Cécile Martel

Glutathionylation of Adenine Nucleotide Translocase Induced by Carbon Monoxide Prevents Mitochondrial Membrane Permeabilization and Apoptosis

The present work demonstrates the ability of CO to prevent apoptosis in a primary culture of astrocytes. For the first time, the antiapoptotic behavior can be clearly attributed to the inhibition of mitochondrial membrane permeabilization (MMP), a key event in the intrinsic apoptotic pathway. In isolated non-synaptic mitochondria, CO partially inhibits (i) loss of potential, (ii) the opening of a nonspecific pore through the inner membrane, (iii) swelling, and (iv) cytochrome c release, which are induced by calcium, diamide, or atractyloside (a ligand of ANT). CO directly modulates ANT function by enhancing ADP/ATP exchange and prevents its pore-forming activity. Additionally, CO induces reactive oxygen species (ROS) generation, and its prevention by β-carotene decreases CO cytoprotection in intact cells as well as in isolated mitochondria, revealing the key role of ROS. On the other hand, CO induces a slight increase in mitochondrial oxidized glutathione, which is essential for apoptosis modulation by (i) delaying astrocytic apoptosis, (ii) decreasing MMP, and (iii) enhancing ADP/ATP translocation activity of ANT. Moreover, CO and GSSG trigger ANT glutathionylation, a post-translational process regulating protein function in response to redox cellular changes. In conclusion, CO protects astrocytes from apoptosis by preventing MMP, acting on ANT (glutathionylation and inhibition of its pore activity) via a preconditioning-like process mediated by ROS and GSSG.

Fusarial Toxin―Induced Toxicity in Cultured Cells and in Isolated Mitochondria Involves PTPC-Dependent Activation of the Mitochondrial Pathway of Apoptosis

Mycotoxins produced by the Fusarium molds can cause a variety of human diseases and economic losses in livestock. Fusaria produce predominantly two types of mycotoxins: the nonestrogenic trichothecenes including T-2 toxin and the mycoestrogens such as zearalenone (ZEN). In a previous report, we demonstrated that the hepatotoxicity of these mycotoxins involves the mitochondrial pathway of apoptosis. Here, we observed that both fusarotoxins induced cell death by a mitochondria-dependent apoptotic process which includes opening of the mitochondrial permeability transition pore complex (PTPC), loss of mitochondrial transmembrane potential, increase in O(2)(.-) production, mitochondrial relocalization of Bax, cytochrome c release, and caspase activation. Studies performed on isolated mouse liver mitochondria showed that both ZEN and T-2 toxin might act directly on mitochondria to induce a PTPC-dependent permeabilization of mitochondrial membranes. Moreover, they may target different members of PTPC. Indeed, although the inner membrane protein adenine nucleotide translocase could be the target of T-2 toxin, ZEN seems to target the outer membrane protein voltage-dependent anion channel. Cells pretreatment with the p53 inhibitor pifithrin-alpha suggested that ZEN but not T-2 toxin triggered a p53-dependent mitochondrial apoptotic pathway. Finally, mitochondrial alterations induced by ZEN and T-2 toxin are mediated by Bcl-2 family proteins, such as Bax, and prevented by Bcl-x(L) and to a lesser extent by Bcl-2. Taken together, these data indicate that mitochondria play a pivotal role in both ZEN- and T-2 toxin-induced apoptosis and that PTPC members and proteins of Bcl-2 family should be interesting targets to overcome fusarotoxin toxicity.

Mitoparan and target-selective chimeric analogues : Membrane translocation and intracellular redistribution induces mitochondrial apoptosis

Mastoparan, and structurally-related amphipathic peptides, may induce cell death by augmentation of necrotic and/or apoptotic pathways. To more precisely delineate cytotoxic mechanisms, we determined that [Lys(5,8)Aib(10)]mastoparan (mitoparan) specifically induces apoptosis of U373MG and ECV304 cells, as demonstrated by endonuclease and caspase-3 activation and phosphatidylserine translocation. Live cell imaging confirmed that, following translocation of the plasma membrane, mitoparan specifically co-localizes with mitochondria. Complementary studies indicated that mitoparan induces swelling and permeabilization of isolated mitochondria, through cooperation with a protein of the permeability transition pore complex VDAC, leading to the release of the apoptogenic factor, cytochrome c. N-terminal acylation of mitoparan facilitated the synthesis of chimeric peptides that incorporated target-specific address motifs including an integrin-specific RGD sequence and a Fas ligand mimetic. Significantly, these sychnologically-organised peptides demonstrated further enhanced cytotoxic potencies. We conclude that the cell penetrant, mitochondriotoxic and apoptogenic properties of mitoparan, and its chimeric analogues, offer new insights to the study and therapeutic induction of apoptosis.

Biochemical and immunochemical properties of B lymphocyte cytochrome b558

Like neutrophils, Epstein-Barr virus (EBV)-immortalized B lymphocytes express all constituents of the NADPH oxidase complex necessary to generate superoxide anion O2-. The NADPH oxidase activity in EBV-B lymphocytes is only 5% of that measured in neutrophils upon PMA stimulation. Cytochrome b558 is the sole redox membrane component of NADPH oxidase; it is the protein core around which cytosolic factors assemble in order to mediate oxidase activity. In the present study, we have compared the structural and functional properties of cytochrome b558 from EBV-B lymphocytes and neutrophils. Cytochrome b558 from EBV-B lymphocyte plasma membrane, like that from neutrophils, is characterized by a heterodimeric structure with a highly glycosylated beta subunit, known as gp91-phox. While the amount of cytochrome b558 recovered after purification from EBV-B lymphocytes (approximately 0.24 nmol from 1010 cells) was low compared to that recovered from neutrophils (approximately 10 nmol), the biochemical properties of purified cytochrome b558 from both EBV-B lymphocytes and neutrophils were quite similar with respect to their differential spectra, redox potential, and FAD binding site. Once cytochrome b558 was extracted from the EBV-B lymphocyte membrane, it was able to mediate, in a reconstituted system of O2- production the same oxidase turnover as that found for cytochrome b558 extracted from neutrophils. A comparison between membrane bound and soluble cytochrome b558 suggested that the weak oxidase activity measured in intact EBV-B cells might be the result not only of the small amount of expressed cytochrome b558, but also of a defect of the activation process in lymphocyte membrane.

Non-Alcoholic Steatohepatitis: New Insights from OMICS Studies

Non-alcoholic fatty liver disease (NAFLD) is the most common liver pathology characterized by fat accumulation in a context of metabolic syndrome or insulin resistance. It can be associated with obesity, diabetes, hyperinsulinemia, dyslipidemia as well as hypertension. NAFLD consists of a large spectrum of hepatic lesions including benign steatosis, non-alcoholic steatohepatitis (NASH), cirrhosis or hepatocellular carcinoma. Upon chronic stress, NASH would occur via at least two-hits process involving modulation of a high number of genes and proteins. Firstly, the accumulation of fat, either due to the increased inflow of free fatty acids or de novo lipogenesis, leads to steatosis. Secondly, when adaptive mechanisms for stress tolerance are overwhelmed, lipotoxicity and chronic inflammation trigger major hepatic damages, mainly via oxidative and inflammatory stress, lipid peroxidation and cell death. As a consequence, all these processes concur to favor steatohepatitis, fibrosis and cancer. Recently, the elucidation of physiopathological signaling cascades controlling NAFLD and NASH benefited from large-scale studies, namely the omics, such as transcriptomics, genomics, proteomics, and lipidomics. The advent of lipidomics would allow shedding light upon the respective roles of triglyceride and fatty acid metabolites in the lipotoxic liver injury hypothesis for the pathogenesis of NASH. In this review, the contribution of the omics to the understanding of the molecular basis of NASH is discussed that could offer perspectives for novel biomarkers discovery.

Characterization of six novel mutations in the CYBB gene leading to different sub-types of X-linked chronic granulomatous disease

Chronic granulomatous disease is an inherited disorder in which phagocytes lack a functional NADPH oxidase and so cannot generate superoxide anions (O2−). The most common form is caused by mutations in CYBB encoding gp91 phox, the heavy chain of flavocytochrome b558 (XCGD). We investigated 11 male patients and their families suspected of suffering from X-linked CGD. These XCGD patients were classified as having different variants (X910, X91− or X91+) according to their cytochrome b558 expression and NADPH oxidase activity. Nine patients had X910 CGD, one had X91− CGD and one had X91+ CGD. Six mutations in CYBB were novel. Of the four new X910 CGD cases, three were point mutations: G65A in exon 2, G387T in exon 5 and G970T in exon 9, leading to premature stop codons at positions Try18, Try125 and Glu320, respectively, in gp91 phox. One case of X910 CGD originated from a new 1005G deletion detected in exon 9. Surprisingly, four nonsense mutations in exon 5 led to the generation of two mRNAs, one with a normal size containing the mutation and the other in which exon 5 had been spliced. A novel X91− CGD case with low gp91 phox expression was diagnosed. It was caused by an 11-bp deletion in the linking region between exon 12 and intron 12, activating a new cryptic site. Finally, a new X91+ CGD case was detected, characterized by a missense mutation Leu505Arg in the potential NADPH-binding site of gp91 phox. No clear correlation between the severity of the clinical symptoms and the sub-type of XCGD could be established.

A novel and unusual case of chronic granulomatous disease in a child with a homozygous 36-bp deletion in the CYBA gene (A220) leading to the activation of a cryptic splice site in intron 4

Abstract. Chronic granulomatous disease (CGD) is a rare congenital disorder in which phagocytes cannot generate superoxide (O2–) and other microbicidal oxidants because of mutations in one of the four components of the O2–-generating NADPH oxidase complex. A subgroup (approximately 5% of identified CGD patients) has been reported to have mutations in the gene encoding the small p22phox subunit of the flavocytochrome b558, the redox element of phagocyte NADPH oxidase. Here, we report the case of an autosomal recessive CGD patient with a defect in the p22phox subunit. Neutrophils failed to produce O2– in response to soluble and particulate stimuli, and cytochrome b558 was absent as measured by immunoblotting and difference absorption spectra. Mutations in the p22phox mRNA of the patient were detected by reverse transcription/polymerase chain reaction amplification and sequencing. The defect in the mRNA was a 179-bp insertion associated with a 21-bp deletion of the beginning of exonxa05 at positionxa0315 from the translation start codon of the p22phox cDNA. This defect was also detected in the patients parents. In the genomic DNA of the patient, the molecular defect was a homozygous 36-bp deletion in the linking sequence between intronxa04 and exonxa05. This genomic deletion corresponded to 15xa0bp of the 3 extremity of intronxa04 and 21xa0bp of the beginning of exonxa05 (the same deletion of exonxa05 seen in the corresponding mRNA). The splicing mRNA error is attributable to the loss of the ag acceptor site of intronxa04 and the utilization of a cryptic splice site with an ag sequence at position 355–356 of intronxa04.

Molecular events involved in ochratoxin A induced mitochondrial pathway of apoptosis, modulation by Bcl-2 family members

In this study, we looked for the role of the mitochondrion in the cytotoxicity of ochratoxin A (OTA), which is one of the most abundant food‐contaminating mycotoxins in the world. In different human carcinoma cell lines, OTA triggered a mitochondria‐dependent apoptotic process, which is characterized by opening of the mitochondrial permeability transition pore (PTPC), loss of mitochondrial transmembrane potential (ΔΨm), increase in O2[chemp]– production, mitochondrial relocalization of Bax, release of cytochrome c, and caspase activation. However, studies performed on purified organelles suggested that OTA does not directly target the mitochondrion. In addition, we showed that mitochondrial alterations induced by this mycotoxin are favored by the proapoptotic protein Bax, but not Bak. These alterations are prevented by the antiapoptotic proteins, Bcl‐2 and to a lesser degree by Bcl‐XL. Taken together, these data indicate that although mitochondria, PTPC members and proteins of Bcl‐2 family play a pivotal role in OTA‐induced apoptosis, they do not constitute real targets to overcome its toxicity.

Functional and genetic characterization of two extremely rare cases of Williams–Beuren Syndrome associated with chronic granulomatous disease

Williams–Beuren syndrome (WBS) is a neurodevelopmental disorder with multi-systemic manifestations, caused by a heterozygous segmental deletion of 1.55–1.83u2009Mb at chromosomal band 7q11.23. The deletion can include the NCF1 gene that encodes the p47phox protein, a component of the leukocyte NADPH oxidase enzyme, which is essential for the defense against microbial pathogens. It has been postulated that WBS patients with two functional NCF1 genes are more susceptible to occurrence of hypertension than WBS patients with only one functional NCF1 gene. We now describe two extremely rare WBS patients without any functional NCF1 gene, because of a mutation in NCF1 on the allele not carrying the NCF1-removing WBS deletion. These two patients suffer from chronic granulomatous disease with increased microbial infections in addition to WBS. Interestingly, one of these patients did suffer from hypertension, indicating that other factors than NADPH oxidase in vascular tissue may be involved in causing hypertension.