Efficient in vivo neuronal genome editing in the mouse brain using nanocapsules containing CRISPR-Cas9 ribonucleoproteins

Expression and function of nicotinic acetylcholine receptors in specific neuronal populations: Focus on striatal and prefrontal circuits

Nicotinic acetylcholine receptors (nAChRs) are widely expressed in the central nervous system and play an important role in the control of neural functions including neuronal activity, transmitter release and synaptic plasticity. Although the common subtypes of nAChRs are abundantly expressed throughout the brain, their expression in different brain regions and by individual neuronal types is not homogeneous or incidental. In recent years, several studies have emerged showing that particular subtypes of nAChRs are expressed by specific neuronal populations in which they have major influence on the activity of local circuits and behavior. It has been demonstrated that even nAChRs expressed by relatively rare neuronal types can induce significant changes in behavior and contribute to pathological processes. Depending on the identity and connectivity of the particular nAChRs-expressing neuronal populations, the activation of nAChRs can have distinct or even opposing effects on local neuronal signaling. In this review, we will summarize the available literature describing the expression of individual nicotinic subunits by different neuronal types in two crucial brain regions, the striatum and the prefrontal cortex. The review will also briefly discuss nicotinic expression in non-neuronal, glial cells, as they cannot be ignored as potential targets of nAChRs-modulating drugs. The final section will discuss options that could allow us to target nAChRs in a neuronal-type-specific manner, not only in the experimental field, but also eventually in clinical practice.

Engineering self-deliverable ribonucleoproteins for genome editing in the brain

The delivery of CRISPR ribonucleoproteins (RNPs) for genome editing in vitro and in vivo has important advantages over other delivery methods, including reduced off-target and immunogenic effects. However, effective delivery of RNPs remains challenging in certain cell types due to low efficiency and cell toxicity. To address these issues, we engineer self-deliverable RNPs that can promote efficient cellular uptake and carry out robust genome editing without the need for helper materials or biomolecules. Screening of cell-penetrating peptides (CPPs) fused to CRISPR-Cas9 protein identifies potent constructs capable of efficient genome editing of neural progenitor cells. Further engineering of these fusion proteins establishes a C-terminal Cas9 fusion with three copies of A22p, a peptide derived from human semaphorin-3a, that exhibits substantially improved editing efficacy compared to other constructs. We find that self-deliverable Cas9 RNPs generate robust genome edits in clinically relevant genes when injected directly into the mouse striatum. Overall, self-deliverable Cas9 proteins provide a facile and effective platform for genome editing in vitro and in vivo.

Quantifying nanoparticle delivery: challenges, tools, and advances

This review explores challenges and methods for quantifying nanoparticle delivery in therapeutic applications. We discuss three main approaches: (1) functional readouts that assess therapeutic effects post nanoparticle administration, (2) nanocarrier tracking that directly monitors the nanoparticle localization, and (3) cargo tracking that infers nanoparticle localization by measuring encapsulated agents or attached surface tags. Reanalysis of the Wilhelm et al. Cancer Nanomedicine Repository dataset found mixed quantification methodologies, which could cause misleading conclusions. We discuss potential pitfalls in each quantification approach and highlight recent advancements in novel technologies. It is important that researchers select appropriate quantification methods based on their objectives and consider integrating multiple approaches for a comprehensive understanding of in vivo nanoparticle behavior to facilitate their clinical translation.

Self-delivering, chemically modified CRISPR RNAs for AAV co-delivery and genome editing in vivo

Guide RNAs offer programmability for CRISPR-Cas9 genome editing but also add challenges for delivery. Chemical modification, which has been key to the success of oligonucleotide therapeutics, can enhance the stability, distribution, cellular uptake, and safety of nucleic acids. Previously, we engineered heavily and fully modified SpyCas9 crRNA and tracrRNA, which showed enhanced stability and retained activity when delivered to cultured cells in the form of the ribonucleoprotein complex. In this study, we report that a short, fully stabilized oligonucleotide (a 'protecting oligo'), which can be displaced by tracrRNA annealing, can significantly enhance the potency and stability of a heavily modified crRNA. Furthermore, protecting oligos allow various bioconjugates to be appended, thereby improving cellular uptake and biodistribution of crRNA in vivo. Finally, we achieved in vivo genome editing in adult mouse liver and central nervous system via co-delivery of unformulated, chemically modified crRNAs with protecting oligos and AAV vectors that express tracrRNA and either SpyCas9 or a base editor derivative. Our proof-of-concept establishment of AAV/crRNA co-delivery offers a route towards transient editing activity, target multiplexing, guide redosing, and vector inactivation.

Nanoparticle-mediated delivery of non-viral gene editing technology to the brain

Neurological disorders pose a significant burden on individuals and society, affecting millions worldwide. These disorders, including but not limited to Alzheimer's disease, Parkinson's disease, and Huntington's disease, often have limited treatment options and can lead to progressive degeneration and disability. Gene editing technologies, including Zinc Finger Nucleases (ZFN), Transcription Activator-Like Effector Nucleases (TALEN), and Clustered Regularly Interspaced Short Palindromic Repeats-associated Protein 9 (CRISPR-Cas9), offer a promising avenue for potential cures by targeting and correcting the underlying genetic mutations responsible for neurologic disorders. However, efficient delivery methods are crucial for the successful application of gene editing technologies in the context of neurological disorders. The central nervous system presents unique challenges to treatment development due to the blood-brain barrier, which restricts the entry of large molecules. While viral vectors are traditionally used for gene delivery, nonviral delivery methods, such as nanoparticle-mediated delivery, offer safer alternatives that can efficiently transport gene editing components. Herein we aim to introduce the three main gene editing nucleases as nonviral treatments for neurologic disorders, the delivery barriers associated with brain targeting, and the current nonviral techniques used for brain-specific delivery. We highlight the challenges and opportunities for future research in this exciting and growing field that could lead to blood-brain barrier bypassing therapeutic gene editing.

Smart antioxidant function enhancing (SAFE) nucleic acid therapy for ROS-related chronic diseases and comorbidities

Reactive oxygen species (ROS)-mediated oxidative stress exacerbates chronic diseases such as organ damage and neurodegenerative disorders. The Keap1-Nrf2-ARE pathway is a widely distributed endogenous antioxidant system. However, ROS under redox homeostasis regulates a wide range of life activities. Therefore, smart scavenging of excess ROS under pathological conditions is essential to treat chronic diseases safely. This study reports a smart antioxidant function enhancement (SAFE) strategy. On-demand release of nucleic acid drugs in a pathological ROS environment smartly activates the endogenous antioxidant system, thereby smartly alleviating oxidative stress in an exogenous antioxidant-independent manner. Through structural modulation and ligand modification, we develop SAFE nanoparticles based on nanohybrid complexes (SAFE-complex) adapted to brain delivery of nucleic acid drugs. SAFE-complex with homogeneous monodisperse structure efficiently treat ROS-related neurodegenerative diseases while protecting the major organ from oxidative stress damage. Moreover, SAFE-complex can stabilize storage in the form of freeze-dried powder. These data indicate that SAFE nanoparticles hold promise for treating ROS-related chronic diseases and comorbidities through rational transformation.

Engineering self-deliverable ribonucleoproteins for genome editing in the brain

The delivery of CRISPR ribonucleoproteins (RNPs) for genome editing in vitro and in vivo has important advantages over other delivery methods, including reduced off-target and immunogenic effects 1 . However, effective delivery of RNPs remains challenging in certain cell types due to low efficiency and cell toxicity. To address these issues, we engineered self-deliverable RNPs that can promote efficient cellular uptake and carry out robust genome editing without the need for helper materials or biomolecules. Screening of cell-penetrating peptides (CPPs) fused to CRISPR-Cas9 protein identified potent constructs capable of efficient genome editing of neural progenitor cells. Further engineering of these fusion proteins identified a C-terminal Cas9 fusion with three copies of A22p, a peptide derived from human semaphorin-3a, that exhibited substantially improved editing efficacy compared to other constructs. We found that self-deliverable Cas9 RNPs generated robust genome edits in clinically relevant genes when injected directly into the mouse striatum. Overall, self-deliverable Cas9 proteins provide a facile and effective platform for genome editing in vitro and in vivo .

Genome editing in the mouse brain with minimally immunogenic Cas9 RNPs

Transient delivery of CRISPR-Cas9 ribonucleoproteins (RNPs) into the central nervous system (CNS) for therapeutic genome editing could avoid limitations of viral vector-based delivery including cargo capacity, immunogenicity, and cost. Here, we tested the ability of cell-penetrant Cas9 RNPs to edit the mouse striatum when introduced using a convection-enhanced delivery system. These transient Cas9 RNPs showed comparable editing of neurons and reduced adaptive immune responses relative to one formulation of Cas9 delivered using AAV serotype 9. The production of ultra-low endotoxin Cas9 protein manufactured at scale further improved innate immunity. We conclude that injection-based delivery of minimally immunogenic CRISPR genome editing RNPs into the CNS provides a valuable alternative to virus-mediated genome editing.

Striatonigral distribution of a fluorescent reporter following intracerebral delivery of genome editors

Introduction: Targeted gene editing is proposed as a therapeutic approach for numerous disorders, including neurological diseases. As the brain is organized into neural networks, it is critical to understand how anatomically connected structures are affected by genome editing. For example, neurons in the substantia nigra pars compacta (SNpc) project to the striatum, and the striatum contains neurons that project to the substantia nigra pars reticulata (SNpr). Methods: Here, we report the effect of injecting genome editors into the striatum of Ai14 reporter mice, which have a LoxP-flanked stop cassette that prevents expression of the red fluorescent protein tdTomato. Two weeks following intracerebral delivery of either synthetic nanocapsules (NCs) containing CRISPR ribonucleoprotein targeting the tdTomato stop cassette or adeno-associated virus (AAV) vectors expressing Cre recombinase, the brains were collected, and the presence of tdTomato was assessed in both the striatum and SN. Results: TdTomato expression was observed at the injection site in both the NC- and AAV-treated groups and typically colocalized with the neuronal marker NeuN. In the SN, tdTomato-positive fibers were present in the pars reticulata, and SNpr area expressing tdTomato correlated with the size of the striatal genome edited area. Conclusion: These results demonstrate in vivo anterograde axonal transport of reporter gene protein products to the SNpr following neuronal genome editing in the striatum.

Non-viral approaches for gene therapy and therapeutic genome editing across the blood-brain barrier

The success of brain-targeted gene therapy and therapeutic genome editing hinges on the efficient delivery of biologics bypassing the blood-brain barrier (BBB), which presents a significant challenge in the development of treatments for central nervous system disorders. This is particularly the case for nucleic acids and genome editors that are naturally excluded by the BBB and have poor chemical stability in the bloodstream and poor cellular uptake capability, thereby requiring judiciously designed nanovectors administered systemically for intracellular delivery to brain cells such as neurons. To overcome this obstacle, various strategies for bypassing the BBB have been developed in recent years to deliver biologics to the brain via intravenous administration using non-viral vectors. This review summarizes various brain targeting strategies and recent representative reports on brain-targeted non-viral delivery systems that allow gene therapy and therapeutic genome editing via intravenous administration, and highlights ongoing challenges and future perspectives for systemic delivery of biologics to the brain via non-viral vectors.

CRISPR/Cas9 Genome Editing for Tissue-Specific In Vivo Targeting: Nanomaterials and Translational Perspective

Clustered randomly interspaced short palindromic repeats (CRISPRs) and its associated endonuclease protein, i.e., Cas9, have been discovered as an immune system in bacteria and archaea; nevertheless, they are now being adopted as mainstream biotechnological/molecular scissors that can modulate ample genetic and nongenetic diseases via insertion/deletion, epigenome editing, messenger RNA editing, CRISPR interference, etc. Many Food and Drug Administration-approved and ongoing clinical trials on CRISPR adopt ex vivo strategies, wherein the gene editing is performed ex vivo, followed by reimplantation to the patients. However, the in vivo delivery of the CRISPR components is still under preclinical surveillance. This review has summarized the nonviral nanodelivery strategies for gene editing using CRISPR/Cas9 and its recent advancements, strategic points of view, challenges, and future aspects for tissue-specific in vivo delivery of CRISPR/Cas9 components using nanomaterials.