Amyotrophic lateral sclerosis (ALS) is a rapidly progressing neurodegenerative disease characterized by motor neuron loss, leading to paralysis and death 2–5 years following disease onset1. Nearly all ALS patients contain aggregates of the RNA-binding protein TDP-43 in the brain and spinal cord2, and rare mutations in the gene encoding TDP-43 can cause ALS3. There are no effective TDP-43-directed therapies for ALS or related TDP-43 proteinopathies, such as frontotemporal dementia (FTD). Antisense oligonucleotides (ASOs) and RNA interference approaches are emerging as attractive therapeutic strategies in neurological diseases4. Indeed, treating a rodent model of inherited ALS (caused by a mutation in SOD1) with ASOs to SOD1 significantly slowed disease progression5. But since SOD1 mutations account for only ~2–5% of ALS cases, additional therapeutic strategies are needed. Silencing TDP-43 itself is probably not warranted given its critical cellular functions1,6 Here we present an unexpectedly powerful alternative therapeutic strategy for ALS, by targeting ataxin 2. Lowering ataxin 2 suppresses TDP-43 toxicity in yeast and flies7, and intermediate-length polyglutamine expansions in the ataxin 2 gene increase risk of ALS7,8. We used two independent approaches to test whether reducing ataxin 2 levels could mitigate disease in a mouse model of TDP-43 proteinopathy9. First, we crossed ataxin 2 knockout mice to TDP-43 transgenic mice. Lowering ataxin 2 reduced TDP-43 aggregation, had a dramatic effect on survival and improved motor function. Second, in a more therapeutically applicable approach, we administered ASOs targeting ataxin 2 to the central nervous system of TDP-43 mice. This single treatment markedly extended survival. Because TDP-43 aggregation is a component of nearly all ALS cases6, targeting ataxin 2 could represent a broadly effective therapeutic strategy.

The comprehensive structure-activity relationships of triantennary GalNAc conjugated ASOs for enhancing potency via ASGR mediated delivery to hepatocytes is reported. Seventeen GalNAc clusters were assembled from six distinct scaffolds and attached to ASOs. The resulting ASO conjugates were evaluated in ASGR binding assays, in primary hepatocytes, and in mice. Five structurally distinct GalNAc clusters were chosen for more extensive evaluation using ASOs targeting SRB-1, A1AT, FXI, TTR, and ApoC III mRNAs. GalNAc-ASO conjugates exhibited excellent potencies (ED50 0.5-2 mg/kg) for reducing the targeted mRNAs and proteins. This work culminated in the identification of a simplified tris-based GalNAc cluster (THA-GN3), which can be efficiently assembled using readily available starting materials and conjugated to ASOs using a solution phase conjugation strategy. GalNAc-ASO conjugates thus represent a viable approach for enhancing potency of ASO drugs in the clinic without adding significant complexity or cost to existing protocols for manufacturing oligonucleotide drugs.

Antisense oligonucleotides (ASOs) have emerged as a new class of drugs to treat a wide range of diseases, including neurological indications. Spinraza, an ASO that modulates splicing of SMN2 RNA, has shown profound disease modifying effects in Spinal Muscular Atrophy (SMA) patients, energizing efforts to develop ASOs for other neurological diseases. While SMA specifically affects spinal motor neurons, other neurological diseases affect different central nervous system (CNS) regions, neuronal and non-neuronal cells. Therefore, it is important to characterize ASO distribution and activity in all major CNS structures and cell types to have a better understanding of which neurological diseases are amenable to ASO therapy. Here we present for the first time the atlas of ASO distribution and activity in the CNS of mice, rats, and non-human primates (NHP), species commonly used in preclinical therapeutic development. Following central administration of an ASO to rodents, we observe widespread distribution and target RNA reduction throughout the CNS in neurons, oligodendrocytes, astrocytes and microglia. This is also the case in NHP, despite a larger CNS volume and more complex neuroarchitecture. Our results demonstrate that ASO drugs are well suited for treating a wide range of neurological diseases for which no effective treatments are available.

Author contributionsML, NJ, PJN, and LEB designed and carried out experiments, performed data analyses, and drafted the manuscript. B Rollo, S Pachernegg, A Sedo, and JH performed qPCR experiments and analyses. KR and A Sedo performed immunohistochemistry experiments and analyses. LD and LJ performed behavioral experiments and analyses. TB and B Roberts performed mass spectrometry experiments and analyses. A Soriano, AN, KD, SM, CAR, FR, and S Petrou designed and coordinated the study. All authors read and contributed to the revision of manuscript.

Therapeutic strategies are needed for the treatment of amyotrophic lateral sclerosis (ALS). One potential target is matrix metalloproteinase-9 (MMP-9), which is expressed only by fast motor neurons (MNs) that are selectively vulnerable to various ALS-relevant triggers. Previous studies have shown that reduction of MMP-9 function delayed motor dysfunction in a mouse model of familial ALS. However, given that the majority of ALS cases are sporadic, we propose preclinical testing in a mouse model which may be more clinically translatable: rNLS8 mice. In rNLS8 mice, neurodegeneration is triggered by the major pathological hallmark of ALS, TDP-43 mislocalization and aggregation. MMP-9 was targeted in 3 different ways in rNLS8 mice: by AAV9-mediated knockdown, using antisense oligonucleotide (ASO) technology, and by genetic modification. All 3 strategies preserved the motor unit during disease, as measured by MN counts, tibialis anterior (TA) muscle innervation, and physiological recordings from muscle. However, the strategies that reduced MMP-9 beyond the motor unit lead to premature deaths in a subset of rNLS8 mice. Therefore, selective targeting of MMP-9 in MNs could be beneficial in ALS, but side effects outside of the motor circuit may limit the most commonly used clinical targeting strategies.