Lethal phenotype in conditional late-onset arginase 1 deficiency in the mouse

Abstract

Human arginase deficiency is characterized by hyperargininemia and infrequent episodes of hyperammonemia, which lead to neurological impairment with spasticity, loss of ambulation, seizures, and severe mental and growth retardation; uncommonly, patients suffer early death from this disorder. In a murine targeted knockout model, onset of the phenotypic abnormality is heralded by weight loss at around day 15, and death occurs typically by postnatal day 17 with hyperargininemia and markedly elevated ammonia. This discrepancy between the more attenuated juvenile-onset human disease and the lethal neonatal murine model has remained suboptimal for studying and developing therapy for the more common presentation of argianse deficiency. These investigations aimed to address this issue by creating an adult conditional knockout mouse to determine whether later onset of arginase deficiency also resulted in lethality. Animal survival and ammonia levels, body weight, circulating amino acids, and tissue arginase levels were examined as outcome parameters after widespread Cre-recombinase activation in a conditional knockout model of arginase 1 deficiency. One hundred percent of adult female and 70 percent of adult male mice died an average of 21.0 and 21.6 days, respectively, after the initiation of tamoxifen administration. Animals demonstrated elevated circulating ammonia and arginine at the onset of phenotypic abnormalities. In addition, brain and liver amino acids demonstrated abnormalities. These studies demonstrate that (a) the absence of arginase in adult animals results in a disease profile (leading to death) similar to that of the targeted knockout and (b) the phenotypic abnormalities seen in the juvenile-onset model are not exclusive to the age of the animal but instead to the biochemistry of the disorder. This adult model will be useful for developing gene- and cell-based therapies for this disorder that will not limited by by the small animal size of neonatal therapy and for developing a better understanding of the characteristics of hyperargininemia.

Functional Human and Murine Tissue-Engineered Liver Is Generated from Adult Stem/Progenitor Cells

“…Actin GFP LOU were implanted 6 weeks before induction of liver failure through tamoxifen induction in the Fah−/− Fah−/−Rag2−/−Il2rg−/−Arg flox/flox UBC‐Cre/ERT2 . This mouse model was previously reported to be uniformly lethal by 21 days after induction in female mice.…”

“…LOU were prepared from human liver or from 2‐week‐old Actin GFP mice and implanted in either nonobese diabetic (NOD)/severe combined immunodeficient (SCID) or Rag2−/−Il2rg−/−Arg flox/flox UBC‐Cre/ERT2 mice in a variation of the protocol we have developed for regions of the intestine . Briefly, under sterile conditions, resected liver was cut into approximately 2‐ to 3‐mm or smaller pieces and washed in ice cold Hank's balanced salt solution, sedimented between washes with centrifugation (150 g ), and then digested in either 800 or 11,000 U/ml of collagenase type I (Worthington Biochemical Corporation, Lakewood, NJ, http://www.worthington-biochem.com) and 0.12 mg/ml of dispase (Thermo Fisher Scientific, Waltham, MA, http://www/thermofisher.com).…”

“…Six Fah−/− Fah−/−Rag2−/−Il2rg−/−Arg flox/flox UBC‐Cre/ERT2 female mice were implanted with 6 implants each derived from Actin GFP mice . Six weeks later, 100 μl tamoxifen (20 mg/ml) (Sigma‐Aldrich), prepared in corn oil, was administered by oral gavage for 10 days.…”

Mutations and common variants in the human arginase 1 (ARG1) gene: Impact on patients, diagnostics, and protein structure considerations

“…To determine if a later onset of ARGD also resulted in death, two inducible ARG1‐deficient mouse models were created using the Cre/loxP‐directed conditional gene KO system (Kasten et al., ; Sin et al., ). Mice died ∼2 weeks after tamoxifen‐induction, regardless of the starting age of inducing the KO (Kasten et al., ; Sin et al., ).…”

Restoring Ureagenesis in Hepatocytes by CRISPR/Cas9-mediated Genomic Addition to Arginase-deficient Induced Pluripotent Stem Cells

“…Instead, the cause of the pathogenesis of neurological deterioration in arginase deficiency is not known and is thought to be due to unique biochemical abnormalities such as elevated guanidino compounds, nitric oxide, or glutamine. 3,8,9,10 …”