficient fibroblast cells, indicating that the genomic fragment has GAA promoter function.