AAV-based gene therapy prevents neuropathology and results in normal cognitive development in the hyperargininemic mouse

Abstract

Complete arginase I deficiency is the least severe urea cycle disorder, characterized by hyperargininemia and infrequent episodes of hyperammonemia. Patients suffer from neurological impairment with cortical and pyramidal tract deterioration, spasticity, loss of ambulation, and seizures, and is associated with intellectual disability. In mice, onset is heralded by weight loss beginning around day 15; gait instability follows progressing to inability to stand and development of tail tremor with seizure-like activity and death. Here we report that hyperargininemic mice treated neonatally with an adeno-associated virus expressing arginase and followed long-term lack any presentation consistent with brain dysfunction. Behavioral and histopathological evaluation demonstrated that treated mice are indistinguishable from littermates and that putative compounds associated with neurotoxicity are diminished. In addition, treatment results in near complete resolution of metabolic abnormalities early in life; however there is the development of some derangement later with decline in transgene expression. Ammonium challenging revealed that treated mice are affected by exogenous loading much greater than littermates. These results demonstrate that AAV-based therapy for hyperargininemia is effective and prevents development of neurological abnormalities and cognitive dysfunction in a mouse model of hyperargininemia; however nitrogen challenging reveals that these mice remain impaired in the handling of waste nitrogen.

Rescue of the Functional Alterations of Motor Cortical Circuits in Arginase Deficiency by Neonatal Gene Therapy

“…However, no confirmatory evidence exists, and some data, in both humans (Deignan et al, 2010) and mice (Lee et al, 2013), refute this hypothesis. Taurine has numerous effects on the mammalian nervous system, having been shown to be involved in many physiological functions (Foos and Wu, 2002), including as a neurotransmitter and in inhibiting Purkinje cell dendrites in the cerebellum (Okamoto et al, 1983) and pyramidal cells in the hippocampus (Taber et al, 1986).…”

“…In the arginase-deficient murine model, both arginine and ammonia are markedly elevated at day 14 of life (Iyer et al, 2002;Gau et al, 2009); however, HET (single-copy loss) and WT animals show no difference in ammonia or plasma arginine and yet a phenotype (cortical circuit described herein, not behavioral; Lee et al, 2013) for the heterozygote is present, suggesting that neither hyperammonemia or hyperargininemia are the mechanism for these findings.…”

“…Mice were kept according to the National Institutes of Health guidelines, and all experimental procedures were conducted in accordance with guidelines for the care and use of research animals at our institution. To generate the gene therapy mice (Treated KO), arginase-deficient pups on postnatal day 2 (determined by PCR genotyping; Gau et al, 2009;Lee et al, 2012) were injected with 1.0 ϫ 10 14 genome copies kg Ϫ1 of AAVrh10 with thyroxine-binding globulin promoter driving murine Arg1 (codon-optimized) diluted in pharmaceutical-grade saline administered by the superficial facial vein as described previously . The injections were performed in a total volume of 50 l with a 28 gauge needle.…”

“…Genomic DNA was prepared from tail tip by using 5 PRIME ArchivePure DNA Purification (catalog #FP2300860). The genotyping was performed by standard PCR amplification as described previously (Gau et al, 2009;Lee et al, 2012).…”

“…Arginase deficiency results from a loss of arginase 1 (Arg1), the final enzyme in the urea cycle (Brusilow and Horwich, 2001;Lee et al, 2012Lee et al, , 2013, resulting in hyperargininemia (Fig. 1A).…”