Critical role of macrophage 12/15-lipoxygenase for atherosclerosis in apolipoprotein E-deficient mice

Photothermal lipolysis accelerates ECM production via macrophage-derived ALOX15-mediated p38 MAPK activation in fibroblasts

Skin and subcutaneous tissue tightening is usually treated by noninvasive photothermal treatment for medical esthetics purpose, while the underlying mechanism remains to be elucidated. Here, we hypothesized that adipocyte injury, as a stimulator, may regulate extracellular matrix (ECM) production by increasing ALOX15 in macrophages, which could lead to fibroblast activation. In this study, we show that lipolysis was induced by laser heating (45°C for 15 min) in patients and rats, and adipocyte thermal injury stimulates the ECM production in fibroblasts by ALOX15 that was increased in cocultured macrophages. These phenomena were evidenced by the ALOX15 knockdown. In addition, ALOX15 metabolite 12(S)-HETE activated p38 MAPK signaling pathway that mediated the production of ECM in fibroblast. In summary, the results of this study demonstrate that the mechanisms of adipose photothermal injury-induced skin and/or subcutaneous tissue tightening may have clinical relevance for noninvasive or minimally invasive photothermal therapeutics.

CD36 down regulation by the macrophage antioxidant 7,8-dihydroneopterin through modulation of PPAR-γ activity

CD36 is the key scavenger receptor driving the formation of cholesterol loaded foam cells, the principal cellular component of atherosclerotic plaques. CD36 is down regulated by 7,8-dihydroneopterin, a potent superoxide and hypochlorite scavenging antioxidant generated by interferon-γ stimulated macrophages. 7,8-dihydroneopterin down regulates CD36 mRNA and protein levels so inhibiting macrophage foam cell formation in vitro.We examined the mechanism of 7,8-dihydroneopterin down regulation of CD36 by measuring CD36 and PPAR-γ levels by western blot analysis, in the monocyte-like U937 cells with a range of PPAR-γ stimulants and inhibitors. Lipoxygenase activity was measured by monitoring linoleic acid oxidation at 234 nm for diene formation.Between 100 and 200 μM, 7,8-dihydroneopterin decreased CD36 levels by 50% within 12 hours with levels dropping below 25% by 24 hours. CD36 levels returned to basal levels after 24 hours. Inhibition of protein synthesis by cycloheximide show 7,8-dihydroneopterin had no effect on CD36 degradation rates. PPAR-γ levels were not altered by the addition of 7,8-dihydroneopterin. MAP Kinase, P38 and NF-κB pathways inhibitors SP600125, PD98059, SB202190 and BAY 11-7082 respectively, did not restore the CD36 levels in the presence of 7,8-dihydroneopterin. The addition the lipophilic PPAR-γ activators rosiglitazone and azelaoyl-PAF prevented the CD36 down regulation by 7,8-dihydroneopterin. 7,8-dihydroneopterin inhibited soybean lipoxygenase and reduced U937 cell basal levels of cellular lipid oxides as measured by HPLC-TBARS analysis.The data shows 7,8-dihydroneopterin down regulates CD36 expression by decreasing the level of lipid oxide stimulation of PPAR-γ promotor activity, potentially through lipoxygenase inhibition.

Myeloid LXR (Liver X Receptor) Deficiency Induces Inflammatory Gene Expression in Foamy Macrophages and Accelerates Atherosclerosis

BACKGROUND

Cholesterol loaded macrophage foam cells are a prominent feature of atherosclerotic plaques. Single-cell RNA sequencing has identified foam cells as TREM2 (triggering receptor expressed on myeloid cells 2) positive populations with low expression of inflammatory genes, resembling the TREM2 positive microglia of neurodegenerative diseases. Cholesterol loading of macrophages in vitro results in activation of LXR (liver X receptor) transcription factors and suppression of inflammatory genes.

METHODS

To test the hypothesis that LXRs mediate anti-inflammatory effects in Trem2 expressing atherosclerotic plaque foam cells, we performed RNA profiling on plaque cells from hypercholesterolemic mice with myeloid LXR deficiency.

RESULTS

Myeloid LXR deficiency led to a dramatic increase in atherosclerosis with increased monocyte entry, foam cell formation, and plaque inflammation. Bulk cell-RNA profiling of plaque myeloid cells showed prominent upregulation of inflammatory mediators including oxidative, chemokine, and chemotactic genes. Single-cell RNA sequencing revealed increased numbers of foamy TREM2-expressing macrophages; however, these cells had reduced expression of the Trem2 gene expression module, including phagocytic and cholesterol efflux genes, and had switched to a proinflammatory and proliferative phenotype. Expression of Trem2 was suppressed by inflammatory signals but not directly affected by LXR activation in bone marrow-derived macrophages.

CONCLUSIONS

Our current studies reveal the key role of macrophage LXRs in promoting the Trem2 gene expression program and in suppressing inflammation in foam cells of atherosclerotic plaques.

New appreciation for an old pathway: the Lands Cycle moves into new arenas in health and disease

The Lands Pathway is a fundamental biochemical process named for its discovery by William EM Lands and revealed in a series of seminal papers published in the Journal of Biological Chemistry between 1958-65. It describes the selective placement in phospholipids of acyl chains, by phospholipid acyltransferases. This pathway has formed a core component of our knowledge of phospholipid and also diglyceride metabolism in mammalian tissues for over 60 years now. Our understanding of how the Lands pathways are enzymatically mediated via large families of related gene products that display both substrate and tissue specificity has grown exponentially since. Recent studies building on this are starting to reveal key roles for the Lands pathway in specific scenarios, in particular inflammation, immunity and inflammation. This review will cover the Lands cycle from historical perspectives first, then present new information on how this important cycle forms a central regulatory node connecting fatty acyl and phospholipid metabolism and how its altered regulation may present new opportunities for therapeutic intervention in human disease.

Macrophage 12(S)-HETE Enhances Angiotensin II-Induced Contraction by a BLT2 (Leukotriene B4 Type-2 Receptor) and TP (Thromboxane Receptor)-Mediated Mechanism in Murine Arteries

12/15-LO (12/15-lipoxygenase), encoded by Alox15 gene, metabolizes arachidonic acid to 12(S)-HETE (12-hydroxyeicosatetraenoic acid). Macrophages are the major source of 12/15-LO among immune cells, and 12/15-LO plays a crucial role in development of hypertension. Global Alox15- or macrophage-deficient mice are resistant to Ang II (angiotensin II)-induced hypertension. This study tests the hypothesis that macrophage 12(S)-HETE contributes to Ang II-mediated arterial constriction and thus to development of Ang II-induced hypertension. Ang II constricted isolated abdominal aortic and mesenteric arterial rings. 12(S)-HETE (100 nmol/L) alone was without effect; however, it significantly enhanced Ang II-induced constriction. The presence of wild-type macrophages also enhanced the Ang II-induced constriction, while Alox15^-/- macrophages did not. Using this model, pretreatment of aortic rings with inhibitors, receptor agonists/antagonists, or removal of the endothelium, systematically uncovered an endothelium-mediated, Ang II receptor-2-mediated and superoxide-mediated enhancing effect of 12(S)-HETE on Ang II constrictions. The role of superoxide was confirmed using aortas from p47^phox-/- mice where 12(S)-HETE failed to enhance constriction to Ang II. In cultured arterial endothelial cells, 12(S)-HETE increased the production of superoxide, and 12(S)-HETE or Ang II increased the production of an isothromboxane-like metabolite. A TP (thromboxane receptor) antagonist inhibited 12(S)-HETE enhancement of Ang II constriction. Both Ang II-induced hypertension and the enhancing effect of 12(S)-HETE on Ang II contractions were eliminated by a BLT2 (leukotriene B₄ receptor-2) antagonist. These results outline a mechanism where the macrophage 12/15-LO pathway enhances the action of Ang II. 12(S)-HETE, acting on the BLT2, contributes to the hypertensive action of Ang II in part by promoting endothelial synthesis of a superoxide-derived TP agonist.

APOE Genotype Modifies the Plasma Oxylipin Response to Omega-3 Polyunsaturated Fatty Acid Supplementation in Healthy Individuals

The omega-3 polyunsaturated fatty acids (n-3 PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), mediate inflammation in large part by affecting pro-inflammatory and anti-inflammatory/pro-resolving oxylipin concentrations. Common gene variants are thought to underlie the large inter-individual variation in oxylipin levels in response to n-3 PUFA supplementation, which in turn is likely to contribute to the overall heterogeneity in response to n-3 PUFA intervention. Given its known role in inflammation and as a modulator of the physiological response to EPA and DHA, here we explore, for the first time, the differential response of plasma hydroxy-, epoxy- and dihydroxy-arachidonic acid, EPA and DHA oxylipins according to apolipoprotein E (APOE) genotype using samples from a dose-response parallel design RCT. Healthy participants were given doses of EPA+DHA equivalent to intakes of 1, 2, and 4 portions of oily fish per week for 12 months. There was no difference in the plasma levels of EPA, DHA or ARA between the wildtype APOE3/E3 and APOE4 carrier groups after 3 or 12 months of n-3 PUFA supplementation. At 12 months, hydroxy EPAs (HEPEs) and hydroxy-DHAs (HDHAs) were higher in APOE4 carriers, with the difference most evident at the highest EPA+DHA intake. A significant APOE^*n-3 PUFA dose effect was observed for the CYP-ω hydroxylase products 19-HEPE (p = 0.027) and 20-HEPE (p = 0.011). 8-HEPE, which, along with several other plasma oxylipins, is an activator of peroxisome proliferator activated receptors (PPARs), showed the highest fold change in APOE4 carriers (14-fold) compared to APOE3/E3 (4-fold) (p = 0.014). Low basal plasma EPA levels (EPA < 0.85% of total fatty acids) were associated with a greater change in 5-HEPE, 9-HEPE, 11-HEPE, and 20-HEPE compared to high basal EPA levels (EPA > 1.22% of total fatty acids). In conclusion, APOE genotype modulated the plasma oxylipin response to increased EPA+DHA intake, with APOE4 carriers presenting with the greatest increases following high dose n-3 PUFA supplementation for 12 months.

Characterization of the Structural Diversity and Structure-Specific Behavior of Oxidized Phospholipids by LC-MS/MS

Polyunsaturated fatty acids (PUFAs), esterified to phospholipids, are susceptible to oxidation. They form oxidized phospholipids (OxPLs) by oxygenases or reactive oxygen species (ROS), or both. These OxPLs are associated with various diseases, such as atherosclerosis, pulmonary injuries, neurodegenerative diseases, cancer, and diabetes. Since many types of OxPLs seem to be generated in vivo, precise determination of their structural diversity is required to understand their potential structure-specific functions. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful method to quantitatively measure the structural diversity of OxPLs present in biological samples. This review outlines recent advances in analytical methods for OxPLs and their physiological relevance in health and diseases.

The Emerging Role of COX-2, 15-LOX and PPARγ in Metabolic Diseases and Cancer: An Introduction to Novel Multi-target Directed Ligands (MTDLs)

Emerging evidence supports an intertwining framework for the involvement of different inflammatory pathways in a common pathological background for a number of disorders. Of importance are pathways involving arachidonic acid metabolism by cyclooxygenase-2 (COX-2) and 15-lipoxygenase (15-LOX). Both enzyme activities and their products are implicated in a range of pathophysiological processes encompassing metabolic impairment leading to adipose inflammation and the subsequent vascular and neurological disorders, in addition to various pro- and antitumorigenic effects. A further layer of complexity is encountered by the disparate, and often reciprocal, modulatory effect COX-2 and 15-LOX activities and metabolites exert on each other or on other cellular targets, the most prominent of which is peroxisome proliferator-activated receptor gamma (PPARγ). Thus, effective therapeutic intervention with such multifaceted disorders requires the simultaneous modulation of more than one target. Here, we describe the role of COX-2, 15-LOX, and PPARγ in cancer and complications of metabolic disorders, highlight the value of designing multi-target directed ligands (MTDLs) modifying their activity, and summarizing the available literature regarding the rationale and feasibility of design and synthesis of these ligands together with their known biological effects. We speculate on the potential impact of MTDLs in these disorders as well as emphasize the need for structured future effort to translate these early results facilitating the adoption of these, and similar, molecules in clinical research.

Regulation of Tissue Inflammation by 12-Lipoxygenases

Lipoxygenases (LOXs) are lipid metabolizing enzymes that catalyze the di-oxygenation of polyunsaturated fatty acids to generate active eicosanoid products. 12-lipoxygenases (12-LOXs) primarily oxygenate the 12th carbon of its substrates. Many studies have demonstrated that 12-LOXs and their eicosanoid metabolite 12-hydroxyeicosatetraenoate (12-HETE), have significant pathological implications in inflammatory diseases. Increased level of 12-LOX activity promotes stress (both oxidative and endoplasmic reticulum)-mediated inflammation, leading to damage in these tissues. 12-LOXs are also associated with enhanced cellular migration of immune cells-a characteristic of several metabolic and autoimmune disorders. Genetic depletion or pharmacological inhibition of the enzyme in animal models of various diseases has shown to be protective against disease development and/or progression in animal models in the setting of diabetes, pulmonary, cardiovascular, and metabolic disease, suggesting a translational potential of targeting the enzyme for the treatment of several disorders. In this article, we review the role of 12-LOXs in the pathogenesis of several diseases in which chronic inflammation plays an underlying role.

Adipose tissue inflammation and systemic insulin resistance in mice with diet-induced obesity is possibly associated with disruption of PFKFB3 in hematopoietic cells

Obesity-associated inflammation in white adipose tissue (WAT) is a causal factor of systemic insulin resistance; however, precisely how immune cells regulate WAT inflammation in relation to systemic insulin resistance remains to be elucidated. The present study examined a role for 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) in hematopoietic cells in regulating WAT inflammation and systemic insulin sensitivity. Male C57BL/6J mice were fed a high-fat diet (HFD) or low-fat diet (LFD) for 12 weeks and examined for WAT inducible 6-phosphofructo-2-kinase (iPFK2) content, while additional HFD-fed mice were treated with rosiglitazone and examined for PFKFB3 mRNAs in WAT stromal vascular cells (SVC). Also, chimeric mice in which PFKFB3 was disrupted only in hematopoietic cells and control chimeric mice were also fed an HFD and examined for HFD-induced WAT inflammation and systemic insulin resistance. In vitro, adipocytes were co-cultured with bone marrow-derived macrophages and examined for adipocyte proinflammatory responses and insulin signaling. Compared with their respective levels in controls, WAT iPFK2 amount in HFD-fed mice and WAT SVC PFKFB3 mRNAs in rosiglitazone-treated mice were significantly increased. When the inflammatory responses were analyzed, peritoneal macrophages from PFKFB3-disrputed mice revealed increased proinflammatory activation and decreased anti-inflammatory activation compared with control macrophages. At the whole animal level, hematopoietic cell-specific PFKFB3 disruption enhanced the effects of HFD feeding on promoting WAT inflammation, impairing WAT insulin signaling, and increasing systemic insulin resistance. In vitro, adipocytes co-cultured with PFKFB3-disrupted macrophages revealed increased proinflammatory responses and decreased insulin signaling compared with adipocytes co-cultured with control macrophages. These results suggest that PFKFB3 disruption in hematopoietic cells only exacerbates HFD-induced WAT inflammation and systemic insulin resistance.

Circulating Vimentin Is Associated With Future Incidence of Stroke in a Population-Based Cohort Study

BACKGROUND AND PURPOSE

VIM (vimentin) is a cytoskeletal intermediate filament protein, which has been linked to atherosclerosis and thrombosis; both are important causes of stroke. We examined the relationship between circulating VIM and incidence of stroke, and if carotid plaque could modify the association in a prospective population-based cohort.

METHODS

This prospective study was based on the Malmö Diet and Cancer Cohort. A total of 4688 participants (39.7% men; mean age, 57.6 years) were examined and blood samples were collected between 1991 and 1994. Incidence of stroke was followed up to 2018. Cox' proportional hazards regression was used to assess the relationship between VIM and stroke.

RESULTS

During a mean follow-up of 22.0 years, a total of 528 subjects were diagnosed with stroke, among which 434 were ischemic stroke. Participants in the highest quartile (vs 1^st quartile) had 1.34× higher risk of total stroke (95% CI, 1.03-1.74) and 1.47× higher of ischemic stroke (95% CI, 1.10-1.98) after adjustment for potential confounders. A significant interaction was found between carotid plaque and VIM with respect to incidence of both total stroke and ischemic stroke (P=0.041 and 0.011, respectively). After stratifying by carotid plaque, high VIM had stronger association with stroke in participants with carotid plaque, especially for the risk of ischemic stroke (adjusted hazard ratio,1.66 [95% CI, 1.23-2.25] for quartile 4 versus quartile 1 to 3).

CONCLUSIONS

VIM is positively associated with the incidence of stroke, especially in individuals with carotid plaque. Further studies are needed to confirm the observed associations.

Formation of atherosclerotic lesions is independent of eosinophils in male mice

BACKGROUND AND AIMS

Oxidation of low-density lipoprotein (LDL) and oxidized LDL-mediated activation of the innate immune system have been recognized as early key events during the pathogenesis of atherosclerosis. Recent evidence identified eosinophils as a major source of enzymatic lipid oxidation and suggested a potential role of type 2 immunity in atherogenesis. However, the involvement of individual type 2 immune cell subsets involved in this process has been incompletely defined. We therefore sought to determine the role of eosinophils during LDL oxidation and the pathogenesis of this disease.

METHODS

Using eosinophil-deficient dblGATA1 mice, we studied the role of eosinophils in two established mouse models of atherosclerosis.

RESULTS

These experiments revealed that the presence of eosinophils did neither affect biomarkers of LDL oxidation nor atherosclerotic lesion development.

CONCLUSIONS

The obtained results show that LDL oxidation and development of atherosclerosis are largely independent of eosinophils or eosinophil-mediated LDL oxidation.

Role of reactive oxygen species in atherosclerosis: Lessons from murine genetic models

Atherosclerosis is a multifactorial chronic and inflammatory disease of medium and large arteries, and the major cause of cardiovascular morbidity and mortality worldwide. The pathogenesis of atherosclerosis involves a number of risk factors and complex events including hypercholesterolemia, endothelial dysfunction, increased permeability to low density lipoproteins (LDL) and their sequestration on extracellular matrix in the intima of lesion-prone areas. These events promote LDL modifications, particularly by oxidation, which generates acute and chronic inflammatory responses implicated in atherogenesis and lesion progression. Reactive oxygen species (ROS) (which include both free radical and non-free radical oxygen intermediates), play a key-role at each step of atherogenesis, in endothelial dysfunction, LDL oxidation, and inflammatory events involved in the initiation and development of atherosclerosis lesions. Most advanced knowledge supporting the "oxidative theory of atherosclerosis" i.e. the nature and the cellular sources of ROS and antioxidant defences, as well as the mechanisms involved in the redox balance, is based on the use of genetically engineered animals, i.e. transgenic, genetically modified, or altered for systems producing or neutralizing ROS in the vessels. This review summarizes the results obtained from animals genetically manipulated for various sources of ROS or antioxidant defences in the vascular wall, and their relevance (advance or limitation), for understanding the place and role of ROS in atherosclerosis.

Macrophages and T cells in atherosclerosis: a translational perspective

Atherosclerosis is now considered a chronic maladaptive inflammatory disease. The hallmark feature in both human and murine disease is atherosclerotic plaques. Macrophages and various T-cell lineages play a crucial role in atherosclerotic plaque establishment and disease progression. Humans and mice share many of the same processes that occur within atherogenesis. The various similarities enable considerable insight into disease mechanisms and those which contribute to cardiovascular complications. The apolipoprotein E-null and low-density lipoprotein receptor-null mice have served as the foundation for further immunological pathway manipulation to identify pro- and antiatherogenic pathways in attempt to reveal more novel therapeutic targets. In this review, we provide a translational perspective and discuss the roles of macrophages and various T-cell lineages in contrasting proatherosclerotic and atheroprotective settings.

Enzymatically oxidized phospholipids assume center stage as essential regulators of innate immunity and cell death

Enzymatically oxidized phospholipids (eoxPLs) are formed through regulated processes by which eicosanoids or prostaglandins are attached to phospholipids (PLs) in immune cells. These eoxPLs comprise structurally diverse families of biomolecules with potent bioactivities, and they have important immunoregulatory roles in both health and disease. The formation of oxPLs through enzymatic pathways and their signaling capabilities are emerging concepts. This paradigm is changing our understanding of eicosanoid, prostaglandin, and PL biology in health and disease. eoxPLs have roles in cellular events such as ferroptosis, apoptosis, and blood clotting and diseases such as arthritis, diabetes, and cardiovascular disease. They are increasingly recognized as endogenous bioactive mediators and potential targets for drug development. This review will describe recent evidence that places eoxPLs and their biosynthetic pathways center stage in immunoregulation.

Secretory vimentin is associated with coronary artery disease in patients and induces atherogenesis in ApoE-/- mice

PURPOSE

The present study aimed to investigate the relationship between serum levels of secretory vimentin and coronary artery disease (CAD). The biological effect of secretory vimentin was ascertained by experiments.

METHODS

We analysed serum levels of secretory vimentin in CAD patients (n = 288) and non-CAD controls (n = 195) by ELISA. To evaluate the pro-inflammatory effects of secreted vimentin, the human aortic endothelial cells (HAECs) and human peripheral blood mononuclear cells (PBMCs) were treated with recombinant vimentin or saline. Intraperitoneal injection of vimentin (1 μg/each) or saline was performed every other day for 12 weeks in ApoE^-/- mice for assessment of atherogenic effect.

RESULTS

Serum levels of secretory vimentin were significantly increased in CAD patients than in health controls (p < 0.05), and correlated with the number of diseased coronary arteries, Syntax and Gensini score (for all comparison, p < 0.01). Logistic regression analysis showed that vimentin level is an independent determinant of CAD. In experiments, recombinant vimentin protein enhanced the expression of adhesion molecules and inflammatory cytokines in both endothelial cells and macrophages. This protein also promoted macrophage-endothelial cells adhesion in vitro and the recruitment of leukocytes to mesenteric venules in C57BL/6 mice. Compared with saline, intraperitoneal injection of recombinant vimentin (1 μg/each) every other day induced atherogenesis in ApoE^-/- mice at 12-weeks, with significant increase of inflammatory cytokine and adhesion molecules expression in aortic tissue (p < 0.05).

CONCLUSION

Serum vimentin levels are associated with the presence and the severity of CAD. Vimentin protein promotes atherogenesis in ApoE^-/- mice.

Emerging role of 12/15-Lipoxygenase (ALOX15) in human pathologies

12/15-lipoxygenase (12/15-LOX) is an enzyme, which oxidizes polyunsaturated fatty acids, particularly omega-6 and -3 fatty acids, to generate a number of bioactive lipid metabolites. A large number of studies have revealed the importance of 12/15-LOX role in oxidative and inflammatory responses. The in vitro studies have demonstrated the ability of 12/15-LOX metabolites in the expression of various genes and production of cytokine related to inflammation and resolution of inflammation. The studies with the use of knockout and transgenic animals for 12/15-LOX have further shown its involvement in the pathogenesis of a variety of human diseases, including cardiovascular, renal, neurological and metabolic disorders. This review summarizes our current knowledge on the role of 12/15-LOX in inflammation and various human diseases.

Myeloid Cell Hypoxia-Inducible Factors Promote Resolution of Inflammation in Experimental Colitis

Colonic tissues in Inflammatory Bowel Disease (IBD) patients exhibit oxygen deprivation and activation of hypoxia-inducible factor 1α and 2α (HIF-1α and HIF-2α), which mediate cellular adaptation to hypoxic stress. Notably, macrophages and neutrophils accumulate preferentially in hypoxic regions of the inflamed colon, suggesting that myeloid cell functions in colitis are HIF-dependent. By depleting ARNT (the obligate heterodimeric binding partner for both HIFα subunits) in a murine model, we demonstrate here that myeloid HIF signaling promotes the resolution of acute colitis. Specifically, myeloid pan-HIF deficiency exacerbates infiltration of pro-inflammatory neutrophils and Ly6C⁺ monocytic cells into diseased tissue. Myeloid HIF ablation also hinders macrophage functional conversion to a protective, pro-resolving phenotype, and elevates gut serum amyloid A levels during the resolution phase of colitis. Therefore, myeloid cell HIF signaling is required for efficient resolution of inflammatory damage in colitis, implicating serum amyloid A in this process.

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.

Female mice carrying a defective Alox15 gene are protected from experimental colitis via sustained maintenance of the intestinal epithelial barrier function

Lipoxygenases (ALOXs) are involved in the regulation of cellular redox homeostasis. They also have been implicated in the biosynthesis of pro- and anti-inflammatory lipid mediators and play a role in the pathogenesis of inflammatory diseases, which constitute a major health challenge owing to increasing incidence and prevalence in all industrialized countries around the world. To explore the pathophysiological role of Alox15 (leukocyte-type 12-LOX) in mouse experimental colitis we tested the impact of systemic inactivation of the Alox15 gene on the extent of dextrane sulfate sodium (DSS) colitis. We found that in wildtype mice expression of the Alox15 gene was augmented during DSS-colitis while expression of other Alox genes (Alox5, Alox15b) was hardly altered. Systemic Alox15 (leukocyte-type 12-LOX) deficiency induced less severe colitis symptoms and suppressed in vivo formation of 12-hydroxyeicosatetraenoic acid (12-HETE), the major Alox15 (leukocyte-type 12-LOX) product in mice. These alterations were paralleled by reduced expression of pro-inflammatory gene products, by sustained expression of the zonula occludens protein 1 (ZO-1) and by a less impaired intestinal epithelial barrier function. These results are consistent with in vitro incubations of colon epithelial cells, in which addition of 12S-HETE compromised enantioselectively transepithelial electric resistance. Consistent with these data transgenic overexpression of human ALOX15 intensified the inflammatory symptoms. In summary, our results indicate that systemic Alox15 (leukocyte-type 12-LOX) deficiency protects mice from DSS-colitis. Since exogenous 12-HETE compromises the expression of the tight junction protein ZO-1 the protective effect has been related to a less pronounced impairment of the intestinal epithelial barrier function.

αMβ2 Is Antiatherogenic in Female but Not Male Mice

Atherosclerosis is a complex inflammatory process characterized by monocyte recruitment into the arterial wall, their differentiation into macrophages, and lipid accumulation. Because integrin α_Mβ₂ (CD11b/CD18) mediates multiple diverse functions of leukocytes, we examined its role in atherogenesis. α_M^-/-/ApoE^-/- and ApoE^-/- mice were fed a control or high fat diet for 3 or 16 wk to induce atherogenesis. Unexpectedly, α_M deficiency accelerated development of atherosclerosis in female but not in male mice. The size of aortic root lesions was 3-4.5-fold larger in female α_M^-/-/ApoE^-/- than in ApoE^-/- mice. Monocyte and macrophage content within the lesions was increased 2.5-fold in female α_M^-/-/ApoE^-/- mice due to enhanced proliferation. α_Mβ₂ elimination promoted gender-dependent foam cell formation due to enhanced uptake of cholesterol by α_M^-/-/ApoE^-/- macrophages. This difference was attributed to enhanced expression of lipid uptake receptors, CD36 and scavenger receptor A1 (SR-A1), in female mice. Macrophages from female α_M^-/-/ApoE^-/- mice showed dramatically reduced expression of FoxM1 transcription factor and estrogen receptors (ER) α and β. As their antagonists inhibited the effect of 17β-estradiol (E₂), E₂ decreased CD36, SR-A1, and foam cell formation in ApoE^-/- macrophages in an ERα- and ERβ-dependent manner. However, female α_M^-/-/ApoE^-/- macrophages failed to respond to E₂ and maintained elevated CD36, SR-A1, and lipid accumulation. FoxM1 inhibition in ApoE^-/- macrophages reduced ERs and enhanced CD36 and SR-A1 expression, whereas FoxM1 overexpression in α_M^-/-/ApoE^-/- macrophages reversed their proatherogenic phenotype. We demonstrate a new, surprising atheroprotective role of α_Mβ₂ in female ApoE^-/- mice. α_Mβ₂ maintains ER expression in macrophages and E₂-dependent inhibition of foam cell formation.

Bone marrow-derived cPLA2α contributes to renal fibrosis progression

The group IVA calcium-dependent cytosolic phospholipase A2 (cPLA2α) enzyme directs a complex "eicosanoid storm" that accompanies the tissue response to injury. cPLA2α and its downstream eicosanoid mediators are also implicated in the pathogenesis of fibrosis in many organs, including the kidney. We aimed to determine the role of cPLA2α in bone marrow-derived cells in a murine model of renal fibrosis, unilateral ureteral obstruction (UUO). WT C57BL/6J mice were irradiated and engrafted with donor bone marrow from either WT mice [WT-bone marrow transplant (BMT)] or mice deficient in cPLA2α (KO-BMT). After full engraftment, mice underwent UUO and kidneys were collected 3, 7, and 14 days after injury. Using picrosirius red, collagen-3, and smooth muscle α actin staining, we determined that renal fibrosis was significantly attenuated in KO-BMT animals as compared with WT-BMT animals. Lipidomic analysis of homogenized kidneys demonstrated a time-dependent upregulation of pro-inflammatory eicosanoids after UUO; KO-BMT animals had lower levels of many of these eicosanoids. KO-BMT animals also had fewer infiltrating pro-inflammatory CD45+CD11b+Ly6C^hi macrophages and reduced message levels of pro-inflammatory cytokines. Our results indicate that cPLA2α and/or its downstream mediators, produced by bone marrow-derived cells, play a major role in eicosanoid production after renal injury and in renal fibrinogenesis.

Molecular mechanisms of nonalcoholic fatty liver disease: Potential role for 12-lipoxygenase

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of pathologies associated with fat accumulation in the liver. NAFLD is the most common cause of liver disease in the United States, affecting up to a third of the general population. It is commonly associated with features of metabolic syndrome, particularly insulin resistance. NAFLD shares the basic pathogenic mechanisms with obesity and insulin resistance, such as mitochondrial, oxidative and endoplasmic reticulum stress. Lipoxygenases catalyze the conversion of poly-unsaturated fatty acids in the plasma membrane-mainly arachidonic acid and linoleic acid-to produce oxidized pro-inflammatory lipid intermediates. 12-Lipoxygenase (12-LOX) has been studied extensively in setting of inflammation and insulin resistance. As insulin resistance is closely associated with development of NAFLD, the role of 12-LOX in pathogenesis of NAFLD has received increasing attention in recent years. In this review we discuss the role of 12-LOX in NAFLD pathogenesis and its potential role in emerging new therapeutics.

Effects of MβCD on Lipoxygenase-Induced LDL Oxidation

Beta-cyclodextrin (β-CD) has been applied as drug/food carriers or potential drugs for treating some diseases. Most recently, some evidence indicated that methyl-β-cyclodextrin (MβCD) and 2-hydroxypropyl-β-cyclodextrin (2-HPβCD), two major derivatives of β-CD, may inhibit atherogenesis, implying that cyclodextrins also can be potential drugs for treating atherosclerosis. It is well known that modification (e.g. oxidation) of low-density lipoprotein (LDL) is one of the most critical steps of atherogenesis. Lipoxygenase, an enzyme able to be expressed by atherosclerosis-related vascular cells, is generally regarded as a possible in vivo agent of LDL oxidation. In this study, the effects of MβCD on LDL oxidation induced by lipoxygenase were investigated by measuring the electrophoretic mobility, conjugated diene formation, malondialdehyde (MDA) production, and amino group blockage of LDL. We found that the lipids depleted from LDL by MβCD could be oxygenated more readily by lipoxygenase whereas the lipoxygenase-induced oxidation of the remaining lipid-depleted LDL decreased. The data imply that MβCD has an inhibitory effect on lipoxygenase-induced LDL oxidation and probably helps to inhibit atherogenesis.

Myeloid 12/15-LOX regulates B cell numbers and innate immune antibody levels in vivo

Background. The myeloid enzyme 12/15-lipoxygenase (LOX), which generates bioactive oxidized lipids, has been implicated in numerous inflammatory diseases, with several studies demonstrating an improvement in pathology in mice lacking the enzyme. However, the ability of 12/15-LOX to directly regulate B cell function has not been studied.

Methods. The influence of 12/15-LOX on B cell phenotype and function, and IgM generation, was compared using wildtype (WT) and 12/15-LOX ( Alox15^-/-) deficient mice. The proliferative and functional capacity of splenic CD19 ⁺ B cells was measured in vitro in response to various toll-like receptor agonists.

Results. WT and Alox15^-/- displayed comparable responses. However in vivo, splenic B cell numbers were significantly elevated in Alox15^-/- mice with a corresponding elevation in titres of total IgM in lung, gut and serum, and lower serum IgM directed against the 12/15-LOX product, 12-hydroxyeicosatetraenoic acid-phosphatidylethanolamine (HETE-PE).

Discussion. Myeloid 12/15-LOX can regulate B cell numbers and innate immune antibody levels in vivo, potentially contributing to its ability to regulate inflammatory disease. Furthermore, the alterations seen in 12/15-LOX deficiency likely result from changes in the equilibrium of the immune system that develop from birth. Further studies in disease models are warranted to elucidate the contribution of 12/15-LOX mediated alterations in B cell numbers and innate immune antibody generation to driving inflammation in vivo.

Elk-1-mediated 15-lipoxygenase expression is required for hypoxia-induced pulmonary vascular adventitial fibroblast dynamics

AIM

15-Lipoxygenase (15-LO) is an important factor in the pathogenesis of pulmonary artery hypertension (PAH). However, the role of 15-LO in the adventitia of the pulmonary arterial wall is unclear. The aim of this study was to explore the role of 15-LO in the modulation of pulmonary adventitial fibroblast (PAF) dynamics.

METHODS

Rats were exposed to normoxic or hypoxic (fraction of inspired O₂  = 0.12) treatments for 7 days. PAF proliferation and cell cycle alterations were measured by MTT assay, cell immunofluorescence, flow cytometry and Western blot analysis. The 15-LO promoter was analysed by luciferase reporter and ChIP assays.

RESULTS

Our results showed that hypoxia induced 15-LO expression in PAFs both in vivo and in vitro. In addition, hypoxia stimulated JNK phosphorylation in PAFs. Blocking 15-LO or JNK suppressed 15-LO-induced PAF proliferation and cell cycle alterations. The inhibition of p27^kipl by gene silencing attenuated 15-LO-induced PAF proliferation and cell cycle alterations. Furthermore, JNK inhibition or Elk-1 knockdown suppressed hypoxia-induced 15-LO expression in PAFs. Luciferase reporter and ChIP assays revealed that the 15-LO promoter contains Elk-1-binding sites and also that Elk-1 increased the hypoxia-induced activity of the 15-LO promoter.

CONCLUSION

These results suggest that hypoxia promotes changes in the cellular dynamics of PAFs by inducing 15-LO expression, which leads to vascular adventitial remodelling. The modulation of p27^kipl expression by 15-LO enhances PAF proliferation and cell cycle alterations. Furthermore, the JNK-dependent increase in Elk-1 signalling is required for hypoxia-induced 15-LO expression in PAFs.

Apoptosis of Endothelial Cells by 13-HPODE Contributes to Impairment of Endothelial Barrier Integrity

Inflammation is an essential host response during bacterial infections such as bovine mastitis. Endothelial cells are critical for an appropriate inflammatory response and loss of vascular barrier integrity is implicated in the pathogenesis of Streptococcus uberis-induced mastitis. Previous studies suggested that accumulation of linoleic acid (LA) oxygenation products derived from 15-lipoxygenase-1 (15-LOX-1) metabolism could regulate vascular functions. The initial LA derivative from the 15-LOX-1 pathway, 13-hydroperoxyoctadecadienoic acid (HPODE), can induce endothelial death, whereas the reduced hydroxyl product, 13-hydroxyoctadecadienoic acid (HODE), is abundantly produced during vascular activation. However, the relative contribution of specific LA-derived metabolites on impairment of mammary endothelial integrity is unknown. Our hypothesis was that S. uberis-induced LA-derived 15-LOX-1 oxygenation products impair mammary endothelial barrier integrity by apoptosis. Exposure of bovine mammary endothelial cells (BMEC) to S. uberis did not increase 15-LOX-1 LA metabolism. However, S. uberis challenge of bovine monocytes demonstrated that monocytes may be a significant source of both 13-HPODE and 13-HODE during mastitis. Exposure of BMEC to 13-HPODE, but not 13-HODE, significantly reduced endothelial barrier integrity and increased apoptosis. Changing oxidant status by coexposure to an antioxidant during 13-HPODE treatment prevented adverse effects of 13-HPODE, including amelioration of apoptosis. A better understanding of how the oxidant status of the vascular microenvironment impacts endothelial barrier properties could lead to more efficacious treatments for S. uberis mastitis.

The double-edged role of 12/15-lipoxygenase during inflammation and immunity

12/15-Lipoxygenase (12/15-LOX) mediates the enzymatic oxidation of polyunsaturated fatty acids, thereby contributing to the generation of various bioactive lipid mediators. Although 12/15-LOX has been implicated in the pathogenesis of multiple chronic inflammatory diseases, its physiologic functions seem to include potent immune modulatory properties that physiologically contribute to the resolution of inflammation and the clearance of inflammation-associated tissue damage. This review aims to give a comprehensive overview about our current knowledge on the role of this enzyme during the regulation of inflammation and immunity. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder.

Physiology and pathophysiology of oxLDL uptake by vascular wall cells in atherosclerosis

Atherosclerosis is a progressive disease in which endothelial cell dysfunction, macrophage foam cell formation, and smooth muscle cell migration and proliferation, lead to the loss of vascular homeostasis. Oxidized low-density lipoprotein (oxLDL) may play a pre-eminent function in atherosclerotic lesion formation, even if their role is still debated. Several types of scavenger receptors (SRs) such as SR-AI/II, SRBI, CD36, lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), toll-like receptors (TLRs) and others can promote the internalization of oxLDL. They are expressed on the surface of vascular wall cells (endothelial cells, macrophages and smooth muscle cells) and they mediate the cellular effects of oxLDL. The key influence of both oxLDL and SRs on the atherogenic process has been established in atherosclerosis-prone animals, in which antioxidant treatment and/or silencing of SRs has been shown to reduce atherogenesis. Despite some discrepancies, the indication from cohort studies that there is an association between oxLDL and cardiovascular (CV) events seems to point toward a role for oxLDL in atherosclerotic plaque progress and disruption. Finally, randomized clinical trials using antioxidants have demonstrated benefits only in high-risk patients, suggesting that additional proofs are still needed to better define the involvement of each type of modified LDL in the development of atherosclerosis.

Skeletal inflammation and attenuation of Wnt signaling, Wnt ligand expression, and bone formation in atherosclerotic ApoE-null mice

ApoE-null (ApoE-KO) mice fed a high-fat diet (HFD) develop atherosclerosis, due in part to activation of vascular inflammation by oxidized low-density lipoprotein. Since bone loss also occurs in these mice, we used them to investigate the impact of oxidized lipids on bone homeostasis and to search for underlying pathogenic pathways. Four-month-old female ApoE-KO mice fed a HFD for three months exhibited increased levels of oxidized lipids in bone, as well as decreased femoral and vertebral trabecular and cortical bone mass, compared with ApoE-KO mice on normal diet. Despite HFD-induced increase in expression of Alox15, a lipoxygenase that oxidizes LDL and promotes atherogenesis, global deletion of this gene failed to ameliorate the skeletal impact of HFD. Osteoblast number and function were dramatically reduced in trabecular and cortical bone of HFD-fed mice, whereas osteoclast number was modestly reduced only in trabecular bone, indicating that an imbalance in favor of osteoclasts was responsible for HFD-induced bone loss. These changes were associated with decreased osteoblast progenitors and increased monocyte/macrophages in the bone marrow as well as increased expression of IL-1β, IL-6, and TNF. HFD also attenuated Wnt signaling as evidenced by reduced expression of Wnt target genes, and it decreased expression of pro-osteoblastogenic Wnt ligands. These results suggest that oxidized lipids decrease bone mass by increasing anti-osteoblastogenic inflammatory cytokines and decreasing pro-osteoblastogenic Wnt ligands.

Autophagic degradation of peroxisomes in mammals

Peroxisomes are essential organelles required for proper cell function in all eukaryotic organisms. They participate in a wide range of cellular processes including the metabolism of lipids and generation, as well as detoxification, of hydrogen peroxide (H2O2). Therefore, peroxisome homoeostasis, manifested by the precise and efficient control of peroxisome number and functionality, must be tightly regulated in response to environmental changes. Due to the existence of many physiological disorders and diseases associated with peroxisome homoeostasis imbalance, the dynamics of peroxisomes have been widely examined. The increasing volume of reports demonstrating significant involvement of the autophagy machinery in peroxisome removal leads us to summarize current knowledge of peroxisome degradation in mammalian cells. In this review we present current models of peroxisome degradation. We particularly focus on pexophagy-the selective clearance of peroxisomes through autophagy. We also critically discuss concepts of peroxisome recognition for pexophagy, including signalling and selectivity factors. Finally, we present examples of the pathological effects of pexophagy dysfunction and suggest promising future directions.

The role of lipoxygenases in pathophysiology; new insights and future perspectives

Lipoxygenases (LOXs) are dioxygenases that catalyze the formation of corresponding hydroperoxides from polyunsaturated fatty acids such as linoleic acid and arachidonic acid. LOX enzymes are expressed in immune, epithelial, and tumor cells that display a variety of physiological functions, including inflammation, skin disorder, and tumorigenesis. In the humans and mice, six LOX isoforms have been known. 15-LOX, a prototypical enzyme originally found in reticulocytes shares the similarity of amino acid sequence as well as the biochemical property to plant LOX enzymes. 15-LOX-2, which is expressed in epithelial cells and leukocytes, has different substrate specificity in the humans and mice, therefore, the role of them in mammals has not been established. 12-LOX is an isoform expressed in epithelial cells and myeloid cells including platelets. Many mutations in this isoform are found in epithelial cancers, suggesting a potential link between 12-LOX and tumorigenesis. 12R-LOX can be found in the epithelial cells of the skin. Defects in this gene result in ichthyosis, a cutaneous disorder characterized by pathophysiologically dried skin due to abnormal loss of water from its epithelial cell layer. Similarly, eLOX-3, which is also expressed in the skin epithelial cells acting downstream 12R-LOX, is another causative factor for ichthyosis. 5-LOX is a distinct isoform playing an important role in asthma and inflammation. This isoform causes the constriction of bronchioles in response to cysteinyl leukotrienes such as LTC4, thus leading to asthma. It also induces neutrophilic inflammation by its recruitment in response to LTB4. Importantly, 5-LOX activity is strictly regulated by 5-LOX activating protein (FLAP) though the distribution of 5-LOX in the nucleus. Currently, pharmacological drugs targeting FLAP are actively developing. This review summarized these functions of LOX enzymes under pathophysiological conditions in mammals.

Structural and functional biology of arachidonic acid 15-lipoxygenase-1 (ALOX15)

Lipoxygenases (LOX) form a family of lipid peroxidizing enzymes, which have been implicated in a number of physiological processes and in the pathogenesis of inflammatory, hyperproliferative and neurodegenerative diseases. They occur in two of the three domains of terrestrial life (bacteria, eucarya) and the human genome involves six functional LOX genes, which encode for six different LOX isoforms. One of these isoforms is ALOX15, which has first been described in rabbits in 1974 as enzyme capable of oxidizing membrane phospholipids during the maturational breakdown of mitochondria in immature red blood cells. During the following decades ALOX15 has extensively been characterized and its biological functions have been studied in a number of cellular in vitro systems as well as in various whole animal disease models. This review is aimed at summarizing the current knowledge on the protein-chemical, molecular biological and enzymatic properties of ALOX15 in various species (human, mouse, rabbit, rat) as well as its implication in cellular physiology and in the pathogenesis of various diseases.

15-Lipoxygenase and 15-hydroxyeicosatetraenoic acid regulate intravascular thrombosis in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a disease characterized by thickening of pulmonary artery walls, elevated pulmonary vascular resistance, pulmonary vascular thrombotic lesions, and right heart failure. Recent studies suggest that 15-lipoxygenase (15-LO)/15-hydroxyeicosatetraenoic acid (15-HETE) play an important role in PAH, acting on arterial walls. Here, we show evidence for the action of the 15-LO/15-HETE signaling in the pulmonary vascular thrombotic lesions in the experimental PAH models. Platelet deposition was augmented in rats exposed to hypoxia and Sugen 5416, which were both prevented by nordihydroguaiaretic acid (NDGA), a 15-LO inhibitor. Chronic hypoxic resulted in the platelet deposition specifically in pulmonary vasculature, which was reversed by 15-LO inhibitor. The 15-LO pathway mediated in the endothelial dysfunction induced by hypoxia in vivo. Meanwhile, 15-HETE positively regulated the generation of IL-6 and monocyte chemoattractant protein-1 (MCP-1). The coagulation and platelet activation induced by hypoxia were reversed by 15-LO inhibitor NDGA or the MCP-1 inhibitor synthesis inhibitor bindarit in rats. The 15-LO/15-HETE signaling promoted the coagulation and platelet activation, which was suppressed by MCP-1 inhibition. These results therefore suggest that 15-LO/15-HETE signaling plays a role in platelet activation and pulmonary vascular thrombosis in PAH, involving MCP-1.

Minireview: 12-Lipoxygenase and Islet β-Cell Dysfunction in Diabetes

The insulin producing islet β-cells have increasingly gained attention for their role in the pathogeneses of virtually all forms of diabetes. Dysfunction, de-differentiation, and/or death of β-cells are pivotal features in the transition from normoglycemia to hyperglycemia in both animal models of metabolic disease and humans. In both type 1 and type 2 diabetes, inflammation appears to be a central cause of β-cell derangements, and molecular pathways that modulate inflammation or the inflammatory response are felt to be prime targets of future diabetes therapy. The lipoxygenases (LOs) represent a class of enzymes that oxygenate cellular polyunsaturated fatty acids to produce inflammatory lipid intermediates that directly and indirectly affect cellular function and survival. The enzyme 12-LO is expressed in all metabolically active tissues, including pancreatic islets, and has received increasing attention for its role in promoting cellular inflammation in the setting of diabetes. Genetic deletion models of 12-LO in mice reveal striking protection from metabolic disease and its complications and an emerging body of literature has implicated its role in human disease. This review focuses on the evidence supporting the proinflammatory role of 12-LO as it relates to islet β-cells, and the potential for 12-LO inhibition as a future avenue for the prevention and treatment of metabolic disease.

Systems pharmacology and molecular docking strategies prioritize natural molecules as cardioprotective agents

Multidimensional prioritization of cardioprotective natural compounds.

Insulin-like growth factor I reduces lipid oxidation and foam cell formation via downregulation of 12/15-lipoxygenase

OBJECTIVE

We have shown that insulin-like growth factor I (IGF-1) infusion in Apoe(-/-) mice decreased atherosclerotic plaque size and plaque macrophage and lipid content suggesting that IGF-1 suppressed formation of macrophage-derived foam cells. Since 12/15-lipoxygenase (12/15-LOX) plays an important role in OxLDL and foam cell formation, we hypothesized that IGF-1 downregulates 12/15-LOX, thereby suppressing lipid oxidation and foam cell formation.

APPROACH AND RESULTS

We found that IGF-1 decreased 12/15-LOX plaque immunopositivity and serum OxLDL levels in Apoe(-/-) mice. IGF-1 reduced 12/15-LOX protein and mRNA levels in cultured THP-1 macrophages and IGF-1 also decreased expression of STAT6 transcription factor. IGF-1 reduction in macrophage 12/15-LOX was mediated in part via a PI3 kinase- and STAT6-dependent transcriptional mechanism. IGF-1 suppressed THP-1 macrophage ability to oxidize lipids and form foam cells. IGF-1 downregulated 12/15-LOX in human blood-derived primary macrophages and IGF-1 decreased LDL oxidation induced by these cells. IGF-1 reduced LDL oxidation and formation of foam cells by wild type murine peritoneal macrophages, however these effects were completely blocked in 12/15-LOX-null macrophages suggesting that the ability of IGF-1 to reduce LDL oxidation and foam cells formation is dependent on its ability to downregulate 12/15-LOX.

CONCLUSIONS

Overall our data demonstrate that IGF-1 reduces lipid oxidation and foam cell formation via downregulation of 12/15-LOX and this mechanism may play a major role in the anti-atherosclerotic effects of IGF-1.

A novel role for 12/15-lipoxygenase in regulating autophagy

12/15-Lipoxygenase (LOX) enzymatically generates oxidized phospholipids in monocytes and macrophages. Herein, we show that cells deficient in 12/15-LOX contain defective mitochondria and numerous cytoplasmic vacuoles containing electron dense material, indicating defects in autophagy or membrane processing, However, both LC3 expression and lipidation were normal both basally and on chloroquine treatment. A LOX-derived oxidized phospholipid, 12-hydroxyeicosatetraenoic acid-phosphatidylethanolamine (12-HETE-PE) was found to be a preferred substrate for yeast Atg8 lipidation, versus native PE, while both native and oxidized PE were effective substrates for LC3 lipidation. Last, phospholipidomics demonstrated altered levels of several phospholipid classes. Thus, we show that oxidized phospholipids generated by 12/15-LOX can act as substrates for key proteins required for effective autophagy and that cells deficient in this enzyme show evidence of autophagic dysfunction. The data functionally link phospholipid oxidation with autophagy for the first time.

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12/15-Lipoxygenase-deficient macrophages show evidence of autophagic dysfunction.

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12-HETE-PE is a substrate for LC2 and Atg8 lipidation.

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Macrophages deficient in 12/15-lipoxygenase show altered phospholipid content.

Mammalian lipoxygenases and their biological relevance

Lipoxygenases (LOXs) form a heterogeneous class of lipid peroxidizing enzymes, which have been implicated not only in cell proliferation and differentiation but also in the pathogenesis of various diseases with major public health relevance. As other fatty acid dioxygenases LOXs oxidize polyunsaturated fatty acids to their corresponding hydroperoxy derivatives, which are further transformed to bioactive lipid mediators (eicosanoids and related substances). On the other hand, lipoxygenases are key players in the regulation of the cellular redox homeostasis, which is an important element in gene expression regulation. Although the first mammalian lipoxygenases were discovered 40 years ago and although the enzymes have been well characterized with respect to their structural and functional properties the biological roles of the different lipoxygenase isoforms are not completely understood. This review is aimed at summarizing the current knowledge on the physiological roles of different mammalian LOX-isoforms and their patho-physiological function in inflammatory, metabolic, hyperproliferative, neurodegenerative and infectious disorders. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Inflammation revisited: inflammation versus resolution of inflammation following myocardial infarction

Myocardial infarction (MI) is the main cause for the progression of the left ventricle towards congestive heart failure. The optimal healing after MI requires timely induction and resolution of inflammation. Primarily, there have been a number of strategies applied to inhibit the post-MI inflammation but approaches that focus on the resolution of inflammation have sparsely been used in the treatment of heart failure. The early attempts to inhibit post-MI inflammation resulted in adverse outcomes that were realized in heart failure trials. We provide here an overview on the cyclooxygenase (COX)- and lipoxygenase (LOX)-derived lipid mediators that are either impairing or resolving the post-MI inflammation. With the evolution of lipidomics there has been emerging novel bioactive-specialized lipid mediators that promise to resolve chronic inflammation rather than promoting inhibition. The current review is focused on post-MI immune cells kinetics and the unexplored array of lipid mediators that are coordinated by COX and LOX. Thus, an emphasis on COX and LOX poses key questions and potential for the development of novel targets in the heart failure treatment strategy. This updated dynamic approach aims to fuse basic pre-clinical discoveries and translational bioactive lipid-based resolvin discoveries that could be potentially used in the clinic for the treatment of heart failure.

Macrophage polarization in inflammatory diseases

Diversity and plasticity are two hallmarks of macrophages. M1 macrophages (classically activated macrophages) are pro-inflammatory and have a central role in host defense against infection, while M2 macrophages (alternatively activated macrophages) are associated with responses to anti-inflammatory reactions and tissue remodeling, and they represent two terminals of the full spectrum of macrophage activation. Transformation of different phenotypes of macrophages regulates the initiation, development, and cessation of inflammatory diseases. Here we reviewed the characters and functions of macrophage polarization in infection, atherosclerosis, obesity, tumor, asthma, and sepsis, and proposed that targeting macrophage polarization and skewing their phenotype to adapt to the microenvironment might hold great promise for the treatment of inflammatory diseases.

Association of polymorphisms in the ALOX15B gene with coronary artery disease

BACKGROUND

Atherosclerosis is a multifactorial disease and the underlying cause of coronary artery disease (CAD), myocardial infarction and stroke. Two main features are involved in the progression of atherosclerosis, lipid retention and inflammation. 12/15-lipoxygenases are involved in inflammation and have been implicated in atherosclerosis. Genetic association studies of the 15-lipoxygenase 1 (ALOX15) in humans revealed a neutral to atheroprotective role of the enzyme. Recently the epidermis-type 15-lipoxygenase 2 (ALOX15B) has been identified in human atherosclerotic plaques but its role in human atherosclerosis is still unclear.

METHODS

We screened the ALOX15B gene for polymorphisms and investigated the association of 18 detected polymorphisms with angiographically documented CAD in a case-control study (n=496). In addition, we measured in vitro the enzyme activity and Michaelis-Menten kinetics of the detected non-synonymous polymorphic variants p.Arg486His (c.1457G>A), p.Gln656Arg (c.1967A>G) and p.Ile676Val (c.2026A>G).

RESULTS

We found that the linked polymorphisms at position c.1458-38G>C, c.1579+71C>T and c.1656G>A are associated with CAD (OR: 0.51 (0.27-0.94), p-value: 0.03). In addition, we show that the activity and the kinetics of the three non-synonymous ALOX15B enzyme variants (p.Arg486His, p.Gln656Arg and p.Ile676Val) are similar to the wild-type enzyme.

CONCLUSIONS

Our data indicate that the ALOX15B gene may be associated with coronary artery disease. However, larger studies would be necessary to confirm the association of these polymorphisms with CAD. In contrast, our study did not find frequent non-synonymous polymorphisms in ALOX15B altering enzyme activity in Europeans.