Repeat Instability in the Fragile X-Related Disorders: Lessons from a Mouse Model.

The fragile X-related disorders (FXDs) are a group of clinical conditions that result primarily from an unusual mutation, the expansion of a CGG-repeat tract in exon 1 of the FMR1 gene. Mouse models are proving useful for understanding many aspects of disease pathology in these disorders. There is also reason to think that such models may be useful for understanding the molecular basis of the unusual mutation responsible for these disorders. This review will discuss what has been learnt to date about mechanisms of repeat instability from a knock-in FXD mouse model and what the implications of these findings may be for humans carrying expansion-prone FMR1 alleles.

7-Keto-cholesterol and 25-hydroxy-1 cholesterol rapidly enhance ROS production in human neutrophils.

PURPOSE: Oxysterols are cholesterol-oxygenated derivatives generated in the organism and also present in foods because of cholesterol oxidation during processing and storage. They are the natural ligands of liver X receptors (LXRs) and are generally recognized as hypocholesterolemic and anti-inflammatory molecules although this latter property is still controversial. Most oxysterol studies have been performed in macrophages, whereas the effects of oxysterols in neutrophils are poorly known. In this study, human neutrophils were exposed to two different oxysterols, 7-keto-cholesterol (7-k-chol) and 25-hydroxy-cholesterol (25-OH-chol), and their possible participation in inflammatory process was evaluated. METHODS: Human neutrophils were incubated with 7-k-chol and 25-OH-chol, and ROS production, translocation of the NADPH oxidase cytosolic components, hemoxygenase-1 (HO-1) expression and lysozyme secretion were analyzed. RESULTS: An increase in ROS production was observed within a short period of time (minutes) with both molecules. These oxysterols also stimulated the cellular membrane translocation of the NADPH oxidase cytosolic components, p47phox and p67phox. On the other hand, HO-1 expression, a cytoprotector enzyme, is inhibited in human neutrophils upon oxysterols treatment. Moreover, both oxysterols were associated with high lysozyme enzyme secretion at 5 and 18 h of incubation. CONCLUSIONS: The present paper describes for the first time that two oxysterols (7-k-chol and 25-OH-chol) enhance the ROS production within a short period of time in human neutrophils, stimulate the translocation of the cytosolic components of NADPH oxidase to the cellular membrane and increase lysozyme secretion. These data suggest that both oxysterols are able to activate pro-inflammatory effects in human neutrophils which contrasts with the role assigned to the oxysterols when they act through LXR at long time of incubation.

Erratum: Emerging topics in FXTAS.

[This corrects the article DOI: 10.1186/1866-1955-6-31.].

Mouse models of the fragile X premutation and fragile X-associated tremor/ataxia syndrome.

Carriers of the fragile X premutation (FPM) have CGG trinucleotide repeat expansions of between 55 and 200 in the 5'-UTR of FMR1, compared to a CGG repeat length of between 5 and 54 for the general population. Carriers were once thought to be without symptoms, but it is now recognized that they can develop a variety of early neurological symptoms as well as being at risk for developing the late onset neurodegenerative disorder fragile X-associated tremor/ataxia syndrome (FXTAS). Several mouse models have contributed to our understanding of FPM and FXTAS, and findings from studies using these models are summarized here. This review also discusses how this information is improving our understanding of the molecular and cellular abnormalities that contribute to neurobehavioral features seen in some FPM carriers and in patients with FXTAS. Mouse models show much of the pathology seen in FPM carriers and in individuals with FXTAS, including the presence of elevated levels of Fmr1 mRNA, decreased levels of fragile X mental retardation protein, and ubiquitin-positive intranuclear inclusions. Abnormalities in dendritic spine morphology in several brain regions are associated with neurocognitive deficits in spatial and temporal memory processes, impaired motor performance, and altered anxiety. In vitro studies have identified altered dendritic and synaptic architecture associated with abnormal Ca(2+) dynamics and electrical network activity. FPM mice have been particularly useful in understanding the roles of Fmr1 mRNA, fragile X mental retardation protein, and translation of a potentially toxic polyglycine peptide in pathology. Finally, the potential for using these and emerging mouse models for preclinical development of therapies to improve neurological function in FXTAS is considered.

Oleic acid modulates mRNA expression of liver X receptor (LXR) and its target genes ABCA1 and SREBP1c in human neutrophils.

PURPOSE: Regulation of liver X receptors (LXRs) is essential for cholesterol homeostasis and inflammation. The present study was conducted to determine whether oleic acid (OA) could regulate mRNA expression of LXRα and LXRα-regulated genes and to assess the potential promotion of oxidative stress by OA in neutrophils. METHODS: Human neutrophils were treated with OA at different doses and LXR target gene expression, oxidative stress production, lipid efflux and inflammation state were analyzed. RESULTS: We describe that mRNA synthesis of both LXRα and ABCA1 (a reverse cholesterol transporter) was induced by OA in human neutrophils. This fatty acid enhanced the effects of LXR ligands on ABCA1 and LXR expression, but it decreased the mRNA levels of sterol regulatory element-binding protein 1c (a transcription factor that regulates the synthesis of triglycerides). Although OA elicited a slight oxidative stress in the short term (15-30 min) in neutrophils, it is unlikely that this is relevant for the modulation of transcription in our experimental conditions, which involve longer incubation time (i.e., 6 h). Of physiological importance is our finding that OA depresses intracellular lipid levels and that markers of inflammation, such as ERK1/2 and p38 mitogen-activated protein kinase phosphorylation, were decreased by OA treatment. In addition, 200 µM OA reduced the migration of human neutrophils, another marker of the inflammatory state. However, OA did not affect lipid peroxidation induced by pro-oxidant agents. CONCLUSIONS: This work presents for the first time evidence that human neutrophils are highly sensitive to OA and provides novel data in support of a protective role of this monounsaturated acid against the activation of neutrophils during inflammation.

Emerging topics in FXTAS.

This paper summarizes key emerging issues in fragile X-associated tremor/ataxia syndrome (FXTAS) as presented at the First International Conference on the FMR1 Premutation: Basic Mechanisms & Clinical Involvement in 2013.

Platelet-activating factor downregulates the expression of liver X receptor-α and its target genes in human neutrophils.

Liver X receptors (LXRs) are ligand-activated members of the nuclear receptor superfamily that regulate the expression of genes involved in lipid metabolism and inflammation, although their role in inflammation and immunity is less well known. It has been reported that oxysterols/LXRs may act as anti-inflammatory molecules, although opposite actions have also been reported. In this study, we investigated the effect of platelet-activating factor (PAF), a proinflammatory molecule, on LXRα signalling in human neutrophils. We found that PAF exerted an inhibitory effect on mRNA expression of TO901317-induced LXRα, ATP-binding cassette transporter A1, ATP-binding cassette transporter G1, and sterol response element binding protein 1c. This negative action was mediated by the PAF receptor, and was dependent on the release of reactive oxygen species elicited by PAF, as it was enhanced by pro-oxidant treatment and reversed by antioxidants. Current data also support the idea that PAF induces phosphorylation of the LXRα molecule in an extracellular signal-regulated kinase 1/2-mediated fashion. These results suggest that a possible mechanism by which PAF exerts its proinflammatory effect is through the downregulation of LXRα and its related genes, which supports the notion that LXRα ligands exert a modulatory role in the neutrophil-mediated inflammatory response.

Abnormal GABA-mediated and cerebellar inhibition in women with the fragile X premutation.

The fragile X syndrome is a mutation-driven developmental disorder caused by a repetition over 200 times of the CGG trinucleotide situated in the 5'-untranslated region of the fragile X mental retardation 1 gene (FMR1). The interval between 55 and 199 CGG repeats, which is over the normal range but below full mutation, is named fragile X premutation. Recent studies have focused on the asymptomatic state of fragile X premutation carriers and their potentially relevant preclinical features. However, the underlying neurological mechanisms leading to altered functions in fragile X premutation carriers are still poorly understood. In this study, we wanted to test the hypothesis that asymptomatic women who carry the fragile X premutation present GABAergic and cerebellar abnormalities compared with healthy women without the premutation. We performed noninvasive brain stimulation protocols on both asymptomatic fragile X premutation carriers and controls comprising of measures of GABAA- and GABAB-mediated intracortical inhibition, afferent inhibition, and cerebello-motor functional interactions. Premutation carriers presented an absence of cerebellar inhibition over primary motor cortex as well as a reduced GABAA-mediated intracortical and afferent inhibition compared with healthy nonpremutated controls. These alterations are most probably dependent on a dysfunctional GABAergic mechanism associated with the fragile X premutation condition as previously found in CGG-repeat animal models. Furthermore, the lack of cerebello-motor inhibition could be related to the cerebellar structural abnormalities previously found in carriers of the premutation.

Transcription of liver X receptor is down-regulated by 15-deoxy-Δ(12,14)-prostaglandin J(2) through oxidative stress in human neutrophils.

Liver X receptors (LXRs) are ligand-activated transcription factors of the nuclear receptor superfamily. They play important roles in controlling cholesterol homeostasis and as regulators of inflammatory gene expression and innate immunity, by blunting the induction of classical pro-inflammatory genes. However, opposite data have also been reported on the consequences of LXR activation by oxysterols, resulting in the specific production of potent pro-inflammatory cytokines and reactive oxygen species (ROS). The effect of the inflammatory state on the expression of LXRs has not been studied in human cells, and constitutes the main aim of the present work. Our data show that when human neutrophils are triggered with synthetic ligands, the synthesis of LXRα mRNA became activated together with transcription of the LXR target genes ABCA1, ABCG1 and SREBP1c. An inflammatory mediator, 15-deoxy-Δ(12,14)-prostaglandin J(2) (15dPGJ(2)), hindered T0901317-promoted induction of LXRα mRNA expression together with transcription of its target genes in both neutrophils and human macrophages. This down-regulatory effect was dependent on the release of reactive oxygen species elicited by 15dPGJ(2), since it was enhanced by pro-oxidant treatment and reversed by antioxidants, and was also mediated by ERK1/2 activation. Present data also support that the 15dPGJ(2)-induced serine phosphorylation of the LXRα molecule is mediated by ERK1/2. These results allow to postulate that down-regulation of LXR cellular levels by pro-inflammatory stimuli might be involved in the development of different vascular diseases, such as atherosclerosis.

Calcineurin expression and activity is regulated by the intracellular redox status and under hypertension in human neutrophils.

Calcineurin (protein phosphatase 2B) (CN) comprises a family of serine/threonine phosphatases that play a pivotal role in signal transduction cascades in a variety of cells, including neutrophils. Angiotensin II (Ang II) increases both activity and de novo synthesis of CN in human neutrophils. This study focuses on the role that intracellular redox status plays in the induction of CN activity by Ang II. Both de novo synthesis of CN and activity increase promoted by Ang II were downregulated when cells were treated with L-buthionine-(S,R)-sulfoximine, an inhibitor of synthesis of the antioxidant glutathione. We have also investigated the effect of pyrrolidine dithiocarbamate and phenazine methosulfate, which are antioxidant and oxidant compounds, respectively, and concluded that the intracellular redox status of neutrophils is highly critical for Ang II-induced increase of CN expression and activity. Results obtained in neutrophils from hypertensive patients were very similar to those obtained in these cells on treatment with Ang II. We have also addressed the possible functional implication of CN activation in the development of hypertension. Present findings indicate that downregulation of hemoxygenase-1 expression in neutrophils from hypertensive subjects is likely mediated by CN, which acts by hindering translocation to the nucleus of the transcription factor NRF2. These data support and extend our previous results and those from other authors on modulation of CN expression and activity levels by the intracellular redox status.

Intermediate alleles at the FRAXA and FRAXE loci in Parkinson's disease.

BACKGROUND: It is debatable whether the size of triplet repeats of the fragile X mental retardation genes FMR1 and FMR2 (found at the FRAXA and FRAXE loci) is associated with Parkinson's disease (PD). The aims of the current study were to investigate the relationship between these genes and PD and to determine whether these genes affected clinical manifestations of PD. METHODS: We recruited 206 PD patients and 227 control subjects from southern Spain. All subjects were screened for the size of CGG and CCG repeats at the FRAXA and FRAXE loci, respectively. Clinical features of each patient were examined in detail to study possible association between these features and genotype. RESULTS: Frequencies of FRAXA and FRAXE intermediate alleles were similar between PD and control groups. Clinical characteristics in PD patients, including severity of the disease, motor and non-motor symptoms, and motor complications and fluctuations were not affected by intermediate alleles at either locus. Two patients carrying FRAXA premutation alleles were identified showing clinical manifestations indistinguishable from idiopathic PD. CONCLUSIONS: FRAXA and FRAXE intermediate alleles do not seem to affect the risk for PD or modify clinical features in PD patients.

Heme oxygenase-1 expression is down-regulated by angiotensin II and under hypertension in human neutrophils.

Angiotensin II (Ang II) is a peptide hormone able to elicit a strong production of reactive oxygen species by human neutrophils. In this work, we have addressed whether expression of heme oxygenase-1 (HO-1), an antioxidant enzyme, becomes altered in these cells upon Ang II treatment or under hypertension conditions. In neutrophils from healthy and hypertensive subjects, induction of HO-1 mRNA and protein expression with a parallel increase in enzyme activity took place upon treatment with 15-deoxy-Delta12,14-PGJ2 (15dPGJ2). However, Ang II prevented HO-1 synthesis by normal neutrophils in vitro, and HO-1 expression was depressed in neutrophils from hypertensive patients in comparison with cells from healthy subjects. In addition, Ang II treatment led to a reduced HO-1 enzyme activity to levels similar to those found in neutrophils from hypertensive patients. NO donors reversed the inhibition of 15dPGJ2-dependent HO-1 expression in neutrophils from hypertensive patients, and conversely, inhibition of inducible NO synthase (NOS2) activity counteracted the stimulatory effect of 15dPGJ2 on HO-1 expression in normal human neutrophils. Moreover, Ang II canceled 15dPGJ2-dependent induction of NOS2 mRNA synthesis. Present findings indicate that down-regulation of HO-1 expression in neutrophils from hypertensive subjects is likely exerted through the inhibition of NOS2 expression. Additionally, they underscore the potential usefulness of NO donors as new, therapeutic agents against hypertension.

Rac2 GTPase activation by angiotensin II is modulated by Ca2+/calcineurin and mitogen-activated protein kinases in human neutrophils.

Angiotensin II (Ang II) highly stimulates superoxide anion production by neutrophils. The G-protein Rac2 modulates the activity of NADPH oxidase in response to various stimuli. Here, we describe that Ang II induced both Rac2 translocation from the cytosol to the plasma membrane and Rac2 GTP-binding activity. Furthermore, Clostridium difficile toxin A, an inhibitor of the Rho-GTPases family Rho, Rac and Cdc42, prevented Ang II-elicited O2-/ROS production, phosphorylation of the mitogen-activated protein kinases (MAPKs) p38, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase 1/2, and Rac2 activation. Rac2 GTPase inhibition by C. difficile toxin A was accompanied by a robust reduction of the cytosolic Ca(2)(+) elevation induced by Ang II in human neutrophils. Furthermore, SB203580 and PD098059 act as inhibitors of p38MAPK and ERK1/2 respectively, wortmannin, an inhibitor of phosphatidylinositol-3-kinase, and cyclosporin A, a calcineurin inhibitor, hindered both translocation of Rac2 from the cytosol to the plasma membrane and enhancement of Rac2 GTP-binding elicited by Ang II. These results provide evidence that the activation of Rac2 by Ang II is exerted through multiple signalling pathways, involving Ca(2)(+)/calcineurin and protein kinases, the elucidation of which should be insightful in the design of new therapies aimed at reversing the inflammation of vessel walls found in a number of cardiovascular diseases.

Study of cerebral cavernous malformation in Spain and Portugal: high prevalence of a 14 bp deletion in exon 5 of MGC4607 (CCM2 gene).

OBJECTIVE: We aimed to study clinical, radiological and molecular genetic features of patients with cerebral cavernous malformations (CCMs) from the Iberian Peninsula. METHODS: We screened Krit1(CCM1), MGC4607(CCM2), and PDCD10(CCM3) by systematic SSCP and direct sequencing of coding exons in 48 nuclear families and 30 sporadic cases of CCM from Spain and Portugal. RESULTS: Screening of CCM patients detected nine different mutations in 19 families. We found four new mutations in Krit1. Three of them were caused by either a small insertion or deletion, which lead to frameshift and premature termination codons. We also found a missense L308H mutation located in a highly conserved sequence within the ankyrin domain of Krit1. In CCM2, we found a redundant 14 bp deletion in exon 5 of MGC4607 which predicts a truncated protein at residue 230. We did not find mutations in CCM3. CONCLUSIONS: Finding that the 14 bp deletion was present in eleven families from the Iberian Peninsula indicates a high prevalence of this mutation. This redundant CCM2 mutation is worth considering in molecular diagnosis and genetic counselling of cerebral cavernous malformations.

Skewed X inactivation of the normal allele in fully mutated female carriers determines the levels of FMRP in blood and the fragile X phenotype.

BACKGROUND: The variable phenotype in female carriers of a full mutation is explained in part by non-random X-chromosome inactivation. The molecular diagnosis of fragile X syndrome is based on the resolution of the number of CGG triplet repeats and the methylation status of a critical CpG in the fragile X mental retardation gene (FMR1) promoter. Neighboring CpGs in the FMR1 promoter are supposed to be equally methylated or unmethylated. METHOD: Southern blot analysis was performed with double digestion, either with EcoRI/EagI or with HindIII/SacII. The EagI restriction site was studied by sequencing. The fragile X encoded protein (FMRP) was detected in white blood cells by Western blot. The fragile X phenotype was evaluated by specific clinical examinations. RESULTS: Within one family we found three female carriers of a full mutation and a different degree of methylation of the normal allele that correlated with the levels of FMRP in blood and the fragile X phenotype. Complete methylation at the EagI CpG target (but partially methylated SacII CpG site) was associated with extremely skewed X inactivation (confirmed by analysis of the methylation status at the PGK locus), undetectable FMRP in blood, and a male-like phenotype. CONCLUSIONS: In fully mutated female carriers the methylation status at the EagI restriction site correlates with the levels of FMRP in blood and the fragile X phenotype. Neighboring CpG sequences in the FMR1 promoter can be differentially methylated, which should be taken into consideration for molecular diagnosis.

Different signaling pathways inhibit DNA methylation activity and up-regulate IFN-gamma in human lymphocytes.

DNA methylation is recognized increasingly for its prominent role in controlling diverse immune processes. In this study, we show that in Jurkat T cells and fresh peripheral lymphocytes, short-time incubation with protein kinase C activators or phosphatase inhibitors down-regulate DNA methylation activity in a dose-dependent manner. This inhibition correlates with the induction of the interferon-gamma (IFN-gamma) gene, which contains several CG sequences in its promoter. The expression of mRNA and protein of the different DNA methyltransferases did not decrease after the treatment. In addition, sulfydryl reagents have a strong inhibitory effect on DNA methylation activity and also induce IFN-gamma gene expression, thus suggesting a link between both effects.

Stimulators of AMP-activated protein kinase inhibit the respiratory burst in human neutrophils.

In the present study, we have examined the potential ability of 5'-AMP-activated protein kinase (AMPK) to modulate NADPH oxidase activity in human neutrophils. AMPK activated with either 5'-aminoimidazole-4-carboxamide ribonucleoside (AICAR) or with 5'-AMP significantly attenuated both phorbol 12-myristate 13-acetate (PMA) and formyl methionyl leucyl phenylalanine-stimulated superoxide anion O2- release by human neutrophils, consistently with a reduced translocation to the cell membrane and phosphorylation of a cytosolic component of NADPH oxidase, namely p47phox. AMPK was found to be present in human neutrophils and to become phosphorylated in response to either AICAR or other stimulators of its enzyme activity. Furthermore, AICAR also strongly reduced PMA-dependent H2O2 release, and induced the phosphorylation of c-jun N-terminal kinase 1 (p46), p38 mitogen-activated protein kinase and extracellular signal-regulated kinase. Present data demonstrate for the first time that the activation of AMPK, in states of low cellular energy charge (such as under high levels of 5'-AMP) or other signals, could be a factor contributing to reduce the host defense mechanisms.

Human neutrophils synthesize IL-8 in an IgE-mediated activation.

It has been demonstrated that neutrophils are responsible for the release of large amounts of the inflammatory chemokine interleukin-8 (IL-8), associated with inflammation. To further define the mechanisms implicated, we have analyzed the response of human neutrophils from allergic patients to specific antigens or challenge with anti-immunoglobulin (Ig)E antibodies. Neutrophils showed a dose- and time-dependent production of IL-8. The release of the cytokine was parallel to expression of IL-8 mRNA analyzed by the polymerase chain reaction. This expression was transient-it occurred after 3 h of anti-IgE treatment and was maintained for 18 h. Trifluoperazine, EGTA, reduced nicotinamide adenine dinucleotide phosphate-oxidase inhibitors, and reactive oxygen species (ROS) scavengers inhibited IL-8 production, indicating a critical dependence of calcium and oxidative stress. Moreover, an inhibitory effect of cyclosporin A, an immunosuppressor that inhibits calcineurin activity, on IL-8 release and IL-8 mRNA expression was observed. This is the first evidence of the involvement of ROS and calcium/calcineurin in IgE-dependent IL-8 production. These findings open new perspectives into the functional role of neutrophils in IgE-associated diseases.

A new role for monoamine oxidases in the modulation of macrophage-inducible nitric oxide synthase gene expression.

This report focuses on the modulatory role of endogenous H(2)O(2) on lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma)-induced inducible nitric oxide synthase (NOS2) gene expression in rat peritoneal macrophages. Exogenously added H(2)O(2) was initially found to inhibit the synthesis of NOS2, which prompted us to assess the effect of the activity of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO) as H(2)O(2)-forming enzymes on NOS2 gene expression. In the presence of their substrates, tyramine for MAO and benzylamine for SSAO, intracellular synthesis of H(2)O(2) took place with concomitant inhibition of LPS/IFN-gamma-induced NOS2 protein synthesis, as detected by Western blotting, flow cytometry, and immunofluorescence microscopy analyses. Pargyline and semicarbazide, specific inhibitors of MAO and SSAO, respectively, canceled this negative effect of MAO substrates on NOS2 expression. In the presence of Fe(2+) and Cu(2+) ions, inhibition of NOS2 expression was enhanced, suggesting the participation in this regulation of species derived from Fenton chemistry. In addition, the negative effect of H(2)O(2), generated by MAOs, was found to be exerted on NOS2 mRNA levels. These data offer a new insight in the control of NOS2 expression through the intracellular levels of H(2)O(2) and other reactive oxygen species (ROS). The hypothesis can be raised that the inhibition of NOS by H(2)O(2) could constitute a protective mechanism against the cytotoxic consequences of the activation of ROS-generating enzymes, thus providing a new, singular role for the MAO family of proteins.