Artificial miRNA-mediated reduction of SNCA for the treatment of α-synucleinopathies

Multiple lines of genetic and neuropathological evidence strongly implicate α-synuclein (αSyn) as a causal factor in synucleinopathies like Parkinson disease (PD), with numerous studies supporting the therapeutic concept of αSyn reduction as a disease-modifying strategy. Artificial miRNAs can be durably expressed from adeno-associated viral (AAV) vectors and have shown increasing promise as a highly specific modality to reduce levels of target mRNA. This modality is therefore well suited for the long-term treatment of PD and related diseases. Here, we assessed the therapeutic potential of the partial reduction of αSyn by AAV-mediated artificial microRNA (amiRNA) expression by using the pre-formed fibril model of α-synucleinopathy to induce the seeding and spreading of αSyn pathology in wild-type animals. We demonstrate that a 50% decrease in endogenous SNCA mRNA levels is sufficient to fully block the spread of pathogenic αSyn protein and prevent the loss of dopaminergic neurons in the substantia nigra. To support clinical translation, human-specific amiRNAs were designed and evaluated in vitro and in vivo. Concatenation of amiRNAs was evaluated to optimize the potency of individual guide sequences. Several candidates had excellent expression, processing, and SNCA reduction, supporting the continued development of αSyn-lowering therapeutics as a safe and efficacious approach for treating patients with synucleinopathies.