Tetraacylated lipid A and paclitaxel-selective activation of TLR4/MD-2 conferred through hydrophobic interactions

Macrophages in tumor cell migration and metastasis

Tumor-associated macrophages (TAMs) are a phenotypically diverse, highly plastic population of cells in the tumor microenvironment (TME) that have long been known to promote cancer progression. In this review, we summarize TAM ontogeny and polarization, and then explore how TAMs enhance tumor cell migration through the TME, thus facilitating metastasis. We also discuss how chemotherapy and host factors including diet, obesity, and race, impact TAM phenotype and cancer progression. In brief, TAMs induce epithelial-mesenchymal transition (EMT) in tumor cells, giving them a migratory phenotype. They promote extracellular matrix (ECM) remodeling, allowing tumor cells to migrate more easily. TAMs also provide chemotactic signals that promote tumor cell directional migration towards blood vessels, and then participate in the signaling cascade at the blood vessel that allows tumor cells to intravasate and disseminate throughout the body. Furthermore, while chemotherapy can repolarize TAMs to induce an anti-tumor response, these cytotoxic drugs can also lead to macrophage-mediated tumor relapse and metastasis. Patient response to chemotherapy may be dependent on patient-specific factors such as diet, obesity, and race, as these factors have been shown to alter macrophage phenotype and affect cancer-related outcomes. More research on how chemotherapy and patient-specific factors impact TAMs and cancer progression is needed to refine treatment strategies for cancer patients.

Trimetazidine alleviates paclitaxel-induced peripheral neuropathy through modulation of TLR4/p38/NFκB and klotho protein expression

Chemotherapy-induced peripheral neuropathy is a common adverse effect associated with a number of chemotherapeutic agents including paclitaxel (PTX) which is commonly used in a wide range of solid tumors. Development of PTX-induced peripheral neuropathy (PIPN) during cancer treatment requires dose reduction which limits its clinical benefits. This study is conducted to investigate the role of toll like receptor-4 (TLR4) and p38 signaling and Klotho protein expression in PIPN and the role of Trimetazidine (TMZ) in this pathway. Sixty-four male Swiss albino mice were divided into 4 groups (n = 16); Group (1) injected intraperitoneally (IP) with ethanol/tween 80/saline for 8 successive days. Group (2) received TMZ (5 mg/kg, IP, day) for 8 successive days. Group (3) treated with 4 doses of PTX (4.5 mg/kg, IP) every other day over a period of 8 days. Group (4) received a combination of TMZ as group 2 and PTX as group 3. The Effect of TMZ on the antitumor activity of PTX was studied in another set of mice-bearing Solid Ehrlich Carcinoma (SEC) that was similarly divided as the above-mentioned set. TMZ mitigated tactile allodynia, thermal hypoalgesia, numbness and fine motor dyscoordination associated with PTX in Swiss mice. The results of the current study show that the neuroprotective effect of TMZ can be attributed to inhibition of TLR4/p38 signaling which also includes a reduction in matrix metalloproteinase-9 (MMP9) protein levels as well as the proinflammatory interleukin-1β (IL-1β) and preserving the levels of the anti-inflammatory IL-10. Moreover, the current study is the first to demonstrate that PTX reduces the neuronal levels of klotho protein and showed its modulation via cotreatment with TMZ. In addition, this study showed that TMZ neither alter the growth of SEC nor the antitumor activity of PTX. In conclusion, we suggest that (1) Inhibition of Klotho protein and upregulation of TLR4/p38 signals in nerve tissues may contribute to PIPN. (2) TMZ attenuates PIPN by modulating TLR4/p38 and Klotho protein expression in without interfering with its antitumor activity.

Nalmefene non-enantioselectively targets myeloid differentiation protein 2 and inhibits toll-like receptor 4 signaling: wet-lab techniques and in silico simulations

Nalmefene is an opiate derivative having a similar structure to naltrexone. Recent evidence suggests that nalmefene, acting as the innate immune protein toll-like receptor 4 (TLR4) antagonist, effectively reduces the injury of lung ischemia-reperfusion and prevents neuroinflammation. However, the molecular recognition mechanism, especially the enantioselectivity, of nalmefene by the innate immune receptor is not well understood. Herein in vitro assays and in silico simulations were performed to dissect the innate immune recognition of nalmefene at the atomic, molecular, and cellular levels. Biophysical binding experiments and molecular dynamic simulations provide direct evidence that (-)-nalmefene and (+)-nalmefene bind to the hydrophobic cavity of myeloid differentiation protein 2 (MD-2) and behave similarly, which is primarily driven by hydrophobic interactions. The inhibition activity and the calculated binding free energies show that no enantioselectivity was observed during the interaction of nalmefene with MD-2 as well as the inhibition of TLR4 signaling. Interestingly, nalmefene showed ∼6 times better TLR4 antagonisic activity than naltrexone, indicating that the bioisosteric replacement with the methylene group is critical for the molecular recognition of nalmefene by MD-2. In all, this study provides molecular insight into the innate immune recognition of nalmefene, which demonstrates that nalmefene is non-enantioselectively sensed by MD-2.

Elicited soybean extract attenuates proinflammatory cytokines expression by modulating TLR3/TLR4 activation in high-fat, high-fructose diet mice

BACKGROUND

The high-fat, high-fructose diet (HFFD) provokes overnutrition and inflammation directly, mainly through Toll-like receptors (TLRs). Soybean (Glycine max L.) contains isoflavone that can be transformed into glyceollin by microbial and physical stimuli. Glyceollin possesses many beneficial effects on health.

OBJECTIVE

This study evaluates the beneficial effect of soybean extract elicited by Saccharomyces cerevisiae and light (ESE) on dendritic cells (DCs) profile and naïve T cells in HFFD mice.

MATERIALS AND METHODS

Female Balb/C mice were fed with HFFD for 24 weeks then orally administered with simvastatin 2.8 mg/kg BW or ESE 78, 104, and 130 mg/kg BW at the last four weeks. The expression of splenic CD11c⁺TLR3⁺, CD11c⁺TLR4⁺, NFκB⁺, CD11c⁺IL-17⁺, CD11c⁺TNF-α⁺, CD4⁺CD62L⁺, and CD8⁺CD62L⁺ subsets was measured by flow cytometry. The molecular docking has been measured using Pyrx 0.8, displayed in PyMol and Biovia Discovery Studio.

RESULT

HFFD significantly increased CD11c⁺TLR3⁺, CD11c⁺TLR4⁺, NFκB⁺, CD11c⁺IL-17⁺, CD11c⁺TNF-α⁺ expression and decreased CD4⁺CD62L⁺ and CD8⁺CD62L⁺ (p < 0.05) compared to normal diet (ND) groups. ESE reduced CD11c⁺TLR3⁺, CD11c⁺TLR4⁺, thereby decreasing NFκB⁺, as well as decreased the CD11c⁺IL-17⁺, CD11c⁺TNF-α⁺, and restores CD4⁺CD62L⁺ and CD8⁺CD62L⁺ subsets in HFFD mice. Glyceollin II exhibited the best binding affinity with an average energy of -7.3 kcal/mol to TLR3 and -7.9 kcal/mol to TLR4.

CONCLUSION

The bioactive compound in ESE act synergistically to modulate TLR3/TLR4 activation, reduced NFκB, IL-17, and TNF-α, and restores naïve T cells expression in HFFD mice. ESE was a favorable candidate to mitigate chronic inflammation.

Trichlorocarban induces developmental and immune toxicity to zebrafish (Danio rerio) by targeting TLR4/MyD88/NF-κB signaling pathway

Trichlorocarban (TCC) is ubiquitously detected in environmental matrices, while there is a paucity of information regarding its systemic toxicity. In the present study, we observed that TCC exposure led to high embryo mortality, delayed hatching and yolk absorption, as well as increased malformations, such as closure of swim sac and yolk sac edema. Meanwhile, TCC affected the formation and branch of subintestinal veins (SIVs), intersegmental vessels and posterior cardinal veins. Especially, the SIVs were shrunk, and their branches were reduced or even broken along with reduced coverage area. TCC-induced oxidative stress and excessive apoptosis resulted from abnormal expression of the anti/pro-apoptotic genes. Significant reduction in the number and aggregation function of immune cells proved that TCC had prominent immunotoxicity to zebrafish. TCC-targeted TLR4 signaling pathway was demonstrated by abnormal expression of the marker genes (tlr4, MyD88 and nf-κb) and release of the downstream inflammatory factors (TNF-α, IL-6, etc.). Inhibition of TLR4/MyD88/NF-κB pathway by an inhibitor (CA-4948) rescued the decreasing trend of the immune cells induced by TCC. Molecular docking results demonstrated that TCC could stably bind to TLR4 receptor to form hydrogen bonds and hydrophobic interactions with amino acids. Overall, these findings reveal the underlying molecular mechanisms on TCC-induced developmental and immune toxicity to zebrafish.

Exploring electrostatic patterns of human, murine, equine and canine TLR4/MD-2 receptors

Electrostatic interactions between phosphate anions and Toll-like receptor 4 / Myeloid differentiation factor-2 (TLR4/MD-2) protein complexes of human, murine, equine and canine species were computed. Such knowledge can provide mechanistic information about recognising LPS-like ligands, since anionic phosphate groups belong to the structural features of LPS with their diphosphorylated diglucosamine backbone. Sequence composition analyses, electrostatic interaction potentials and docked energies as well as molecular dynamics studies evaluated the phosphate interactions within the triangular LPS binding site (wedge). According to electrostatic analyses, human, horse and dog wedges possess phosphate-binding sites with indistinct positive and negative charge distributions, but the murine wedge shows a unique strong negative net charge at the site where antagonists bind in other species (Pan). Docking of a phosphate mono-anion (probe) confirmed its repulsion at this Pan site, but the Pag site of the murine wedge attracted the probe. It is occupied by phosphate groups of agonists in other species (Pag). Molecular dynamics trajectories show a variable degree of random walk across the wedges, that is, not following electrostatic preferences (neither Pag nor Pan). In summary, two opposing electrostatic patterns exist -murine versus human, equine and canine species - all of which reflect the potential dual activity mode of under-acylated ligands such as lipid IV_A.

MD-2 Homologue Recognizes the White Spot Syndrome Virus Lipid Component and Induces Antiviral Molecule Expression in Shrimp

The myeloid differentiation factor 2 (MD-2)-related lipid-recognition (ML) domain is found in multiple proteins, including MD-2, MD-1, Niemann-Pick disease type C2, and mite major allergen proteins. The significance of ML proteins in antibacterial signal transduction and in lipid metabolism has been well studied. However, their function in host-virus interaction remains poorly understood. In the current study, we found that the ML protein family is involved in resistance against white spot syndrome virus in kuruma shrimp, Marsupenaeus japonicus One member, which showed a high similarity to mammalian MD-2/MD-1 and was designated as ML1, participated in the antiviral response by recognizing cholesta-3,5-diene (CD), a lipid component of the white spot syndrome virus envelope. After recognizing CD, ML1 induced the translocation of Rel family NF-κB transcription factor Dorsal into the nucleus, resulting in the expression of Vago, an IFN-like antiviral cytokine in arthropods. Overall, this study revealed the significance of an MD-2 homologue as an immune recognition protein for virus lipids. The identification and characterization of CD-ML1-Dorsal-Vago signaling provided new insights into invertebrate antiviral immunity.

Hydroxysafflor Yellow A Alleviates Lipopolysaccharide-Induced Acute Respiratory Distress Syndrome in Mice

Hydroxysafflor yellow A (HSYA) is an effective ingredient of the Chinese herb Carthamus tinctorius L. The present study investigated the protective effect of HSYA on lipopolysaccharide (LPS)-induced acute respiratory distress syndrome in mice, and the underlying mechanisms involved. HSYA (14, 28, 56 mg/kg) was intraperitoneally injected to mice once daily from day 1 to 10 after LPS administration. HSYA attenuated the body weight loss, the augmented left index and the increase of pathologic changes in pulmonary inflammation caused by LPS. Treatment with HSYA also alleviated increased expressions of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, transforming growth factor (TGF)-β1, collagen (Col) I, Col III, α-smooth muscle actin (α-SMA), myeloid differentiation (MD)-2, Toll-like receptor 4 (TLR4) and cluster differentiation (CD)14 at the mRNA (RT-PCR) and protein levels (Western blot and enzyme-linked immuno sorbent assay). Moreover, HSYA inhibited the elevated levels of nuclear factor (NF)-κB and α-SMA in lung tissue (immunohistochemistry), and alleviated the slight collagen deposition in pulmonary tissues (Masson's trichrome staining). HSYA inhibited the specific binding of fluorescein isothiocyanate (FITC)-LPS on human lung epithelial cell line (A549) or human umbilical vein cell line (Eahy926) cells (flow cytometry). These findings suggested that HSYA has a protective effect on acute respiratory distress syndrome (ARDS) induced by LPS through blocking the TLR4/NF-κB pathway, and that the TLR4 receptor might be a target of HSYA on the cell membrane.

Monophosphoryl lipid A-induced pro-inflammatory cytokine expression does not require CD14 in primary human dendritic cells

OBJECTIVE

To elucidate if TLR4-mediated MyD88 and TRIF signalling by the clinically applicable Lipopolysaccharide (LPS)-derivative monophosphoryl lipid A (MPLA) in primary human dendritic cells requires LPS cofactors LPS-binding protein (LBP) and CD14.

METHODS

Cytokine production by monocyte-derived DCs stimulated with MPLA or LPS was determined using ELISA. To investigate involvement of CD14 for action of LPS or MPLA, CD14 was inhibited using blocking antibodies or down-modulated using specific siRNA. To assess involvement of LBP monocyte-derived DCs were stimulated in serum-free culture medium in absence or presence of purified LBP.

RESULTS

LBP and CD14 are not required for and do not enhance the capacity of MPLA to induce MyD88- and TRIF-dependent pro-inflammatory IL-6 and TNF-α. Interestingly, although CD14 is required for TRIF-dependent downstream events in mice, we show that in human CD14 is redundant for MPLA-induced TRIF-dependent chemokine production.

CONCLUSIONS

These findings provide novel insight in the modes of action of MPLA in human and show that, compared to LPS, MyD88 and TRIF signalling in dendritic cells by MPLA is not mediated nor amplified by TLR4 cofactors. This gives insight why MPLA induces immune activation without provoking toxicity in human and clarifies why MPLA can be used as activating compound for clinically applicable immuno-activatory cellular products grown in serum-free regimens.

Bordetella pertussis Lipid A Recognition by Toll-like Receptor 4 and MD-2 Is Dependent on Distinct Charged and Uncharged Interfaces

Lipid A in LPS activates innate immunity through the Toll-like receptor 4 (TLR4)-MD-2 complex on host cells. Variation in lipid A has significant consequences for TLR4 activation and thus may be a means by which Gram-negative bacteria modulate host immunity. However, although even minor changes in lipid A structure have been shown to affect downstream immune responses, the mechanism by which the TLR4-MD-2 receptor complex recognizes these changes is not well understood. We previously showed that strain BP338 of the human pathogen Bordetella pertussis, the causative agent of whooping cough, modifies its lipid A by the addition of glucosamine moieties that promote TLR4 activation in human, but not mouse, macrophages. Using site-directed mutagenesis and an NFκB reporter assay screen, we have identified several charged amino acid residues in TLR4 and MD-2 that are important for these species-specific responses; some of these are novel for responses to penta-acyl B. pertussis LPS, and their mutation does not affect the response to hexa-acylated Escherichia coli LPS or tetra-acylated lipid IVA. We additionally show evidence that suggests that recognition of penta-acylated B. pertussis lipid A is dependent on uncharged amino acids in TLR4 and MD-2 and that this is true for both human and mouse TLR4-MD-2 receptors. Taken together, we have demonstrated that the TLR4-MD-2 receptor complex recognizes variation in lipid A molecules using multiple sites for receptor-ligand interaction and propose that host-specific immunity to a particular Gram-negative bacterium is, at least in part, mediated by very subtle tuning of one of the earliest interactions at the host-pathogen interface.

Purified monomeric ligand.MD-2 complexes reveal molecular and structural requirements for activation and antagonism of TLR4 by Gram-negative bacterial endotoxins

A major focus of work in our laboratory concerns the molecular mechanisms and structural bases of Gram-negative bacterial endotoxin recognition by host (e.g., human) endotoxin-recognition proteins that mediate and/or regulate activation of Toll-like receptor (TLR) 4. Here, we review studies of wild-type and variant monomeric endotoxin.MD-2 complexes first produced and characterized in our laboratories. These purified complexes have provided unique experimental reagents, revealing both quantitative and qualitative determinants of TLR4 activation and antagonism. This review is dedicated to the memory of Dr. Theresa L. Gioannini (1949-2014) who played a central role in many of the studies and discoveries that are reviewed.

Insights into the species-specific TLR4 signaling mechanism in response to Rhodobacter sphaeroides lipid A detection

TLR4 in complex with MD2 senses the presence of lipid A (LA) and initiates a signaling cascade that curb the infection. This complex is evolutionarily conserved and can initiate the immune system in response to a variety of LAs. In this study, molecular dynamics simulation (25 ns) was performed to elucidate the differential behavior of TLR4/MD2 complex in response to Rhodobacter sphaeroides lipid A (RsLA). Penta-acyl chain-containing RsLA is at the verge of agonist (6 acyl-chains) and antagonist (4 acyl-chains) structure, and activates the TLR4 pathway in horses and hamsters, while inhibiting in humans and murine. In the time-evolved coordinates, the promising factors that dictated the differential response included the local and global mobility pattern of complexes, solvent-accessible surface area of ligand, and surface charge distributions of TLR4 and MD2. We showed that the GlcN1-GlcN2 backbone acquires agonist (3FXI)-like configurations in horses and hamsters, while acquiring antagonist (2E59)-like configurations in humans and murine systems. Moreover, analysis of F126 behavior in the MD2 F126 loop (amino acids 123-129) and loop EF (81-89) suggested that certain sequence variations also contribute to species-specific response. This study underlines the TLR4 signaling mechanism and provides new therapeutic opportunities.

Molecular and cellular regulation of toll-like receptor-4 activity induced by lipopolysaccharide ligands

As well as being the primary signaling receptor for bacterial endotoxin or lipopolysaccharide Toll-like receptor-4 function is modulated by numerous factors not only in the context of microbial pathogenesis but also autoimmune and allergic diseases. TLR4 is subject to multiple levels of endogenous control and regulation from biosynthesis and trafficking to signal transduction and degradation. On the other hand regulation of TLR4 activity breaks down during Gram −ve sepsis leading to systemic damage, multi organ failure, and death. In this article, we review how TLR4 traffics from the early secretory pathway, the cis/trans Golgi to the cell surface and endolysosomal compartments. We will present evidence about how these processes influence signaling and can potentially lead to increased sensitivity to ligand-dependent activation as well as ligand-independent constitutive activation that may contribute to pathogenesis in sepsis. We will also discuss how sustained signaling may be coupled to endocytosis and consider the potential molecular mechanisms of immuno-modulators that modify TLR4 signaling function including the cat allergen FelD1 and endogenous protein ligands such as the extracellular matrix protein tenascin C and calprotectin (MRP8/14).

The molecular mechanism of species-specific recognition of lipopolysaccharides by the MD-2/TLR4 receptor complex

Lipid A, a component of bacterial lipopolysaccharide, is a conserved microbe-associated molecular pattern that activates the MD-2/TLR4 receptor complex. Nevertheless, bacteria produce lipid A molecules of considerable structural diversity. The human MD-2/TLR4 receptor most efficiently recognizes hexaacylated bisphosphorylated lipid A produced by enterobacteria, but in some animal species the immune response can be elicited also by alternative lipid A varieties, such as tetraacylated lipid IVa or pentaacylated lipid A of Rhodobacter spheroides. Several crystal structures revealed that hexaacylated lipid A and tetraacylated lipid IVa activate the murine MD-2/TLR4 in a similar manner, but failed to explain the antagonistic vs. agonistic activity of lipid IVa in the human vs. equine receptor, respectively. Targeted mutagenesis studies of the receptor complex revealed intricate combination of electrostatic and hydrophobic interactions primarily within the MD-2 co-receptor, but with a contribution of TLR4 as well, that contribute to species-specific recognition of lipid A. We will review current knowledge regarding lipid A diversity and species-specific activation of the MD-2/TLR4 receptor complex in different species (e.g. human, mouse or equine) by lipid A varieties.