Cotransfer of syntenic human genes into mouse cells using isolated metaphase chromosomes or cellular DNA

Lentiviral gene therapy of murine hematopoietic stem cells ameliorates the Pompe disease phenotype

Pompe disease (acid alpha-glucosidase deficiency) is a lysosomal glycogen storage disorder characterized in its most severe early-onset form by rapidly progressive muscle weakness and mortality within the first year of life due to cardiac and respiratory failure. Enzyme replacement therapy prolongs the life of affected infants and supports the condition of older children and adults but entails lifelong treatment and can be counteracted by immune responses to the recombinant enzyme. We have explored the potential of lentiviral vector-mediated expression of human acid alpha-glucosidase in hematopoietic stem cells (HSCs) in a Pompe mouse model. After mild conditioning, transplantation of genetically engineered HSCs resulted in stable chimerism of approximately 35% hematopoietic cells that overexpress acid alpha-glucosidase and in major clearance of glycogen in heart, diaphragm, spleen, and liver. Cardiac remodeling was reversed, and respiratory function, skeletal muscle strength, and motor performance improved. Overexpression of acid alpha-glucosidase did not affect overall hematopoietic cell function and led to immune tolerance as shown by challenge with the human recombinant protein. On the basis of the prominent and sustained therapeutic efficacy without adverse events in mice we conclude that ex vivo HSC gene therapy is a treatment option worthwhile to pursue.

Chemical chaperones improve transport and enhance stability of mutant alpha-glucosidases in glycogen storage disease type II

Glycogen storage disease type II (GSDII; Pompe disease or acid maltase deficiency) is an autosomal recessive disorder caused by lysosomal acid alpha-glucosidase (AalphaGlu) deficiency and manifests predominantly as skeletal muscle weakness. Defects in post-translational modification and transport of mutant AalphaGlu species are frequently encountered and may potentially be corrected with chaperone-mediated therapy. In the present study, we have tested this hypothesis by using deoxynojirimycin and derivatives as chemical chaperones to correct the AalphaGlu deficiency in cultured fibroblasts from patients with GSDII. Four mutant phenotypes were chosen: Y455F/Y455F, P545L/P545L, 525del/R600C and D645E/R854X. In case of Y455F/Y455F and P545L/P545L, N-(n-butyl)deoxynojirimycin (NB-DNJ) restored the transport, maturation and activity of AalphaGlu in a dose dependent manner, while it had no effect on the reference enzyme beta-hexosaminidase. NB-DNJ promoted export from the endoplasmic reticulum (ER) to the lysosomes and stabilized the activity of mutant AalphaGlu species, Y455F and P545L, inside the lysosomes. In long-term culture, the AalphaGlu activity in the fibroblasts from the patients with mutant phenotypes, Y455F/Y455F and P545L/P545L, increased up to 14.0- and 7.9-fold, respectively, in the presence of 10mumol/L NB-DNJ. However, the effect of NB-DNJ on Y455F/Y455F subsided quickly after removal of the compound. We conclude that NB-DNJ acts in low concentration as chemical chaperone for certain mutant forms of AalphaGlu that are trapped in the ER, poorly transported or labile in the lysosomal environment. Chemical chaperone therapy could create new perspectives for therapeutic intervention in GSDII.

Age-related morphological changes in skeletal muscle cells of acid α-glucosidase knockout mice

Glycogen storage disease type II (GSDII), caused by a genetic defect in acid alpha-glucosidase (AGLU), leads to a decline in muscle contractility caused by both muscle wasting and a decrease in muscle quality, i.e., force generated per unit muscle mass. A previous study has shown that loss of muscle mass can only explain one-third of the decrease in contractile performance. Here we report on changes in the intramyocellular structural organization in a mouse knockout model (AGLU(-/-) mice) as a possible cause for the decline in muscle quality. Swollen, glycogen-filled lysosomes and centrally localized cores with cellular debris partially contribute to the decline in muscle quality. Altered localization and deposition of cytoskeletal proteins desmin and titin may reflect adaptive mechanisms at the age of 13 months, but a decline in quality at 20 months of age. The early deposition of lipofuscin in AGLU-deficient myocytes (13 months) is most likely a reflection of enhanced oxidative stress, which may also affect muscle quality. These collective findings, on the one hand, may explain the decrease in tissue quality and, on the other, may represent markers for efficacy of therapeutic interventions to restore muscle function in patients suffering from GSDII.

Age-related decline in muscle strength and power output in acid 1-4 α-glucosidase knockout mice

A hallmark of glycogen storage disease type II, caused by defective alpha-glucosidase (AGLU) activity, is a progressive decline in muscle performance. The objective of this study was to determine the relative contribution to this decline in muscle performance of (1) decline in muscle mass; (2) decline in muscle protein content per unit mass; and (3) accumulation of glycogen. To this end, isometric torque and power in AGLU(-/-) mice at 7, 13, and 20 months were assessed in situ. Power (approximately 24 mW) and torque (approximately 2.45 Nmm) did not change with age in control animals, but declined significantly in AGLU(-/-) mice, in the three age groups. No decline in protein content per unit muscle mass was observed. Muscle atrophy explained one third of the decline in muscle performance; the remaining part was attributed to a decrease in muscle quality--a decrease in mechanical performance per unit muscle mass. Mechanical effects of glycogen inclusions could not fully explain this decrease. Additional factors must therefore play a role.

Efficient in-vitro transfer of a 60-Mb mammalian artificial chromosome into murine and hamster cells using cationic lipids and dendrimers

Non-integrating artificial chromosomes represent a potentially promising approach to ex-vivo and in-vivo gene therapy applications. These large vectors require an efficient means for delivery to target cells. We have evaluated a panel of twenty-one commercially available transfection agents for their ability to mediate the in-vitro transfer of a 60-Mb murine artificial chromosome consisting of mouse major satellite DNA and a payload including a marker gene (hygromycin B) and a reporter gene (lacZ). A rapid screening procedure utilizing iododeoxyuridine-incorporated artificial chromosomes facilitated the assessment of different transfection conditions. The results were confirmed by cytogenetic analysis of positively transfected clones. By transfecting both hamster lung fibroblast cells (V79-4) and murine connective tissue cells [L-M(TK-)], the best results were obtained using either Superfect (cationic dendrimer) or LipofectAMINE 2000 (cationic lipid) with protocols adapted for metaphase chromosome preparation. Transfection efficiencies of 10(-4)-10(-2) (0.01-1%) were routinely observed, and recipient cells were able to maintain expression of the reporter gene over the total length of the experiment. This represents a significant advance over our previous attempts at mass-transfection of artificial chromosomes using microcell fusion, where we routinely achieved efficiencies at least two orders of magnitudes less than reported here. These data are particularly noteworthy given that lipid-mediated gene transfer typically involves transfecting millions of plasmids (1 microg of DNA from a 5 kb plasmid is approximately 1.2 x 10(11) copies) to each cell whereas the much larger artificial chromosomes comprise only a one-to-one ratio, yet achieve transfection efficiencies of (10(-2)-10(-1)), that is, comparable to our results. These data suggest that artificial chromosomes containing therapeutic genes can be successfully delivered to target cells in vitro using well-established transfection agents.

Human acid alpha-glucosidase from rabbit milk has therapeutic effect in mice with glycogen storage disease type II

Pompe's disease or glycogen storage disease type II (GSDII) belongs to the family of inherited lysosomal storage diseases. The underlying deficiency of acid alpha-glucosidase leads in different degrees of severity to glycogen storage in heart, skeletal and smooth muscle. There is currently no treatment for this fatal disease, but the applicability of enzyme replacement therapy is under investigation. For this purpose, recombinant human acid alpha-glucosidase has been produced on an industrial scale in the milk of transgenic rabbits. In this paper we demonstrate the therapeutic effect of this enzyme in our knockout mouse model of GSDII. Full correction of acid alpha-glucosidase deficiency was obtained in all tissues except brain after a single dose of i.v. enzyme administration. Weekly enzyme infusions over a period of 6 months resulted in degradation of lysosomal glycogen in heart, skeletal and smooth muscle. The tissue morphology improved substantially despite the advanced state of disease at the start of treatment. The results have led to the start of a Phase II clinical trial of enzyme replacement therapy in patients.

Generalized glycogen storage and cardiomegaly in a knockout mouse model of Pompe disease

Glycogen storage disease type II (GSDII; Pompe disease), caused by inherited deficiency of acid alpha-glucosidase, is a lysosomal disorder affecting heart and skeletal muscles. A mouse model of this disease was obtained by targeted disruption of the murine acid alpha-glucosidase gene (Gaa) in embryonic stem cells. Homozygous knockout mice (Gaa -/-) lack Gaa mRNA and have a virtually complete acid alpha-glucosidase deficiency. Glycogen-containing lysosomes are detected soon after birth in liver, heart and skeletal muscle cells. By 13 weeks of age, large focal deposits of glycogen have formed. Vacuolar spaces stain positive for acid phosphatase as a sign of lysosomal pathology. Both male and female knockout mice are fertile and can be intercrossed to produce progeny. The first born knockout mice are at present 9 months old. Overt clinical symptoms are still absent, but the heart is typically enlarged and the electrocardiogram is abnormal. The mouse model will help greatly to understand the pathogenic mechanism of GSDII and is a valuable instrument to explore the efficacy of different therapeutic interventions.

Expression of cDNA-encoded human acid alpha-glucosidase in milk of transgenic mice

Enzyme replacement therapy is at present the option of choice for treatment of lysosomal storage diseases. To explore the feasibility of lysosomal enzyme production in milk of transgenic animals, the human acid alpha-glucosidase cDNA was placed under control of the alpha S1-casein promoter and expressed in mice. The milk contained recombinant enzyme at a concentration up to 1.5 micrograms/ml. Enzyme purified from milk of transgenic mice was internalized via the mannose 6-phosphate receptor and corrected enzyme deficiency in fibroblasts from patients. We conclude that transgenically produced human acid alpha-glucosidase meets the criteria for therapeutic application.

Localization and ordering of acid alpha-glucosidase (GAA) and thymidine kinase (TK1) by fluorescence in situ hybridization

Genomic DNA clones of human acid alpha glucosidase (GAA) and thymidine kinase (TK1) were used to map the exact location and order of these genes on human chromosome 17. Both genes were localized to the 17q25-qter band (17q25.2-q25.3), with GAA distal to TK1. They were also shown to be, respectively, distal and proximal to an anonymous cosmid (cK17.71) previously mapped to this region.

Gene mapping of ocular diseases

Increasing awareness of the role of genetic factors in the causation of many human eye diseases has made ocular genetics one of the fastest growing areas of ophthalmology. The objective of this paper is to present the basic principles of gene mapping and their application to ophthalmology. The techniques used to map the genome are reviewed with emphasis placed on molecular genetics. The advances in this area have already provided the major impetus to the areas of diagnosis and prevention of some genetic eye disorders. Tables are presented that list the autosomal, X-linked and mitochondrial assignment of eye genes and disorders with ocular involvement.

Intravenous administration of phosphorylated acid alpha-glucosidase leads to uptake of enzyme in heart and skeletal muscle of mice

The lysosomal storage disorder glycogenosis type II is caused by acid alpha-glucosidase deficiency. In this study we have investigated the possible applicability of mannose 6-phosphate receptor-mediated enzyme replacement therapy to correct the enzyme deficiency in the most affected tissues. Bovine testes acid alpha-glucosidase containing phosphorylated mannose residues was intravenously administered to mice and found to be taken up by heart (70% increase of activity) and skeletal muscle (43% increase); the major target organs. The uptake of nonphosphorylated human placenta acid alpha-glucosidase by heart and skeletal muscle appeared to be significantly less efficient, whereas uptake of dephosphorylated bovine testes enzyme was not detectable. The phosphorylated bovine testes acid alpha-glucosidase remained present in mouse skeletal muscle up to 9-15 d after administration, with a half-life of 2-4 d. Besides being measured in skeletal muscle and heart, uptake of phosphorylated bovine testes and nonphosphorylated human placenta acid alpha-glucosidase was measured in several other organs, but not in brain. The increase of acid alpha-glucosidase activity was highest in liver and spleen. We concluded that application of mannose 6-phosphate receptor-mediated enzyme replacement therapy may offer new perspectives for treatment of glycogenesis type II.

Expression and routeing of human lysosomal alpha-glucosidase in transiently transfected mammalian cells

Previously isolated lysosomal alpha-glucosidase cDNA clones were ligated to full-length constructs for expression in vitro and in mammalian cells. One of these constructs (pSHAG1) did not code for functional enzyme, due to an arginine residue instead of a tryptophan residue at amino acid position 402. The mutation does not affect the rate of enzyme synthesis, but interferes with post-translational modification and intracellular transport of the acid alpha-glucosidase precursor. Using immunocytochemistry it is demonstrated that the mutant precursor traverses the endoplasmic reticulum and the Golgi complex, but does not reach the lysosomes. Pulse-chase experiments suggest premature degradation. The Trp-402-containing enzyme (encoded by construct pSHAG2) is processed properly, and has catalytic activity. A fraction of the enzyme is localized at the plasma membrane. It is hypothesized that membrane association of the acid alpha-glucosidase precursor, as demonstrated by Triton X-114 phase separation, is responsible for transport to this location. Transiently expressed acid alpha-glucosidase also enters the secretory pathway, since a catalytically active precursor is found in the culture medium. This precursor has the appropriate characteristics for use in enzyme replacement therapy. Efficient uptake via the mannose 6-phosphate receptor results in degradation of lysosomal glycogen in cultured fibroblasts and muscle cells from patients with glycogenosis type II.

Primary structure and processing of lysosomal alpha-glucosidase; homology with the intestinal sucrase-isomaltase complex

Lysosomal alpha-glucosidase (acid maltase) is essential for degradation of glycogen in lysosomes. Enzyme deficiency results in glycogenosis type II. The amino acid sequence of the entire enzyme was derived from the nucleotide sequence of cloned cDNA. The cDNA comprises 3636 nt, and hybridizes with a messenger RNA of approximately 3.6 kb, which is absent in fibroblasts of two patients with glycogenosis type II. The encoded protein has a molecular mass of 104.645 kd and starts with a signal peptide. Sites of proteolytic processing are established by identification of N-terminal amino acid sequences of the 110-kd precursor, and the 76-kd and 70-kd mature forms of the enzyme encoded by the cDNA. Interestingly, both amino-terminal and carboxy-terminal processing occurs. Sites of sugar-chain attachment are proposed. A remarkable homology is observed between this soluble lysosomal alpha-glucosidase and the membrane-bound intestinal brush border sucrase-isomaltase enzyme complex. It is proposed that these enzymes are derived from the same ancestral gene. Around the putative active site of sucrase and isomaltase, 10 out of 13 amino acids are identical to the corresponding amino acids of lysosomal alpha-glucosidase. This strongly suggests that the aspartic acid residue at this position is essential for catalytic function of lysosomal alpha-glucosidase.

Chromosome mediated gene transfer of six DNA markers linked to the cystic fibrosis locus on human chromosome seven

The DNA probes met and pJ3.11 are derived from loci on chromosome seven that are closely linked to, and probably flanking, the gene mutation causing cystic fibrosis (CF). We have shown that mitotic chromosomes from the cell line MNNG-HOS, which contains an activated met oncogene, can induce morphological transformation of mouse NIH-3T3 cells. Southern analysis of isolated transfectant cell lines with cloned dispersed repetitive human DNA sequences as probes demonstrated that several lines of transformed NIH 3T3 cells had stabley incorporated large segments of chromosome seven DNA. Southern blot analysis also demonstrated the presence of met, pJ3.11 and several other single copy sequences that had been previously localised to chromosome 7 within the transgenomes. In this way a further four genetic markers were shown to be physically linked to met, and thus to CF. These probes may prove useful in confirming the order of loci around CF and in the prenatal diagnosis of this common autosomal recessive disease.