Ligand Recognition by the Macrophage Galactose-Type C-Type Lectin: Self or Non-Self?-A Way to Trick the Host's Immune System

The cells and numerous macromolecules of living organisms carry an array of simple and complex carbohydrates on their surface, which may be recognized by many types of proteins, including lectins. Human macrophage galactose-type lectin (MGL, also known as hMGL/CLEC10A/CD301) is a C-type lectin receptor expressed on professional antigen-presenting cells (APCs) specific to glycans containing terminal GalNAc residue, such as Tn antigen or LacdiNAc but also sialylated Tn antigens. Macrophage galactose-type lectin (MGL) exhibits immunosuppressive properties, thus facilitating the maintenance of immune homeostasis. Hence, MGL is exploited by tumors and some pathogens to trick the host immune system and induce an immunosuppressive environment to escape immune control. The aims of this article are to discuss the immunological outcomes of human MGL ligand recognition, provide insights into the molecular aspects of these interactions, and review the MGL ligands discovered so far. Lastly, based on the human fetoembryonic defense system (Hu-FEDS) hypothesis, this paper raises the question as to whether MGL-mediated interactions may be relevant in the development of maternal tolerance toward male gametes and the fetus.

Site-Specific and Multiple Fluorogenic Metabolic Glycan Labeling and Glycoproteomic Profiling in Live Cells

Multicolor labeling for monitoring the intracellular localization of the same target type in the native environment using chemical fluorescent dyes is a challenging task. This approach requires both bioorthogonal and biocompatible ligations with an excellent fluorescence signal-to-noise ratio. Here, we present a metabolic glycan labeling technique that uses homemade fluorogenic dyes to investigate glycosylation patterns in live cells. These dyes allowed us to demonstrate rapid and efficient simultaneous multilabeling of glycoconjugates with minimum fluorescence noise. Our results demonstrate that this approach is capable of not only probing sialylation and GlcNAcylation in cells but also specifically labeling the cell-surface and intracellular sialylated glycoconjugates in live cells. In particular, we performed site-specific dual-channel fluorescence imaging of extra and intracellular sialylated glycans in HeLa and PC9 cancer cells as well as identified fluorescently labeled sialylated glycoproteins and glycans by a direct enrichment approach combined with an MS-based proteomic analysis in the same experiment. In conclusion, this study provides multilabeling tools in cellular systems for simultaneous site-specific glycan imaging and glycoproteomic analysis to study potential cancer- and disease-associated glycoconjugates.

Endocannabinoid 2-Arachidonoylglycerol Synthesis and Metabolism at Neuronal Nuclear Matrix Fractions Derived from Adult Rat Brain Cortex

In this report, we describe the kinetics characteristics of the diacylglycerol lipase-α (DGLα) located at the nuclear matrix of nuclei derived from adult cortical neurons. Thus, using high-resolution fluorescence microscopy, classical biochemical subcellular fractionation, and Western blot techniques, we demonstrate that the DGLα enzyme is located in the matrix of neuronal nuclei. Furthermore, by quantifying the 2-arachidonoylglycerol (2-AG) level by liquid chromatography and mass spectrometry when 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG) was exogenously added as substrate, we describe the presence of a mechanism for 2-AG production through DGLα dependent biosynthesis with an apparent K_m (K_m^app) of 180 µM and a V_max of 1.3 pmol min^-1 µg^-1 protein. We also examined the presence of enzymes with hydrolytic and oxygenase activities that are able to use 2-AG as substrate, and described the localization and compartmentalization of the major 2-AG degradation enzymes, namely monoacylglycerol lipase (MGL), fatty acid amide hydrolase (FAAH), α/β-hydrolase domain 12 protein (ABHD12) and cyclooxygenase-2 (COX2). Of these, only ABHD12 exhibited the same distribution with respect to chromatin, lamin B1, SC-35 and NeuN as that described for DGLα. When 2-AG was exogenously added, we observed the production of arachidonic acid (AA), which was prevented by inhibitors (but not specific MGL or ABHD6 inhibitors) of the ABHD family. Overall, our results expand knowledge about the subcellular distribution of neuronal DGLα, and provide biochemical and morphological evidence to ensure that 2-AG is produced in the neuronal nuclear matrix. Thus, this work paves the way for proposing a working hypothesis about the role of 2-AG produced in neuronal nuclei.

Monoglyceride Lipase Deficiency Is Associated with Altered Thrombogenesis in Mice

Monoglyceride lipase (MGL) hydrolyzes monoacylglycerols (MG) to glycerol and one fatty acid. Among the various MG species, MGL also degrades 2-arachidonoylglycerol, the most abundant endocannabinoid and potent activator of the cannabinoid receptors 1 and 2. We investigated the consequences of MGL deficiency on platelet function using systemic (Mgl-/-) and platelet-specific Mgl-deficient (platMgl-/-) mice. Despite comparable platelet morphology, loss of MGL was associated with decreased platelet aggregation and reduced response to collagen activation. This was reflected by reduced thrombus formation in vitro, accompanied by a longer bleeding time and a higher blood volume loss. Occlusion time after FeCl3-induced injury was markedly reduced in Mgl-/- mice, which is consistent with contraction of large aggregates and fewer small aggregates in vitro. The absence of any functional changes in platelets from platMgl-/- mice is in accordance with lipid degradation products or other molecules in the circulation, rather than platelet-specific effects, being responsible for the observed alterations in Mgl-/- mice. We conclude that genetic deletion of MGL is associated with altered thrombogenesis.

Whole-cell tumor vaccines desialylated to uncover tumor antigenic Gal/GalNAc epitopes elicit anti-tumor immunity

BACKGROUND

Aberrant sialoglycans on the surface of tumor cells shield potential tumor antigen epitopes, escape recognition, and suppress activation of immunocytes. α2,3/α2,6Gal- and α2,6GalNAc (Gal/GalNAc)-linked sialic acid residues of sialoglycans could affect macrophage galactose-type lectins (MGL) mediated-antigen uptake and presentation and promote sialic acid-binding immunoglobulin-like lectins (Siglecs) mediated-immunosuppression. Desialylating sialoglycans on tumor cells could present tumor antigens with Gal/GalNAc residues and overcome glyco-immune checkpoints. Thus, we explored whether vaccination with desialylated whole-cell tumor vaccines (DWCTVs) triggers anti-tumor immunity in ovarian cancer (OC).

METHODS

Sialic acid (Sia) and Gal/GalNAc residues on OC A2780, OVCAR3, and ID8 cells treated with α2-3 neuraminidase (α2-3NA) and α2-6NA, and Sigec-9 or Siglec-E and MGL on DCs pulsed with desialylated OC cells were identified using flow cytometry (FCM); RT-qPCR determined IFNG expression of T cells, TRBV was sequenced using Sanger sequencing and cytotoxicity of αβ T cells was measured with LDH assay; Anti-tumor immunity in vivo was validated via vaccination with desialylated whole-cell ID8 vaccine (ID8 DWCTVs).

RESULTS

Gal/GalNAc but not Sia residues were significantly increased in the desialylated OC cells. α2-3NA-modified DWCTV increased MGL but decreased Siglec-9 or Siglec E expression on DCs. MGL^bright/Siglec-9^dim DCs significantly up-regulated IFNG expression and CD4/CD8 ratio of T cells and diversified the TCR repertoire of αβ T-cells that showed enhanced cytotoxic activity. Vaccination with α2-3NA-modified ID8 DWCTVs increased MGL^bright/Siglec-E^dim DCs in draining lymph nodes, limited tumor growth, and extended survival in tumor-challenged mice.

CONCLUSION

Desialylated tumor cell vaccine could promote anti-tumor immunity and provide a strategy for OC immunotherapy in a clinical setting.

Off-target effects of the lysosomal acid lipase inhibitors Lalistat-1 and Lalistat-2 on neutral lipid hydrolases

OBJECTIVES

Lysosomal acid lipase (LAL) is the key enzyme, which degrades neutral lipids at an acidic pH in lysosomes. The role of LAL in various cellular processes has mostly been studied in LAL-knockout mice, which share phenotypical characteristics with humans suffering from LAL deficiency. In vitro, the cell-specific functions of LAL have been commonly investigated by using the LAL inhibitors Lalistat-1 and Lalistat-2.

METHODS

We performed lipid hydrolase activity assays and serine hydrolase-specific activity-based labeling combined with quantitative proteomics to investigate potential off-target effects of Lalistat-1 and -2.

RESULTS

Pharmacological LAL inhibition but not genetic loss of LAL impairs isoproterenol-stimulated lipolysis as well as neutral triglyceride and cholesteryl ester hydrolase activities. Apart from LAL, Lalistat-1 and -2 also inhibit major cytosolic lipid hydrolases responsible for lipid degradation in primary cells at neutral pH through off-target effects. Their binding to the active center of the enzymes leads to a decrease in neutral lipid hydrolase activities in cells overexpressing the respective enzymes.

CONCLUSIONS

Our findings are critically important since they demonstrate that commonly used concentrations of these inhibitors are not suitable to investigate the role of LAL-specific lipolysis in lysosomal function, signaling pathways, and autophagy. The interpretation of their effects on lipid metabolism should be taken with caution and the applied inhibitor concentrations in cell culture studies should not exceed 1 μM.

Glycan-Lectin Interactions in Cancer and Viral Infections and How to Disrupt Them

Glycan-lectin interactions play an essential role in different cellular processes. One of their main functions is involvement in the immune response to pathogens or inflammation. However, cancer cells and viruses have adapted to avail themselves of these interactions. By displaying specific glycosylation structures, they are able to bind to lectins, thus promoting pathogenesis. While glycan-lectin interactions promote tumor progression, metastasis, and/or chemoresistance in cancer, in viral infections they are important for viral entry, release, and/or immune escape. For several years now, a growing number of investigations have been devoted to clarifying the role of glycan-lectin interactions in cancer and viral infections. Various overviews have already summarized and highlighted their findings. In this review, we consider the interactions of the lectins MGL, DC-SIGN, selectins, and galectins in both cancer and viral infections together. A possible transfer of ways to target and disrupt them might lead to new therapeutic approaches in different pathological backgrounds.

Increasing Endocannabinoid Tone Alters Anxiety-Like and Stress Coping Behaviour in Female Rats Prenatally Exposed to Valproic Acid

Given the sex differences evident in the prevalence of autism, there is an increased awareness of the importance of including females in autism research to determine sexual dimorphism and sex-specific treatments. Cannabinoids and endocannabinoid modulators have been proposed as potential novel treatments for autism-related symptoms; however, few studies to date have examined if these pharmacological agents elicit sex-specific effects. The aim of the present study was to use the valproic acid (VPA) model of autism to compare the behavioural responses of male and female rats and examine the effects of increasing endocannabinoid tone on the behavioural responses of VPA-exposed female rats. These data revealed that VPA-exposed male, but not female, rats exhibit reduced social responding in the three-chamber and olfactory habituation/dishabituation (OHD) test during adolescence. In comparison, VPA-exposed female, but not male, adolescent rats exhibited anxiety-like behaviour in the elevated plus maze (EPM) and open field test (OFT). In VPA-exposed female rats, increasing 2-AG levels augmented anxiety-like behaviour in the EPM and OFT, while increasing AEA levels reduced stress coping behaviour in the swim stress test. These data highlight sexual dimorphic behaviours in the VPA model and indicate that enhancing endocannabinoid levels may exacerbate negative affective behaviour in VPA-exposed females. Thus, considerations should be paid to the possible sex-specific effects of cannabinoids for the treatment of symptoms associated with autism.

Absence of Adiponutrin (PNPLA3) and Monoacylglycerol Lipase Synergistically Increases Weight Gain and Aggravates Steatohepatitis in Mice

Altered lipid metabolic pathways including hydrolysis of triglycerides are key players in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Whether adiponutrin (patatin-like phospholipase domain containing protein-3-PNPLA3) and monoacylglycerol lipase (MGL) synergistically contribute to disease progression remains unclear. We generated double knockout (DKO) mice lacking both Mgl and Pnpla3; DKO mice were compared to Mgl-/- after a challenge by high-fat diet (HFD) for 12 weeks to induce steatosis. Serum biochemistry, liver transaminases as well as histology were analyzed. Fatty acid (FA) profiling was assessed in liver and adipose tissue by gas chromatography. Markers of inflammation and lipid metabolism were analyzed. Bone marrow derived macrophages (BMDMs) were isolated and treated with oleic acid. Combined deficiency of Mgl and Pnpla3 resulted in weight gain on a chow diet; when challenged by HFD, DKO mice showed increased hepatic FA synthesis and diminished beta-oxidation compared to Mgl-/-.DKO mice exhibited more pronounced hepatic steatosis with inflammation and recruitment of immune cells to the liver associated with accumulation of saturated FAs. Primary BMDMs isolated from the DKO mice showed increased inflammatory activities, which could be reversed by oleic acid supplementation. Pnpla3 deficiency aggravates the effects of Mgl deletion on steatosis and inflammation in the liver under HFD challenge.

The Pathogenic Role of Demodex Mites in Rosacea: A Potential Therapeutic Target Already in Erythematotelangiectatic Rosacea?

Rosacea is a common facial dermatosis but its definition and classification are still unclear, especially in terms of its links with demodicosis. Triggers of rosacea (ultraviolet light, heat, spicy foods, alcohol, stress, microbes) are currently considered to induce a cascading innate and then adaptive immune response that gets out of control. Recent histological and biochemical studies support the concept that this inflammatory response is a continuum, already present from the onset of the disease, even when no clinical signs of inflammation are visible. The Demodex mite is beginning to be accepted as one of the triggers of this inflammatory cascade, and its proliferation as a marker of rosacea; moreover, the papulopustules of rosacea can be effectively treated with topical acaricidal agents. Demodex proliferation appears to be a continuum process in rosacea, and may not be clinically visible at the onset of the disease. Molecular studies suggest that Demodex may induce tolerogenic dendritic cells and collaborate with vascular endothelial growth factor (VEGF) to induce T cell exhaustion and favor its own proliferation. These interactions among VEGF, Demodex, and immunity need to be explored further and the nosology of rosacea adapted accordingly. However, treating early rosacea, with only clinically visible vascular symptoms, with an acaricide may decrease early inflammation, limit potential flare-ups following laser treatment, and prevent the ultimate development of the papulopustules of rosacea. The effectiveness of this approach needs to be confirmed by prospective controlled clinical trials with long-term follow-up. Currently, the evidence suggests that patients with only vascular symptoms of rosacea should be carefully examined for the presence of follicular scales as signs of Demodex overgrowth or pityriasis folliculorum so that these patients, at least, can be treated early with an acaricidal cream.

Macrophage galactose-type lectin (MGL) is induced on M2 microglia and participates in the resolution phase of autoimmune neuroinflammation

BACKGROUND

Multiple sclerosis (MS) involves a misdirected immune attack against myelin in the brain and spinal cord, leading to profound neuroinflammation and neurodegeneration. While the mechanisms of disease pathogenesis have been widely studied, the suppression mechanisms that lead to the resolution of the autoimmune response are still poorly understood. Here, we investigated the role of the C-type lectin receptor macrophage galactose-type lectin (MGL), usually expressed on tolerogenic antigen-presenting cells (APCs), as a negative regulator of autoimmune-driven neuroinflammation.

METHODS

We used in silico, immunohistochemical, immunofluorescence, quantitative real-time polymerase chain reaction (qRT-PCR) and flow cytometry analysis to explore the expression and functionality of MGL in human macrophages and microglia, as well as in MS post-mortem tissue. In vitro, we studied the capacity of MGL to mediate apoptosis of experimental autoimmune encephalomyelitis (EAE)-derived T cells and mouse CD4⁺ T cells. Finally, we evaluated in vivo and ex vivo the immunomodulatory potential of MGL in EAE.

RESULTS

MGL plays a critical role in the resolution phase of EAE as MGL1-deficient (Clec10a^-/-) mice showed a similar day of onset but experienced a higher clinical score to that of WT littermates. We demonstrate that the mouse ortholog MGL1 induces apoptosis of autoreactive T cells and diminishes the expression of pro-inflammatory cytokines and inflammatory autoantibodies. Moreover, we show that MGL1 but not MGL2 induces apoptosis of activated mouse CD4⁺ T cells in vitro. In human settings, we show that MGL expression is increased in active MS lesions and on alternatively activated microglia and macrophages which, in turn, induces the secretion of the immunoregulatory cytokine IL-10, underscoring the clinical relevance of this lectin.

CONCLUSIONS

Our results show a new role of MGL-expressing APCs as an anti-inflammatory mechanism in autoimmune neuroinflammation by dampening pathogenic T and B cell responses, uncovering a novel clue for neuroprotective therapeutic strategies with relevance for in MS clinical applications.

MGL Ligand Expression Is Correlated to Lower Survival and Distant Metastasis in Cervical Squamous Cell and Adenosquamous Carcinoma

Cervical cancer is the fourth most common cancer type in women worldwide and is characterized by a highly immune-suppressive microenvironment. Here, we describe aberrant glycosylation as a factor mediating this immunosuppressive microenvironment. Expression of a specific carbohydrate ligand for the immune-regulatory C-type lectin MGL was correlated to poor disease-specific survival and distant recurrences in squamous cell carcinoma (SCC) and adenosquamous carcinoma (ASC), the most common histological subtypes of cervical cancer. MGL ligand expression was also associated with lymph node metastasis, the absence of CD14+ myeloid cells and the presence of CD14-CD163+ myeloid cells. Indeed, expression of the MGL receptor itself could be detected on CD163+ cells, suggesting that MGL+ myeloid cells are able to interact locally with MGL ligand+ tumor cells. Additionally, MGL ligand expression correlated to the occurrence of PIK3CA mutations, the most frequently observed oncogenic alteration in cervical cancer. In conclusion, we present prognostic value for MGL ligand expression in SCC/ASC patients, which further supports an immune evasive role for the C-type lectin MGL in the tumor immune compartment.

Identification of a secondary binding site in human macrophage galactose-type lectin by microarray studies: Implications for the molecular recognition of its ligands

The human macrophage galactose-type lectin (MGL) is a C-type lectin characterized by a unique specificity for terminal GalNAc residues present in the tumor-associated Tn antigen (αGalNAc-Ser/Thr) and its sialylated form, the sialyl-Tn antigen. However, human MGL has multiple splice variants, and whether these variants have distinct ligand-binding properties is unknown. Here, using glycan microarrays, we compared the binding properties of the short MGL 6C (MGL^short) and the long MGL 6B (MGL^long) splice variants, as well as of a histidine-to-threonine mutant (MGL^short H259T). Although the MGL^short and MGL^long variants displayed similar binding properties on the glycan array, the MGL^short H259T mutant failed to interact with the sialyl-Tn epitope. As the MGL^short H259T variant could still bind a single GalNAc monosaccharide on this array, we next investigated its binding characteristics to Tn-containing glycopeptides derived from the MGL ligands mucin 1 (MUC1), MUC2, and CD45. Strikingly, in the glycopeptide microarray, the MGL^short H259T variant lost high-affinity binding toward Tn-containing glycopeptides, especially at low probing concentrations. Moreover, MGL^short H259T was unable to recognize cancer-associated Tn epitopes on tumor cell lines. Molecular dynamics simulations indicated that in WT MGL^short, His²⁵⁹ mediates H bonds directly or engages the Tn-glycopeptide backbone through water molecules. These bonds were lost in MGL^short H259T, thus explaining its lower binding affinity. Together, our results suggest that MGL not only connects to the Tn carbohydrate epitope, but also engages the underlying peptide via a secondary binding pocket within the MGL carbohydrate recognition domain containing the His²⁵⁹ residue.

Cellular localization and regulation of receptors and enzymes of the endocannabinoid system in intestinal and systemic inflammation

Surveys suggest that Cannabis provides benefit for people with inflammatory bowel disease. However, mechanisms underlying beneficial effects are not clear. We performed in situ hybridization RNAscope^® combined with immunohistochemistry to show cell-specific distribution and regulation of cannabinoid receptor 1 and 2 (CB₁, CB₂), G protein-coupled receptor 55 (GPR55), and monoacylglycerol lipase (MGL) mRNA in immune cells using murine models of intestinal and systemic inflammation. In healthy animals, the presence in enteric ganglia is high for CB₁ mRNA, but low for CB₂ and GPR55 mRNAs. MGL mRNA is predominant throughout the intestinal wall including myenteric neurons, epithelium, circular and longitudinal muscular layers, and the lamina propria. Within the immune system, B220⁺ cells exhibit high gene expression for CB₂ while the expression of CB₂ in F4/80⁺ and CD3⁺ cells is less prominent. In contrast, GPR55 mRNA is highly present in F4/80⁺ and CD3⁺ cells. qRT-PCR of total colonic segments shows that the expression of GPR55 and MGL genes drops during intestinal inflammation. Also at cellular levels, GPR55 and MGL gene expression is reduced in F4/80⁺, but not CD3⁺ cells. As to systemic inflammation, reduced gene expression of MGL is observed in ileum by qRT-PCR, while at cellular levels, altered gene expression is also seen for CB₁ and GPR55 in CD3⁺ but not F4/80⁺ cells. In summary, our study reveals changes in gene expression of members of the endocannabinoid system in situ attesting particularly GPR55 and MGL a distinct cellular role in the regulation of the immune response to intestinal and systemic inflammation.

Monoglyceride lipase as a drug target: At the crossroads of arachidonic acid metabolism and endocannabinoid signaling

Monoglyerides (MGs) are short-lived, intermediary lipids deriving from the degradation of phospho- and neutral lipids, and monoglyceride lipase (MGL), also designated as monoacylglycerol lipase (MAGL), is the major enzyme catalyzing the hydrolysis of MGs into glycerol and fatty acids. This distinct function enables MGL to regulate a number of physiological and pathophysiological processes since both MGs and fatty acids can act as signaling lipids or precursors thereof. The most prominent MG species acting as signaling lipid is 2-arachidonoyl glycerol (2-AG) which is the most abundant endogenous agonist of cannabinoid receptors in the body. Importantly, recent observations demonstrate that 2-AG represents a quantitatively important source for arachidonic acid, the precursor of prostaglandins and other inflammatory mediators. Accordingly, MGL-mediated 2-AG degradation affects lipid signaling by cannabinoid receptor-dependent and independent mechanisms. Recent genetic and pharmacological studies gave important insights into MGL's role in (patho-)physiological processes, and the enzyme is now considered as a promising drug target for a number of disorders including cancer, neurodegenerative and inflammatory diseases. This review summarizes the basics of MG (2-AG) metabolism and provides an overview on the therapeutic potential of MGL.

MGL ligand expression is correlated to BRAF mutation and associated with poor survival of stage III colon cancer patients

Colorectal cancer (CRC) is the third most prevalent cancer type worldwide with a mortality rate of approximately 50%. Elevated cell-surface expression of truncated carbohydrate structures such as Tn antigen (GalNAcα-Ser/Thr) is frequently observed during tumor progression. We have previously demonstrated that the C-type lectin macrophage galactose-type lectin (MGL), expressed by human antigen presenting cells, can distinguish healthy tissue from CRC through its specific recognition of Tn antigen. Both MGL binding and oncogenic BRAF mutations have been implicated in establishing an immunosuppressive microenvironment. Here we aimed to evaluate whether MGL ligand expression has prognostic value and whether this was correlated to BRAF(V600E) mutation status. Using a cohort of 386 colon cancer patients we demonstrate that high MGL binding to stage III tumors is associated with poor disease-free survival, independent of microsatellite instability or adjuvant chemotherapy. In vitro studies using CRC cell lines showed an association between MGL ligand expression and the presence of BRAF(V600E). Administration of specific BRAF(V600E) inhibitors resulted in decreased expression of MGL-binding glycans. Moreover, a positive correlation between induction of BRAF(V600E) and MGL binding to epithelial cells of the gastrointestinal tract was found in vivo using an inducible BRAF(V600E) mouse model. We conclude that the BRAF(V600E) mutation induces MGL ligand expression, thereby providing a direct link between oncogenic transformation and aberrant expression of immunosuppressive glycans. The strong prognostic value of MGL ligands in stage III colon cancer patients, i.e. when tumor cells disseminate to lymph nodes, further supports the putative immune evasive role of MGL ligands in metastatic disease.

Measurement of lipolysis

Lipolysis is defined as the hydrolytic cleavage of ester bonds in triglycerides (TGs), resulting in the generation of fatty acids (FAs) and glycerol. The two major TG pools in the body of vertebrates comprise intracellular TGs and plasma/nutritional TGs. Accordingly, this leads to the discrimination between intracellular and intravascular/gastrointestinal lipolysis, respectively. This chapter focuses exclusively on intracellular lipolysis, referred to as lipolysis herein. The lipolytic cleavage of TGs occurs in essentially all cells and tissues of the body. In all of them, the resulting FAs are utilized endogenously for energy production or biosynthetic pathways with one exception, white adipose tissue (WAT). WAT releases FAs and glycerol to supply nonadipose tissues at times of nutrient deprivation. The fundamental role of lipolysis in lipid and energy homeostasis requires the accurate measurement of lipase activities and lipolytic rates. The recent discovery of new enzymes and regulators that mediate the hydrolysis of TG has made these measurements more complex. Here, we describe detailed methodology for how to measure lipolysis and specific enzymes' activities in cells, organs, and their respective extracts.

A role for glutamate-333 of Saccharomyces cerevisiae cystathionine γ-lyase as a determinant of specificity

Cystathionine γ-lyase (CGL) catalyzes the hydrolysis of l-cystathionine (l-Cth), producing l-cysteine (l-Cys), α-ketobutyrate and ammonia, in the second step of the reverse transsulfuration pathway, which converts l-homocysteine (l-Hcys) to l-Cys. Site-directed variants substituting residues E48 and E333 with alanine, aspartate and glutamine were characterized to probe the roles of these acidic residues, conserved in fungal and mammalian CGL sequences, in the active-site of CGL from Saccharomyces cerevisiae (yCGL). The pH optimum of variants containing the alanine or glutamine substitutions of E333 is increased by 0.4-1.2 pH units, likely due to repositioning of the cofactor and modification of the pKa of the pyridinium nitrogen. The pH profile of yCGL-E48A/E333A resembles that of Escherichia coli cystathionine β-lyase. The effect of substituting E48, E333 or both residues is the 1.3-3, 26-58 and 124-568-fold reduction, respectively, of the catalytic efficiency of l-Cth hydrolysis. The Km(l-Cth) of E333 substitution variants is increased ~17-fold, while Km(l-OAS) is within 2.5-fold of the wild-type enzyme, indicating that residue E333 interacts with the distal amine moiety of l-Cth, which is not present in the alternative substrate O-acetyl-l-serine. The catalytic efficiency of yCGL for α,γ-elimination of O-succinyl-l-homoserine (kcat/Km(l-OSHS)=7±2), which possesses a distal carboxylate, but lacks an amino group, is 300-fold lower than that of the physiological l-Cth substrate (kcat/Km(l-Cth)=2100±100) and 260-fold higher than that of l-Hcys (kcat/Km(l-Hcys)=0.027±0.005), which lacks both distal polar moieties. The results of this study suggest that the glutamate residue at position 333 is a determinant of specificity.

Regulation of macrophage and dendritic cell function by pathogens and through immunomodulation in the avian mucosa

Macrophages (MPh) and dendritic cells (DC) are members of the mononuclear phagocyte system. In chickens, markers to distinguish MPh from DC are lacking, but whether MPh and DC can be distinguished in humans and mice is under debate, despite the availability of numerous markers. Mucosal MPh and DC are strategically located to ingest foreign antigens, suggesting they can rapidly respond to invading pathogens. This review addresses our current understanding of DC and MPh function, the receptors expressed by MPh and DC involved in pathogen recognition, and the responses of DC and MPh against respiratory and intestinal pathogens in the chicken. Furthermore, potential opportunities are described to modulate MPh and DC responses to enhance disease resistance, highlighting modulation through nutraceuticals and vaccination.

Impact of hematopoietic cyclooxygenase-1 deficiency on obesity-linked adipose tissue inflammation and metabolic disorders in mice

OBJECTIVE

Adipose tissue (AT)-specific inflammation is considered to mediate the pathological consequences of obesity and macrophages are known to activate inflammatory pathways in obese AT. Because cyclooxygenases play a central role in regulating the inflammatory processes, we sought to determine the role of hematopoietic cyclooxygenase-1 (COX-1) in modulating AT inflammation in obesity.

MATERIALS/METHODS

Bone marrow transplantation was performed to delete COX-1 in hematopoietic cells. Briefly, female wild type (wt) mice were lethally irradiated and injected with bone marrow (BM) cells collected from wild type (COX-1+/+) or COX-1 knock-out (COX-1-/-) donor mice. The mice were fed a high fat diet for 16 weeks.

RESULTS

The mice that received COX-1-/- bone marrow (BM-COX-1-/-) exhibited a significant increase in fasting glucose, total cholesterol and triglycerides in the circulation compared to control (BM-COX-1+/+) mice. Markers of AT-inflammation were increased and were associated with increased leptin and decreased adiponectin in plasma. Hepatic inflammation was reduced with a concomitant reduction in TXB2 levels. The hepatic mRNA expression of genes involved in lipogenesis and lipid transport was increased while expression of genes involved in regulating hepatic glucose output was reduced in BM-COX-1-/- mice. Finally, renal inflammation and markers of renal glucose release were increased in BM-COX-1-/- mice.

CONCLUSION

Hematopoietic COX-1 deletion results in impairments in metabolic homeostasis which may be partly due to increased AT inflammation and dysregulated adipokine profile. An increase in renal glucose release and hepatic lipogenesis/lipid transport may also play a role, at least in part, in mediating hyperglycemia and dyslipidemia, respectively.

Endocannabinoids decrease neuropathic pain-related behavior in mice through the activation of one or both peripheral CB₁ and CB₂ receptors

The two most studied endocannabinoids are anandamide (AEA), principally catalyzed by fatty-acid amide hydrolase (FAAH), and 2-arachidonoyl glycerol (2-AG), mainly hydrolyzed by monoacylglycerol lipase (MGL). Inhibitors targeting these two enzymes have been described, including URB597 and URB602, respectively. Several recent studies examining the contribution of CB₁ and/or CB₂ receptors on the peripheral antinociceptive effects of AEA, 2-AG, URB597 and URB602 in neuropathic pain conditions using either pharmacological tools or transgenic mice separately have been reported, but the exact mechanism is still uncertain. Mechanical allodynia and thermal hyperalgesia were evaluated in 436 male C57BL/6, cnr1KO and cnr2KO mice in the presence or absence of cannabinoid CB₁ (AM251) or CB₂ (AM630) receptor antagonists in a mouse model of neuropathic pain. Peripheral subcutaneous injections of AEA, 2-AG, WIN55,212-2 (WIN; a CB₁/CB₂ synthetic agonist), URB597 and URB602 significantly decreased mechanical allodynia and thermal hyperalgesia. These effects were inhibited by both cannabinoid antagonists AM251 and AM630 for treatments with 2-AG, WIN and URB602 but only by AM251 for treatments with AEA and URB597 in C57BL/6 mice. Furthermore, the antinociceptive effects for AEA and URB597 were observed in cnr2KO mice but absent in cnr1KO mice, whereas the effects of 2-AG, WIN and URB602 were altered in both of these transgenic mice. Complementary genetic and pharmacological approaches revealed that the anti-hyperalgesic effects of 2-AG and URB602 required both CB₁ and CB₂ receptors, but only CB₂ receptors mediated its anti-allodynic actions. The antinociceptive properties of AEA and URB597 were mediated only by CB₁ receptors.

Conformational plasticity and ligand binding of bacterial monoacylglycerol lipase

Monoacylglycerol lipases (MGLs) play an important role in lipid catabolism across all kingdoms of life by catalyzing the release of free fatty acids from monoacylglycerols. The three-dimensional structures of human and a bacterial MGL were determined only recently as the first members of this lipase family. In addition to the α/β-hydrolase core, they showed unexpected structural similarities even in the cap region. Nevertheless, the structural basis for substrate binding and conformational changes of MGLs is poorly understood. Here, we present a comprehensive study of five crystal structures of MGL from Bacillus sp. H257 in its free form and in complex with different substrate analogs and the natural substrate 1-lauroylglycerol. The occurrence of different conformations reveals a high degree of conformational plasticity of the cap region. We identify a specific residue, Ile-145, that might act as a gatekeeper restricting access to the binding site. Site-directed mutagenesis of Ile-145 leads to significantly reduced hydrolase activity. Bacterial MGLs in complex with 1-lauroylglycerol, myristoyl, palmitoyl, and stearoyl substrate analogs enable identification of the binding sites for the alkyl chain and the glycerol moiety of the natural ligand. They also provide snapshots of the hydrolytic reaction of a bacterial MGL at different stages. The alkyl chains are buried in a hydrophobic tunnel in an extended conformation. Binding of the glycerol moiety is mediated via Glu-156 and water molecules. Analysis of the structural features responsible for cap plasticity and the binding modes of the ligands suggests conservation of these features also in human MGL.

Helminth-excreted/secreted products are recognized by multiple receptors on DCs to block the TLR response and bias Th2 polarization in a cRAF dependent pathway

Dendritic cells (DCs) recognize pathogens and initiate the T-cell response. The DC-helminth interaction induces an immature phenotype in DCs; as a result, these DCs display impaired responses to TLR stimulation and prime Th2-type responses. However, the DC receptors and intracellular pathways targeted by helminth molecules and their importance in the initiation of the Th2 response are poorly understood. In this report, we found that products excreted/secreted by Taenia crassiceps (TcES) triggered cRAF phosphorylation through MGL, MR, and TLR2. TcES interfered with the LPS-induced NFκB p65 and p38 MAPK signaling pathways. In addition, TcES-induced cRAF signaling pathway was critical for down-regulation of the TLR-mediated DC maturation and secretion of IL-12 and TNF-α. Finally, we show for the first time that blocking cRAF in DCs abolishes their ability to induce Th2 polarization in vitro after TcES exposure. Our data demonstrate a new mechanism by which helminths target intracellular pathways to block DC maturation and efficiently program Th2 polarization.