Compositional and functional differences of the mucosal microbiota along the intestine of healthy individuals

Gut mucosal microbes evolved closest to the host, developing specialized local communities. There is, however, insufficient knowledge of these communities as most studies have employed sequencing technologies to investigate faecal microbiota only. This work used shotgun metagenomics of mucosal biopsies to explore the microbial communities' compositions of terminal ileum and large intestine in 5 healthy individuals. Functional annotations and genome-scale metabolic modelling of selected species were then employed to identify local functional enrichments. While faecal metagenomics provided a good approximation of the average gut mucosal microbiome composition, mucosal biopsies allowed detecting the subtle variations of local microbial communities. Given their significant enrichment in the mucosal microbiota, we highlight the roles of Bacteroides species and describe the antimicrobial resistance biogeography along the intestine. We also detail which species, at which locations, are involved with the tryptophan/indole pathway, whose malfunctioning has been linked to pathologies including inflammatory bowel disease. Our study thus provides invaluable resources for investigating mechanisms connecting gut microbiota and host pathophysiology.

Chemical Genetics of AGC-kinases Reveals Shared Targets of Ypk1, Protein Kinase A and Sch9

Protein phosphorylation cascades play a central role in the regulation of cell growth and protein kinases PKA, Sch9 and Ypk1 take center stage in regulating this process in S. cerevisiae To understand how these kinases co-ordinately regulate cellular functions we compared the phospho-proteome of exponentially growing cells without and with acute chemical inhibition of PKA, Sch9 and Ypk1. Sites hypo-phosphorylated upon PKA and Sch9 inhibition were preferentially located in RRxS/T-motifs suggesting that many are directly phosphorylated by these enzymes. Interestingly, when inhibiting Ypk1 we not only detected several hypo-phosphorylated sites in the previously reported RxRxxS/T-, but also in an RRxS/T-motif. Validation experiments revealed that neutral trehalase Nth1, a known PKA target, is additionally phosphorylated and activated downstream of Ypk1. Signaling through Ypk1 is therefore more closely related to PKA- and Sch9-signaling than previously appreciated and may perform functions previously only attributed to the latter kinases.

Id4 promotes the elimination of the pro-activation factor Ascl1 to maintain quiescence of adult hippocampal stem cells

Quiescence is essential for the long-term maintenance of adult stem cells but how stem cells maintain quiescence is poorly understood. Here, we show that neural stem cells (NSCs) in the adult mouse hippocampus actively transcribe the pro-activation factor Ascl1 regardless of their activated or quiescent states. We found that the inhibitor of DNA binding protein Id4 is enriched in quiescent NSCs and that elimination of Id4 results in abnormal accumulation of Ascl1 protein and premature stem cell activation. Accordingly, Id4 and other Id proteins promote elimination of Ascl1 protein in NSC cultures. Id4 sequesters Ascl1 heterodimerization partner E47, promoting Ascl1 protein degradation and stem cell quiescence. Our results highlight the importance of non-transcriptional mechanisms for the maintenance of NSC quiescence and reveal a role for Id4 as a quiescence-inducing factor, in contrast with its role of promoting the proliferation of embryonic neural progenitors.

System-Wide Quantitative Proteomics of the Metabolic Syndrome in Mice: Genotypic and Dietary Effects

Advances in mass spectrometry have made the quantitative measurement of proteins across multiple samples a reality, allowing for the study of complex biological systems such as the metabolic syndrome. Although the deregulation of lipid metabolism and increased hepatic storage of triacylglycerides are known to play a part in the onset of the metabolic syndrome, its molecular basis and dependency on dietary and genotypic factors are poorly characterized. Here, we used an experimental design with two different mouse strains and dietary and metabolic perturbations to generate a compendium of quantitative proteome data using three mass spectrometric techniques. The data reproduce known properties of the metabolic system and indicate differential molecular adaptation of the two mouse strains to perturbations, contributing to a better understanding of the metabolic syndrome. We show that high-quality, high-throughput proteomic data sets provide an unbiased broad overview of the behavior of complex systems after perturbation.

Parallel feedback loops control the basal activity of the HOG MAPK signaling cascade

Tight regulation of the MAP kinase Hog1 is crucial for survival under changing osmotic conditions. Interestingly, we found that Hog1 phosphorylates multiple upstream components, implying feedback regulation within the signaling cascade. Taking advantage of an unexpected link between glucose availability and Hog1 activity, we used quantitative single cell measurements and computational modeling to unravel feedback regulation operating in addition to the well-known adaptation feedback triggered by glycerol accumulation. Indeed, we found that Hog1 phosphorylates its activating kinase Ssk2 on several sites, and cells expressing a non-phosphorylatable Ssk2 mutant are partially defective for feedback regulation and proper control of basal Hog1 activity. Together, our data suggest that Hog1 activity is controlled by intertwined regulatory mechanisms operating with varying kinetics, which together tune the Hog1 response to balance basal Hog1 activity and its steady-state level after adaptation to high osmolarity.

Target of Rapamycin Complex 2 Regulates Actin Polarization and Endocytosis via Multiple Pathways

Target of rapamycin is a Ser/Thr kinase that operates in two conserved multiprotein complexes, TORC1 and TORC2. Unlike TORC1, TORC2 is insensitive to rapamycin, and its functional characterization is less advanced. Previous genetic studies demonstrated that TORC2 depletion leads to loss of actin polarization and loss of endocytosis. To determine how TORC2 regulates these readouts, we engineered a yeast strain in which TORC2 can be specifically and acutely inhibited by the imidazoquinoline NVP-BHS345. Kinetic analyses following inhibition of TORC2, supported with quantitative phosphoproteomics, revealed that TORC2 regulates these readouts via distinct pathways as follows: rapidly through direct protein phosphorylation cascades and slowly through indirect changes in the tensile properties of the plasma membrane. The rapid signaling events are mediated in large part through the phospholipid flippase kinases Fpk1 and Fpk2, whereas the slow signaling pathway involves increased plasma membrane tension resulting from a gradual depletion of sphingolipids. Additional hits in our phosphoproteomic screens highlight the intricate control TORC2 exerts over diverse aspects of eukaryote cell physiology.

Phosphoproteomic analyses reveal novel cross-modulation mechanisms between two signaling pathways in yeast

Cells respond to environmental stimuli via specialized signaling pathways. Concurrent stimuli trigger multiple pathways that integrate information, predominantly via protein phosphorylation. Budding yeast responds to NaCl and pheromone via two mitogen-activated protein kinase cascades, the high osmolarity, and the mating pathways, respectively. To investigate signal integration between these pathways, we quantified the time-resolved phosphorylation site dynamics after pathway co-stimulation. Using shotgun mass spectrometry, we quantified 2,536 phosphopeptides across 36 conditions. Our data indicate that NaCl and pheromone affect phosphorylation events within both pathways, which thus affect each other at more levels than anticipated, allowing for information exchange and signal integration. We observed a pheromone-induced down-regulation of Hog1 phosphorylation due to Gpd1, Ste20, Ptp2, Pbs2, and Ptc1. Distinct Ste20 and Pbs2 phosphosites responded differently to the two stimuli, suggesting these proteins as key mediators of the information exchange. A set of logic models was then used to assess the role of measured phosphopeptides in the crosstalk. Our results show that the integration of the response to different stimuli requires complex interconnections between signaling pathways.

Phosphoproteomic analysis identifies proteins involved in transcription-coupled mRNA decay as targets of Snf1 signaling

Stresses, such as glucose depletion, activate Snf1, the Saccharomyces cerevisiae ortholog of adenosine monophosphate-activated protein kinase (AMPK), enabling adaptive cellular responses. In addition to affecting transcription, Snf1 may also promote mRNA stability in a gene-specific manner. To understand Snf1-mediated signaling, we used quantitative mass spectrometry to identify proteins that were phosphorylated in a Snf1-dependent manner. We identified 210 Snf1-dependent phosphopeptides in 145 proteins. Thirteen of these proteins are involved in mRNA metabolism. Of these, we found that Ccr4 (the major cytoplasmic deadenylase), Dhh1 (an RNA helicase), and Xrn1 (an exoribonuclease) were required for the glucose-induced decay of Snf1-dependent mRNAs that were activated by glucose depletion. Unexpectedly, deletion of XRN1 reduced the accumulation of Snf1-dependent transcripts that were synthesized during glucose depletion. Deletion of SNF1 rescued the synthetic lethality of simultaneous deletion of XRN1 and REG1, which encodes a regulatory subunit of a phosphatase that inhibits Snf1. Mutation of three Snf1-dependent phosphorylation sites in Xrn1 reduced glucose-induced mRNA decay. Thus, Xrn1 is required for Snf1-dependent mRNA homeostasis in response to nutrient availability.

Yeast endosulfines control entry into quiescence and chronological life span by inhibiting protein phosphatase 2A

The TORC1 and PKA protein kinases are central elements of signaling networks that regulate eukaryotic cell proliferation in response to growth factors and/or nutrients. In yeast, attenuation of signaling by these kinases following nitrogen and/or carbon limitation activates the protein kinase Rim15, which orchestrates the initiation of a reversible cellular quiescence program to ensure normal chronological life span. The molecular elements linking Rim15 to distal readouts including the expression of Msn2/4- and Gis1-dependent genes involve the endosulfines Igo1/2. Here, we show that Rim15, analogous to the greatwall kinase in Xenopus, phosphorylates endosulfines to directly inhibit the Cdc55-protein phosphatase 2A (PP2A(Cdc55)). Inhibition of PP2A(Cdc55) preserves Gis1 in a phosphorylated state and consequently promotes its recruitment to and activation of transcription from promoters of specific nutrient-regulated genes. These results close a gap in our perception of and delineate a role for PP2A(Cdc55) in TORC1-/PKA-mediated regulation of quiescence and chronological life span.

Mid-term evaluation of the effects of dynamic neutralization system on lumbar intervertebral discs using quantitative molecular MR imaging

PURPOSE

To evaluate the mid-term effects of implant of dynamic neutralization system (Dynesys) on disc tissue in patients with lumbar discopathy, through the quantification of glycosaminoglycans (GAG) concentration, both in treated and adjacent levels, by analysis of delayed gadolinium-enhanced MRI contrast (dGEMRIC) images.

MATERIALS AND METHODS

Ten patients with low back pain underwent the dGEMRIC diagnostic protocol before, 6-months and after 2 years from surgery. Each patient was also evaluated with visual analog (VAS), Oswestry, and Prolo scales both at presurgery and during follow-up. From dGEMRIC images, a ΔT1 parametric map was obtained for each disc, as quantitative indicator of its GAG concentration, and divided in 13 sectors, which were classified at presurgery as normal or abnormal, based on a 70-ms threshold. Evolution of ΔT1 was studied during the follow-up.

RESULTS

Nine of ten patients completed the follow-up. VAS, Oswestry, and Prolo grades showed an improvement. This was accompanied by a reduction of ΔT1 in abnormal segments while normal segments showed a pattern of initial worsening at 6 months, followed by an improvement after 2 years.

CONCLUSION

Our study confirmed the improvement in clinical evaluation, and for the first time related this to the changes in discs GAG concentration.

Quantitative assessment of intervertebral disc glycosaminoglycan distribution by gadolinium-enhanced MRI in orthopedic patients

Our hypothesis was that the enhanced MRI of cartilage (dGEMRIC) imaging protocol could be used in patients to quantify the sulfated glycosaminoglycan (sGAG) in intervertebral discs (IVD). To test this hypothesis, 23 patients with degenerative disc pathology scheduled for surgery were studied by a specific dGEMRIC protocol: each patient underwent two MRI scans, before and 3.5 hr after Gd(DTPA)2-injection of a nonconventional dose of 40 mL. Then, T(1PRE-ENH) and T(1POST-ENH) parametric images of the disc were obtained, from which a new index DeltaT(1) of the molecular status of the IVD was computed (T(1PRE-ENH) - T(1POST-ENH)). A total of 31 tissue samples (one or two from each patient) obtained at herniectomy were collected and biochemically analyzed for sGAG content and used as the gold standard for comparison. DeltaT(1) values in correspondence to degenerated sectors were higher (158 +/- 36 ms) compared to normal sectors (80 +/- 13 ms). Linear regression analysis between MRI-derived and biochemistry-derived measurements resulted in a significant correlation (r = 0.73, P < 0.0001). The DeltaT(1) parametric images, calculated using the modified dGEMRIC technique, provided noninvasive quantitative information about sGAG content within discal tissue in vivo, which resulted in agreement with biochemical analysis. The application of this new MRI method could provide diagnostic information for standard treatment of lumbar discopathy and for innovative therapies of regenerative medicine.