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How animals rewire cellular programs to survive cold is a fascinating problem with potential biomedical implications, ranging from emergency medicine to space travel. Studying a hibernation-like response in the free-living nematode Caenorhabditis elegans, we uncovered a regulatory axis that enhances the natural resistance of nematodes to severe cold. This axis involves conserved transcription factors, DAF-16/FoxO and PQM-1, which jointly promote cold survival by upregulating FTN-1, a protein related to mammalian ferritin heavy chain (FTH1). Moreover, we show that inducing expression of FTH1 also promotes cold survival of mammalian neurons, a cell type particularly sensitive to deterioration in hypothermia. Our findings in both animals and cells suggest that FTN-1/FTH1 facilitates cold survival by detoxifying ROS-generating iron species. We finally show that mimicking the effects of FTN-1/FTH1 with drugs protects neurons from cold-induced degeneration, opening a potential avenue to improved treatments of hypothermia.

ACKNOWLEDGEMENTSThis work is dedicated to the memory of Professor Wlodzimierz J. Krzyzosiak. We thank Professor Marta Olejniczak from Department of Genome Engineering for reviewing the manuscript and every day stimulating discussions. We thank Professor Jerzy Ciesiolka from Department of RNA Biochemistry for helpful suggestions. The confocal microscopy analyses were performed in the ABSTRACT Spinocerebellar ataxia type 3 (SCA3) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in the ATXN3 gene encoding the ataxin-3 protein. Despite extensive research the exact pathogenic mechanisms of SCA3 are still not understood in depth. In the present study, to gain insight into the toxicity induced by the expanded CAG repeats in SCA3, we comprehensively investigated repeat-associated non-ATG (RAN) translation in various cellular models expressing translated or non-canonically translated ATXN3 sequences with an increasing number of CAG repeats.We demonstrate that two SCA3 RAN proteins, polyglutamine (polyQ) and polyalanine (polyA), are found only in the case of CAG repeats of pathogenic length. Despite having distinct cellular localization, RAN polyQ and RAN polyA proteins are very often coexpressed in the same cell, impairing nuclear integrity and inducing apoptosis. We provide for the first time mechanistic insights into SCA3 RAN translation indicating that ATXN3 sequences surrounding the repeat region have an impact on SCA3 RAN translation initiation and efficiency. We revealed that RAN translation of polyQ proteins starts at noncognate codons upstream of the CAG repeats, whereas RAN polyA proteins are likely translated within repeats. Furthermore, integrated stress response activation enhances SCA3 RAN translation. We suggest that RAN translation in SCA3 is a common event substantially contributing to SCA3 pathogenesis and that the ATXN3 sequence context plays an important role in triggering this unconventional translation. KEYWORDSSCA3, CAG repeat expansion, RAN translation, translation initiation, non-cognate initiation codon, integrated stress response ABBREVIATIONS ATXN3 -ataxin-3, c9ALS/FTD -c9orf72 amyotrophic lateral sclerosis/frontotemporal dementia, CHOP -C/EBP homologous protein, DM1 -myotonic dystrophy type 1 and type 2, ER -endoplasmic reticulum, FECD -Fuchs' endothelial corneal dystrophy, FXTAS -fragile X tremor ataxia syndrome, iMet-tRNAinitiator Met-tRNA, ISR -integrated stress response, MetAPs -methionine aminopeptidases, NAT -Nterminal acetyltransferase, NPC -nuclear pore complex, polyApolyalanine, polyQpolyglutamine, polySpolyserine, RAN translation -repeat associated non-ATG translation, SA -sodium arsenite, SCA3 -spinocerebellar ataxia type 3, TG -thapsigargin INTRODUCTIONSpinocerebellar ataxia type 3 (SCA3) is the most common form of dominantly inherited ataxia in the world and one of nine polyglutamine (polyQ) neurodegenerative diseases. This progressive and fatal disorder is primarily characterized by neuronal dysfunction and degeneration of the cerebellum and functionall...

SUMMARYHow animals rewire cellular programs to survive cold is a fascinating problem with potential biomedical implications, ranging from emergency medicine to space travel. Studying a hibernation-like response in the free-living nematode Caenorhabditis elegans, we uncovered a regulatory axis that enhances the natural resistance of nematodes to severe cold. This axis involves conserved transcription factors, DAF-16/FoxO and PQM-1, which jointly promote cold survival by upregulating FTN-1, a protein related to mammalian Fth1/ferritin. Moreover, we show that inducing expression of Fth1 also promotes cold survival of mammalian neurons, a cell type particularly sensitive to deterioration in hypothermia. Our findings in both animals and cells suggest that FTN-1/Fth1 facilitates cold survival by detoxifying ROS-generating iron species. We finally show that mimicking the effects of FTN-1/Fth1 with drugs protects neurons from cold-induced degeneration, opening a potential avenue to improved treatments of hypothermia.

Regnase-1 is an evolutionarily conserved endoribonuclease. It degrades diverse mRNAs important for many biological processes including immune homeostasis, development and cancer. There are two competing models of Regnase-1-mediated mRNA silencing. One model postulates that Regnase-1 works together with another RNA-binding protein, Roquin-1, which recruits Regnase-1 to specific mRNAs. The other model proposes that the two proteins function separately. Studying REGE-1, the Caenorhabditis elegans ortholog of Regnase-1, we have uncovered its functional relationship with RLE-1, the nematode counterpart of Roquin-1. While both proteins are essential for mRNA silencing, REGE-1 and RLE-1 appear to associate with target mRNA independently of each other. Thus, although the functional interdependence between REGE-1/Regnase-1 and RLE-1/Roquin-1 is conserved, the underlying mechanisms may display species-specific variation, providing a rare perspective on the evolution of this important post-transcriptional regulatory mechanism.