The Characterization of theCaenorhabditis elegansMitochondrial Thioredoxin System Uncovers an Unexpected Protective Role of Thioredoxin Reductase 2 in β-Amyloid Peptide Toxicity

[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.