Rétroactions positives et mémoire cellulaire (exemples dans l'expression génétique et le métabolisme cellulaire)

Au-delà de l'information génétique contenue dans la séquence de l'ADN des cellules, il existe une mémoire cellulaire, dite épigénétique comprenant l'ensemble des circuits génétiques avec rétroactions positives permettant d'amplifier ou de maintenir une réponse cellulaire dans le temps. Nous nous sommes intéressés, à travers deux exemples, aux boucles de rétrocontrôle positif comme élément de réponse à un signal, permettant de fixer, de manière à la fois dynamique et robuste, le comportement cellulaire. Dans un premier temps, nous avons identifié une boucle d'auto-amplification dans la production de vitellogénine chez la truite et permettant d'expliquer l' effet mémoire de la vitellogénèse (une seconde stimulation à l'œstradiol induit une plus forte production de vitellogénine et plus rapidement que lors de la première stimulation, alors même que le niveau de vitellogénine retombe à zéro entre les deux stimulations). Le modèle que nous proposons implique un récepteur tronqué à l'œstradiol possédant une activité basale même en l'absence de son ligand, permettant de maintenir la cellule dans un état d'aptitude à répondre sans pour autant produire de vitellogénine. Dans un deuxième temps, nous nous sommes intéressés à une des causes possibles provoquant la transition épithélio-mésenchymateuse (EMT), responsable des métastases dans les cancers. L'EMT témoigne d'un état plus agressif des cellules tumorales et s'accompagne notamment d'un changement du métabolisme des cellules cancéreuses, diminuant la part de la phosphorylation oxydative au profit de la glycolyse (effet Warburg). Cela entraîne une baisse d'efficacité de la production d'ATP, obligeant les cellules à prélever davantage de nutriments dans leur milieu. Cette observation a suscité le développement de thérapies basées sur la privation de glucose et qui, a priori, devraient nuire principalement aux cellules cancéreuses. Nous avons étudié les effets d'un faible contenu cellulaire en ATP sur la transformation cellulaire. Nous avons observé qu'un traitement par un analogue non métabolisable du glucose diminue drastiquement le contenu en ATP des cellules ayant passé l'EMT et induit des changements morphologiques et génétiques orientés vers le phénotype mésenchymateux. La protéine MKL1, cofacteur de transcription dont l'activité est régulée par la polymérisation de l'actine, pourrait être un relais génétique entre l'état métabolique cellulaire et le maintien de l'EMT. Ces résultats suggèrent de fortes connections entre l'EMT et le niveau énergétique des cellules, faisant d'une privation d'énergie une cause possible de l'aggravation du phénotype mésenchymateux et remettant en cause les bienfaits sur le long terme de thérapies visant à affamer les cellules tumorales.Beyond the genetic information contained in the DNA sequence of cells, there is a cellular memory called epigenetic, including genetic circuits with positive feedback loops amplifying or maintaining cellular states in time. We studied through two examples, the positive feedback loops as part of response to a signal, able to set cell behavior, in a dynamic and robust way. As a first step, we identified a self-amplification loop in the production of trout vitellogenin explaining the "vitellogenesis memory effect" (a second estradiol stimulation induces higher and faster vitellogenin production than during the first stimulation, even though the vitellogenin level falls to zero between the two stimuli). The model we propose involves a truncated estradiol receptor, with a basal activity even in the absence of its ligand, which is able to maintain the cell in an estrogen-responsive state without producing vitellogenin. In a second step, we studied one of the possible causes leading to the epithelial-mesenchymal transition (EMT), involved in cancer metastasis. The EMT reflects a more aggressive state of tumor cells and is associated with a particular change in the metabolism of cancer cells, reducing the part of oxidative phosphorylation in favor of glycolysis (Warburg effect). This leads to a reduction in the efficiency of ATP production, forcing the cells to take more nutrients from their environment. This observation led to the development of treatments based on glucose deprivation which should mainly affect cancer cells. We studied the effects of a low cellular ATP content on cell transformation. We observed that a treatment with a non-metabolizable glucose analogue drastically reduces the ATP content of cells that had undergone EMT and induces morphological and genetic changes enforcing the mesenchymal phenotype. We identified the transcriptional coactivator MKL1, whose activity is regulated by actin polymerization, as a possible genetic link between the cellular metabolic state and maintenance of EMT. These results suggest strong connections between the EMT and the energy level of the cells, and raise serious questions about the benefits of the long-term therapy "starving" tumor cells, considering that energy deprivation could aggravate the mesenchymal cell phenotype.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF

L’activité métallurgique à l’abbaye de Morimond (Haute-Marne) : nouvel éclairage de la fouille à partir de l’analyse archéomagnétique de deux foyers

Une étude archéomagnétique à des fins de datation a été menée sur deux foyers en carreaux de terre cuite mis au jour sur le site de l’ancienne abbaye cistercienne de Morimond (Haute-Marne). La désaimantation thermique complète des échantillons prélevés a permis de définir pour chacun des deux foyers une direction archéomagnétique moyenne précise, acquise lors de leur dernière utilisation. Pour dater cet instant, les directions archéomagnétiques ont été comparées à une courbe des variations directionnelles du champ géomagnétique construite à partir de données obtenues en France et dans des pays voisins. Nous obtenons, à 95% de confiance, une datation comprise entre 1585 et 1615 après J.-C. pour le premier foyer et entre 1525 et 1605 après J.-C. pour le second foyer. Bien que leurs deux intervalles d'âge se recouvrent partiellement, les deux directions archéomagnétiques moyennes ne sont pas compatibles à 95% ce qui indique que les arrêts de fonctionnement des deux foyers ne sont pas contemporains. Ces résultats archéomagnétiques confirment deux phases métallurgiques observées indépendamment lors des fouilles. Ils précisent les datations issues des radiocarbones qui ne permettaient pas de discriminer chronologiquement les deux phases. Les datations envisagées se calent avant l’abandon du bâtiment suite à plusieurs saccages évoqués dans les sources écrites.This paper presents the archeomagnetic dating results obtained from two brick fireplaces excavated inside the ancient Cistercian Abbey of Morimond (Haute-Marne). Complete thermal demagnetization of the collected samples allowed us to define a precise mean archeomagnetic direction acquired during the last cooling of each of the two structures. The dating of the last use of the two fireplaces was derived from the statistical comparison between a reference geomagnetic field directional variation curve constructed using the available French data set together with other data from nearby countries and the two directions obtained in this study. The two dating results lie, with a 95% confidence level, between 1585 and 1615 AD and between 1525 and 1605 AD. Although these dates partially overlap, the two mean archeomagnetic directions are not compatible at the 95% confidence level, indicating a chronology in the abandonment of the two structures. These archeomagnetic results therefore confirm the existence of two metallurgical phases, which were independently observed during the excavations. They further refine the radiocarbon dating unable to discriminate the two phases. The two time intervals defined by archeomagnetism pre-date the abandonment of the building due to severe damages mentioned in written sources

Clinical features of H1N1 2009 infection in critically ill immunocompromised patients

Seasonal influenza virus has been described as an emerging and severe pathogen in immunocompromised hosts. Since the beginning of the 2009 influenza A novel H1N1 pandemic, several series have described the clinical course of the disease in various populations. We report the clinical course of H1N1 2009 infection in 10 immunocompromised patients. Half of the patients received long-term steroid therapy. Disease was characterized by a clinical picture similar to that of non-immunocompromised patients but with prolonged course and higher mortality

A combination of methotrexate and zoledronic acid prevents bone erosions and systemic bone mass loss in collagen induced arthritis

Introduction Osteoclasts play a key role in the pathogenesis of bone erosion and systemic bone mass loss during rheumatoid arthritis (RA). In this study, we aimed to determine the effect of methotrexate (MTX) and zoledronic acid (ZA), used alone or in combination, on osteoclast-mediated bone erosions and systemic bone mass loss in a rat model of collagen induced arthritis (CIA). We hypothesized that MTX and ZA could have an additive effect to prevent both bone erosion and systemic bone loss. Methods Arthritis was induced in 64 female Sprague-Dawley rats. After the clinical onset of CIA, rats were assigned to treatment with MTX (1 mg/kg/week), ZA (100 μg/kg twice weekly), both treatments at the same regimens, or vehicle. Arthritis score and paw thickness were recorded twice weekly. The rats were sacrificed on D28 and hind paws were removed for radiographic, histological and immunohistochemical analysis. The effects of treatments on osteoclastogenesis were determined by Tartrate resistant acid phosphatase (TRAP) staining. Micro-CT of the tibia was carried out for histomorphometric analysis. Bone mass density was evaluated by densitometry. Results MTX significantly decreased the severity of CIA, whereas ZA slightly exacerbated it. When these two drugs were used in combination, MTX prevented the pro-inflammatory effect of ZA. The combination of ZA with MTX was more effective than MTX alone for reducing structural joint damage with a dramatic decrease of osteoclasts' number in the eroded joints. However, MTX alone also significantly reduced the number of osteoclasts and the number of CD68+ mononuclear cells. ZA alone, or ZA with MTX, significantly increased the systemic bone mass density measured by densitometry and bone volume on histomorphometric analysis. Conclusions A combination of MTX and ZA prevented both bone erosion and systemic bone loss in a rat model of arthritis. Both treatments independently decreased the number of osteoclasts in the eroded joint. However, while MTX probably acts mainly through a decrease of inflammation, ZA has a direct effect on osteoclasts, allowing a dramatic down-regulation of these cells in inflamed joints. These two different mechanisms of action provide support for the use of a combination of these two drugs to improve the prevention of structural joint damage in RA

Ulvan Activates Chicken Heterophils and Monocytes Through Toll-Like Receptor 2 and Toll-Like Receptor 4

Responsiveness to invasive pathogens, clearance via the inflammatory response, and activation of appropriate acquired responses are all coordinated by innate host defenses. Toll-like receptor (TLR) ligands are potent immune-modulators with profound effects on the generation of adaptive immune responses. This property is being exploited in TLR-based vaccines and therapeutic agents in chickens. However, for administering the TLR agonist, all previous studies used in ovo, intra-muscular or intra-venous routes that cannot be performed in usual farming conditions, thus highlighting the need for TLR ligands that display systemic immune effects when given orally (per os). Here we have demonstrated that an ulvan extract of Ulva armoricana is able to activate avian heterophils and monocytes in vitro. Using specific inhibitors, we have evidenced that ulvan may be a new ligand for TLR2 and TLR4; and that they regulate heterophil activation in slightly different manner. Moreover, activation of heterophils as well as of monocytes leads to release pro-inflammatory cytokines, including interleukin1-β, interferon α and interferon γ, through pathways that we partly identified. Finally, when given per os to animals ulvan induces heterophils and monocytes to be activated in vivo thus leading to a transient release of pro-inflammatory cytokines with plasma concentrations returning toward baseline levels at day 3

Pharmacodynamics of bisphosphonates in arthritis.

Inflammatory arthritis is a group of autoimmune diseases characterized by chronic inflammation of the joints. Rheumatoid arthritis, the most common form of arthritis, is associated with local joint destruction and systemic bone loss. Osteoclasts, the only cells of the body able to resorbe bone, are key players in these two types of bone loss. Bisphosphonates are analogs of pyrophosphate that inhibit osteoclast action and bone resorption. They are indicated in pathology associated with excess resorption. Besides their effect on bone they also exhibit extra-osseous properties, acting on tumor cells, inflammation and angiogenesis. As a result, they have been trialed in the context of arthritis. It is now clear that they do not have any significant direct effect on disease activity or pain. If their indication in the prevention of glucocorticoid-induced osteoporosis is clear, any beneficial effects on bone erosions are still controversial but interesting preliminary results warrant further investigations

Bone Morphogenetic Protein 2 and Transforming Growth Factor β1 Inhibit the Expression of the Proinflammatory Cytokine IL-34 in Rheumatoid Arthritis Synovial Fibroblasts

IL-34 is a proinflammatory cytokine implicated in rheumatoid arthritis (RA). The current study aimed to assess the IL-34 expression in response to two members of the transforming growth factor (TGF)-β family, TGF-β1 and bone morphogenetic protein (BMP)-2, in synovial fibroblasts from RA patients. IL-34, TGF-β1, and BMP-2 productions were measured in patient synovial fluids by enzyme-linked immunosorbent assay. IL-34 mRNA levels were quantified by real-time quantitative PCR in human synovial fibroblasts and murine mesenchymal stem cells. Pharmacologic inhibitions were used to determine the involvement of activin receptor-like kinase 1 (ALK1) and ALK5 downstream TGF-β1 and BMP-2. IL-34, TGF-β1, and BMP-2 were expressed in synovial fluids from RA patients. We found a significant correlation between IL-34 and TGF-β1 expressions. Levels of both IL-34 and TGF-β1 were thus correlated with the total leukocyte counts in the synovial fluids. TGF-β1 and BMP-2 decreased IL-34 expression in the synovial fibroblasts or in murine mesenchymal stem cells in a dose- and time-dependent manner through ALK5 and ALK1 pathways, respectively. In addition, TGF-β1 and BMP-2 antagonized tumor necrosis factor α–induced IL-34 gene expression. This work identifies TGF-β1 and BMP-2 as potent inhibitors of IL-34 expression in RA synovial fibroblasts. These cytokines, as upstream inhibitors of IL-34, may thus contribute to antagonize inflammation and bone erosions in RA

In Antisynthetase Syndrome, ACPA Are Associated With Severe and Erosive Arthritis: An Overlapping Rheumatoid Arthritis and Antisynthetase Syndrome

International audienceAbstract: Anticitrullinated peptide/protein antibodies (ACPA), which are highly specific for rheumatoid arthritis (RA), may be found in some patients with other systemic autoimmune diseases. The clinical significance of ACPA in patients with antisynthetase syndrome (ASS), a systemic disease characterized by the association of myositis, interstitial lung disease, polyarthralgia, and/or polyarthritis, has not yet been evaluated with regard to phenotype, prognosis, and response to treatment. ACPA-positive ASS patients were first identified among a French multicenter registry of patients with ASS. Additionally, all French rheumatology and internal medicine practitioners registered on the Club Rhumatismes et Inflammation web site were asked to report their observations of ASS patients with ACPA. The 17 collected patients were retrospectively studied using a standardized questionnaire and compared with 34 unselected ACPA-negative ASS patients in a case–control study. All ACPA-positive ASS patients suffered from arthritis versus 41% in the control group (P 7-year mean follow-up, extra-articular outcomes and survival were not different. ACPA-positive ASS patients showed an overlapping RA–ASS syndrome, were at high risk of refractory erosive arthritis, and might experience ASS flare when treated with antitumor necrosis factor drugs. In contrast, other biologics such as anti-CD20 mAb were effective in this context, without worsening systemic involvements

Pathogenic variants in THSD4, encoding the ADAMTS-like 6 protein, predispose to inherited thoracic aortic aneurysm

Purpose Thoracic aortic aneurysm and dissection (TAAD) is a life-threatening disease with often unrecognized inherited forms. We sought to identify novel pathogenic variants associated with autosomal dominant inheritance of TAAD. Methods We analyzed exome sequencing data from 35 French TAAD families and performed next-generation sequencing capture panel of genes in 1114 unrelated TAAD patients. Functional effects of pathogenic variants identified were validated in cell, tissue, and mouse models. Results We identified five functional variants inTHSD4of which two heterozygous variants lead to a premature termination codon.THSD4encodes ADAMTSL6 (member of the ADAMTS/L superfamily), a microfibril-associated protein that promotes fibrillin-1 matrix assembly. TheTHSD4variants studied lead to haploinsufficiency or impaired assembly of fibrillin-1 microfibrils.Thsd4(+/-)mice showed progressive dilation of the thoracic aorta. Histologic examination of aortic samples from a patient carrying aTHSD4variant and fromThsd4(+/-)mice, revealed typical medial degeneration and diffuse disruption of extracellular matrix. Conclusion These findings highlight the role of ADAMTSL6 in aortic physiology and TAAD pathogenesis. They will improve TAAD management and help develop new targeted therapies

Differential effects of hnRNP D/AUF1 isoforms on HIV-1 gene expression

Control of RNA processing plays a major role in HIV-1 gene expression. To explore the role of several hnRNP proteins in this process, we carried out a siRNA screen to examine the effect of depletion of hnRNPs A1, A2, D, H, I and K on HIV-1 gene expression. While loss of hnRNPs H, I or K had little effect, depletion of A1 and A2 increased expression of viral structural proteins. In contrast, reduced hnRNP D expression decreased synthesis of HIV-1 Gag and Env. Loss of hnRNP D induced no changes in viral RNA abundance but reduced the accumulation of HIV-1 unspliced and singly spliced RNAs in the cytoplasm. Subsequent analyses determined that hnRNP D underwent relocalization to the cytoplasm upon HIV-1 infection and was associated with Gag protein. Screening of the four isoforms of hnRNP D determined that, upon overexpression, they had differential effects on HIV-1 Gag expression, p45 and p42 isoforms increased viral Gag synthesis while p40 and p37 suppressed it. The differential effect of hnRNP D isoforms on HIV-1 expression suggests that their relative abundance could contribute to the permissiveness of cell types to replicate the virus, a hypothesis subsequently confirmed by selective depletion of p45 and p42