Is sociality driven by the costs of dispersal or the benefits of philopatry? A role for kin-discrimination mechanisms.

The role of ecological constraints in promoting sociality is currently much debated. Using a direct-fitness approach, we show this role to depend on the kin-discrimination mechanisms underlying social interactions. Altruism cannot evolve under spatially based discrimination, unless ecological constraints prevent complete dispersal. Increasing constraints enhances both the proportion of philopatric (and thereby altruistic) individuals and the level of altruistic investments conceded in pairwise interactions. Familiarity-based discrimination, by contrast, allows philopatry and altruism to evolve at significant levels even in the absence of ecological constraints. Increasing constraints further enhances the proportion of philopatric (and thereby altruistic) individuals but not the level of altruism conceded. Ecological constraints are thus more likely to affect social evolution in species in which restricted cognitive abilities, large group size, and/or limited period of associative learning force investments to be made on the basis of spatial cues.

Mechanisms of inflammation in gout.

An acute attack of gout is a paradigm of acute sterile inflammation, as opposed to pyogenic inflammation. Recent studies suggest that the triggering of IL-1beta release from leucocytes lies at the heart of a cascade of processes that involves multiple cytokines and mediators. The NLRP3 inflammasome appears to have a specific role in this regard, but the biochemical events leading to its activation are still not well understood. We review the known mechanisms that underlie the inflammatory process triggered by urate crystals and suggest areas that require further research.

NEUROPATHOPHYSIOLOGICAL MECHANISMS IN GLUTARIC ACIDURIA TYPE I: 3-HYDROXYGLUTARIC ACID LEADS TO AMMONIA INCREASE AND NON-APOPTOTIC CELL DEATH

A 3D in vitro model of rat organotypic brain cell cultures in aggregates was used to investigate neurotoxicity mechanisms in glutaric aciduria type I (GA-I). 1 mM glutarate (GA) or 3-hydroxyglutarate (3OHGA) were repeatedly added to the culture media at two different time points. In cultures treated with 3OHGA, we observed an increase in lactate in the medium, pointing to a possible inhibition of Krebs cycle and respiratory chain. We further observed that 3OHGA and to a lesser extend GA induced an increase in ammonia production with concomitant decrease of glutamine concentrations, which may suggest an inhibition of the astrocytic enzyme glutamine synthetase. These previously unreported findings may uncover a pathogenic mechanism in this disease which has deleterious effects on early stages of brain development. By immunohistochemistry we showed that 3OHGA increased non-apoptotic cell death. On the cellular level, 3OHGA and to a lesser extend GA led to cell swelling and loss of astrocytic fibers whereas a loss of oligodendrocytes was only observed for 3OHGA. We conclude that 3OHGAwas the most toxic metabolite in our model for GA-I. 3OHGA induced deleterious effects on glial cells, an increase of ammonia production, and resulted in accentuated cell death of non-apoptotic origin.

Molecular mechanisms for the regulation of skin homeostasis

L'ubiquitination est une modification des protéines conservée, consistant en l'addition de résidus « ubiquitine » et régulant le destin cellulaire des protéines. La protéine « TRAF-interacting protein » TRAIP (ou TRIP) est une ligase E3 qui catalyse l'étape finale de l'ubiquitination. TRAIP est conservé dans l'évolution et est nécessaire au développement des organismes puisque l'ablation de TRAIP conduit à la mort embryonnaire aussi bien de la drosophile que de la souris. De plus, la réduction de l'expression de TRAIP dans des kératinocytes épidermiques humains réprime la prolifération cellulaire et induit un arrêt du cycle cellulaire en phase Gl, soulignant le lien étroit entre TRAIP et la prolifération cellulaire. Comme les mécanismes de régulation de la prolifération jouent un rôle majeur dans l'homéostasie de la peau, il est important de caractériser la fonction de TRAIP dans ces mécanismes. En utilisant des approches in vitro, nous avons déterminé que la protéine TRAIP est instable, modifiée par l'addition d'ubiquitine et ayant une demi-vie d'environ 4 heures. Nos analyses ont également révélé que l'expression de TRAIP est dépendante du cycle cellulaire, atteignant un pic d'expression en phase G2/M et que l'induction de son expression s'effectue principalement au cours de la transition Gl/S. Nous avons identifié le facteur de transcription E2F1 comme en étant le responsable, en régulant directement le promoteur de TRAIP. Aussi, TRAIP endogène ou surexprimée est surtout localisée au niveau du nucléole, une organelle nucléaire qui est désassemblée pendant la division cellulaire. Pour examiner la localisation subcellulaire de TRAIP pendant la mitose, nous avons imagé la protéine TRAIP fusionnée à une protéine fluorescente, à l'intérieur de cellules vivantes nommées HeLa, à l'aide d'un microscope confocal. Dans ces conditions, TRAIP est majoritairement localisée autour des chromosomes en début de mitose, puis est arrangée au niveau de l'ADN chromosomique en fin de mitose. La détection de TRAIP endogène à l'aide d'un anticorps spécifique a confirmé cette localisation. Enfin, l'inactivation de TRAIP dans les cellules HeLa par interférence ARN a inhibé leur capacité à s'arrêter en milieu de mitose. Nos résultats suggèrent que le mécanisme sous-jacent peut être lié au point de contrôle de l'assemblage du fuseau mitotique. - Ubiquitination of proteins is a post-translational modification which decides the cellular fate of the protein. The TRAF-interacting protein (TRAIP, TRIP) functions as an E3 ubiquitin ligase mediating addition of ubiquitin moieties to proteins. TRAIP interacts with the deubiquitinase CYLD, a tumor suppressor whose functional inactivation leads to skin appendage tumors. TRAIP is required for early embryonic development since removal of TRAIP either in Drosophila or mice by mutations or knock¬out is lethal due to aberrant regulation of cell proliferation and apoptosis. Furthermore, shRNA- mediated knock-down of TRAIP in human epidermal keratinocytes (HEK) repressed cell proliferation and induced a Gl/S phase block in the cell cycle. Additionally, TRAIP expression is strongly down- regulated during keratinocyte differentiation supporting the notion of a tight link between TRAIP and cell proliferation. We thus examined the biological functions of TRAIP in epithelial cell proliferation. Using an in vitro approach, we could determine that the TRAIP protein is unstable, modified by addition of ubiquitin moieties after translation and exhibits a half-life of 3.7+/-1-6 hours. Our analysis revealed that the TRAIP expression is modulated in a cell-cycle dependent manner, reaching a maximum expression level in G2/M phases. In addition, the expression of TRAIP was particularly activated during Gl/S phase transition and we could identify the transcription factor E2F1 as an activator of the TRAIP gene promoter. Both endogenous and over-expressed TRAIP mainly localized to the nucleolus, a nuclear organelle which is disassembled during cell division. To examine the subcellular localization of TRAIP during M phase, we performed confocal live-cell imaging of a functional fluorescent protein TRAIP-GFP in HeLa cells. TRAIP was distributed in the cytoplasm and accumulated around mitotic chromosomes in pro- and meta-phasic cells. TRAIP was then confined to chromosomal DNA location in anaphase and later phases of mitosis. Immune-detection of endogenous TRAIP protein confirmed its particular localization in mitosis. Finally, inactivating TRAIP expression in HeLa cells using RNA interference abrogated the cells ability to stop or delay mitosis progression. Our results suggested that TRAIP may involve the spindle assembly checkpoint.

Transplantation tolerance induced by regulatory T cells: in vivo mechanisms and sites of action.

The mechanisms by which CD4(+)CD25(+)Foxp3(+) T (Treg) cells regulate effector T cells in a transplantation setting and their in vivo homeostasis still remain to be clarified. Using a mouse adoptive transfer model, we analyzed the in vivo expansion, trafficking, and effector function of alloreactive T cells and donor-specific Treg cells, in response to a full-thickness skin allograft. Fluorescent-labeled CD4(+)CD25(-) and antigen-specific Treg cells were transferred alone or co-injected into syngeneic BALB/c-Nude recipients transplanted with skins from (C57BL/6 x BALB/c) F1 donors. Treg cells divided in vivo, migrated and accumulated in the allograft draining lymph nodes as well as within the graft. The co-transfer of Treg cells did not modify the early activation and homing of CD4(+)CD25(-) T cells in secondary lymphoid organs. However, in the presence of Treg cells, alloreactive CD4(+)CD25(-) T cells produced significantly less IFN-gamma and were present in reduced numbers in the secondary lymphoid organs. Furthermore, time-course studies showed that Treg cells were recruited into the allograft at a very early stage after transplantation and effectively prevented the infiltration of effector T cells. In conclusion, suppression of rejection requires the early recruitment to the site of antigenic challenge of donor-specific Treg cells, which then mainly regulate the effector arm of T cell alloresponses.

Vascular dysfunction in children conceived by assisted reproductive technologies: underlying mechanisms and future implications.

Epidemiological studies in humans have demonstrated a relationship between pathological events during fetal development and increased cardiovascular risk later in life and have led to the so called "Fetal programming of cardiovascular disease hypothesis". The recent observation of generalised vascular dysfunction in young apparently healthy children conceived by assisted reproductive technologies (ART) provides a novel and potentially very important example of this hypothesis. This review summarises recent data in ART children demonstrating premature subclinical atherosclerosis in the systemic circulation and pulmonary vascular dysfunction predisposing to exaggerated hypoxia-induced pulmonary hypertension. These problems appear to be related to the ART procedure per se. Studies in ART mice demonstrating premature vascular aging and arterial hypertension further demonstrate the potential of ART to increase cardiovascular risk and have allowed to unravel epigenetic alterations of the eNOS gene as an underpinning mechanism. The roughly 25% shortening of the life span in ART mice challenged with a western style high-fat-diet demonstrates the potential importance of these alterations for the long-term outcome. Given the young age of the ART population, data on cardiovascular endpoints will not be available before 20 to 30 years from now. However, already now cohort studies of the ART population are needed to early detect cardiovascular alterations with the aim to prevent or at least optimally treat cardiovascular complications. Finally, a debate needs to be engaged on the future of ART and the consequences of its exponential growth for public health.

Plastic brain mechanisms for attaining auditory temporal order judgment proficiency.

Accurate perception of the order of occurrence of sensory information is critical for the building up of coherent representations of the external world from ongoing flows of sensory inputs. While some psychophysical evidence reports that performance on temporal perception can improve, the underlying neural mechanisms remain unresolved. Using electrical neuroimaging analyses of auditory evoked potentials (AEPs), we identified the brain dynamics and mechanism supporting improvements in auditory temporal order judgment (TOJ) during the course of the first vs. latter half of the experiment. Training-induced changes in brain activity were first evident 43-76 ms post stimulus onset and followed from topographic, rather than pure strength, AEP modulations. Improvements in auditory TOJ accuracy thus followed from changes in the configuration of the underlying brain networks during the initial stages of sensory processing. Source estimations revealed an increase in the lateralization of initially bilateral posterior sylvian region (PSR) responses at the beginning of the experiment to left-hemisphere dominance at its end. Further supporting the critical role of left and right PSR in auditory TOJ proficiency, as the experiment progressed, responses in the left and right PSR went from being correlated to un-correlated. These collective findings provide insights on the neurophysiologic mechanism and plasticity of temporal processing of sounds and are consistent with models based on spike timing dependent plasticity.

Cellular source and mechanisms of high transcriptome complexity in the Mammalian testis.

Understanding the extent of genomic transcription and its functional relevance is a central goal in genomics research. However, detailed genome-wide investigations of transcriptome complexity in major mammalian organs have been scarce. Here, using extensive RNA-seq data, we show that transcription of the genome is substantially more widespread in the testis than in other organs across representative mammals. Furthermore, we reveal that meiotic spermatocytes and especially postmeiotic round spermatids have remarkably diverse transcriptomes, which explains the high transcriptome complexity of the testis as a whole. The widespread transcriptional activity in spermatocytes and spermatids encompasses protein-coding and long noncoding RNA genes but also poorly conserves intergenic sequences, suggesting that it may not be of immediate functional relevance. Rather, our analyses of genome-wide epigenetic data suggest that this prevalent transcription, which most likely promoted the birth of new genes during evolution, is facilitated by an overall permissive chromatin in these germ cells that results from extensive chromatin remodeling.

Inhibition of tumor angiogenesis by non-steroidal anti-inflammatory drugs: emerging mechanisms and therapeutic perspectives.

Chronic intake of non steroidal anti-inflammatory drugs (NSAIDs) is associated with a reduced risk of developing gastrointestinal tumors, in particular colon cancer. Increasing evidence indicates that NSAID exert tumor-suppressive activity on pre-malignant lesions (polyps) in humans and on established experimental tumors in mice. Some of the tumor-suppressive effects of NSAIDs depend on the inhibition of cyclooxygenase-2 (COX-2), a key enzyme in the synthesis of prostaglandins and thromboxane, which is highly expressed in inflammation and cancer. Recent findings indicate that NSAIDs exert their anti-tumor effects by suppressing tumor angiogenesis. The availability of COX-2-specific NSAIDs opens the possibility of using this drug class as anti-angiogenic agents in combination with chemotheapy or radiotherapy for the treatment of human cancer. Here we will briefly review recent advances in the understanding of the mechanism by which NSAIDs suppress tumor angiogenesis and discuss their potential clinical application as anti-cancer agents.

Mechanisms of protein homeostasis in health, aging and disease.

When emerging from the ribosomes, new polypeptides need to fold properly, eventually translocate, and then assemble into stable, yet functionally flexible complexes. During their lifetime, native proteins are often exposed to stresses that can partially unfold and convert them into stably misfolded and aggregated species, which can in turn cause cellular damage and propagate to other cells. In animal cells, especially in aged neurons, toxic aggregates may accumulate, induce cell death and lead to tissue degeneration via different mechanisms, such as apoptosis as in Parkinson's and Alzheimer's diseases and aging in general. The main cellular mechanisms effectively controlling protein homeostasis in youth and healthy adulthood are: (1) the molecular chaperones, acting as aggregate unfolding and refolding enzymes, (2) the chaperone-gated proteases, acting as aggregate unfolding and degrading enzymes, (3) the aggresomes, acting as aggregate compacting machineries, and (4) the autophagosomes, acting as aggregate degrading organelles. For unclear reasons, these cellular defences become gradually incapacitated with age, leading to the onset of degenerative diseases. Understanding these mechanisms and the reasons for their incapacitation in late adulthood is key to the design of new therapies against the progression of aging, degenerative diseases and cancers.