Modulation of nuclear REST by alternative splicing: a potential therapeutic target for Huntington's disease

Abstract

Huntington's disease (HD) is caused by a genetically mutated huntingtin (mHtt) protein with expanded polyQ stretch, which impairs cytosolic sequestration of the repressor element‐1 silencing transcription factor (REST), resulting in excessive nuclear REST and subsequent repression of neuronal genes. We recently demonstrated that REST undergoes extensive, context‐dependent alternative splicing, of which exon‐3 skipping (∆E3)—a common event in human and nonhuman primates—causes loss of a motif critical for REST nuclear targeting. This study aimed to determine whether ∆E3 can be targeted to reduce nuclear REST and rescue neuronal gene expression in mouse striatal‐derived, mHtt‐expressing STHdhQ111/Q111 cells—a well‐established cellular model of HD. We designed two morpholino antisense oligos (ASOs) targeting the splice sites of Rest E3 and examined their effects on ∆E3, nuclear Rest accumulation and Rest‐controlled gene expression in STHdhQ111/Q111 cells. We found that (1) the ASOs treatment significantly induced ∆E3, reduced nuclear Rest, and rescued transcription and/or mis‐splicing of specific neuronal genes (e.g. Syn1 and Stmn2) in STHdhQ111/Q111 cells; and (2) the ASOs‐induced transcriptional regulation was dependent on ∆E3 induction and mimicked by siRNA‐mediated knock‐down of Rest expression. Our findings demonstrate modulation of nuclear REST by ∆E3 and its potential as a new therapeutic target for HD and provide new insights into environmental regulation of genome function and pathogenesis of HD. As ∆E3 is modulated by cellular signalling and linked to various types of cancer, we anticipate that ∆E3 contributes to environmentally tuned REST function and may have a broad range of clinical implications.

News about the Role of the Transcription Factor REST in Neurons: From Physiology to Pathology

“…Another property of interest, i.e., the REST alternative splicing, has not been discussed in general terms [63]. Here, however, it has been considered in several specific cases [31,42,45,58].…”

“…An effect the Huntington's mutation is the inhibited expression of specific genes, including the gene of the nuclear neurotrophin factor BDNF, relevant for the survival of neurons [3,11,12]. Two recent studies demonstrated that decreased REST levels in the nucleus, induced by alternative splicing of its gene [31], and decreased REST binding to the heat shock protein Hsp90 [32], reduce the accumulation of the transcription factor within the nucleus, with attenuation of its toxic effects. At present, both REST-induced events are considered as potential targets for future therapies [31,32].…”

“…During the last few years, the therapeutic potential of REST has attracted attention concerning both specific conditions and their deacetylases (examples in [57,58]). Recent therapeutic attempts have been included in numerous studies reporting neurodegenerative diseases [31][32][33][34] and epilepsy [38,39]. These studies, however, concerned primarily pathology, not therapies of diseases.…”

More than a Corepressor: The Role of CoREST Proteins in Neurodevelopment

“…For example, in Huntington's disease (HD), the accumulation of nuclear REST in medium spiny neurons of the striatum results in enhanced repression of BDNF transcription contributing to an increased susceptibility to neuronal loss (Zuccato et al, 2003). A potential therapeutic for HD pathogenesis is targeting splicing of REST using antisense oligonucleotides in vitro to reduce the accumulation of nuclear REST (Chen et al, 2017). However, as REST targets the RE1 site in ;2000 genes in the human genome, the modulation of REST remains a difficult target as it has the potential to have multiple downstream effects.…”

Alternative REST Splicing Underappreciated

“…In their paper describing altered nuclear REST in ageing and AD brain, Lu et al claimed that REST4 mRNA (N 3c ) level in brain tissues comprised only 0.1-0.5% of REST mRNA 12 , while splice variants caused by ∆E 2 , ∆E 3 and ∆E 4 (or inclusion of E 5 ) exhibit neuronal expression, of which ∆E 3 eliminates a motif critical for nuclear targeting 20,21 and therefore affects nuclear REST 22 ) were not mentioned. It can be simply inferred that if only the full-length REST mRNA exists, all segments of it should share the same level of expression; however, in accordance with our above-mentioned notion of inconsistent results yielded by different primers, qRT-PCR data in Lu et al indicated that 4 primer sets (P1-P4) targeting different exons of REST yielded strikingly different mRNA expression change.…”