A programmable dual-targeting siRNA scaffold supports potent two-gene modulation in the central nervous system

Divalent short-interfering RNA (siRNA) holds promise as a therapeutic approach allowing for the sequence-specific modulation of a target gene within the central nervous system (CNS). However, an siRNA modality capable of simultaneously modulating gene pairs would be invaluable for treating complex neurodegenerative disorders, where more than one pathway contributes to pathogenesis. Currently, the parameters and scaffold considerations for multi-targeting nucleic acid modalities in the CNS are undefined. Here, we propose a framework for designing unimolecular 'dual-targeting' divalent siRNAs capable of co-silencing two genes in the CNS. We systematically adjusted the original CNS-active divalent siRNA and identified that connecting two sense strands 3' and 5' through an intra-strand linker enabled a functional dual-targeting scaffold, greatly simplifying the synthetic process. Our findings demonstrate that the dual-targeting siRNA supports at least two months of maximal distribution and target silencing in the mouse CNS. The dual-targeting divalent siRNA is highly programmable, enabling simultaneous modulation of two different disease-relevant gene pairs (e.g. Huntington's disease: MSH3 and HTT; Alzheimer's disease: APOE and JAK1) with similar potency to a mixture of single-targeting divalent siRNAs against each gene. This work enhances the potential for CNS modulation of disease-related gene pairs using a unimolecular siRNA.

More than 185 CAG repeats: a point of no return in Huntington's disease biology

This scientific commentary refers to ‘A CAG repeat threshold for therapeutics targeting somatic instability in Huntington’s disease’ by Aldous et al. (https://doi.org/10.1093/brain/awae063).

Nucleic Acid Therapeutics: Successes, Milestones, and Upcoming Innovation

Nucleic acid-based therapies have become the third major drug class after small molecules and antibodies. The role of nucleic acid-based therapies has been strengthened by recent regulatory approvals and tremendous clinical success. In this review, we look at the major obstacles that have hindered the field, the historical milestones that have been achieved, and what is yet to be resolved and anticipated soon. This review provides a view of the key innovations that are expanding nucleic acid capabilities, setting the stage for the future of nucleic acid therapeutics.

A programmable dual-targeting di-valent siRNA scaffold supports potent multi-gene modulation in the central nervous system

Di-valent short interfering RNA (siRNA) is a promising therapeutic modality that enables sequence-specific modulation of a single target gene in the central nervous system (CNS). To treat complex neurodegenerative disorders, where pathogenesis is driven by multiple genes or pathways, di-valent siRNA must be able to silence multiple target genes simultaneously. Here we present a framework for designing unimolecular "dual-targeting" di-valent siRNAs capable of co-silencing two genes in the CNS. We reconfigured di-valent siRNA - in which two identical, linked siRNAs are made concurrently - to create linear di-valent siRNA - where two siRNAs are made sequentially attached by a covalent linker. This linear configuration, synthesized using commercially available reagents, enables incorporation of two different siRNAs to silence two different targets. We demonstrate that this dual-targeting di-valent siRNA is fully functional in the CNS of mice, supporting at least two months of maximal target silencing. Dual-targeting di-valent siRNA is highly programmable, enabling simultaneous modulation of two different disease-relevant gene pairs (e.g., Huntington's disease: MSH3 and HTT; Alzheimer's disease: APOE and JAK1) with similar potency to a mixture of single-targeting di-valent siRNAs against each gene. This work potentiates CNS modulation of virtually any pair of disease-related targets using a simple unimolecular siRNA.

COVID-19 in the intensive care unit: Unmasking the critical factors impacting patient survival

In the midst of the coronavirus disease 2019 (COVID-19) pandemic, intensive care units (ICUs) around the world have been pushed to their limits as they grapple with the effects of the severe acute respiratory syndrome coronavirus 2 virus. Identifying prognostic factors that influence mortality in COVID-19 patients admitted to the ICU could offer valuable insights for clinicians seeking to prevent disease progression. A retrospective analysis was conducted on COVID-19 patients admitted to the ICU between January and September 2020. The analysis considered patient demographics, comorbidities, neurological and non-neurological symptoms, as well as laboratory markers. The multivariate logistic regression analysis aims to uncover associations between these factors and patient outcomes. Of the 387 patients included in this study, nearly half (48.5%) of the ICU patients succumbed to COVID-19. Factors that contributed to increased mortality included being 60 years of age or older, impaired consciousness, lung disease, elevated international normalized ratio (INR), and elevated blood urea nitrogen (BUN) levels. Surprisingly, symptoms such as dizziness/lightheadedness, myalgia, and headache were associated with a higher likelihood of survival. In addition, elevated D-dimer and aspartate aminotransferase (AST) levels, as well as lymphopenia, were more commonly observed in deceased patients. The study concluded that those who died in the ICU tended to be older, white, and burdened with more comorbidities and impaired consciousness. With the intriguing link between specific symptoms and survival, further research is essential to uncover the underlying pathophysiological mechanisms that influence ICU patient outcomes in the context of COVID-19.

A single-center retrospective study of hospitalized COVID-19 patients: demographics, laboratory markers, neurological complications, ICU admission, and mortality

The coronavirus disease 2019 (COVID-19) pandemic has unveiled a wide array of clinical biomarkers, and neurological manifestations in affected patients, necessitating further exploration.

Methods

This single-center retrospective study evaluated clinical and neurological sequelae, demographics, as well as laboratory markers, in hospitalized COVID-19 patients from January to September 2020.

Results

Among 1248 inpatients (median age: 68 years; 651 women), 387 (31%) were admitted to the ICU. Central nervous system (CNS) manifestations were present in 521 (41.74%) patients, while peripheral nervous system manifestations were observed in 84 (6.73%). COVID-19-related mortality occurred in 314 (25.16%) cases. ICU-admitted patients were predominantly male (P<0.0001), older (age≥60; P=0.037) and had more comorbidities such as diabetes (P=0.001), hyperlipidemia (P=0.043), and coronary artery disease (P=0.015). ICU patients exhibited more CNS manifestations (P=0.001), including impaired consciousness (P<0.0001) and acute cerebrovascular disease (P=0.023). Biomarkers linked to admission to the ICU included elevated white blood cell count, ferritin, lactate dehydrogenase, creatine kinase, blood urea nitrogen, creatinine, and acute phase reactants (e.g. erythrocyte sedimentation rate and C-reactive protein). ICU patients demonstrated lower lymphocyte and platelet counts compared to non-ICU patients. Those with CNS involvement in the ICU often exhibited elevated blood urea nitrogen, creatinine, and creatine kinase levels. Higher mortality from COVID-19 was observed in ICU patients (P<0.0001).

Conclusions

Multiple serum biomarkers, comorbidities, and neurological manifestations in COVID-19 patients have been consistently documented and may be linked to increased morbidity, ICU admission, and mortality. Recognizing and addressing these clinical and laboratory markers is essential for effective COVID-19 management.

Di-valent siRNA-mediated silencing of MSH3 blocks somatic repeat expansion in mouse models of Huntington's disease

Huntington's disease (HD) is a severe neurodegenerative disorder caused by the expansion of the CAG trinucleotide repeat tract in the huntingtin gene. Inheritance of expanded CAG repeats is needed for HD manifestation, but further somatic expansion of the repeat tract in non-dividing cells, particularly striatal neurons, hastens disease onset. Called somatic repeat expansion, this process is mediated by the mismatch repair (MMR) pathway. Among MMR components identified as modifiers of HD onset, MutS homolog 3 (MSH3) has emerged as a potentially safe and effective target for therapeutic intervention. Here, we identify a fully chemically modified short interfering RNA (siRNA) that robustly silences Msh3 in vitro and in vivo. When synthesized in a di-valent scaffold, siRNA-mediated silencing of Msh3 effectively blocked CAG-repeat expansion in the striatum of two HD mouse models without affecting tumor-associated microsatellite instability or mRNA expression of other MMR genes. Our findings establish a promising treatment approach for patients with HD and other repeat expansion diseases.

The RITA-T (Rapid Interactive Screening Test for Autism in Toddlers) Community Model to Improve Access and Early Identification of Autism in Young Children

Objective: To evaluate improved identification and the generalization of the RITA-T (Rapid interactive Screening Test for Autism in Toddlers) model through partnerships with Primary Care (PC), Early Intervention (EI), and Autism Diagnosticians. Methods: Over 3 years (2018-2021), 15 EI and 9 PC (MD and NP) centers participated in this project. We trained providers on the RITA-T and established screening models. We reviewed charts of all toddlers referred through this model and compared wait times, and diagnoses, to those evaluated through regular referral in a tertiary-based autism clinic. We also examined the RITA-T psychometrics. Results: 377 toddlers met our inclusion criteria. Wait time for diagnosis was an average of 2.8 months and led to further collaboration between community providers. RITA-T cut-off scores stayed consistent. Providers reported improved confidence and easy integration of this model. Conclusions: This model is generalizable and improves the Early Identification of ASD.

Autophagy in Myelinating Glia

Autophagy is the cellular process involved in transportation and degradation of membrane, proteins, pathogens, and organelles. This fundamental cellular process is vital in development, plasticity, and response to disease and injury. Compared with neurons, little information is available on autophagy in glia, but it is paramount for glia to perform their critical responses to nervous system disease and injury, including active tissue remodeling and phagocytosis. In myelinating glia, autophagy has expanded roles, particularly in phagocytosis of mature myelin and in generating the vast amounts of membrane proteins and lipids that must be transported to form new myelin. Notably, autophagy plays important roles in removing excess cytoplasm to promote myelin compaction and development of oligodendrocytes, as well as in remyelination by Schwann cells after nerve trauma. This review summarizes the cell biology of autophagy, detailing the major pathways and proteins involved, as well as the roles of autophagy in Schwann cells and oligodendrocytes in development, plasticity, and diseases in which myelin is affected. This includes traumatic brain injury, Alexander's disease, Alzheimer's disease, hypoxia, multiple sclerosis, hereditary spastic paraplegia, and others. Promising areas for future research are highlighted.

Oligodendrocyte involvement in Gulf War Illness

Low level sarin nerve gas and other anti‐cholinesterase agents have been implicated in Gulf War illness (GWI), a chronic multi‐symptom disorder characterized by cognitive, pain and fatigue symptoms that continues to afflict roughly 32% of veterans from the 1990–1991 Gulf War. How disrupting cholinergic synaptic transmission could produce chronic illness is unclear, but recent research indicates that acetylcholine also mediates communication between axons and oligodendrocytes. Here we investigated the hypothesis that oligodendrocyte development is disrupted by Gulf War agents, by experiments using the sarin‐surrogate acetylcholinesterase inhibitor, diisopropyl fluorophosphate (DFP). The effects of corticosterone, which is used in some GWI animal models, were also investigated. The data show that DFP decreased both the number of mature and dividing oligodendrocytes in the rat prefrontal cortex (PFC), but differences were found between PFC and corpus callosum. The differences seen between the PFC and corpus callosum likely reflect the higher percentage of proliferating oligodendroglia in the adult PFC. In cell culture, DFP also decreased oligodendrocyte survival through a non‐cholinergic mechanism. Corticosterone promoted maturation of oligodendrocytes, and when used in combination with DFP it had protective effects by increasing the pool of mature oligodendrocytes and decreasing proliferation. Cell culture studies indicate direct effects of both DFP and corticosterone on OPCs, and by comparison with in vivo results, we conclude that in addition to direct effects, systemic effects and interruption of neuron–glia interactions contribute to the detrimental effects of GW agents on oligodendrocytes. Our results demonstrate that oligodendrocytes are an important component of the pathophysiology of GWI.

Epigenome Interactions with Patterned Neuronal Activity

The temporal coding of action potential activity is fundamental to nervous system function. Here we consider how gene expression in neurons is regulated by specific patterns of action potential firing, with an emphasis on new information on epigenetic regulation of gene expression. Patterned action potential activity activates intracellular signaling networks selectively in accordance with the kinetics of activation and inactivation of second messengers, phosphorylation and dephosphorylation of protein kinases, and cytoplasmic and nuclear calcium dynamics, which differentially activate specific transcription factors. Increasing evidence also implicates activity-dependent regulation of epigenetic mechanisms to alter chromatin architecture. Changes in three-dimensional chromatin structure, including chromatin compaction, looping, double-stranded DNA breaks, histone and DNA modification, are altered by action potential activity to selectively inhibit or promote transcription of specific genes. These mechanisms of activity-dependent regulation of gene expression are important in neural development, plasticity, and in neurological and psychological disorders.

Cholinergic signaling in myelination

There is a long history of research on acetylcholine (ACh) function in myelinating glia, but a resurgence of interest recently as a result of the therapeutic potential of manipulating ACh signaling to promote remyelination, and the broader interest in neurotransmitter signaling in activity-dependent myelination. Myelinating glia express all the major types of muscarinic and nicotinic ACh receptors at different stages of development, and acetylcholinesterase and butyrylcholinesterase are highly expressed in white matter. This review traces the history of research on ACh signaling in Schwann cells, oligodendrocytes, and in the myelin sheath, and summarizes current knowledge on the intracellular signaling and functional consequences of ACh signaling in myelinating glia. Implications of ACh in diseases, such as Alzheimer's disease, multiple sclerosis, and white matter toxicity caused by pesticides are considered, together with an outline of major questions for future research. GLIA 2017;65:687-698.