Next Generation Precision Medicine: CRISPR-mediated Genome Editing for the Treatment of Neurodegenerative Disorders

Abstract

Despite significant advancements in the field of molecular neurobiology especially neuroinflammation and neurodegeneration, the highly complex molecular mechanisms underlying neurodegenerative diseases remain elusive. As a result, the development of the next generation neurotherapeutics has experienced a considerable lag phase. Recent advancements in the field of genome editing offer a new template for dissecting the precise molecular pathways underlying the complex neurodegenerative disorders. We believe that the innovative genome and transcriptome editing strategies offer an excellent opportunity to decipher novel therapeutic targets, develop novel neurodegenerative disease models, develop neuroimaging modalities, develop next-generation diagnostics as well as develop patient-specific precision-targeted personalized therapies to effectively treat neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic lateral sclerosis, Frontotemporal dementia etc. Here, we review the latest developments in the field of CRISPR-mediated genome editing and provide unbiased futuristic insights regarding its translational potential to improve the treatment outcomes and minimize financial burden. However, despite significant advancements, we would caution the scientific community that since the CRISPR field is still evolving, currently we do not know the full spectrum of CRISPR-mediated side effects. In the wake of the recent news regarding CRISPR-edited human babies being born in China, we urge the scientific community to maintain high scientific and ethical standards and utilize CRISPR for developing in vitro disease in a dish model, in vivo testing in nonhuman primates and lower vertebrates and for the development of neurotherapeutics for the currently incurable neurodegenerative disorders. Graphical Abstract.

Keywords: Alzheimer’s disease; Amyotrophic lateral sclerosis; CRISPR; Frontotemporal dementia; Huntington’s disease; Parkinson’s disease; genome editing; neurodegeneration; neuroinflammation.

Figure 1:. CRISPR-Mediated Genome Editing for Neurodegenerative Diseases:

Neuroinflammation plays a crucial role in the initiation and progression of various neurodegenerative disorders. Activation of astrocytes and microglia induces the expression of proinflammatory cytokines and chemokines including GMF, IL1-β, IL-6, IL-8, TNF, IL-12, IL-23, IL-33, CXCL10 and CXCL12. Because of neuroinflammation, there is increased phosphorylation of p38MAPK/ERK pathways, which leads to activation, and nuclear translocation of NFκB thereby causing increased oxidative stress, mitochondrial dysfunction and apoptosis. These deleterious effects ultimately lead to neurodegenerative disorders and impaired blood brain barrier. The progression of neurodegenerative cascade results in impaired cognitive function and loss of memory. CRISPR/Cas9-mediated genome editing is a powerful tool for inducing gene correction, disease modeling, transcriptional regulation, epigenome engineering, chromatin visualization as well as development of neurotherapeutics. It can be used to increase the levels of anti-inflammatory cytokines (IL-4, IL-6, IL-10, IL-11, IL-13, IL-33, TGFβ, CXCL16) and neurotrophic factors (BDNF, CDNF, GDNF, MANF, NGF, NT3, NT4, NRTN) which in turn can stimulate the proliferation and expansion of neural stem cells, neurogenesis, gliogenesis, remyelination and neural plasticity thereby ultimately leading to improved cognitive function and memory enhancement.

Figure 2:. Role of Glia Maturation Factor (GMF) in Neuroinflammation and Neurodegenerative Diseases:

GMF is a 141 amino acid multifunctional intracellular protein, which is predominantly expressed in the central nervous system and plays a crucial role in the growth and differentiation of glia and neurons. GMF overexpression, which is observed in several neurodegenerative diseases, induces the activation of the p38MAPK/ERK signaling leading to activation and nuclear translocation of NFκB resulting in a significant increase in the secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF). GM-CSF is a proinflammatory cytokine and a potent mitogenic factor for microglia. Activation and proliferation of microglia induces the secretion of various proinflammatory cytokines/chemokines including TNF-α, IL-1β, IL-6 and IFNγ (represented as red spheres) and leads to oxidative stress, mitochondrial dysfunction as well as apoptosis. These deleterious effects induce neurodegeneration and blood brain barrier dysfunction, which in turn lead to impaired cognitive function and loss of memory. CRISPR-mediated targeted GMF gene editing leads to GMF knockdown and very effectively blocks the proinflammatory downstream signaling pathways thereby delaying or halting the progression of neurodegenerative disorders, enhancing the proliferation and differentiation of neural stem cells, improving neurogenesis, producing neurotrophins (depicted as blue spheres) neuroplasticity and improving the cognitive function.

Figure 3:. CRISPR-mediated Genome Editing of Neuroinflammation and Neurodegenerative Disorders:

A wide spectrum of neurodegenerative disorders can be efficiently targeted by CRISPR-mediated genome editing to either correct the genetic defect, restore the functional expression of the protein, knockdown the expression of the defective protein, as well as achieve epigenetic modifications. A wide variety of CRISPR enzymes are available to achieve desired genetic modification. Temporo-spatial regulation of precision-targeted CRISPR-mediated genome editing holds the key to successful correction of the genetic defect without any off target effects.