Ultrastructural immunogold localization of prostaglandin endoperoxide synthase (cyclooxygenase) to non-membrane-bound cytoplasmic lipid bodies in human lung mast cells, alveolar macrophages, type II pneumocytes, and neutrophils

Feasibility of a clinical-radiomics combined model to predict the occurrence of stroke-associated pneumonia

PURPOSE

To explore the predictive value of radiomics in predicting stroke-associated pneumonia (SAP) in acute ischemic stroke (AIS) patients and construct a prediction model based on clinical features and DWI-MRI radiomics features.

METHODS

Univariate and multivariate logistic regression analyses were used to identify the independent clinical predictors for SAP. Pearson correlation analysis and the least absolute shrinkage and selection operator with ten-fold cross-validation were used to calculate the radiomics score for each feature and identify the predictive radiomics features for SAP. Multivariate logistic regression was used to combine the predictive radiomics features with the independent clinical predictors. The prediction performance of the SAP models was evaluated using receiver operating characteristics (ROC), calibration curves, decision curve analysis, and subgroup analyses.

RESULTS

Triglycerides, the neutrophil-to-lymphocyte ratio, dysphagia, the National Institutes of Health Stroke Scale (NIHSS) score, and internal carotid artery stenosis were identified as clinically independent risk factors for SAP. The radiomics scores in patients with SAP were generally higher than in patients without SAP (P < 0. 05). There was a linear positive correlation between radiomics scores and NIHSS scores, as well as between radiomics scores and infarct volume. Infarct volume showed moderate performance in predicting the occurrence of SAP, with an AUC of 0.635. When compared with the other models, the combined prediction model achieved the best area under the ROC (AUC) in both training (AUC = 0.859, 95% CI 0.759-0.936) and validation (AUC = 0.830, 95% CI 0.758-0.896) cohorts (P < 0.05). The calibration curves and decision curve analysis further confirmed the clinical value of the nomogram. Subgroup analysis showed that this nomogram had potential generalization ability.

CONCLUSION

The addition of the radiomics features to the clinical model improved the prediction of SAP in AIS patients, which verified its feasibility.

Inhibition of Granuloma Triglyceride Synthesis Imparts Control of Mycobacterium tuberculosis Through Curtailed Inflammatory Responses

Lipid metabolism plays a complex and dynamic role in host-pathogen interaction during Mycobacterium tuberculosis infection. While bacterial lipid metabolism is key to the success of the pathogen, the host also offers a lipid rich environment in the form of necrotic caseous granulomas, making this association beneficial for the pathogen. Accumulation of the neutral lipid triglyceride, as lipid droplets within the cellular cuff of necrotic granulomas, is a peculiar feature of pulmonary tuberculosis. The role of triglyceride synthesis in the TB granuloma and its impact on the disease outcome has not been studied in detail. Here, we identified diacylglycerol O-acyltransferase 1 (DGAT1) to be essential for accumulation of triglyceride in necrotic TB granulomas using the C3HeB/FeJ murine model of infection. Treatment of infected mice with a pharmacological inhibitor of DGAT1 (T863) led to reduction in granuloma triglyceride levels and bacterial burden. A decrease in bacterial burden was associated with reduced neutrophil infiltration and degranulation, and a reduction in several pro-inflammatory cytokines including IL1β, TNFα, IL6, and IFNβ. Triglyceride lowering impacted eicosanoid production through both metabolic re-routing and via transcriptional control. Our data suggests that manipulation of lipid droplet homeostasis may offer a means for host directed therapy in Tuberculosis.

Lipid droplets and lipid mediators in viral infection and immunity

Lipid droplets (LDs) contribute to key pathways important for the physiology and pathophysiology of cells. In a homeostatic view, LDs regulate the storage of neutral lipids, protein sequestration, removal of toxic lipids and cellular communication; however, recent advancements in the field show these organelles as essential for various cellular stress response mechanisms, including inflammation and immunity, with LDs acting as hubs that integrate metabolic and inflammatory processes. The accumulation of LDs has become a hallmark of infection, and is often thought to be virally driven; however, recent evidence is pointing to a role for the upregulation of LDs in the production of a successful immune response to viral infection. The fatty acids housed in LDs are also gaining interest due to the role that these lipid species play during viral infection, and their link to the synthesis of bioactive lipid mediators that have been found to have a very complex role in viral infection. This review explores the role of LDs and their subsequent lipid mediators during viral infections and poses a paradigm shift in thinking in the field, whereby LDs may play pivotal roles in protecting the host against viral infection.

Categorization of lung mesenchymal cells in development and fibrosis

Pulmonary mesenchymal cells are critical players in both the mouse and human during lung development and disease states. They are increasingly recognized as highly heterogeneous, but there is no consensus on subpopulations or discriminative markers for each subtype. We completed scRNA-seq analysis of mesenchymal cells from the embryonic, postnatal, adult and aged fibrotic lungs of mice and humans. We consistently identified and delineated the transcriptome of lipofibroblasts, myofibroblasts, smooth muscle cells, pericytes, mesothelial cells, and a novel population characterized by Ebf1 expression. Subtype selective transcription factors and putative divergence of the clusters during development were described. Comparative analysis revealed orthologous subpopulations with conserved transcriptomic signatures in murine and human lung mesenchymal cells. All mesenchymal subpopulations contributed to matrix gene expression in fibrosis. This analysis would enhance our understanding of mesenchymal cell heterogeneity in lung development, homeostasis and fibrotic disease conditions.

Lipid Droplets as Regulators of Metabolism and Immunity

Abstract

A hallmark of sterile and nonsterile inflammation is the increased accumulation of cytoplasmic lipid droplets (LDs) in non-adipose cells. LDs are ubiquitous organelles specialized in neutral lipid storage and hydrolysis. Originating in the ER, LDs are comprised of a core of neutral lipids (cholesterol esters, triglycerides) surrounded by a phospholipid monolayer and several LD-associated proteins. The perilipin (PLIN1-5) family are the most abundant structural proteins present on the surface of LDs. While PLIN1 is primarily expressed in adipocytes, PLIN2 and PLIN3 are ubiquitously expressed. LDs also acquire a host of enzymes and proteins that regulate LD metabolism. Amongst these are neutral lipases and selective lipophagy factors that promote hydrolysis of LD-associated neutral lipid. In addition, LDs physically associate with other organelles such as mitochondria through inter-organelle membrane contact sites that facilitate lipid transport. Beyond serving as a source of energy storage, LDs participate in inflammatory and infectious diseases, regulating both innate and adaptive host immune responses. Here, we review recent studies on the role of LDs in the regulation of immunometabolism.

The "discovery" of lipid droplets: A brief history of organelles hidden in plain sight

Mammalian lipid droplets (LDs), first described as early as the 1880s, were virtually ignored for more than 100 years. Between 1991 and the early 2000s, however, a series of discoveries and conceptual breakthroughs led to a resurgent interest in obesity as a disease, in the metabolism of intracellular triacylglycerol (TAG), and in the physical locations of LDs as cellular structures with their associated proteins. Insights included the recognition that obesity underlies major chronic diseases, that appetite is hormonally controlled, that hepatic steatosis is not a benign finding, and that diabetes might fundamentally be a disorder of lipid metabolism. In this brief review, I describe the metamorphosis of LDs from overlooked globs of stored fat to dynamic organelles that control insulin resistance, mitochondrial oxidation, and viral replication.

Lipid droplets: platforms with multiple functions in cancer hallmarks

Lipid droplets (also known as lipid bodies) are lipid-rich, cytoplasmic organelles that play important roles in cell signaling, lipid metabolism, membrane trafficking, and the production of inflammatory mediators. Lipid droplet biogenesis is a regulated process, and accumulation of these organelles within leukocytes, epithelial cells, hepatocytes, and other nonadipocyte cells is a frequently observed phenotype in several physiologic or pathogenic situations and is thoroughly described during inflammatory conditions. Moreover, in recent years, several studies have described an increase in intracellular lipid accumulation in different neoplastic processes, although it is not clear whether lipid droplet accumulation is directly involved in the establishment of these different types of malignancies. This review discusses current evidence related to the biogenesis, composition and functions of lipid droplets related to the hallmarks of cancer: inflammation, cell metabolism, increased proliferation, escape from cell death, and hypoxia. Moreover, the potential of lipid droplets as markers of disease and targets for novel anti-inflammatory and antineoplastic therapies will be discussed.

Tanycytes: A rich morphological history to underpin future molecular and physiological investigations

Tanycytes are located at the base of the brain and retain characteristics from their developmental origins, such as radial glial cells, throughout their life span. With transport mechanisms and modulation of tight junction proteins, tanycytes form a bridge connecting the cerebrospinal fluid with the external limiting basement membrane. They also retain the powers of self-renewal and can differentiate to generate neurones and glia. Similar to radial glia, they are a heterogeneous family with distinct phenotypes. Although the four subtypes so far distinguished display distinct characteristics, further research is likely to reveal new subtypes. In this review, we have re-visited the work of the pioneers in the field, revealing forgotten work that is waiting to inspire new research with today's cutting-edge technologies. We have conducted a systematic ultrastructural study of α-tanycytes that resulted in a wealth of new information, generating numerous questions for future study. We also consider median eminence pituicytes, a closely-related cell type to tanycytes, and attempt to relate pituicyte fine morphology to molecular and functional mechanism. Our rationale was that future research should be guided by a better understanding of the early pioneering work in the field, which may currently be overlooked when interpreting newer data or designing new investigations.

Lipid Droplet, a Key Player in Host-Parasite Interactions

Lipid droplets (lipid bodies, LDs) are dynamic organelles that have important roles in regulating lipid metabolism, energy homeostasis, cell signaling, membrane trafficking, and inflammation. LD biogenesis, composition, and functions are highly regulated and may vary according to the stimuli, cell type, activation state, and inflammatory environment. Increased cytoplasmic LDs are frequently observed in leukocytes and other cells in a number of infectious diseases. Accumulating evidence reveals LDs participation in fundamental mechanisms of host-pathogen interactions, including cell signaling and immunity. LDs are sources of eicosanoid production, and may participate in different aspects of innate signaling and antigen presentation. In addition, intracellular pathogens evolved mechanisms to subvert host metabolism and may use host LDs, as ways of immune evasion and nutrients source. Here, we review mechanisms of LDs biogenesis and their contributions to the infection progress, and discuss the latest discoveries on mechanisms and pathways involving LDs roles as regulators of the immune response to protozoan infection.

Host Lipid Bodies as Platforms for Intracellular Survival of Protozoan Parasites

Pathogens induce several changes in the host cell signaling and trafficking mechanisms in order to evade and manipulate the immune response. One prominent pathogen-mediated change is the formation of lipid-rich organelles, termed lipid bodies (LBs) or lipid droplets, in the host cell cytoplasm. Protozoan parasites, which contribute expressively to the burden of infectious diseases worldwide, are able to induce LB genesis in non-immune and immune cells, mainly macrophages, key players in the initial resistance to the infection. Under host–parasite interaction, LBs not only accumulate in the host cytoplasm but also relocate around and move into parasitophorous vacuoles. There is increasing evidence that protozoan parasites may target host-derived LBs either for gaining nutrients or for escaping the host immune response. Newly formed, parasite-induced LBs may serve as lipid sources for parasite growth and also produce inflammatory mediators that potentially act in the host immune response deactivation. In this mini review, we summarize current knowledge on the formation and role of host LBs as sites exploited by intracellular protozoan parasites as a strategy to maintain their own survival.

Biology and pathobiology of lipid droplets and their potential role in the protection of the organ of Corti

The current review article seeks to extend our understanding on the role of lipid droplets within the organ of Corti. In addition to presenting an overview of the current information about the origin, structure and function of lipid droplets we draw inferences from the collective body of knowledge about this cellular organelle to build a conceptual framework to better understanding their role in auditory function. This conceptual model considers that lipid droplets play a significant role in the synthesis, storage, and release of lipids and proteins for energetic use and/or modulating cell signaling pathways. We describe the role and mechanism by which LD play a role in human diseases, and we also review emerging data from our laboratory revealing the potential role of lipid droplets from Hensen cells in the auditory organ. We suggest that lipid droplets might help to develop rapidly and efficiently the resolution phase of inflammatory responses in the mammalian cochlea, preventing inflammatory damage of the delicate inner ear structures and, consequently, sensorineural hearing loss.

Lipid droplets in leukocytes: Organelles linked to inflammatory responses

Studies on lipid droplets (LDs) in leukocytes have attracted attention due to their association with human diseases. In these cells, LDs are rapidly formed in response to inflammatory stimuli or allergic/inflammatory diseases including infections with parasites and bacteria. Leukocyte LDs are linked to the regulation of immune responses by compartmentalization of several proteins and lipids involved in the control and biosynthesis of inflammatory mediators (eicosanoids). In this mini review, we summarize current knowledge on the composition, structure and function of leukocyte LDs, organelles now considered as structural markers of inflammation.

Chronic Insulin Exposure Induces ER Stress and Lipid Body Accumulation in Mast Cells at the Expense of Their Secretory Degranulation Response

Lipid bodies (LB) are reservoirs of precursors to inflammatory lipid mediators in immunocytes, including mast cells. LB numbers are dynamic, increasing dramatically under conditions of immunological challenge. We have previously shown in vitro that insulin-influenced lipogenic pathways induce LB biogenesis in mast cells, with their numbers attaining steatosis-like levels. Here, we demonstrate that in vivo hyperinsulinemia resulting from high fat diet is associated with LB accumulation in murine mast cells and basophils. We characterize the lipidome of purified insulin-induced LB, and the shifts in the whole cell lipid landscape in LB that are associated with their accumulation, in both model (RBL2H3) and primary mast cells. Lipidomic analysis suggests a gain of function associated with LB accumulation, in terms of elevated levels of eicosanoid precursors that translate to enhanced antigen-induced LTC4 release. Loss-of-function in terms of a suppressed degranulation response was also associated with LB accumulation, as were ER reprogramming and ER stress, analogous to observations in the obese hepatocyte and adipocyte. Taken together, these data suggest that chronic insulin elevation drives mast cell LB enrichment in vitro and in vivo, with associated effects on the cellular lipidome, ER status and pro-inflammatory responses.

A cyclooxygenase-2-dependent prostaglandin E2 biosynthetic system in the Golgi apparatus

Cyclooxygenases (COXs) catalyze the committed step in prostaglandin (PG) biosynthesis. COX-1 is constitutively expressed and stable, whereas COX-2 is inducible and short lived. COX-2 is degraded via endoplasmic reticulum (ER)-associated degradation (ERAD) following post-translational glycosylation of Asn-594. COX-1 and COX-2 are found in abundance on the luminal surfaces of the ER and inner membrane of the nuclear envelope. Using confocal immunocytofluorescence, we detected both COX-2 and microsomal PGE synthase-1 (mPGES-1) but not COX-1 in the Golgi apparatus. Inhibition of trafficking between the ER and Golgi retarded COX-2 ERAD. COX-2 has a C-terminal STEL sequence, which is an inefficient ER retention signal. Substituting this sequence with KDEL, a robust ER retention signal, concentrated COX-2 in the ER where it was stable and slowly glycosylated on Asn-594. Native COX-2 and a recombinant COX-2 having a Golgi targeting signal but not native COX-1 exhibited efficient catalytic coupling to mPGES-1. We conclude that N-glycosylation of Asn-594 of COX-2 occurs in the ER, leading to anterograde movement of COX-2 to the Golgi where the Asn-594-linked glycan is trimmed prior to retrograde COX-2 transport to the ER for ERAD. Having an inefficient ER retention signal leads to sluggish Golgi to ER transit of COX-2. This permits significant Golgi residence time during which COX-2 can function catalytically. Cytosolic phospholipase A2α, which mobilizes arachidonic acid for PG synthesis, preferentially translocates to the Golgi in response to physiologic Ca(2+) mobilization. We propose that cytosolic phospholipase A2α, COX-2, and mPGES-1 in the Golgi comprise a dedicated system for COX-2-dependent PGE2 biosynthesis.

Comparative analysis of lipotoxicity induced by endocrine, pharmacological, and innate immune stimuli in rat basophilic leukemia cells

Cellular lipotoxicity manifests as the steatotic accumulation of lipid droplets or lipid bodies, and/or induction of phospholipidosis. Lipotoxicity can be induced by hyperinsulinemia/nutrient overload, cationic amphiphilic drugs (CAD), and innate immunological stimuli, all of which are stimuli relevant to mast cell physiology. Hyper-accumulation of mast cell lipid bodies in response to hyperinsulinemia has been documented, but lipotoxicity in response to CAD or innate immunologic stimuli has not been analysed comparatively. Moreover, gaps in our understanding of this steatosis remain, specifically as to whether hyperinsulinemia-driven steatosis in these cells attains lipotoxic levels or is accompanied by phospholipidosis. To compare endocrine, pharmacological, and innate immunological stimuli for their ability to induce steatosis and phospholipidosis in a rat basophilic leukemia mast cell model (RBL2H3), differential fluorescence microscopy staining and quantitation of phospholipidosis and steatosis in the RBL2H3 cell line was examined. The three classes of stimuli differentially induced phospholipidosis and steatosis. PPARγ up-regulation was not uniformly associated with the expansion of the lipid body population. Fluorescence imaging of lipid-enriched structures generated in response to lipotoxic cationic amphiphilic drugs, chronic insulin exposure, and TLR2/4 ligands revealed differential staining patterns when visualized using lipophilic dyes. It is concluded that lipotoxicity-inducing pathways in this model mast cell system are diverse, and include steatotic responses to an endocrine stimulus, as well as phospholipidosis responses to cationic lipophilic drugs not previously described in this cell type.

Unraveling the complexity of lipid body organelles in human eosinophils

Lipid-rich organelles are common in many cell types. In cells, such as adipocytes, these organelles are termed LDs, whereas in other cells, such as leukocytes, they are called LBs. The study of leukocyte LBs has attracted attention as a result of their association with human diseases. In leukocytes, such as eosinophils, LB accumulation has been documented extensively during inflammatory conditions. In these cells, LBs are linked to the regulation of immune responses by compartmentalization of several proteins and lipids involved in the control and biosynthesis of inflammatory mediators (eicosanoids). However, it has been unclear how diverse proteins, including membrane-associated enzymes involved in eicosanoid formation, incorporate into LBs, especially if the internal content of LBs is assumed to consist solely of stores of neutral lipids, as present within adipocyte LDs. Studies of the formation, function, and ultrastructure of LBs in eosinophils have been providing insights pertinent to LBs in other leukocytes. Here, we review current knowledge of the composition and function of leukocyte LBs as provided by studies of human eosinophil LBs, including recognitions of the internal architecture of eosinophil LBs based on 3D electron tomographic analyses.

How common is the lipid body-containing interstitial cell in the mammalian lung?

Pulmonary lipofibroblasts are thought to be involved in lung development, regeneration, vitamin A storage, and surfactant synthesis. Most of the evidence for these important functions relies on mouse or rat studies. Therefore, the present study was designed to investigate the presence of lipofibroblasts in a variety of early postnatal and adult mammalian species (including humans) to evaluate the ability to generalize functions of this cell type for other species. For this purpose, lung samples from 14 adult mammalian species as well as from postnatal mice, rats, and humans were investigated using light and electron microscopic stereology to obtain the volume fraction and the total volume of lipid bodies. In adult animals, lipid bodies were observed only, but not in all rodents. In all other species, no lipofibroblasts were observed. In rodents, lipid body volume scaled with body mass with an exponent b = 0.73 in the power law equation. Lipid bodies were not observed in postnatal human lungs but showed a characteristic postnatal increase in mice and rats and persisted at a lower level in the adult animals. Among 14 mammalian species, lipofibroblasts were only observed in rodents. The great increase in lipid body volume during early postnatal development of the mouse lung confirms the special role of lipofibroblasts during rodent lung development. It is evident that the cellular functions of pulmonary lipofibroblasts cannot be transferred easily from rodents to other species, in particular humans.

The intriguing ultrastructure of lipid body organelles within activated macrophages

Macrophages are widely distributed immune system cells with essential functions in tissue homeostasis, apoptotic cell clearance, and first defense in infections. A distinguishing feature of activated macrophages participating in different situations such as inflammatory and metabolic diseases is the presence of increased numbers of lipid-rich organelles, termed lipid bodies (LBs) or lipid droplets, in their cytoplasm. LBs are considered structural markers of activated macrophages and are involved in different functions such as lipid metabolism, intracellular trafficking, and synthesis of inflammatory mediators. In this review, we revisit the distinct morphology of LB organelles actively formed within macrophages in response to infections and cell clearance, taking into account new insights provided by ultrastructural studies. We also discuss the LB interactions within macrophages, revealed by transmission electron microscopy, with a focus on the remarkable LB-phagosome association and discuss potential links between structural aspects and function.

Role of prostaglandin F2α production in lipid bodies from Leishmania infantum chagasi: insights on virulence

Lipid bodies (LB; lipid droplets) are cytoplasmic organelles involved in lipid metabolism. Mammalian LBs display an important role in host-pathogen interactions, but the role of parasite LBs in biosynthesis of prostaglandin F2α (PGF2α) has not been investigated. We report herein that LBs increased in abundance during development of Leishmania infantum chagasi to a virulent metacyclic stage, as did the expression of PGF2α synthase (PGFS). The amount of parasite LBs and PGF2α were modulated by exogenous arachidonic acid. During macrophage infection, LBs were restricted to parasites inside the parasitophorous vacuoles (PV). We detected PGF2α receptor (FP) on the Leishmania PV surface. The blockage of FP with AL8810, a selective antagonist, hampered Leishmania infection, whereas the irreversible inhibition of cyclooxygenase with aspirin increased the parasite burden. These data demonstrate novel functions for parasite-derived LBs and PGF2α in the cellular metabolism of Leishmania and its evasion of the host immune response.

Oleic acid inhibits lung Na/K-ATPase in mice and induces injury with lipid body formation in leukocytes and eicosanoid production

BACKGROUND

Acute respiratory distress syndrome (ARDS) can emerge from certain pathologies, such as sepsis, fat embolism and leptospirosis, in which the levels of unesterified fatty acids are increased in the patient's plasma. ARDS is characterized by edema formation, and edema resolution occurs mainly due to the pneumocyte Na/K-ATPase activity. As previously described, increased oleic acid (OA) plasma concentrations induce lung injury by interfering with sodium transport. The first aim of this study was to develop a radioactivity-free assay to detect Na,K-ATPase activity ex vivo using a model of OA-induced lung injury in mice. We also investigated the relationship between Na/K-ATPase inhibition and OA-induced lung injury using ouabain-induced lung injury as a comparison, because of the well-described effect of ouabain as a Na/K-ATPase inhibitor.

METHODS

We developed a Na/K-ATPase assay based on the capture of non-radioactive Rb+ ions by mice lung tissue in the absence or presence of ouabain, a specific Na/K-ATPase inhibitor. Rb+ incorporation into the lung was measured by inductively coupled plasma-optical emission spectrometry (ICP-OES) after lung tissue mineralization. Na/K-ATPase activity was considered as the difference between Rb+ incorporation in the absence and in the presence of ouabain. Bronchoalveolar lavage fluid was collected for lung injury assessment. For this assessment, cell counting, lipid body enumeration and lipid mediator concentrations were measured. Histological analyses were used to determinate lung pathology. Whole body plethysmographic analysis was performed to assay lung function.

RESULTS

The lung Na/K-ATPase activity of mice was completely inhibited by an OA dose of 10 μmol, an effect also obtained with 10-3 μmol of ouabain, as demonstrated by the decreased Rb+ incorporation in the lungs. The same OA dose induced lung edema and inflammation with cell influx, lipid body formation, and leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) production. Ouabain also induced lung inflammation, as detected by histological examinations. As far as we know, this is the first time that ouabain-induced lung injury was shown. Both OA and ouabain induced functional lung pathology in mice simultaneously with inhibition of the lung Na/K-ATPase activity.

CONCLUSIONS

We developed a new non-radioactive assay to quantified Na/K-ATPase in vivo. OA and ouabain inhibited in vivo Na/K-ATPase activity in the lungs and induced lung injury. Our data reinforce the idea that Na/K-ATPase inhibitors may worsen lung injury in specific pathological conditions.

Mast cells: from lipid droplets to lipid mediators

LDs (lipid droplets) are metabolically highly active intracellular organelles. The lipid and protein profiles of LDs are cell-type-specific, and they undergo dynamic variation upon changes in the physiological state of a cell. It is well known that the main function of the LDs in adipocytes is to ensure energy supply and to maintain lipid homoeostasis in the body. In contrast, LDs in inflammatory cells have been implicated in eicosanoid biosynthesis, particularly under inflammatory conditions, thereby enabling them to regulate immune responses. Human mast cells are potent effector cells of the innate immune system, and the triacylglycerol (triglyceride) stores of their cytoplasmic LDs have been shown to contain large amounts of arachidonic acid, the main precursor of pro-inflammatory eicosanoids. In the present review, we discuss the current knowledge about the formation and function of LDs in inflammatory cells with specific emphasis on arachidonic acid and eicosanoid metabolism. On the basis of findings reported previously and our new observations, we propose a model in which lipolysis of LD-triacylglycerols provides arachidonic acid for lipid mediator generation in human mast cells.

The internal architecture of leukocyte lipid body organelles captured by three-dimensional electron microscopy tomography

Lipid bodies (LBs), also known as lipid droplets, are complex organelles of all eukaryotic cells linked to a variety of biological functions as well as to the development of human diseases. In cells from the immune system, such as eosinophils, neutrophils and macrophages, LBs are rapidly formed in the cytoplasm in response to inflammatory and infectious diseases and are sites of synthesis of eicosanoid lipid mediators. However, little is known about the structural organization of these organelles. It is unclear whether leukocyte LBs contain a hydrophobic core of neutral lipids as found in lipid droplets from adipocytes and how diverse proteins, including enzymes involved in eicosanoid formation, incorporate into LBs. Here, leukocyte LB ultrastructure was studied in detail by conventional transmission electron microscopy (TEM), immunogold EM and electron tomography. By careful analysis of the two-dimensional ultrastructure of LBs from human blood eosinophils under different conditions, we identified membranous structures within LBs in both resting and activated cells. Cyclooxygenase, a membrane inserted protein that catalyzes the first step in prostaglandin synthesis, was localized throughout the internum of LBs. We used fully automated dual-axis electron tomography to study the three-dimensional architecture of LBs in high resolution. By tracking 4 nm-thick serial digital sections we found that leukocyte LBs enclose an intricate system of membranes within their “cores”. After computational reconstruction, we showed that these membranes are organized as a network of tubules which resemble the endoplasmic reticulum (ER). Our findings explain how membrane-bound proteins interact and are spatially arranged within LB “cores” and support a model for LB formation by incorporating cytoplasmic membranes of the ER, instead of the conventional view that LBs emerge from the ER leaflets. This is important to understand the functional capabilities of leukocyte LBs in health and during diverse diseases in which these organelles are functionally involved.

Oleic acid induces lung injury in mice through activation of the ERK pathway

Oleic acid (OA) can induce acute lung injury in experimental models. In the present work, we used intratracheal OA injection to show augmented oedema formation, cell migration and activation, lipid mediator, and cytokine productions in the bronchoalveolar fluids of Swiss Webster mice. We also demonstrated that OA-induced pulmonary injury is dependent on ERK1/2 activation, since U0126, an inhibitor of ERK1/2 phosphorylation, blocked neutrophil migration, oedema, and lipid body formation as well as IL-6, but not IL-1β production. Using a mice strain carrying a null mutation for the TLR4 receptor, we proved that increased inflammatory parameters after OA challenges were not due to the activation of the TLR4 receptor. With OA being a Na/K-ATPase inhibitor, we suggest the possible involvement of this enzyme as an OA target triggering lung inflammation.

Lipid body-phagosome interaction in macrophages during infectious diseases: host defense or pathogen survival strategy?

Phagocytosis of invading microorganisms by specialized cells such as macrophages and neutrophils is a key component of the innate immune response. These cells capture and engulf pathogens and subsequently destroy them in intracellular vacuoles—the phagosomes. Pathogen phagocytosis and progression and maturation of pathogen-containing phagosomes, a crucial event to acquire microbicidal features, occurs in parallel with accentuated formation of lipid-rich organelles, termed lipid bodies (LBs), or lipid droplets. Experimental and clinical infections with different pathogens such as bacteria, parasites, and viruses induce LB accumulation in cells from the immune system. Within these cells, LBs synthesize and store inflammatory mediators and are considered structural markers of inflammation. In addition to LB accumulation, interaction of these organelles with pathogen-containing phagosomes has increasingly been recognized in response to infections and may have implications in the outcome or survival of the microorganism within host cells. In this review, we summarize our current knowledge on the LB-phagosome interaction within cells from the immune system, with emphasis on macrophages, and discuss the functional meaning of this event during infectious diseases.

Insulin-containing lipogenic stimuli suppress mast cell degranulation potential and up-regulate lipid body biogenesis and eicosanoid secretion in a PPARγ-independent manner

Lipid bodies are most studied in adipocytes, where the lipogenic action of insulin initiates their formation. Here, we test the hypothesis that insulin may regulate lipid body content in mast cells and hence, modify their proinflammatory potential. Our data show that insulin causes lipid body accumulation in RBL2H3 and BMMCs. Lipid body accumulation in mast cells is associated with enhanced levels of leukotriene-synthesizing enzymes (LTC4S and 5-LO). Increased basal and antigen-stimulated release of LTC4 is observed in insulin-treated mast cells. Concomitantly, the insulin-containing lipogenic stimulus induces a phenotypic change in mast cells, where this enhancement in leukotriene levels is accompanied by a marked down-regulation in secretory granule content and release in response to stimulus. Mast cells exposed to insulin exhibit altered scatter and fluorescence properties, accumulating in a SSC(lo)FSC(hi) population that exhibits decreased BS staining and degranulation responses and is enriched in NR-positive lipid bodies and eicosanoid synthesis enzymes. Lipid body accumulation in mast cells is mechanistically distinct from the process in adipocytes; for example, it is independent of PPARγ up-regulation and does not involve significant accumulation of conjugated glycerides. Thus, chronic exposure to metabolic stimuli, such as insulin, may be a determinant of the proinflammatory potential of the mast cell.

Mice spermatogonial stem cells transplantation induces macrophage migration into the seminiferous epithelium and lipid body formation: high-resolution light microscopy and ultrastructural studies

Transplantation of spermatogonial stem cells (SSCs), the male germline stem cells, in experimental animal models has been successfully used to study mechanisms involved in SSC self-renewal and to restore fertility. However, there are still many challenges associated with understanding the recipient immune response for SSCs use in clinical therapies. Here, we have undertaken a detailed structural study of macrophages elicited by SSCs transplantation in mice using both high-resolution light microscopy (HRLM) and transmission electron microscopy (TEM). We demonstrate that SSCs transplantation elicits a rapid and potent recruitment of macrophages into the seminiferous epithelium (SE). Infiltrating macrophages were derived from differentiation of peritubular monocyte-like cells into typical activated macrophages, which actively migrate through the SE, accumulate in the tubule lumen, and direct phagocytosis of differentiating germ cells and spermatozoa. Quantitative TEM analyses revealed increased formation of lipid bodies (LBs), organelles recognized as intracellular platforms for synthesis of inflammatory mediators and key markers of macrophage activation, within both infiltrating macrophages and Sertoli cells. LBs significantly increased in number and size in parallel to the augmented macrophage migration during different times post-transplantation. Our findings suggest that LBs may be involved with immunomodulatory mechanisms regulating the seminiferous tubule niche after SSC transplantation.

Lipid body function in eicosanoid synthesis: an update

Eicosanoids (prostaglandins, leukotrienes and lipoxins) are signaling lipids derived from arachidonic acid metabolism that have important roles in physiological and pathological processes. Lately, intracellular compartmentalization of eicosanoid-synthetic machinery has emerged as a key component in the regulation of eicosanoid synthesis and functions. Over the past years substantial progresses have been made demonstrating that precursors and enzymes involved in eicosanoid synthesis localize at lipid bodies (also known as lipid droplets) and lipid bodies are distinct sites for eicosanoid generation. Here we will review the current knowledge on the functions of lipid bodies as specialized intracellular sites of compartmentalization of signaling with major roles in eicosanoid formation within cells engaged in inflammatory, infectious and neoplastic process.

Lipid bodies in inflammatory cells: structure, function, and current imaging techniques

Lipid bodies (LBs), also known as lipid droplets, have increasingly been recognized as functionally active organelles linked to diverse biological functions and human diseases. These organelles are actively formed in vivo within cells from the immune system, such as macrophages, neutrophils, and eosinophils, in response to different inflammatory conditions and are sites for synthesis and storage of inflammatory mediators. In this review, the authors discuss structural and functional aspects of LBs and current imaging techniques to visualize these organelles in cells engaged in inflammatory processes, including infectious diseases. The dynamic morphological aspects of LBs in leukocytes as inducible, newly formable organelles, elicitable in response to stimuli that lead to cellular activation, contribute to the evolving understanding of LBs as organelles that are critical regulators of different inflammatory diseases, key markers of leukocyte activation, and attractive targets for novel anti-inflammatory therapies.

Not just fat: the structure and function of the lipid droplet

Lipid droplets (LDs) are independent organelles that are composed of a lipid ester core and a surface phospholipid monolayer. Recent studies have revealed many new proteins, functions, and phenomena associated with LDs. In addition, a number of diseases related to LDs are beginning to be understood at the molecular level. It is now clear that LDs are not an inert store of excess lipids but are dynamically engaged in various cellular functions, some of which are not directly related to lipid metabolism. Compared to conventional membrane organelles, there are still many uncertainties concerning the molecular architecture of LDs and how each function is placed in a structural context. Recent findings and remaining questions are discussed.

Cross-talk between macrophage migration inhibitory factor and eotaxin in allergic eosinophil activation forms leukotriene C₄-synthesizing lipid bodies

Recent studies have demonstrated an essential and nonredundant role for macrophage migration inhibitory factor (MIF) in asthma pathogenesis. Here we investigate the mechanisms involved in MIF-induced eosinophil activation. By using a model of allergic pulmonary inflammation, we observed that allergen challenge-elicited eosinophil influx, lipid body (also known as lipid droplets) biogenesis, and leukotriene (LT) C₄ synthesis are markedly reduced in Mif(-/-) compared with wild-type mice. Likewise, in vivo administration of MIF induced formation of new lipid bodies within eosinophils recruited to the inflammatory reaction site that corresponded to the intracellular compartment of increased LTC₄ synthesis. MIF-mediated eosinophil activation was at least in part due to a direct effect on eosinophils, because MIF was able to elicit lipid body assembly within human eosinophils in vitro, a phenomenon that was blocked by neutralization of the MIF receptor, CD74. MIF-induced eosinophil lipid body biogenesis, both in vivo and in vitro, was dependent on the cooperation of MIF and eotaxin acting in a positive-feedback loop, because anti-eotaxin and anti-CCR3 antibodies inhibit MIF-elicited lipid body formation, whereas eotaxin-induced lipid body formation is affected by anti-CD74 and MIF expression deficiency. Therefore, allergy-elicited inflammatory MIF acts in concert with eotaxin as a key activator of eosinophils to form LTC₄-synthesizing lipid bodies via cross-talk between CD74 and CCR3. Due to the effect of MIF on eosinophils, strategies that inhibit MIF activity might be of therapeutic value in controlling allergic inflammation.

Fatty acids from very low-density lipoprotein lipolysis products induce lipid droplet accumulation in human monocytes

One mechanism by which monocytes become activated postprandially is by exposure to triglyceride-rich lipoproteins such as very low-density lipoproteins (VLDL). VLDL are hydrolyzed by lipoprotein lipase at the blood-endothelial cell interface, releasing free fatty acids. In this study, we examined postprandial monocyte activation in more detail, and found that lipolysis products generated from postprandial VLDL induce the formation of lipid-filled droplets within cultured THP-1 monocytes, characterized by coherent antistokes Raman spectroscopy. Organelle-specific stains revealed an association of lipid droplets with the endoplasmic reticulum, confirmed by electron microscopy. Lipid droplet formation was reduced when lipoprotein lipase-released fatty acids were bound by BSA, which also reduced cellular inflammation. Furthermore, saturated fatty acids induced more lipid droplet formation in monocytes compared with mono- and polyunsaturated fatty acids. Monocytes treated with postprandial VLDL lipolysis products contained lipid droplets with more intense saturated Raman spectroscopic signals than monocytes treated with fasting VLDL lipolysis products. In addition, we found that human monocytes isolated during the peak postprandial period contain more lipid droplets compared with those from the fasting state, signifying that their development is not limited to cultured cells but also occurs in vivo. In summary, circulating free fatty acids can mediate lipid droplet formation in monocytes and potentially be used as a biomarker to assess an individual's risk of developing atherosclerotic cardiovascular disease.

Lipid droplets in inflammation and cancer

Accumulation of lipid droplets (also known as lipid bodies or adiposomes) within leukocytes, epithelial cells, hepatocytes and other non-adipocytic cells is a frequently observed phenotype in infectious, neoplastic and other inflammatory conditions. Lipid droplet biogenesis is a regulated cellular process that culminates in the compartmentalization of lipids and of an array of enzymes, protein kinases and other proteins, suggesting that lipid droplets are inducible organelles with roles in cell signaling, regulation of lipid metabolism, membrane trafficking and control of the synthesis and secretion of inflammatory mediators. Enzymes involved in eicosanoid synthesis are localized at lipid droplets and lipid droplets are sites for eicosanoid generation in cells during inflammation and cancer. In this review, we discuss the current evidence related to the biogenesis and function of lipid droplets in cell metabolism and signaling in inflammation and cancer. Moreover, the potential of lipid droplets as markers of disease and targets for novel anti-inflammatory and antineoplastic therapies will be discussed.

Leukocyte lipid bodies - Biogenesis and functions in inflammation

Lipid body accumulation within leukocytes is a common feature in both clinical and experimental infectious, neoplasic and other inflammatory conditions. Here, we will review the contemporary evidence related to the biogenesis and structure of leukocyte lipid bodies (also known as lipid droplets) as inflammatory organelles. Studies of leukocyte lipid bodies are providing functional, ultrastructural and protein compositional evidences that lipid bodies are not solely storage depots of neutral lipid. Over the past years substantial progresses have been made to demonstrate that lipid body biogenesis is a highly regulated process, that culminate in the compartmentalization of a specific set of proteins and lipids, that place leukocyte lipid bodies as inducible cytoplasmic organelles with roles in cell signaling and activation, regulation of lipid metabolism, membrane trafficking and control of the synthesis and secretion of inflammatory mediators. Pertinent to the roles of lipid bodies in inflammation and cell signaling, enzymes involved in eicosanoid synthesis are localized at lipid bodies and lipid bodies are sites for eicosanoid generation. Collectively, lipid bodies in leukocytes are emerging as critical regulators of different inflammatory diseases, key markers of leukocyte activation and attractive targets for novel anti-inflammatory therapies.

Acute heart inflammation: ultrastructural and functional aspects of macrophages elicited by Trypanosoma cruzi infection

The heart is the main target organ of the parasite Trypanosoma cruzi, the causal agent of Chagas' disease, a significant public health issue and still a major cause of morbidity and mortality in Latin America. During the acute disease, tissue damage in the heart is related to the intense myocardium parasitism. To control parasite multiplication, cells of the monocytic lineage are highly mobilized. In response to inflammatory and immune stimulation, an intense migration and extravasation of monocytes occurs from the bloodstream into heart. Monocyte differentiation leads to the formation of tissue phagocytosing macrophages, which are strongly activated and direct host defence. Newly elicited monocyte-derived macrophages both undergo profound physiological changes and display morphological heterogeneity that greatly differs from originally non-inflammatory macrophages, and underlie their functional activities as potent inflammatory cells. Thus, activated macrophages play a critical role in the outcome of parasite infection. This review covers functional and ultrastructural aspects of heart inflammatory macrophages triggered by the acute Chagas' disease, including recent discoveries on morphologically distinct, inflammation-related organelles, termed lipid bodies, which are actively formed in vivo within macrophages in response to T. cruzi infection. These findings are defining a broader role for lipid bodies as key markers of macrophage activation during innate immune responses to infectious diseases and attractive targets for novel anti-inflammatory therapies. Modulation of macrophage activation may be central in providing therapeutic benefits for Chagas' disease control.

Biogenesis of cytoplasmic lipid droplets: from the lipid ester globule in the membrane to the visible structure

The cytoplasmic lipid droplet (CLD) and very low-density lipoprotein are generated from the lipid ester synthesized in the endoplasmic reticulum. The lipid ester deposited between the two membrane leaflets is supposed to bulge toward the cytoplasm to make a nascent CLD, but its size must be below the resolution limit of conventional techniques and the detectable CLD should only form after acquisition of additional lipid esters. The CLD is different from vesicular organelles in that the internal content is highly hydrophobic and the shape is invariably spherical. Due to its unique characteristics, quantitative discordance between the surface and the volume may occur in the growth and/or involution processes of the CLD. The possibility that these processes may give rise to the structural and functional diversities of the CLD is discussed.

Neutrophils recruited to the site of Mycobacterium bovis BCG infection undergo apoptosis and modulate lipid body biogenesis and prostaglandin E production by macrophages

Neutrophil influx to sites of mycobacterial infections is one of the first events of tuberculosis pathogenesis. However, the role of early neutrophil recruitment in mycobacterial infection is not completely understood. We investigated the rate of neutrophil apoptosis and the role of macrophage uptake of apoptotic neutrophils in a pleural tuberculosis model induced by BCG. Recruited neutrophils were shown to phagocyte BCG and a large number of neutrophils undergo apoptosis within 24 h. Notably, the great majority of apoptotic neutrophils were infected by BCG. Increased lipid body (lipid droplets) formation, accompanied by prostaglandin E(2) (PGE(2)) and TGF-beta1 synthesis, occurred in parallel to macrophage uptake of apoptotic cells. Lipid body and PGE(2) formation was observed after macrophage exposure to apoptotic, but not necrotic or live neutrophils. Blockage of BCG-induced lipid body formation significantly inhibited PGE(2) synthesis. Pre-treatment with the pan-caspase inhibitor zVAD inhibited BCG-induced neutrophil apoptosis and lipid body formation, indicating a role for apoptotic neutrophils in macrophage lipid body biogenesis in infected mice. In conclusion, BCG infection induced activation and apoptosis of infected neutrophils at the inflammatory site. The uptake of apoptotic neutrophils by macrophages leads to TGF-beta1 generation and PGE(2)-derived lipid body formation, and may have modulator roles in mycobacterial pathogenesis.

Lipid droplets: a classic organelle with new outfits

Lipid droplets are depots of neutral lipids that exist virtually in any kind of cell. Recent studies have revealed that the lipid droplet is not a mere lipid blob, but a major contributor not only to lipid homeostasis but also to diverse cellular functions. Because of the unique structure as well as the functional importance in relation to obesity, steatosis, and other prevailing diseases, the lipid droplet is now reborn as a brand new organelle, attracting interests from researchers of many disciplines.

Eosinophilic granulocytes and damage-associated molecular pattern molecules (DAMPs): role in the inflammatory response within tumors

The development of a tumor over many years typically leads to reciprocal alternations in the host and the tumor, enabling tumor growth paradoxically in the setting of substantial necrosis and inflammation. When evaluating a tumor, it is important to assess 3 elements: (1) the quantity and quality of tumor-associated leukocytes, (2) their state of activation, and (3) tumor microenvironment. Peripheral blood eosinophilia and tumor-associated tissue eosinophilia are frequently associated with some tumor types and also found after immunotherapy with IL-2, IL-4, granulocyte-macrophage colony-stimulating factor, and antibody to CTLA-4. Within several tumor types including gastrointestinal tumors, tumor-associated tissue eosinophilia is associated with a significantly better prognosis. The converse is true in other tumor types such as differentiated oral squamous cell carcinoma. On the basis of the emergent data, tumor-associated eosinophils have at least 2 dominant nonoverlapping activities: (1) destructive effector functions potentially limiting tumor growth as well as causing recruitment and activation of other leukocytes, (2) immunoregulative and remodeling activities which suppress immune response and promote tumor proliferation. The mechanism by which eosinophils in particular are recruited into tumor tissue is largely unknown. Candidates for causing eosinophil chemotaxis into tumor tissue are the released damage-associated molecular pattern molecules (DAMPs) including the nuclear protein high mobility group box 1. High mobility group box 1 is released upon necrotic cell death and secreted by many cells, particularly during periods of nutrient, hypoxic, or oxidant stress. This overview on eosinophil biology in the context of cancer and necrosis, introduces intriguing and novel strategies targeting eosinophils to enable more effective biologic therapy for cancer patients.

Roles and origins of leukocyte lipid bodies: proteomic and ultrastructural studies

Lipid bodies (LBs), multifunctional organelles present in most eukaryotic cells, are sites of eicosanoid formation in leukocytes; but little is known about the composition of leukocyte LBs or the biogenesis and internal structures of LBs from mammalian cells. Proteomic analyses of LBs purified from human monocytic U937 cells detected, common to LBs in other cells, proteins involved in cholesterol and triglyceride metabolism, Rab GTPases, and many membrane and endoplasmic reticulum (ER)-associated proteins. Newly lipid body (LB)-associated proteins included MRP-14, potentially involved in arachidonate transport, and ribosomal subunit proteins and translation regulatory proteins. Ultrastructurally, in U937 cells as well as human neutrophils and eosinophils, ribosomes are attached to and distributed within LBs, and LBs contain extensive ER-like membranes. The presence of ribosomes, ER-like membranes and many membrane-associated and ER luminal proteins within LBs, supports a new model by which enveloped ER-membranes and domains form LBs and indicates that LBs may be sites of protein synthesis.

Leukocyte lipid bodies regulation and function: contribution to allergy and host defense

Lipid bodies are lipid-rich organelles found in the cytoplasm of a variety of cells, including leukocytes. Lipid body morphology, its ability to interact with other organelles and its functions are dictated by its lipid arrangement, as well as its protein composition. Both may vary according to the cell type and with the specific lipid body biogenic stimulatory pathways. Nascent lipid bodies, which are formed in vivo in the course of a variety of immunopathological conditions, are sites of enzyme localization, eicosanoid production, as well as, sites for cytokine storage in inflammatory leukocytes, suggesting that lipid bodies function as inducible intracellular platforms for spatial segregation and organization of signaling leading to inflammatory mediator secretion during inflammation. The emerging role of lipid bodies as inflammatory organelles raises lipid body status to critical regulators of different inflammatory diseases, key markers of leukocyte activation and attractive targets for novel anti-inflammatory therapies.

Localization and expression of prostaglandin E2 receptors in human placenta and corresponding fetal membranes with labor

OBJECTIVE

The effects of prostaglandin E2 (PGE2) are mediated through G-protein coupled receptors, acting via different second messengers. The aim of this study was to characterize the temporal and tissue specific localization and expression of the PGE2 receptor subtypes (EP1-4) in uteroplacental tissues during human pregnancy.

STUDY DESIGN

Placenta and fetal membranes were collected after delivery at preterm or term, each with or without labor. The localization and expression of the PGE2 receptor subtypes were determined by immunohistochemistry and Western blot.

RESULTS

All 4 receptors were expressed in the placenta and fetal membranes; only EP3 was present in the syncytiotrophoblast layer. EP1 to EP4 were consistently expressed across gestation in the fetal membranes; however, a different cellular localization with labor was observed in the amnion for EP1, EP2, and EP4.

CONCLUSION

The presence of these receptors in the placenta and fetal membranes may indicate autocrine roles for PGE2 in the signaling pathways associated with placental function and parturition.

Mechanisms of leukocyte lipid body formation and function in inflammation

An area of increasingly interest for the understanding of cell signaling are the spatio-temporal aspects of the different enzymes involved in lipid mediator generation (eicosanoid-forming enzymes, phospholipases and their regulatory kinases and phosphatases) and pools of lipid precursors. The compartmentalization of signaling components within discrete and dynamic sites in the cell is critical for specificity and efficiency of enzymatic reactions of phosphorilation, enzyme activation and function. We hypothesized that lipid bodies--inducible non-membrane bound cytoplasmic lipid domains--function as specialized intracellular sites of compartmentalization of signaling with major roles in lipid mediator formation within leukocytes engaged in inflammatory process. Over the past years substantial progresses have been made demonstrating that all enzymes involved in eicosanoid synthesis localize at lipid bodies and lipid bodies are distinct sites for eicosanoid generation. Here we will review our current knowledge on the mechanisms of formation and functions of lipid bodies pertinent to inflammation.

Occurence of lipid bodies in canine type II pneumocytes during hypothermic lung ischemia

Type II pneumocytes defend the pulmonary alveolus by synthesis and secretion of surfactant and by contributing to alveolar epithelial regeneration. Lipid bodies are regarded as intracellular domains for the synthesis of eicosanoid mediators that can be induced by inflammatory stimuli. The aim of the present study was to establish whether hypothermic ischemic lung storage without further preservation measures leads to an induction of lipid body formation in canine type II pneumocytes. The lungs of 18 dogs were fixed for transmission electron microscopy (TEM) immediately after cardiac arrest (six double lungs) and after ischemic storage in Tutofusin solution at 4 degrees C for 20 min, 4 hr, 8 hr, and 12 hr (six single lungs, respectively). Type II pneumocytes were analyzed qualitatively by conventional TEM (CTEM) and quantitatively by stereology. The relative phosphorus content of surfactant containing lamellar bodies, lipid bodies, and intermediate forms was investigated by energy-filtering TEM (EFTEM). By CTEM, lipid bodies as well as forms intermediate between lipid bodies and lamellar bodies were already noted in the control group but were more pronounced in the ischemia groups. Beginning at 20 min of ischemic storage, a significant increase in the volume density of lipid bodies was noted in the ischemic groups as compared to the control group. By EFTEM, the highest intracellular phosphorus signals were recorded over lamellar bodies and lamellar areas of intermediate forms in all experimental groups, while lipid bodies and homogeneous areas of intermediate forms did not show a clear phosphorus signal. These results indicate that the formation of lipid bodies in canine type II pneumocytes is induced early during ischemic lung storage.

Electron microscope immunocytochemical localization of cyclooxygenase-1 and -2 in pseudopregnant rat corpus luteum during luteolysis

Prostaglandins converted from arachidonic acid by cyclooxygenases play an important regulatory role in regression of the corpus luteum. To reveal luteal distribution of cyclooxygenase isoforms during luteolysis, an electron microscope immunocytochemical study was performed. Cyclooxygenase-1 and -2 were found both in luteal steroid-producing and interstitial cells on days 13, 15 and 18 of the adult pseudopregnant rat. Cyclooxygenase-2 immunolabelling was predominantly seen in non-luteal cells. The two enzymes were localized in similar fashion to the plasma membrane, rough and smooth endoplasmic reticulum, lipid bodies and mitochondria, but differently in the nuclear compartment. Cyclooxygenase-1 labelling was found only in the perinuclear region, while cyclooxygenase-2 was localized to the nuclear envelope, region of condensed heterochromatin as well as at the perimeter of the heterochromatin. Nuclear residence may indicate additional roles for cyclooxygenase-2 in regulating gene expression. Identification of both enzymes on lipid bodies suggests that these inclusions may be involved in luteal prostanoid production.

Synergism between platelet-activating factor-like phospholipids and peroxisome proliferator-activated receptor gamma agonists generated during low density lipoprotein oxidation that induces lipid body formation in leukocytes

Oxidized low density lipoprotein (LDL) has an important proinflammatory role in atherogenesis. In this study, we investigated the ability of oxidized LDL (oxLDL) and its phospholipid components to induce lipid body formation in leukocytes. Incubation of mouse peritoneal macrophages with oxidized, but not with native LDL led to lipid body formation within 1 h. This was blocked by platelet-activating factor (PAF) receptor antagonists or by preincubation of oxLDL with rPAF acetylhydrolase. HPLC fractions of phospholipids purified from oxLDL induced calcium flux in neutrophils as well as lipid body formation in macrophages. Injection of the bioactive phospholipid fractions or butanoyl and butenoyl PAF, a phospholipid previously shown to be present in oxLDL, into the pleural cavity of mice induced lipid body formation in leukocytes recovered after 3 h. The 5-lipoxygenase and cyclooxygenase-2 colocalized within lipid bodies formed after stimulation with oxLDL, bioactive phospholipid fractions, or butanoyl and butenoyl PAF. Lipid body formation was inhibited by 5-lipoxygenase antagonists, but not by cyclooxygenase-2 inhibitors. Azelaoyl-phosphatidylcholine, a peroxisome proliferator-activated receptor-gamma agonist in oxLDL phospholipid fractions, induced formation of lipid bodies at late time points (6 h) and synergized with suboptimal concentrations of oxLDL. We conclude that lipid body formation is an important proinflammatory effect of oxLDL and that PAF-like phospholipids and peroxisome proliferator-activated receptor-gamma agonists generated during LDL oxidation are important mediators in this phenomenon.