Abstracts
In this page you will find a selection of our most recent scientific publications.
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Exp Mol Pathol. 2005 Jun;78(3):239-46. Epub 2005 Mar 2.
2',5'-Oligoadenylate size is critical to protect RNase L against proteolytic cleavage in chronic fatigue syndrome.
Frémont M, El Bakkouri K, Vaeyens F, Herst CV, De Meirleir K, Englebienne P.
A dysregulation in the 2',5'-oligoadenylate (2-5A)-dependent RNase L antiviral pathway has been detected in peripheral blood mononuclear cells (PBMC) of chronic fatigue syndrome (CFS) patients, which is characterized by upregulated 2-5A synthetase and RNase L activities, as well as by the presence of a low molecular weight (LMW) 2-5A-binding protein of 37-kDa related to RNase L. This truncated protein has been shown to originate from proteolytic cleavage of the native 83-kDa RNase L by m-calpain and human leukocyte elastase (HLE). We investigated the possible role of 2-5A oligomers in the proteolytic action toward the endonuclease and show that incubation of CFS PBMC extracts with 2-5A trimer and tetramer, but not with the dimer, results in a significant protection of the native 83-kDa RNase L against cleavage by endogenous and purified proteases. Similar results are obtained with a purified recombinant RNase L. An analysis of the size of 2-5A oligomers produced by the catalytic activity of the 2-5A synthetase present in PBMC extracts further shows that samples containing the 37-kDa RNase L preferentially produce 2-5A dimers instead of higher oligomers. Taken together, our results indicate that homodimerization of RNase L by 2-5A oligomers higher than the dimer prevents its cleavage by proteolytic enzymes. The presence of the truncated 37-kDa RNase L in PBMC extracts is therefore likely to result, not only from the abnormal activation of inflammatory proteases, but also from a dysregulation in 2-5A synthetase induction or activation towards the preferential production of 2-5A dimers.
PMID: 15924878 [PubMed - indexed for MEDLINE]
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Life Sci. 2006 Mar 13;78(16):1845-56. Epub 2005 Dec 1.
Double-stranded RNA-dependent protein kinase (PKR) is a stress-responsive kinase that induces NFkappaB-mediated resistance against mercury cytotoxicity.
Frémont M, Vaeyens F, Herst CV, De Meirleir KL, Englebienne P.
The interferon-inducible, double-stranded (ds)RNA-dependent protein kinase (PKR) plays a major role in antiviral defense mechanisms where it down-regulates translation via phosphorylation of eukaryotic translation initiation factor 2alpha. PKR is also involved in the activation of nuclear factor kappaB (NFkappaB) through activation of the IkappaB kinase complex. Activation of PKR can occur in the absence of dsRNA and in such case is controlled by intracellular regulators like the PKR-activating protein (PACT), the PKR inhibitor p58(IPK), or heat-shock proteins (Hsp). These regulators are activated by stress stimuli, supporting a role for PKR in response to stress; however the final outcome of PKR activation in stress situations is unclear. We present here evidence that expression and activation of PKR contributes to an increased cellular resistance to mercury cytotoxicity. In two cell lines constitutively expressing PKR (THP-1 and Molt-3), treatment with the PKR inhibitor 2-aminopurine increases their sensitivity to mercury. In contrast, Ramos cells, which do not constitutively express PKR, present an increased resistance to mercury when PKR expression is induced by polyIC or interferon-beta treatment. This protective effect is inhibited by 2-aminopurine. We also show that exposure of Ramos cells to mercury leads to the induction of Hsp70. Treatment of cells with Hsp70 or NFkappaB inhibitors suppresses the PKR-dependent protection. We propose a model where PKR, modulated by Hsp70, activates a NFkappaB-mediated protective pathway. Because the cytotoxicity of mercury is primarily due to the generation of reactive oxygen species, our results suggest a more general function of PKR in the mechanisms of cellular response to oxidative stress.
PMID: 16324719 [PubMed - indexed for MEDLINE]
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Expert Opin Ther Targets. 2008 Mar;12(3):281-9.
Intracellular immune dysfunction in myalgic encephalomyelitis/chronic fatigue syndrome: state of the art and therapeutic implications.
Nijs J, Frémont M.
BACKGROUND: Evidence in support of intracellular immune dysfunctions in people with myalgic encephalomyelitis (ME)/chronic fatigue syndrome (CFS) is accumulating, but few studies have addressed intracellular immunity as a potential therapeutic target. OBJECTIVE: To provide an overview of our present understanding of intracellular immunity in ME/CFS, to relate the intracellular immune dysfunctions to other aspects of the illness like decreased natural killer cell function, the presence of infections and poor exercise performance, and to point to potential therapeutic targets. METHODS: An in-depth review of the scientific literature of intracellular immunity in people with ME/CFS was performed. RESULTS/CONCLUSION: From the scientific literature it is concluded that proteolytic cleavage of the native RNase L enzyme is characteristic of the dysregulation of intracellular immunity in people with ME/CFS, but the origin of the dysregulation is speculative. There is increasing evidence for immune cell apoptosis and upregulation of various aspects of the 2'-5' oligoadenylate (2-5A) synthetase/RNase L pathway in ME/CFS. This review provides the theoretical rationale for conducting studies examining the effectiveness of direct or indirect drug targeting of the 2-5A synthetase/RNase L pathway in ME/CFS patients.
PMID: 18269338 [PubMed - indexed for MEDLINE]
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Biochem Biophys Res Commun. 2008 Nov 7;376(1):231-3. Epub 2008 Sep 5.
Lower frequency of IL-17F sequence variant (His161Arg) in chronic fatigue syndrome patients.
Metzger K, Frémont M, Roelant C, De Meirleir K.
Chronic fatigue syndrome (CFS) is characterized by immune dysfunctions including chronic immune activation, inflammation, and alteration of cytokine profiles. T helper 17 (Th17) cells belong to a recently identified subset of T helper cells, with crucial regulatory function in inflammatory and autoimmune processes. Th17 cells are implicated in allergic inflammation, intestinal diseases, central nervous system inflammation, disorders that may all contribute to the pathophysiology of CFS. IL-17F is one of the pro-inflammatory cytokines secreted by Th17 cells. We investigated the association between CFS and the frequency of rs763780, a C/T genetic polymorphism leading to His161Arg substitution in the IL-17F protein. The His161Arg variant (C allele) antagonizes the pro-inflammatory effects of the wild-type IL-17F. A significantly lower frequency of the C allele was observed in the CFS population, suggesting that the His161Arg variant may confer protection against the disease. These results suggest a role of Th17 cells in the pathogenesis of CFS.
PMID: 18774769 [PubMed - indexed for MEDLINE]
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In Vivo. 2008 Jan-Feb;22(1):115-21.
Unravelling intracellular immune dysfunctions in chronic fatigue syndrome: interactions between protein kinase R activity, RNase L cleavage and elastase activity, and their clinical relevance.
Meeus M, Nijs J, McGregor N, Meeusen R, De Schutter G, Truijen S, Frmont M, Van Hoof E, De Meirleir K. This study examined possible interactions between immunological abnormalities and symptoms in CFS. Sixteen CFS patients filled in a battery of questionnaires, evaluating daily functioning, and underwent venous blood sampling, in order to analyse immunological abnormalities. Ribonuclease (RNase) L cleavage was associated with RNase L activity (rs=0.570; p=0.021), protein kinase R (PKR) (rs=0.716; p=0.002) and elastase activity (rs=0.500; p=0.049). RNase L activity was related to elastase (rs=0.547; p=0.028) and PKR activity (rs=0.625; p=0.010). RNase L activity (rs=0.535; p=0.033), elastase activity (rs=0.585; p=0.017) and RNase L cleavage (rs=0.521; p=0.038) correlated with daily functioning. This study suggests that in CFS patients an increase in elastase activity and subsequent RNase L cleavage is accompanied by increased activity of both the PKR and RNase L enzymes. RNase L and elastase activity are related to daily functioning, thus evidence supporting the clinical importance of these immune dysfunctions in CFS patients was provided.
PMID: 18396793 [PubMed - indexed for MEDLINE]
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In Vivo. 2009 Mar-Apr;23(2):209-13.
Detection of herpesviruses and parvovirus B19 in gastric and intestinal mucosa of chronic fatigue syndrome patients.
Frémont M, Metzger K, Rady H, Hulstaert J, De Meirleir K.
BACKGROUND: Human herpesvirus-6 (HHV-6), Epstein-Barr virus and parvovirus B19 have been suggested as etiological agents of chronic fatigue syndrome but none of these viruses is consistently detected in all patients. However, active viral infections may be localized in specific tissues, and, therefore, are not easily detectable. The aim of this study was to investigate the presence of HHV-6, HHV-7, EBV and parvovirus B19 in the gastro-intestinal tract of CFS patients. PATIENTS AND METHODS: Using real-time PCR, viral DNA loads were quantified in gastro-intestinal biopsies of 48 CFS patients and 35 controls. RESULTS: High loads of HHV-7 DNA were detected in most CFS and control biopsies. EBV and HHV-6 were detected in 15-30% of all biopsies. Parvovirus B19 DNA was detected in 40% of the patients versus less than 15% of the controls. CONCLUSION: Parvovirus B19 may be involved in the pathogenesis of CFS, at least for a subset of patients. The gastro-intestinal tract appears as an important reservoir of infection for several potentially pathogenic viruses.
PMID: 19414405 [PubMed - in process]
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