Proteasome inhibitors to alleviate aberrant IKBKAP mRNA splicing and low IKAP/hELP1 synthesis in familial dysautonomia

Abstract

FD is a rare neurodegenerative disorder caused by a mutation of the IKBKAP gene, which induces low expression levels of the Elongator subunit IKAP/hELP1 protein. A rational strategy for FD treatment could be to identify drugs increasing IKAP/hELP1 expression levels by blocking protein degradation pathways such as the 26S proteasome. Proteasome inhibitors are promising molecules emerging in cancer treatment and could thus constitute an enticing pharmaceutical strategy for FD treatment. Therefore, we tested three proteasome inhibitors on FD human olfactory ecto-mesenchymal stem cells (hOE-MSCs): two approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA), bortezomib and carfilzomib, as well as epoxomicin. Although all 3 inhibitors demonstrated activity in correcting IKBKAP mRNA aberrant splicing, carfilzomib was superior in enhancing IKAP/hELP1 quantity. Moreover, we observed a synergistic effect of suboptimal doses of carfilzomib on kinetin in improving IKBKAP isoforms ratio and IKAP/hELP1 expression levels allowing to counterbalance carfilzomib toxicity. Finally, we identified several dysregulated miRNAs after carfilzomib treatment that target proteasome-associated mRNAs and determined that IKAP/hELP1 deficiency in FD pathology is correlated to an overactivity of the 26S proteasome. Altogether, these results reinforce the rationale for using chemical compounds inhibiting the 26S proteasome as an innovative option for FD and a promising therapeutic pathway for many other neurodegenerative diseases.

Antisense oligonucleotides correct the familial dysautonomia splicing defect in IKBKAP transgenic mice

“…Most attempts to develop FD therapeutics have focused on correcting the splicing defect by increasing the levels of exon 20 inclusion through treatment with various small molecules, with varying degrees of success. Notable among these small molecules are rectifier of aberrant mRNA splicing (RECTAS) ( 13 ), epigallocatechin gallate ( 17 ), protease inhibitors ( 18 ), phosphatidylserine ( 5 , 19 , 20 ), tocotrienols ( 21 ), and kinetin ( 22 , 23 ). In clinical trials, tocotrienols did not demonstrate significant clinical efficacy ( 21 ), whereas kinetin administered orally moderately improved IKBKAP splicing in the white blood cells of the treated patients ( 22 ).…”

Animal and cellular models of familial dysautonomia

“…For example, what precipitates the cell type-specific splicing patterns: lymphoblasts and multiple non-neuronal cells can very effectively splice the mutant FD pre-mRNA, conferring protection on those cells, while most neurons are much less capable of accommodating the splice site mutation and consequently suffer from reduced levels of IKAP protein. Investigation of neuron-specific splicing factors could clarify this question[67]. Another important problem that can be pursued with the existing model systems is a search for genetic modifiers that may mediate the variation in FD phenotype severity.…”

“…Genome-wide analysis (both mRNA and microRNA screening) using FD hOR-MSCs was performed to investigate dysregulated genes in FD and to test potential therapeutics [10, 65, 66]. Recent work with these FD and control hOR-MSCs indicated over-activity of the 26S proteasome in patient cells compared to controls, which lowered the level of IKAP protein, and that this reduction could be reversed by proteasome inhibitors [67]. Since some proteasome inhibitors have been clinically approved for cancer treatment, this study warrants further investigation.…”

Elongator promotes neuritogenesis via regulation of tau stability through acly activity

“…Therefore, it is possible that under such hypoacetylation conditions increased proteasomal degradation of multiple proteins takes place in FD cells by default which might have a profound impact in neuronal function and survival. Ibrahim and others’ work on FD human olfactory ectomesenchymal stem cells (hOE-MSCs) supports this assumption ( Hervé and Chérif, 2017 ) where Elp1 deficiency could induce proteasome alterations and that Elongator dysfunction in FD disturbs proteasome activity. Together with it, transcriptome and proteome analyses that have been done on DRG of mice in which Elp1 is conditionally ablated in the peripheral nervous system (PNS) suggest that the translational defects observed in Elongator loss are affecting downstream misregulation of numerous genes that function in ubiquitination, resulting in polyubiquitylation and proteasomal degradation of proteins ( Goffena et al, 2018 ).…”