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In the presence of aggregation-prone proteins, the cytosol and endoplasmic reticulum (ER) undergo a dramatic shift in their respective redox status, with the cytosol becoming more oxidized and the ER more reducing. However, whether and how changes in the cellular redox status may affect protein aggregation is unknown. Here, we show that C. elegans loss-of-function mutants for the glutathione reductase gsr-1 gene enhance the deleterious phenotypes of heterologous human, as well as endogenous worm aggregation-prone proteins. These effects are phenocopied by the GSH-depleting agent diethyl maleate. Additionally, gsr-1 mutants abolish the nuclear translocation of HLH-30/TFEB transcription factor, a key inducer of autophagy, and strongly impair the degradation of the autophagy substrate p62/SQST-1::GFP, revealing glutathione reductase may have a role in the clearance of protein aggregates by autophagy. Blocking autophagy in gsr-1 worms expressing aggregation-prone proteins results in strong synthetic developmental phenotypes and lethality, supporting the physiological importance of glutathione reductase in the regulation of misfolded protein clearance. Furthermore, impairing redox homeostasis in both yeast and mammalian cells induces toxicity phenotypes associated with protein aggregation. Together, our data reveal that glutathione redox homeostasis may be central to proteostasis maintenance through autophagy regulation., Cristina Ayuso García and the Live Cell Imaging Facility, Karolinska Institutet, Sweden (supported by grants from the Knut and Alice Wallenberg Foundation, the Swedish Research Council, the Centre for Innovative Medicine and the Jonasson Centre at RIT, Sweden) are acknowledged for technical assistance. The Spanish Ministry of Economy and Competitiveness supported EF-S and VG (BFU2016–78265-P), PA (BFU2016–79313-P and MDM-2016–0687), and AM-V (BFU2015–64408-P). AM-V was also supported by the Instituto de Salud Carlos III (PI11/00072) and RPV-M (CPII16/00004, PI14/00949 and PI17/00011). All projects were cofinanced by the Fondo Social Europeo (FEDER). AM-V is a member of the GENIE and EU-ROS Cost Actions of the European Union and RPV-M is a Marie Curie Fellow (CIG322034, EU).

[Aim]: Functional in vivo studies on the mitochondrial thioredoxin system are hampered by the embryonic or larval lethal phenotypes displayed by murine or Drosophila knock-out models. Thus, the access to alternative metazoan knock-out models for the mitochondrial thioredoxin system is of critical importance. [Results]: We report here the characterization of the mitochondrial thioredoxin system of Caenorhabditis elegans that is composed of the genes trx-2 and trxr-2. We demonstrate that the proteins thioredoxin 2 (TRX-2) and thioredoxin reductase 2 (TRXR-2) localize to the mitochondria of several cells and tissues of the nematode and that trx-2 and trxr-2 are upregulated upon induction of the mitochondrial unfolded protein response. Surprisingly, C. elegans trx-2 (lof ) and trxr-2 (null) single and double mutants are viable and display similar growth rates as wild-type controls. Moreover, the lack of the mitochondrial thioredoxin system does not affect longevity, reactive oxygen species production or the apoptotic program. Interestingly, we found a protective role of TRXR-2 in a transgenic nematode model of Alzheimer's disease (AD) that expresses human β-amyloid peptide and causes an age-dependent progressive paralysis. Hence, trxr-2 downregulation enhanced the paralysis phenotype, while a strong decrease of β-amyloid peptide and amyloid deposits occurred when TRXR-2 was overexpressed. [Innovation]: C. elegans provides the first viable metazoan knock-out model for the mitochondrial thioredoxin system and identifies a novel role of this system in β-amyloid peptide toxicity and AD. [Conclusion]: The nematode strains characterized in this work make C. elegans an ideal model organism to study the pathophysiology of the mitochondrial thioredoxin system at the level of a complete organism., A.M.-V. was supported by the Instituto de Salud Carlos III [Projects PI050065 and PI080557, co-financed by the Fondo Social Europeo, FEDER] and Junta de Andalucía [Projects P07-CVI-02697 and P08-CVI-03629], Spain. B.C.-V. was supported by a fellowship from the Consejo Nacional de Ciencia y Tecnología (CONACYT) from the Government of Mexico. P.N. was supported by the Instituto de Salud Carlos III [project PI080500, co-financed by the Fondo Social Europeo, FEDER], and Junta de Andalucía [project P08-CTS-03988]. Work in the laboratory of P.S., a member of the NordForsk Nordic C. elegans network, was supported by a grant from the Swedish Research Council. J.C. was supported by the Spanish Ministry of Education and Science Grant BFU2010-21794 and the RiojaSalud Foundation.

et al., [Aims]: Cells have developed quality control systems for protection against proteotoxicity. Misfolded and aggregation-prone proteins, which are behind the initiation and progression of many neurodegenerative diseases (ND), are known to challenge the proteostasis network of the cells. We aimed to explore the role of DNJ-27/ERdj5, an endoplasmic reticulum (ER)-resident thioredoxin protein required as a disulfide reductase for the degradation of misfolded proteins, in well-established Caenorhabditis elegans models of Alzheimer, Parkinson and Huntington diseases. [Results]: We demonstrate that DNJ-27 is an ER luminal protein and that its expression is induced upon ER stress via IRE-1/XBP-1. When dnj-27 expression is downregulated by RNA interference we find an increase in the aggregation and associated pathological phenotypes (paralysis and motility impairment) caused by human β-Amyloid peptide (Aβ), α-synuclein (α-syn) and polyglutamine (polyQ) proteins. In turn, DNJ-27 overexpression ameliorates these deleterious phenotypes. Surprisingly, despite being an ER-resident protein, we show that dnj-27 downregulation alters cytoplasmic protein homeostasis and causes mitochondrial fragmentation. We further demonstrate that DNJ-27 overexpression substantially protects against the mitochondrial fragmentation caused by human Aβ and α-syn peptides in these worm models. [Innovation]: We identify C. elegans dnj-27 as a novel protective gene for the toxicity associated with the expression of human Aβ, α-syn and polyQ proteins, implying a protective role of ERdj5 in Alzheimer, Parkinson and Huntington diseases. Conclusion: Our data support a scenario where the levels of DNJ-27/ERdj5 in the ER impact cytoplasmic protein homeostasis and the integrity of the mitochondrial network which might underlie its protective effects in models of proteotoxicity associated to human ND. Antioxid. Redox Signal. 20, 217-235., A.M.-V. was supported by the Instituto de Salud Carlos III (Projects PI080557 and PI1100072, cofinanced by the Fondo Social Europeo [FEDER]), Junta de Andalucía (Projects P07-CVI-02697 and P08-CVI-03629) and CSIC (Project PIE 200920I118). F.S. and N.J.S. were supported by NIH (AR-05342).