CRISPR System: A High-throughput Toolbox for Research and Treatment of Parkinson's Disease

Abstract

In recent years, the innovation of gene-editing tools such as the CRISPR/Cas9 system improves the translational gap of treatments mediated by gene therapy. The privileges of CRISPR/Cas9 such as working in living cells and organs candidate this technology for using in research and treatment of the central nervous system (CNS) disorders. Parkinson's disease (PD) is a common, debilitating, neurodegenerative disorder which occurs due to loss of dopaminergic neurons and is associated with progressive motor dysfunction. Knowledge about the pathophysiological basis of PD has altered the classification system of PD, which manifests in familial and sporadic forms. The first genetic linkage studies in PD demonstrated the involvement of Synuclein alpha (SNCA) mutations and SNCA genomic duplications in the pathogenesis of PD familial forms. Subsequent studies have also insinuated mutations in leucine repeat kinase-2 (LRRK2), Parkin, PTEN-induced putative kinase 1 (PINK1), as well as DJ-1 causing familial forms of PD. This review will attempt to discuss the structure, function, and development in genome editing mediated by CRISP/Cas9 system. Further, it describes the genes involved in the pathogenesis of PD and the pertinent alterations to them. We will pursue this line by delineating the PD linkage studies in which CRISPR system was employed. Finally, we will discuss the pros and cons of CRISPR employment vis-à-vis the process of genome editing in PD patients' iPSCs.

Keywords: CRISPR-associated protein 9; Gene editing; Induced pluripotent stem cells; Neuroinflammation; Parkinson disease.

Fig. 1

Illustration of the main molecular pathways involve in PD pathogenesis. Mitochondrial dysfunction and the proteasomal impairment play key roles in contributing to the pathogenic process. PD-associated genes play critical roles in regulation of mitochondrial homeostasis, protein folding and the activity of intracellular clearance systems. The PINK1-parkin axis has significant roles in regulation of the fundamental dynamic properties of mitochondria such as fission–fusion events, mitochondrial arrest, and mitophagy. Furthermore, PINK1 and parkin independently control mitochondrial biogenesis and calcium homeostasis. Mutations in PINK1 and parkin disrupt the autophagy which results in neural cell death. Mutation in α-SYN and LRRK2 also affect mitochondrial function, by impairing membrane potential and oxidative phosphorylation, and inducing reactive oxygen species production and cytochrome-c release. Moreover, PINK1, parkin, and DJ-1 directly promote the degradation of proteasomal substrates, whereas α-SYN is able to impair activity of the ubiquitin-proteasome system (UPS). Finally, SNCA and UCHL-1 mutations impair α-SYN degradation through the chaperone-mediated autophagy (CMA), resulting in α-SYN aggregation and formation of inclusions. Of note, ATP13A2 counteracts the production of α-SYN aggregates. Alpha-SYN and other misfolded proteins accumulate within Lewy bodies, which are the pathologic hallmark of the disease

Fig. 2

Downregulation of p 13 triggers the assembly of mitochondrial complex I and inhibits cell death mediated by mitochondrial dysfunction in Parkinson’s disease

Fig. 3

Knocked out PK2 mediated by CRISPR/Cas9 illustrates the protective role of PK2 in anti-apoptotic responses against neurotoxic stress in both neurons and astrocytes. Neurotoxic stress can activate a variety of transcription factors, including HIF1α. This transcription factor binds to the promoter of the PK2 gene and upregulates the expression of this protein. PK2 enhances the mitochondrial biogenesis and upregulates the BCL-2 and PGC1α which result in the cell survival. In addition, PK2 in astrocytes upregulates the expression of genes associated with the anti-inflammatory alternative activation (A2) phenotype. PK2 gene ablation by CRISPR-Cas9 produces unintended effects and increases the cell susceptibility to a neurotoxic stress