Mediators of innate immune recognition of bacteria concentrate in lipid rafts and facilitate lipopolysaccharide-induced cell activation

Association between the pig genome and its gut microbiota composition

The gut microbiota has been evolving with its host along the time creating a symbiotic relationship. In this study, we assess the role of the host genome in the modulation of the microbiota composition in pigs. Gut microbiota compositions were estimated through sequencing the V3-V4 region of the 16S rRNA gene from rectal contents of 285 pigs. A total of 1,261 operational taxonomic units were obtained and grouped in 18 phyla and 101 genera. Firmicutes (45.36%) and Bacteroidetes (37.47%) were the two major phyla obtained, whereas at genus level Prevotella (7.03%) and Treponema (6.29%) were the most abundant. Pigs were also genotyped with a high-throughput method for 45,508 single nucleotide polymorphisms that covered the entire pig genome. Subsequently, genome-wide association studies were made among the genotypes of these pigs and their gut microbiota composition. A total of 52 single-nucleotide polymorphisms distributed in 17 regions along the pig genome were associated with the relative abundance of six genera; Akkermansia, CF231, Phascolarctobacterium, Prevotella, SMB53, and Streptococcus. Our results suggest 39 candidate genes that may be modulating the microbiota composition and manifest the association between host genome and gut microbiota in pigs.

Rab7b participation on the TLR4 (Toll-like receptor) endocytic pathway in Shiga toxin-associated Hemolytic Uremic Syndrome (HUS)

BACKGROUND

The inflammatory response of the host to Shiga toxin and/or lipopolysaccharide (LPS) of Escherichia coli (E. coli) is included in (HUS). The TLR4-LPS complex is internalized and TLR4 induced inflammatory signaling is stopped by targeting the complex for degradation. Rab7b, a small guanosine triphosphatase (GTPase) expressed in monocytes, regulates the later stages of the endocytic pathway.

OBJECTIVE

we studied the Rab7b participation on the TLR4 endocytic pathway and its effect on monocyte cytokine production along the acute course of pediatric Shiga toxin-associated HUS.

METHODS AND RESULTS

Monocytes were identified according to their positivity in CD14 expression. Surface TLR4 expression in monocytes from 18 HUS patients significantly increased by day 1 to 6, showing the highest increase on day 4 compared to monocytes of 10 healthy children. Significant higher surface TLR4 expression was accompanied by increased proinflammatory intracellular cytokines, tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). In contrast, after these time points, surface TLR4 expression and intracellular TNF-α levels, returned to near control levels after 10 days. Furthermore, confocal immunofluorescence microscopy proved colocalization of increased intracellular TLR4/Rab7b determined by Pearson's coefficient in monocytes from HUS patients from day 1 on the highest colocalization of both proteins by day 4. Decreased TLR4/Rab7b colocalization was shown 10 days after HUS onset.

CONCLUSION

The colocalization of TLR4 and Rab7b allows us to suggest Rab7b participation in the control of the TLR4 endocytic pathway in HUS patient monocytes. A consequential fall in cytokine production throughout the early follow up of HUS is demonstrated.

Nanoscale distribution of TLR4 on primary human macrophages stimulated with LPS and ATI

Toll-like receptor 4 (TLR4) plays a crucial role in the recognition of invading pathogens. Upon activation by lipopolysaccharides (LPS), TLR4 is recruited into specific membrane domains and dimerizes. In addition to LPS, TLR4 can be stimulated by wheat amylase-trypsin inhibitors (ATI). ATI are proteins associated with gluten containing grains, whose ingestion promotes intestinal and extraintestinal inflammation. However, the effect of ATI vs. LPS on the membrane distribution of TLR4 at the nanoscale has not been analyzed. In this study, we investigated the effect of LPS and ATI stimulation on the membrane distribution of TLR4 in primary human macrophages using single molecule localization microscopy (SMLM). We found that in unstimulated macrophages the majority of TLR4 molecules are located in clusters, but with donor-dependent variations from ∼51% to ∼75%. Depending on pre-clustering, we found pronounced variations in the fraction of clustered molecules and density of clusters on the membrane upon LPS and ATI stimulation. Although clustering differed greatly among the human donors, we found an almost constant cluster diameter of ∼44 nm for all donors, independent of treatment. Together, our results show donor-dependent but comparable effects between ATI and LPS stimulation on the membrane distribution of TLR4. This may indicate a general mechanism of TLR4 activation in primary human macrophages. Furthermore, our methodology visualizes TLR4 receptor clustering and underlines its functional role as a signaling platform.

Vibrio cholerae OmpU Mediates CD36-Dependent Reactive Oxygen Species Generation Triggering an Additional Pathway of MAPK Activation in Macrophages

OmpU, one of the porins of Gram-negative bacteria Vibrio cholerae, induces TLR1/2-MyD88-NF-κB-dependent proinflammatory cytokine production by monocytes and macrophages of human and mouse origin. In this study, we report that in both the cell types, OmpU-induced proinflammatory responses involve activation of MAPKs (p38 and JNK). Interestingly, we observed that in OmpU-treated macrophages, p38 activation is TLR2 dependent, but JNK activation happens through a separate pathway involving reactive oxygen species (ROS) generation by NADPH oxidase complex and mitochondrial ROS. Further, we observed that OmpU-mediated mitochondrial ROS generation probably depends on OmpU translocation to mitochondria and NADPH oxidase-mediated ROS production is due to activation of scavenger receptor CD36. For the first time, to our knowledge, we are reporting that a Gram-negative bacterial protein can activate CD36 as a pattern recognition receptor. Additionally, we found that in OmpU-treated monocytes, both JNK and p38 activation is linked to the TLR2 activation only. Therefore, the ability of macrophages to employ multiple receptors such as TLR2 and CD36 to recognize a single ligand, as in this case OmpU, probably explains the very basic nature of macrophages being more proinflammatory than monocytes.

Effects of antimicrobial peptides on serum biochemical parameters, antioxidant activity and non-specific immune responses in Epinephelus coioides

Antimicrobial peptides (AMPs) are small proteins showing broad-spectrum antimicrobial activity that have been known to be powerful agents against a variety of pathogens (bacteria, fungi and viruses). In this study, the effects of AMPs from Bacillus subtilis on Epinephelus coioides were examined. E. coioides were fed with diets containing AMPs (0, 100, 200, 400 or 800 mg/kg) for four weeks. Results showed that the levels of total protein (TP), albumin (ALB), alanine aminotransferase (ALT), aspartate aminotransferase (AST), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and blood glucose (GLU) and lipopolysaccharide (LPS) in the serum of E. coioides changed than those of the control group; compared to the control group, the levels of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA) and lysozyme (LZM) levels in E. coioides fed with different dosages AMP diets were also different; in addition, the mRNA expression of tumor necrosis factor alpha (TNF-α), interleukin-1-beta (IL-1β), and heat shock protein 90 (Hsp90) in the tissues of E. coioides were measured, the three genes in the tissues examined were significantly upregulated. The results demonstrated that diets containing AMPs can enhance the antioxidant capacity and innate immune ability of E. coioides, indicating that AMPs might be a potential alternative to antibiotics in E. coioides.

Role of Liver X Receptor in Mastitis Therapy and Regulation of Milk Fat Synthesis

Mastitis is important disease that causes huge economic losses in the dairy industry. In recent years, antibiotic therapy has become the primary treatment for mastitis, however, due to drug residue in milk and food safety factors, we lack safe and effective drugs for treating mastitis. Therefore, new targets and drugs are urgently needed to control mastitis. LXRα, one of the main members of the nuclear receptor superfamily, is reported to play important roles in metabolism, infection and immunity. Activation of LXRα could inhibit LPS-induced mastitis. Furthermore, LXRα is reported to enhance milk fat production, thus, LXRα may serve as a new target for mastitis therapy and regulation of milk fat synthesis. This review summarizes the effects of LXRα in regulating milk fat synthesis and treatment of mastitis and highlights the potential agonists involved in both issues.

Hsp70 interactions with membrane lipids regulate cellular functions in health and disease

Beyond guarding the cellular proteome the major stress inducible heat shock protein Hsp70 has been shown to interact with lipids. Non-cytosolic Hsp70 stabilizes membranes during stress challenges and, in pathophysiological states, facilitates endocytosis, counteracts apoptotic mechanisms, sustains survival pathways or represents a signal that can be recognized by the immune system. Disease-coupled lipid-associated functions of Hsp70 may be targeted via distinct subcellular localizations of Hsp70 itself or its specific interacting lipids. With a special focus on interacting lipids, here we discuss localization-dependent roles of the membrane-bound Hsp70 in the context of its therapeutic potential, particularly in cancer and neurodegenerative diseases.

Macrophage Lysophosphatidylcholine Acyltransferase 3 Deficiency-Mediated Inflammation Is Not Sufficient to Induce Atherosclerosis in a Mouse Model

Mammalian cell membrane phosphatidylcholines (PCs), the major phospholipids, exhibit diversity which is controlled by Lands' cycle or PC remodeling pathway. Lysophosphatidylcholine acyltransferase (LPCAT) is one of the major players in the pathway and plays an important role in maintaining cell membrane structure and function. LPCAT3 is highly expressed in macrophages, however, its role in mediating inflammation is still not understood, since contradictory results were reported previously. The order of LPCAT mRNA levels in mouse macrophages is as follows: LPCAT3 > LPCAT1 > LPCAT2 >> LPCAT4. In order to investigate the role of LPCAT3 in macrophages, we prepared myeloid cell-specific Lpcat3 knockout (KO) mice and found that the deficiency significantly reduced certain polyunsaturated phosphatidylcholines, such as 16:0/20:4, 18:1/18:2, 18:0/20:4, and 18:1/20:4 in macrophage plasma membrane. Lpcat3 deficiency significantly increased toll like receptor 4 protein and phosphorylated c-Src in membrane lipid rafts, and increased LPS-induced IL-6 and TNFα releasing through activation of MAP kinases and NFκB. Moreover, the ablation of LPCAT3 in macrophages significantly increase of M1 macrophages. However, macrophage deletion of Lpcat3 in (LDL receptor) Ldlr KO mice, both male and female, on a Western type diet, did not have a significant impact on atherogenesis. In conclusion, LPCAT3 is one of LPCATs in macrophages, involved in PC remodeling. LPCAT3 deficiency has no effect on cholesterol efflux. However, the deficiency promotes macrophage inflammatory response, but such an effect has a marginal influence on the development of atherosclerosis.

Maternal Inflammation and Neurodevelopmental Programming: A Review of Preclinical Outcomes and Implications for Translational Psychiatry

Early disruptions to neurodevelopment are highly relevant to understanding both psychiatric risk and underlying pathophysiology that can be targeted by new treatments. Much convergent evidence from the human literature associates inflammation during pregnancy with later neuropsychiatric disorders in offspring. Preclinical models of prenatal inflammation have been developed to examine the causal maternal physiological and offspring neural mechanisms underlying these findings. Here we review the strengths and limitations of preclinical models used for these purposes and describe selected studies that have shown maternal immune impacts on the brain and behavior of offspring. Maternal immune activation in mice, rats, nonhuman primates, and other mammalian model species have demonstrated convergent outcomes across methodologies. These outcomes include shifts and/or disruptions in the normal developmental trajectory of molecular and cellular processes in the offspring brain. Prenatal developmental origins are critical to a mechanistic understanding of maternal immune activation-induced alterations to microglia and immune molecules, brain growth and development, synaptic morphology and physiology, and anxiety- and depression-like, sensorimotor, and social behaviors. These phenotypes are relevant to brain functioning across domains and to anxiety and mood disorders, schizophrenia, and autism spectrum disorder, in which they have been identified. By turning a neurodevelopmental lens on this body of work, we emphasize the importance of acute changes to the prenatal offspring brain in fostering a better understanding of potential mechanisms for intervention. Collectively, overlapping results across maternal immune activation studies also highlight the need to examine preclinical offspring neurodevelopment alterations in terms of a multifactorial immune milieu, or immunome, to determine potential mechanisms of psychiatric risk.

Host membrane glycosphingolipids and lipid microdomains facilitate Histoplasma capsulatum internalisation by macrophages

Recognition and internalisation of intracellular pathogens by host cells is a multifactorial process, involving both stable and transient interactions. The plasticity of the host cell plasma membrane is fundamental in this infectious process. Here, the participation of macrophage lipid microdomains during adhesion and internalisation of the fungal pathogen Histoplasma capsulatum (Hc) was investigated. An increase in membrane lateral organisation, which is a characteristic of lipid microdomains, was observed during the first steps of Hc-macrophage interaction. Cholesterol enrichment in macrophage membranes around Hc contact regions and reduced levels of Hc-macrophage association after cholesterol removal also suggested the participation of lipid microdomains during Hc-macrophage interaction. Using optical tweezers to study cell-to-cell interactions, we showed that cholesterol depletion increased the time required for Hc adhesion. Additionally, fungal internalisation was significantly reduced under these conditions. Moreover, macrophages treated with the ceramide-glucosyltransferase inhibitor (P4r) and macrophages with altered ganglioside synthesis (from B4galnt1^-/- mice) showed a deficient ability to interact with Hc. Coincubation of oligo-GM1 and treatment with Cholera toxin Subunit B, which recognises the ganglioside GM1, also reduced Hc association. Although purified GM1 did not alter Hc binding, treatment with P4 significantly increased the time required for Hc binding to macrophages. The content of CD18 was displaced from lipid microdomains in B4galnt1^-/- macrophages. In addition, macrophages with reduced CD18 expression (CD18^low ) were associated with Hc at levels similar to wild-type cells. Finally, CD11b and CD18 colocalised with GM1 during Hc-macrophage interaction. Our results indicate that lipid rafts and particularly complex gangliosides that reside in lipid rafts stabilise Hc-macrophage adhesion and mediate efficient internalisation during histoplasmosis.

Leucine-rich repeats and calponin homology containing 4 (Lrch4) regulates the innate immune response

Toll-like receptors (TLRs) are pathogen-recognition receptors that trigger the innate immune response. Recent reports have identified accessory proteins that provide essential support to TLR function through ligand delivery and receptor trafficking. Herein, we introduce leucine-rich repeats (LRRs) and calponin homology containing 4 (Lrch4) as a novel TLR accessory protein. Lrch4 is a membrane protein with nine LRRs in its predicted ectodomain. It is widely expressed across murine tissues and has two expression variants that are both regulated by lipopolysaccharide (LPS). Predictive modeling indicates that Lrch4 LRRs conform to the horseshoe-shaped structure typical of LRRs in pathogen-recognition receptors and that the best structural match in the protein database is to the variable lymphocyte receptor of the jawless vertebrate hagfish. Silencing Lrch4 attenuates cytokine induction by LPS and multiple other TLR ligands and dampens the in vivo innate immune response. Lrch4 promotes proper docking of LPS in lipid raft membrane microdomains. We provide evidence that this is through regulation of lipid rafts as Lrch4 silencing reduces cell surface gangliosides, a metric of raft abundance, as well as expression and surface display of CD14, a raft-resident LPS co-receptor. Taken together, we identify Lrch4 as a broad-spanning regulator of the innate immune response and a potential molecular target in inflammatory disease.

Versatility of cell-penetrating peptides for intracellular delivery of siRNA

The plasma membrane is a large barrier to systemic drug delivery into cells, and it limits the efficacy of drug cargo. This issue has been overcome using cell-penetrating peptides (CPPs). CPPs are short peptides (6-30 amino acid residues) that are potentially capable of intracellular penetration to deliver drug molecules. CPPs broadened biomedical applications and provide a means to deliver a range of biologically active molecules, such as small molecules, proteins, imaging agents, and pharmaceutical nanocarriers, across the plasma membrane with high efficacy and low toxicity. This review is focused on the versatility of CPPs and advanced approaches for siRNA delivery.

Mass Spectrometry-based Structural Analysis and Systems Immunoproteomics Strategies for Deciphering the Host Response to Endotoxin

One cause of sepsis is systemic maladaptive immune response of the host to bacteria and specifically, to Gram-negative bacterial outer-membrane glycolipid lipopolysaccharide (LPS). On the host myeloid cell surface, proinflammatory LPS activates the innate immune system via Toll-like receptor-4/myeloid differentiation factor-2 complex. Intracellularly, LPS is also sensed by the noncanonical inflammasome through caspase-11 in mice and 4/5 in humans. The minimal functional determinant for innate immune activation is the membrane anchor of LPS called lipid A. Even subtle modifications to the lipid A scaffold can enable, diminish, or abolish immune activation. Bacteria are known to modify their LPS structure during environmental stress and infection of hosts to alter cellular immune phenotypes. In this review, we describe how mass spectrometry-based structural analysis of endotoxin helped uncover major determinations of molecular pathogenesis. Through characterization of LPS modifications, we now better understand resistance to antibiotics and cationic antimicrobial peptides, as well as how the environment impacts overall endotoxin structure. In addition, mass spectrometry-based systems immunoproteomics approaches can assist in elucidating the immune response against LPS. Many regulatory proteins have been characterized through proteomics and global/targeted analysis of protein modifications, enabling the discovery and characterization of novel endotoxin-mediated protein translational modifications.

Postprandial endotoxemia may influence the development of type 2 diabetes mellitus: From the CORDIOPREV study

BACKGROUND & AIMS

Insulin resistance (IR) and impaired beta-cell function are key determinants of type 2 diabetes mellitus (T2DM). Intestinal absorption of bacterial components activates the toll-like receptors inducing inflammation, and this in turn IR. We evaluated the role of endotoxemia in promoting inflammation-induced insulin resistance (IR) in the development of T2DM, and its usefulness as predictive biomarker.

METHODS

We included in this study 462 patients from the CORDIOPREV study without T2DM at baseline. Of these, 107 patients developed T2DM according to the American Diabetes Association (ADA) diagnosis criteria after a median follow-up of 60 months (Incident-DIAB group), whereas 355 patients did not developed it during this period of time (Non-DIAB group).

RESULTS

We observed a postprandial increase in lipopolysaccharides (LPS) levels in the Incident-DIAB at baseline (P < 0.001), whereas LPS levels were not modified in the Non-DIAB. Disease-free survival curves based on the LPS postprandial fold change improved T2DM Risk Assessment as compared with the previously described FINDRISC score (hazard ratio of 2.076, 95% CI 1.149-3.750 vs. 1.384, 95% CI 0.740-2.589). Moreover, disease-free survival curves combining the LPS postprandial fold change and FINDRISC score together showed a hazard ratio of 3.835 (95% CI 1.323-11.114), linked to high values of both parameters.

CONCLUSION

Our results suggest that a high postprandial endotoxemia precedes the development of T2DM. Our results also showed the potential use of LPS plasma levels as a biomarker predictor of T2DM development. CLINICAL TRIALS.GOV.

IDENTIFIER

NCT00924937.

An unexpected link between fatty acid synthase and cholesterol synthesis in proinflammatory macrophage activation

Different immune activation states require distinct metabolic features and activities in immune cells. For instance, inhibition of fatty acid synthase (FASN), which catalyzes the synthesis of long-chain fatty acids, prevents the proinflammatory response in macrophages; however, the precise role of this enzyme in this response remains poorly defined. Consistent with previous studies, we found here that FASN is essential for lipopolysaccharide-induced, Toll-like receptor (TLR)-mediated macrophage activation. Interestingly, only agents that block FASN upstream of acetoacetyl-CoA synthesis, including the well-characterized FASN inhibitor C75, inhibited TLR4 signaling, while those acting downstream had no effect. We found that acetoacetyl-CoA could overcome C75's inhibitory effect, whereas other FASN metabolites, including palmitate, did not prevent C75-mediated inhibition. This suggested an unexpected role for acetoacetyl-CoA in inflammation that is independent of its role in palmitate synthesis. Our evidence further suggested that acetoacetyl-CoA arising from FASN activity promotes cholesterol production, indicating a surprising link between fatty acid synthesis and cholesterol synthesis. We further demonstrate that this process is required for TLR4 to enter lipid rafts and facilitate TLR4 signaling. In conclusion, we have uncovered an unexpected link between FASN and cholesterol synthesis that appears to be required for TLR signal transduction and proinflammatory macrophage activation.

Lipid bilayer stress in obesity-linked inflammatory and metabolic disorders

The maintenance of the characteristic lipid compositions and physicochemical properties of biological membranes is essential for their proper function. Mechanisms allowing to sense and restore membrane homeostasis have been identified in prokaryotes for a long time and more recently in eukaryotes. A membrane remodeling can result from aberrant metabolism as seen in obesity. In this review, we describe how such lipid bilayer stress can account for the modulation of membrane proteins involved in the pathogenesis of obesity-linked inflammatory and metabolic disorders. We address the case of the Toll-like receptor 4 that is implicated in the obesity-related low grade inflammation and insulin resistance. The lipid raft-mediated TLR4 activation is promoted by an enrichment of the plasma membrane with saturated lipids or cholesterol increasing the lipid phase order. We discuss of the plasma membrane Na, K-ATPase that illustrates a new concept according to which direct interactions between specific residues and particular lipids determine both stability and activity of the pump in parallel with indirect effects of the lipid bilayer. The closely related sarco(endo)-plasmic Ca-ATPase embedded in the more fluid ER membrane seems to be more sensitive to a lipid bilayer stress as demonstrated by its inactivation in cholesterol-loaded macrophages or its inhibition mediated by an increased PtdCho/PtdEtn ratio in obese mice hepatocytes. Finally, we describe the model recently proposed for the activation of the conserved IRE-1 protein through alterations in the ER membrane lipid packing and thickness. Such IRE-1 activation could occur in response to abnormal lipid synthesis and membrane remodeling as observed in hepatocytes exposed to excess nutrients. Since the IRE-1/XBP1 branch also stimulates the lipid synthesis, this pathway could create a vicious cycle "lipogenesis-ER lipid bilayer stress-lipogenesis" amplifying hepatic ER pathology and the obesity-linked systemic metabolic defects.

Saikosaponin a inhibits LPS-induced inflammatory response by inducing liver X receptor alpha activation in primary mouse macrophages

The aim of this study was to investigate the effects of SSa on LPS-induced endotoxemia in mice and clarify the possible mechanism. An LPS-induced endotoxemia mouse model was used to confirm the anti-inflammatory activity of SSa in vivo. The primary mouse macrophages were used to investigate the molecular mechanism and targets of SSa in vitro. In vivo, the results showed that SSa improved survival during lethal endotoxemia. In vitro, our results showed that SSa dose-dependently inhibited the expression of TNF-α, IL-6, IL-1β, IFN-β-and RANTES in LPS-stimulated primary mouse macrophages. Western blot analysis showed that SSa suppressed LPS-induced NF-κB and IRF3 activation. Furthermore, SSa disrupted the formation of lipid rafts by depleting cholesterol and inhibited TLR4 translocation into lipid rafts. Moreover, SSa activated LXRα, ABCA1 and ABCG1. Silencing LXRα abrogated the effect of SSa. In conclusion, the anti-inflammatory effects of SSa is associated with activating LXRα dependent cholesterol efflux pathway which result in disrupting lipid rafts by depleting cholesterol and reducing translocation of TLR4 to lipid rafts, thereby attenuating LPS mediated inflammatory response.

Different Dietary Proportions of Fish Oil Regulate Inflammatory Factors but Do Not Change Intestinal Tight Junction ZO-1 Expression in Ethanol-Fed Rats

Sixty male Wistar rats were fed a control or an ethanol-containing diet in groups C or E. The fat compositions were adjusted with 25% or 57% fish oil substituted for olive oil in groups CF25, CF57, EF25, and EF57. Hepatic thiobarbituric acid-reactive substance (TBARS) levels, cytochrome P450 2E1 protein expression, and tumor necrosis factor- (TNF-) α, interleukin- (IL-) 1β, IL-6, and IL-10 levels, as well as intracellular adhesion molecule (ICAM)-1 levels were significantly elevated, whereas plasma adiponectin level was significantly reduced in group E (p < 0.05). Hepatic histopathological scores of fatty change and inflammation, in group E were significantly higher than those of group C (p < 0.05). Hepatic TBARS, plasma ICAM-1, and hepatic TNF-α, IL-1β, and IL-10 levels were significantly lower, and plasma adiponectin levels were significantly higher in groups EF25 and EF57 than those in group E (p < 0.05). The immunoreactive area of the intestinal tight junction protein, ZO-1, showed no change between groups C and E. Only group CF57 displayed a significantly higher ZO-1 immunoreactive area compared to group C (p = 0.0415). 25% or 57% fish oil substituted for dietary olive oil could prevent ethanol-induced liver damage in rats, but the mechanism might not be related to intestinal tight junction ZO-1 expression.

Low-Density Lipoprotein Receptor Deficiency Attenuates Neuroinflammation through the Induction of Apolipoprotein E

Objective

We aimed to determine the role of the low-density lipoprotein receptor (LDLr) in neuroinflammation by inducing experimental autoimmune encephalomyelitis (EAE) in ldlr knock out mice.

Methods

MOG_35-55 induced EAE in male and female ldlr^-/- mice was assessed clinically and histopathologically. Expression of inflammatory mediators and apolipoprotein E (apoE) was investigated by qPCR. Changes in protein levels of apoE and tumor necrosis factor alpha (TNFα) were validated by western blot and ELISA, respectively.

Results

Ldlr^-/--attenuated EAE disease severity in female, but not in male, EAE mice marked by a reduced proinflammatory cytokine production in the central nervous system of female ldlr^-/- mice. Macrophages from female ldlr^-/- mice showed a similar decrease in proinflammatory mediators, an impaired capacity to phagocytose myelin and enhanced secretion of the anti-inflammatory apoE. Interestingly, apoE/ldlr double knock out abrogated the beneficial effect of ldlr depletion in EAE.

Conclusion

Collectively, we show that ldlr^-/- reduces EAE disease severity in female but not in male EAE mice, and that this can be explained by increased levels of apoE in female ldlr^-/- mice. Although the reason for the observed sexual dimorphism remains unclear, our findings show that LDLr and associated apoE levels are involved in neuroinflammatory processes.

Interaction of Hsp90 with phospholipid model membranes

Heat shock protein 90 (Hsp90) is an essential molecular chaperone with versatile functions in cell homeostatic control under both normal and stress conditions. Hsp90 has been found to be expressed on the cell surface, but the mechanism of Hsp90 association to the membrane remains obscure. In this study, the direct interaction of Hsp90 and phospholipid vesicles was characterized, and the role of Hsp90 on membrane physical state was explored. Using surface plasmon resonance (SPR), we observed a strong interaction between Hsp90 and different compositions of lipid. Hsp90 had a preference to bind with more unsaturated phospholipid species and the affinity was higher with negatively charged lipids than zwitterionic lipids. Increasing the mole fraction of cholesterol in the phospholipid led to a decrease of binding affinity to Hsp90. Circular dichroism (CD) spectroscopy of Hsp90 in PC membranes showed more α-helix structure than in aqueous buffer. The differential scanning calorimeter (DSC) and fluorescence polarization results showed Hsp90 could affect the transition temperature and fluidity of the bilayer. We postulate from these results that the association between Hsp90 and membranes may involve both electrostatic and hydrophobic force, and constitute a possible mechanism that modulates membrane lipid order during thermal fluctuations.

Probiotic Modulation of Innate Cell Pathogen Sensing and Signaling Events

There is a growing body of evidence documenting probiotic bacteria to have a beneficial effect to the host through their ability to modulate the mucosal immune system. Many probiotic bacteria can be considered to act as either immune activators or immune suppressors, which have appreciable influence on homeostasis, inflammatory- and suppressive-immunopathology. What is becoming apparent is the ability of these probiotics to modulate innate immune responses via direct or indirect effects on the signaling pathways that drive these activatory or suppressive/tolerogenic mechanisms. This review will focus on the immunomodulatory role of probiotics on signaling pathways in innate immune cells: from positive to negative regulation associated with innate immune cells driving gut mucosal functionality. Research investigations have shown probiotics to modulate innate functionality in many ways including, receptor antagonism, receptor expression, binding to and expression of adaptor proteins, expression of negative regulatory signal molecules, induction of micro-RNAs, endotoxin tolerisation and finally, the secretion of immunomodulatory proteins, lipids and metabolites. The detailed understanding of the immunomodulatory signaling effects of probiotic strains will facilitate strain-specific selective manipulation of innate cell signal mechanisms in the modulation of mucosal adjuvanticity, immune deviation and tolerisation in both healthy subjects and patients with inflammatory and suppressive pathology.

Lipopolysaccharide Detection across the Kingdoms of Life

Studies in recent years have uncovered a diverse set of eukaryotic receptors that recognize lipopolysaccharide (LPS), the major outer-membrane component of Gram-negative bacteria. Indeed, Toll-like receptors, G-protein-coupled receptors, integrins, receptor-like kinases, and caspases have emerged as important LPS-interacting proteins. In this review, the mammalian receptors that detect LPS are described. I highlight how no host protein is involved in all LPS responses, but a single lipid (phosphatidylinositol-4,5-bisphosphate) regulates many LPS responses, including endocytosis, phagocytosis, inflammation, and pyroptosis. I further describe LPS response systems that operate specifically in plants, and discuss potentially new LPS response systems that await discovery. This diversity of receptors for a single microbial product underscores the importance of host-microbe interactions in multiple kingdoms of life.

Spatial structure of TLR4 transmembrane domain in bicelles provides the insight into the receptor activation mechanism

Toll-like receptors (TLRs) play a key role in the innate and adaptive immune systems. While a lot of structural data is available for the extracellular and cytoplasmic domains of TLRs, and a model of the dimeric full-length TLR3 receptor in the active state was build, the conformation of the transmembrane (TM) domain and juxtamembrane regions in TLR dimers is still unclear. In the present work, we study the transmembrane and juxtamembrane parts of human TLR4 receptor using solution NMR spectroscopy in a variety of membrane mimetics, including phospholipid bicelles. We show that the juxtamembrane hydrophobic region of TLR4 includes a part of long TM α-helix. We report the dimerization interface of the TM domain and claim that long TM domains with transmembrane charged aminoacids is a common feature of human toll-like receptors. This fact is analyzed from the viewpoint of protein activation mechanism, and a model of full-length TLR4 receptor in the dimeric state has been proposed.

Extraordinarily potent proinflammatory properties of lactoferrin-containing immunocomplexes against human monocytes and macrophages

Lactoferrin (LTF), an important first line defense molecule against infection, is a common target for humoral autoimmune reactions in humans. Since LTF is a multifunctional protein capable of activating innate immune cells via various surface receptors, we hypothesized that LTF-containing immune complexes (ICs) (LTF-ICs), likely formed in patients with high titer anti-LTF autoantibodies, could possess unique monocyte/macrophage-activating properties compared with other ICs. ELISA analysis on serum samples from rheumatoid arthritis (RA) patients (n = 80) and healthy controls (n = 35) for anti-LTF autoantibodies confirmed a positive correlation between circulating LTF-specific IgG and RA. ICs between human LTF and LTF-specific IgG purified from patient sera or immunized rabbits and mice, but not control ICs, LTF or Abs alone, elicited strong production of TNF-α and IL-1β by freshly fractionated human peripheral blood monocytes and monocytes-derived macrophages. Furthermore, LTF-ICs utilized both membrane-anchored CD14 and CD32a (FcγRIIa) to trigger monocyte activation in an internalization-, Toll-like receptor (TLR)4- and TLR9-dependent manner, and also that LTF-IC-induced cytokine production was blocked by specific inhibitors of caspase-1, NF-κB and MAPK. These results uncover a possible pathway for LTF-ICs perpetuating local inflammation and contributing to the pathogenesis of autoimmune diseases by triggering activation of infiltrating monocytes or tissue macrophages in vivo.

Chemical Tools for Studying TLR Signaling Dynamics

The detection of infectious pathogens is essential for the induction of antimicrobial immune responses. The innate immune system detects a wide array of microbes using a limited set of pattern-recognition receptors (PRRs). One family of PRRs with a central role in innate immunity are the Toll-like receptors (TLRs). Upon ligation, these receptors initiate signaling pathways culminating in the release of pro-inflammatory cytokines and/or type I interferons (IFN-I). In recent years, it has become evident that the specific subcellular location and timing of TLR activation affect signaling outcome. The subtlety of this signaling has led to a growing demand for chemical tools that provide the ability to conditionally control TLR activation. In this review, we survey current models for TLR signaling in time and space, discuss how chemical tools have contributed to our understanding of TLR ligands, and describe how they can aid further elucidation of the dynamic aspects of TLR signaling.

In Vivo Chronic Stimulation Unveils Autoreactive Potential of Wiskott-Aldrich Syndrome Protein-Deficient B Cells

Wiskott–Aldrich syndrome (WAS) is a primary immunodeficiency caused by mutations in the gene encoding the hematopoietic-specific WAS protein (WASp). WAS is frequently associated with autoimmunity, indicating a critical role of WASp in maintenance of tolerance. The role of B cells in the induction of autoreactive immune responses in WAS has been investigated in several settings, but the mechanisms leading to the development of autoimmune manifestations have been difficult to evaluate in the mouse models of the disease that do not spontaneously develop autoimmunity. We performed an extensive characterization of Was^−/− mice that provided evidence of the potential alteration in B cell selection, because of the presence of autoantibodies against double-stranded DNA, platelets, and tissue antigens. To uncover the mechanisms leading to the activation of the potentially autoreactive B cells in Was^−/− mice, we performed in vivo chronic stimulations with toll-like receptors agonists (LPS and CpG) and apoptotic cells or infection with lymphocytic choriomeningitis virus. All treatments led to increased production of autoantibodies, increased proteinuria, and kidney tissue damage in Was^−/− mice. These findings demonstrate that a lower clearance of pathogens and/or self-antigens and the resulting chronic inflammatory state could cause B cell tolerance breakdown leading to autoimmunity in WAS.

Membrane targeting of TIRAP is negatively regulated by phosphorylation in its phosphoinositide-binding motif

Pathogen-activated Toll-like receptors (TLRs), such as TLR2 and TLR4, dimerize and move laterally across the plasma membrane to phosphatidylinositol (4,5)-bisphosphate-enriched domains. At these sites, TLRs interact with the TIR domain-containing adaptor protein (TIRAP), triggering a signaling cascade that leads to innate immune responses. Membrane recruitment of TIRAP is mediated by its phosphoinositide (PI)-binding motif (PBM). We show that TIRAP PBM transitions from a disordered to a helical conformation in the presence of either zwitterionic micelles or monodispersed PIs. TIRAP PBM bound PIs through basic and nonpolar residues with high affinity, favoring a more ordered structure. TIRAP is phosphorylated at Thr28 within its PBM, which leads to its ubiquitination and degradation. We demonstrate that phosphorylation distorts the helical structure of TIRAP PBM, reducing PI interactions and cell membrane targeting. Our study provides the basis for TIRAP membrane insertion and the mechanism by which it is removed from membranes to avoid sustained innate immune responses.

Bacterial translocation in critical illness

Bacterial translocation involves the passage of intestinal bacteria to extraintestinal sites and has been shown to increase morbidity and mortality in critical illness. This review outlines the pathophysiology of bacterial translocation, host defence mechanisms, and reviews the evidence for the clinical management of critically ill patients in order to minimise the negative outcomes associated with bacterial translocation.

Extracellular Hsp70 Enhances Mesoangioblast Migration via an Autocrine Signaling Pathway

Mouse mesoangioblasts are vessel-associated progenitor stem cells endowed with the ability of multipotent mesoderm differentiation. Therefore, they represent a promising tool in the regeneration of injured tissues. Several studies have demonstrated that homing of mesoangioblasts into blood and injured tissues are mainly controlled by cytokines/chemokines and other inflammatory factors. However, little is known about the molecular mechanisms regulating their ability to traverse the extracellular matrix (ECM). Here, we demonstrate that membrane vesicles released by mesoangioblasts contain Hsp70, and that the released Hsp70 is able to interact by an autocrine mechanism with Toll-like receptor 4 (TLR4) and CD91 to stimulate migration. We further demonstrate that Hsp70 has a positive role in regulating matrix metalloproteinase 2 (MMP2) and MMP9 expression and that MMP2 has a more pronounced effect on cell migration, as compared to MMP9. In addition, the analysis of the intracellular pathways implicated in Hsp70 regulated signal transduction showed the involvement of both PI3K/AKT and NF-κB. Taken together, our findings present a paradigm shift in our understanding of the molecular mechanisms that regulate mesoangioblast stem cells ability to traverse the extracellular matrix (ECM). J. Cell. Physiol. 232: 1845-1861, 2017. © 2016 Wiley Periodicals, Inc.

Protective Effects of Platycodin D on Lipopolysaccharide-Induced Acute Lung Injury by Activating LXRα-ABCA1 Signaling Pathway

The purpose of this study was to investigate the protective effects of platycodin D (PLD) on lipopolysaccharide (LPS)-induced acute lung injury (ALI) and clarify the possible mechanism. An LPS-induced ALI model was used to confirm the anti-inflammatory activity of PLD in vivo. The A549 lung epithelial cells were used to investigate the molecular mechanism and targets of PLD in vitro. In vivo, the results showed that PLD significantly attenuated lung histopathologic changes, myeloperoxidase activity, and pro-inflammatory cytokines levels, including TNF-α, IL-1β, and IL-6. In vitro, PLD inhibited LPS-induced IL-6 and IL-8 production in LPS-stimulated A549 lung epithelial cells. Western blot analysis showed that PLD suppressed LPS-induced NF-κB and IRF3 activation. Moreover, PLD did not act though affecting the expression of TLR4. We also showed that PLD disrupted the formation of lipid rafts by depleting cholesterol and prevented LPS-induced TLR4 trafficking to lipid rafts, thereby blocking LPS-induced inflammatory response. Finally, PLD activated LXRα-ABCA1-dependent cholesterol efflux. Knockdown of LXRα abrogated the anti-inflammatory effects of PLD. The anti-inflammatory effects of PLD was associated with upregulation of the LXRα-ABCA1 pathway, which resulted in disrupting lipid rafts by depleting cholesterol and reducing translocation of TLR4 to lipid rafts.

Microbe-inducible trafficking pathways that control Toll-like receptor signaling

The receptors of the mammalian innate immune system are designed for rapid microbial detection, and are located in organelles that are conducive to serve these needs. However, emerging evidence indicates that the sites of microbial detection are not the sites of innate immune signal transduction. Rather, microbial detection triggers the movement of receptors to regions of the cell where factors called sorting adaptors detect active receptors and promote downstream inflammatory responses. These findings highlight the critical role that membrane trafficking pathways play in the initiation of innate immunity to infection. In this review, we describe pathways that promote the microbe-inducible endocytosis of Toll-like receptors (TLRs), and the microbe-inducible movement of TLRs between intracellular compartments. We highlight a new class of proteins called Transporters Associated with the eXecution of Inflammation (TAXI), which have the unique ability to transport TLRs and their microbial ligands to signaling-competent regions of the cell, and we discuss the means by which the subcellular sites of signal transduction are defined.

Disruption of Lipid Raft Function Increases Expression and Secretion of Monocyte Chemoattractant Protein-1 in 3T3-L1 Adipocytes

The adipocyte is unique in its capacity to store lipids. In addition to triglycerides, the adipocyte stores a significant amount of cholesterol. Moreover, obese adipocytes are characterized by a redistribution of cholesterol with depleted cholesterol in the plasma membrane, suggesting that cholesterol perturbation may play a role in adipocyte dysfunction. We used methyl-β-cyclodextrin (MβCD), a molecule with high affinity for cholesterol, to rapidly deplete cholesterol level in differentiated 3T3-L1 adipocytes. We tested whether this perturbation altered adipocyte secretion of monocyte chemoattractant protein-1 (MCP-1), a chemokine that is elevated in obesity and is linked to obesity-associated chronic diseases. Depletion of cholesterol by MβCD increased MCP-1 secretion as well as the mRNA and protein levels, suggesting perturbation at biosynthesis and secretion. Pharmacological inhibition revealed that NF-κB, but not MEK, p38 and JNK, was involved in MβCD-stimulated MCP-1 biosynthesis and secretion in adipocytes. Finally, another cholesterol-binding drug, filipin, also induced MCP-1 secretion without altering membrane cholesterol level. Interestingly, both MβCD and filipin disturbed the integrity of lipid rafts, the membrane microdomains enriched in cholesterol. Thus, the depletion of membrane cholesterol in obese adipocytes may result in dysfunction of lipid rafts, leading to the elevation of proinflammatory signaling and MCP-1 secretion in adipocytes.

Lyn prevents aberrant inflammatory responses to Pseudomonas infection in mammalian systems by repressing a SHIP-1-associated signaling cluster

The pleiotropic Src kinase Lyn has critical roles in host defense in alveolar macrophages against bacterial infection, but the underlying mechanism for Lyn-mediated inflammatory response remains largely elusive. Using mouse Pseudomonas aeruginosa infection models, we observed that Lyn^-/- mice manifest severe lung injury and enhanced inflammatory responses, compared with wild-type littermates. We demonstrate that Lyn exerts this immune function through interaction with IL-6 receptor and cytoskeletal protein Ezrin via its SH2 and SH3 domains. Depletion of Lyn results in excessive STAT3 activation, and enhanced the Src homology 2-containing inositol-5-phopsphatase 1 (SHIP-1) expression. Deletion of SHIP-1 in Lyn^-/- mice (double knockout) promotes mouse survival and reduces inflammatory responses during P. aeruginosa infection, revealing the rescue of the deadly infectious phenotype in Lyn deficiency. Mechanistically, loss of SHIP-1 reduces NF-κB-dependent cytokine production and dampens MAP kinase activation through a TLR4-independent PI3K/Akt pathway. These findings reveal Lyn as a regulator for host immune response against P. aeruginosa infection through SHIP-1 and IL-6/STAT3 signaling pathway in alveolar macrophages.

Mammary inflammatory gene expression was associated with reproductive stage and regulated by docosahexenoic acid: in vitro and in vivo studies

Background

Periparturient mastitis is the most prevalent disease affecting lactating animals. However, it has long been relied on antibiotics to deal with mastitis, leading to a potential threat to food safety. This study was aimed to investigate the expression of pro-inflammatory cytokines in mammary glands of sows around parturition when mastitis and oxidative stress usually occur, and evaluate the anti-inflammatory effect of docosahexenoic acid (DHA) in porcine mammary epithelial cells (PMEC) challenged by lipopolysaccharide (LPS).

Methods

Mammary tissues and blood samples were collected from seven pregnant sows at different reproductive stages. Primarily cultured PMEC at passage 4 were assigned to four treatments: basal medium (control), basal medium with LPS (10 μg/mL) (LPS treatment), basal medium with LPS (10 μg/mL) and DHA (100 or 200 μM) (LPS + DHA treatments), and cell samples were harvested after 24 h incubation. The measurements included oxidative stress markers in blood samples and gene expression in mammary tissues and PMEC samples.

Results

Serum α-tocopherol concentration was lower at parturition than at day 90 of gestation and day 28 post parturition, while serum malondialdehyde concentration was higher at day 28 post parturition than at day 90 of gestation. Higher interleukin (IL)-1β mRNA abundance while lower LPS binding protein mRNA abundance in mammary tissues were observed at day 90 of gestation compared with that at parturition and at day 28 and 35 post parturition. Mammary tumor necrosis factor (TNF)-α mRNA abundance were lower at parturition than at day 90 of gestation and day 28 and 35 post parturition, whereas mammary IL-8 mRNA abundance were lower at parturition than at day 35 post parturition. In the PMEC experiment, compared with the control, increased mRNA abundances of Toll-like receptor (TLR)-4 downstream target, myeloid differentiation factor 88 (MyD88), IL-6 and IL-8 were observed in LPS treatment, whereas DHA appeared to decrease mRNA abundances of MyD88, IL-6 and IL-8 induced by LPS.

Conclusions

The down-regulated expression of pro-inflammatory cytokines in mammary tissues and aggravated systemic oxidative stress at parturition suggest that sows are in a vulnerable status during periparturient period. DHA appears to attenuate inflammatory responses in LPS-challenged PMEC through modulation of TLR4 signalling pathway.

The Physiological Roles of Extracellular Metallothionein

Metallothionein (MT) is a low-molecular-weight protein with a number of roles to play in cellular homeostasis. MT is synthesized as a consequence of a variety of cellular stressors, and has been found in both intracellular compartments and in extracellular spaces. The intracellular pool of this cysteine-rich protein can act as a reservoir of essential heavy metals, as a scavenger of reactive oxygen and nitrogen species, as an antagonist of toxic metals and organic molecules, and as a regulator of transcription factor activity. The presence of MT outside of cells due to the Influence of stressors suggests that this protein may make important contributions as a “danger signal” that influences the management of responses to cellular damage. While conventional wisdom has held that extracellular MT is the result of cell death or leakage from stressed cells, there are numerous examples of selective release of proteins by nontraditional mechanisms, including stress response proteins. This suggests that MT may similarly be selectively released, and that the pool of extracellular MT represents an important regulator of various cellular functions. For example, extracellular MT has effects both on the severity of autoimmune disease, and on the development of adaptive immune functions. Extracellular MT may operate as a chemotactic factor that governs the trafficking of inflammatory cells that move to resolve damaged tissues, as a counter to extracellular oxidant-mediated damage, and as a signal that influences the functional behavior of wounded cells. A thorough understanding of the mechanisms of MT release from cells, the conditions under which MT is released to the extracellular environment, and the ways in which MT Interacts with sensitive cells may both illuminate our understanding of an important control mechanism that operates in stressful conditions, and should indicate new opportunities for therapeutic management via the manipulation of this pool of extracellular MT.

Lipid raft-dependent endocytosis negatively regulates responsiveness of J774 macrophage-like cells to LPS by down regulating the cell surface expression of LPS receptors

Acting through CD14 and TLR4/MD-2, lipopolysaccharide (LPS) triggers strong pro-inflammatory activation of macrophages, which, if not appropriately controlled, may lead to lethal septic shock. Therefore, numerous mechanisms of negative regulation of responses to LPS exist, but whether they include down-regulation of LPS receptors is not clear. We have found that in J774 cells, the clathrin-dependent endocytic pathway enables activation of TRIF-dependent TLR4 signaling within endosomes, but is not associated with the down-regulation of TLR4 or CD14 surface expression. In contrast, lipid raft-dependent endocytosis negatively regulates the basal cell surface expression of LPS receptors and, consequently, responsiveness to LPS. Together with observations that treatments, known to selectively disrupt lipid rafts, do not inhibit LPS-stimulated cytokine production, our results suggest that lipid rafts may serve as sites in which LPS receptors are sorted for endocytosis, rather than being platforms for the assembly of TLR4-centered signaling complexes, as suggested previously.

Comparative Endocytosis Mechanisms and Anticancer Effect of HPMA Copolymer- and PAMAM Dendrimer-MTCP Conjugates for Photodynamic Therapy

Polymer architecture can influence biodistribution and the mode of presentation of bioactive agents to cells. Herein delivery, loading efficiency, and mode of cellular entry of polymer conjugates of the photosensitizer Meso-Tetra (4-Carboxyphenyl) Porphyrine (MTCP) are examined when attached to hyperbranched amine terminated poly(amido amine) (PAMAM) dendrimer or random coil linear N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer containing free amines in the side chains. The in vitro dark cytotoxicity and phototoxicity of MTCP and related conjugates are assessed on mouth epidermal carcinoma (KB) and human adenocarcinoma alveolar basal epithelial (A549) cells. Phototoxicity of polymeric conjugates increases by ≈100 and 4000 fold in KB and A549 cells compared with nonconjugated MTCP. The increase in phototoxicity activity is shown to result from increased rate of cellular uptake, whereas, cellular internalization of MTCP is negligible in comparison with the conjugated forms. The results of this study suggest the superiority of amine-terminated HPMA copolymer versus PAMAM dendrimer under study for delivery of MTCP. Treatment with various pharmacological inhibitors of endocytosis shows that polymer architecture influences the mechanism of cellular uptake of the conjugated photosensitizer. Results show that polymeric conjugates of MTCP improve solubility, influence the route and the rate of cellular internalization, and drastically enhance the uptake of the photosensitizer.

Induction of Dendritic Cell Maturation and Activation by a Potential Adjuvant, 2-Hydroxypropyl-β-Cyclodextrin

2-Hydroxypropyl-β-cyclodextrin (HP-β-CD) is a chemically modified cyclic oligosaccharide produced from starch that is commonly used as an excipient. Although HP-β-CD has been suggested as a potential adjuvant for vaccines, its immunological properties and mechanism of action have yet to be characterized. In the present study, we investigated the maturation and activation of human dendritic cells (DCs) treated with HP-β-CD. We found that DCs stimulated with HP-β-CD exhibited a remarkable upregulation of costimulatory molecules, MHC proteins, and PD-L1/L2. In addition, the production of cytokines, such as TNF-α, IL-6, and IL-10, was modestly increased in DCs when treated with HP-β-CD. Furthermore, HP-β-CD-sensitized DCs markedly induced the proliferation and activation of autologous T lymphocytes. HP-β-CD also induced a lipid raft formation in DCs. In contrast, filipin, a lipid raft inhibitor, attenuated HP-β-CD-induced DC maturation, the cytokine expression, and the T lymphocyte-stimulating activities. To determine the in vivo relevance of the results, we investigated the adjuvanticity of HP-β-CD and the modulation of DCs in a mouse footpad immunization model. When mice were immunized with ovalbumin in the presence of HP-β-CD through a hind footpad, serum ovalbumin-specific antibodies were markedly elevated. Concomitantly, DC populations expressing CD11c and MHC class II were increased in the draining lymph nodes, and the expression of costimulatory molecules was upregulated. Collectively, our data suggest that HP-β-CD induces phenotypic and functional maturation of DCs mainly mediated through lipid raft formation, which might mediate the adjuvanticity of HP-β-CD.

Epithelial Cholesterol Deficiency Attenuates Human Antigen R-linked Pro-inflammatory Stimulation via an SREBP2-linked Circuit

Patients with chronic intestinal ulcerative diseases, such as inflammatory bowel disease, tend to exhibit abnormal lipid profiles, which may affect the gut epithelial integrity. We hypothesized that epithelial cholesterol depletion may trigger inflammation-checking machinery via cholesterol sentinel signaling molecules whose disruption in patients may aggravate inflammation and disease progression. In the present study, sterol regulatory element-binding protein 2 (SREBP2) as the cholesterol sentinel was assessed for its involvement in the epithelial inflammatory responses in cholesterol-depleted enterocytes. Patients and experimental animals with intestinal ulcerative injuries showed suppression in epithelial SREBP2. Moreover, SREBP2-deficient enterocytes showed enhanced pro-inflammatory signals in response to inflammatory insults, indicating regulatory roles of SREBP2 in gut epithelial inflammation. However, epithelial cholesterol depletion transiently induced pro-inflammatory chemokine expression regardless of the well known pro-inflammatory nuclear factor-κB signals. In contrast, cholesterol depletion also exerts regulatory actions to maintain epithelial homeostasis against excessive inflammation via SREBP2-associated signals in a negative feedback loop. Mechanistically, SREBP2 and its induced target EGR-1 were positively involved in induction of peroxisome proliferator-activated receptor γ (PPARγ), a representative anti-inflammatory transcription factor. As a crucial target of the SREBP2-EGR-1-PPARγ-associated signaling pathways, the mRNA stabilizer, human antigen R (HuR) was retained in nuclei, leading to reduced stability of pro-inflammatory chemokine transcripts. This mechanistic investigation provides clinical insights into protective roles of the epithelial cholesterol deficiency against excessive inflammatory responses via the SREBP2-HuR circuit, although the deficiency triggers transient pro-inflammatory signals.

Phospholipid flippases attenuate LPS-induced TLR4 signaling by mediating endocytic retrieval of Toll-like receptor 4

P4-ATPases are lipid flippases that catalyze the transport of phospholipids to create membrane phospholipid asymmetry and to initiate the biogenesis of transport vesicles. Here we show, for the first time, that lipid flippases are essential to dampen the inflammatory response and to mediate the endotoxin-induced endocytic retrieval of Toll-like receptor 4 (TLR4) in human macrophages. Depletion of CDC50A, the β-subunit that is crucial for the activity of multiple P4-ATPases, resulted in endotoxin-induced hypersecretion of proinflammatory cytokines, enhanced MAP kinase signaling and constitutive NF-κB activation. In addition, CDC50A-depleted THP-1 macrophages displayed reduced tolerance to endotoxin. Moreover, endotoxin-induced internalization of TLR4 was strongly reduced and coincided with impaired endosomal MyD88-independent signaling. The phenotype of CDC50A-depleted cells was also induced by separate knockdown of two P4-ATPases, namely ATP8B1 and ATP11A. We conclude that lipid flippases are novel elements of the innate immune response that are essential to attenuate the inflammatory response, possibly by mediating endotoxin-induced internalization of TLR4.

LPS-Induced Macrophage Activation and Plasma Membrane Fluidity Changes are Inhibited Under Oxidative Stress

Macrophage activation is essential for a correct and efficient response of innate immunity. During oxidative stress membrane receptors and/or membrane lipid dynamics can be altered, leading to dysfunctional cell responses. Our aim is to analyze membrane fluidity modifications and cell function under oxidative stress in LPS-activated macrophages. Membrane fluidity of individual living THP-1 macrophages was evaluated by the technique two-photon microscopy. LPS-activated macrophage function was determined by TNFα secretion. It was shown that LPS activation causes fluidification of macrophage plasma membrane and production of TNFα. However, oxidative stress induces rigidification of macrophage plasma membrane and inhibition of cell activation, which is evidenced by a decrease of TNFα secretion. Thus, under oxidative conditions macrophage proinflammatory response might develop in an inefficient manner.

Receptor cluster formation during activation by bacterial products

The recognition of bacterial products, such as lipopolysaccharide (LPS) by the innate immune system lead to a strong pro-inflammatory response that can eventually lead to fatal sepsis syndrome in humans. Although CD14 and TLR4 have been identified as the key molecules involved in LPSinduced signal transduction, accumulating evidence indicates that multiple receptors are also involved. Our group has recently identified a cluster of receptors, involving heat-shock proteins 70 and 90, chemokine receptor 4 as well as growth differentiation factor 5, that are formed following LPS stimulation. In addition, we present data demonstrating that these molecules associate with TLR4 and accumulate in membrane microdomains following LPS ligation. Our results suggest that the entire bacterial recognition is based around the recruitment of multiple signalling molecules, in addition to CD14 and TLRs, within the lipid rafts. We propose that different combinational associations of receptors within activation clusters determine the different responses to a variety of bacterial stimuli.