Engineering Therapeutics for Glutaric Aciduria Type I

Abstract

Glutaric Aciduria Type I is a serious metabolic disorder caused by a deficiency in Glutaryl-CoA Dehydrogenase (GCDH), a crucial enzyme in the lysine and tryptophan degradation pathway. The deficiency of GCDH prevents the breakdown of these amino acids, resulting in the accumulation of organic acids in the brain, leading to striatal injury and movement disorders if untreated. Early detection, strict dietary control, and emergency interventions can reduce the risk of severe cerebral injury. Nevertheless, complex movement disorders can still occur in one-third of patients despite treatment. Moreover, GA-1 patients require intensive and specialized care to prevent encephalopathic crisis and the irreversible brain damage associated with the crisis. Therefore, there is a need for a targeted, effective therapy that can prevent severe diseases and reduce the burden of GA-1 care. We previously showed that restoring a normal lysine catabolism in the liver of adult Gcdh-/- mice is sufficient to rescue the lethality and the neurological phenotype. Moreover, liver-specific CRISPR-mediated deletion of Aminoadipic 6-Semialdehyde Synthase (AASS), upstream of GCDH in lysine degradation, revealed a novel therapeutic strategy for GA-1. In this dissertation, I will explore several potential liver targeting platforms for a clinically relevant GA-1 therapy: messenger RNA (mRNA), antisense oligonucleotide (ASO), and small interfering RNA (siRNA). Utilizing in vitro assays and a Gcdh-/- mouse model, I evaluated all 3 platforms in their efficacy to reduce organic acid buildup and rescue the lethality of the animal model. In this work, we showed that both mRNA and ASO showed moderate success in restoring lysine metabolism, but immune responses and expression levels limit mRNA efficacy, and the in vivo efficacy of ASOs is yet to be evaluated. Lastly, a N-acetylgalactosamine (GalNAc) conjugated siRNA showed the most success both in vitro and in vivo, rescuing both neonatal and adult Gcdh-/- mice, reducing organic acid in relevant compartments, and effectively eliminating the brain phenotype. In conclusion, while all three platforms showed promise, a liver-targeted siRNA therapy is an effective treatment for the GA-1 mouse model. These findings hold promise for an effective targeted therapy for GA-1 patients.