Differential Impact In Vivo of Pf4-ΔCre-Mediated and Gp1ba-ΔCre-Mediated Depletion of Cyclooxygenase-1 in Platelets in Mice

BACKGROUND

Low-dose aspirin is widely used for the secondary prevention of cardiovascular disease. The beneficial effects of low-dose aspirin are attributable to its inhibition of platelet Cox (cyclooxygenase)-1-derived thromboxane A2. Until recently, the use of the Pf4 (platelet factor 4) Cre has been the only genetic approach to generating megakaryocyte/platelet ablation of Cox-1 in mice. However, Pf4-ΔCre displays ectopic expression outside the megakaryocyte/platelet lineage, especially during inflammation. The use of the Gp1ba (glycoprotein 1bα) Cre promises a more specific, targeted approach.

METHODS

To evaluate the role of Cox-1 in platelets, we crossed Pf4-ΔCre or Gp1ba-ΔCre mice with Cox-1flox/flox mice to generate platelet Cox-1-/- mice on normolipidemic and hyperlipidemic (Ldlr-/-) backgrounds.

RESULTS

Ex vivo platelet aggregation induced by arachidonic acid or adenosine diphosphate in platelet-rich plasma was inhibited to a similar extent in Pf4-ΔCre Cox-1-/-/Ldlr-/- and Gp1ba-ΔCre Cox-1-/-/Ldlr-/- mice. In a mouse model of tail injury, Pf4-ΔCre-mediated and Gp1ba-ΔCre-mediated deletions of Cox-1 were similarly efficient in suppressing platelet prostanoid biosynthesis. Experimental thrombogenesis and attendant blood loss were similar in both models. However, the impact on atherogenesis was divergent, being accelerated in the Pf4-ΔCre mice while restrained in the Gp1ba-ΔCres. In the former, accelerated atherogenesis was associated with greater suppression of PGI2 biosynthesis, a reduction in the lipopolysaccharide-evoked capacity to produce PGE2 and PGD2, activation of the inflammasome, elevated plasma levels of IL-1β, reduced plasma levels of HDL-C, and a reduction in the capacity for reverse cholesterol transport. By contrast, in the latter, plasma HDL-C and α-tocopherol were elevated, and MIP-1α (macrophage inflammatory protein-1α) and MCP-1 (monocyte chemoattractant protein 1) were reduced.

CONCLUSIONS

Both approaches to Cox-1 deletion similarly restrain thrombogenesis, but a differential impact on Cox-1-dependent prostanoid formation by the vasculature may contribute to an inflammatory phenotype and accelerated atherogenesis in Pf4-ΔCre mice.

Circadian regulation of lung repair and regeneration

Optimal lung repair and regeneration are essential for recovery from viral infections, including influenza A virus (IAV). We have previously demonstrated that acute inflammation and mortality induced by IAV is under circadian control. However, it is not known whether the influence of the circadian clock persists beyond the acute outcomes. Here, we utilize the UK Biobank to demonstrate an association between poor circadian rhythms and morbidity from lower respiratory tract infections, including the need for hospitalization and mortality after discharge; this persists even after adjusting for common confounding factors. Furthermore, we use a combination of lung organoid assays, single-cell RNA sequencing, and IAV infection in different models of clock disruption to investigate the role of the circadian clock in lung repair and regeneration. We show that lung organoids have a functional circadian clock and the disruption of this clock impairs regenerative capacity. Finally, we find that the circadian clock acts through distinct pathways in mediating lung regeneration - in tracheal cells via the Wnt/β-catenin pathway and through IL-1β in alveolar epithelial cells. We speculate that adding a circadian dimension to the critical process of lung repair and regeneration will lead to novel therapies and improve outcomes.

LncRNAs and Cardiovascular Disease

A novel class of RNA molecule emerged from human transcriptome sequencing studies termed long non-coding RNAs. These RNA molecules differ from other classes of non-coding RNAs such as microRNAs in their sizes, sequence motifs and structures. Studies have demonstrated that long non-coding RNAs play a prominent role in the development and progression of cardiovascular disease. They provide the cell with tiered levels of gene regulation interacting with DNA, other RNA molecules or proteins acting in various capacities to control a variety of cellular mechanisms. Cell specificity is a hallmark of lncRNA studies and they have been identified in macrophages, smooth muscle cells, endothelial cells and hepatocytes. Recent lncRNA studies have uncovered functional micropeptides encoded within lncRNA genes that can have a different function to the lncRNA. Disease associated mutations in the genome tend to occur in non-coding regions signifying the importance of non-coding genes in disease associations. There is a great deal of work to be done in the non-coding RNA field and tremendous therapeutic potential due to their cell type specificity. A better understanding of the functions and interactions of lncRNAs will inevitably have clinical implications.

Sex-dependent compensatory mechanisms preserve blood pressure homeostasis in prostacyclin receptor-deficient mice

Inhibitors of microsomal prostaglandin E synthase 1 (mPGES-1) are in the early phase of clinical development. Deletion of mPges-1 in mice confers analgesia, restrains atherogenesis, and fails to accelerate thrombogenesis, while suppressing prostaglandin E2 (PGE2), but increasing the biosynthesis of prostacyclin (PGI2). In low-density lipoprotein receptor-deficient (Ldlr-/-) mice, this last effect represents the dominant mechanism by which mPges-1 deletion restrains thrombogenesis, while suppression of PGE2 accounts for its antiatherogenic effect. However, the effect of mPges-1 depletion on blood pressure (BP) in this setting remains unknown. Here, we show that mPges-1 depletion significantly increased the BP response to salt loading in male Ldlr-/- mice, whereas, despite the direct vasodilator properties of PGI2, deletion of the I prostanoid receptor (Ipr) suppressed this response. Furthermore, combined deletion of the Ipr abrogated the exaggerated BP response in male mPges-1-/- mice. Interestingly, these unexpected BP phenotypes were not observed in female mice fed a high-salt diet (HSD). This is attributable to the protective effect of estrogen in Ldlr-/- mice and in Ipr-/- Ldlr-/- mice. Thus, estrogen compensates for a deficiency in PGI2 to maintain BP homeostasis in response to high salt in hyperlipidemic female mice. In male mice, by contrast, the augmented formation of atrial natriuretic peptide (ANP) plays a similar compensatory role, restraining hypertension and oxidant stress in the setting of Ipr depletion. Hence, men with hyperlipidemia on a HSD might be at risk of a hypertensive response to mPGES-1 inhibitors.

Battle for supremacy: nucleic acid interactions between viruses and cells

Since the COVID-19 pandemic swept across the globe, researchers have been trying to understand its origin, life cycle, and pathogenesis. There is a striking variability in the phenotypic response to infection with SARS-CoV-2 that may reflect differences in host genetics and/or immune response. It is known that the human epigenome is influenced by ethnicity, age, lifestyle, and environmental factors, including previous viral infections. This Review examines the influence of viruses on the host epigenome. We describe general lessons and methodologies that can be used to understand how the virus evades the host immune response. We consider how variation in the epigenome may contribute to heterogeneity in the response to SARS-CoV-2 and may identify a precision medicine approach to treatment.

The long noncoding RNA CHROME regulates cholesterol homeostasis in primate

The human genome encodes thousands of long non-coding RNAs (lncRNAs), the majority of which are poorly conserved and uncharacterized. Here we identify a primate-specific lncRNA (CHROME), elevated in the plasma and atherosclerotic plaques of individuals with coronary artery disease, that regulates cellular and systemic cholesterol homeostasis. LncRNA CHROME expression is influenced by dietary and cellular cholesterol via the sterol-activated liver X receptor transcription factors, which control genes mediating responses to cholesterol overload. Using gain- and loss-of-function approaches, we show that CHROME promotes cholesterol efflux and HDL biogenesis by curbing the actions of a set of functionally related microRNAs that repress genes in those pathways. CHROME knockdown in human hepatocytes and macrophages increases levels of miR-27b, miR-33a, miR-33b and miR-128, thereby reducing expression of their overlapping target gene networks and associated biologic functions. In particular, cells lacking CHROME show reduced expression of ABCA1, which regulates cholesterol efflux and nascent HDL particle formation. Collectively, our findings identify CHROME as a central component of the non-coding RNA circuitry controlling cholesterol homeostasis in humans.

Genetic Models Reveal cis and trans Immune-Regulatory Activities for lincRNA-Cox2

An inducible gene expression program is a hallmark of the host inflammatory response. Recently, long intergenic non-coding RNAs (lincRNAs) have been shown to regulate the magnitude, duration, and resolution of these responses. Among these is lincRNA-Cox2, a dynamically regulated gene that broadly controls immune gene expression. To evaluate the in vivo functions of this lincRNA, we characterized multiple models of lincRNA-Cox2-deficient mice. LincRNA-Cox2-deficient macrophages and murine tissues had altered expression of inflammatory genes. Transcriptomic studies from various tissues revealed that deletion of the lincRNA-Cox2 locus also strongly impaired the basal and inducible expression of the neighboring gene prostaglandin-endoperoxide synthase (Ptgs2), encoding cyclooxygenase-2, a key enzyme in the prostaglandin biosynthesis pathway. By utilizing different genetic manipulations in vitro and in vivo, we found that lincRNA-Cox2 functions through an enhancer RNA mechanism to regulate Ptgs2. More importantly, lincRNA-Cox2 also functions in trans, independently of Ptgs2, to regulate critical innate immune genes in vivo.

Abstract 594: Long Non-coding RNA Regulation of the Interleukin-1 Gene Family Cluster

Long non-coding RNAs (lncRNAs) are a poorly understood class of regulatory RNAs, known to be highly species specific and capable of binding DNA, RNA, and/or protein to regulate transcriptional and epigenetic networks. Although thousands of lncRNAs have been identified in disease-related screens, only a few have been functionally characterized. Here we identify a primate-specific lncRNA, CHROME, located on human chr2 in a locus associated with premature cardiovascular disease, which regulates the expression of the IL-1 family of cytokines. Using RNA fluorescence in situ hybridization (FISH) and cell fractionation, we show that CHROME is abundant in the nucleus. Furthermore, its expression is induced in primary human macrophages treated with pro-inflammatory Toll-like receptor (TLR) agonists. To investigate CHROME function, we used RNA immunoprecipitation (RIP) to map RNA-protein interactions, and found that CHROME has strong histone binding affinity, suggesting a potential role in gene regulation. Notably, repression of CHROME using anti-sense oligonucleotides leads to a decrease in expression of genes in the IL-1 family gene cluster located nearby on the q arm of chromosome 2, including IL1A , IL1B and IL1RL1 . These data suggest that CHROME may act as a scaffold for chromatin modification of the IL-1 locus, thereby regulating transcription of these potent inflammatory cytokines. This hypothesis is currently being tested using ChIRP (chromatin isolation by RNA purification) coupled with high throughput DNA sequencing and mass spectrometry. As studies support a causal role for IL-1α and IL-1β in the promotion of atherosclerosis, further characterization of CHROME and its regulatory network may uncover novel opportunities for therapeutic intervention in cardiovascular diseases, and other inflammatory diseases in which IL-1 cytokines predominate.

Abstract 403: Identification of CHROME as a Competing Endogenous RNA that Regulates Cholesterol Homeostasis

The discovery of microRNAs (miRNA) targeting gene pathways involved in HDL and LDL metabolism illuminated the potent role of non-coding RNAs in the regulation of cholesterol homeostasis. Long non-coding RNAs (lncRNA) have also been identified as crucial regulators of gene expression; however, few have been fully characterized. Here we report a novel human lncRNA, CHROME (Cholesterol Homeostasis Regulator Of MicroRNA Expression), that functions as a competing endogenous RNA to regulate cellular cholesterol homeostasis. We show that CHROME has 7 broadly expressed variants that are transcriptionally regulated by the cholesterol-sensing liver X receptors. Computational analyses revealed that CHROME harbors binding sites for multiple (11) miRNAs involved in cholesterol homeostasis, including miR-27b and miR-33a/b, which function as hubs controlling the expression of genes involved in cholesterol efflux and HDL metabolism. Using CHROME knock-down and overexpression, we demonstrate that CHROME acts as a ‘miRNA sponge’ that sequesters these miRNAs, limiting their ability to repress target genes, including ABCA1, OSBPL6 and ANGPTL3. Consistent with this, we show that overexpression of CHROME increases cholesterol efflux, whereas its silencing reduces cholesterol efflux from primary human hepatocytes and macrophages. As hepatic cholesterol efflux via ABCA1 plays a central role in HDL biogenesis, we investigated the relationship of CHROME to its miRNA targets and plasma levels of HDL cholesterol in liver samples from a cohort of 200 healthy individuals. This analysis showed that CHROME is inversely correlated with miR-27b and miR-33a/b levels, and positively correlated with levels of their target genes and plasma HDL cholesterol. Collectively, these findings identify CHROME as a key regulatory component of the non-coding RNA circuitry that controls cellular cholesterol efflux and plasma HDL levels in humans.

miRNA Targeting of Oxysterol-Binding Protein-Like 6 Regulates Cholesterol Trafficking and Efflux

OBJECTIVE

Cholesterol homeostasis is fundamental to human health and is, thus, tightly regulated. MicroRNAs exert potent effects on biological pathways, including cholesterol metabolism, by repressing genes with related functions. We reasoned that this mode of pathway regulation could be exploited to identify novel genes involved in cholesterol homeostasis.

APPROACH AND RESULTS

Here, we identify oxysterol-binding protein-like 6 (OSBPL6) as a novel target of 2 miRNA hubs regulating cholesterol homeostasis: miR-33 and miR-27b. Characterization of OSBPL6 revealed that it is transcriptionally regulated in macrophages and hepatocytes by liver X receptor and in response to cholesterol loading and in mice and nonhuman primates by Western diet feeding. OSBPL6 encodes the OSBPL-related protein 6 (ORP6), which contains dual membrane- and endoplasmic reticulum-targeting motifs. Subcellular localization studies showed that ORP6 is associated with the endolysosomal network and endoplasmic reticulum, suggesting a role for ORP6 in cholesterol trafficking between these compartments. Accordingly, knockdown of OSBPL6 results in aberrant clustering of endosomes and promotes the accumulation of free cholesterol in these structures, resulting in reduced cholesterol esterification at the endoplasmic reticulum. Conversely, ORP6 overexpression enhances cholesterol trafficking and efflux in macrophages and hepatocytes. Moreover, we show that hepatic expression of OSBPL6 is positively correlated with plasma levels of high-density lipoprotein cholesterol in a cohort of 200 healthy individuals, whereas its expression is reduced in human atherosclerotic plaques.

CONCLUSIONS

These studies identify ORP6 as a novel regulator of cholesterol trafficking that is part of the miR-33 and miR-27b target gene networks that contribute to the maintenance of cholesterol homeostasis.

Abstract 14: Identification of Linc-OSBPL6 as a Competing Endogenous RNA that Regulates Cholesterol Homeostasis

Long non-coding RNAs (lncRNAs) have emerged as important regulators of gene expression in diverse biological contexts. Although several thousand lncRNAs have been identified in humans, only a small number have been fully characterized. Here we identify a novel human lncRNA, linc-OSBPL6, that functions as a competing endogenous RNA to regulate cellular cholesterol homeostasis. Linc-OSBPL6 has 7 variants that are broadly expressed in various cell types and tissues, and are controlled at the transcriptional level by the cholesterol-sensing nuclear receptor liver X receptor. We noted that each of the linc-OSBPL6 variants harbors binding sites for miR-27b and miR-33a/b, microRNAs recently identified as hubs controlling the expression of genes involved in cellular cholesterol efflux and HDL metabolism. Using linc-OSBPL6 knockdown and overexpression, combined with RNA profiling, we demonstrate that linc-OSBPL6 acts as a ‘microRNA sponge’ to limit availability of miR-27b and miR33a/b and inversely regulate expression of their target genes (ABCA1, OSBPL6, ANGPTL3, CROT, ABCB11). Consistent with the role of miR-27b and miR-33a/b in repressing cellular cholesterol export, we show that overexpression of linc-OSBPL6 increases cholesterol efflux, while shRNA-silencing of linc-OSBPL6 reduces cholesterol efflux from hepatocytes and macrophages. As cholesterol efflux in the liver plays a central role in HDL biogenesis, we investigated the relationship of hepatic linc-OSBPL6 to its microRNA-targets and plasma levels of HDL cholesterol in a cohort of 200 healthy individuals. We found that expression of linc-OSBPL6 is negatively correlated with levels of miR-27b and miR-33a/b in the liver, and positively correlated with levels of their target genes and plasma HDL cholesterol. These findings identify linc-OSBPL6 as a key regulatory component of the non-coding RNA circuitry that controls cellular cholesterol efflux and plasma HDL levels in humans.

Abstract 610: Netrin-1 Promotes Macrophage Accumulation and Insulin Resistance in Obesity

Obesity and its co-morbidities, type 2 diabetes and cardiovascular disease, continue to increase and are a major threat to global health. Studies in mice and humans have shown that expansion of adipose tissue mass is closely associated with the recruitment of cells of the myeloid and lymphoid lineage, which gives rise to a state of chronic inflammation that contributes to insulin resistance and type 2 diabetes. The factors that regulate the metabolic-dependent accrual of macrophages in adipose are not well understood. We show that the neuroimmune guidance cue netrin-1 is highly expressed in obese, but not lean adipose tissue of humans and mice, where it directs the retention of macrophages. In a mouse model of diet-induced obesity, we show that adipose tissue macrophages exhibit reduced migratory capacity ex vivo, which is reversed by blocking the effects of netrin-1. In vitro, expression of netrin-1 is induced in macrophages by the saturated fatty acid palmitate, and it acts by the receptor Unc5b to block macrophage migration to the chemokine CCL19, which directs the emigration of inflammatory macrophages from tissues. Using bone marrow transplantation, we show that hematopoietic deletion of Ntn1 facilitates adipose tissue macrophage emigration to the mesenteric lymph nodes, reduces inflammation, and improves insulin sensitivity and signaling in target tissues. Collectively, these findings identify netrin-1 as a macrophage retention signal that is induced in adipose tissue during obesity, which promotes chronic inflammation and insulin resistance.

Using microRNA as an alternative treatment for hyperlipidemia and cardiovascular disease: cardio-miRs in the pipeline

It is now appreciated that over 90% of the human genome is comprised of noncoding RNAs that have the ability to affect other components of the genome and regulate gene expression. This has galvanized the development of RNA-based therapeutics for a myriad of diseases, including cancer, inflammatory conditions, and cardiovascular disease. Several classes of RNA therapeutics are currently under clinical development, including antisense oligonucleotides, small interfering RNA, and microRNA mimetics and inhibitors. The field of antisense technology saw a huge leap forward with the recent Food and Drug Administration approval of the first antisense therapy, directed against apolipoprotein B, for the treatment of familial hypercholesterolemia. In addition, recent progress in the development of approaches to inhibit microRNAs has helped to illuminate their roles in repressing gene networks and also revealed their potential as therapeutic targets. In this review, these exciting opportunities in the field of drug discovery, with a focus on emerging therapeutics in the field of cardiovascular disease, are summarized.

Netrin-1 promotes adipose tissue macrophage retention and insulin resistance in obesity

During obesity, macrophage accumulation in adipose tissue propagates the chronic inflammation and insulin resistance associated with type 2 diabetes. The factors, however, that regulate the accrual of macrophages in adipose tissue are not well understood. Here we show that the neuroimmune guidance cue netrin-1 is highly expressed in obese but not lean adipose tissue of humans and mice, where it directs the retention of macrophages. Netrin-1, whose expression is induced in macrophages by the saturated fatty acid palmitate, acts via its receptor Unc5b to block their migration. In a mouse model of diet-induced obesity, we show that adipose tissue macrophages exhibit reduced migratory capacity, which can be restored by blocking netrin-1. Furthermore, hematopoietic deletion of Ntn1 facilitates adipose tissue macrophage emigration, reduces inflammation and improves insulin sensitivity. Collectively, these findings identify netrin-1 as a macrophage retention signal in adipose tissue during obesity that promotes chronic inflammation and insulin resistance.

Single step reconstitution of multifunctional high-density lipoprotein-derived nanomaterials using microfluidics

High-density lipoprotein (HDL) is a natural nanoparticle that transports peripheral cholesterol to the liver. Reconstituted high-density lipoprotein (rHDL) exhibits antiatherothrombotic properties and is being considered as a natural treatment for cardiovascular diseases. Furthermore, HDL nanoparticle platforms have been created for targeted delivery of therapeutic and diagnostic agents. The current methods for HDL reconstitution involve lengthy procedures that are challenging to scale up. A central need in the synthesis of rHDL, and multifunctional nanomaterials in general, is to establish large-scale production of reproducible and homogeneous batches in a simple and efficient fashion. Here, we present a large-scale microfluidics-based manufacturing method for single-step synthesis of HDL-mimicking nanomaterials (μHDL). μHDL is shown to have the same properties (e.g., size, morphology, bioactivity) as conventionally reconstituted HDL and native HDL. In addition, we were able to incorporate simvastatin (a hydrophobic drug) into μHDL, as well as gold, iron oxide, quantum dot nanocrystals or fluorophores to enable its detection by computed tomography (CT), magnetic resonance imaging (MRI), or fluorescence microscopy, respectively. Our approach may contribute to effective development and optimization of lipoprotein-based nanomaterials for medical imaging and drug delivery.

Abstract 22: OSBPL6 is a Novel miR-33 Target Gene Involved in Cellular Cholesterol Efflux

Cellular lipid homeostasis is fundamental to human health. Recent studies indicate that microRNAs (miRNAs) play important roles in the post-transcriptional regulation of lipid metabolism genes. This is illustrated by the discovery, by our group and others, of miR-33 as a central regulator of multiple aspects of lipid metabolism, including cholesterol efflux, fatty acid oxidation, and plasma levels of HDL cholesterol and VLDL triglycerides. In a study of miR-33 antagonism in non-human primates, we identified the most highly de-repressed miR-33 target gene as OSBPL6 (oxysterol binding protein like 6). A member of the OSBP family of cytosolic proteins that bind cholesterol/oxysterols, OSBPL6 contains an ER-targeting FFAT motif as well as a predicted plasma membrane-targeting pleckstrin homology domain, suggesting a putative role for OSBPL6 in vesicular traffic between these compartments. Notably, the OSBPL6 gene resides in a chromosome 2 locus associated with a predisposition to CAD in two major human heart disease studies (Family Heart Study, Framingham Heart Study). We therefore sought to further understand the regulation and function of OSBPL6 in cellular lipid homeostasis.

Results

We show that OSBPL6 is induced in macrophages and hepatocytes in response to cholesterol loading in vitro, as well as in the livers of LDLR-/- mice and non-human primates fed a high fat diet. Overexpression of miR-33 reduces OSBPL6-3’UTR activity by 40%, and this repression is relieved by mutation of the putative miR-33 binding site in the 3’UTR, confirming that OSBPL6 is a direct target of miR-33. Accordingly, transfection of HEPG2 cells with miR-33 mimic decreases mRNA expression of Osbpl6, but not the related family member Osbpl1. Notably, siRNA-mediated knockdown of OSBPL6 in cholesterol-loaded HEPG2 cells or THP-1 macrophages impairs cholesterol efflux to both apoA-I and HDL, and conversely, OSBPL6 overexpression enhances cholesterol efflux to these acceptors.

Conclusion

These data identify OSBPL6 as a novel miR-33 target gene in mice and humans that regulates cellular cholesterol trafficking and efflux via the ABC transporters, further highlighting the coordinated regulation by miR-33 of pathways that promote cellular cholesterol clearance.

Extracellular communication via microRNA: lipid particles have a new message

The complexity of microRNA (miRNA)-mediated pathway control has burgeoned since the discovery that miRNAs are found in the extracellular space and constitute a form of cell-cell communication. miRNAs have been found in plasma, urine, and saliva and have recently been shown to be carried on lipoproteins. This has led to the proposal that circulating miRNAs may be useful biomarkers of various diseases, including cardiovascular disease, diabetes, and other forms of dysregulated metabolism. Although our understanding of the cellular machinery responsible for the secretion of miRNA is incomplete, it has been demonstrated that miRNAs are packaged into exosomes, microvesicles, and apoptotic bodies by a broad range of cell types. Intriguingly, a large portion of extracellular miRNA is found outside of any lipid-containing vesicle, and instead is associated with RNA binding proteins like argonautes 1 and 2, which may aid in their protection from abundant nucleases in the extracellular space. The excitement for miRNAs as biomarkers is mounting as more and more evidence supports that these noncoding RNAs are actively secreted from diseased tissues, possibly before the onset of overt disease. While caution should be taken in these early days, there is little doubt that extracellular miRNAs will hold tremendous potential as both diagnostic and therapeutic agents.

Toll-like receptor-4 (TLR4) down-regulates microRNA-107, increasing macrophage adhesion via cyclin-dependent kinase 6

Toll-like receptors (TLRs) modulate the expression of multiple microRNAs (miRNAs). Here, we report the down-regulation of miR-107 by TLR4 in multiple cell types. The miR-107 sequence occurs in an intron within the sequence encoding the gene for pantothenate kinase 1α (PanK1α), which is regulated by the transcription factor peroxisome proliferator-activating receptor α (PPAR-α). PanK1α is also decreased in response to lipopolysaccharide (LPS). The effect on both miR-107 and PanK1α is consistent with a decrease in PPAR-α expression. We have found that the putative miR-107 target cyclin-dependent kinase 6 (CDK6) expression is increased by TLR4 as a result of the decrease in miR-107. This effect is required for increased adhesion of macrophages in response to LPS, and CDK6-deficient mice are resistant to the lethal effect of LPS. We have therefore identified a mechanism for LPS signaling which involves a decrease in miR-107 leading to an increase in CDK6.

Targeting Toll-like receptors: emerging therapeutics?

There is a growing interest in the targeting of Toll-like receptors (TLRs) for the prevention and treatment of cancer, rheumatoid arthritis, inflammatory bowel disease and systemic lupus erythematosus (SLE). Several new compounds are now undergoing preclinical and clinical evaluation, with a particular focus on TLR7 and TLR9 activators as adjuvants in infection and cancer, and inhibitors of TLR2, TLR4, TLR7 and TLR9 for the treatment of sepsis and inflammatory diseases. Here, we focus on TLRs that hold the most promise for drug discovery research, highlighting agents that are in the discovery phase and in clinical trials,and on the emerging new aspects of TLR-mediated signalling - such as control by ubiquitination and regulation by microRNAs - that might offer further possibilities of therapeutic manipulation.

Negative regulation of TLR4 via targeting of the proinflammatory tumor suppressor PDCD4 by the microRNA miR-21

The tumor suppressor PDCD4 is a proinflammatory protein that promotes activation of the transcription factor NF-kappaB and suppresses interleukin 10 (IL-10). Here we found that mice deficient in PDCD4 were protected from lipopolysaccharide (LPS)-induced death. The induction of NF-kappaB and IL-6 by LPS required PDCD4, whereas LPS enhanced IL-10 induction in cells lacking PDCD4. Treatment of human peripheral blood mononuclear cells with LPS resulted in lower PDCD4 expression, which was due to induction of the microRNA miR-21 via the adaptor MyD88 and NF-kappaB. Transfection of cells with a miR-21 precursor blocked NF-kappaB activity and promoted IL-10 production in response to LPS, whereas transfection with antisense oligonucleotides to miR-21 or targeted protection of the miR-21 site in Pdcd4 mRNA had the opposite effect. Thus, miR-21 regulates PDCD4 expression after LPS stimulation.

A systems biology analysis of the Drosophila phagosome

Phagocytes have a critical function in remodelling tissues during embryogenesis and thereafter are central effectors of immune defence. During phagocytosis, particles are internalized into 'phagosomes', organelles from which immune processes such as microbial destruction and antigen presentation are initiated. Certain pathogens have evolved mechanisms to evade the immune system and persist undetected within phagocytes, and it is therefore evident that a detailed knowledge of this process is essential to an understanding of many aspects of innate and adaptive immunity. However, despite the crucial role of phagosomes in immunity, their components and organization are not fully defined. Here we present a systems biology analysis of phagosomes isolated from cells derived from the genetically tractable model organism Drosophila melanogaster and address the complex dynamic interactions between proteins within this organelle and their involvement in particle engulfment. Proteomic analysis identified 617 proteins potentially associated with Drosophila phagosomes; these were organized by protein-protein interactions to generate the 'phagosome interactome', a detailed protein-protein interaction network of this subcellular compartment. These networks predicted both the architecture of the phagosome and putative biomodules. The contribution of each protein and complex to bacterial internalization was tested by RNA-mediated interference and identified known components of the phagocytic machinery. In addition, the prediction and validation of regulators of phagocytosis such as the 'exocyst', a macromolecular complex required for exocytosis but not previously implicated in phagocytosis, validates this strategy. In generating this 'systems-based model', we show the power of applying this approach to the study of complex cellular processes and organelles and expect that this detailed model of the phagosome will provide a new framework for studying host-pathogen interactions and innate immunity.

Response to Staphylococcus aureus requires CD36-mediated phagocytosis triggered by the COOH-terminal cytoplasmic domain

Phagocyte recognition and clearance of bacteria play essential roles in the host response to infection. In an on-going forward genetic screen, we identify the Drosophila melanogaster scavenger receptor Croquemort as a receptor for Staphylococcus aureus, implicating for the first time the CD36 family as phagocytic receptors for bacteria. In transfection assays, the mammalian Croquemort paralogue CD36 confers binding and internalization of Gram-positive and, to a lesser extent, Gram-negative bacteria. By mutational analysis, we show that internalization of S. aureus and its component lipoteichoic acid requires the COOH-terminal cytoplasmic portion of CD36, specifically Y463 and C464, which activates Toll-like receptor (TLR) 2/6 signaling. Macrophages lacking CD36 demonstrate reduced internalization of S. aureus and its component lipoteichoic acid, accompanied by a marked defect in tumor necrosis factor-α and IL-12 production. As a result, Cd36^−/− mice fail to efficiently clear S. aureus in vivo resulting in profound bacteraemia. Thus, response to S. aureus requires CD36-mediated phagocytosis triggered by the COOH-terminal cytoplasmic domain, which initiates TLR2/6 signaling.

Heart-lung interactions: the sigh and autonomic control in the bronchial and coronary circulations

1. The Darwin hypothesis that human and animal expressions of emotion are the product of evolution and are tied to patterns of autonomic activity specified to progress the emotion remains under challenge. 2. The sigh is a respiratory behaviour linked with emotional expression in animals and humans from birth to death. The aim of the present study was to explore Darwin's hypothesis with respect to tied autonomic activity underlying sigh-induced changes in the bronchial and coronary circulations. 3. Awake dogs were prepared using pulsed ultrasonic flow probes on the right bronchial artery, parent intercostal artery and brachial artery, or on the right, circumflex and anterior descending coronary arteries. Central venous (CVP) and arterial pressures (AP) were measured; heart rate and flow conductances were derived. Three spontaneous sighs were monitored before and during random blockade of individual and combinations of cholinoceptors, alpha-adrenoceptors and beta-adrenoceptors using methscopolamine, phentolamine and propranolol infusions. The data were subject to a 2(3) factorial analysis. 4. A spontaneous sigh is marked by a transient fall and return (< 3 s) in CVP of 18 mmHg (from 4 +/- 1 to -14 +/- 2 mmHg), usually followed by apnoea lasting 23 +/- 2 s. There is an immediate tachycardia and small rise in AP (phase 1) then, during apnoea, bradycardia and a fall in AP (phase 2). During phase 2, bronchial and coronary blood flow and conductance rise two- to three-fold over 30s (peak at 8s). The vascular changes are absent in parent intercostal and brachial beds.

Baroreflex control of coronary blood flow varies regionally in awake dogs

1. Baroreflex responses to changes in aortic pressure were measured simultaneously in three main coronary regions of awake dogs. 2. Pulsed Doppler flow probes were mounted at prior surgery on the right, circumflex and anterior descending coronary arteries; the animals were placed in complete heart block and the left ventricle was paced. After 2-4 weeks recovery, baroreflexes were evoked by inflating a balloon catheter placed in the mid-thoracic aorta via the femoral arteriotomy. Flow and pressure data were collected at rest, and during acute (8s) and steady-state (25s) baroreflex challenge. 3. Changing ventricular rate alone caused a fall in aortic pressure at low rates; however, over the range 60 to 180 b.p.m., circumflex and anterior descending coronary flow and conductance changed directly with ventricular rate, but right coronary flow and conductance remained unchanged. 4. Acute aortic pressure elevation increased flow at 8s in all beds at all rates. Conductance effects at 60 b.p.m. were negligible in all three beds, but rose at 100 and 180 b.p.m. in the right and circumflex beds. 5. Sustained aortic pressure elevation (25s) caused flow to return towards control in all beds ventricular rates, but in the right coronary at 60 b.p.m. flow fell below control. Conductance at this time was unchanged at all rates in the anterior descending bed, fell modestly in the circumflex, and decreased to below resting in the right coronary bed. 6. Baroreflex control of coronary flow and conductance thus varies between territories, and within territories, depending on ventricular rate. The right coronary bed appears to be regulated by a bidirectional, baroreflex-linked mechanism, which is functionally opposite in action to that found in most vascular beds.

Appearance of IgG and IgA antibodies in human bile after tetanus toxoid immunization

Humans immunized intramuscularly with one dose of tetanus toxoid exhibited IgG, and in some cases IgA antibody, in their bile as well as serum. Both isotypes appeared in bile transiently with titres declining after about day 10 for both classes. These kinetics resembled those of the serum IgA response but were markedly different to those for IgG antibody in serum. Measured IgG titres in bile were between 0.07 and 4.2% of those in paired sera, and IgA titres were between 6.8 and 124% of sera. Peak responses in bile, while generally of smaller size, exceeded those of paired sera when expressed as antibody/mg of IgG or IgA present. This calculation showed that during the peak response bile was up to nineteen-fold more abundant in IgG antibody than was serum taken at the same time, and up to forty-five-fold more for IgA. Enrichment of antibody in bile is not consistent with the Ig of bile being solely conferred by plasma, and may mean the involvement of local synthesis too. This study indicates that tetanus toxoid immunization of humans results in biliary antibody and raises the possibility of intra-hepatic antibody production for export to the intestinal tract in man.

Regulation of IgA secretion in polyclonally induced in vitro human lymphocyte cultures: the function of T and B cells from mesenteric lymph nodes and peripheral blood

Human gut-associated immunoregulatory events were studied in a pokeweed mitogen (PWM)-stimulated culture system using lymphocytes obtained from the mesenteric lymph nodes (MLN) of female subjects undergoing gastroplasty for obesity. Compared with peripheral blood lymphocytes, lymphocytes obtained from MLN secreted IgG, IgA and IgM isotypes that differ in pattern and distribution despite similar proportions of T cells and B cells expressing isotype-specific surface membrane immunoglobulin (SmIg). Among the isotypes secreted, IgA appeared to be increased relatively to other isotypes in MLN cultures. Crossover coculture experiments using T and B cells isolated from both MLN and blood by E-rosetting and cell panning procedures demonstrated that IgA was particularly sensitive to help and suppression exerted by MLN T cells and T cell subsets defined by monoclonal antibodies OKT4 and OKT8 respectively, when compared with similar subsets isolated from blood. The results presented provide a basis for study of gut handling of ingested antigen in man, and of disturbed immunoregulatory events in inflammatory and neoplastic disease of the human gut.

Study of lymphocyte interaction in human mesenteric lymph nodes in vitro

The immune function of lymphocytes isolated from human mesenteric lymph nodes (MLN) has been examined. Large yields of viable lymphocytes were obtained from MLN without the need for using enzyme or mucolytic agents. In comparison to gut mucosal lymphocytes, MLN lymphocytes (MLNL) were technically easier to manipulate and to use in providing a more quantitative analysis of T-B cell interaction. The results presented indicate that the pattern of immunoglobulin secretion and immunoregulation of lymphocytes isolated from MLN was similar to that in cells isolated from the lamina propria, supporting that MLN constitute an important component of gut-associated lymphoid tissue (GALT).

Perforated peptic ulcer long-term follow-up

A series of 349 survivors of perforated peptic ulcer was followed for periods of up to 23 years. Almost nine out of every 10 patients suffered from dyspepsia during follow-up. Subsequent elective gastroduodenal surgery was required in more than a quarter of the cases. The surgery rate for gastric ulcer was more than one and a half times that for pyloroduodenal ulcer, and for females almost double that for males. The highest rate of all was for females with gastric ulcer, of whom almost one half came for surgery. One in five patients bled during follow-up. One in eight developed stenosis of the stomach of duodenum, and one in 11 perforated again. There was a significantly increased incidence of subsequent perforation and stenosis in those with an initial perforation of 5 mm or more in diameter. Gastric carcinoma occurred in less than 2% of cases and was restricted to cases of pyloroduodenal perforation. When complications occurred, the majority did so within five years. Only 15% of the 262 patients about whom complete information was available had no complications on follow-up. The indications for definitive surgery at perforation should be extended to include perforated gastric ulcer in the female, particularly if the ulcer is large.