New personalized genetic mouse model of Lesch-Nyhan syndrome for pharmacology and gene therapy

CRISPR/Cas9-generated mouse model with humanizing single-base substitution in the Gnao1 for safety studies of RNA therapeutics

The development of personalized medicine for genetic diseases requires preclinical testing in the appropriate animal models. GNAO1 encephalopathy is a severe neurodevelopmental disorder caused by heterozygous de novo mutations in the GNAO1 gene. GNAO1 c.607 G>A is one of the most common pathogenic variants, and the mutant protein Gαo-G203R likely adversely affects neuronal signaling. As an innovative approach, sequence-specific RNA-based therapeutics such as antisense oligonucleotides or effectors of RNA interference are potentially applicable for selective suppression of the mutant GNAO1 transcript. While in vitro validation can be performed in patient-derived cells, a humanized mouse model to rule out the safety of RNA therapeutics is currently lacking. In the present work, we employed CRISPR/Cas9 technology to introduce a single-base substitution into exon 6 of the Gnao1 to replace the murine Gly203-coding triplet (GGG) with the codon used in the human gene (GGA). We verified that genome-editing did not interfere with the Gnao1 mRNA or Gαo protein synthesis and did not alter localization of the protein in the brain structures. The analysis of blastocysts revealed the off-target activity of the CRISPR/Cas9 complexes; however, no modifications of the predicted off-target sites were detected in the founder mouse. Histological staining confirmed the absence of abnormal changes in the brain of genome-edited mice. The created mouse model with the “humanized” fragment of the endogenous Gnao1 is suitable to rule out unintended targeting of the wild-type allele by RNA therapeutics directed at lowering GNAO1 c.607 G>A transcripts.

HPRT1 Deficiency Induces Alteration of Mitochondrial Energy Metabolism in the Brain

Alterations in function of hypoxanthine guanine phosphoribosyl transferase (HPRT), one of the major enzymes involved in purine nucleotide exchange, lead to overproduction of uric acid and produce various symptoms of Lesch-Nyhan syndrome (LNS). One of the hallmarks of LNS is maximal expression of HPRT in the central nervous system with the highest activity of this enzyme in the midbrain and basal ganglia. However, the nature of neurological symptoms has yet to be clarified in details. Here, we studied whether HPRT1 deficiency changes mitochondrial energy metabolism and redox balance in murine neurons from the cortex and midbrain. We found that HPRT1 deficiency inhibits complex I-dependent mitochondrial respiration resulting in increased levels of mitochondrial NADH, reduction of the mitochondrial membrane potential, and increased rate of reactive oxygen species (ROS) production in mitochondria and cytosol. However, increased ROS production did not induce oxidative stress and did not decrease the level of endogenous antioxidant glutathione (GSH). Thus, disruption of mitochondrial energy metabolism but not oxidative stress could play a role of potential trigger of brain pathology in LNS.