Purwar, I. | bioRxiv Science

bioRxiv2026

Altered neuronal start codon stringency favors cap-independent repeat-associated non-AUG translation

Intronic GGGGCC repeat expansions in C9orf72 cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). This expansion supports a non-canonical form of translational initiation known as repeat-associated non-AUG (RAN) translation to produce toxic dipeptide repeat proteins that contribute to neurodegeneration. Here, we find that the efficiency of RAN translation and its dependency on the 5' 7-methylguanosine mRNA cap are variable across cell types, with both rodent neurons and human iNeurons favoring cap-independent RAN translation from two distinct repeats (CGG and GGGGCC) across multiple reading frames. Treatment with an eIF4E inhibitor that blocks global cap-dependent translation enhances RAN translation specifically in neurons. Intriguingly, cap-independent RAN translation exhibits less reliance on near-cognate codons for initiation than cap-dependent RAN translation. This finding led us to identify a surprising global increase in start codon stringency in neurons as a contributor to the relatively higher cap-independent RAN translation in this cell type. This effect correlates with a cytoplasmic redistribution of eIF1 in neurons and is reversed with neuronal overexpression of the eukaryotic initiation factor eIF5, which relaxes start codon stringency and selectively enhances cap-dependent RAN translation. Taken together, these findings reveal several neuron-specific features of translational regulation that favor cap-independent RAN translation with implications for nucleotide repeat expansion disorder pathogenesis and neuronal translational regulation. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=82 SRC="FIGDIR/small/739042v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@61a6cforg.highwire.dtl.DTLVardef@10e8e64org.highwire.dtl.DTLVardef@a6689aorg.highwire.dtl.DTLVardef@11d683b_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

Dysregulated RNA splicing induces regeneration failure in alcohol-associated liver disease

Individuals with progressive liver failure are at a high risk of mortality without liver transplantation. However, our understanding of derailed regenerative responses in failing livers is limited. Here, we performed comprehensive multi-omic profiling of healthy and diseased human livers using bulk and single-nucleus RNA-plus ATAC-seq. We report that hepatic immune milieu alterations in alcohol-associated liver disease (ALD) prevent hepatocytes from transitioning to a proliferative progenitor-like state, trapping them into an unproductive intermediate state. We discovered striking changes in RNA binding protein (RBP) expression, particularly ESRP, PTBP, and SR families, that cause misregulation of developmentally controlled RNA splicing in ALD. Our data pinpoint ESRP2 as a pivotal disease-sensitive RBP and support a causal role of its deficiency in ALD pathogenesis. Notably, splicing defects in ESRP2-targets Tcf4 and Slk, amongst others, directly alter their nuclear localization and activities, disrupting WNT and Hippo signaling pathways, which are critical for normal liver regeneration. We demonstrate that changes in stromal cell populations enrich failing ALD livers with TGF-{beta}, which suppresses ESRP2-driven epithelial splicing program and replaces functional parenchyma with quasi-progenitor-like cells lacking liver-specific functions. This unprecedented account of transcriptional and post-transcriptional dysregulation in ALD suggests that targeting misspliced RNAs could improve recovery and serve as biomarkers for poor ALD outcomes.

molecular biology↗