Sphingolipids in host-microbial interactions

Gut Microbiota Regulation of T Cells During Inflammation and Autoimmunity

The intestinal microbiota plays a crucial role in influencing the development of host immunity, and in turn the immune system also acts to regulate the microbiota through intestinal barrier maintenance and immune exclusion. Normally, these interactions are homeostatic, tightly controlled, and organized by both innate and adaptive immune responses. However, a combination of environmental exposures and genetic defects can result in a break in tolerance and intestinal homeostasis. The outcomes of these interactions at the mucosal interface have broad, systemic effects on host immunity and the development of chronic inflammatory or autoimmune disease. The underlying mechanisms and pathways the microbiota can utilize to regulate these diseases are just starting to emerge. Here, we discuss the recent evidence in this area describing the impact of microbiota-immune interactions during inflammation and autoimmunity, with a focus on barrier function and CD4⁺ T cell regulation.

Interaction between nitric oxide and storage temperature on sphingolipid metabolism of postharvest peach fruit

Both nitric oxide (NO) and cold storage have positive effects on the maintenance of fruit quality during storage. However, the roles of NO and storage temperatures in regulating the responses of sphingolipids metabolism to chilling injury of peach fruit during storage remain unknown. Peaches were treated by immersion in distilled water and 15 μmol L^-1 NO solution, then stored at 25 °C and 0 °C, respectively. The effects of NO-treatment and storage temperature on the activities of enzymes in sphingolipid metabolism and the contents of sphingolipids in peach fruits were studied. NO maintained higher activities of acid phosphatase (AP) and alkaline phosphatase (ALP) in peach fruits at 25 °C, but promoted the decrease in the activities of AP and ALP at 0 °C, suggesting the regulation by NO on AP and ALP could be modulated by temperature. Compared with the storage at 25 °C, cold storage at 0 °C decreased the activities of phospholipase A (PLA), alkaline phosphatase (ALP), 3-ketodihydrosphingosine reductase (KDSR), sphingosine kinase (SPHK), ceramide synthase (CERS), ceramide kinase (CERK), and the contents of sphingosine (SPH), ceramide (CER), sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P), sphingomyelin (SM), and increased the activities of phospholipase C (PLC), phospholipase D (PLD), sphingomyelin synthase (SMS). NO significantly increased the contents of sphingolipid metabolites, and the activities of PLA, KDSR, SPHK, CERS, CERK, but decreased the activities of PLC, PLD, SMS of peaches. The results suggested that NO could maintain sphingolipid metabolism to relieve the response of the postharvest fruit to low temperature.

Sphingolipids produced by gut bacteria enter host metabolic pathways impacting ceramide levels

Gut microbes are linked to host metabolism, but specific mechanisms remain to be uncovered. Ceramides, a type of sphingolipid (SL), have been implicated in the development of a range of metabolic disorders from insulin resistance (IR) to hepatic steatosis. SLs are obtained from the diet and generated by de novo synthesis in mammalian tissues. Another potential, but unexplored, source of mammalian SLs is production by Bacteroidetes, the dominant phylum of the gut microbiome. Genomes of Bacteroides spp. and their relatives encode serine palmitoyltransfease (SPT), allowing them to produce SLs. Here, we explore the contribution of SL-production by gut Bacteroides to host SL homeostasis. In human cell culture, bacterial SLs are processed by host SL-metabolic pathways. In mouse models, Bacteroides-derived lipids transfer to host epithelial tissue and the hepatic portal vein. Administration of B. thetaiotaomicron to mice, but not an SPT-deficient strain, reduces de novo SL production and increases liver ceramides. These results indicate that gut-derived bacterial SLs affect host lipid metabolism.

Isolation of Anti-Inflammatory and Epithelium Reinforcing Bacteroides and Parabacteroides Spp. from A Healthy Fecal Donor

Altered intestinal microbiota is associated with systemic and intestinal diseases, such as inflammatory bowel disease (IBD). Dysbiotic microbiota with enhanced proinflammatory capacity is characterized by depletion of anaerobic commensals, increased proportion of facultatively anaerobic bacteria, as well as reduced diversity and stability. In this study, we developed a high-throughput in vitro screening assay to isolate intestinal commensal bacteria with anti-inflammatory capacity from a healthy fecal microbiota transplantation donor. Freshly isolated gut bacteria were screened for their capacity to attenuate Escherichia coli lipopolysaccharide (LPS)-induced interleukin 8 (IL-8) release from HT-29 cells. The screen yielded a number of Bacteroides and Parabacteroides isolates, which were identified as P. distasonis, B. caccae, B. intestinalis, B. uniformis, B. fragilis, B. vulgatus and B. ovatus using whole genome sequencing. We observed that a cell-cell contact with the epithelium was not necessary to alleviate in vitro inflammation as spent culture media from the isolates were also effective and the anti-inflammatory action did not correlate with the enterocyte adherence capacity of the isolates. The anti-inflammatory isolates also exerted enterocyte monolayer reinforcing action and lacked essential genes to synthetize hexa-acylated, proinflammatory lipid A, part of LPS. Yet, the anti-inflammatory effector molecules remain to be identified. The Bacteroides strains isolated and characterized in this study have potential to be used as so-called next-generation probiotics.

A Solution to Antifolate Resistance in Group B Streptococcus: Untargeted Metabolomics Identifies Human Milk Oligosaccharide-Induced Perturbations That Result in Potentiation of Trimethoprim

Adjuvants can be used to potentiate the function of antibiotics whose efficacy has been reduced by acquired or intrinsic resistance. In the present study, we discovered that human milk oligosaccharides (HMOs) sensitize strains of group B Streptococcus (GBS) to trimethoprim (TMP), an antibiotic to which GBS is intrinsically resistant. Reductions in the MIC of TMP reached as high as 512-fold across a diverse panel of isolates. To better understand HMOs' mechanism of action, we characterized the metabolic response of GBS to HMO treatment using ultrahigh-performance liquid chromatography-high-resolution tandem mass spectrometry (UPLC-HRMS/MS) analysis. These data showed that when challenged by HMOs, GBS undergoes significant perturbations in metabolic pathways related to the biosynthesis and incorporation of macromolecules involved in membrane construction. This study represents reports the metabolic characterization of a cell that is perturbed by HMOs.IMPORTANCE Group B Streptococcus is an important human pathogen that causes serious infections during pregnancy which can lead to chorioamnionitis, funisitis, premature rupture of gestational membranes, preterm birth, neonatal sepsis, and death. GBS is evolving antimicrobial resistance mechanisms, and the work presented in this paper provides evidence that prebiotics such as human milk oligosaccharides can act as adjuvants to restore the utility of antibiotics.

Impact of the gut microbiota on the m6A epitranscriptome of mouse cecum and liver

The intestinal microbiota modulates host physiology and gene expression via mechanisms that are not fully understood. Here we examine whether host epitranscriptomic marks are affected by the gut microbiota. We use methylated RNA-immunoprecipitation and sequencing (MeRIP-seq) to identify N6-methyladenosine (m6A) modifications in mRNA of mice carrying conventional, modified, or no microbiota. We find that variations in the gut microbiota correlate with m6A modifications in the cecum, and to a lesser extent in the liver, affecting pathways related to metabolism, inflammation and antimicrobial responses. We analyze expression levels of several known writer and eraser enzymes, and find that the methyltransferase Mettl16 is downregulated in absence of a microbiota, and one of its target mRNAs, encoding S-adenosylmethionine synthase Mat2a, is less methylated. We furthermore show that Akkermansia muciniphila and Lactobacillus plantarum affect specific m6A modifications in mono-associated mice. Our results highlight epitranscriptomic modifications as an additional level of interaction between commensal bacteria and their host.

Gut Microbial-Derived Metabolomics of Asthma

In this review, we discuss gut microbial-derived metabolites involved with the origins and pathophysiology of asthma, a chronic respiratory disease that is influenced by the microbiome. Although both gut and airway microbiomes may be important in asthma development, we focus here on the gut microbiome and metabolomic pathways involved in immune system ontogeny. Metabolite classes with existing evidence that microbial-derived products influence asthma risk include short chain fatty acids, polyunsaturated fatty acids and bile acids. While tryptophan metabolites and sphingolipids have known associations with asthma, additional research is needed to clarify the extent to which the microbiome contributes to the effects of these metabolites on asthma. These metabolite classes can influence immune function in one of two ways: (i) promoting growth or maturity of certain immune cell populations or (ii) influencing antigenic load by enhancing the number or species of specific bacteria. A more comprehensive understanding of how gut microbes and metabolites interact to modify asthma risk and morbidity will pave the way for targeted diagnostics and treatments.

Porphyromonas gingivalis Sphingolipid Synthesis Limits the Host Inflammatory Response

Porphyromonas gingivalis, like other bacteria belonging to the phylum Bacteroidetes, synthesizes sphingolipids (SLs). However, their exact roles in microbial physiology and their potential role in mediating interactions with their eukaryotic host are unclear. Our working hypothesis for this study was that synthesis of SLs (host-like lipids) affords a mechanism that allows P. gingivalis to persist in homeostasis with its host. In a previous study, we deleted a gene (PG1780 in strain W83) predicted to encode a serine palmitoyl transferase (SPT)-the enzyme that catalyzes the first conserved step in the synthesis of SLs-and we determined that the mutant was unable to synthesize SLs. Here, we characterized the SPT enzyme encoded by PG1780, analyzed the impact of SPT deletion on P. gingivalis gene expression (RNA-Seq analysis), and began to define the impact of SL synthesis on its interactions with host cells. Enzymatic analysis verified that the protein encoded by PG1780 is indeed an SPT. RNA-Seq analysis determined that a lack of SL synthesis results in differential expression of extracytoplasmic function sigma factors, components of the type IX secretion system (T9SS), and CRISPR and cas genes. Our data demonstrate that when human THP1 macrophage-like cells were challenged with the wild type (W83) and the SL-null mutant (W83 ΔSPT), the SL-null strain elicited a robust inflammatory response (elevated IL-1β, IL-6, IL-10, IL-8, RANTES, and TNFα) while the response to the parent strain W83 was negligible. Interestingly, we also discovered that SLs produced by P. gingivalis can be delivered to host cells independent of cell-to-cell contact. Overall, our results support our working hypothesis that synthesis of SLs by P. gingivalis is central to its ability to manipulate the host inflammatory response, and they demonstrate the integral importance of SLs in the physiology of P. gingivalis.

Fecal Metabolomic Signatures in Colorectal Adenoma Patients Are Associated with Gut Microbiota and Early Events of Colorectal Cancer Pathogenesis

Colorectal adenomas are precancerous lesions of colorectal cancer (CRC) that offer a means of viewing the events key to early CRC development. A number of studies have investigated the changes and roles of gut microbiota in adenoma and carcinoma development, highlighting its impact on carcinogenesis. However, there has been less of a focus on the gut metabolome, which mediates interactions between the host and gut microbes. Here, we investigated metabolomic profiles of stool samples from patients with advanced adenoma (n = 102), matched controls (n = 102), and patients with CRC (n = 36). We found that several classes of bioactive lipids, including polyunsaturated fatty acids, secondary bile acids, and sphingolipids, were elevated in the adenoma patients compared to the controls. Most such metabolites showed directionally consistent changes in the CRC patients, suggesting that those changes may represent early events of carcinogenesis. We also examined gut microbiome-metabolome associations using gut microbiota profiles in these patients. We found remarkably strong overall associations between the microbiome and metabolome data and catalogued a list of robustly correlated pairs of bacterial taxa and metabolomic features which included signatures of adenoma. Our findings highlight the importance of gut metabolites, and potentially their interplay with gut microbes, in the early events of CRC pathogenesis.IMPORTANCE Colorectal adenomas are precursors of CRC. Recently, the gut microbiota, i.e., the collection of microbes residing in our gut, has been recognized as a key player in CRC development. There have been a number of gut microbiota profiling studies for colorectal adenoma and CRC; however, fewer studies have considered the gut metabolome, which serves as the chemical interface between the host and gut microbiota. Here, we conducted a gut metabolome profiling study of colorectal adenoma and CRC and analyzed the metabolomic profiles together with paired microbiota composition profiles. We found several chemical signatures of colorectal adenoma that were associated with some gut microbes and potentially indicative of future CRC. This study highlights potential early-driver metabolites in CRC pathogenesis and guides further targeted experiments and thus provides an important stepping stone toward developing better CRC prevention strategies.

Fatty acid activation and utilization by Alistipes finegoldii, a representative Bacteroidetes resident of the human gut microbiome

Members of the Bacteroidetes phylum, represented by Alistipes finegoldii, are prominent anerobic, Gram-negative inhabitants of the gut microbiome. The lipid biosynthetic pathways were analyzed using bioinformatic analyses, lipidomics, metabolic labeling and biochemistry to characterize exogenous fatty acid metabolism. A. finegoldii only produced the saturated fatty acids. The most abundant lipids were phosphatidylethanolamine (PE) and sulfonolipid (SL). Neither phosphatidylglycerol nor cardiolipin are present. PE synthesis is initiated by the PlsX/PlsY/PlsC pathway, whereas the SL pathway is related to sphingolipid biosynthesis. A. finegoldii incorporated medium-chain fatty acids (≤14 carbons) into PE and SL after their elongation, whereas long-chain fatty acids (≥16 carbons) were not elongated. Fatty acids >16 carbons were primarily incorporated into the 2-position of phosphatidylethanolamine at the PlsC step, the only biosynthetic enzyme that utilizes long-chain acyl-ACP. The ability to assimilate a broad-spectrum of fatty acid chain lengths present in the gut environment is due to the expression of two acyl-acyl carrier protein (ACP) synthetases. Acyl-ACP synthetase 1 had a substrate preference for medium-chain fatty acids and synthetase 2 had a substrate preference for long-chain fatty acids. This unique combination of synthetases allows A. finegoldii to utilize both the medium- and long-chain fatty acid nutrients available in the gut environment to assemble its membrane lipids.

In ovo Injection of a Galacto-Oligosaccharide Prebiotic in Broiler Chickens Submitted to Heat-Stress: Impact on Transcriptomic Profile and Plasma Immune Parameters

This study investigated the effects of a galactooligosaccharide (GOS) prebiotic in ovo injected on intestinal transcriptome and plasma immune parameters of broiler chickens kept under thermoneutral (TN) or heat stress (HS) conditions. Fertilized Ross 308 eggs were injected in ovo with 0.2 mL physiological saline without (control, CON) or with 3.5 mg of GOS (GOS). Three-hundred male chicks/injection treatment (25 birds/pen) were kept in TN or HS (30 °C) conditions during the last growing phase, in a 2 × 2 factorial design. At slaughter, from 20 birds/injection group (half from TN and half from HS), jejunum and cecum were collected for transcriptome analysis, and plasma was collected. No differences in plasma parameters (IgA and IgG, serum amyloid) and no interaction between injection treatment and environment condition were found. GOS-enriched gene sets related to energetic metabolism in jejunum, and to lipid metabolism in cecum, were involved in gut barrier maintenance. A homogeneous reaction to heat stress was determined along the gut, which showed downregulation of the genes related to energy and immunity, irrespective of in ovo treatment. GOS efficacy in counteracting heat stress was scarce after ten days of environmental treatment, but the in ovo supplementation modulates group of genes in jejunum and cecum of broiler chickens.

Bacteroides-Derived Sphingolipids Are Critical for Maintaining Intestinal Homeostasis and Symbiosis

Sphingolipids are structural membrane components and important eukaryotic signaling molecules. Sphingolipids regulate inflammation and immunity and were recently identified as the most differentially abundant metabolite in stool from inflammatory bowel disease (IBD) patients. Commensal bacteria from the Bacteroidetes phylum also produce sphingolipids, but the impact of these metabolites on host pathways is largely uncharacterized. To determine whether bacterial sphingolipids modulate intestinal health, we colonized germ-free mice with a sphingolipid-deficient Bacteroides thetaiotaomicron strain. A lack of Bacteroides-derived sphingolipids resulted in intestinal inflammation and altered host ceramide pools in mice. Using lipidomic analysis, we described a sphingolipid biosynthesis pathway and revealed a variety of Bacteroides-derived sphingolipids including ceramide phosphoinositol and deoxy-sphingolipids. Annotating Bacteroides sphingolipids in an IBD metabolomic dataset revealed lower abundances in IBD and negative correlations with inflammation and host sphingolipid production. These data highlight the role of bacterial sphingolipids in maintaining homeostasis and symbiosis in the gut.

Analysis of 1-Deoxysphingoid Bases and Their N-Acyl Metabolites and Exploration of Their Occurrence in Some Food Materials

Most common sphingolipids are comprised of "typical" sphingoid bases (sphinganine, sphingosine, and structurally related compounds) and are produced via the condensation of l-serine with a fatty acyl-CoA by serine palmitoyltransferase. Some organisms, including mammals, also produce "atypical" sphingoid bases that lack a 1-hydroxyl group as a result of the utilization of l-alanine or glycine instead of l-serine, resulting in the formation of 1-deoxy- or 1-desoxymethylsphingoid bases, respectively. Elevated production of "atypical" sphingolipids has been associated with human disease, but 1-deoxysphingoid bases have also been found to have potential as anticancer compounds, hence, the importance of knowing more about the occurrence of these compounds in food. Most of the "typical" and "atypical" sphingoid bases are found as the N-acyl metabolites (e.g., ceramides and 1-deoxyceramides) in mammals, but this has not been uniformly assessed in previous studies nor determined in consumed food. Therefore, we developed a method for the quantitative analysis of "typical" and "atypical" sphingoid bases and their N-acyl derivatives by reverse-phase liquid chromatography coupled to electrospray ionization tandem mass spectrometry. On the basis of these analyses, there was considerable variability in the amounts and molecular subspecies of atypical sphingoid bases and their N-acyl metabolites found in different edible sources. These findings demonstrate that a broader assessment of the types of sphingolipids in foods is needed because some diets might contain sufficient amounts of atypical as well as typical sphingolipids that could have beneficial or possibly deleterious effects on human health.

Alterations of endogenous sphingolipid metabolism in cardiometabolic diseases: Towards novel therapeutic approaches

The increasing prevalence of obesity and metabolic diseases is a worldwide public health concern, and the advent of new analytical technologies has made it possible to highlight the involvement of some molecules, such as sphingolipids (SL), in their pathophysiology. SL are constituents of cell membranes, lipoproteins and lipid droplets (LD), and are now considered as bioactive molecules. Indeed, growing evidence suggests that SL, characterized by diverse families and species, could represent one of the main regulators of lipid metabolism. There is an increasing amount of data reporting that plasma SL profile is altered in metabolic diseases. However, less is known about SL metabolism dysfunction in cells and tissues and how it may impact the lipoprotein metabolism, its functionality and composition. In cardiometabolic pathologies, the link between serum SL concentrations and alterations of their metabolism in various organs and LD is still unclear. Pharmacological approaches have been developed in order to activate or inhibit specific key enzymes of the SL metabolism, and to positively modulate SL profile or related metabolic pathways. Nevertheless, little is known about the long-term impact of such approaches in humans and the current literature still focuses on the decomposition of the different parts of this complex system rather than performing an integrated analysis of the whole SL metabolism. In addition, since SL can be provided from exogenous sources, it is also of interest to evaluate their impact on the homeostasis of endogenous SL metabolism, which could be beneficial in prevention or treatment of obesity and related metabolic disorders.

The human gut chemical landscape predicts microbe-mediated biotransformation of foods and drugs

Microbes are nature's chemists, capable of producing and metabolizing a diverse array of compounds. In the human gut, microbial biochemistry can be beneficial, for example vitamin production and complex carbohydrate breakdown; or detrimental, such as the reactivation of an inactive drug metabolite leading to patient toxicity. Identifying clinically relevant microbiome metabolism requires linking microbial biochemistry and ecology with patient outcomes. Here we present MicrobeFDT, a resource which clusters chemically similar drug and food compounds and links these compounds to microbial enzymes and known toxicities. We demonstrate that compound structural similarity can serve as a proxy for toxicity, enzyme sharing, and coarse-grained functional similarity. MicrobeFDT allows users to flexibly interrogate microbial metabolism, compounds of interest, and toxicity profiles to generate novel hypotheses of microbe-diet-drug-phenotype interactions that influence patient outcomes. We validate one such hypothesis experimentally, using MicrobeFDT to reveal unrecognized gut microbiome metabolism of the ovarian cancer drug altretamine.

Synthetic genetic circuits for programmable biological functionalities

Living organisms evolve complex genetic networks to interact with the environment. Due to the rapid development of synthetic biology, various modularized genetic parts and units have been identified from these networks. They have been employed to construct synthetic genetic circuits, including toggle switches, oscillators, feedback loops and Boolean logic gates. Building on these circuits, complex genetic machines with capabilities in programmable decision-making could be created. Consequently, these accomplishments have led to novel applications, such as dynamic and autonomous modulation of metabolic networks, directed evolution of biological units, remote and targeted diagnostics and therapies, as well as biological containment methods to prevent release of engineered microorganisms and genetic materials. Herein, we outline the principles in genetic circuit design that have initiated a new chapter in transforming concepts to realistic applications. The features of modularized building blocks and circuit architecture that facilitate realization of circuits for a variety of novel applications are discussed. Furthermore, recent advances and challenges in employing genetic circuits to impart microorganisms with distinct and programmable functionalities are highlighted. We envision that this review gives new insights into the design of synthetic genetic circuits and offers a guideline for the implementation of different circuits in various aspects of biotechnology and bioengineering.

Anaerobes in cystic fibrosis patients' airways

Anaerobes are known to constitute an important part of the airway microbiota in both healthy subjects and cystic fibrosis (CF) patients. Studies on the potential role of anaerobic bacteria in CF and thus their involvement in CF pathophysiology have reported contradictory results, and the question is still not elucidated. The aim of this study was to summarize anaerobe diversity in the airway microbiota and its potential role in CF, to provide an overview of the state of knowledge on anaerobe antibiotic resistances (resistome), and to investigate the detectable metabolites produced by anaerobes in CF airways (metabolome). This review emphasizes key metabolites produced by strict anaerobic bacteria (sphingolipids, fermentation-induced metabolites and metabolites involved in quorum-sensing), which may be essential for the better understanding of lung disease pathophysiology in CF.

The Role of Ceramide and Sphingosine-1-Phosphate in Alzheimer's Disease and Other Neurodegenerative Disorders

Bioactive sphingolipids-ceramide, sphingosine, and their respective 1-phosphates (C1P and S1P)-are signaling molecules serving as intracellular second messengers. Moreover, S1P acts through G protein-coupled receptors in the plasma membrane. Accumulating evidence points to sphingolipids' engagement in brain aging and in neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis. Metabolic alterations observed in the course of neurodegeneration favor ceramide-dependent pro-apoptotic signaling, while the levels of the neuroprotective S1P are reduced. These trends are observed early in the diseases' development, suggesting causal relationship. Mechanistic evidence has shown links between altered ceramide/S1P rheostat and the production, secretion, and aggregation of amyloid β/α-synuclein as well as signaling pathways of critical importance for the pathomechanism of protein conformation diseases. Sphingolipids influence multiple aspects of Akt/protein kinase B signaling, a pathway that regulates metabolism, stress response, and Bcl-2 family proteins. The cross-talk between sphingolipids and transcription factors including NF-κB, FOXOs, and AP-1 may be also important for immune regulation and cell survival/death. Sphingolipids regulate exosomes and other secretion mechanisms that can contribute to either the spread of neurotoxic proteins between brain cells, or their clearance. Recent discoveries also suggest the importance of intracellular and exosomal pools of small regulatory RNAs in the creation of disturbed signaling environment in the diseased brain. The identified interactions of bioactive sphingolipids urge for their evaluation as potential therapeutic targets. Moreover, the early disturbances in sphingolipid metabolism may deliver easily accessible biomarkers of neurodegenerative disorders.

Dietary Effects on Microbiota-New Trends with Gluten-Free or Paleo Diet

A well-balanced diet is the basis for a healthy life. Both the western diet and special diets can have a relevant impact on the microbiome and promote the development of various diseases. There has been an increase in food-related disorders in recent years, largely associated with dramatic changes in food consumption trends and main nutrients. A major response to food intolerances has been the adoption of new dietary trends involving the reduction or exclusion of specific food ingredients. Especially gluten-containing, but also gluten-free cereals are in the cross-fire. Supporters of the gluten-free diet argue that gluten triggers inflammation and related diseases, while followers of the Paleo diet drastically impeach all cereals as dangerous for human health. To date, no controlled studies support or reject a positive health effect of a gluten-free or cereal-free diet. Future large-scale studies need to evaluate the effect of gluten-containing and gluten-free cereals and the various diets on human health, inflammatory parameters, clinical symptoms, and the gut microbiota (including the bacteria, fungi, and viruses). Dietary-associated changes in compositional and functional microbiota traits should be correlated with the health status for the future development of dietary recommendations and potential clinical interventions.

Symbiont-derived sphingolipids regulate inflammatory responses in rainbow trout (Oncorhynchus mykiss)

Farmed fish live in association with diverse bacterial communities that produce wide arrays of metabolites. In rainbow trout, the skin and the gills are colonized by Flectobacillus major, a bacterium known to produce sphingolipids (SLs). The goal of this study is to evaluate the ability of F. major SLs to regulate rainbow trout inflammatory responses. F. major SLs were delivered by themselves or in combination with Freund's Complete Adjuvant (FCA), an oil-based adjuvant known to cause severe abdominal inflammation when injected to fish. Trout injected with SL + FCA showed decreased severity of FCA toxic effects including necrosis, granuloma formation and presence of oil droplets. However, inclusion of SLs in the FCA preparation did not decrease infiltration of immune cells intramuscularly at the site of injection. Intraperitoneal or intravenous delivery of F. major SLs resulted in increased expression of IgT, IgM and TGFβ transcripts in the gills but not the head-kidney and had no effects on IL-10 expression. These results indicate the F. major SLs regulate rainbow trout inflammatory responses and indicate that this compound can have important applications in farmed fish health management.

Sphingolipid biosynthesis in man and microbes

A new review covering up to 2018 Sphingolipids are essential molecules that, despite their long history, are still stimulating interest today. The reasons for this are that, as well as playing structural roles within cell membranes, they have also been shown to perform a myriad of cell signalling functions vital to the correct function of eukaryotic and prokaryotic organisms. Indeed, sphingolipid disregulation that alters the tightly-controlled balance of these key lipids has been closely linked to a number of diseases such as diabetes, asthma and various neuropathologies. Sphingolipid biogenesis, metabolism and regulation is mediated by a large number of enzymes, proteins and second messengers. There appears to be a core pathway common to all sphingolipid-producing organisms but recent studies have begun to dissect out important, species-specific differences. Many of these have only recently been discovered and in most cases the molecular and biochemical details are only beginning to emerge. Where there is a direct link from classic biochemistry to clinical symptoms, a number a drug companies have undertaken a medicinal chemistry campaign to try to deliver a therapeutic intervention to alleviate a number of diseases. Where appropriate, we highlight targets where natural products have been exploited as useful tools. Taking all these aspects into account this review covers the structural, mechanistic and regulatory features of sphingolipid biosynthetic and metabolic enzymes.

Sphingolipid metabolism in non-alcoholic fatty liver diseases

Non-alcoholic fatty liver disease (NAFLD) involves a panel of pathologies starting with hepatic steatosis and continuing to irreversible and serious conditions like steatohepatitis (NASH) and hepatocarcinoma. NAFLD is multifactorial in origin and corresponds to abnormal fat deposition in liver. Even if triglycerides are mostly associated with these pathologies, other lipid moieties seem to be involved in the development and severity of NAFLD. That is the case with sphingolipids and more particularly ceramides. In this review, we explore the relationship between NAFLD and sphingolipid metabolism. After providing an analysis of complex sphingolipid metabolism, we focus on the potential involvement of sphingolipids in the different pathologies associated with NAFLD. An unbalanced ratio between ceramides and terminal metabolic products in the liver and plasma promotes weight gain, inflammation, and insulin resistance. In the etiology of NAFLD, some sphingolipid species such as ceramides may be potential biomarkers for NAFLD. We review the clinical relevance of sphingolipids in liver diseases.

Are Sphingolipids and Serine Dipeptide Lipids Underestimated Virulence Factors of Porphyromonas gingivalis?

The keystone periodontal pathogen Porphyromonas gingivalis produces phosphorylated dihydroceramide lipids (sphingolipids) such as phosphoethanolamine dihydroceramide (PE DHC) and phosphoglycerol dihydroceramide (PG DHC) lipids. Phosphorylated DHCs (PDHCs) from P. gingivalis can affect a number of mammalian cellular functions, such as potentiation of prostaglandin secretion from gingival fibroblasts, promotion of RANKL-induced osteoclastogenesis, promotion of apoptosis, and enhancement of autoimmunity. In P. gingivalis, these lipids affect anchoring of surface polysaccharides, resistance to oxidative stress, and presentation of surface polysaccharides (anionic polysaccharides and K-antigen capsule). In addition to phosphorylated dihydroceramide lipids, serine dipeptide lipids of P. gingivalis are implicated in alveolar bone loss in chronic periodontitis through interference with osteoblast differentiation and function and promotion of osteoclast activity. As a prerequisite for designation as bacterial virulence factors, bacterial sphingolipids and serine dipeptide lipids are recovered in gingival/periodontal tissues, tooth calculus, human blood, vascular tissues, and brain. In addition to P. gingivalis, other bacteria of the genera Bacteroides, Parabacteroides, Porphyromonas, Tannerella, and Prevotella produce sphingolipids and serine dipeptide lipids. The contribution of PDHCs and serine dipeptide lipids to the pathogenesis of periodontal and extraoral diseases may be an underappreciated area in microbe-host interaction and should be more intensively investigated.