Abstract
Huntington’s disease (HD) is a dominantly inherited monogenetic disorder characterized by motor and cognitive dysfunction due to neurodegeneration. The disease is caused by the polyglutamine (polyQ) expansion at the 5′ terminal of the exon 1 of the huntingtin (HTT) gene, IT15, which results in the accumulation of mutant HTT (mHTT) aggregates in neurons and cell death. The monogenetic cause and the loss of specific neural cell population make HD a suitable candidate for stem cell and gene therapy. In this study, we demonstrate the efficacy of the combination of stem cell and gene therapy in a transgenic HD mouse model (N171-82Q; HD mice) using rhesus monkey (Macaca mulatta) neural progenitor cells (NPCs). We have established monkey NPC cell lines from induced pluripotent stem cells (iPSCs) that can differentiate into GABAergic neurons in vitro as well as in mouse brains without tumor formation. Wild-type monkey NPCs (WT-NPCs), NPCs derived from a transgenic HD monkey (HD-NPCs), and genetically modified HD-NPCs with reduced mHTT levels by stable expression of small-hairpin RNA (HD-shHD-NPCs), were grafted into the striatum of WT and HD mice. Mice that received HD-shHD-NPC grafts showed a significant increase in lifespan compared to the sham injection group and HD mice. Both WT-NPC and HD-shHD-NPC grafts in HD mice showed significant improvement in motor functions assessed by rotarod and grip strength. Also, immunohistochemistry demonstrated the integration and differentiation. Our results suggest the combination of stem cell and gene therapy as a viable therapeutic option for HD treatment.
Highlights
Huntington’s disease (HD) is a monogenic hereditary neurodegenerative disease characterized by progressive brain atrophy in the striatum, cortex, and other brain regions associated with cognitive, behavioral, and motor impairment.[1,2,3,4,5] The causative factor of HD is the mutation in exon 1 of the huntingtin (HTT) gene resulting in the expansion of the polyglutamine residue at the N-terminus of the HTT protein.[1,6,7] The onset and severity of the disease are governed by the size of the polyQ tract.[8]
We evaluated the efficacy of using a combination of stem cell therapy and gene therapy by grafting neural progenitor cells (NPCs) derived from WT and HD monkey, and HD-NPC expressing small hairpin RNA (shRNA) against HTT (HD-shHD-NPCs) in HD mice
In order to confirm the phenotype, HD-shHD-NPC cells were subjected to Zeocin selection (100 μg/mL), and the suppression of HTT expression was confirmed by using qRT-PCR before the surgery (Fig. 1a)
Summary
Huntington’s disease (HD) is a monogenic hereditary neurodegenerative disease characterized by progressive brain atrophy in the striatum, cortex, and other brain regions associated with cognitive, behavioral, and motor impairment.[1,2,3,4,5] The causative factor of HD is the mutation in exon 1 of the huntingtin (HTT) gene resulting in the expansion of the polyglutamine (polyQ) residue at the N-terminus of the HTT protein.[1,6,7] The onset and severity of the disease are governed by the size of the polyQ tract.[8]. Multiple proteolytic cleavage sites create unique splicing patterns in the HTT protein and produce a variety of Nterminal fragments.[1,6,7] the expanded polyQ tract creates aberrant splicing of the HTT protein that results in the formation of small oligomeric fragments.[1,9,11] These oligomeric fragments fold, form aggregates, accumulate in cells, and disrupt cellular functions.[1,9,10] there is a great advancement in the understanding of HD pathogenesis and the development of drugs and therapeutics, HD remains incurable and the search for effective treatments continues. In a more recent study, ablation of Htt in adult mouse showed significant motor and behavioral decline.[24] Unlike gene editing, gene silencing, such as shRNA and mHTT lowering therapy such as ASO, is a more validated treatment option for HD. Limitations in delivery method and biodistribution of the ASO, RNAi, and other therapeutic reagents in the brain remain major obstacles for clinical translation
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