Nuestros investigadores

José María Argemí Ballbé

Publicaciones científicas más recientes (desde 2010)

Autores: Monte, M. J.; Alonso-Pena, M.; Briz, O.; et al.
ISSN 0168-8278  Vol. 66  Nº 3  2017  págs. 581 - 588
Background & Aims: Acyl-CoA oxidase (ACOX2) is involved in the shortening of C27 cholesterol derivatives to generate C24 bile acids. Inborn errors affecting the rest of peroxisomal enzymes involved in bile acid biosynthesis have been described. Here we aimed at investigating the case of an adolescent boy with persistent hypertransaminasemia of unknown origin and suspected dysfunction in bile acid metabolism. Methods: Serum and urine samples were taken from the patient, his sister and parents and underwent HPLC-MS/MS and HPLC-TOF analyses. Coding exons in genes of interest were amplified by high-fidelity PCR and sequenced. Wild-type or mutated (mutACOX2) variants were overexpressed in human hepatoblastoma HepG2 cells to determine ACOX2 enzymatic activity, expression and subcellular location. Results: The patient's serum and urine showed negligible amounts of C24 bile acids, but augmented levels of C27 intermediates, mainly tauroconjugated trihydroxycholestanoic acid (THCA). Genetic analysis of enzymes potentially involved revealed a homozygous missense mutation (c.673C>T; R225W) in ACOX2. His only sister was also homozygous for this mutation and exhibited similar alterations in bile acid profiles. Both parents were heterozygous and presented normal C24 and C27 bile acid levels. Immunofluorescence studies showed similar protein size and peroxisomal localization for both normal and mutated variants. THCA biotransformation into cholic acid was enhanced in cells overexpressing ACOX2, but not in those overexpressing mutACOX2. Both cell types showed similar sensitivity to oxidative stress caused by C24 bile acids. In contrast, THCA-induced oxidative stress and cell death were reduced by overexpressing ACOX2, but not mutACOX2. Conclusion: ACOX2 deficiency, a condition characterized by accumulation of toxic C27 bile acid intermediates, is a novel cause of isolated persistent hypertransaminasemia. Lay summary: Elevation of serum transaminases is a biochemical sign of liver damage due to multiplicity of causes (viruses, toxins, autoimmunity, metabolic disorders). In rare cases the origin of this alteration remains unknown. We have identified by the first time in a young patient and his only sister a familiar genetic defect of an enzyme called ACOX2, which participates in the transformation of cholesterol into bile acids as a cause of increased serum transaminases in the absence of any other symptomatology. This treatable condition should be considered in the diagnosis of those patients where the cause of elevated transaminases remains obscure. (C) 2016 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
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: 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: Argemí, José María; Cabezas, J.; Massey, V. L.; et al.
ISSN 0270-9139  Vol. 66  Nº Supl. 1  2017  págs. 93A - 94A
Background: Alcoholic liver disease (ALD) is the main cause of cirrhosis worldwide and the main driver of health expenditure in hospitalized patients with liver disease in the US. The development of targeted therapies is hampered by a poor knowledge of the underlying mechanisms. It is unknown why some patients develop severe forms (i. e. alcoholic hepatitis -AH-) characterized by poor hepatocyte function. We hypothesize that global changes in the transcription factor activity may play a role in the development of severe forms. To test this hypothesis, we performed a functional analysis of RNAseq data from livers of patients with different ALD phenotypes compared to normal livers and cirrhosis. Methods: Liver biopsy specimens were collected from ALD patients in different stages of disease progression: early compensated ASH (N=12), non severe AH (N=11), severe AH non responders to steroids (N=9), severe AH responders (N=9) and liver explants from transplanted patients with severe AH (N=1l). Compensated HCV cirrhosis (n=10) and fragments from normal livers (N=10) were also studied. High-throughput RNA sequencing (RNA-Seq) was done. Unsupervised clustering (Bioconductor), gene ontology analysis (GSEA) and upstream regulator prediction (Ingenuity Pathway Analysis and Opossum) were performed. Results: Clustering analysis showed a specific transcriptome pattern across different ALD phenotypes. Major changes in ALD progression included the inhibition of hepatocyte biosynthetic pathways, drug metabolism, hepatocyte differentiation and the activation of cell proliferation, ECM deposition, inflammation and hypoxia. Importantly, AH mortality was associated with inhibition of cell responses to hypoxia and inflammation. Analysis of upstream regulators revealed profound transcription factor reprogramming Changes in the transcriptome along disease progression predicted a marked inhibition of nuclear factors responsible for hepatocyte differentiation (i. e. HNF4A, HNF1A and FOXA1), while factors implicated in cell damage and inflammation (i. e. NFATC2, STAT1 and NFKB1) were significantly activated Bioinformatic prediction showed an involvement of EGFR signaling in disease progression Studies in cultured hepatocytes demonstrated the inhibitory effect of EGFR activity on HNF4A expression and stability Conclusion: Progression to severe forms of ALD including AH is characterized by decreased activity of transcription factors implicated in hepatocyte differentiation. These results suggest that targeting transcription factors that maintain normal hepatocellular function represent a potential novel therapeutic strategy in these patients.
Autores: Monte, M. J.; Alonso, M.; Briz, O.; et al.
ISSN 0168-8278  Vol. 64  Nº 2, Supl.  2016  págs. S301