A New Mouse Model of Mild Ornithine Transcarbamylase Deficiency (spf-j) Displays Cerebral Amino Acid Perturbations at Baseline and upon Systemic Immune Activation

Abstract

Ornithine transcarbamylase deficiency (OTCD, OMIM# 311250) is an inherited X-linked urea cycle disorder that is characterized by hyperammonemia and orotic aciduria. In this report, we describe a new animal model of OTCD caused by a spontaneous mutation in the mouse Otc gene (c.240T>A, p.K80N). This transversion in exon 3 of ornithine transcarbamylase leads to normal levels of mRNA with low levels of mature protein and is homologous to a mutation that has also been described in a single patient affected with late-onset OTCD. With higher residual enzyme activity, spf-J were found to have normal plasma ammonia and orotate. Baseline plasma amino acid profiles were consistent with mild OTCD: elevated glutamine, and lower citrulline and arginine. In contrast to WT, spf-J displayed baseline elevations in cerebral amino acids with depletion following immune challenge with polyinosinic:polycytidylic acid. Our results indicate that the mild spf-J mutation constitutes a new mouse model that is suitable for mechanistic studies of mild OTCD and the exploration of cerebral pathophysiology during acute decompensation that characterizes proximal urea cycle dysfunction in humans.

Ketogenic Diet Consumption Inhibited Mitochondrial One-Carbon Metabolism

“… 1 Plasma samples were extracted and analyzed for measuring the amino acid and formate concentrations ( n = 8–12/group). These results are within mice’s normal range compared to the literature [ 22 ]. 2 Plasma formate enrichments in mice received L-[2,3,3- 2 H 3 ]-Serine or [2- 13 C]-Glycine tracers ( n = 2–3/group).…”

Comprehensive characterization of ureagenesis in the spfash mouse, a model of human ornithine transcarbamylase deficiency, reveals age‐dependency of ammonia detoxification

“…10 Recently, Tarasenko described the spf-j mouse affected by a spontaneous mutation in the Otc gene (c.240T>A, p.Lys80Asn), in which the transversion in exon 3 results in normal levels of mRNA with low levels of mature protein. 11 This variation was described in one OTCD patient with late onset. 12 The hypomorphic spf-j mouse displays a very mild phenotype with residual enzyme activity of 10% to 12% and has normal plasma ammonia and orotic acid excretion.…”

“…12 The hypomorphic spf-j mouse displays a very mild phenotype with residual enzyme activity of 10% to 12% and has normal plasma ammonia and orotic acid excretion. 11 Another model, which in fact has been widely used, is the spf ash (abnormal skin and hair) mouse. This mouse carries a point mutation that is also found in human patients, Otc c.386G>A, and that affects the last nucleotide of exon 4, which leads to a benign missense change p.Arg129His and to an abnormal splicing of exon 4.…”

Humanized liver mouse model with transplanted human hepatocytes from patients with ornithine transcarbamylase deficiency

“…Several recent studies have demonstrated that HHs isolated from patients with genetic metabolic diseases, including OTCD and other UCDs, proliferate in humanized liver mouse models. 15,16,23,24 Furthermore, some have a disease phenotype, such as carbamoyl phosphate synthetase-1 (CPS-1) deficiency 24 and familial hypercholesterolemia, 21 but not OTCD. In these studies, another representative humanized liver mouse model, FRG mice, with a genetic background of fumarylacetoacetate hydrolase (FAH) deficiency and immunodeficiency (Rag2 −/− IL2rg −/− ) were used.…”

“…OTC enzyme activity was determined by a colorimetric method based on the production of L-citrulline as described previously. 20,21 Citrulline production was determined by measuring the absorbance at 490 nm using a SpectraMax i3 Multimode microplate platform (Molecular Devices). The enzyme activity was expressed as citrulline μmol/mg protein/h.…”