Exon7 Targeted CRISPR-Prime Editing Approaches for SMN2 Gene Editing in Spinal Muscular Atrophy (SMA) Disease Can Increase In Vitro SMN Expression

Abstract

Spinal Muscular Atrophy (SMA) is a fatal neuromuscular disease characterized by motor neuron loss and advanced muscle weakness, which occurs in functional SMN (Survival Motor Neuron) protein deficiency with SMN1 gene-induced deletions and mutations. The incidence of SMA, which is an autosomal recessive disease, is 1/10,000 in the world. The SMN protein acts as a molecular chaperone in the formation of the spliceosome complex, which catalyzes the splicing of pre-mRNA, enabling mRNAs and non-coding RNAs to mature. Since the current SMN1-encoding Adeno-associated virus (AAV) or SMN2 gene targeting antisense oligonucleotide-based strategies cannot provide long-term stable SMN expression in neuron cells, more effective methods need to be developed. CRISPR technology, which adds a new dimension to genetic engineering and gene therapies, makes it possible to treat many genetic diseases. In terms of SMA, some previous studies in the literature prove that it is possible to treat SMA with the CRISPR strategy. Homology Directed Repair (HDR)-based CRISPR technology, which results in a high rate of in-del (insertion-deletion) mutations rather than editing, was shown unsuitable for therapeutic applications. CRISPR-Prime editing (PE) technology is a new generation of gene editing approach that precisely provides various genomic modifications without the need for double-strand breakage or donor DNA sequences. CRISPR-Prime Editing method has also been used in rare diseases such as sickle cell anemia and Tay-Sachs, and their efficiency in editing various pathogenic mutations has been demonstrated. However, CRISPR Prime Editing-mediated gene editing for Spinal Muscular Atrophy (SMA) have not yet been investigated. The c.840 T-C transition and c.859 G-C transformations in the SMN2 gene and the correction of these point mutations with a single pegRNA at the same time were investigated for the first time in this study. Here, we showed that CRISPR-PE systems could increase SMN2 gene activity and SMN protein expression by ensuring exon 7 participation by editing c.840 T-C transition and c.859 G-C transformations. The fact that Prime Editing method showed the efficacy and stability of modifications in SMN2 genes that were investigated in SMN-low Jurkat cells as a proof-of-concept. This study enabled the next step with the CRISPR-Prime Editing approach to be tested ex vivo in primary cell lines from SMA patients and SMN-low neuronal cells.