Adipocyte ATP-binding cassette G1 promotes triglyceride storage, fat mass growth, and human obesity

The role of ATP-binding Cassette G1 (ABCG1) transporter in human pathophysiology is still largely unknown. Indeed, beyond its role in mediating free cholesterol efflux to HDL, ABCG1 transporter equally promotes lipid accumulation in a triglyceride (TG)-rich environment through regulation of the bioavailability of Lipoprotein Lipase (LPL).As both ABCG1 and LPL are expressed in adipose tissue, we hypothesize that ABCG1 is implicated in adipocyte TG storage and could be then a major actor in adipose tissue fat accumulation.Silencing of Abcg1 expression by RNAi in 3T3-L1 preadipocytes compromised LPL-dependent TG accumulation during initial phase of differentiation. Generation of stable Abcg1 Knockdown 3T3-L1 adipocytes revealed that Abcg1 deficiency reduces TG storage and diminishes lipid droplet size through inhibition of Pparγ expression. Strikingly, local inhibition of adipocyte Abcg1 in adipose tissue from mice fed a high fat diet led to a rapid decrease of adiposity and weight gain. Analysis of two frequent ABCG1 SNPs (rs1893590 (A/C) and rs1378577 (T/G)) in morbidly obese individuals indicated that elevated ABCG1 expression in adipose tissue was associated with an increased PPARγ expression and adiposity concomitant to an increased fat mass and BMI (haplotype AT>GC). The critical role of ABCG1 regarding obesity was further confirmed in independent populations of severe obese and diabetic obese individuals.For the first time, this study identifies a major role of adipocyte ABCG1 in adiposity and fat mass growth and suggests that adipose ABCG1 might represent a potential therapeutic target in obesity

The Pleiotropic CymR Regulator of Staphylococcus aureus Plays an Important Role in Virulence and Stress Response

We have characterized a novel pleiotropic role for CymR, the master regulator of cysteine metabolism. We show here that CymR plays an important role both in stress response and virulence of Staphylococcus aureus. Genes involved in detoxification processes, including oxidative stress response and metal ion homeostasis, were differentially expressed in a ΔcymR mutant. Deletion of cymR resulted in increased sensitivity to hydrogen peroxide-, disulfide-, tellurite- and copper-induced stresses. Estimation of metabolite pools suggests that this heightened sensitivity could be the result of profound metabolic changes in the ΔcymR mutant, with an increase in the intracellular cysteine pool and hydrogen sulfide formation. Since resistance to oxidative stress within the host organism is important for pathogen survival, we investigated the role of CymR during the infectious process. Our results indicate that the deletion of cymR promotes survival of S. aureus inside macrophages, whereas virulence of the ΔcymR mutant is highly impaired in mice. These data indicate that CymR plays a major role in virulence and adaptation of S. aureus for survival within the host

Working Document - Project Web Site NOAH ESPRIT

Rapport de contrat.This document introduces the Web Site of NOAH ESPRIT Project at the end of may 1998. Ti shows the whole site in 7 parts : - Welcome : Welcome page - Objectives : This page presents the main objectives of the project in terms of standardisation and expected results - Workplan : Througt 7 different pages, containing text and drawings, the 7 work packages are briefly described - Partners : This page gives the names of the members and their companies incolved in NOAH ESPRIT Project. Each logo is linked to the sweb site of the company - News : Currently empty, this section is due to be filled with press releases - Meetings : This page gives the date s of important meetings - Pilot Trial : This part of the site will allow people to follow the increase of the pilot tria

New Insights into the WalK/WalR (YycG/YycF) Essential Signal Transduction Pathway Reveal a Major Role in Controlling Cell Wall Metabolism and Biofilm Formation in Staphylococcus aureus▿

The highly conserved WalK/WalR (also known as YycG/YycF) two-component system is specific to low-G+C gram-positive bacteria. While this system is essential for cell viability, both the nature of its regulon and its physiological role have remained mostly uncharacterized. We observed that, unexpectedly, Staphylococcus aureus cell death induced by WalKR depletion was not followed by lysis. We show that WalKR positively controls autolytic activity, in particular that of the two major S. aureus autolysins, AtlA and LytM. By using our previously characterized consensus WalR binding site and carefully reexamining the genome annotations, we identified nine genes potentially belonging to the WalKR regulon that appeared to be involved in S. aureus cell wall degradation. Expression of all of these genes was positively controlled by WalKR levels in the cell, leading to high resistance to Triton X-100-induced lysis when the cells were starved for WalKR. Cells lacking WalKR were also more resistant to lysostaphin-induced lysis, suggesting modifications in cell wall structure. Indeed, lowered levels of WalKR led to a significant decrease in peptidoglycan biosynthesis and turnover and to cell wall modifications, which included increased peptidoglycan cross-linking and glycan chain length. We also demonstrated a direct relationship between WalKR levels and the ability to form biofilms. This is the first example in S. aureus of a regulatory system positively controlling autolysin synthesis and biofilm formation. Taken together, our results now define this signal transduction pathway as a master regulatory system for cell wall metabolism, which we have accordingly renamed WalK/WalR to reflect its true function

SpdC, a novel virulence factor, controls histidine kinase activity in Staphylococcus aureus.

The success of Staphylococcus aureus, as both a human and animal pathogen, stems from its ability to rapidly adapt to a wide spectrum of environmental conditions. Two-component systems (TCSs) play a crucial role in this process. Here, we describe a novel staphylococcal virulence factor, SpdC, an Abi-domain protein, involved in signal sensing and/or transduction. We have uncovered a functional link between the WalKR essential TCS and the SpdC Abi membrane protein. Expression of spdC is positively regulated by the WalKR system and, in turn, SpdC negatively controls WalKR regulon genes, effectively constituting a negative feedback loop. The WalKR system is mainly involved in controlling cell wall metabolism through regulation of autolysin production. We have shown that SpdC inhibits the WalKR-dependent synthesis of four peptidoglycan hydrolases, SceD, SsaA, LytM and AtlA, as well as impacting S. aureus resistance towards lysostaphin and cell wall antibiotics such as oxacillin and tunicamycin. We have also shown that SpdC is required for S. aureus biofilm formation and virulence in a murine septicemia model. Using protein-protein interactions in E. coli as well as subcellular localization in S. aureus, we showed that SpdC and the WalK kinase are both localized at the division septum and that the two proteins interact. In addition to WalK, our results indicate that SpdC also interacts with nine other S. aureus histidine kinases, suggesting that this membrane protein may act as a global regulator of TCS activity. Indeed, using RNA-Seq analysis, we showed that SpdC controls the expression of approximately one hundred genes in S. aureus, many of which belong to TCS regulons

Transcriptional Analysis and Subcellular Protein Localization Reveal Specific Features of the Essential WalKR System in Staphylococcus aureus

International audienceThe WalKR two-component system, controlling cell wall metabolism, is highly conserved among Bacilli and essential for cell viability. In Staphylococcus aureus, walR and walK are followed by three genes of unknown function: walH, walI and walJ. Sequence analysis and transcript mapping revealed a unique genetic structure for this locus in S. aureus: the last gene of the locus, walJ, is transcribed independently, whereas transcription of the tetra-cis-tronic walRKHI operon occurred from two independent promoters located upstream from walR. Protein topology analysis and protein-protein interactions in E. coli as well as subcel-lular localization in S. aureus allowed us to show that WalH and WalI are membrane-bound proteins, which associate with WalK to form a complex at the cell division septum. While these interactions suggest that WalH and WalI play a role in activity of the WalKR regulatory pathway, deletion of walH and/or walI did not have a major effect on genes whose expression is strongly dependent on WalKR or on associated phenotypes. No effect of WalH or WalI was seen on tightly controlled WalKR regulon genes such as sle1 or saouhsc_00773, which encodes a CHAP-domain amidase. Of the genes encoding the two major S. aureus autolysins, AtlA and Sle1, only transcription of atlA was increased in the ΔwalH or ΔwalI mutants. Likewise, bacterial autolysis was not increased in the absence of WalH and/or WalI and biofilm formation was lowered rather than increased. Our results suggest that contrary to their major role as WalK inhibitors in B. subtilis, the WalH and WalI proteins have evolved a different function in S. aureus, where they are more accessory. A phylogenomic analysis shows a striking conservation of the 5 gene wal cluster along the evolutionary history of Bacilli, supporting the key importance of this signal transduction system, and indicating that the walH and walI genes were lost in the ancestor of Streptococcaceae, leading to their atypical 3 wal gene cluster, walRKJ

Peptidoglycan Crosslinking Relaxation Plays an Important Role in Staphylococcus aureus WalKR-Dependent Cell Viability

International audienceThe WalKR two-component system is essential for viability of Staphylococcus aureus, a major pathogen. We have shown that WalKR acts as the master controller of peptidoglycan metabolism, yet none of the identified regulon genes explain its requirement for cell viability. Transmission electron micrographs revealed cell wall thickening and aberrant division septa in the absence of WalKR, suggesting its requirement may be linked to its role in coordinating cell wall metabolism and cell division. We therefore tested whether uncoupling autolysin gene expression from WalKR-dependent regulation could compensate for its essential nature. Uncoupled expression of genes encoding lytic transglycosylases or amidases did not restore growth to a WalKR-depleted strain. We identified only two WalKR-regulon genes whose expression restored cell viability in the absence of WalKR: lytM and ssaA. Neither of these two genes are essential under our conditions and a ΔlytM ΔssaA mutant does not present any growth defect. LytM is a glycyl-glycyl endopeptidase, hydrolyzing the pentaglycine interpeptide crossbridge, and SsaA belongs to the CHAP amidase family, members of which such as LysK and LytA have been shown to have D-alanyl-glycyl endopeptidase activity, cleaving between the crossbridge and the stem peptide. Taken together, our results strongly suggest that peptidoglycan crosslinking relaxation through crossbridge hydrolysis plays a crucial role in the essential requirement of the WalKR system for cell viability

SpdC impacts cell wall homeostasis.

<p>A. The Δ<i>spdC</i> mutant displays increased resistance to lysostaphin-induced lysis. Cells were grown in TSB until mid-exponential phase, harvested and incubated in PBS with lysostaphin (200 ng/ml) with aeration at 37°C. Bacterial lysis was measured by monitoring OD_600nm over time. Results are shown as the mean and standard deviation of three independent assays. HG001 parental strain (); Δ<i>spdC</i> mutant (■); Δ<i>spdC</i>/pMK4Pprot-<i>spdC</i> complemented strain (▲). B. The absence of SpdC leads to sensitivity to oxacillin and tunicamycin. Dilution series of the HG001, Δ<i>spdC</i> and Δ<i>spdC</i>/ pMK4Pprot-<i>spdC</i> strains on TSA plates with or without antibiotics. Oxacillin: 0.1 μg/ml; fosfomycin: 4 μg/ml; tunicamycin: 1 μg/ml.</p

SpdC is involved in gene regulation.

<p>A. Ontological grouping of SpdC-regulated genes according to their annotated functions. Variations in gene expression were identified by RNA-Seq analysis of a Δ<i>spdC</i> strain compared to the HG001 parental strain grown in TSB until mid-exponential phase. B. qRT-PCR comparison of gene expression in a Δ<i>spdC</i> strain and the HG001 parental strain. Strains were grown in TSB until mid-exponential phase and RNA was extracted and treated as described in Materials and Methods. Expression levels were normalized using 16S rRNA as internal standard and presented as the <i>n-</i>fold change of the Δ<i>spdC</i> mutant strain compared to the HG001 parental strain. C. Western blot analysis of LytM (upper panel) and Spa (lower panel) production. Crude extracts (LytM) and cell wall extracts (Spa) were prepared from stationary phase cultures. Lanes: 1: Purified <i>Staphylococcus aureus</i> Protein A (50 ng) 2: HG001 strain; 3: Δ<i>spdC</i> mutant strain; 4: Δ<i>spdC</i>/pMK4Pprot-<i>spdC</i> complemented strain.</p