The mechanisms of inflammation in gout and pseudogout (CPP-induced arthritis).

Recent advances have stimulated new interest in the area of crystal arthritis, as microcrystals can be considered to be endogenous "danger signals" and are potent stimulators of immune as well as non-immune cells. The best known microcrystals include urate (MSU), and calcium pyrophosphate (CPP) crystals, associated with gout and pseudogout, respectively. Acute inflammation is the hallmark of the acute tissue reaction to crystals in both gout and pseudogout. The mechanisms leading to joint inflammation in these diseases involve first crystal formation and subsequent coating with serum proteins. Crystals can then interact with plasma cell membrane, either directly or via membrane receptors, leading to NLRP3 activation, proteolytic cleavage and maturation of pro-interleukin-1β (pro-IL1β) and secretion of mature IL1β. Once released, this cytokine orchestrates a series of events leading to endothelial cell activation and neutrophil recruitment. Ultimately, gout resolution involves several mechanisms including monocyte differentiation into macrophage, clearance of apoptotic neutrophils by macrophages, production of Transforming Growth Factor (TGF-β) and modification of protein coating on the crystal surface. This review will examine these different steps.

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.

Theoretical study on receptor-G protein recognition: new insights into the mechanisms of the alpha1b-adrenergic recptor activation

This work compares the structural/dynamics features of the wild-type alb-adrenergic receptor (AR) with those of the D142A active mutant and the agonist-bound state. The two active receptor forms were compared in their isolated states as well as in their ability to form homodimers and to recognize the G alpha q beta 1 gamma 2 heterotrimer. The analysis of the isolated structures revealed that, although the mutation- and agonist-induced active states of the alpha 1b-AR are different, they, however, share several structural peculiarities including (a) the release of some constraining interactions found in the wild-type receptor and (b) the opening of a cytosolic crevice formed by the second and third intracellular loops and the cytosolic extensions of helices 5 and 6. Accordingly, also their tendency to form homodimers shows commonalties and differences. In fact, in both the active receptor forms, helix 6 plays a crucial role in mediating homodimerization. However, the homodimeric models result from different interhelical assemblies. On the same line of evidence, in both of the active receptor forms, the cytosolic opened crevice recognizes similar domains on the G protein. However, the docking solutions are differently populated and the receptor-G protein preorientation models suggest that the final complexes should be characterized by different interaction patterns.

Molecular mechanisms of drug resistance in clinical Candida species isolated from tunisian hospitals.

Antifungal resistance of Candida species is a clinical problem in the management of diseases caused by these pathogens. In this study we identified from a collection of 423 clinical samples taken from Tunisian hospitals two clinical Candida species (Candida albicans JEY355 and Candida tropicalis JEY162) with decreased susceptibility to azoles and polyenes. For JEY355, the fluconazole (FLC) MIC was 8 μg/ml. Azole resistance in C. albicans JEY355 was mainly caused by overexpression of a multidrug efflux pump of the major facilitator superfamily, Mdr1. The regulator of Mdr1, MRR1, contained a yet-unknown gain-of-function mutation (V877F) causing MDR1 overexpression. The C. tropicalis JEY162 isolate demonstrated cross-resistance between FLC (MIC > 128 μg/ml), voriconazole (MIC > 16 μg/ml), and amphotericin B (MIC > 32 μg/ml). Sterol analysis using gas chromatography-mass spectrometry revealed that ergosterol was undetectable in JEY162 and that it accumulated 14α-methyl fecosterol, thus indicating a perturbation in the function of at least two main ergosterol biosynthesis proteins (Erg11 and Erg3). Sequence analyses of C. tropicalis ERG11 (CtERG11) and CtERG3 from JEY162 revealed a deletion of 132 nucleotides and a single amino acid substitution (S258F), respectively. These two alleles were demonstrated to be nonfunctional and thus are consistent with previous studies showing that ERG11 mutants can only survive in combination with other ERG3 mutations. CtERG3 and CtERG11 wild-type alleles were replaced by the defective genes in a wild-type C. tropicalis strain, resulting in a drug resistance phenotype identical to that of JEY162. This genetic evidence demonstrated that CtERG3 and CtERG11 mutations participated in drug resistance. During reconstitution of the drug resistance in C. tropicalis, a strain was obtained harboring only defective Cterg11 allele and containing as a major sterol the toxic metabolite 14α-methyl-ergosta-8,24(28)-dien-3α,6β-diol, suggesting that ERG3 was still functional. This strain therefore challenged the current belief that ERG11 mutations cannot be viable unless accompanied by compensatory mutations. In conclusion, this study, in addition to identifying a novel MRR1 mutation in C. albicans, constitutes the first report on a clinical C. tropicalis with defective activity of sterol 14α-demethylase and sterol Δ(5,6)-desaturase leading to azole-polyene cross-resistance.

Multiple expression control mechanisms of peroxisome proliferator-activated receptors and their target genes.

The peroxisome proliferator-activated receptors (PPAR) alpha, beta/delta and gamma belong to the nuclear hormone receptor superfamily. As ligand-activated receptors, they form a functional transcriptional unit upon heterodimerization with retinoid X receptors (RXRs). PPARs are activated by fatty acids and their derivatives, whereas RXR is activated by 9-cis retinoic acid. This heterodimer binds to peroxisome proliferator response elements (PPRE) residing in target genes and stimulates their expression. Recent reports now indicate that PPARs and RXRs can function independently, in the absence of a hetero-partner, to modulate gene expression. Of importance, these non-canonical mechanisms underscore the impact of both cofactors and DNA on gene expression. Furthermore, these different mechanisms reveal the increasing repertoire of PPAR 'target' genes that now encompasses non-PPREs containing genes. It is also becoming apparent that understanding the regulation of PPAR expression and activity, can itself have a significant influence on how the expression of subgroups of target genes is studied and integrated in current knowledge.

Mechanisms of skin adherence and invasion by dermatophytes.

Dermatophytes are keratinophilic fungi that can be pathogenic for humans and animals by infecting the stratum corneum, nails, claws or hair. The first infection step consists of adherence of arthroconidia to the stratum corneum. The mechanisms and the kinetics of adherence have been investigated using different in vitro and ex vivo experimental models, most notably showing the role of a secreted serine protease from Microsporum canis in fungal adherence to feline corneocytes. After germination of the arthroconidia, dermatophytes invade keratinised structures that have to be digested into short peptides and amino acids to be assimilated. Although many proteases, including keratinolytic ones, have been characterised, the understanding of dermatophyte invasion mechanisms remains speculative. To date, research on mechanisms of dermatophyte infection focused mainly on both secreted endoproteases and exoproteases, but their precise role in both fungal adherence and skin invasion should be further explored.

Mechanisms of postprandial hyperglycemia in liver transplant recipients: comparison of liver transplant patients with kidney transplant patients and healthy controls.

Impaired glucose tolerance or diabetes mellitus are frequent complications after organ transplantation, and are usually attributed to glucocorticoid and immunosuppressive treatments. Liver transplantation results in total hepatic denervation which may also affect glucoregulation. We therefore evaluated postprandial glucose metabolism in a group of patients with liver cirrhosis before and after orthotopic liver transplantation. Seven patients with liver cirrhosis of various etiologies, 6 patients having received a kidney transplant, and 6 healthy subjects were studied. Their glucose metabolism was evaluated in the basal state and over 4 hours after ingestion of a glucose load with 6.6 (2) H glucose dilution analysis. The patients with liver cirrhosis were studied before, and again 4 weeks (range 2-6) and 38 weeks (range 20-76, n=6) after orthotopic liver transplantation. Basal glucose metabolism was similar in liver and kidney transplant recipients. Impaired glucose tolerance was present in both groups, but postprandial hyperglycemia was exaggerated and lasted longer in liver transplant patients. Postprandial insulinemia was lower in liver transplant recipients, while C-peptide concentrations were comparable to those of kidney transplant recipients, indicating increased insulin clearance. Glucose turnover was not altered in both groups of patients during the initial 3 hours after glucose ingestion, but was higher in liver transplant early after transplantation during the fourth hour. Postprandial hyperglycemia remained unchanged in liver transplant recipients 38 weeks after liver transplantation, despite substantial reduction of immunosuppressive and glucocorticoid doses. We conclude that liver transplant recipients have severe postprandial hyperglycemia which can be attributed to insulinopenia (secondary, at least in part, to increased insulin clearance) and a late increased glucose turnover. These changes may be secondary to hepatic denervation.

Stable isotope geochemistry and formation mechanisms of quartz veins; Extreme paleoaltitudes of the Central Alps in the Neogene

Quartz veins ranging in size from less than 50 cm length and 5 cm width to greater than 10 m in length and 5 m in width are found throughout the Central Swiss Alps. In some cases, the veins are completely filled with milky quartz, while in others, sometimes spectacular void-filling quartz crystals are found. The style of vein filling and size is controlled by host rock composition and deformation history. Temperatures of vein formation, estimated using stable isotope thermometry and mineral equilibria, cover a range of 450 degrees C down to 150 degrees C. Vein formation started at 18 to 20 Ma and continued for over 10 My. The oxygen isotope values of quartz veins range from 10 to 20 permil, and in almost all cases are equal to those of the hosting lithology. The strongly rock-buffered veins imply a low fluid/rock ratio and minimal fluid flow. In order to explain massive, nearly morromineralic quartz formation without exceptionally large fluid fluxes, a mechanism of differential pressure and silica diffusion, combined with pressure solution, is proposed for early vein formation. Fluid inclusions and hydrous minerals in late-formed veins have extremely low delta D values, consistent with meteoric water infiltration. The change from rock-buffered, static fluid to infiltration from above can be explained in terms of changes in the large-scale deformation style occurring between 20 and 15 Ma. The rapid cooling of the Central Alps identified in previous studies may be explained in part, by infiltration of cold meteoric waters along fracture systems down to depths of 10 km or more. An average water flux of 0.15 cm 3 cm(-2)yr(-1) entering the rock and reemerging heated by 40 degrees C is sufficient to cool rock at 10 km depth by 100 degrees C in 5 million years. The very negative delta D values of < -130 permil for the late stage fluids are well below the annual average values measured in meteoric water in the region today. The low fossil delta D values indicate that the Central Alps were at a higher elevation in the Neogene. Such a conclusion is supported by an earlier work, where a paleoaltitude of 5000 meters was proposed on the basis of large erratic boulders found at low elevations far from their origin.

Mechanisms of reproductive isolation between an ant species of hybrid origin and one of its parents.

The establishment of new species by hybridization is difficult because it requires the development of reproductive isolation (RI) in sympatry to escape the homogenizing effects of gene flow from the parental species. Here we investigated the role of two pre- and two postzygotic mechanisms of RI in a system comprising two interdependent Pogonomyrmex harvester ant lineages (the H1 and H2 lineages) of hybrid origin and one of their parental species (P. rugosus). Similar to most other ants, P. rugosus is characterized by an environmental system of caste determination with female brood developing either into queens or workers depending on nongenetic factors. By contrast, there is a strong genetic component to caste determination in the H1 and H2 lineages because the developmental fate of female brood depends on the genetic origin of the parents, with interlineage eggs developing into workers and intralineage eggs developing into queens. The study of a mixed mating aggregation revealed strong differences in mating flight timing between P. rugosus and the two lineages as a first mechanism of RI. A second important prezygotic mechanism was assortative mating. Laboratory experiments also provided support for one of the two investigated mechanisms of postzygotic isolation. The majority of offspring produced from the few matings between P. rugosus and the lineages aborted at the egg stage. This hybrid inviability was under maternal influence, with hybrids produced by P. rugosus queens being always inviable whereas a small proportion of H2 lineage queens produced large numbers of adult hybrid offspring. Finally, we found no evidence that genetic caste determination acted as a second postzygotic mechanism reducing gene flow between P. rugosus and the H lineages. The few viable P. rugosus-H hybrids were not preferentially shunted into functionally sterile workers but developed into both workers and queens. Overall, these results reveal that the nearly complete (99.5%) RI between P. rugosus and the two hybrid lineages stems from the combination of two typical prezygotic mechanisms (mating time divergence and assortative mating) and one postzygotic mechanism (hybrid inviability).

New insights into the regulatory mechanisms of the NALP3 inflammasome

Résumé : Les vertébrés ont recours au système immunitaire inné et adaptatif pour combattre les pathogènes. La découverte des récepteurs Toll, il y a dix ans, a fortement augmenté l'intérêt porté à l'immunité innée. Depuis lors, des récepteurs intracellulaires tels que les membres de la famille RIG-like helicase (RLHs) et NOD-like receptor (NLRs) ont été décrits pour leur rôle dans la détection des pathogènes. L'interleukine-1 beta (IL-1β) est une cytokine pro-inflammatoire qui est synthétisée sous forme de précurseur, la proIL-1β. La proIL-1β requiert d'être clivée par la caspase-1 pour devenir active. La caspase-1 est elle-même activée par un complexe appelé inflammasome qui peut être formé par divers membres de la famille NLR. Plusieurs inflammasomes ont été décrits tels que le NALP3 inflammasome ou l'IPAF inflammasome. Dans cette étude nous avons identifié la co-chaperone SGT1 et la chaperone HSP90 comme partenaires d'interaction de NALP3. Ces deux protéines sont bien connues chez les plantes pour leurs rôles dans la régulation des gènes de résistance (gène R) qui sont structurellement apparentés à la famille NLR. Nous avons pu montrer que SGT1 et HSP90 jouent un rôle similaire dans la régulation de NALP3 et des protéines R. En effet, nous avons démontré que les deux protéines sont nécessaires pour l'activité du NALP3 inflammasome. De plus, la HSP90 est également requise pour la stabilité de NALP3. En se basant sur ces observations, nous avons proposé un modèle dans lequel SGT1 et HSP90 maintiennent NALP3 inactif mais prêt à percevoir un ligand activateur qui initierait la cascade inflammatoire. Nous avons également montré une interaction entre SGT1 et HSP90 avec plusieurs NLRs. Cette observation suggère qu'un mécanisme similaire pourrait être impliqué dans la régulation des membres de la famille des NLRs. Ces dernières années, plusieurs PAMPs mais également des DAMPs ont été identifiés comme activateurs du NALP3 inflammasome. Dans la seconde partie de cette étude, nous avons identifié la réponse au stress du réticulum endoplasmique (RE) comme nouvel activateur du NALP3 inflammasome. Cette réponse est initiée lors de l'accumulation dans le réticulum endoplasmique de protéines ayant une mauvaise conformation ce qui conduit, en autre, à l'arrêt de la synthèse de nouvelles protéines ainsi qu'une augmentation de la dégradation des protéines. Les mécanismes par lesquels la réponse du réticulum endoplasmique induit l'activation du NALP3 inflammasome doivent encore être déterminés. Summary : Vertebrates rely on the adaptive and the innate immune systems to fight pathogens. Awarness of the importance of the innate system increased with the identification of Toll-like receptors a decade ago. Since then, intracellular receptors such as the RIG-like helicase (RLH) and the NOD-like receptor (NLR) families have been described for their role in the recognition of microbes. Interleukin- 1ß (IL-1ß) is a key mediator of inflammation. This proinflammatory cytokine is synthesised as an inactive precursor that requires processing by caspase-1 to become active. Caspase-1 is, itself, activated in a complex termed the inflammasome that can be formed by members of the NLR family. Various inflammasome complexes have been described such as the IPAF and the NALP3 inflammasome. In this study, we have identified the co-chaperone SGT1 and the chaperone HSP90 as interacting partners of NALP3. SGT1 and HSP90 are both known for their role in the activity of plant resistance proteins (R proteins) which are structurally related to the NLR family. We have shown that HSP90 and SGT1 play a similar role in the regulation of NALP3 and in the regulation of plant R proteins. Indeed, we demonstrated that both HSP90 and SGT1 are essential for the activity of the NALP3 inflammasome complex. In addition, HSP90 is required for the stability of NALP3. Based on these observations, we have proposed a model in which SGT1 and HSP90 maintain NALP3 in an inactive but signaling-competent state, ready to receive an activating ligand that induces the inflammatory cascade. An interaction between several NLR members, SGTI and HSP90 was also shown, suggesting that similar mechanisms could be involved in the regulation of other NLRs. Several pathogen-associated molecular patterns (PAMPs) but also danger associated molecular patterns (DAMPs) have been identified as NALP3 activators. In the second part of this study, we have identified the ER stress response as a new NALP3 activator. The ER stress response is activated upon the accumulation of unfolded protein in the endoplasmic reticulum and results in a block in protein synthesis and increased protein degradation. The mechanisms of ER stress-mediated NALP3 activation remain to be determined.

Mécanismes physiopathologiques impliqués dans la dysfonction d'organes au cours du sepsis [Pathophysiological mechanisms of organ dysfunction in sepsis].

Sepsis is defined as the systemic inflammatory response to an infection. The occurrence of organ dysfunction increases the severity of sepsis. Complex interactions between multiple immunomodulating mediators and various cell populations, activated secondarily to the initial infectious insult, promote the development of organ dysfunction in sepsis. Although septic organ dysfunction has long been considered as the end result of chaotic, uncontrolled and deregulated inflammatory cascades, it might instead represent an adaptive response to avoid the occurrence of irreversible tissue damage and end-organ injury. In this article, we review the major mechanisms involved in organ dysfunction during sepsis, and also present the concept of organ dysfunction as an adaptive response to the septic process.