Annexin A2 Is a Natural Extrahepatic Inhibitor of the PCSK9-Induced LDL Receptor Degradation

Proprotein convertase subtilisin/kexin-9 (PCSK9) enhances the degradation of hepatic low-density lipoprotein receptor (LDLR). Deletion of PCSK9, and loss-of-function mutants in humans result in lower levels of circulating LDL-cholesterol and a strong protection against coronary heart disease. Accordingly, the quest for PCSK9 inhibitors has major clinical implications. We have previously identified annexin A2 (AnxA2) as an endogenous binding partner and functional inhibitor of PCSK9. Herein, we studied the relevance of AnxA2 in PCSK9 inhibition and lipid metabolism in vivo. Plasma analyses of AnxA2(-/-) mice revealed: i) a ～1.4-fold increase in LDL-cholesterol without significant changes in VLDLs or HDLs, and ii) a ～2-fold increase in circulating PCSK9 levels. Western blotting and immunohistochemistry of AnxA2(-/-) tissues revealed that the LDLR was decreased by ～50% in extrahepatic tissues, such as adrenals and colon. We also show that AnxA2-derived synthetic peptides block the PCSK9≡LDLR interaction in vitro, and adenoviral overexpression of AnxA2 in mouse liver increases LDLR protein levels in vivo. These results suggest that AnxA2 acts as an endogenous regulator of LDLR degradation, mostly in extrahepatic tissues. Finally, we identified an AnxA2 coding polymorphism, V98L, that correlates with lower circulating levels of PCSK9 thereby extending our results on the physiological role of AnxA2 in humans.     

The scaffolding protein Dlg1 is a negative regulator of cell-free virus infectivity but not of cell-to-cell HIV-1 transmission in T cells

Background

Cell-to-cell virus transmission of Human immunodeficiency virus type-1 (HIV-1) is predominantly mediated by cellular structures such as the virological synapse (VS). The VS formed between an HIV-1-infected T cell and a target T cell shares features with the immunological synapse (IS). We have previously identified the human homologue of the Drosophila Discs Large (Dlg1) protein as a new cellular partner for the HIV-1 Gag protein and a negative regulator of HIV-1 infectivity. Dlg1, a scaffolding protein plays a key role in clustering protein complexes in the plasma membrane at cellular contacts. It is implicated in IS formation and T cell signaling, but its role in HIV-1 cell-to-cell transmission was not studied before.

Methodology/Principal Findings

Kinetics of HIV-1 infection in Dlg1-depleted Jurkat T cells show that Dlg1 modulates the replication of HIV-1. Single-cycle infectivity tests show that this modulation does not take place during early steps of the HIV-1 life cycle. Immunofluorescence studies of Dlg1-depleted Jurkat T cells show that while Dlg1 depletion affects IS formation, it does not affect HIV-1-induced VS formation. Co-culture assays and quantitative cell-to-cell HIV-1 transfer analyses show that Dlg1 depletion does not modify transfer of HIV-1 material from infected to target T cells, or HIV-1 transmission leading to productive infection via cell contact. Dlg1 depletion results in increased virus yield and infectivity of the viral particles produced. Particles with increased infectivity present an increase in their cholesterol content and during the first hours of T cell infection these particles induce higher accumulation of total HIV-1 DNA.

Conclusion

Despite its role in the IS formation, Dlg1 does not affect the VS and cell-to-cell spread of HIV-1, but plays a role in HIV-1 cell-free virus transmission. We propose that the effect of Dlg1 on HIV-1 infectivity is at the stage of virus entry.     

PARP-1 Modulation of mTOR Signaling in Response to a DNA Alkylating Agent

Poly(ADP-ribose) polymerase-1 (PARP-1) is widely involved in cell death responses. Depending on the degree of injury and on cell type, PARP activation may lead to autophagy, apoptosis or necrosis. In HEK293 cells exposed to the alkylating agent N-methyl-N’-nitro-N’-nitrosoguanine (MNNG), we show that PARP-1 activation triggers a necrotic cell death response. The massive poly(ADP-ribose) (PAR) synthesis following PARP-1 activation leads to the modulation of mTORC1 pathway. Shortly after MNNG exposure, NAD⁺ and ATP levels decrease, while AMP levels drastically increase. We characterized at the molecular level the consequences of these altered nucleotide levels. First, AMP-activated protein kinase (AMPK) is activated and the mTORC1 pathway is inhibited by the phosphorylation of Raptor, in an attempt to preserve cellular energy. Phosphorylation of the mTORC1 target S6 is decreased as well as the phosphorylation of the mTORC2 component Rictor on Thr1135. Finally, Akt phosphorylation on Ser473 is lost and then, cell death by necrosis occurs. Inhibition of PARP-1 with the potent PARP inhibitor AG14361 prevents all of these events. Moreover, the antioxidant N-acetyl-L-cysteine (NAC) can also abrogate all the signaling events caused by MNNG exposure suggesting that reactive oxygen species (ROS) production is involved in PARP-1 activation and modulation of mTOR signaling. In this study, we show that PARP-1 activation and PAR synthesis affect the energetic status of cells, inhibit the mTORC1 signaling pathway and possibly modulate the mTORC2 complex affecting cell fate. These results provide new evidence that cell death by necrosis is orchestrated by the balance between several signaling pathways, and that PARP-1 and PAR take part in these events.     

Nuclear microsatellite loci for Arabidopsis halleri (Brassicaceae), a model species to study plant adaptation to heavy metals

? Premise of the study: Arabidopsis halleri is a model species to study the adaptation of plants to soils contaminated by zinc, cadmium, and lead. To provide a neutral genetic background with which adaptive genetic markers could be compared, we developed highly polymorphic neutral microsatellite markers. ? Methods and Results: Using a microsatellite-enriched library method, we identified 120 microsatellite loci for quantitative trait locus (QTL) mapping analysis, of which eight primer pairs were developed in a single multiplex for population genetic studies. Analyses were performed on 508 individuals from 26 populations. All loci were polymorphic with six to 23 alleles per locus. Genetic diversity varied between 0.56 and 0.76. ? Conclusions: Our results demonstrated the value of these eight microsatellite markers to investigate neutral population genetic structure in A. halleri. To increase the resolution of population genetic analyses, we suggest adding them to the 11 markers previously developed independently.     

Human annexin A6 interacts with influenza a virus protein M2 and negatively modulates infection

The influenza A virus M2 ion channel protein has the longest cytoplasmic tail (CT) among the three viral envelope proteins and is well conserved between different viral strains. It is accessible to the host cellular machinery after fusion with the endosomal membrane and during the trafficking, assembly, and budding processes. We hypothesized that identification of host cellular interactants of M2 CT could help us to better understand the molecular mechanisms regulating the M2-dependent stages of the virus life cycle. Using yeast two-hybrid screening with M2 CT as bait, a novel interaction with the human annexin A6 (AnxA6) protein was identified, and their physical interaction was confirmed by coimmunoprecipitation assay and a colocalization study of virus-infected human cells. We found that small interfering RNA (siRNA)-mediated knockdown of AnxA6 expression significantly increased virus production, while its overexpression could reduce the titer of virus progeny, suggesting a negative regulatory role for AnxA6 during influenza A virus infection. Further characterization revealed that AnxA6 depletion or overexpression had no effect on the early stages of the virus life cycle or on viral RNA replication but impaired the release of progeny virus, as suggested by delayed or defective budding events observed at the plasma membrane of virus-infected cells by transmission electron microscopy. Collectively, this work identifies AnxA6 as a novel cellular regulator that targets and impairs the virus budding and release stages of the influenza A virus life cycle.     

Defining cut-off values for disease activity states and improvement scores for patient-reported outcomes: the example of the Rheumatoid Arthritis Impact of Disease (RAID)

Introduction

The Rheumatoid Arthritis Impact of Disease (RAID) is a patient-reported outcome measure evaluating the impact of rheumatoid arthritis (RA) on patient quality of life. It comprises 7 domains that are evaluated as continuous variables from 0 (best) to 10 (worst). The objective was to define and identify cut-off values for disease activity states as well as improvement scores in order to present results at the individual level (for example, patient in acceptable state, improved patient).

Methods

Patients with definite active RA requiring anti-tumour necrosis factor (anti-TNF) therapy were seen at screening, baseline and after 4 and 12 weeks of etanercept therapy. Answers to "Gold standard" questions on improvement (MCII: Minimum Clinically Important Improvement) and an acceptable status (PASS: Patient Acceptable Symptom State) were collected as well as the RAID score and Disease Activity Score 28- erythrocyte sedimentation rate (DAS28-ESR). Cut-offs were defined by different techniques including empirical, measurement error and gold standard anchors. The external validity of these cut-offs was evaluated using the positive likelihood ratio (LR) based on the patient's perspective (for example, patient's global) and on low disease activity status (such as DAS28-ESR).

Results

Ninety-seven (97) of the 108 recruited patients (age: 54 ± 13 years old, female gender: 75%, rheumatoid factor positive: 81%, disease duration: 8 ± 7 years, CRP: 18 ± 30 mg/l, DAS28-ESR: 5.4 ± 0.8) completed the 12 weeks of the study. The different techniques suggested thresholds ranging from 0.2 to 3 (absolute change) and from 6 to 50% (relative change) for defining MCII and thresholds from less than 1 to less than 4.2 for defining PASS. The evaluation of external validity (LR+) showed the highest LR+ was obtained with thresholds of 3 for absolute change; 50% for relative change and less than 2 for an acceptable status.

Conclusions

This study showed that thresholds defined for continuous variables are closely related to the methodological technique, justifying a systematic evaluation of their validity. Our results suggested that a change of at least 3 points (absolute) or 50% (relative) in the RAID score should be used to define a MCII and that a maximal value of 2 defines an acceptable status.

Trial Registration

Clinicaltrial.gov: NCT004768053     

Perturbations in dynamical models of whole-brain activity dissociate between the level and stability of consciousness

Consciousness transiently fades away during deep sleep, more stably under anesthesia, and sometimes permanently due to brain injury. The development of an index to quantify the level of consciousness across these different states is regarded as a key problem both in basic and clinical neuroscience. We argue that this problem is ill-defined since such an index would not exhaust all the relevant information about a given state of consciousness. While the level of consciousness can be taken to describe the actual brain state, a complete characterization should also include its potential behavior against external perturbations. We developed and analyzed whole-brain computational models to show that the stability of conscious states provides information complementary to their similarity to conscious wakefulness. Our work leads to a novel methodological framework to sort out different brain states by their stability and reversibility, and illustrates its usefulness to dissociate between physiological (sleep), pathological (brain-injured patients), and pharmacologically-induced (anesthesia) loss of consciousness.