Nuestros investigadores

Tomás Aragón Amonárriz

Publicaciones científicas más recientes (desde 2010)

Autores: Larrea, L. ; et al.
ISSN 0969-9961  Vol. 137  2020  págs. 104781
Alpha-synuclein (aSyn) protein levels are sufficient to drive Parkinson's disease (PD) and other synucleinopathies. Despite the biomedical/therapeutic potential of aSyn protein regulation, little is known about mechanisms that limit/control aSyn levels. Here, we investigate the role of a post-translational modification, N-terminal acetylation, in aSyn neurotoxicity. N-terminal acetylation occurs in all aSyn molecules and has been proposed to determine its lipid binding and aggregation capacities; however, its effect in aSyn stability/neurotoxicity has not been evaluated. We generated N-terminal mutants that alter or block physiological aSyn N-terminal acetylation in wild-type or pathological mutant E46K aSyn versions and confirmed N-terminal acetylation status by mass spectrometry. By optical pulse-labeling in living primary neurons we documented a reduced half-life and accumulation of aSyn N-terminal mutants. To analyze the effect of N-terminal acetylation mutants in neuronal toxicity we took advantage of a neuronal model where aSyn toxicity was scored by longitudinal survival analysis. Salient features of aSyn neurotoxicity were previously investigated with this approach. aSyn-dependent neuronal death was recapitulated either by higher aSyn protein levels in the case of WT aSyn, or by the combined effect of protein levels and enhanced neurotoxicity conveyed by the E46K mutation. aSyn N-terminal mutations decreased E46K aSyn-dependent neuronal death both by reducing protein levels and, importantly, by reducing the intrinsic E46K aSyn toxicity, being the D2P mutant the least toxic. Together, our results illustrate that the N-terminus determines, most likely through its acetylation, aSyn protein levels and toxicity, identifying this modification as a potential therapeutic target.
Autores: Argemie, J.; Latasa, María Ujué; Atkinson, S. R.; et al.
ISSN 2041-1723  Vol. 10  Nº 3126  2019 
Alcoholic hepatitis (AH) is a life-threatening condition characterized by profound hepatocellular dysfunction for which targeted treatments are urgently needed. Identification of molecular drivers is hampered by the lack of suitable animal models. By performing RNA sequencing in livers from patients with different phenotypes of alcohol-related liver disease (ALD), we show that development of AH is characterized by defective activity of liver-enriched transcription factors (LETFs). TGF beta 1 is a key upstream transcriptome regulator in AH and induces the use of HNF4 alpha P2 promoter in hepatocytes, which results in defective metabolic and synthetic functions. Gene polymorphisms in LETFs including HNF4 alpha are not associated with the development of AH. In contrast, epigenetic studies show that AH livers have profound changes in DNA methylation state and chromatin remodeling, affecting HNF4 alpha-dependent gene expression. We conclude that targeting TGF beta 1 and epigenetic drivers that modulate HNF4 alpha-dependent gene expression could be beneficial to improve hepatocellular function in patients with AH.
Autores: Deodati, A. ; Argemí, José María; Germani, D. ; et al.
Revista: PLOS ONE
ISSN 1932-6203  Vol. 13  Nº 6  2018  págs. e0198490
Early life events are associated with the susceptibility to chronic diseases in adult life. Perturbations of endoplasmic reticulum (ER) homeostasis activate the unfolded protein response (UPR), which contributes to the development of metabolic alterations. Our aim was to evaluate liver UPR in an animal model of intrauterine growth restriction (IUGR). A significantly increased expression of X-box binding protein-1 spliced (XBP1s) mRNA (p<0.01), Endoplasmic Reticulum-localized DnaJ homologue (Erdj4) mRNA (p<0.05) and Bip/GRP78-glucose-regulated protein 78 (Bip) mRNA (p<0.05) was observed in the liver of IUGR rats at birth. Furthermore, the expression of gluconeogenesis genes and lipogenesis genes were significantly upregulated (p<0.05) in IUGR pups. At 105 d, IUGR male rats showed significantly reduced glucose tolerance (p<0.01). A significant decreased expression of XBP1s mRNA (p<0.01) and increased expression of double-stranded RNA-dependent protein kinase-like ER kinase (PERK) and Asparagine synthetase (ASNS) (p<0.05) was observed in the liver of IUGR male adult rats. Liver focal steatosis and periportal fibrosis were observed in IUGR rats. These findings show for the first time that fetal exposure to uteroplacental insufficiency is associated with the activation of hepatic UPR and suggest that UPR signaling may play a role in the metabolic risk.
Autores: Argemí, José María; Kress, T. R.; et al.
ISSN 0016-5085  Vol. 152  Nº 5  2017  págs. 1203 - 1216.e15
BACKGROUND & AIMS: Liver regeneration after partial hepatectomy ( PH) increases the protein folding burden at the endoplasmic reticulum of remnant hepatocytes, resulting in induction of the unfolded protein response. We investigated the role of the core unfolded protein response transcription factor X-box binding protein 1 ( XBP1) in liver regeneration using genome-wide chromatin immunoprecipitation analysis. METHODS: We performed studies with C57Bl6-J ( control) and interleukin 6-knockout mice. Mice underwent PH or sham surgeries. In some mice, hepatic expression of XBP1 was knocked down by injection of adenoviral vectors encoding small hairpin RNAs against Xbp1 messenger RNA. Liver tissues were collected before surgery and at 6 and 48 hours after surgery and analyzed by chromatin immunoprecipitation followed by sequencing. We also performed functional analyses of HepG2 cells. RESULTS: Expression of XBP1 by hepatocytes increased immediately after PH ( priming phase of liver regeneration) in control mice, but this effect was delayed in interleukin 6-deficient mice. In mice with knockdown of XBP1, we observed of liver tissue persistent endoplasmic reticulum stress, defects in acute-phase response, and increased hepatocellular damage, compared with control mice. Chromatin immunoprecipitation analyses of liver tissue showed that at 6 hours after PH, liver XBP1 became bound to a large set of genes implicated in proteostasis, the acute-phase response, metabolism, and the DNA damage response ( DDR). At this time point, XBP1 bound the promoter of the signal transducer and activator of transcription 3 gene ( Stat3). Livers of XBP1-knockdown mice showed reduced expression of STAT3 and had lower levels of STAT3 phosphorylation at Ser727, a modification that promotes cell proliferation and the DDR. Regenerating livers from XBP1-knockdown mice expressed high levels of a marker of DNA double-strand breaks, phosphorylated histone 2A, member X ( H2AX), compared with control mice. The inhibition of XBP1 expression caused a reduced up-regulation of DDR messenger RNAs in regenerating hepatocytes. CONCLUSION: In livers of mice, we found that PH induces expression of XBP1, and that this activity requires interleukin 6. XBP1 expression regulates the unfolded protein response, acute-phase response, and DDR in hepatocytes. In regenerating livers, XBP1 deficiency leads to endoplasmic reticulum stress and DNA damage.
Autores: Cohen, N.; Breker, M.; Bakunts, A.; et al.
ISSN 0021-9533  Vol. 130  Nº 19  2017  págs. 3222 - 3233
The unfolded protein response (UPR) allows cells to adjust secretory pathway capacity according to need. Ire1, the endoplasmic reticulum (ER) stress sensor and central activator of the UPR is conserved from the budding yeast Saccharomyces cerevisiae to humans. Under ER stress conditions, Ire1 clusters into foci that enable optimal UPR activation. To discover factors that affect Ire1 clustering, we performed a high-content screen using a whole-genome yeast mutant library expressing Ire1-mCherry. We imaged the strains following UPR induction and found 154 strains that displayed alterations in Ire1 clustering. The hits were enriched for iron and heme effectors and binding proteins. By performing pharmacological depletion and repletion, we confirmed that iron (Fe3+) affects UPR activation in both yeast and human cells. We suggest that Ire1 clustering propensity depends on membrane composition, which is governed by heme-dependent biosynthesis of sterols. Our findings highlight the diverse cellular functions that feed into the UPR and emphasize the cross-talk between organelles required to concertedly maintain homeostasis.
Autores: Aragón, Tomás; Martínez-Velez, N.; et al.
ISSN 1522-8517  Vol. 18  Nº 8  2016  págs. 1109-1119
These findings provide a strong rationale for combining temozolomide with ER stress-inducing drugs as an alternative therapeutic strategy for glioblastoma.
Autores: Argemí, José María; Kress, T.; et al.
ISSN 0270-9139  Vol. 64  Nº Supl. 1  2016  págs. 266A
Autores: Aragón, Tomás; et al.
Revista: PLOS ONE
ISSN 1932-6203  Vol. 8  Nº 8  2013  págs. e71082
Understanding how neural cells handle proteostasis stress in the endoplasmic reticulum (ER) is important to decipher the mechanisms that underlie the cell death associated with neurodegenerative diseases and to design appropriate therapeutic tools. Here we have compared the sensitivity of a human neuroblastoma cell line (SH-SY5H) to the ER stress caused by an inhibitor of protein glycosylation with that observed in human embryonic kidney (HEK-293T) cells. In response to stress, SH-SY5H cells increase the expression of mRNA encoding downstream effectors of ER stress sensors and transcription factors related to the unfolded protein response (the spliced X-box binding protein 1, CCAAT-enhancer-binding protein homologous protein, endoplasmic reticulum-localized DnaJ homologue 4 and asparagine synthetase). Tunicamycin-induced death of SH-SY5H cells was prevented by terminal aromatic substituted butyric or valeric acids, in association with a decrease in the mRNA expression of stress-related factors, and in the accumulation of the ATF4 protein. Interestingly, this decrease in ATF4 protein occurs without modifying the phosphorylation of the translation initiation factor eIF2¿. Together, these results show that when short chain phenyl acyl acids alleviate ER stress in SH-SY5H cells their survival is enhanced.
Autores: Mauleon, Miren Itsaso; et al.
ISSN 0964-6906  Vol. 22  Nº 14  2013  págs. 2929-40
Acute intermittent porphyria (AIP) is a hepatic metabolic disease that results from haplo-insufficient activity of porphobilinogen deaminase (PBGD). The dominant clinical feature is acute intermittent attacks when hepatic heme synthesis is activated by endocrine or exogenous factors. Gene therapy vectors over-expressing PBGD protein in the liver offers potential as a cure for AIP. Here, we developed a helper-dependent adenovirus (HDA) encoding human PBGD (hPBGD) and assessed its therapeutic efficacy in a murine model of AIP. Intravenous or intrahepatic administration of HDA-hPBGD to AIP mice resulted in a sustained hepatic hPBGD expression in a dose-dependent manner. Intrahepatic administration conveyed full protection against induced porphyria attacks at a significantly lower viral dose than intravenous injection. Transgenic hPBGD accumulated only in the cytosol of hepatocytes as the endogenous protein. Characterization of PBGD-deficient mouse strains revealed that a strong PBGD deficiency causes the chronic disturbance of cytosolic and endoplasmic reticulum folding machineries. This disturbance was completely restored over time by the over-expression of hPBGD. HDA-hPBGD is a promising vector that protects against porphyria attacks and resolves the chronic folding stress associated with low levels of PBGD activity.
Autores: Kimmig P; Diaz M; Zheng J; et al.
Revista: ELIFE
ISSN 2050-084X  Vol. 1  2012  págs. e00048
The unfolded protein response (UPR) monitors the protein folding capacity of the endoplasmic reticulum (ER). In all organisms analyzed to date, the UPR drives transcriptional programs that allow cells to cope with ER stress. The non-conventional splicing of Hac1 (yeasts) and XBP1 (metazoans) mRNA, encoding orthologous UPR transcription activators, is conserved and dependent on Ire1, an ER membrane-resident kinase/endoribonuclease. We found that the fission yeast Schizosaccharomyces pombe lacks both a Hac1/XBP1 ortholog and a UPR-dependent-transcriptional-program. Instead, Ire1 initiates the selective decay of a subset of ER-localized-mRNAs that is required to survive ER stress. We identified Bip1 mRNA, encoding a major ER-chaperone, as the sole mRNA cleaved upon Ire1 activation that escapes decay. Instead, truncation of its 3' UTR, including loss of its polyA tail, stabilized Bip1 mRNA, resulting in increased Bip1 translation. Thus, S. pombe uses a universally conserved stress-sensing machinery in novel ways to maintain homeostasis in the ER.DOI:
Autores: Pincus, D.; Chevalier, M. W.; Aragón, Tomás; et al.
ISSN 1544-9173  Vol. 8  Nº 7  2010  págs. e1000415
The unfolded protein response (UPR) is an intracellular signaling pathway that counteracts variable stresses that impair protein folding in the endoplasmic reticulum (ER). As such, the UPR is thought to be a homeostat that finely tunes ER protein folding capacity and ER abundance according to need. The mechanism by which the ER stress sensor Ire1 is activated by unfolded proteins and the role that the ER chaperone protein BiP plays in Ire1 regulation have remained unclear. Here we show that the UPR matches its output to the magnitude of the stress by regulating the duration of Ire1 signaling. BiP binding to Ire1 serves to desensitize Ire1 to low levels of stress and promotes its deactivation when favorable folding conditions are restored to the ER. We propose that, mechanistically, BiP achieves these functions by sequestering inactive Ire1 molecules, thereby providing a barrier to oligomerization and activation, and a stabilizing interaction that facilitates de-oligomerization and deactivation. Thus BiP binding to or release from Ire1 is not instrumental for switching the UPR on and off as previously posed. By contrast, BiP provides a buffer for inactive Ire1 molecules that ensures an appropriate response to restore protein folding homeostasis to the ER by modulating the sensitivity and dynamics of Ire1 activity.