Selective α-Synuclein Knockdown in Monoamine Neurons by Intranasal Oligonucleotide Delivery: Potential Therapy for Parkinson’s Disease

Abstract

Progressive neuronal death in brainstem nuclei and widespread accumulation of α-synuclein are neuropathological hallmarks of Parkinson's disease (PD). Reduction of α-synuclein levels is therefore a potential therapy for PD. However, because α-synuclein is essential for neuronal development and function, α-synuclein elimination would dramatically impact brain function. We previously developed conjugated small interfering RNA (siRNA) sequences that selectively target serotonin (5-HT) or norepinephrine (NE) neurons after intranasal administration. Here, we used this strategy to conjugate inhibitory oligonucleotides, siRNA and antisense oligonucleotide (ASO), with the triple monoamine reuptake inhibitor indatraline (IND), to selectively reduce α-synuclein expression in the brainstem monoamine nuclei of mice after intranasal delivery. Following internalization of the conjugated oligonucleotides in monoamine neurons, reduced levels of endogenous α-synuclein mRNA and protein were found in substantia nigra pars compacta (SNc), ventral tegmental area (VTA), dorsal raphe nucleus (DR), and locus coeruleus (LC). α-Synuclein knockdown by ∼20%-40% did not cause monoaminergic neurodegeneration and enhanced forebrain dopamine (DA) and 5-HT release. Conversely, a modest human α-synuclein overexpression in DA neurons markedly reduced striatal DA release. These results indicate that α-synuclein negatively regulates monoamine neurotransmission and set the stage for the testing of non-viral inhibitory oligonucleotides as disease-modifying agents in α-synuclein models of PD.

Regionally selective knockdown of astroglial glutamate transporters in infralimbic cortex induces a depressive phenotype in mice

“…In cell cultures, delivery agents (such as cationic lipids or polymers) are required to achieve significant siRNA effects(Juliano, Alam, Dixit, & Kang, 2008). However, small amounts of naked nonviral siRNAs efficiently knockdown gene expression in vivo(Alarcón-Arís et al, 2018;Cryan, Thakker, & Hoyer, 2007;Ferrés-Coy, Pilar-Cuellar et al, 2013;…”

Targeting α-Synuclein for PD Therapeutics: A Pursuit on All Fronts

“…Using this non-invasive methodology, they succeeded in silencing human SNCA by 60% in four mice brain regions (hippocampus, SN, olfactory bulb and dorsal motor nucleus) after systemic delivery of AAV-shSNCA vectors through the tail vein of transgenic mice overexpressing human SNCA, with no deleterious side effects [103]. Another group proposed the use of intranasal delivery-a semi-permeable BBB region-of antisense oligonucleotide against SNCA conjugated with indatraline, a triple monoamine transporter blocker with differential affinities, to specifically target monoamine neurons involved in PD pathology [104]. They obtained a time-dependent knockdown of α-syn specifically in serotoninergic and dopaminergic neurons of the SN, the ventral tegmental area, the putamen, the caudate and the locus coeruleus [104].…”

“…Another group proposed the use of intranasal delivery-a semi-permeable BBB region-of antisense oligonucleotide against SNCA conjugated with indatraline, a triple monoamine transporter blocker with differential affinities, to specifically target monoamine neurons involved in PD pathology [104]. They obtained a time-dependent knockdown of α-syn specifically in serotoninergic and dopaminergic neurons of the SN, the ventral tegmental area, the putamen, the caudate and the locus coeruleus [104]. Finally, a non-viral vector approach was developed based on the systemic injection of a small peptide derived from the envelope protein of the rabies virus (C2-9r) complexed with siRNA targeting α-syn in MPTP-mice [105].…”

Antisense therapies for movement disorders

“…Additionally, lowering LRRK2 expression in an α‐synuclein PD mouse model reduced α‐synuclein aggregations in relevant CNS tissues . Some efforts have also been made to develop an ASO therapeutic targeting α‐synuclein directly for PD . Uehara and colleagues used gapmer‐type ASOs containing amido‐bridged nucleic acid.…”

“…68 Some efforts have also been made to develop an ASO therapeutic targeting α-synuclein directly for PD. 69 Uehara and colleagues used gapmer-type ASOs containing amido-bridged nucleic acid. This novel LNA analogue, based on a cyclic amide structure, showed high nuclease resistance and binding affinities toward complementary strands.…”