Brain region-resolved pharmacodynamics of an antisense oligonucleotide targeting human SNCA 3′UTR in BAC-hSNCA rats

Abstract Background Alpha-synuclein accumulation contributes to Parkinson’s disease (PD), and lowering α-synuclein expression is a candidate disease-modifying approach. The brain-wide pharmacodynamic profile of human-targeting antisense oligonucleotides (ASOs) remains incompletely defined in humanized models that preserve the regulatory architecture of the human SNCA locus. Methods BAC-h SNCA rats were treated at an early stage, when human α-synuclein is elevated, but striatal dopamine content remains largely preserved. A single intracerebroventricular dose of an ASO targeting human SNCA 3′UTR (SNCA ASO3.0) was administered, and outcomes were assessed 45 days later by isoform-specific RT-qPCR, immunoblotting of soluble and detergent-insoluble α-synuclein species, bulk RNA-seq across selected regions, multiplex cytokine profiling, phospho-kinase assays, neurotransmitter quantification, and behavioral testing. Results SNCA ASO3.0 reduced human SNCA mRNA and multiple α-synuclein protein species in a regionally graded manner, with the strongest effects in the olfactory bulb and striatum. Bulk RNA-seq identified anatomically distinct transcriptional responses, including synaptic and metabolic pathway shifts in the olfactory bulbs and immune-related enrichment within glial signatures in the striatum and midbrain, without detectable changes in protein levels of glial fibrillary acidic protein or ionized calcium-binding adapter molecule 1. Cytokine profiling showed selective modulation of a subset of analytes, and phospho-kinase assays indicated reduced AKT1S1/PRAS40 phosphorylation. Striatal dopamine levels were unchanged, whereas the striatal tyrosine hydroxylase level was increased. SNCA ASO3.0 increased locomotor activity and improved exploratory behavior and selected measures of olfactory discrimination. Conclusions Partial suppression of human α-synuclein in a humanized rat model yields region-specific molecular adaptations accompanied by early behavioral changes at a stage preceding overt dopamine depletion. These data provide a framework for evaluating region-resolved consequences of α-synuclein-lowering interventions in synucleinopathies.