12/15-lipoxygenase-dependent myeloid production of interleukin-12 is essential for resistance to chronic toxoplasmosis

A review on the relationship between Arachidonic acid 15-Lipoxygenase (ALOX15) and diabetes mellitus

Arachidonic acid 15-lipoxygenase (ALOX15), as one of the lipoxygenase family, is mainly responsible for catalyzing the oxidation of various fatty acids to produce a variety of lipid components, contributing to the pathophysiological processes of various immune and inflammatory diseases. Studies have shown that ALOX15 and its related products are widely distributed in human tissues and related to multiple diseases such as liver, cardiovascular, cerebrovascular diseases, diabetes mellitus and other diseases. Diabetes mellitus (DM), the disease studied in this article, is a metabolic disease characterized by a chronic increase in blood glucose levels, which is significantly related to inflammation, oxidative stress, ferroptosis and other mechanisms, and it has a high incidence in the population, accompanied by a variety of complications. Figuring out how ALOX15 is involved in DM is critical to understanding its role in diseases. Therefore, ALOX15 inhibitors or combination therapy containing inhibitors may deliver a novel research direction for the treatment of DM and its complications. This article aims to review the biological effect and the possible function of ALOX15 in the pathogenesis of DM.

Human gut bacterial metabolism drives Th17 activation and colitis

Bacterial activation of T helper 17 (Th17) cells exacerbates mouse models of autoimmunity, but how human-associated bacteria impact Th17-driven disease remains elusive. We show that human gut Actinobacterium Eggerthella lenta induces intestinal Th17 activation by lifting inhibition of the Th17 transcription factor Rorγt through cell- and antigen-independent mechanisms. E. lenta is enriched in inflammatory bowel disease (IBD) patients and worsens colitis in a Rorc-dependent manner in mice. Th17 activation varies across E. lenta strains, which is attributable to the cardiac glycoside reductase 2 (Cgr2) enzyme. Cgr2 is sufficient to induce interleukin (IL)-17a, a major Th17 cytokine. cgr2+ E. lenta deplete putative steroidal glycosides in pure culture; related compounds are negatively associated with human IBD severity. Finally, leveraging the sensitivity of Cgr2 to dietary arginine, we prevented E. lenta-induced intestinal inflammation in mice. Together, these results support a role for human gut bacterial metabolism in driving Th17-dependent autoimmunity.

Skin metabolome reveals immune responses in yellow drum Nibea albiflora to Cryptocaryon irritans infection

The yellow drum Nibea albiflora is less susceptible to Cryptocaryon irritans infection than is the case with other marine fishes such as Larimichthys crocea, Lateolabrax japonicus, and Pagrus major. To investigate further their resistance mechanism, we infected the N. albiflora with the C. irritans at a median lethal concentration of 2050 theronts/g fish. The skins of the infected and the uninfected fishes were sampled at 24 h and 72 h followed by an extensive analysis of metabolism. The study results revealed that there were 2694 potential metabolites. At 24 h post-infection, 12 metabolites were up-regulated and 17 were down-regulated whereas at 72 h post-infection, 22 metabolites were up-regulated and 26 were down-regulated. Pathway enrichment analysis shows that the differential enriched pathways were higher at 24 h with 22 categories and 58 subcategories (49 up, 9 down) than at 72 h whereby the differential enriched pathways were 6 categories and 8 subcategories (4 up, 4 down). In addition, the principal component analysis (PCA) plot shows that at 24 h the metabolites composition of infected group were separately clustered to uninfected group while at 72 h the metabolites composition in infected group were much closer to uninfected group. This indicated that C. irritans caused strong metabolic stress on the N. albiflora at 24 h and restoration of the dysregulated metabolic state took place at 72 h of infection. Also, at 72 h post infection a total of 17 compounds were identified as potential biomarkers. Furthermore, out of 2694 primary metabolites detected, 23 metabolites could be clearly identified and semi quantified with a known identification number and assigned into 66 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Most of the enriched KEGG pathways were mainly from metabolic pathway classes, including the metabolic pathway, biosynthesis of secondary metabolites, taurine and hypotaurine metabolism, purine metabolism, linoleic acid metabolism, phenylalanine, tyrosine and tryptophan biosynthesis. Others were glyoxylate and dicarboxylate metabolism, glutathione metabolism, and alanine, aspartate, and glutamate metabolism. Moreover, out of the identified metabolites, only 6 metabolites were statistically differentially expressed, namely, L -glutamate (up-regulated) at 24 h was important for energy and precursor for other glutathiones and instruments of preventing oxidative injury; 15-hydroxy- eicosatetraenoic acid (15-HETE), (S)-(-)-2-Hydroxyisocaproic acid, and adenine (up-regulated) at 72 h were important for anti-inflammatory and immune responses during infection; others were delta-valerolactam and betaine which were down-regulated compared to uninfected group at 72 h, might be related to immure responses including stimulation of immune system such as production of antibodies. Our results therefore further advance our understanding on the immunological regulation of N. albiflora during immune response against infections as they indicated a strong relationship between skin metabolome and C. irritans infection.

The Eicosanoids, Redox-Regulated Lipid Mediators in Immunometabolic Disorders

SIGNIFICANCE

The oxidation of arachidonic acid via cyclooxygenase (COX) and lipoxygenase (LOX) activity to produce eicosanoids during inflammation is a well-known biosynthetic pathway. These lipid mediators are involved in fever, pain, and thrombosis and are produced from multiple cells as well as cell/cell interactions, for example, immune cells and epithelial/endothelial cells. Metabolic disorders, including hyperlipidemia, hypertension, and diabetes, are linked with chronic low-grade inflammation, impacting the immune system and promoting a variety of chronic diseases. Recent Advances: Multiple studies have corroborated the important function of eicosanoids and their receptors in (non)-inflammatory cells in immunometabolic disorders (e.g., insulin resistance, obesity, and cardiovascular and nonalcoholic fatty liver diseases). In this context, LOX and COX products are involved in both pro- and anti-inflammatory responses. In addition, recent work has elucidated the potent function of specialized proresolving mediators (i.e., lipoxins and resolvins) in resolving inflammation, protecting organs, and stimulating tissue repair and remodeling.

CRITICAL ISSUES

Inhibiting/stimulating selected eicosanoid pathways may result in anti-inflammatory and proresolution responses leading to multiple beneficial effects, including the abrogation of reactive oxygen species production, increased speed of resolution, and overall improvement of diseases related to immunometabolic perturbations.

FUTURE DIRECTIONS

Despite many achievements, it is crucial to understand the molecular and cellular mechanisms underlying immunological/metabolic cross talk to offer substantial therapeutic promise. Antioxid. Redox Signal. 29, 275-296.

Responses of Bovine Innate Immunity to Mycobacterium avium subsp. paratuberculosis Infection Revealed by Changes in Gene Expression and Levels of MicroRNA

Paratuberculosis in cattle is a chronic granulomatous gastroenteritis caused by Mycobacterium avium subsp. paratubercolosis (MAP) which is endemic worldwide. In dairy herds, it is responsible for huge economic losses. However, current diagnostic methods do not detect subclinical infection making control of the disease difficult. The identification of MAP infected animals during the sub-clinical phase of infection would play a key role in preventing the dissemination of the pathogen and in reducing transmission. Gene expression and circulating microRNA (miRNA) signatures have been proposed as biomarkers of disease both in the human and veterinary medicine. In this paper, gene expression and related miRNA levels were investigated in cows positive for MAP, by ELISA and culture, in order to identify potential biomarkers to improve diagnosis of MAP infection. Three groups, each of 5 animals, were used to compare the results of gene expression from positive, exposed and negative cows. Overall 258 differentially expressed genes were identified between unexposed, exposed, but ELISA negative and positive groups which were involved in biological functions related to inflammatory response, lipid metabolism and small molecule biochemistry. Differentially expressed miRNA was also found among the three groups: 7 miRNAs were at a lower level and 2 at a higher level in positive animals vs unexposed animals, while 5 and 3 miRNAs were respectively reduced and increased in the exposed group compared to the unexposed group. Among the differentially expressed miRNAs 6 have been previously described as immune-response related and two were novel miRNAs. Analysis of the miRNA levels showed correlation with expression of their target genes, known to be involved in the immune process. This study suggests that miRNA expression is affected by MAP infection and play a key role in tuning the host response to infection. The miRNA and gene expression profiles may be biomarkers of infection and potential diagnostic of MAP infection earlier than the current ELISA based diagnostic tests.

Design of a novel thiophene inhibitor of 15-lipoxygenase-1 with both anti-inflammatory and neuroprotective properties

The enzyme 15-lipoxygenase-1 (15-LOX-1) plays a dual role in diseases with an inflammatory component. On one hand 15-LOX-1 plays a role in pro-inflammatory gene expression and on the other hand it has been shown to be involved in central nervous system (CNS) disorders by its ability to mediate oxidative stress and damage of mitochondrial membranes under hypoxic conditions. In order to further explore applications in the CNS, novel 15-LOX-1 inhibitors with favorable physicochemical properties need to be developed. Here, we present Substitution Oriented Screening (SOS) in combination with Multi Component Chemistry (MCR) as an effective strategy to identify a diversely substituted small heterocyclic inhibitors for 15-LOX-1, denoted ThioLox, with physicochemical properties superior to previously identified inhibitors. Ex vivo biological evaluation in precision-cut lung slices (PCLS) showed inhibition of pro-inflammatory gene expression and in vitro studies on neuronal HT-22 cells showed a strong protection against glutamate toxicity for this 15-LOX-1 inhibitor. This provides a novel approach to identify novel small with favorable physicochemical properties for exploring 15-LOX-1 as a drug target in inflammatory diseases and neurodegeneration.

Transcriptome analysis of mouse brain infected with Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite that invades a wide range of vertebrate host cells. Chronic infections with T. gondii become established in the tissues of the central nervous system, where the parasites may directly or indirectly modulate neuronal function. However, the mechanisms underlying parasite-induced neuronal disorder in the brain remain unclear. This study evaluated host gene expression in mouse brain following infection with T. gondii. BALB/c mice were infected with the PLK strain, and after 32 days of infection, histopathological lesions in the frontal lobe were found to be more severe than in other areas of the brain. Total RNA extracted from infected and uninfected mouse brain samples was subjected to transcriptome analysis using RNA sequencing (RNA-seq). In the T. gondii-infected mice, 935 mouse brain genes were upregulated, whereas 12 genes were downregulated. GOstat analysis predicted that the upregulated genes were primarily involved in host immune responses and cell activation. Positive correlations were found between the numbers of parasites in the infected mouse brains and the expression levels of genes involved in host immune responses. In contrast, genes that had a negative correlation with parasite numbers were predicted to be involved in neurological functions, such as small-GTPase-mediated signal transduction and vesicle-mediated transport. Furthermore, differential gene expression was observed between mice exhibiting the clinical signs of toxoplasmosis and those that did not. Our findings may provide insights into the mechanisms underlying neurological changes during T. gondii infection.

Chitinase dependent control of protozoan cyst burden in the brain

Chronic infections represent a continuous battle between the host's immune system and pathogen replication. Many protozoan parasites have evolved a cyst lifecycle stage that provides it with increased protection from environmental degradation as well as endogenous host mechanisms of attack. In the case of Toxoplasma gondii, these cysts are predominantly found in the immune protected brain making clearance of the parasite more difficult and resulting in a lifelong infection. Currently, little is known about the nature of the immune response stimulated by the presence of these cysts or how they are able to propagate. Here we establish a novel chitinase-dependent mechanism of cyst control in the infected brain. Despite a dominant Th1 immune response during Toxoplasma infection there exists a population of alternatively activated macrophages (AAMØ) in the infected CNS. These cells are capable of cyst lysis via the production of AMCase as revealed by live imaging, and this chitinase is necessary for protective immunity within the CNS. These data demonstrate chitinase activity in the brain in response to a protozoan pathogen and provide a novel mechanism to facilitate cyst clearance during chronic infections.

Described here is a novel mechanism of protozoan cyst clearance in the CNS during chronic infection. These data show the presence of a population of alternatively activated macrophages in the brain that secrete the active chitinase, AMCase, in response to chitin in the cyst wall. Using both chemical and genetic inhibition in vitro, it is revealed that this enzyme is required for efficient degradation and destruction of the cyst. The necessity for AMCase is demonstrated in vivo, as the absence of the enzyme resulted in a significant increase in cyst burden and decrease in survival during chronic infection. Together, these data identify an important mechanism of parasite control and cyst clearance in the CNS. Currently, no therapies exist that lead to the total clearance of this parasite from the brain. Therefore, developing an understanding of the natural mechanisms of cyst clearance has the potential to lead to new and effective therapies for this and other chronic infections.

Toxoplasma on the brain: understanding host-pathogen interactions in chronic CNS infection

Toxoplasma gondii is a prevalent obligate intracellular parasite which chronically infects more than a third of the world's population. Key to parasite prevalence is its ability to form chronic and nonimmunogenic bradyzoite cysts, which typically form in the brain and muscle cells of infected mammals, including humans. While acute clinical infection typically involves neurological and/or ocular damage, chronic infection has been more recently linked to behavioral changes. Establishment and maintenance of chronic infection involves a balance between the host immunity and parasite evasion of the immune response. Here, we outline the known cellular interplay between Toxoplasma gondii and cells of the central nervous system and review the reported effects of Toxoplasma gondii on behavior and neurological disease. Finally, we review new technologies which will allow us to more fully understand host-pathogen interactions.

Differential gene expression in mice infected with distinct Toxoplasma strains

Toxoplasma gondii is the causative agent of toxoplasmosis in human and animals. In a mouse model, T. gondii strains can be divided into three groups, including the virulent, intermediately virulent, and nonvirulent. The clonal type I, II, and III T. gondii strains belong to these three groups, respectively. To better understand the basis of virulence phenotypes, we investigated mouse gene expression responses to the infection of different T. gondii strains at day 5 after intraperitoneal inoculation with 500 tachyzoites. The transcriptomes of mouse peritoneal cells showed that 1,927, 1,573, and 1,009 transcripts were altered more than 2-fold by type I, II, and III infections, respectively, and that the majority of altered transcripts were shared. Overall transcription patterns were similar in type I and type II infections, and both had greater changes than infection with type III. Quantification of parasite burden in mouse spleens showed that the burden with type I infection was 1,000 times higher than that of type II and that the type II burden was 20 times higher than that of type III. Fluorescence-activated cell sorting revealed that type I and II infections had comparable macrophage populations, and both were higher than the population with type III infection. In addition, type I infection had a higher percentage of neutrophils than type II and III infections. Taken together, these results suggested that there is a common gene expression response to T. gondii infection in mice. This response is further modified by parasite strain-specific factors that determine their distinct virulence phenotypes.

Tumor-associated macrophages mediate immunosuppression in the renal cancer microenvironment by activating the 15-lipoxygenase-2 pathway

Renal cell carcinoma (RCC), the most common human kidney cancer, is frequently infiltrated with tumor-associated macrophages (TAM) that can promote malignant progression. Here, we show that TAMs isolated from human RCC produce substantial amounts of the proinflammatory chemokine CCL2 and immunosuppressive cytokine IL-10, in addition to enhanced eicosanoid production via an activated 15-lipoxygenase-2 (15-LOX2) pathway. TAMs isolated from RCC tumors had a high 15-LOX2 expression and secreted substantial amounts of 15(S)-hydroxyeicosatetraenoic acid, its major bioactive lipid product. Inhibition of lipoxygenase activity significantly reduced production of CCL2 and IL-10 by RCC TAMs. In addition, TAMs isolated from RCC were capable of inducing in T lymphocytes, the pivotal T regulatory cell transcription factor forkhead box P3 (FOXP3), and the inhibitory cytotoxic T-lymphocyte antigen 4 (CTLA-4) coreceptor. However, this TAM-mediated induction of FOXP3 and CTLA-4 in T cells was independent of lipoxygenase and could not be reversed by inhibiting lipoxygenase activity. Collectively, our results show that TAMs, often present in RCCs, display enhanced 15-LOX2 activity that contributes to RCC-related inflammation, immunosuppression, and malignant progression. Furthermore, we show that TAMs mediate the development of immune tolerance through both 15-LOX2-dependent and 15-LOX2-independent pathways. We propose that manipulating LOX-dependent arachidonic acid metabolism in the tumor microenvironment could offer new strategies to block cancer-related inflammation and immune escape in patients with RCC.

Pathogenesis of chagas' disease: parasite persistence and autoimmunity

Acute Trypanosoma cruzi infections can be asymptomatic, but chronically infected individuals can die of Chagas' disease. The transfer of the parasite mitochondrial kinetoplast DNA (kDNA) minicircle to the genome of chagasic patients can explain the pathogenesis of the disease; in cases of Chagas' disease with evident cardiomyopathy, the kDNA minicircles integrate mainly into retrotransposons at several chromosomes, but the minicircles are also detected in coding regions of genes that regulate cell growth, differentiation, and immune responses. An accurate evaluation of the role played by the genotype alterations in the autoimmune rejection of self-tissues in Chagas' disease is achieved with the cross-kingdom chicken model system, which is refractory to T. cruzi infections. The inoculation of T. cruzi into embryonated eggs prior to incubation generates parasite-free chicks, which retain the kDNA minicircle sequence mainly in the macrochromosome coding genes. Crossbreeding transfers the kDNA mutations to the chicken progeny. The kDNA-mutated chickens develop severe cardiomyopathy in adult life and die of heart failure. The phenotyping of the lesions revealed that cytotoxic CD45, CD8(+) γδ, and CD8α(+) T lymphocytes carry out the rejection of the chicken heart. These results suggest that the inflammatory cardiomyopathy of Chagas' disease is a genetically driven autoimmune disease.

IL-6 mediates the susceptibility of glycoprotein 130 hypermorphs to Toxoplasma gondii

IL-6 and IL-27 are closely related cytokines that play critical but distinct roles during infection with Toxoplasma gondii. Thus, IL-6 is required for the development of protective immunity to this pathogen, whereas IL-27 is required to limit infection-induced pathology. Paradoxically, these factors both signal through gp130, but little is known about how the signals downstream of gp130 are integrated to coordinate the immune response to infection. To better understand these events, gp130 Y757F mice that have a mutation in gp130 at the binding site for suppressor of cytokine signaling 3, a critical negative regulator of gp130 signaling, were infected with T. gondii. These mutant mice were acutely susceptible to this challenge, characterized by an early defect in the production of IL-12 and IFN-γ and increased parasite burdens. Consistent with the reduced IL-12 levels, IL-6, but not other gp130 cytokines, was a potent antagonist of IL-12 production by gp130 Y757F macrophages and dendritic cells in vitro. Moreover, in gp130 Y757F mice, blocking IL-6 in vivo, or administration of rIL-12, during infection restored IFN-γ production and protective immunity. Collectively, these studies highlight that a failure to abbreviate IL-6-mediated gp130 signaling results in a profound anti-inflammatory signal that blocks the generation of protective immunity to T. gondii.

Functional and pathological roles of the 12- and 15-lipoxygenases

The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer's disease and Parkinson's disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases.