Therapeutic AASS inhibition by AAV-miRNA rescues glutaric aciduria type I severe phenotype in mice

Glutaric aciduria type I (GA1) is an inherited disorder caused by the enzymatic defect of glutaryl-coenzyme A dehydrogenase in the lysine degradation pathway, characterized by the accumulation of toxic metabolites in the central nervous system. We reasoned that substrate reduction therapy targeting the α-aminoadipic semialdehyde synthase (AASS), the first enzyme in the catabolism of lysine, could provide an attractive therapeutic alternative. We explored reducing the expression of AASS by an artificial microRNA with AASS target sequences embedded in a miR-16 backbone (miR_AASS). We analyzed several delivery routes and AAV serotypes and evaluated the therapeutic efficacy of a systemic neonatal delivery of AAV9_miR_AASS in the Gcdh^-/- mouse model of GA1. We detected dose-dependent miR-AASS expression and AASS inhibition in liver and striatum, the main tissues affected in GA1. Treatment with AAV9_miR_AASS in lysine overload-challenged mice reduced the accumulation of neurotoxic metabolites up to 6 months post-treatment in the striatum, prevented the neuropathological alterations, and improved mouse survival. Our results show that AAV9_miR_AASS supports AASS lowering as a potential gene therapy strategy for GA1.