Acyloxyacyl hydrolase, a leukocyte enzyme that deacylates bacterial lipopolysaccharides, has phospholipase, lysophospholipase, diacylglycerollipase, and acyltransferase activities in vitro

CD1a and skin T cells: a pathway for therapeutic intervention

The CD1 and MR1 protein families present lipid antigens and small molecules to T cells, complementing well-studied major histocompatibility complex-peptide mechanisms. The CD1a subtype is highly and continuously expressed within the skin, most notably on Langerhans cells, and has been demonstrated to present self and foreign lipids to T cells, highlighting its cutaneous sentinel role. Alteration of CD1a-dependent T-cell responses has recently been discovered to contribute to the pathogenesis of several inflammatory skin diseases. In this review, we overview the structure and role of CD1a and outline the current evidence implicating CD1a in the development of psoriasis, atopic dermatitis and allergic contact dermatitis.

Gut barrier dysfunction and endotoxemia in heart failure: A dangerous connubium?

Heart failure (HF) is a leading cause of death worldwide despite recent advances in pharmacological treatments. Gut microbiota dysbiosis and gut barrier dysfunction with consequent bacterial translocation and increased blood endotoxemia has gained much attention as one of the key pathogenetic mechanisms contributing to increased mortality of patients at risk or with cardiovascular disease. Indeed, increased blood levels of lipopolysaccharide (LPS), a glycolipid of outer membrane of gut gram-negative bacteria, have been detected in patients with diabetes, obesity and nonalcoholic fatty liver disease or in patients with established coronary disease such as myocardial infarction or atrial fibrillation, suggesting endotoxemia as aggravating factor via systemic inflammation and eventually vascular damage. Upon interaction with its receptor Toll-like receptor 4 (TLR4) LPS may, in fact, act at different cellular levels so eliciting formation of proinflammatory cytokines or exerting a procoagulant activity. Increasing body of evidence pointed to endotoxemia as factor potentially deteriorating the clinical course of patients with HF, that, in fact, is associated with gut dysbiosis-derived changes of gut barrier functionality and eventually bacteria or bacterial product translocation into systemic circulation. The aim of this review is to summarize current experimental and clinical evidence on the mechanisms linking gut dysbiosis-related endotoxemia with HF, its potential negative impact with HF progression, and the therapeutic strategies that can counteract endotoxemia.

CD1-mediated immune responses in mucosal tissues: molecular mechanisms underlying lipid antigen presentation system

The cluster of differentiation 1 (CD1) molecule differs from major histocompatibility complex class I and II because it presents glycolipid/lipid antigens. Moreover, the CD1-restricted T cells that recognize these self and foreign antigens participate in both innate and adaptive immune responses. CD1s are constitutively expressed by professional and nonprofessional antigen-presenting cells in mucosal tissues, namely, the skin, lung, and intestine. This suggests that CD1-reactive T cells are involved in the immune responses of these tissues. Indeed, evidence suggests that these cells play important roles in diverse diseases, such as inflammation, autoimmune disease, and infection. Recent studies elucidating the molecular mechanisms by which CD1 presents lipid antigens suggest that defects in these mechanisms could contribute to the activities of CD1-reactive T cells. Thus, improving our understanding of these mechanisms could lead to new and effective therapeutic approaches to CD1-associated diseases. In this review, we discuss the CD1-mediated antigen presentation system and its roles in mucosal tissue immunity.

Bifidobacterium longum supplementation improves age-related delays in fracture repair

Age-related delays in bone repair remains an important clinical issue that can prolong pain and suffering. It is now well established that inflammation increases with aging and that this exacerbated inflammatory response can influence skeletal regeneration. Recently, simple dietary supplementation with beneficial probiotic bacteria has been shown to influence fracture repair in young mice. However, the contribution of the gut microbiota to age-related impairments in fracture healing remains unknown. Here, we sought to determine whether supplementation with a single beneficial probiotic species, Bifidobacterium longum (B. longum), would promote fracture repair in aged (18-month-old) female mice. We found that B. longum supplementation accelerated bony callus formation which improved mechanical properties of the fractured limb. We attribute these pro-regenerative effects of B. longum to preservation of intestinal barrier, dampened systemic inflammation, and maintenance of the microbiota community structure. Moreover, B. longum attenuated many of the fracture-induced systemic pathologies. Our study provides evidence that targeting the gut microbiota using simple dietary approaches can improve fracture healing outcomes and minimize systemic pathologies in the context of aging.

Acyloxyacyl hydrolase deficiency induces chronic inflammation and bone loss in male mice

Hormonal homeostasis is essential in bone remodeling. Recent studies have shown that the treatment of intestinal inflammation can result in the regulation of bone resorption in distant bones. Increased intestinal permeability may lead to systemic inflammation and bone loss, also known as gut-bone axis. However, the underlying mechanism remains to be elucidated. Lipopolysaccharide (LPS) is a component of gram-negative bacteria that can increase osteoclastic differentiation in vitro. Acyloxyacyl hydrolase (AOAH) is a specific degrading enzyme of LPS, but little is known about the role of AOAH in bone metabolism. In this study, adult Aoah^-/- mice showed a chronic inflammatory state and osteopenic phenotype analyzed by micro-CT and HE staining. Tartrate-resistant acid phosphatase (TRAP) staining of femurs showed an increase in TRAP-positive cells from Aoah^-/- mice. AOAH depletion enhanced the osteoclast differentiation and bone resorption capacity of bone marrow-derived macrophages (BMMs). The enhanced osteoclast differentiation and bone resorption capacity of Aoah^-/- BMMs were reversed by rAOAH. In conclusion, the chronic inflammatory state of adult Aoah^-/- mice promotes bone resorption. AOAH participates in bone metabolism, which is mainly mediated by inhibiting osteoclast differentiation. LPS may be a key mediator of the gut-bone axis, and targeting AOAH may represent a feasible strategy for the treatment of chronic inflammatory bone resorption. KEY MESSAGES : AOAH knockout mice exhibited chronic inflammation mediated by LPS, and LPS may also serve as an important mediator in the regulation of bone metabolism in the gut-bone axis. AOAH regulated bone resorption by blocking the osteoclast differentiation via classical ERK and JNK pathways. rAOAH could rescue the enhanced osteoclast differentiation caused by AOAH deficiency.

Acyloxyacyl hydrolase regulates microglia-mediated pelvic pain

Chronic pelvic pain conditions such as interstitial cystitis/bladder pain syndrome (IC/BPS) remain clinical and mechanistic enigmas. Microglia are resident immune cells of the central nervous system (CNS) that respond to changes in the gut microbiome, and studies have linked microglial activation to acute and chronic pain in a variety of models, including pelvic pain. We have previously reported that mice deficient for the lipase acyloxyacyl hydrolase (AOAH) develop pelvic allodynia and exhibit symptoms, comorbidities, and gut dysbiosis mimicking IC/BPS. Here, we assessed the role of AOAH in microglial activation and pelvic pain. RNAseq analyses using the ARCHS4 database and confocal microscopy revealed that AOAH is highly expressed in wild type microglia but at low levels in astrocytes, suggesting a functional role for AOAH in microglia. Pharmacologic ablation of CNS microglia with PLX5622 resulted in decreased pelvic allodynia in AOAH-deficient mice and resurgence of pelvic pain upon drug washout. Skeletal analyses revealed that AOAH-deficient mice have an activated microglia morphology in the medial prefrontal cortex and paraventricular nucleus, brain regions associated with pain modulation. Because microglia express Toll-like receptors and respond to microbial components, we also examine the potential role of dysbiosis in microglial activation. Consistent with our hypothesis of microglia activation by leakage of gut microbes, we observed increased serum endotoxins in AOAH-deficient mice and increased activation of cultured BV2 microglial cells by stool of AOAH-deficient mice. Together, these findings demonstrate a role for AOAH in microglial modulation of pelvic pain and thus identify a novel therapeutic target for IC/BPS.

Phospholipase activity of acyloxyacyl hydrolase induces IL-22-producing CD1a-autoreactive T cells in individuals with psoriasis

Psoriasis is a chronic inflammatory skin disease characterized by Th17 responses. Recent evidence has identified Langerhans cells to have a key role in disease pathogenesis, with constitutive high expression of CD1a and capacity to present lipid antigens to T cells. Phospholipase A2 enzymes generate neolipid antigens for recognition by CD1a-reactive T cells; however, the broader enzymatic pathways of CD1a lipid ligand generation have not been thoroughly investigated. In this study, we used immunofluorescence of skin and ELISpot analyses of CD1a-reactive T cells to investigate the role of the lipase acyloxyacyl hydrolase (AOAH) in CD1a ligand generation with relevance to the pathogenesis of psoriasis. We found that the PLA2 activity of rAOAH leads to the activation of circulating CD1a auto-reactive T cells, leading to the production of IFN-γ and IL-22. Circulating AOAH-responsive CD1a-reactive T cells from patients with psoriasis showed elevated IL-22 production. We observed that AOAH is highly expressed in psoriatic lesions compared to healthy skin. Overall, these data present a role for AOAH in generating antigens that activate circulating lipid-specific CD1a-restricted T cells and, thus, contribute to psoriatic inflammation. These findings suggest that inhibition of PLA2 activity of AOAH may have therapeutic potential for individuals with psoriasis.

A highly conserved host lipase deacylates oxidized phospholipids and ameliorates acute lung injury in mice

Oxidized phospholipids have diverse biological activities, many of which can be pathological, yet how they are inactivated in vivo is not fully understood. Here, we present evidence that a highly conserved host lipase, acyloxyacyl hydrolase (AOAH), can play a significant role in reducing the pro-inflammatory activities of two prominent products of phospholipid oxidation, 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine. AOAH removed the sn-2 and sn-1 acyl chains from both lipids and reduced their ability to induce macrophage inflammasome activation and cell death in vitro and acute lung injury in mice. In addition to transforming Gram-negative bacterial lipopolysaccharide from stimulus to inhibitor, its most studied activity, AOAH can inactivate these important danger-associated molecular pattern molecules and reduce tissue inflammation and injury.

Acyloxyacyl hydrolase is a host determinant of gut microbiome-mediated pelvic pain

Dysbiosis of gut microbiota is associated with many pathologies, yet host factors modulating microbiota remain unclear. Interstitial cystitis/bladder pain syndrome (IC/BPS) is a debilitating condition of chronic pelvic pain often with comorbid urinary dysfunction and anxiety/depression, and recent studies find fecal dysbiosis in patients with IC/BPS. We identified the locus encoding acyloxyacyl hydrolase, Aoah, as a modulator of pelvic pain severity in a murine IC/BPS model. AOAH-deficient mice spontaneously develop rodent correlates of pelvic pain, increased responses to induced pelvic pain models, voiding dysfunction, and anxious/depressive behaviors. Here, we report that AOAH-deficient mice exhibit dysbiosis of gastrointestinal (GI) microbiota. AOAH-deficient mice exhibit an enlarged cecum, a phenotype long associated with germ-free rodents, and a "leaky gut" phenotype. AOAH-deficient ceca showed altered gene expression consistent with inflammation, Wnt signaling, and urologic disease. 16S sequencing of stool revealed altered microbiota in AOAH-deficient mice, and GC-MS identified altered metabolomes. Cohousing AOAH-deficient mice with wild-type mice resulted in converged microbiota and altered predicted metagenomes. Cohousing also abrogated the pelvic pain phenotype of AOAH-deficient mice, which was corroborated by oral gavage of AOAH-deficient mice with stool slurry of wild-type mice. Converged microbiota also alleviated comorbid anxiety-like behavior in AOAH-deficient mice. Oral gavage of AOAH-deficient mice with anaerobes cultured from IC/BPS stool resulted in exacerbation of pelvic allodynia. Together, these data indicate that AOAH is a host determinant of normal gut microbiota, and dysbiosis associated with AOAH deficiency contributes to pelvic pain. These findings suggest that the gut microbiome is a potential therapeutic target for IC/BPS.

Biochemical transformation of bacterial lipopolysaccharides by acyloxyacyl hydrolase reduces host injury and promotes recovery

Animals can sense the presence of microbes in their tissues and mobilize their own defenses by recognizing and responding to conserved microbial structures (often called microbe-associated molecular patterns (MAMPs)). Successful host defenses may kill the invaders, yet the host animal may fail to restore homeostasis if the stimulatory microbial structures are not silenced. Although mice have many mechanisms for limiting their responses to lipopolysaccharide (LPS), a major Gram-negative bacterial MAMP, a highly conserved host lipase is required to extinguish LPS sensing in tissues and restore homeostasis. We review recent progress in understanding how this enzyme, acyloxyacyl hydrolase (AOAH), transforms LPS from stimulus to inhibitor, reduces tissue injury and death from infection, prevents prolonged post-infection immunosuppression, and keeps stimulatory LPS from entering the bloodstream. We also discuss how AOAH may increase sensitivity to pulmonary allergens. Better appreciation of how host enzymes modify LPS and other MAMPs may help prevent tissue injury and hasten recovery from infection.

AOAH remodels arachidonic acid-containing phospholipid pools in a model of interstitial cystitis pain: A MAPP Network study

Interstitial cystitis/bladder pain syndrome (IC) is a debilitating condition of chronic pelvic pain with unknown etiology. Recently, we used a genetic approach in a murine model of IC to identify the lipase acyloxyacyl hydrolase (AOAH) as a modulator of pelvic pain. We found that AOAH-deficient mice have elevated pelvic pain responses, and AOAH immunoreactivity was detected along the bladder-brain axis. Lipidomic analyses identified arachidonic acid (AA) and its metabolite PGE₂ as significantly elevated in the sacral spinal cord of AOAH-deficient mice, suggesting AA is a substrate for AOAH. Here, we quantified the effects of AOAH on phospholipids containing AA. Spinal cord lipidomics revealed increased AA-containing phosphatidylcholine in AOAH-deficient mice and concomitantly decreased AA-phosphatidylethanolamine, consistent with decreased CoA-independent transferase activity (CoIT). Overexpression of AOAH in cell cultures similarly altered distribution of AA in phospholipid pools, promoted AA incorporation, and resulted in decreased membrane fluidity. Finally, administration of a PGE₂ receptor antagonist reduced pelvic pain in AOAH-deficient mice. Together, these findings suggest that AOAH represents a potential CoA-independent AA transferase that modulates CNS pain pathways at the level of phospholipid metabolism.

Acyloxyacyl hydrolase regulates voiding activity

Corticotropin-releasing factor (CRF) regulates diverse physiological functions, including bladder control. We recently reported that Crf expression is under genetic control of Aoah, the locus encoding acyloxyacyl hydrolase (AOAH), suggesting that AOAH may also modulate voiding. Here, we examined the role of AOAH in bladder function. AOAH-deficient mice exhibited enlarged bladders relative to wild-type mice and had decreased voiding frequency and increased void volumes. AOAH-deficient mice had increased nonvoiding contractions and increased peak voiding pressure in awake cystometry. AOAH-deficient mice also exhibited increased bladder permeability and higher neuronal firing rates of bladder afferents in response to stretch. In wild-type mice, AOAH was expressed in bladder projecting neurons and colocalized in CRF-expressing neurons in Barrington's nucleus, an important brain area for voiding behavior, and Crf was elevated in Barrington's nucleus of AOAH-deficient mice. We had previously identified aryl hydrocarbon receptor (AhR) and peroxisome proliferator-activated receptor-γ as transcriptional regulators of Crf, and conditional knockout of AhR or peroxisome proliferator-activated receptor-γ in Crf-expressing cells restored normal voiding in AOAH-deficient mice. Finally, an AhR antagonist improved voiding in AOAH-deficient mice. Together, these data demonstrate that AOAH regulates bladder function and that the AOAH-Crf axis is a therapeutic target for treating voiding dysfunction.

Acyloxyacyl hydrolase modulates depressive-like behaviors through aryl hydrocarbon receptor

Corticotropin-releasing factor (CRF) regulates stress responses, and aberrant CRF signals are associated with depressive disorders. Crf expression is responsive to arachidonic acid (AA), where CRF is released from the hypothalamic paraventricular nucleus (PVN) to initiate the hypothalamic-pituitary-adrenal axis, culminating in glucocorticoid stress hormone release. Despite this biological and clinical significance, Crf regulation is unclear. Here, we report that acyloxyacyl hydrolase, encoded by Aoah, is expressed in the PVN, and Aoah regulates Crf through the aryl hydrocarbon receptor (AhR). We previously showed that AOAH-deficient mice mimicked interstitial cystitis/bladder pain syndrome, a condition frequently associated with comorbid anxiety and depression. With the use of novelty-suppressed feeding and sucrose preference assays to quantify rodent correlates of anxiety/depression, AOAH-deficient mice exhibited depressive behaviors. AOAH-deficient mice also had increased CNS AA, increased Crf expression in the PVN, and elevated serum corticosterone, consistent with dysfunction of the hypothalamic-pituitary-adrenal axis. The human Crf promoter has putative binding sites for AhR and peroxisome proliferator-activated receptor (PPARγ). PPARγ did not affect AA-dependent Crf expression in vitro, and conditional Pparγ knockout did not alter the AOAH-deficient depressive phenotype, despite previous studies implicating PPARγ as a therapeutic target for depression. In contrast, Crf induction was mediated by AhR binding sites in vitro and increased by AhR overexpression. Furthermore, conditional Ahr knockout rescued the depressive phenotype of AOAH-deficient mice. Finally, an AhR antagonist rescued the AOAH-deficient depressive phenotype. Together, our results demonstrate that Aoah is a novel genetic regulator of Crf mediated through AhR, and AhR is a therapeutic target for depression.

Crystal structure of the mammalian lipopolysaccharide detoxifier

LPS is a potent bacterial endotoxin that triggers the innate immune system. Proper recognition of LPS by pattern-recognition receptors requires a full complement of typically six acyl chains in the lipid portion. Acyloxyacyl hydrolase (AOAH) is a host enzyme that removes secondary (acyloxyacyl-linked) fatty acids from LPS, rendering it immunologically inert. This activity is critical for recovery from immune tolerance that follows Gram-negative infection. To understand the molecular mechanism of AOAH function, we determined its crystal structure and its complex with LPS. The substrate's lipid moiety is accommodated in a large hydrophobic pocket formed by the saposin and catalytic domains with a secondary acyl chain inserted into a narrow lateral hydrophobic tunnel at the active site. The enzyme establishes dispensable contacts with the phosphate groups of LPS but does not interact with its oligosaccharide portion. Proteolytic processing allows movement of an amphipathic helix possibly involved in substrate access at membranes.

Acyloxyacyl hydrolase modulates pelvic pain severity

Chronic pelvic pain causes significant patient morbidity and is a challenge to clinicians. Using a murine neurogenic cystitis model that recapitulates key aspects of interstitial cystitis/bladder pain syndrome (IC), we recently showed that pseudorabies virus (PRV) induces severe pelvic allodynia in BALB/c mice relative to C57BL/6 mice. Here, we report that a quantitative trait locus (QTL) analysis of PRV-induced allodynia in F2_CxB progeny identified a polymorphism on chromosome 13, rs6314295 , significantly associated with allodynia (logarithm of odds = 3.11). The nearby gene encoding acyloxyacyl hydrolase ( Aoah) was induced in the sacral spinal cord of PRV-infected mice. AOAH-deficient mice exhibited increased vesicomotor reflex in response to bladder distension, consistent with spontaneous bladder hypersensitivity, and increased pelvic allodynia in neurogenic cystitis and postbacterial chronic pain models. AOAH deficiency resulted in greater bladder pathology and tumor necrosis factor production in PRV neurogenic cystitis, markers of increased bladder mast cell activation. AOAH immunoreactivity was detectable along the bladder-brain axis, including in brain sites previously correlated with human chronic pelvic pain. Finally, AOAH-deficient mice had significantly higher levels of bladder vascular endothelial growth factor, an emerging marker of chronic pelvic pain in humans. These findings indicate that AOAH modulates pelvic pain severity, suggesting that allelic variation in Aoah influences pelvic pain in IC.

Innate immune response to lipooligosaccharide: pivotal regulator of the pathobiology of invasive Neisseria meningitidis infections

Infections due to Neisseria meningitidis afflict more than one million people worldwide annually and cause death or disability in many survivors. The clinical course of invasive infections has been well studied, but our understanding of the cause of differences in patient outcomes has been limited because these are dependent on multiple factors including the response of the host, characteristics of the bacteria and interactions between the host and the bacteria. The meningococcus is a highly inflammatory organism, and the lipooligosaccharide (LOS) on the outer membrane is the most potent inflammatory molecule it expresses due to the interactions of the lipid A moiety of LOS with receptors of the innate immune system. We previously reported that increased phosphorylation of hexaacylated neisserial lipid A is correlated with greater inflammatory potential. Here we postulate that variability in lipid A phosphorylation can tip the balance of innate immune responses towards homeostatic tolerance or proinflammatory signaling that affects adaptive immune responses, causing disease with meningitis only, or septicemia with or without meningitis, respectively. Furthermore, we propose that studies of the relationship between bacterial virulence and gene expression should consider whether genetic variation could affect properties of biosynthetic enzymes resulting in LOS structural differences that alter disease pathobiology.

Activity in the Limulus amebocyte lysate assay and induction of tumor necrosis factor-α by diverse Helicobacter pylori lipopolysaccharide preparations

Different chemically characterized H. pylori LPS preparations, such as smooth (S)- and rough (R)-form LPS, a completely dephosphorylated R-LPS, and three lipid A chemotypes, from the S- and R- form LPS (S- and R-lipid A) as well as a dephosphorylated derivative of S-lipid A, respectively, were evaluated for expression of potency in a quantitative chromogenic Limulus amebocyte (CLAL) lysate assay and for release of tumor necrosis factor-α (TNF-α) from activated human mononuclear cells. As far as the CLAL activity is concerned, no statistically significant differences could be observed between S- and R-LPS. Dephosphorylation of both R-LPS and S-lipid A caused a significant decrease of CLAL activity. In general terms, all the lipid A chemotypes were significantly less effective than the native LPS molecule and, in particular, R-lipid A expressed the lowest Limulus activity of all preparations. With regard to TNF-α release, R-LPS was the most potent inducer of this cytokine, even though its dephosphorylation reduced activity. In conclusion, the results show that phosphate groups influence both CLAL activity and, to a lesser extent, TNF-α release, and that the core oligosaccharide synergically cooperates with lipid A for the production of this cytokine, being, however, not essential for the expression of CLAL activity. Furthermore, preliminary structural data show that H. pylori D-glucosamine disaccharide backbone, besides being underphosphorylated at position 4', is also characterized by a reduced number of acyloxyacyl residues in comparison with enterobacterial lipid A. These findings, besides providing useful information on the structure-bioactivity relationships within H. pylori LPS, further support the evidence that this non-invasive, slow bacterium possesses the ability to modulate the local cellular immune response via LPS and related inflammatory cytokines.

Effect of inflammatory and antiinflammatory stimuli on acyloxyacyl hydrolase gene expression and enzymatic activity in murine macrophages

Acyloxyacyl hydrolase (AOAH) is an enzyme found in macrophages and neutrophils that specifically cleaves the acyloxyacyl moieties of lipopolysaccharide (LPS), thus rendering it non-toxic for human cells. In the present study, we demonstrate that LPS augments AOAH mRNA expression (10-20-fold) in murine macrophages. Following LPS treatment (100 ng/m]), AOAH mRNA was induced by 2 h, peaked at 6 h, and was sustained over 72 h. Optimal induction of AOAH mRNA was observed with as little as 0.1 ng/ml LPS. LPS also induced a concomitant increase in AOAH enzymatic activity in cytosolic extracts from murine macrophages and the ability of macrophages to deacylate LPS was not diminished in endotoxin-tolerized macrophages. LPS-stimulated AOAH mRNA expression was cycloheximide sensitive, indicating that de novo protein synthesis is required for AOAH mRNA production. Moreover, AOAH mRNA expression was also induced by IFN-γ. LPS-stimulated mRNA expression was not suppressed by either dexamethasone or IL-10. Finally, intraperitoneal challenge of mice with 25 μg of LPS resulted in increases in AOAH mRNA in both the lung (∼3-fold) and in the liver (∼6-fold). A possible role for LPS-inducible AOAH in the elimination of LPS is discussed.

Distinct Gene Regulatory Pathways for Human Innate versus Adaptive Lymphoid Cells

Innate lymphoid cells (ILCs) serve as sentinels in mucosal tissues, sensing release of soluble inflammatory mediators, rapidly communicating danger via cytokine secretion, and functioning as guardians of tissue homeostasis. Although ILCs have been extensively studied in model organisms, little is known about these "first responders" in humans, especially their lineage and functional kinships to cytokine-secreting T helper (Th) cell counterparts. Here, we report gene regulatory circuitries for four human ILC-Th counterparts derived from mucosal environments, revealing that each ILC subset diverges as a distinct lineage from Th and circulating natural killer cells but shares circuitry devoted to functional polarization with their Th counterparts. Super-enhancers demarcate cohorts of cell-identity genes in each lineage, uncovering new modes of regulation for signature cytokines, new molecules that likely impart important functions to ILCs, and potential mechanisms for autoimmune disease SNP associations within ILC-Th subsets.

Novel and disruptive biological strategies for resolving gut health challenges in monogastric food animal production

Use of feed antibiotics as growth promoters for control of pathogens associated with monogastric food animal morbidity and mortality has contributed to the development of antimicrobial resistance, which has now become a threat to public health on a global scale. Presently, a number of alternative feed additives have been developed and are divided into two major categories, including 1) the ones that are supposed to directly and indirectly control pathogenic bacterial proliferation; and 2) the other ones that are intended to up-regulate host gut mucosal trophic growth, whole body growth performance and active immunity. A thorough review of literature reports reveal that efficacy responses of current alternative feed additives in replacing feed antibiotics to improve performances and gut health are generally inconsistent dependent upon experimental conditions. Current alternative feed additives typically have no direct detoxification effects on endotoxin lipopolysaccharides (LPS) and this is likely the major reason that their effects are limited. It is now understood that pathogenic bacteria mediate their negative effects largely through LPS interactions with toll-like receptor 4, causing immune responses and infectious diseases. Therefore, disruptive biological strategies and a novel and new generation of feed additives need to be developed to replace feed antibiotic growth promoters and to directly and effectively detoxify the endotoxin LPS and improve gut health and performance in monogastric food animals.

Thermal stress and predation risk trigger distinct transcriptomic responses in the intertidal snail Nucella lapillus

Thermal stress and predation risk have profound effects on rocky shore organisms, triggering changes in their feeding behaviour, morphology and metabolism. Studies of thermal stress have shown that underpinning such changes in several intertidal species are specific shifts in gene and protein expression (e.g. upregulation of heat-shock proteins). But relatively few studies have examined genetic responses to predation risk. Here, we use next-generation RNA sequencing (RNA-seq) to examine the transcriptomic (mRNA) response of the snail Nucella lapillus to thermal stress and predation risk. We found that like other intertidal species, N. lapillus displays a pronounced genetic response to thermal stress by upregulating many heat-shock proteins and other molecular chaperones. In contrast, the presence of a crab predator (Carcinus maenas) triggered few significant changes in gene expression in our experiment, and this response showed no significant overlap with the snail's response to thermal stress. These different gene expression profiles suggest that thermal stress and predation risk could pose distinct and potentially additive challenges for N. lapillus and that genetic responses to biotic stresses such as predation risk might be more complex and less uniform across species than genetic responses to abiotic stresses such as thermal stress.

Crosstalk between reverse cholesterol transport and innate immunity

Although lipid metabolism and host defense are widely considered to be very divergent disciplines, compelling evidence suggests that host cell handling of self- and microbe-derived (e.g. lipopolysaccharide, LPS) lipids may have common evolutionary roots, and that they indeed may be inseparable processes. The innate immune response and the homeostatic network controlling cellular sterol levels are now known to regulate each other reciprocally, with important implications for several common diseases, including atherosclerosis. In the present review we discuss recent discoveries that provide new insight into the bidirectional crosstalk between reverse cholesterol transport and innate immunity, and highlight the broader implications of these findings for the development of therapeutics.

Chapter 2: Kill the bacteria...and also their messengers?

We consider here a previously neglected aspect of recovery from infectious diseases: how animals dispose of the dead microbes in their tissues. For one of the most important disease-causing microorganisms, Gram-negative bacteria, there is now evidence that the host catabolism of a key microbial molecule is essential for full recovery. As might be expected, it is the same bacterial molecule that animals sense to detect the presence of Gram-negative bacteria in their tissues, the cell wall lipopolysaccharide (LPS). Here, we discuss current knowledge about LPS sensing with emphasis on the host enzyme that inactivates this microbial "messenger" molecule. We also consider the possibility that the rate at which stimulatory microbial molecules undergo inactivation may influence the duration and severity of diseases caused by other infectious agents.

Proteomics of the lysosome

Defects in lysosomal function have been associated with numerous monogenic human diseases typically classified as lysosomal storage diseases. However, there is increasing evidence that lysosomal proteins are also involved in more widespread human diseases including cancer and Alzheimer disease. Thus, there is a continuing interest in understanding the cellular functions of the lysosome and an emerging approach to this is the identification of its constituent proteins by proteomic analyses. To date, the mammalian lysosome has been shown to contain approximately 60 soluble luminal proteins and approximately 25 transmembrane proteins. However, recent proteomic studies based upon affinity purification of soluble components or subcellular fractionation to obtain both soluble and membrane components suggest that there may be many more of both classes of protein resident within this organelle than previously appreciated. Discovery of such proteins has important implications for understanding the function and the dynamics of the lysosome but can also lead the way towards the discovery of the genetic basis for human diseases of hitherto unknown etiology. Here, we describe current approaches to lysosomal proteomics and data interpretation and review the new lysosomal proteins that have recently emerged from such studies.

A novel Dps-type protein from insect gut bacteria catalyses hydrolysis and synthesis of N-acyl amino acids

A novel type of a microbial N-acyl amino acid hydrolase (AAH) from insect gut bacteria was purified, cloned and functionally characterized. The enzyme was obtained from Microbacterium arborescens SE14 isolated from the foregut of larvae of the generalist herbivore Spodoptera exigua. The substrates of AAH are N-acyl-glutamines previously reported to elicit plant defence reactions after introduction into the leaf during feeding. The isolated AAH catalyses the hydrolysis of the amide bond (K(m) = 36 micromol l(-1)) and, less efficient, the formation (K(m) = 3 mmol l(-1)) of the elicitor active N-acyl amino acids. The AAH from M. arborescens SE14 shows no homology to known fatty acyl amidases (EC 3.5.1.4) but belongs to the family of Dps proteins (DNA-binding protein from starved cell). In line with other DPS proteins AAH is a homododecamer (monomer 17 181 Da) and contains iron atoms (c. 1-16 iron atoms per subunit). Unlike genuine DPS proteins the enzyme does not significantly bind DNA. Amino acid hydrolase is the first member of the DPS family that catalyses the cleavage or formation of amide bonds. The participation of a microbial enzyme in the homeostasis of N-acyl-glutamines in the insect gut adds further complexity to the interaction between plants and their herbivores.

A host lipase detoxifies bacterial lipopolysaccharides in the liver and spleen

Much of the inflammatory response of the body to bloodborne Gram-negative bacteria occurs in the liver and spleen, the major organs that remove these bacteria and their lipopolysaccharide (LPS, endotoxin) from the bloodstream. We show here that LPS undergoes deacylation in the liver and spleen by acyloxyacyl hydrolase (AOAH), an endogenous lipase that selectively removes the secondary fatty acyl chains that are required for LPS recognition by its mammalian signaling receptor, MD-2-TLR4. We further show that Kupffer cells produce AOAH and are required for hepatic LPS deacylation in vivo. AOAH-deficient mice did not deacylate LPS and, whereas their inflammatory responses to low doses of LPS were similar to those of wild type mice for approximately 3 days after LPS challenge, they subsequently developed pronounced hepatosplenomegaly. Providing recombinant AOAH restored LPS deacylating ability to Aoah(-/-) mice and prevented LPS-induced hepatomegaly. AOAH-mediated deacylation is a previously unappreciated mechanism that prevents prolonged inflammatory reactions to Gram-negative bacteria and LPS in the liver and spleen.

The cellular Toll-like receptor 4 antagonist E5531 can act as an agonist in horse whole blood

Sepsis and endotoxaemia are important causes of morbidity and mortality in humans. Research on sepsis focuses on rodent models most of which are poorly responsive to lipopolysaccharide (LPS), and thus do not mimic very well the high sensitivity of humans. Therefore, there is a need to develop more clinically relevant models. Horses suffer from a similar endotoxaemic syndrome to humans with high morbidity and mortality. LPS analogues that act as antagonists at Toll-like receptor 4 (TLR4) are being developed as novel treatments for endotoxaemia. Due to differences in recognition of ligands by TLR4 from different mammalian species, individual LPS molecules may act as agonists in some species and antagonists in others. The synthetic lipid A analogue E5531 is an antagonist at TLR4 in humans and mice, but its effects at TLR4 from other species are unknown. In the studies reported here, Escherichia coli LPS is a full agonist on equine bone marrow macrophage-like cells and its effects are antagonised by E5531. Similarly, E. coli LPS is an agonist and E5531 an antagonist on monocytes isolated from peripheral blood of healthy horses and human embryonic kidney (HEK) cells, transiently transfected to express horse TLR4 and its associated cell surface proteins MD2 and CD14. In contrast, both E. coli LPS and E5531 behave as agonists in horse whole blood by inducing production of equivalent amounts of the inflammatory mediator prostaglandin. This finding suggests that modification of E5531 may occur in whole blood, for example, deacylation, which alters its activity. This comparative study has revealed a novel pharmacological action of E5531 and emphasises the importance of extending studies of this nature beyond the normal rodent models.

Comparative transcriptional profiling of the lung reveals shared and distinct features of Streptococcus pneumoniae and influenza A virus infection

Pneumonia is the most common cause of death from infectious disease in the western hemisphere. Pathophysiological and protective processes are initiated by pattern recognition of microbial structures. To provide the molecular framework for a better understanding of processes relevant to host defence in pneumonia, we performed pulmonary transcriptome analysis in mice infected with the major bacterial and viral agents of community-acquired pneumonia, Streptococcus pneumoniae and influenza A virus. We detected differential expression of 1300 genes after infection with either pathogen. Of these, approximately 36% or 30% were specific for pneumococcal or influenza infection, respectively, yielding pathogen-specific as well as shared inflammatory transcriptional signatures. These results not only reveal a differential response on the cytokine and chemokine levels but also emphasize the important role of genes implicated in regulation and fine tuning of inflammation. As one, albeit unexpected, key feature of pneumococcal pneumonia we discovered down-regulation of B-cell responses, probably reflecting a pneumococcal virulence strategy. The pathophysiological consequences of influenza A virus infection were reflected by the emerging protective T-cell response and differential induction of genes involved in tissue regeneration and proliferation. These data provide new insights into pathogenesis of the most common forms of pneumonia, highlighting the value of transcriptional profiling for the elucidation of underlying mechanisms.

A short guided tour through functional and structural features of saposin-like proteins

SAPLIPs (saposin-like proteins) are a diverse family of lipid-interacting proteins that have various and only partly understood, but nevertheless essential, cellular functions. Their existence is conserved in phylogenetically most distant organisms, such as primitive protozoa and mammals. Owing to their remarkable sequence variability, a common mechanism for their actions is not known. Some shared principles beyond their diversity have become evident by analysis of known three-dimensional structures. Whereas lipid interaction is the basis for their functions, the special cellular tasks are often defined by interaction partners other than lipids. Based on recent findings, this review summarizes phylogenetic relations, function and structural features of the members of this family.

Identification of acyloxyacyl hydrolase, a lipopolysaccharide-detoxifying enzyme, in the murine urinary tract

Acyloxyacyl hydrolase (AOAH) is an unusual but highly conserved lipase, previously described only in myeloid cells, that removes secondary fatty acyl chains from bacterial lipopolysaccharides (LPS) and may also act on various glycero(phospho)lipids. Deacylation by AOAH greatly reduces the ability of LPS to stimulate cells via CD14-MD-2-Toll-like receptor 4. We report here that renal cortical tubule cells produce AOAH and secrete it into urine, where it can deacylate LPS. In vitro studies revealed that proximal tubule cells secrete pro-AOAH, which can be taken up by bladder cells and processed to the heterodimeric, more enzymatically active, mature form of AOAH. AOAH can then be used by the recipient cells to deacylate LPS. The enzyme produced by proximal tubule epithelium may thus be shared with downstream cells. In addition, mature AOAH is found in the urine. We suggest that cortical tubule cells may produce and secrete AOAH to limit inflammatory responses to gram-negative bacteria throughout the urinary tract.

Deletion of the GPIdeAc Gene Alters the Location and Fate of Glycosylphosphatidylinositol Precursors in Trypanosoma brucei

Glycosylphosphatidylinositol (GPI) membrane anchors are ubiquitous among the eukaryotes. In most organisms, the pathway of GPI biosynthesis involves inositol acylation and inositol deacylation as discrete steps at the beginning and end of the pathway, respectively. The bloodstream form of the protozoan parasite Trypanosoma brucei is unusual in that these reactions occur on multiple GPI intermediates and that it can express side chains of up to six galactose residues on its mature GPI anchors. An inositol deacylase gene, T. brucei GPIdeAc, has been identified. A null mutant was created and shown to be capable of expressing normal mature GPI anchors on its variant surface glycoprotein. Here, we show that the null mutant synthesizes galactosylated forms of the mature GPI precursor, glycolipid A, at an accelerated rate (2.8-fold compared to wild type). These free GPIs accumulate at the cell surface as metabolic end products. Using continuous and pulse-chase labeling experiments, we show that there are two pools of glycolipid A. Only one pool is competent for transfer to nascent variant surface glycoprotein and represents 38% of glycolipid A in wild-type cells. This pool rises to 75% of glycolipid A in the GPIdeAc null mutant. We present a model for the pathway of GPI biosynthesis in T. brucei that helps to explain the complex phenotype of the GPIdeAc null mutant.

Mechanisms of disposal of bacterial lipopolysaccharides by animal hosts

Much of the very extensive literature describing the (bio)chemistry and biology of bacterial lipopolysaccharides (LPS, endotoxin) has dealt with the properties of these molecules as potent triggers of host responses. This brief review will focus on what has been learned recently about mechanisms by which the host can dispose of LPS and counter its often excessive stimulatory effects.

Deacylation of lipopolysaccharide in whole Escherichia coli during destruction by cellular and extracellular components of a rabbit peritoneal inflammatory exudate

Deacylation of purified lipopolysaccharides (LPS) markedly reduces its toxicity toward mammals. However, the biological significance of LPS deacylation during infection of the mammalian host is uncertain, particularly because the ability of acyloxyacyl hydrolase, the leukocyte enzyme that deacylates purified LPS, to attack LPS residing in the bacterial cell envelope has not been established. We recently showed that the cellular and extracellular components of a rabbit sterile inflammatory exudate are capable of extensive and selective removal of secondary acyl chains from purified LPS. We now report that LPS as a constituent of the bacterial envelope is also subject to deacylation in the same inflammatory setting. Using Escherichia coli LCD25, a strain that exclusively incorporates radiolabeled acetate into fatty acids, we quantitated LPS deacylation as the loss of radiolabeled secondary (laurate and myristate) and primary fatty acids (3-hydroxymyristate) from the LPS backbone. Isolated mononuclear cells and neutrophils removed 50% and 20-30%, respectively, of the secondary acyl chains of the LPS of ingested whole bacteria. When bacteria were killed extracellularly during incubation with ascitic fluid, no LPS deacylation occurred. In this setting, the addition of neutrophils had no effect, but addition of mononuclear cells resulted in removal of >40% of the secondary acyl chains by 20 h. Deacylation of LPS was always restricted to the secondary acyl chains. Thus, in an inflammatory exudate, primarily in mononuclear phagocytes, the LPS in whole bacteria undergoes substantial and selective acyloxyacyl hydrolase-like deacylation, both after phagocytosis of intact bacteria and after uptake of LPS shed from extracellularly killed bacteria. This study demonstrates for the first time that the destruction of Gram-negative bacteria by a mammalian host is not restricted to degradation of phospholipids, protein, and RNA, but also includes extensive deacylation of the envelope LPS.

Deacylation of purified lipopolysaccharides by cellular and extracellular components of a sterile rabbit peritoneal inflammatory exudate

The extent to which the mammalian host is capable of enzymatic degradation and detoxification of bacterial lipopolysaccharides (LPS) is still unknown. Partial deacylation of LPS by the enzyme acyloxyacyl hydrolase (AOAH) provides such a mechanism, but its participation in the disposal of LPS under physiological conditions has not been established. In this study, deacylation of isolated radiolabeled LPS by both cellular and extracellular components of a sterile inflammatory peritoneal exudate elicited in rabbits was examined ex vivo. AOAH-like activity, tested under artificial conditions (pH 5.4, 0.1% Triton X-100), was evident in all components of the exudate (mononuclear cells [MNC] > polymorphonuclear leukocytes [PMN] > inflammatory [ascitic] fluid [AF]). Under more physiological conditions, in a defined medium containing purified LPS-binding protein, the LPS-deacylating activity of MNC greatly exceeded that of PMN. In AF, MNC (but not PMN) also produced rapid and extensive CD14-dependent LPS deacylation. Under these conditions, almost all MNC-associated LPS underwent deacylation within 1 h, a rate greatly exceeding that previously found in any cell type. The remaining extracellular LPS was more slowly subject to CD14-independent deacylation in AF. Quantitative analysis showed a comparable release of laurate and myristate but no release of 3-hydroxymyristate, consistent with an AOAH-like activity. These findings suggest a major role for CD14(+) MNC and a secondary role for AF in the deacylation of cell-free LPS at extravascular inflammatory sites.

Acyloxyacyl hydrolase activity of neutrophil leukocytes in normal early postpartum dairy cows and in cows with retained placenta

Acyloxyacyl hydrolase (AOAH) is an enzyme of bovine polymorphonuclear neutrophil leukocytes (PMN) that is capable of detoxifying endotoxin (25). The activity of AOAH in PMN isolated from the blood was investigated in dairy cows that expelled the fetal membranes normally (Group NFM) and in cows with retained fetal membranes (Group RFM) to obtain better insight into the role of the AOAH enzyme of neutrophils in endotoxin-related diseases, which occur frequently in dairy cows during the early postpartum period, especially in RFM cows. Twenty early postpartum dairy cows were used in the study: 13 NFM cows and 7 RFM cows. In the RFM cows, the percentage of PMN in blood (29+/-4%) was significantly (P<0.05) lower than in NFM cows (43+/-4%). The average AOAH activity in RFM cows (mean +/- SEM = 89+/-13 pmol fatty acid/10(7) PMN/h) was lower than in NFM cows (107+/-6 pmol fatty acid/10(7) PMN/h), but the difference in neutrophil AOAH activity between the 2 groups was not significant. There was also a higher percentage of immature neutrophils in isolated leukocyte suspensions from RFM cows (22+/-8%) than from NFM cows (15+/-4%), so that impairment of AOAH activity in early postpartum cows could be explained, in part, by immaturity of the neutrophils. These results suggest that the decreased AOAH activity of PMN could play a role in the pathogenesis of endotoxin-related diseases in dairy cows during the early postpartum period.