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Down syndrome (DS) significantly increases the risk of Alzheimer's disease (DS-AD), with dysfunctions in the endolysosomal network (ELN) and autophagy pathways playing central roles in its pathogenesis. Dysregulation of the ELN, particularly involving RAB5 and lysosomal cathepsins, has been implicated in DS-AD, but the specific role of RAB5 hyperactivation remains poorly understood. Postmortem brain samples from individuals with DS, DS-AD, a partial trisomy 21 case, and the Dp16 DS mouse model were examined to assess the impact of APP gene dosage on ELN and autophagy. We measured RAB5 activation, the activity of RAB7 and RAB11, their guanine nucleotide exchange factors (GEFs), lysosomal cathepsins, and autophagy-related pathways. Additionally, Dp16 mice were treated with App- and Rab5-specific antisense oligonucleotides (ASOs) to evaluate their therapeutic potential. Our findings revealed substantial ELN dysfunction in both DS and Dp16 brains, characterized by RAB5 hyperactivation, increased RAB7 and RAB11 activation, elevated levels of their GEFs, and increased lysosomal cathepsin levels-all in an APP dose-dependent manner. Reduced expression of TSC1/2 and hyperphosphorylation of mTOR were associated with impaired autophagy. These abnormalities were absent in a partial trisomy 21 individual with two copies of APP. Treatment with ASOs in Dp16 mice restored RAB5 activity, normalized ELN function, and improved autophagic flux, alleviating DS-AD-related pathologies including tau hyperphosphorylation, neurotrophin signaling deficits, and synaptic protein loss. Our results demonstrate that APP dose-driven RAB5 hyperactivation disrupts endosomal Rab cascades, endosome maturation, and autophagy function in DS. Targeting either APP or Rab5 may offer promising therapeutic strategies to restore cellular function and mitigate DS-AD pathologies.

Degeneration of the neuromuscular system is a characteristic feature of spinal and bulbar muscular atrophy (SBMA), a CAG/polyglutamine (polyQ) expansion disorder caused by mutation in the androgen receptor (AR). Using a gene-targeted mouse model of SBMA, AR113Q mice, we demonstrate age-dependent degeneration of the neuromuscular system that initially manifests with muscle weakness and atrophy and progresses to include denervation of neuromuscular junctions and lower motor neuron soma atrophy. Using this model, we tested the hypothesis that therapeutic intervention targeting skeletal muscle during this period of disease progression arrests degeneration of the neuromuscular system. To accomplish this, AR-targeted antisense oligonucleotides were administered subcutaneously to symptomatic AR113Q mice to reduce expression of polyQ AR in peripheral tissues but not in the spinal cord. This intervention rescued muscle atrophy, neuromuscular junction innervation, lower motor neuron soma size, and survival in aged AR113Q mice. Single-nucleus RNA sequencing revealed age-dependent transcriptional changes in the AR113Q spinal cord during disease progression, which were mitigated by peripheral AR gene silencing. Our findings underscore the intricate interplay between peripheral tissues and the central nervous system in SBMA and emphasize the therapeutic effectiveness of peripheral gene knockdown in symptomatic disease.

Mutations in PLP1 , the gene that encodes proteolipid protein (PLP), result in failure of myelination and neurological dysfunction in the X-chromosome-linked leukodystrophy Pelizaeus–Merzbacher disease (PMD) 1 , 2 . Most PLP1 mutations, including point mutations and supernumerary copy variants, lead to severe and fatal disease. Patients who lack PLP1 expression, and Plp1 -null mice, can display comparatively mild phenotypes, suggesting that PLP1 suppression might provide a general therapeutic strategy for PMD 1 , 3 – 5 . Here we show, using CRISPR–Cas9 to suppress Plp1 expression in the jimpy ( Plp1 jp ) point-mutation mouse model of severe PMD, increased myelination and restored nerve conduction velocity, motor function and lifespan of the mice to wild-type levels. To evaluate the translational potential of this strategy, we identified antisense oligonucleotides that stably decrease the levels of Plp1 mRNA and PLP protein throughout the neuraxis in vivo. Administration of a single dose of Plp1 -targeting antisense oligonucleotides in postnatal jimpy mice fully restored oligodendrocyte numbers, increased myelination, improved motor performance, normalized respiratory function and extended lifespan up to an eight-month end point. These results suggest that PLP1 suppression could be developed as a treatment for PMD in humans. More broadly, we demonstrate that oligonucleotide-based therapeutic agents can be delivered to oligodendrocytes in vivo to modulate neurological function and lifespan, establishing a new pharmaceutical modality for myelin disorders. In a mouse model of the leukodystrophy Pelizaeus–Merzbacher disease, myelination, motor performance, respiratory function and lifespan are improved by suppressing proteolipid protein expression, suggesting PLP1 as a therapeutic target for human patients with this disease and, more broadly, antisense oligonucleotides as a pharmaceutical modality for treatment of myelin disorders.

Autosomal dominant pathogenic mutations in Leucine-rich repeat kinase 2 (LRRK2) cause Parkinson’s disease (PD). The most common mutation, G2019S-LRRK2, increases the kinase activity of LRRK2 causing hyper-phosphorylation of its substrates. One of these substrates, Rab10, is phosphorylated at a conserved Thr73 residue (pRab10), and is one of the most abundant LRRK2 Rab GTPases expressed in various tissues. The involvement of Rab10 in neurodegenerative disease, including both PD and Alzheimer’s disease makes pinpointing the cellular and subcellular localization of Rab10 and pRab10 in the brain an important step in understanding its functional role, and how post-translational modifications could impact function. To establish the specificity of antibodies to the phosphorylated form of Rab10 (pRab10), Rab10 specific antisense oligonucleotides were intraventricularly injected into the brains of mice. Further, Rab10 knock out induced neurons, differentiated from human induced pluripotent stem cells were used to test the pRab10 antibody specificity. To amplify the weak immunofluorescence signal of pRab10, tyramide signal amplification was utilized. Rab10 and pRab10 were expressed in the cortex, striatum and the substantia nigra pars compacta. Immunofluorescence for pRab10 was increased in G2019S-LRRK2 knockin mice. Neurons, astrocytes, microglia and oligodendrocytes all showed Rab10 and pRab10 expression. While Rab10 colocalized with endoplasmic reticulum, lysosome and trans-Golgi network markers, pRab10 did not localize to these organelles. However, pRab10, did overlap with markers of the presynaptic terminal in both mouse and human cortex, including α-synuclein. Results from this study suggest Rab10 and pRab10 are expressed in all brain areas and cell types tested in this study, but pRab10 is enriched at the presynaptic terminal. As Rab10 is a LRRK2 kinase substrate, increased kinase activity of G2019S-LRRK2 in PD may affect Rab10 mediated membrane trafficking at the presynaptic terminal in neurons in disease.

Parkinson's disease (PD) is a prevalent neurodegenerative disease with no approved disease-modifying therapies. Multiplications, mutations, and single nucleotide polymorphisms in the SNCA gene, encoding α-synuclein (aSyn) protein, either cause or increase risk for PD. Intracellular accumulations of aSyn are pathological hallmarks of PD. Taken together, reduction of aSyn production may provide a disease-modifying therapy for PD. We show that antisense oligonucleotides (ASOs) reduce production of aSyn in rodent preformed fibril (PFF) models of PD. Reduced aSyn production leads to prevention and removal of established aSyn pathology and prevents dopaminergic cell dysfunction. In addition, we address the translational potential of the approach through characterization of human SNCA-targeting ASOs that efficiently suppress the human SNCA transcript in vivo. We demonstrate broad activity and distribution of the human SNCA ASOs throughout the nonhuman primate brain and a corresponding decrease in aSyn cerebral spinal fluid (CSF) levels. Taken together, these data suggest that, by inhibiting production of aSyn, it may be possible to reverse established pathology; thus, these data support the development of SNCA ASOs as a potential disease-modifying therapy for PD and related synucleinopathies.

No treatments exist to slow or halt Parkinson’s disease (PD) progression; however, inhibition of leucine-rich repeat kinase 2 (LRRK2) activity represents one of the most promising therapeutic strategies. Genetic ablation and pharmacological LRRK2 inhibition have demonstrated promise in blocking α-synuclein (α-syn) pathology. However, LRRK2 kinase inhibitors may reduce LRRK2 activity in several tissues and induce systemic phenotypes in the kidney and lung that are undesirable. Here, we test whether antisense oligonucleotides (ASOs) provide an alternative therapeutic strategy, as they can be restricted to the CNS and provide a stable, long-lasting reduction of protein throughout the brain. Administration of LRRK2 ASOs to the brain reduces LRRK2 protein levels and fibril-induced α-syn inclusions. Mice exposed to α-syn fibrils treated with LRRK2 ASOs show more tyrosine hydroxylase (TH)-positive neurons compared to control mice. Furthermore, intracerebral injection of LRRK2 ASOs avoids unwanted phenotypes associated with loss of LRRK2 expression in the periphery. This study further demonstrates that a reduction of endogenous levels of normal LRRK2 reduces the formation of α-syn inclusions. Importantly, this study points toward LRRK2 ASOs as a potential therapeutic strategy for preventing PD-associated pathology and phenotypes without causing potential adverse side effects in peripheral tissues associated with LRRK2 inhibition. Antisense oligonucleotides targeting LRRK2 mRNA for degradation in the brain can attenuate α-synuclein inclusion formation and neurodegeneration caused by exposure to pre-formed α-synuclein fibrils, while bypassing the adverse systemic effects in the kidney and lung that are associated with the loss of LRRK2 expression in the periphery.

Prion protein (PrP) concentration controls the kinetics of prion replication and is a genetically and pharmacologically validated therapeutic target for prion disease. In order to evaluate PrP concentration as a pharmacodynamic biomarker and assess its contribution to known prion disease risk factors, we developed and validated a plate-based immunoassay reactive for PrP across 6 species of interest and applicable to brain and cerebrospinal fluid (CSF). PrP concentration varied dramatically across different brain regions in mice, cynomolgus macaques, and humans. PrP expression did not appear to contribute to the known risk factors of age, sex, or common PRNP genetic variants. CSF PrP was lowered in the presence of rare pathogenic PRNP variants, with heterozygous carriers of P102L displaying 55%, and D178N just 31%, of the CSF PrP concentration of mutation-negative controls. In rodents, pharmacologic reduction of brain Prnp RNA was reflected in brain parenchyma PrP and, in turn in CSF PrP, validating CSF as a sampling compartment for the effect of PrP-lowering therapy. Our findings support the use of CSF PrP as a pharmacodynamic biomarker for PrP-lowering drugs and suggest that relative reduction from individual baseline CSF PrP concentration may be an appropriate marker for target engagement.

Antisense oligonucleotides (ASOs) designed to lower prion protein (PrP) expression in the brain through RNase H1-mediated degradation of PrP RNA are in development as prion disease therapeutics. ASOs were previously reported to sequence-independently interact with PrP and inhibit prion accumulation in cell culture, yet in vivo studies using a new generation of ASOs found that only PrP-lowering sequences were effective at extending survival. Cerebrospinal fluid (CSF) PrP has been proposed as a pharmacodynamic biomarker for trials of such ASOs, but is only interpretable if PrP lowering is indeed the relevant mechanism of action in vivo and if measurement of PrP is unconfounded by any PrP–ASO interaction. Here, we examine the PrP-binding and antiprion properties of ASOs in vitro and in cell culture. Binding parameters determined by isothermal titration calorimetry were similar across all ASOs tested, indicating that ASOs of various chemistries bind full-length recombinant PrP with low- to mid-nanomolar affinity in a sequence-independent manner. Nuclear magnetic resonance, dynamic light scattering, and visual inspection of ASO–PrP mixtures suggested, however, that this interaction is characterized by the formation of large aggregates, a conclusion further supported by the salt dependence of the affinity measured by isothermal titration calorimetry. Sequence-independent inhibition of prion accumulation in cell culture was observed. The inefficacy of non-PrP-lowering ASOs against prion disease in vivo may be because their apparent activity in vitro is an artifact of aggregation, or because the concentration of ASOs in relevant compartments within the central nervous system (CNS) quickly drops below the effective concentration for sequence-independent antiprion activity after bolus dosing into CSF. Measurements of PrP concentration in human CSF were not impacted by the addition of ASO. These findings support the further development of PrP-lowering ASOs and of CSF PrP as a pharmacodynamic biomarker.

Background Down syndrome (DS) significantly increases the risk of Alzheimer's disease (DS‐AD), with dysfunctions in the endolysosomal network (ELN) and autophagy pathways playing central roles in its pathogenesis. Dysregulation of the ELN, particularly involving RAB5 and lysosomal cathepsins, has been implicated in DS‐AD, but the specific role of RAB5 hyperactivation remains poorly understood. Methods Postmortem brain samples from individuals with DS, DS‐AD, a partial trisomy 21 case, and the Dp16 DS mouse model were examined to assess the impact of APP gene dosage on ELN and autophagy. We measured RAB5 activation, the activity of RAB7 and RAB11, their guanine nucleotide exchange factors (GEFs), lysosomal cathepsins, and autophagy‐related pathways. Additionally, Dp16 mice were treated with App‐ and Rab5‐specific antisense oligonucleotides (ASOs) to evaluate their therapeutic potential. Results Our findings revealed substantial ELN dysfunction in both DS and Dp16 brains, characterized by RAB5 hyperactivation, increased RAB7 and RAB11 activation, elevated levels of their GEFs, and increased lysosomal cathepsin levels—all in an APP dose‐dependent manner. Reduced expression of TSC1/2 and hyperphosphorylation of mTOR were associated with impaired autophagy. These abnormalities were absent in a partial trisomy 21 individual with two copies of APP. Treatment with ASOs in Dp16 mice restored RAB5 activity, normalized ELN function, and improved autophagic flux, alleviating DS‐AD‐related pathologies including tau hyperphosphorylation, neurotrophin signaling deficits, and synaptic protein loss. Conclusion Our results demonstrate that APP dose‐driven RAB5 hyperactivation disrupts endosomal Rab cascades, endosome maturation, and autophagy function in DS. Targeting either APP or Rab5 may offer promising therapeutic strategies to restore cellular function and mitigate DS‐AD pathologies.

Degeneration of the neuromuscular system is a characteristic feature of spinal and bulbar muscular atrophy (SBMA), a CAG/ polyglutamine (polyQ) expansion disorder caused by mutation in the androgen receptor (AR). Using a gene-targeted mouse model of SBMA, AR113Q mice, we demonstrate age-dependent degeneration of the neuromuscular system that initially manifests with muscle weakness and atrophy and progresses to include denervation of neuromuscular junctions and lower motor neuron soma atrophy. Using this model, we tested the hypothesis that therapeutic intervention targeting skeletal muscle during this period of disease progression arrests degeneration of the neuromuscular system. To accomplish this, ARtargeted antisense oligonucleotides were administered subcutaneously to symptomatic AR113Q mice to reduce expression of polyQ AR in peripheral tissues but not in the spinal cord. This intervention rescued muscle atrophy, neuromuscular junction innervation, lower motor neuron soma size, and survival in aged AR113Q mice. Single-nucleus RNA sequencing revealed agedependent transcriptional changes in the AR113Q spinal cord during disease progression, which were mitigated by peripheral AR gene silencing. Our findings underscore the intricate interplay between peripheral tissues and the central nervous system in SBMA and emphasize the therapeutic effectiveness of peripheral gene knockdown in symptomatic disease.