Systemic delivery of a Peptide-linked morpholino oligonucleotide neutralizes mutant RNA toxicity in a mouse model of myotonic dystrophy.

Expansions of CUG trinucleotide sequences in RNA transcripts provide the basis for toxic RNA gain-of-function that leads to detrimental changes in RNA metabolism. A CTG repeat element normally resides in the 3' untranslated region of the dystrophia myotonica-protein kinase (DMPK) gene, but when expanded it is the genetic lesion of myotonic dystrophy type 1 (DM1), a hereditary neuromuscular disease. The pathogenic DMPK transcript containing the CUG expansion is retained in ribonuclear foci as part of a complex with RNA-binding proteins such as muscleblind-like 1 (MBNL1), resulting in aberrant splicing of numerous RNA transcripts and consequent physiological abnormalities including myotonia. Herein, we demonstrate molecular and physiological amelioration of the toxic effects of mutant RNA in the HSA(LR) mouse model of DM1 by systemic administration of peptide-linked morpholino (PPMO) antisense oligonucleotides bearing a CAG repeat sequence. Intravenous administration of PPMO conjugates to HSA(LR) mice led to redistribution of Mbnl1 protein in myonuclei and corrections in abnormal RNA splicing. Additionally, myotonia was completely eliminated in PPMO-treated HSA(LR) mice. These studies provide proof of concept that neutralization of RNA toxicity by systemic delivery of antisense oligonucleotides that target the CUG repeat is an effective therapeutic approach for treating the skeletal muscle aspects of DM1 pathology.

Increased hepatic insulin action in diet-induced obese mice following inhibition of glucosylceramide synthase.

BACKGROUND: Obesity is characterized by the accumulation of fat in the liver and other tissues, leading to insulin resistance. We have previously shown that a specific inhibitor of glucosylceramide synthase, which inhibits the initial step in the synthesis of glycosphingolipids (GSLs), improved glucose metabolism and decreased hepatic steatosis in both ob/ob and diet-induced obese (DIO) mice. Here we have determined in the DIO mouse model the efficacy of a related small molecule compound, Genz-112638, which is currently being evaluated clinically for the treatment of Gaucher disease, a lysosomal storage disorder. METHODOLOGY/PRINCIPAL FINDINGS: DIO mice were treated with the Genz-112638 for 12 to 16 weeks by daily oral gavage. Genz-112638 lowered HbA1c levels and increased glucose tolerance. Whole body adiposity was not affected in normal mice, but decreased in drug-treated obese mice. Drug treatment also significantly lowered liver triglyceride levels and reduced the development of hepatic steatosis. We performed hyperinsulinemic-euglycemic clamps on the DIO mice treated with Genz-112638 and showed that insulin-mediated suppression of hepatic glucose production increased significantly compared to the placebo treated mice, indicating a marked improvement in hepatic insulin sensitivity. CONCLUSIONS/SIGNIFICANCE: These results indicate that GSL inhibition in obese mice primarily results in an increase in insulin action in the liver, and suggests that GSLs may have an important role in hepatic insulin resistance in conditions of obesity.

Inhibiting glycosphingolipid synthesis ameliorates hepatic steatosis in obese mice.

UNLABELLED: Steatosis in the liver is a common feature of obesity and type 2 diabetes and the precursor to the development of nonalcoholic steatohepatitis (NASH), cirrhosis, and liver failure. It has been shown previously that inhibiting glycosphingolipid (GSL) synthesis increases insulin sensitivity and lowers glucose levels in diabetic rodent models. Here we demonstrate that inhibiting GSL synthesis in ob/ob mice not only improved glucose homeostasis but also markedly reduced the development of hepatic steatosis. The ob/ob mice were treated for 7 weeks with a specific inhibitor of glucosylceramide synthase, the initial enzyme involved in the synthesis of GSLs. Besides lowering glucose and hemoglobin A1c (HbA1c) levels, drug treatment also significantly reduced the liver/body weight ratio, decreased the accumulation of triglycerides, and improved several markers of liver pathology. Drug treatment reduced liver glucosylceramide (GL1) levels in the ob/ob mouse. Treatment also reduced the expression of several genes associated with hepatic steatosis, including those involved in lipogenesis, gluconeogenesis, and inflammation. In addition, inhibiting GSL synthesis in diet-induced obese mice both prevented the development of steatosis and partially reversed preexisting steatosis. CONCLUSION: These data indicate that inhibiting GSL synthesis ameliorates the liver pathology associated with obesity and diabetes, and may represent a novel strategy for treating fatty liver disease and NASH.

Inhibiting glycosphingolipid synthesis improves glycemic control and insulin sensitivity in animal models of type 2 diabetes.

Previous reports have shown that glycosphingolipids can modulate the activity of the insulin receptor, and studies in transgenic mice suggest a link between altered levels of various gangliosides and the development of insulin resistance. Here, we show that an inhibitor of glycosphingolipid synthesis can improve glucose control and increase insulin sensitivity in two different diabetic animal models. In the Zucker diabetic fatty rat, the glucosylceramide synthase inhibitor (1R,2R)-nonanoic acid[2-(2',3'-dihydro-benzo [1, 4] dioxin-6'-yl)-2-hydroxy-1-pyrrolidin-1-ylmethyl-ethyl]- amide-l-tartaric acid salt (Genz-123346) lowered glucose and A1C levels and improved glucose tolerance. Drug treatment also prevented the loss of pancreatic beta-cell function normally observed in the Zucker diabetic fatty rat and preserved the ability of the animals to secrete insulin. In the diet-induced obese mouse, treatment with Genz-123346 normalized A1C levels and improved glucose tolerance. Analysis of the phosphorylation state of the insulin receptor and downstream effectors showed increased insulin signaling in the muscles of the treated Zucker diabetic fatty rats and diet-induced obese mice. These results suggest that inhibiting glycosphingolipid synthesis can significantly improve insulin sensitivity and glucose homeostasis and may therefore represent a novel therapeutic approach for the treatment of type 2 diabetes.

AAV vector-mediated correction of brain pathology in a mouse model of Niemann-Pick A disease.

Niemann-Pick A disease (NPA) is a fatal lysosomal storage disorder caused by a deficiency in acid sphingomyelinase (ASM) activity. The lack of functional ASM results in cellular accumulation of sphingomyelin and cholesterol within distended lysosomes throughout the brain. In this study, we investigated the potential of AAV-mediated expression of ASM to correct the brain pathology in an ASM knockout (ASMKO) mouse model of NPA. An AAV serotype 2 vector encoding human ASM (AAV2-hASM) was injected directly into the adult ASMKO hippocampus of one hemisphere. This resulted in expression of human ASM in all major cell layers of the ipsilateral hippocampus for at least 15 weeks postinjection. Transduced cells were also present in the entorhinal cortex, medial septum, and contralateral hippocampus in a pattern consistent with retrograde axonal transport of AAV2. There was a substantial reduction of distended lysosomes and an almost complete reversal of cholesterol accumulation in all areas of the brain that were targeted by AAV2-hASM. These findings show that the ASMKO brain is responsive to ASM replacement and that retrograde transport of AAV2 functions as a platform for widespread gene delivery and reversal of pathology in affected brain.

Partial correction of the alpha-galactosidase A deficiency and reduction of glycolipid storage in Fabry mice using synthetic vectors.

BACKGROUND: Fabry disease is a recessive, X-linked disorder caused by a deficiency of the lysosomal enzyme alpha-galactosidase A, leading to an accumulation of the glycosphingolipid globotriaosylceramide (GL-3) in most tissues of the body. The goal of this study was to determine if systemic delivery of a nonviral vector could correct the enzyme deficiency and reduce the levels of GL-3 in different tissues of a transgenic knockout mouse model of the disease. METHODS: Cationic lipid was complexed with a CpG-depleted plasmid DNA vector and then injected intravenously into Fabry mice. The levels of alpha-galactosidase A and GL-3 in different tissues were assayed at various time points after injection. RESULTS: Expression of alpha-galactosidase A was detected in the different tissues of Fabry mice for up to 3 months after complex administration, but resulted in minimal reductions in GL-3 levels. However, the use of the anti-inflammatory drug dexamethasone and multiple dosing increased alpha-galactosidase A expression and resulted in significant reductions of GL-3 in all the organs with the exception of the kidney. In addition, injecting complex into young Fabry mice partially prevented the normal accumulation of GL-3 in the heart, lung, and liver. CONCLUSIONS: Systemic delivery of a cationic lipid-pDNA complex partially corrected the enzyme deficiency and reduced glycolipid storage in a mouse model of Fabry disease. The results are one of the few demonstrations of long-term efficacy in a genetic disease model using nonviral vectors. However, substantial improvements in expression, especially in critical organs such as the kidney, are required before these vectors can become a viable approach to treat Fabry disease and other lysosomal storage disorders.

CpG-depleted plasmid DNA vectors with enhanced safety and long-term gene expression in vivo.

Systemic delivery of cationic lipid-plasmid DNA (pDNA) complexes induces an acute inflammatory response with adverse hematologic changes and liver damage. Immunostimulatory CpG motifs in the pDNA are known to contribute substantially to this response. Here we constructed a pDNA vector (pGZB) that has been depleted of 80% of the CpG motifs present in the original vector. Compared with the unmodified vector, systemic administration of pGZB induced considerably fewer changes in blood parameters, reduced levels of inflammatory cytokines, and decreased liver damage. Despite the extensive sequence modifications within pGZB, there were still robust levels of transgene expression. Furthermore, in contrast to the transient expression observed from the unmodified vector, we observed sustained or increasing expression for up to 49 days from pGZB in the lung and liver of immunocompetent BALB/c mice. Studies adding CpG motifs in trans or in cis indicate that the reduced CpG content of pGZB was the major determinant for its persistent expression. This combination of decreased toxicity and sustained expression suggests that CpG-depleted pDNA vectors can greatly improve the safety and efficacy of synthetic gene delivery systems.