Regulation of vascular permeability by sphingosine 1-phosphate

Fingolimod (FTY720), an FDA-approved sphingosine 1-phosphate (S1P) receptor agonist, restores endothelial hyperpermeability in cellular and animal models of dengue virus serotype 2 infection

Extensive vascular leakage and shock is a major cause of dengue-associated mortality. At present, there are no specific treatments available. Sphingolipid pathway is a key player in the endothelial barrier integrity; and is mediated through the five sphingosine-1-phosphate receptors (S1PR1-S1PR5). Signaling through S1PR2 promotes barrier disruption; and in Dengue virus (DENV)-infection, there is overexpression of this receptor. Fingolimod (FTY720) is a specific agonist that targets the remaining barrier-protective S1P receptors, without targeting S1PR2. In the present study, we explored whether FTY720 treatment can alleviate DENV-induced endothelial hyperpermeability. In functional assays, in both in vitro systems and in AG129 animal models, FTY720 treatment was found effective. Upon treatment, there was complete restoration of the monolayer integrity in DENV serotype 2-infected human microvascular endothelial cells (HMEC-1). At the molecular level, the treatment reversed activation of the S1P pathway. It significantly reduced the phosphorylation of the key molecules such as PTEN, RhoA, and VE-Cadherin; and also, the expression levels of S1PR2. In DENV2-infected AG129 mice treated with FTY720, there was significant improvement in weight gain, in overall clinical symptoms, and in survival. Whereas 100% of the DENV2-infected, untreated animals died by day-10 post-infection, 70% of the FTY720-treated animals were alive; and at the end of the 15-day post-infection observation period, 30% of them were still surviving. There was a significant reduction in the Evan's-blue dye permeability in the organs of FTY720-treated, DENV-2 infected animals; and also improvement in the hemogram, with complete restoration of thrombocytopenia and hepatic function. Our results show that the FDA-approved molecule Fingolimod (FTY720) is a promising therapeutic intervention in severe dengue.

Sphingosine-1-phosphate receptor 3 regulates the transendothelial transport of high-density lipoproteins and low-density lipoproteins in opposite ways

AIMS

The entry of lipoproteins from blood into the arterial wall is a rate-limiting step in atherosclerosis. It is controversial whether this happens by filtration or regulated transendothelial transport.Because sphingosine-1-phosphate (S1P) preserves the endothelial barrier, we investigated in vivo and in vitro, whether S1P and its cognate S1P-receptor 3 (S1P3) regulate the transendothelial transport of lipoproteins.

METHODS AND RESULTS

Compared to apoE-haploinsufficient mice (CTRL), apoE-haploinsufficient mice with additional endothelium-specific knock-in of S1P3 (S1P3-iECKI) showed decreased transport of LDL and Evan's Blue but increased transport of HDL from blood into the peritoneal cave. After 30 weeks of high-fat diet feeding, S1P3-iECKI mice had lower levels of non-HDL-cholesterol and less atherosclerosis than CTRL mice. In vitro stimulation with an S1P3 agonist increased the transport of 125I-HDL but decreased the transport of 125I-LDL through human aortic endothelial cells (HAECs). Conversely, inhibition or knock-down of S1P3 decreased the transport of 125I-HDL but increased the transport of 125I-LDL. Silencing of SCARB1 encoding scavenger receptor B1 (SR-BI) abrogated the stimulation of 125I-HDL transport by the S1P3 agonist. The transendothelial transport of 125I-LDL was decreased by silencing of SCARB1 or ACVLR1 encoding activin-like kinase 1 but not by interference with LDLR. None of the three knock-downs prevented the stimulatory effect of S1P3 inhibition on transendothelial 125I-LDL transport.

CONCLUSION

S1P3 regulates the transendothelial transport of HDL and LDL oppositely by SR-BI-dependent and SR-BI-independent mechanisms, respectively. This divergence supports a contention that lipoproteins pass the endothelial barrier by specifically regulated mechanisms rather than passive filtration.

Investigation of the differentiation potential of pericyte cells as an alternative source of mesenchymal stem cells

BACKGROUND

The mesenchymal stem cells (MSCs) with characterized by their multipotency and capacity to differentiate into various tissue cell types, have led to their incorporation in regenerative medicine research. However, the limited numbers of MSCs in the human body and their diverse differentiation capabilities in tissues highlight the need for exploring alternative regenerative cell sources. In this study, therefore, we conducted molecular level examinations to determine whether pericytes, specialized cell communities situated near blood vessels, could serve as a substitute for human bone marrow-derived mesenchymal stem cells (hBM-MSCs). In this context, the potential application of pericytes surrounds the vessels when MSCs are insufficient for functional purposes.

METHODS

The pericytes utilized in this investigation were derived from the placenta and characterized at the third passage. Similarly, the hBM-MSCs were also characterized at the third passage. The pluripotent properties of the two cell types were assessed at the gene expression level. Thereafter, both pericytes and hBM-MSCs were directed towards adipogenic, osteogenic and chondrogenic differentiation. The cells in both groups were examined on days 7, 14, and, 21 and their differentiation status was compared both immunohistochemically and through gene expression analysis.

RESULTS

Upon comparing the pluripotency characteristics of placental pericytes and hBM-MSCs, it was discovered that there was a substantial upregulation of the pluripotency genes FoxD3, Sox2, ZPF42, UTF1, and, Lin28 in both cell types. However, no significant expression of the genes Msx1, Nr6a1, Pdx1, and, GATA6 was observed in either cell type. It was also noted that pericytes differentiate into adipogenic, osteogenic and, chondrogenic lineages similar to hBM-MSCs.

DISCUSSION

As a result, it has been determined that pericytes exhibit high differentiation and proliferation properties similar to those of MSCs, and therefore can be considered a suitable alternative cell source for regenerative medicine and tissue engineering research, in cases where MSCs are not available or insufficient. It is notable that pericytes have been suggested as a potential substitute in studies where MSCs are lacking.

A mechanical modeling framework to study endothelial permeability

The inner lining of blood vessels, the endothelium, is made up of endothelial cells. Vascular endothelial (VE)-cadherin protein forms a bond with VE-cadherin from neighboring cells to determine the size of gaps between the cells and thereby regulate the size of particles that can cross the endothelium. Chemical cues such as thrombin, along with mechanical properties of the cell and extracellular matrix are known to affect the permeability of endothelial cells. Abnormal permeability is found in patients suffering from diseases including cardiovascular diseases, cancer, and COVID-19. Even though some of the regulatory mechanisms affecting endothelial permeability are well studied, details of how several mechanical and chemical stimuli acting simultaneously affect endothelial permeability are not yet understood. In this article, we present a continuum-level mechanical modeling framework to study the highly dynamic nature of the VE-cadherin bonds. Taking inspiration from the catch-slip behavior that VE-cadherin complexes are known to exhibit, we model the VE-cadherin homophilic bond as cohesive contact with damage following a traction-separation law. We explicitly model the actin cytoskeleton and substrate to study their role in permeability. Our studies show that mechanochemical coupling is necessary to simulate the influence of the mechanical properties of the substrate on permeability. Simulations show that shear between cells is responsible for the variation in permeability between bicellular and tricellular junctions, explaining the phenotypic differences observed in experiments. An increase in the magnitude of traction force due to disturbed flow that endothelial cells experience results in increased permeability, and it is found that the effect is higher on stiffer extracellular matrix. Finally, we show that the cylindrical monolayer exhibits higher permeability than the planar monolayer under unconstrained cases. Thus, we present a contact mechanics-based mechanochemical model to investigate the variation in the permeability of endothelial monolayer due to multiple loads acting simultaneously.

Myocardial Oedema as a Consequence of Viral Infection and Persistence-A Narrative Review with Focus on COVID-19 and Post COVID Sequelae

Microvascular integrity is a critical factor in myocardial fluid homeostasis. The subtle equilibrium between capillary filtration and lymphatic fluid removal is disturbed during pathological processes leading to inflammation, but also in hypoxia or due to alterations in vascular perfusion and coagulability. The degradation of the glycocalyx as the main component of the endothelial filtration barrier as well as pericyte disintegration results in the accumulation of interstitial and intracellular water. Moreover, lymphatic dysfunction evokes an increase in metabolic waste products, cytokines and inflammatory cells in the interstitial space contributing to myocardial oedema formation. This leads to myocardial stiffness and impaired contractility, eventually resulting in cardiomyocyte apoptosis, myocardial remodelling and fibrosis. The following article reviews pathophysiological inflammatory processes leading to myocardial oedema including myocarditis, ischaemia-reperfusion injury and viral infections with a special focus on the pathomechanisms evoked by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In addition, clinical implications including potential long-term effects due to viral persistence (long COVID), as well as treatment options, are discussed.

Signaling pathways and potential therapeutic targets in acute respiratory distress syndrome (ARDS)

Acute respiratory distress syndrome (ARDS) is a common condition associated with critically ill patients, characterized by bilateral chest radiographical opacities with refractory hypoxemia due to noncardiogenic pulmonary edema. Despite significant advances, the mortality of ARDS remains unacceptably high, and there are still no effective targeted pharmacotherapeutic agents. With the outbreak of coronavirus disease 19 worldwide, the mortality of ARDS has increased correspondingly. Comprehending the pathophysiology and the underlying molecular mechanisms of ARDS may thus be essential to developing effective therapeutic strategies and reducing mortality. To facilitate further understanding of its pathogenesis and exploring novel therapeutics, this review provides comprehensive information of ARDS from pathophysiology to molecular mechanisms and presents targeted therapeutics. We first describe the pathogenesis and pathophysiology of ARDS that involve dysregulated inflammation, alveolar-capillary barrier dysfunction, impaired alveolar fluid clearance and oxidative stress. Next, we summarize the molecular mechanisms and signaling pathways related to the above four aspects of ARDS pathophysiology, along with the latest research progress. Finally, we discuss the emerging therapeutic strategies that show exciting promise in ARDS, including several pharmacologic therapies, microRNA-based therapies and mesenchymal stromal cell therapies, highlighting the pathophysiological basis and the influences on signal transduction pathways for their use.

Amphipathic Helical Peptide L37pA Protects against Lung Vascular Endothelial Dysfunction Caused by Truncated Oxidized Phospholipids via Antagonism with CD36 Receptor

The generation of bioactive truncated oxidized phospholipids (Tr-OxPLs) from oxidation of cell-membrane or circulating lipoproteins is a common feature of various pathological states. Scavenger receptor CD36 is involved in lipid transport and acts as a receptor for Tr-OxPLs. Interestingly, Tr-OxPLs and CD36 are involved in endothelial dysfunction-derived acute lung injury, but the precise mechanistic connections remain unexplored. In the present study, we investigated the role of CD36 in mediating pulmonary endothelial cell (EC) dysfunction caused by Tr-OxPLs. Our results demonstrated that the Tr-OxPLs KOdia-PC, Paz-PC, PGPC, PON-PC, POV-PC, and lysophosphocholine caused an acute EC barrier disruption as revealed by measurements of transendothelial electrical resistance and VE-cadherin immunostaining. More importantly, a synthetic amphipathic helical peptide, L37pA, targeting human CD36 strongly attenuated Tr-OxPL-induced EC permeability. L37pA also suppressed Tr-OxPL-induced endothelial inflammatory activation monitored by mRNA expression of inflammatory cytokines/chemokines and adhesion molecules. In addition, L37pA blocked Tr-OxPL-induced NF-κB activation and tyrosine phosphorylation of Src kinase and VE-cadherin. The Src inhibitor SU6656 attenuated KOdia-PC-induced EC permeability and inflammation, but inhibition of the Toll-like receptors (TLRs) TLR1, TLR2, TLR4, and TLR6 had no such protective effects. CD36-knockout mice were more resistant to Tr-OxPL-induced lung injury. Treatment with L37pA was equally effective in ameliorating Tr-OxPL-induced vascular leak and lung inflammation as determined by an Evans blue extravasation assay and total cell and protein content in BAL fluid. Altogether, these results demonstrate an essential role of CD36 in mediating Tr-OxPL-induced EC dysfunction and suggest a strong therapeutic potential of CD36 inhibitory peptides in mitigating lung injury and inflammation.

Organotypic heterogeneity in microvascular endothelial cell responses in sepsis-a molecular treasure trove and pharmacological Gordian knot

In the last decades, it has become evident that endothelial cells (ECs) in the microvasculature play an important role in the pathophysiology of sepsis-associated multiple organ dysfunction syndrome (MODS). Studies on how ECs orchestrate leukocyte recruitment, control microvascular integrity and permeability, and regulate the haemostatic balance have provided a wealth of knowledge and potential molecular targets that could be considered for pharmacological intervention in sepsis. Yet, this information has not been translated into effective treatments. As MODS affects specific vascular beds, (organotypic) endothelial heterogeneity may be an important contributing factor to this lack of success. On the other hand, given the involvement of ECs in sepsis, this heterogeneity could also be leveraged for therapeutic gain to target specific sites of the vasculature given its full accessibility to drugs. In this review, we describe current knowledge that defines heterogeneity of organ-specific microvascular ECs at the molecular level and elaborate on studies that have reported EC responses across organ systems in sepsis patients and animal models of sepsis. We discuss hypothesis-driven, single-molecule studies that have formed the basis of our understanding of endothelial cell engagement in sepsis pathophysiology, and include recent studies employing high-throughput technologies. The latter deliver comprehensive data sets to describe molecular signatures for organotypic ECs that could lead to new hypotheses and form the foundation for rational pharmacological intervention and biomarker panel development. Particularly results from single cell RNA sequencing and spatial transcriptomics studies are eagerly awaited as they are expected to unveil the full spatiotemporal signature of EC responses to sepsis. With increasing awareness of the existence of distinct sepsis subphenotypes, and the need to develop new drug regimen and companion diagnostics, a better understanding of the molecular pathways exploited by ECs in sepsis pathophysiology will be a cornerstone to halt the detrimental processes that lead to MODS.

Role of sphingosine 1-phosphate (S1P) in sepsis-associated intestinal injury

Sphingosine-1-phosphate (S1P) is a widespread lipid signaling molecule that binds to five sphingosine-1-phosphate receptors (S1PRs) to regulate downstream signaling pathways. Sepsis can cause intestinal injury and intestinal injury can aggravate sepsis. Thus, intestinal injury and sepsis are mutually interdependent. S1P is more abundant in intestinal tissues as compared to other tissues, exerts anti-inflammatory effects, promotes immune cell trafficking, and protects the intestinal barrier. Despite the clinical importance of S1P in inflammation, with a very well-defined mechanism in inflammatory bowel disease, their role in sepsis-induced intestinal injury has been relatively unexplored. In addition to regulating lymphocyte exit, the S1P-S1PR pathway has been implicated in the gut microbiota, intestinal epithelial cells (IECs), and immune cells in the lamina propria. This review mainly elaborates on the physiological role of S1P in sepsis, focusing on intestinal injury. We introduce the generation and metabolism of S1P, emphasize the maintenance of intestinal barrier homeostasis in sepsis, and the protective effect of S1P in the intestine. We also review the link between sepsis-induced intestinal injury and S1P-S1PRs signaling, as well as the underlying mechanisms of action. Finally, we discuss how S1PRs affect intestinal function and become targets for future drug development to improve the translational capacity of preclinical studies to the clinic.

An erythrocyte-centric view on the MFSD2B sphingosine-1-phosphate transporter

MFSD2B has been identified as the exclusive sphingosine-1-phosphate (S1P) transporter in red blood cells (RBC) and platelets. MFSD2B-mediated S1P export from platelets is required for aggregation and thrombus formation, whereas RBC MFSD2B maintains plasma S1P levels in concert with SPNS2, the vascular and lymphatic endothelial cell S1P exporter, to control endothelial permeability and ensure normal vascular development. However, the physiological function of MFSD2B in RBC remains rather elusive despite mounting evidence that the intracellular S1P pool plays important roles in RBC glycolysis, adaptation to hypoxia and the regulation of cell shape, hydration, and cytoskeletal organisation. The large accumulation of S1P and sphingosine in MFSD2B-deficient RBC coincides with stomatocytosis and membrane abnormalities, the reasons for which have remained obscure. MFS family members transport substrates in a cation-dependent manner along electrochemical gradients, and disturbances in cation permeability are known to alter cell hydration and shape in RBC. Furthermore, the mfsd2 gene is a transcriptional target of GATA together with mylk3, the gene encoding myosin light chain kinase (MYLK). S1P is known to activate MYLK and thereby impact on myosin phosphorylation and cytoskeletal architecture. This suggests that metabolic, transcriptional and functional interactions may exist between MFSD2B-mediated S1P transport and RBC deformability. Here, we review the evidence for such interactions and the implications for RBC homeostasis.

The effect of Fingolimod on patients with moderate to severe COVID-19

Hyper-inflammation, cytokine storm, and recruitment of immune cells lead to uncontrollable endothelial cell damage in patients with coronavirus disease 2019 (COVID-19). Sphingosine 1-phosphate (S1P) signaling is needed for endothelial integrity and its decreased serum level is a predictor of clinical severity in COVID-19. In this clinical trial, the effect of Fingolimod, an agonist of S1P, was evaluated on patients with COVID-19. Forty patients with moderate to severe COVID-19 were enrolled and divided into two groups including (1) the control group (n = 21) receiving the national standard regimen for COVID-19 patients and (2) the intervention group (n = 19) that prescribed daily Fingolimod (0.5 mg) for 3 days besides receiving the standard national regimen for COVID-19. The hospitalization period, re-admission rate, intensive care unit (ICU) administration, need for mechanical ventilation, and mortality rate were assessed as primary outcomes in both groups. The results showed that re-admission was significantly decreased in COVID-19 patients who received Fingolimod compared to the controls (p = .04). In addition, the hemoglobin levels of the COVID-19 patients in the intervention group were increased compared to the controls (p = .018). However, no significant differences were found regarding the intubation or mortality rate between the groups (p > .05). Fingolimod could significantly reduce the re-admission rate after hospitalization with COVID-19. Fingolimod may not enhance patients' outcomes with moderate COVID-19. It is necessary to examine these findings in a larger cohort of patients with severe to critical COVID-19.

Tight Junctions, the Epithelial Barrier, and Toll-like Receptor-4 During Lung Injury

Lung epithelium is constantly exposed to the environment and is critically important for the orchestration of initial responses to infectious organisms, toxins, and allergic stimuli, and maintenance of normal gaseous exchange and pulmonary function. The integrity of lung epithelium, fluid balance, and transport of molecules is dictated by the tight junctions (TJs). The TJs are formed between adjacent cells. We have focused on the topic of the TJ structure and function in lung epithelial cells. This review includes a summary of the last twenty years of literature reports published on the disrupted TJs and epithelial barrier in various lung conditions and expression and regulation of specific TJ proteins against pathogenic stimuli. We discuss the molecular signaling and crosstalk among signaling pathways that control the TJ structure and function. The Toll-like receptor-4 (TLR4) recognizes the pathogen- and damage-associated molecular patterns released during lung injury and inflammation and coordinates cellular responses. The molecular aspects of TLR4 signaling in the context of TJs or the epithelial barrier are not fully known. We describe the current knowledge and possible networking of the TLR4-signaling with cellular and molecular mechanisms of TJs, lung epithelial barrier function, and resistance to treatment strategies.

Molecular Pharmacology and Novel Potential Therapeutic Applications of Fingolimod

Fingolimod is a well-tolerated, highly effective disease-modifying therapy successfully utilized in the management of multiple sclerosis. The active metabolite, fingolimod-phosphate, acts on sphingosine-1-phosphate receptors (S1PRs) to bring about an array of pharmacological effects. While being initially recognized as a novel agent that can profoundly reduce T-cell numbers in circulation and the CNS, thereby suppressing inflammation and MS, there is now rapidly increasing knowledge on its previously unrecognized molecular and potential therapeutic effects in diverse pathological conditions. In addition to exerting inhibitory effects on sphingolipid pathway enzymes, fingolimod also inhibits histone deacetylases, transient receptor potential cation channel subfamily M member 7 (TRMP7), cytosolic phospholipase A2α (cPLA2α), reduces lysophosphatidic acid (LPA) plasma levels, and activates protein phosphatase 2A (PP2A). Furthermore, fingolimod induces apoptosis, autophagy, cell cycle arrest, epigenetic regulations, macrophages M1/M2 shift and enhances BDNF expression. According to recent evidence, fingolimod modulates a range of other molecular pathways deeply rooted in disease initiation or progression. Experimental reports have firmly associated the drug with potentially beneficial therapeutic effects in immunomodulatory diseases, CNS injuries, and diseases including Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, and even cancer. Attractive pharmacological effects, relative safety, favorable pharmacokinetics, and positive experimental data have collectively led to its testing in clinical trials. Based on the recent reports, fingolimod may soon find its way as an adjunct therapy in various disparate pathological conditions. This review summarizes the up-to-date knowledge about molecular pharmacology and potential therapeutic uses of fingolimod.

MRSA-induced endothelial permeability and acute lung injury are attenuated by FTY720 S-phosphonate

Disruption of the lung endothelial barrier is a hallmark of acute respiratory distress syndrome (ARDS), for which no effective pharmacologic treatments exist. Prior work has demonstrated that FTY720 S-phosphonate (Tys), an analog of sphingosine-1-phosphate (S1P) and FTY720, exhibits potent endothelial cell (EC) barrier protective properties. In this study, we investigated the in vitro and in vivo efficacy of Tys against methicillin-resistant Staphylococcus aureus (MRSA), a frequent bacterial cause of ARDS. Tys-protected human lung EC from barrier disruption induced by heat-killed MRSA (HK-MRSA) or staphylococcal α-toxin and attenuated MRSA-induced cytoskeletal changes associated with barrier disruption, including actin stress fiber formation and loss of peripheral VE-cadherin and cortactin. Tys-inhibited Rho and myosin light chain (MLC) activation after MRSA and blocked MRSA-induced NF-κB activation and release of the proinflammatory cytokines, IL-6 and IL-8. In vivo, intratracheal administration of live MRSA in mice caused significant vascular leakage and leukocyte infiltration into the alveolar space. Pre- or posttreatment with Tys attenuated MRSA-induced lung permeability and levels of alveolar neutrophils. Posttreatment with Tys significantly reduced levels of bronchoalveolar lavage (BAL) VCAM-1 and plasma IL-6 and KC induced by MRSA. Dynamic intravital imaging of mouse lungs demonstrated Tys attenuation of HK-MRSA-induced interstitial edema and neutrophil infiltration into lung tissue. Tys did not directly inhibit MRSA growth or viability in vitro. In conclusion, Tys inhibits lung EC barrier disruption and proinflammatory signaling induced by MRSA in vitro and attenuates acute lung injury induced by MRSA in vivo. These results support the potential utility of Tys as a novel ARDS therapeutic strategy.

Hypogelsolinemia and Decrease in Blood Plasma Sphingosine-1-Phosphate in Patients Diagnosed with Severe Acute Pancreatitis

BACKGROUND

Acute pancreatitis (AP) is a frequent hospitalization cause of patients suffering from gastrointestinal disorders. Gelsolin has an ability to bind bioactive lipids including different sphingolipids engaged in inflammatory response. Importantly, hypogelsolinemia was observed in patients with different states of acute and chronic inflammation.

AIMS

The aim of the present study was to assess the interplay of blood plasma gelsolin and blood plasma sphingosine-1-phosphate (S1P) concentration in patients diagnosed with acute pancreatitis.

MATERIALS AND METHODS

To assess the concentration of gelsolin and S1P, immunoblotting and HPLC technique were employed, respectively. Additionally, the concentrations of amylase, lipase, C-reactive protein (CRP), procalcitonin (PCT) and the number of white blood cells (WBC) and platelet (PLT) were recorded.

RESULTS

We found that both pGSN and S1P concentrations in the plasma of the AP patients were significantly lower (pGSN ~ 15-165 mg/L; S1P ~ 100-360 pmol/mL) when compared to the levels of pGSN and S1P in a control group (pGSN ~ 130-240 mg/L; S1P ~ 260-400 pmol/mL). Additionally, higher concentrations of CRP, WBC, amylase and lipase were associated with low level of gelsolin in the blood of AP patients. No correlations between the level of PCT and PLT with gelsolin concentration were noticed.

CONCLUSION

Plasma gelsolin and S1P levels decrease during severe acute pancreatitis. Simultaneous assessment of pGSN and S1P can be useful in development of more accurate diagnostic strategies for patients with severe acute pancreatitis.

Renin Cells, the Kidney, and Hypertension

Renin cells are essential for survival perfected throughout evolution to ensure normal development and defend the organism against a variety of homeostatic threats. During embryonic and early postnatal life, they are progenitors that participate in the morphogenesis of the renal arterial tree. In adult life, they are capable of regenerating injured glomeruli, control blood pressure, fluid-electrolyte balance, tissue perfusion, and in turn, the delivery of oxygen and nutrients to cells. Throughout life, renin cell descendants retain the plasticity or memory to regain the renin phenotype when homeostasis is threatened. To perform all of these functions and maintain well-being, renin cells must regulate their identity and fate. Here, we review the major mechanisms that control the differentiation and fate of renin cells, the chromatin events that control the memory of the renin phenotype, and the major pathways that determine their plasticity. We also examine how chronic stimulation of renin cells alters their fate leading to the development of a severe and concentric hypertrophy of the intrarenal arteries and arterioles. Lastly, we provide examples of additional changes in renin cell fate that contribute to equally severe kidney disorders.

Lysophospholipids in Lung Inflammatory Diseases

The lysophospholipids (LPLs) belong to a group of bioactive lipids that play pivotal roles in several physiological and pathological processes. LPLs are derivatives of phospholipids and consist of a single hydrophobic fatty acid chain, a hydrophilic head, and a phosphate group with or without a large molecule attached. Among the LPLs, lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are the simplest, and have been shown to be involved in lung inflammatory symptoms and diseases such as acute lung injury, asthma, and chronic obstructive pulmonary diseases. G protein-coupled receptors (GPCRs) mediate LPA and S1P signaling. In this chapter, we will discuss on the role of LPA, S1P, their metabolizing enzymes, inhibitors or agonists of their receptors, and their GPCR-mediated signaling in lung inflammatory symptoms and diseases, focusing specially on acute respiratory distress syndrome, asthma, and chronic obstructive pulmonary disease.

Sphingosine-1-Phosphate Receptor Modulators and Oligodendroglial Cells: Beyond Immunomodulation

Multiple sclerosis (MS) is an autoimmune inflammatory disease characterized by demyelination, axonal loss, and synaptic impairment in the central nervous system (CNS). The available therapies aim to reduce the severity of the pathology during the early inflammatory stages, but they are not effective in the chronic stage of the disease. In this phase, failure in endogenous remyelination is associated with the impairment of oligodendrocytes progenitor cells (OPCs) to migrate and differentiate into mature myelinating oligodendrocytes. Therefore, stimulating differentiation of OPCs into myelinating oligodendrocytes has become one of the main goals of new therapeutic approaches for MS. Different disease-modifying therapies targeting sphingosine-1-phosphate receptors (S1PRs) have been approved or are being developed to treat MS. Besides their immunomodulatory effects, growing evidence suggests that targeting S1PRs modulates mechanisms beyond immunomodulation, such as remyelination. In this context, this review focuses on the current understanding of S1PR modulators and their direct effect on OPCs and oligodendrocytes.

Lipid Mediators Regulate Pulmonary Fibrosis: Potential Mechanisms and Signaling Pathways

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease of unknown etiology characterized by distorted distal lung architecture, inflammation, and fibrosis. The molecular mechanisms involved in the pathophysiology of IPF are incompletely defined. Several lung cell types including alveolar epithelial cells, fibroblasts, monocyte-derived macrophages, and endothelial cells have been implicated in the development and progression of fibrosis. Regardless of the cell types involved, changes in gene expression, disrupted glycolysis, and mitochondrial oxidation, dysregulated protein folding, and altered phospholipid and sphingolipid metabolism result in activation of myofibroblast, deposition of extracellular matrix proteins, remodeling of lung architecture and fibrosis. Lipid mediators derived from phospholipids, sphingolipids, and polyunsaturated fatty acids play an important role in the pathogenesis of pulmonary fibrosis and have been described to exhibit pro- and anti-fibrotic effects in IPF and in preclinical animal models of lung fibrosis. This review describes the current understanding of the role and signaling pathways of prostanoids, lysophospholipids, and sphingolipids and their metabolizing enzymes in the development of lung fibrosis. Further, several of the lipid mediators and enzymes involved in their metabolism are therapeutic targets for drug development to treat IPF.

Mechanisms Ensuring Endothelial Junction Integrity Beyond VE-Cadherin

Endothelial junctions provide blood and lymph vessel integrity and are essential for the formation of a vascular system. They control the extravasation of solutes, leukocytes and metastatic cells from blood vessels and the uptake of fluid and leukocytes into the lymphatic vascular system. A multitude of adhesion molecules mediate and control the integrity and permeability of endothelial junctions. VE-cadherin is arguably the most important adhesion molecule for the formation of vascular structures, and the stability of their junctions. Interestingly, despite this prominence, its elimination from junctions in the adult organism has different consequences in the vasculature of different organs, both for blood and lymph vessels. In addition, even in tissues where the lack of VE-cadherin leads to strong plasma leaks from venules, the physical integrity of endothelial junctions is preserved. Obviously, other adhesion molecules can compensate for a loss of VE-cadherin and this review will discuss which other adhesive mechanisms contribute to the stability and regulation of endothelial junctions and cooperate with VE-cadherin in intact vessels. In addition to adhesion molecules, endothelial receptors will be discussed, which stimulate signaling processes that provide junction stability by modulating the actomyosin system, which reinforces tension of circumferential actin and dampens pulling forces of radial stress fibers. Finally, we will highlight most recent reports about the formation and control of the specialized button-like junctions of initial lymphatics, which represent the entry sites for fluid and cells into the lymphatic vascular system.

Significance of sphingosine-1-phosphate in cardiovascular physiology and pathology

Sphingosine-1-phosphate (S1P) is a signaling lipid, synthetized by sphingosine kinases (SPHK1 and SPHK2), that affects cardiovascular function in various ways. S1P signaling is complex, particularly since its molecular action is reliant on the differential expression of its receptors (S1PR1, S1PR2, S1PR3, S1PR4, S1PR5) within various tissues. Significance of this sphingolipid is manifested early in vertebrate development as certain defects in S1P signaling result in embryonic lethality due to defective vasculo- or cardiogenesis. Similar in the mature organism, S1P orchestrates both physiological and pathological processes occurring in the heart and vasculature of higher eukaryotes. S1P regulates cell fate, vascular tone, endothelial function and integrity as well as lymphocyte trafficking, thus disbalance in its production and signaling has been linked with development of such pathologies as arterial hypertension, atherosclerosis, endothelial dysfunction and aberrant angiogenesis. Number of signaling mechanisms are critical - from endothelial nitric oxide synthase through STAT3, MAPK and Akt pathways to HDL particles involved in redox and inflammatory balance. Moreover, S1P controls both acute cardiac responses (cardiac inotropy and chronotropy), as well as chronic processes (such as apoptosis and hypertrophy), hence numerous studies demonstrate significance of S1P in the pathogenesis of hypertrophic/fibrotic heart disease, myocardial infarction and heart failure. This review presents current knowledge concerning the role of S1P in the cardiovascular system, as well as potential therapeutic approaches to target S1P signaling in cardiovascular diseases.

Downregulation of S1P Lyase Improves Barrier Function in Human Cerebral Microvascular Endothelial Cells Following an Inflammatory Challenge

Sphingosine 1-phosphate (S1P) is a key bioactive lipid that regulates a myriad of physiological and pathophysiological processes, including endothelial barrier function, vascular tone, vascular inflammation, and angiogenesis. Various S1P receptor subtypes have been suggested to be involved in the regulation of these processes, whereas the contribution of intracellular S1P (iS1P) through intracellular targets is little explored. In this study, we used the human cerebral microvascular endothelial cell line HCMEC/D3 to stably downregulate the S1P lyase (SPL-kd) and evaluate the consequences on endothelial barrier function and on the molecular factors that regulate barrier tightness under normal and inflammatory conditions. The results show that in SPL-kd cells, transendothelial electrical resistance, as a measure of barrier integrity, was regulated in a dual manner. SPL-kd cells had a delayed barrier build up, a shorter interval of a stable barrier, and, thereafter, a continuous breakdown. Contrariwise, a protection was seen from the rapid proinflammatory cytokine-mediated barrier breakdown. On the molecular level, SPL-kd caused an increased basal protein expression of the adherens junction molecules PECAM-1, VE-cadherin, and β-catenin, increased activity of the signaling kinases protein kinase C, AMP-dependent kinase, and p38-MAPK, but reduced protein expression of the transcription factor c-Jun. However, the only factors that were significantly reduced in TNFα/SPL-kd compared to TNFα/control cells, which could explain the observed protection, were VCAM-1, IL-6, MCP-1, and c-Jun. Furthermore, lipid profiling revealed that dihydro-S1P and S1P were strongly enhanced in TNFα-treated SPL-kd cells. In summary, our data suggest that SPL inhibition is a valid approach to dampenan inflammatory response and augmente barrier integrity during an inflammatory challenge.

Determinants of Serum- and Plasma Sphingosine-1-Phosphate Concentrations in a Healthy Study Group

Introduction  To correctly interpret plasma- or serum-sphingosine-1-phosphate (S1P) concentrations measured in clinical studies it is critical to understand all major determinants in healthy controls.

Methods  Serum- and plasma-S1P from 174 healthy blood donors was measured by liquid chromatography-tandem mass spectrometry and correlated to clinical laboratory data. Selected plasma samples, 10 with high and 10 with low S1P concentrations, were fractionated into very low-density lipoprotein (VLDL)-, low density lipoprotein (LDL)-, high density lipoprotein (HDL)-, and lipoprotein-free fractions. S1P was then measured in each fraction to determine its distribution.

Results  The mean S1P concentration in serum (1.04 ± 0.24 nmol/mL) was found 39% higher compared with plasma (0.75 ± 0.16 nmol/mL) and overall was not different between men and women. Only when stratified for age and gender, older women were found to exhibit higher circulatory S1P levels than men. In plasma, S1P levels correlate to red blood cell (RBC) counts but not to platelet counts. Conversely, serum-S1P correlates to platelet counts but not to RBC counts. In addition, eosinophil counts are strongly associated with serum-S1P concentrations. Both serum- and plasma-S1P correlate to total cholesterol but not to HDL-C. The distribution of S1P between VLDL-, LDL-, HDL-, and lipoprotein-free fractions is independent of total plasma-S1P concentrations. S1P concentrations in HDL but not in LDL are highly variable.

Conclusion  These data indicate S1P concentrations in plasma and serum to be differentially associated with cell counts and S1P carrier proteins. Besides platelets, eosinophil counts are identified as a novel determinant for serum-S1P concentrations further suggesting a role for S1P in eosinophil pathologies.

Macular oedema and changes in macular thickness in multiple sclerosis patients treated with fingolimod

Macular oedema is a known side effect to fingolimod, but changes in specific areas of the retina are only sparsely described. Our aim was to investigate the prevalence of macular oedema and characterize macular changes after initiation of fingolimod based on routine ophthalmological examinations in all consecutive patients treated at our hospital. We evaluated macular thickness change from baseline to 3-4 months after initiation of treatment. Central retinal thickness, total macular volume, total macular thickness, average thickness and inner-/outer macular thickness were automatically measured using optical coherence tomography (OCT). A total of 190 eyes completed the study, and none of those developed visible macular oedema. All macular areas showed a small, but statistically significant increase in thickness. Total macular volume increased by a mean of 0.05 mm³ (P = <.001). Mean best-corrected visual acuity only changed by .03 (P = .074). We observed a minimal change in macular thickness and no clinically relevant affection on visual acuity after 3-4 months of fingolimod treatment. Thus, our results do not underpin the need for routine screening for macular oedema in asymptomatic MS patients without diabetes or uveitis receiving 0.5 mg fingolimod daily.

Sphingosine-1-phosphate receptor-independent lung endothelial cell barrier disruption induced by FTY720 regioisomers

RATIONALE

Vascular permeability is a hallmark of acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury pathobiology; however, the mechanisms underlying this vascular dysregulation remain unclear, thereby impairing the development of desperately needed effective therapeutics. We have shown that sphingosine-1-phosphate (S1P) and 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol (FTY720) analogues are useful tools for exploring vascular barrier regulation mechanisms.

OBJECTIVE

To experimentally define the effects of FTY720 regioisomers on lung endothelial cell barrier regulation.

METHODS

Specific barrier-regulatory receptor and kinase inhibitors were utilized to probe signaling mechanisms involved in FTY720 regioisomer-mediated human lung endothelial cell barrier responses (trans-endothelial electrical resistance, TER). Docking simulations with the S1P1 receptor were performed to further evaluate FTY720 regioisomer signaling.

RESULTS

FTY720 regioisomers produced potent endothelial cell barrier disruption reflected by declines in TER alterations. Pharmacologic inhibition of Gi-coupled S1P receptors (S1P1, S1P2, S1P3) failed to alter FTY720 regioisomer-mediated barrier disruption; findings that were corroborated by docking simulations demonstrating FTY720 regiosomers were repelled from S1P1 docking, in contrast to strong S1P1 binding elicited by S1P. Inhibition of either the barrier-disrupting PAR-1 receptor, the VEGF receptor, Rho-kinase, MAPK, NFkB, or PI3K failed to alter FTY720 regioisomer-induced endothelial cell barrier disruption. While FTY720 regioisomers significantly increased protein phosphatase 2 (PP2A) activity, PP2A inhibitors failed to alter FTY720 regioisomer-induced endothelial cell barrier disruption.

CONCLUSIONS

Together, these results imply a vexing model of pulmonary vascular barrier dysregulation in response to FTY720-related compounds and highlight the need for further insights into mechanisms of vascular integrity required to promote the development of novel therapeutic tools to prevent or reverse the pulmonary vascular leak central to ARDS outcomes.

Drugging cancer metabolism: Expectations vs. reality

As compared to their normal counterparts, neoplastic cells exhibit a variety of metabolic changes that reflect not only genetic and epigenetic defects underlying malignant transformation, but also the nutritional and immunobiological conditions of the tumor microenvironment. Such alterations, including the so-called Warburg effect (an increase in glucose uptake largely feeding anabolic and antioxidant metabolism), have attracted considerable attention as potential targets for the development of novel anticancer therapeutics. However, very few drugs specifically conceived to target bioenergetic cancer metabolism are currently approved by regulatory agencies for use in humans. This reflects the elevated degree of heterogeneity and redundancy in the metabolic circuitries exploited by neoplastic cells from different tumors (even of the same type), as well as the resemblance of such metabolic pathways to those employed by highly proliferating normal cells. Here, we summarize the major metabolic alterations that accompany oncogenesis, the potential of targeting bioenergetic metabolism for cancer therapy, and the obstacles that still prevent the clinical translation of such a promising therapeutic paradigm.

Combination of sphingosine-1-phosphate receptor 1 (S1PR1) agonist and antiviral drug: a potential therapy against pathogenic influenza virus

The pandemic 2009 influenza A H1N1 virus is associated with significant mortality. Targeting S1PR1, which is known to modulate the immune response, provides protection against pathogenic influenza virus. The functional role and molecular mechanism of S1PR1 were analysed by generating inducible endothelial cell-specific S1PR1 knockout mice and assessing the therapeutic efficacy of the selective S1PR1 agonist CYM5442 against acute lung injury (ALI) induced by the 2009 influenza A H1N1 virus. Immune-mediated pulmonary injury is aggravated by the absence of endothelial S1PR1 and alleviated by treatment with CYM-5442, suggesting a protective function of S1PR1 signaling during H1N1 infection. S1PR1 signaling does not affect viral clearance in mice infected with influenza. Mechanistically, the MAPK and NF-kB signaling pathways are involved in the ALI mediated by S1PR1 in infected mice. Combined administration of the S1PR1 agonist CYM-5442 and the antiviral drug oseltamivir provides maximum protection from ALI. Our current study provides insight into the molecular mechanism of S1PR1 mediating the ALI induced by H1N1 infection and indicates that the combination of S1PR1 agonist with antiviral drug could potentially be used as a therapeutic remedy for future H1N1 virus pandemics.

Alterations in arginine and energy metabolism, structural and signalling lipids in metastatic breast cancer in mice detected in plasma by targeted metabolomics and lipidomics

Background

The early detection of metastasis based on biomarkers in plasma may improve cancer prognosis and guide treatment. The aim of this work was to characterize alterations in metabolites of the arginine pathway, energy metabolism, and structural and signalling lipids in plasma in the early and late stages of murine breast cancer metastasis.

Methods

Mice were orthotopically inoculated with 4T1 metastatic breast cancer cells, and plasma was analysed along the pulmonary metastasis progression using LC-MS/MS-based targeted metabolomics and lipidomics.

Results

Based on primary tumour growth and pulmonary metastases, 1–2 weeks after 4T1 cancer cell inoculation was defined as an early metastatic stage, and 3–4 weeks after 4T1 cancer cell inoculation was defined as a late metastatic stage. Early metastasis was featured in plasma by a shift of L-arginine metabolism towards arginase (increased ornithine/arginine ratio) and polyamine synthesis (increased putrescine). Late metastasis was reflected in plasma by further progression of changes in the arginine pathway with an additional increase in asymmetric dimethylarginine plasma concentration, as well as by a profound energy metabolism reprogramming towards glycolysis, an accelerated pentose phosphate pathway and a concomitant decrease in tricarboxylic cycle rate (“Warburg effect”). The late but not the early phase of metastasis was also characterized by a different lipid profile pattern in plasma, including a decrease in total phosphatidylcholines, a decrease in diester-bound phospholipid fraction and an increase in lysophospholipids associated with an increase in total sphingomyelins.

Conclusions

The early phase of metastasis in murine 4T1 metastatic breast cancer was associated with plasma metabolome changes characteristic of arginase activation and polyamine synthesis. The late metastasis was reflected in plasma not only by the alterations in arginine pathways but also by a shift towards glycolysis and the pentose pathway, remodelling of structural lipids and activation of lipid signalling, all of which coincided with metastasis progression.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1075-y) contains supplementary material, which is available to authorized users.

The role of sphingosine 1 phosphate in coronary artery disease and ischemia reperfusion injury

Coronary artery disease (CAD) is a common cause of morbidity and mortality worldwide. Atherosclerotic plaques, as a hallmark of CAD, cause chronic narrowing of coronary arteries over time and could also result in acute myocardial infarction (AMI). The standard treatments for ameliorating AMI are reperfusion strategies, which paradoxically result in ischemic reperfusion (I/R) injury. Sphingosine 1 phosphate (S1P), as a potent lysophospholipid, plays an important role in various organs, including immune and cardiovascular systems. In addition, high-density lipoprotein, as a negative predictor of atherosclerosis and CAD, is a major carrier of S1P in blood circulation. S1P mediates its effects through binding to specific G protein-coupled receptors, and its signaling contributes to a variety of responses, including cardiac inflammation, dysfunction, and I/R injury protection. In this review, we will focus on the role of S1P in CAD and I/R injury as a potential therapeutic target.

Cortical Actin Dynamics in Endothelial Permeability

The pulmonary endothelial cell forms a critical semi-permeable barrier between the vascular and interstitial space. As part of the blood-gas barrier in the lung, the endothelium plays a key role in normal physiologic function and pathologic disease. Changes in endothelial cell shape, defined by its plasma membrane, determine barrier integrity. A number of key cytoskeletal regulatory and effector proteins including non-muscle myosin light chain kinase, cortactin, and Arp 2/3 mediate actin rearrangements to form cortical and membrane associated structures in response to barrier enhancing stimuli. These actin formations support and interact with junctional complexes and exert forces to protrude the lipid membrane to and close gaps between individual cells. The current knowledge of these cytoskeletal processes and regulatory proteins are the subject of this review. In addition, we explore novel advancements in cellular imaging that are poised to shed light on the complex nature of pulmonary endothelial permeability.

Colonoscopic-Guided Pinch Biopsies in Mice as a Useful Model for Evaluating the Roles of Host and Luminal Factors in Colonic Inflammation

Colonic inflammation, a hallmark of inflammatory bowel disease, can be influenced by host intrinsic and extrinsic factors. There continues to be a need for models of colonic inflammation that can both provide insights into disease pathogenesis and be used to investigate potential therapies. Herein, we tested the utility of colonoscopic-guided pinch biopsies in mice for studying colonic inflammation and its treatment. Gene expression profiling of colonic wound beds after injury showed marked changes, including increased expression of genes important for the inflammatory response. Interestingly, many of these gene expression changes mimicked those alterations found in inflammatory bowel disease patients. Biopsy-induced inflammation was associated with increases in neutrophils, macrophages, and natural killer cells. Injury also led to elevated levels of sphingosine-1-phosphate (S1P), a bioactive lipid that is an important mediator of inflammation mainly through its receptor, S1P₁. Genetic deletion of S1P₁ in the endothelium did not alter the inflammatory response but led to increased colonic bleeding. Bacteria invaded into the wound beds, raising the possibility that microbes contributed to the observed changes in mucosal gene expression. In support of this, reducing bacterial abundance markedly attenuated the inflammatory response to wounding. Taken together, this study demonstrates the utility of the pinch biopsy model of colonic injury to elucidate the molecular underpinnings of colonic inflammation and its treatment.

The Pulmonary Endothelial Glycocalyx in ARDS: A Critical Role for Heparan Sulfate

The endothelial glycocalyx is a glycosaminoglycan-enriched endovascular layer that, with the development of novel fixation and in vivo microscopy techniques, has been increasingly recognized as a major contributor to vascular homeostasis. Sepsis-associated degradation of the endothelial glycocalyx mediates the onset of the alveolar microvascular dysfunction characteristic of sepsis-induced lung injury (such as the Acute Respiratory Distress Syndrome, ARDS). Emerging evidence indicates that processes of glycocalyx reconstitution are necessary for endothelial repair and, as such, are promising therapeutic targets to accelerate lung injury recovery. This review discusses what has been learned about the homeostatic and pathophysiologic role of the pulmonary endothelial glycocalyx during lung health and injury, with the goal to identify promising new areas for future mechanistic investigation.

Development of the renal vasculature

The kidney vasculature has a unique and complex architecture that is central for the kidney to exert its multiple and essential physiological functions with the ultimate goal of maintaining homeostasis. An appropriate development and coordinated assembly of the different vascular cell types and their association with the corresponding nephrons is crucial for the generation of a functioning kidney. In this review we provide an overview of the renal vascular anatomy, histology, and current knowledge of the embryological origin and molecular pathways involved in its development. Understanding the cellular and molecular mechanisms involved in renal vascular development is the first step to advance the field of regenerative medicine.

Sphingolipid signaling modulates trans-endothelial cell permeability in dengue virus infected HMEC-1 cells

Dengue has emerged as a major mosquito-borne disease in the tropics and subtropics. In severe dengue, enhanced microvascular endothelial permeability leads to plasma leakage. Direct dengue virus (DENV) infection in human microvascular endothelial cells (HMEC-1) can enhance trans-endothelial leakage. Using a microarray-based analysis, we identified modulation of key endothelial cell signaling pathways in DENV-infected HMEC-1 cells. One among them was the sphingolipid pathway that regulates vascular barrier function. Sphingosine-1-phosphate receptor 2 (S1PR2) and S1PR5 showed significant up-regulation in the microarray data. In DENV-infected cells, the kinetics of S1PR2 transcript expression and enhanced in vitro trans-endothelial permeability showed a correlation. We also observed an internalization and cytoplasmic translocation of VE-Cadherin, a component of adherens junctions (AJ), upon infection indicating AJ disassembly. Further, inhibition of S1PR2 signaling by a specific pharmacological inhibitor prevented translocation of VE-Cadherin, thus helping AJ maintenance, and abrogated DENV-induced trans-endothelial leakage. Our results show that sphingolipid signaling, especially that involving S1PR2, plays a critical role in vascular leakage in dengue.

Chronic lung injury and impaired pulmonary function in a mouse model of acid ceramidase deficiency

Farber disease (FD) is a debilitating lysosomal storage disorder (LSD) caused by a deficiency of acid ceramidase (ACDase) activity due to mutations in the gene ASAH1. Patients with ACDase deficiency may develop a spectrum of clinical phenotypes. Severe cases of FD are frequently associated with neurological involvement, failure to thrive, and respiratory complications. Mice homozygous ( Asah1P361R/P361R) for an orthologous patient mutation in Asah1 recapitulate human FD. In this study, we show significant impairment in lung function, including low compliance and increased airway resistance in a mouse model of ACDase deficiency. Impaired lung mechanics in Farber mice resulted in decreased blood oxygenation and increased red blood cell production. Inflammatory cells were recruited to both perivascular and peribronchial areas of the lung. We observed large vacuolated foamy histiocytes that were full of storage material. An increase in vascular permeability led to protein leakage, edema, and impacted surfactant homeostasis in the lungs of Asah1P361R/P361R mice. Bronchial alveolar lavage fluid (BALF) extraction and analysis revealed accumulation of a highly turbid lipoprotein-like substance that was composed in part of surfactants, phospholipids, and ceramides. The phospholipid composition of BALF from Asah1P361R/P361R mice was severely altered, with an increase in both phosphatidylethanolamine (PE) and sphingomyelin (SM). Ceramides were also found at significantly higher levels in both BALF and lung tissue from Asah1P361R/P361R mice when compared with levels from wild-type animals. We demonstrate that a deficiency in ACDase leads to sphingolipid and phospholipid imbalance, chronic lung injury caused by significant inflammation, and increased vascular permeability, leading to impaired lung function.

New Insights into the Immune Molecular Regulation of the Pathogenesis of Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome is an inflammatory disease characterized by dysfunction of pulmonary epithelial and capillary endothelial cells, infiltration of alveolar macrophages and neutrophils, cell apoptosis, necroptosis, NETosis, and fibrosis. Inflammatory responses have key effects on every phase of acute respiratory distress syndrome. The severe inflammatory cascades impaired the regulation of vascular endothelial barrier and vascular permeability. Therefore, understanding the relationship between the molecular regulation of immune cells and the pulmonary microenvironment is critical for disease management. This article reviews the current clinical and basic research on the pathogenesis of acute respiratory distress syndrome, including information on the microenvironment, vascular endothelial barrier and immune mechanisms, to offer a strong foundation for developing therapeutic interventions.

Sphingosine-1-phosphate Maintains Normal Vascular Permeability by Preserving Endothelial Surface Glycocalyx in Intact Microvessels

OBJECTIVE

S1P was found to protect the ESG by inhibiting MMP activity-dependent shedding of ESG in cultured endothelial cell studies. We aimed to further test that S1P contributes to the maintenance of normal vascular permeability by protecting the ESG in intact microvessels.

METHODS

We quantified the ESG in post-capillary venules of rat mesentery and measured the vascular permeability to albumin in the presence and absence of 1 μM S1P. We also measured permeability to albumin in the presence of MMP inhibitors and compared the measured permeability with those predicted by a transport model for the inter-endothelial cleft.

RESULTS

We found that in the absence of S1P, the fluorescence intensity of the FITC-anti-HS-labeled ESG was ~10% of that in the presence of S1P, whereas the measured permeability to albumin was ~6.5-fold of that in the presence of S1P. Similar results were observed with MMP inhibition. The predictions by the mathematical model further confirmed that S1P maintains microvascular permeability by preserving ESG.

CONCLUSIONS

Our results show that S1P contributes to the maintenance of normal vascular permeability by protecting the ESG in intact microvessels, consistent with parallel observation in cultured endothelial monolayers.

Mind the gap: mechanisms regulating the endothelial barrier

The endothelial barrier consists of intercellular contacts localized in the cleft between endothelial cells, which is covered by the glycocalyx in a sievelike manner. Both types of barrier-forming junctions, i.e. the adherens junction (AJ) serving mechanical anchorage and mechanotransduction and the tight junction (TJ) sealing the intercellular space to limit paracellular permeability, are tethered to the actin cytoskeleton. Under resting conditions, the endothelium thereby builds a selective layer controlling the exchange of fluid and solutes with the surrounding tissue. However, in the situation of an inflammatory response such as in anaphylaxis or sepsis intercellular contacts disintegrate in post-capillary venules leading to intercellular gap formation. The resulting oedema can cause shock and multi-organ failure. Therefore, maintenance as well as coordinated opening and closure of interendothelial junctions is tightly regulated. The two principle underlying mechanisms comprise spatiotemporal activity control of the small GTPases Rac1 and RhoA and the balance of the phosphorylation state of AJ proteins. In the resting state, junctional Rac1 and RhoA activity is enhanced by junctional components, actin-binding proteins, cAMP signalling and extracellular cues such as sphingosine-1-phosphate (S1P) and angiopoietin-1 (Ang-1). In addition, phosphorylation of AJ components is prevented by junction-associated phosphatases including vascular endothelial protein tyrosine phosphatase (VE-PTP). In contrast, inflammatory mediators inhibiting cAMP/Rac1 signalling cause strong activation of RhoA and induce AJ phosphorylation finally leading to endocytosis and cleavage of VE-cadherin. This results in dissolution of TJs the outcome of which is endothelial barrier breakdown.

Fingolimod targets cerebral endothelial activation to block leukocyte recruitment in the central nervous system

Fingolimod (FTY720), an immunomodulator, is approved as an oral treatment for patients with relapsing forms of multiple sclerosis. Its effects are largely attributed to its mechanism of selectively retaining lymphocytes in the lymph nodes to reduce autoreactive T-cell recruitment in the CNS. In this study, we investigated the therapeutic effect of FTY720 on an animal model of CNS inflammation induced by intracerebral ventricle LPS injection. We found that FTY720 treatment significantly prevented LPS-induced neutrophil recruitment in the CNS by inhibiting leukocyte recruitment in cerebral microvessels. Furthermore, FTY720 also inhibited the expressions of adhesion molecules on the cerebral endothelium, but did not affect the expression levels of pro-inflammatory cytokines (TNF-α and IL-6) and chemokines (CXCL1 and CXCL2) in the CNS parenchyma. The inhibition of endothelial activation was accompanied by reduced phosphorylation of signaling molecules, including serine/threonine-specific protein kinase (Akt), STAT6, and nuclear factor-κB. This FTY720-attenuated inhibition of leukocyte recruitment and endothelial activation was reversed by blocking the functions of sphingosine kinase 2 or sphingosine-1-phosphate receptor 1. Our study demonstrated, for the first time, that FTY720 directly inhibits the phosphorylation of multiple signaling molecules in endothelial cells, thereby effectively blocking leukocyte recruitment in the CNS.

Lipid mediators in the regulation of endothelial barriers

Lipid mediators play a critical role in the development and resolution of vascular endothelial barrier dysfunction caused by various pathologic interventions. The accumulation of excess lipids directly impairs endothelial cell (EC) barrier function that is known to contribute to the development of atherosclerosis and metabolic disorders such as obesity and diabetes as well as chronic inflammation in the vascular endothelium. Certain products of phospholipid oxidation (OxPL) such as fragmented phospholipids generated during oxidative and nitrosative stress show pro-inflammatory potential and cause endothelial barrier dysfunction. In turn, other OxPL products enhance basal EC barrier and exhibit potent barrier-protective effects in pathologic settings of acute vascular leak caused by pro-inflammatory mediators, barrier disruptive agonists and pathologic mechanical stimulation. These beneficial effects were further confirmed in rodent models of lung injury and inflammation. The bioactive oxidized lipid molecules may serve as important therapeutic prototype molecules for future treatment of acute lung injury syndromes associated with endothelial barrier dysfunction and inflammation. This review will summarize recent studies of biological effects exhibited by various groups of lipid mediators with a focus on the role of oxidized phospholipids in control of vascular endothelial barrier, agonist induced EC permeability, inflammation, and barrier recovery related to clinical settings of acute lung injury and inflammatory vascular leak.

A sphingosine-1-phosphate receptor type 1 agonist, ASP4058, suppresses intracranial aneurysm through promoting endothelial integrity and blocking macrophage transmigration

Background and Purpose

Intracranial aneurysm (IA), common in the general public, causes lethal subarachnoid haemorrhage on rupture. It is, therefore, of utmost importance to prevent the IA from rupturing. However, there is currently no medical treatment. Recent studies suggest that IA is the result of chronic inflammation in the arterial wall caused by endothelial dysfunction and infiltrating macrophages. The sphingosine‐1‐phosphate receptor type 1 (S1P₁ receptor) is present on the endothelium and promotes its barrier function. Here we have tested the potential of an S1P₁ agonist, ASP4058, to prevent IA in an animal model.

Experimental Approach

The effects of a selective S1P₁ agonist, ASP4058, on endothelial permeability and migration of macrophages across an endothelial cell monolayer were tested in vitro using a Transwell system, and its effects on the size of IAs were evaluated in a rat model of IA.

Key Results

S1P₁ receptor was expressed in endothelial cells of human IA lesions and control arterial walls. ASP4058 significantly reduced FITC‐dextran leakage through an endothelial monolayer and suppressed the migration of macrophages across the monolayer in vitro. Oral administration of ASP4058 reduced the vascular permeability, macrophage infiltration and size of the IAs by acting as an S1P₁ agonist in the rat model. This effect was mimicked by another two structurally‐unrelated S1P₁ agonists.

Conclusion and Implications

A selective S1P₁ agonist is a strong drug candidate for IA treatment as it promotes the endothelial cell barrier and suppresses the trans‐endothelial migration of macrophages in IA lesions.

Simvastatin-induced sphingosine 1-phosphate receptor 1 expression is KLF2-dependent in human lung endothelial cells

We have demonstrated that simvastatin and sphingosine 1−phosphate (S1P) both attenuate increased vascular permeability in preclinical models of acute respiratory distress syndrome. However, the underlying mechanisms remain unclear. As Krüppel-like factor 2 (KLF2) serves as a critical regulator for cellular stress response in endothelial cells (EC), we hypothesized that simvastatin enhances endothelial barrier function via increasing expression of the barrier-promoting S1P receptor, S1PR1, via a KLF2-dependent mechanism. S1PR1 luciferase reporter promoter activity in human lung artery EC (HPAEC) was tested after simvastatin (5 μM), and S1PR1 and KLF2 protein expression detected by immunoblotting. In vivo, transcription and expression of S1PR1 and KLF2 in mice lungs were detected by microarray profiling and immunoblotting after exposure to simvastatin (10 mg/kg). Endothelial barrier function was measured by trans-endothelial electrical resistance with the S1PR1 agonist FTY720-(S)-phosphonate. Both S1PR1 and KLF2 gene expression (mRNA, protein) were significantly increased by simvastatin in vitro and in vivo. S1PR1 promoter activity was significantly increased by simvastatin (P < 0.05), which was significantly attenuated by KLF2 silencing (siRNA). Simvastatin induced KLF2 recruitment to the S1PR1 promoter, and consequently, significantly augmented the effects of the S1PR1 agonist on EC barrier enhancement (P < 0.05), which was significantly attenuated by KLF2 silencing (P < 0.05). These results suggest that simvastatin upregulates S1PR1 transcription and expression via the transcription factor KLF2, and consequently augments the effects of S1PR1 agonists on preserving vascular barrier integrity. These results may lead to novel combinatorial therapeutic strategies for lung inflammatory syndromes.

Sphingosine-1-phosphate restores endothelial barrier integrity in ovarian hyperstimulation syndrome

STUDY QUESTION

Are follicular fluid (FF) sphingosine-1-phosphate (S1P) levels in patients at risk of developing ovarian hyperstimulation syndrome (OHSS) altered and in part responsible for the high vascular permeability observed in these patients.

STUDY ANSWER

FF S1P levels are lower in FF from patients at risk of OHSS and treatment with S1P may reduce vascular permeability in these patients.

WHAT IS KNOWN ALREADY

Although advances have been made in the diagnosis, and management of OHSS and in basic knowledge of its development, complete prevention has proven difficult.

STUDY DESIGN, SIZE, DURATION

A total of 40 FF aspirates were collected from patients undergoing ART. The women (aged 25-39 years old) were classified into a control group (n = 20) or a group at risk of OHSS (n = 20). The EA.hy926 endothelial cell line was used to assess the efffects of FF from patients at risk of OHSS with or without the addition of S1P. An animal model that develops OHSS in immature Sprague-Dawley rats were also used.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Migration assays, confocal microscopy analysis of actin filaments, immunoblotting and quail chorioallantoic membrane (CAM) assays of in-vivo angiogenesis were performed and statistical comparisons between groups were made.

MAIN RESULTS AND THE ROLE OF CHANCE

The S1P concentration was significantly lower in FF from patients at risk of OHSS (P = 0.03). The addition of S1P to this FF decreased cell migration (P < 0.05) and prevented VE-cadherin phosphorylation in endothelial cells (P < 0.05). S1P in the FF from patients at risk of OHSS increased the levels of VE-cadherin (P < 0.05), N-cadherin (P < 0.05) and β-catenin (P < 0.05), and partially reversed actin redistribution in endothelial cells. The addition of S1P in FF from patients at risk of OHSS also decreased the levels of vascular endothelial growth factor (VEGF121; P < 0.01) and S1P lyase (SPL; P < 0.05) and increased the levels of S1PR1 (P < 0.05) in endothelial cells. In CAMs incubated with FF from patients at risk of OHSS with S1P, the number of vessel branch points decreased while the periendothelial cell coverage increased. Additionally, in a rat OHSS model, we demonstrated that vascular permeability and VEGF121 and its receptor KDR expression were increased in the OHSS group compared to the control group and that S1P administration decreased these parameters.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The results of this study were generated from an in-vitro system. This model reflects the microvasculature in vivo. Even though the ideal model would be the use of human endothelial cells from the ovary, it is obviously not possible to carry out this kind of approach in ovaries of patients from ART. More studies will be necessary to delineate the effects of S1P in the pathogenesis of OHSS. Hence, clinical studies are needed in order to choose the most appropriate method of prevention and management.

WIDER IMPLICATIONS OF THE FINDINGS

The use of bioactive sphingolipid metabolites may contribute to finding better and safer therapeutic strategies for the treatment of OHSS and other human diseases that display aberrant vascular leakage.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants ANPCyT (PICT 2012-897), CONICET (PIP 5471), Roemmers and Baron Foundation, Argentina. The authors declare no conflict of interest.

Targeting sphingosine-1-phosphate signaling in lung diseases

Sphingosine-1-phosphate (S1P), a simple, bioactive sphingolipid metabolite, plays a key role, both intracellularly and extracellularly, in various cellular processes such as proliferation, survival, migration, inflammation, angiogenesis, and endothelial barrier integrity. The cellular S1P level is low and is tightly regulated by its synthesis and degradation. Sphingosine Kinases (SphKs) 1 and 2, catalyze the ATP-dependent phosphorylation of sphingosine to S1P, while the degradation is mediated by the reversible dephosphorylation catalyzed by the S1P phosphatases and lipid phosphate phosphatases and the irreversible degradation to hexadecenal and ethanolamine phosphate by sphingosine-1-phosphate lyase (S1PL). As a ligand for specific G-protein-coupled receptors, S1P1-5, which are differentially expressed in different cell types, S1P generates downstream signals that play crucial role in developmental and disease related pathologies. In addition to acting extracellularly on receptors located on the plasma membrane, S1P can also act intracellularly, independently of S1P1-5, affecting calcium homeostasis and cell proliferation. The SphKs /S1P /S1PL metabolic pathway is implicated in numerous human pathologies including respiratory disorders, thereby raising the possibility that manipulating intracellular S1P levels could offer therapeutic potential in ameliorating lung diseases. This review focuses on the prospects of targeting S1P signaling and S1P metabolizing enzymes using small molecule inhibitors, receptor agonists, and antagonists in the treatment of lung diseases.

Neoatherosclerosis after Drug-Eluting Stent Implantation: Roles and Mechanisms

In-stent neoatherosclerosis (NA), characterized by a relatively thin fibrous cap and large volume of yellow-lipid accumulation after drug-eluting stents (DES) implantation, has attracted much attention owing to its close relationship with late complications, such as revascularization and late stent thrombosis (ST). Accumulating evidence has demonstrated that more than one-third of patients with first-generation DES present with NA. Even in the advent of second-generation DES, NA still occurs. It is indicated that endothelial dysfunction induced by DES plays a critical role in neoatherosclerotic development. Upregulation of reactive oxygen species (ROS) induced by DES implantation significantly affects endothelial cells healing and functioning, therefore rendering NA formation. In light of the role of ROS in suppression of endothelial healing, combining antioxidant therapies with stenting technology may facilitate reestablishing a functioning endothelium to improve clinical outcome for patients with stenting.

Differential elastic responses to barrier-altering agonists in two types of human lung endothelium

Vascular integrity is primarily determined by endothelial cell (EC) cytoskeletal structure that is differentially regulated by various stimuli. In this study, atomic force microscopy (AFM) was used to characterize structural and mechanical properties in the cytoskeleton of cultured human pulmonary artery EC (HPAEC) and human lung microvascular EC (HLMVEC) by determining elastic properties (Young's modulus) in response to endogenous barrier protective agents sphingosine 1-phosphate (S1P) and hepatocyte growth factor (HGF), or the barrier disruptive molecule thrombin. Initial studies in unstimulated cells indicate higher baseline peripheral elastic modulus values in HPAEC (mean 2.9 KPa) than in HLMVEC (1.8 KPa). After 30 min of stimulation, S1P induced the highest Young's modulus increase (6.1 KPa) compared to the other barrier enhancing stimuli, HGF (5.8 KPa) and the pharmaceutical agent and S1P analog FTY720 (4.1 KPa). In contrast, the barrier disruptive agent thrombin decreased values from 2.5 KPa to 0.7 KPa depending on the cell type and treatment time. AFM topographical imaging supports these quantitative biophysical data regarding differential peripheral elastic properties in EC. Overall, these AFM studies provide novel insights into the biomechanical properties of human lung EC that regulate vascular barrier function and have potential applicability to pathophysiologic vascular leak syndromes such as acute lung injury.

Sphingosine 1-phosphate receptor-1 in cardiomyocytes is required for normal cardiac development

Sphingosine 1-phosphate (S1P) is a bioactive lipid that acts via G protein-coupled receptors. The S1P receptor S1P1, encoded by S1pr1, is expressed in developing heart but its roles there remain largely unexplored. Analysis of S1pr1 LacZ knockin embryos revealed β-galactosidase staining in cardiomyocytes in the septum and in the trabecular layer of hearts collected at 12.5 days post coitus (dpc) and weak staining in the inner aspect of the compact layer at 15.5 dpc and later. Nkx2-5-Cre- and Mlc2a-Cre-mediated conditional knockout of S1pr1 led to ventricular noncompaction and ventricular septal defects at 18.5 dpc and to perinatal lethality in the majority of mutants. Further analysis of Mlc2a-Cre conditional mutants revealed no gross phenotype at 12.5 dpc but absence of the normal increase in the number of cardiomyocytes and the thickness of the compact layer at 13.5 dpc and after. Consistent with relative lack of a compact layer, in situ hybridization at 13.5 dpc revealed expression of trabecular markers extending almost to the epicardium in mutants. Mutant hearts also showed decreased myofibril organization in the compact but not trabecular myocardium at 12.5 dpc. These results suggest that S1P signaling via S1P1 in cardiomyocytes plays a previously unknown and necessary role in heart development in mice.