Endothelial Nogo-B regulates sphingolipid biosynthesis to promote pathological cardiac hypertrophy during chronic pressure overload

Ceramides are fuel gauges on the drive to cardiometabolic disease

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways that maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides and in turn reprogram cellular metabolism and stimulate apoptosis. Finally, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

High fat diet ameliorates mitochondrial cardiomyopathy in CHCHD10 mutant mice

Mutations in CHCHD10, a mitochondrial protein with undefined functions, are associated with autosomal dominant mitochondrial diseases. Chchd10 knock-in mice harboring a heterozygous S55L mutation (equivalent to human pathogenic S59L) develop a fatal mitochondrial cardiomyopathy caused by CHCHD10 aggregation and proteotoxic mitochondrial integrated stress response (mtISR). In mutant hearts, mtISR is accompanied by a metabolic rewiring characterized by increased reliance on glycolysis rather than fatty acid oxidation. To counteract this metabolic rewiring, heterozygous S55L mice were subjected to chronic high-fat diet (HFD) to decrease insulin sensitivity and glucose uptake and enhance fatty acid utilization in the heart. HFD ameliorated the ventricular dysfunction of mutant hearts and significantly extended the survival of mutant female mice affected by severe pregnancy-induced cardiomyopathy. Gene expression profiles confirmed that HFD increased fatty acid utilization and ameliorated cardiomyopathy markers. Importantly, HFD also decreased accumulation of aggregated CHCHD10 in the S55L heart, suggesting activation of quality control mechanisms. Overall, our findings indicate that metabolic therapy can be effective in mitochondrial cardiomyopathies associated with proteotoxic stress.

Rewiring Endothelial Sphingolipid Metabolism to Favor S1P Over Ceramide Protects From Coronary Atherosclerosis

BACKGROUND

Growing evidence correlated changes in bioactive sphingolipids, particularly S1P (sphingosine-1-phosphate) and ceramides, with coronary artery diseases. Furthermore, specific plasma ceramide species can predict major cardiovascular events. Dysfunction of the endothelium lining lesion-prone areas plays a pivotal role in atherosclerosis. Yet, how sphingolipid metabolism and signaling change and contribute to endothelial dysfunction and atherosclerosis remain poorly understood.

METHODS

We used an established model of coronary atherosclerosis in mice, combined with sphingolipidomics, RNA-sequencing, flow cytometry, and immunostaining to investigate the contribution of sphingolipid metabolism and signaling to endothelial cell (EC) activation and dysfunction.

RESULTS

We demonstrated that hemodynamic stress induced an early metabolic rewiring towards endothelial sphingolipid de novo biosynthesis, favoring S1P signaling over ceramides as a protective response. This finding is a paradigm shift from the current belief that ceramide accrual contributes to endothelial dysfunction. The enzyme SPT (serine palmitoyltransferase) commences de novo biosynthesis of sphingolipids and is inhibited by NOGO-B (reticulon-4B), an ER membrane protein. Here, we showed that NOGO-B is upregulated by hemodynamic stress in myocardial EC of ApoE-/- mice and is expressed in the endothelium lining coronary lesions in mice and humans. We demonstrated that mice lacking NOGO-B specifically in EC (Nogo-A/BECKOApoE-/-) were resistant to coronary atherosclerosis development and progression, and mortality. Fibrous cap thickness was significantly increased in Nogo-A/BECKOApoE-/- mice and correlated with reduced necrotic core and macrophage infiltration. Mechanistically, the deletion of NOGO-B in EC sustained the rewiring of sphingolipid metabolism towards S1P, imparting an atheroprotective endothelial transcriptional signature.

CONCLUSIONS

These data demonstrated that hemodynamic stress induced a protective rewiring of sphingolipid metabolism, favoring S1P over ceramide. NOGO-B deletion sustained the rewiring of sphingolipid metabolism toward S1P protecting EC from activation under hemodynamic stress and refraining coronary atherosclerosis. These findings also set forth the foundation for sphingolipid-based therapeutics to limit atheroprogression.

Nogo-B mediates endothelial oxidative stress and inflammation to promote coronary atherosclerosis in pressure-overloaded mouse hearts

AIMS

Endothelial dysfunction plays a pivotal role in atherosclerosis, but the detailed mechanism remains incomplete understood. Nogo-B is an endoplasmic reticulum (ER)-localized protein mediating ER-mitochondrial morphology. We previously showed endothelial Nogo-B as a key regulator of endothelial function in the setting of hypertension. Here, we aim to further assess the role of Nogo-B in coronary atherosclerosis in ApoE-/- mice with pressure overload.

METHODS AND RESULTS

We generated double knockout (DKO) mouse models of systemically or endothelium-specifically excising Nogo-A/B gene on an ApoE-/- background. After 7 weeks of transverse aortic constriction (TAC) surgery, compared to ApoE-/- mice DKO mice were resistant to the development of coronary atherosclerotic lesions and plaque rapture. Sustained elevation of Nogo-B and adhesion molecules (VCAM-1/ICAM-1), early markers of atherosclerosis, was identified in heart tissues and endothelial cells (ECs) isolated from TAC ApoE-/- mice, changes that were significantly repressed by Nogo-B deficiency. In cultured human umbilical vein endothelial cells (HUVECs) exposure to inflammatory cytokines (TNF-α, IL-1β), Nogo-B was upregulated and activated reactive oxide species (ROS)-p38-p65 signaling axis. Mitofusin 2 (Mfn2) is a key protein tethering ER to mitochondria in ECs, and we showed that Nogo-B expression positively correlated with Mfn2 protein level. And Nogo-B deletion in ECs or in ApoE-/- mice reduced Mfn2 protein content and increased ER-mitochondria distance, reduced ER-mitochondrial Ca2+ transport and mitochondrial ROS generation, and prevented VCAM-1/ICAM-1 upregulation and EC dysfunction, eventually restrained atherosclerotic lesions development.

CONCLUSION

Our study revealed that Nogo-B is a critical modulator in promoting endothelial dysfunction and consequent pathogenesis of coronary atherosclerosis in pressure overloaded hearts of ApoE-/- mice. Nogo-B may hold the promise to be a common therapeutic target in the setting of hypertension.

Downregulation of Nogo-B ameliorates cerebral ischemia/reperfusion injury in mice through regulating microglia polarization via TLR4/NF-kappaB pathway

Many studies have shown a close association between Nogo-B and inflammation-related diseases. However, uncertainty does exist, regarding Nogo-B function in the pathological progression of cerebral ischemia/reperfusion (I/R) injury. Middle cerebral artery occlusion/reperfusion (MCAO/R) model was utilized in C57BL/6L mice to mimic ischemic stroke in vivo. Using oxygen-glucose deprivation and reoxygenation (ODG/R) model in microglia cells (BV-2) to establish cerebral I/R injury in vitro. Various methods, including Nogo-B siRNA transfection, mNSS and the rotarod test, TTC, HE and Nissl staining, immunofluorescence staining, immunohistochemistry, Western blot, ELISA, TUNEL and qRT-PCR were employed to probe into the effect of Nogo-B downregulation on cerebral I/R injury and the potential mechanisms. A small amount of Nogo-B expression (protein and mRNA) was observed in cortex and hippocampus before ischemia, then Nogo-B expression increased significantly on day 1, reaching the maximum on day 3, remaining stable on day 14 after I/R, and decreasing gradually after 21 days, but it still rose significantly compared with that observed preischemia. Nogo-B down-regulation could markedly reduce the neurological score and infarct volume, improve the histopathological changes and neuronal apoptosis, lower the number of CD86⁺/Iba1⁺ cells and the levels of IL-1β, IL-6, and TNF-α, and raise the density of NeuN fluorescence, the number of CD206⁺/Iba1⁺ cells, and the level of IL-4, IL-10 and TGF-β in brain of MCAO/R mice. Treatment with Nogo-B siRNA or TAK-242 in BV-2 cells could obviously decrease the CD86 fluorescence density and the mRNA expression of IL-1β, IL-6 and TNF-α, increase CD206 fluorescence density and the mRNA expression of IL-10 after OGD/R injury. In addition, the expression of TLR4, p-IκBα and p-p65 proteins significantly increased in the brain after MCAO/R and BV-2 cells exposed to OGD/R. Treatment with Nogo-B siRNA or TAK-242 prominently reduced the expression of TLR4, p-IκBα and p-p65. Our findings suggest that the down-regulation of Nogo-B exerts protective effect on cerebral I/R injury by modulating the microglia polarization through inhibiting TLR4/NF-κB signaling pathway. Nogo-B may be a potential therapeutic target for ischemic stroke.

Circulating sphingolipids in heart failure

Lack of significant advancements in early detection and treatment of heart failure have precipitated the need for discovery of novel biomarkers and therapeutic targets. Over the past decade, circulating sphingolipids have elicited promising results as biomarkers that premonish adverse cardiac events. Additionally, compelling evidence directly ties sphingolipids to these events in patients with incident heart failure. This review aims to summarize the current literature on circulating sphingolipids in both human cohorts and animal models of heart failure. The goal is to provide direction and focus for future mechanistic studies in heart failure, as well as pave the way for the development of new sphingolipid biomarkers.

Nogo-A reduces ceramide de novo biosynthesis to protect from heart failure

AIMS

Growing evidence correlate the accrual of the sphingolipid ceramide in plasma and cardiac tissue with heart failure (HF). Regulation of sphingolipid metabolism in the heart and the pathological impact of its derangement remain poorly understood. Recently, we discovered that Nogo-B, a membrane protein of endoplasmic reticulum, abundant in the vascular wall, down-regulates the sphingolipid de novo biosynthesis via serine palmitoyltransferase (SPT), first and rate liming enzyme, to impact vascular functions and blood pressure. Nogo-A, a splice isoform of Nogo, is transiently expressed in cardiomyocyte (CM) following pressure overload. Cardiac Nogo is up-regulated in dilated and ischaemic cardiomyopathies in animals and humans. However, its biological function in the heart remains unknown.

METHODS AND RESULTS

We discovered that Nogo-A is a negative regulator of SPT activity and refrains ceramide de novo biosynthesis in CM exposed to haemodynamic stress, hence limiting ceramide accrual. At 7 days following transverse aortic constriction (TAC), SPT activity was significantly up-regulated in CM lacking Nogo-A and correlated with ceramide accrual, particularly very long-chain ceramides, which are the most abundant in CM, resulting in the suppression of 'beneficial' autophagy. At 3 months post-TAC, mice lacking Nogo-A in CM showed worse pathological cardiac hypertrophy and dysfunction, with ca. 50% mortality rate.

CONCLUSION

Mechanistically, Nogo-A refrains ceramides from accrual, therefore preserves the 'beneficial' autophagy, mitochondrial function, and metabolic gene expression, limiting the progression to HF under sustained stress.

Sphingosine-1-phosphate controls endothelial sphingolipid homeostasis via ORMDL

Disruption of sphingolipid homeostasis and signaling has been implicated in diabetes, cancer, cardiometabolic, and neurodegenerative disorders. Yet, mechanisms governing cellular sensing and regulation of sphingolipid homeostasis remain largely unknown. In yeast, serine palmitoyltransferase, catalyzing the first and rate-limiting step of sphingolipid de novo biosynthesis, is negatively regulated by Orm1 and 2. Lowering sphingolipids triggers Orms phosphorylation, upregulation of serine palmitoyltransferase activity and sphingolipid de novo biosynthesis. However, mammalian orthologs ORMDLs lack the N-terminus hosting the phosphosites. Thus, which sphingolipid(s) are sensed by the cells, and mechanisms of homeostasis remain largely unknown. Here, we identify sphingosine-1-phosphate (S1P) as key sphingolipid sensed by cells via S1PRs to maintain homeostasis. The increase in S1P-S1PR signaling stabilizes ORMDLs, restraining SPT activity. Mechanistically, the hydroxylation of ORMDLs at Pro137 allows a constitutive degradation of ORMDLs via ubiquitin-proteasome pathway, preserving SPT activity. Disrupting S1PR/ORMDL axis results in ceramide accrual, mitochondrial dysfunction, impaired signal transduction, all underlying endothelial dysfunction, early event in the onset of cardio- and cerebrovascular diseases. Our discovery may provide the molecular basis for therapeutic intervention restoring sphingolipid homeostasis.

S1P receptor modulators and the cardiovascular autonomic nervous system in multiple sclerosis: a narrative review

Sphingosine 1-phosphate (S1P) receptor (S1PR) modulators have a complex mechanism of action, which are among the most efficient therapeutic options in multiple sclerosis (MS) and represent a promising approach for other immune-mediated diseases. The S1P signaling pathway involves the activation of five extracellular S1PR subtypes (S1PR1-S1PR5) that are ubiquitous and have a wide range of effects. Besides the immunomodulatory beneficial outcome in MS, S1P signaling regulates the cardiovascular function via S1PR1-S1PR3 subtypes, which reside on cardiac myocytes, endothelial, and vascular smooth muscle cells. In our review, we describe the mechanisms and clinical effects of S1PR modulators on the cardiovascular system. In the past, mostly short-term effects of S1PR modulators on the cardiovascular system have been studied, while data on long-term effects still need to be investigated. Immediate effects detected after treatment initiation are due to parasympathetic overactivation. In contrast, long-term effects may arise from a shift of the autonomic regulation toward sympathetic predominance along with S1PR1 downregulation. A mild increase in blood pressure has been reported in long-term studies, as well as decreased baroreflex sensitivity. In most studies, sustained hypertension was found to represent a significant adverse event related to treatment. The shift in the autonomic control and blood pressure values could not be just a consequence of disease progression but also related to S1PR modulation. Reduced cardiac autonomic activation and decreased heart rate variability during the long-term treatment with S1PR modulators may increase the risk for subsequent cardiac events. For second-generation S1PR modulators, this observation has to be confirmed in further studies with longer follow-ups. The periodic surveillance of cardiovascular function and detection of any cardiac autonomic dysfunction can help predict cardiac outcomes not only after the first dose but also throughout treatment.

PLAIN LANGUAGE SUMMARY

What is the cardiovascular effect of S1P receptor modulator therapy in multiple sclerosis? Sphingosine 1-phosphate (S1P) receptor (S1PR) modulators are among the most efficient therapies for multiple sclerosis. As small molecules, they are not only acting on the immune but on cardiovascular and nervous systems as well. Short-term effects of S1PR modulators on the cardiovascular system have already been extensively described, while long-term effects are less known. Our review describes the mechanisms of action and the short- and long-term effects of these therapeutic agents on the cardiovascular system in different clinical trials. We systematically reviewed the literature that had been published by January 2022. One hundred seven articles were initially identified by title and abstract using targeted keywords, and thirty-nine articles with relevance to cardiovascular effects of S1PR therapy in multiple sclerosis patients were thereafter considered, including their references for further accurate clarification. Studies on fingolimod, the first S1PR modulator approved for treating multiple sclerosis, primarily support the safety profile of this therapeutic class. The second-generation therapeutic agents along with a different treatment initiation approach helped mitigate several of the cardiovascular adverse effects that had previously been observed at the start of treatment. The heart rate may decrease when initiating S1PR modulators and, less commonly, the atrioventricular conduction may be prolonged, requiring cardiac monitoring for the first 6 h of medication. Continuous therapy with S1PR modulators can increase blood pressure values; therefore, the presence of arterial hypertension should be checked during long-term treatment. Periodic surveillance of the cardiovascular and autonomic functions can help predict cardiac outcomes and prevent possible adverse events in S1PR modulators treatment. Further studies with longer follow-ups are needed, especially for the second-generation of S1PR modulators, to confirm the safety profile of this therapeutic class.

Association between high serum Nogo-B and hypertension in Chinese Han

Background

Cellular and animal studies have shown that endoplasmic reticulum protein B (Nogo-B) is associated with hypertension, but that association has not been fully studied in humans. Therefore, the expression levels of Nogo-B were investigated in hypertensive patients.

Methods

The plasma Nogo-B levels of 74 patients with hypertension and 67 non-hypertensive patients were measured by enzyme-linked immunosorbent assay.

Results

The plasma Nogo-B levels in the hypertensive group [523.43(411.41−746.79)] were higher than in the non-hypertensive group [380.29(281.57−462.13)] (P < 0.01). Pearson’s correlation analysis indicated that systolic blood pressure and diastolic blood pressure were linearly and positively correlated with plasma Nogo-B levels. Multivariable logistic regression analysis was performed based on sex, age, BMI, smoking history, drinking history, and levels of TC, TG, LDL, and HDL. The results indicated that the plasma Nogo-B levels were independently associated with hypertension (OR = 1.007, 95%CI: 1.004–1.010, P < 0.01).

Conclusions

The present study suggests that hypertensive participants exhibited higher plasma Nogo-B levels than those without hypertension. Plasma Nogo-B levels are independently associated with hypertension.

Involvement of Ceramide Metabolism in Cerebral Ischemia

Ischemic stroke, caused by the interruption of blood flow to the brain and subsequent neuronal death, represents one of the main causes of disability in worldwide. Although reperfusion therapies have shown efficacy in a limited number of patients with acute ischemic stroke, neuroprotective drugs and recovery strategies have been widely assessed, but none of them have been successful in clinical practice. Therefore, the search for new therapeutic approaches is still necessary. Sphingolipids consist of a family of lipidic molecules with both structural and cell signaling functions. Regulation of sphingolipid metabolism is crucial for cell fate and homeostasis in the body. Different works have emphasized the implication of its metabolism in different pathologies, such as diabetes, cancer, neurodegeneration, or atherosclerosis. Other studies have shown its implication in the risk of suffering a stroke and its progression. This review will highlight the implications of sphingolipid metabolism enzymes in acute ischemic stroke.

Cardiac Hypertrophy: From Pathophysiological Mechanisms to Heart Failure Development

Cardiac hypertrophy develops in response to increased workload to reduce ventricular wall stress and maintain function and efficiency. Pathological hypertrophy can be adaptive at the beginning. However, if the stimulus persists, it may progress to ventricular chamber dilatation, contractile dysfunction, and heart failure, resulting in poorer outcome and increased social burden. The main pathophysiological mechanisms of pathological hypertrophy are cell death, fibrosis, mitochondrial dysfunction, dysregulation of Ca 2 + -handling proteins, metabolic changes, fetal gene expression reactivation, impaired protein and mitochondrial quality control, altered sarcomere structure, and inadequate angiogenesis. Diabetic cardiomyopathy is a condition in which cardiac pathological hypertrophy mainly develop due to insulin resistance and subsequent hyperglycaemia, associated with altered fatty acid metabolism, altered calcium homeostasis and inflammation. In this review, we summarize the underlying molecular mechanisms of pathological hypertrophy development and progression, which can be applied in the development of future novel therapeutic strategies in both reversal and prevention.

Nogo-B promotes angiogenesis and improves cardiac repair after myocardial infarction via activating Notch1 signaling

Nogo-B (Reticulon 4B) is reportedly a regulator of angiogenesis during the development and progression of cancer. However, whether Nogo-B regulates angiogenesis and post-myocardial infarction (MI) cardiac repair remains elusive. In the present study, we aimed to explore the role and underlying mechanisms of Nogo-B in cardiac repair during MI. We observed an increased expression level of Nogo-B in the heart of mouse MI models, as well as in isolated cardiac microvascular endothelial cells (CMECs). Moreover, Nogo-B was significantly upregulated in CMECs exposed to oxygen-glucose deprivation (OGD). Nogo-B overexpression in the endothelium via cardiotropic adeno-associated virus serotype 9 (AAV9) with the mouse endothelial-specific promoter Tie2 improved heart function, reduced scar size, and increased angiogenesis. RNA-seq data indicated that Notch signaling is a deregulated pathway in isolated CMECs along the border zone of the infarct with Nogo-B overexpression. Mechanistically, Nogo-B activated Notch1 signaling and upregulated Hes1 in the MI hearts. Inhibition of Notch signaling using a specific siRNA and γ-secretase inhibitor abolished the promotive effects of Nogo-B overexpression on network formation and migration of isolated cardiac microvascular endothelial cells (CMECs). Furthermore, endothelial Notch1 heterozygous deletion inhibited Nogo-B-induced cardioprotection and angiogenesis in the MI model. Collectively, this study demonstrates that Nogo-B is a positive regulator of angiogenesis by activating the Notch signaling pathway, suggesting that Nogo-B is a novel molecular target for ischemic disease.

Sphingolipid Metabolism and Signaling in Endothelial Cell Functions

The endothelium, inner layer of blood vessels, constitutes a metabolically active paracrine, endocrine, and autocrine organ, able to sense the neighboring environment and exert a variety of biological functions important to preserve the health of vasculature, tissues, and organs. Sphingolipids are both fundamental structural components of the eukaryotic membranes and signaling molecules regulating a variety of biological functions. Ceramide and sphingosine-1-phosphate (S1P), bioactive sphingolipids, have emerged as important regulators of cardiovascular functions in health and disease. In this review we discuss recent insights into the role of ceramide and S1P biosynthesis and signaling in regulating endothelial cell functions, in health and diseases. We also highlight advances into the mechanisms regulating serine palmitoyltransferase, the first and rate-limiting enzyme of de novo sphingolipid biosynthesis, with an emphasis on its inhibitors, ORMDL and NOGO-B. Understanding the molecular mechanisms regulating the sphingolipid de novo biosynthesis may provide the foundation for therapeutic modulation of this pathway in a variety of conditions, including cardiovascular diseases, associated with derangement of this pathway.

Deletion of Sphingosine 1-Phosphate receptor 1 in cardiomyocytes during development leads to abnormal ventricular conduction and fibrosis

Sphingosine 1-Phosphate receptor 1 (S1P1 , encoded by S1pr1) is a G protein-coupled receptor that signals in multiple cell types including endothelial cells and cardiomyocytes. Cardiomyocyte-specific deletion of S1pr1 during mouse development leads to ventricular noncompaction, with 44% of mutant mice surviving to adulthood. Adult survivors of embryonic cardiomyocyte S1pr1 deletion showed cardiac hypertrabeculation consistent with ventricular noncompaction. Surprisingly, systolic function in mutant mice was preserved through at least 1 year of age. Cardiac conduction was abnormal in cardiomyocyte S1pr1 mutant mice, with prolonged QRS intervals in mutants as compared with littermate control mice. Immunostaining of hearts from S1pr1 mutant embryos displayed a zone of intermediate Connexin 40 (Cx40) expression in the trabecular myocardium. However, we observed no significant differences in Cx40 and Connexin 43 immunostaining in hearts from adult survivors of embryonic cardiomyocyte S1pr1 deletion, which suggests normalized development of the ventricular conduction system in mutant mice. By contrast, the adult survivors of embryonic cardiomyocyte S1pr1 deletion showed increased cardiac fibrosis as compared with littermate controls. These results demonstrate that ventricular hypertrabeculation caused by embryonic deletion of cardiomyocyte S1pr1 correlates with cardiac fibrosis, which contributes to abnormal ventricular conduction. These results also reveal conduction abnormalities in the setting of hypertrabeculation with normal systolic function, which may be of clinical relevance in humans with ventricular hypertrabeculation.

Endothelial Spns2 and ApoM Regulation of Vascular Tone and Hypertension Via Sphingosine-1-Phosphate

Background Most of the circulating sphingosine-1-phosphate (S1P) is bound to ApoM (apolipoprotein M) of high-density lipoprotein (HDL) and mediates many beneficial effects of HDL on the vasculature via G protein-coupled S1P receptors. HDL-bound S1P is decreased in atherosclerosis, myocardial infarction, and diabetes mellitus. In addition to being the target, the endothelium is a source of S1P, which is transported outside of the cells by Spinster-2, contributing to circulating S1P as well as to local signaling. Mice lacking endothelial S1P receptor 1 are hypertensive, suggesting a vasculoprotective role of S1P signaling. This study investigates the role of endothelial-derived S1P and ApoM-bound S1P in regulating vascular tone and blood pressure. Methods and Results ApoM knockout (ApoM KO) mice and mice lacking endothelial Spinster-2 (ECKO-Spns2) were infused with angiotensin II for 28 days. Blood pressure, measured by telemetry and tail-cuff, was significantly increased in both ECKO-Spns2 and ApoM KO versus control mice, at baseline and following angiotensin II. Notably, ECKO-Spns2 presented an impaired vasodilation to flow and blood pressure dipping, which is clinically associated with increased risk for cardiovascular events. In hypertension, both groups presented reduced flow-mediated vasodilation and some degree of impairment in endothelial NO production, which was more evident in ECKO-Spns2. Increased hypertension in ECKO-Spns2 and ApoM KO mice correlated with worsened cardiac hypertrophy versus controls. Conclusions Our study identifies an important role for Spinster-2 and ApoM-HDL in blood pressure homeostasis via S1P-NO signaling and dissects the pathophysiological impact of endothelial-derived S1P and ApoM of HDL-bound S1P in hypertension and cardiac hypertrophy.

CDR132L improves systolic and diastolic function in a large animal model of chronic heart failure

Aims

Cardiac miR-132 activation leads to adverse remodelling and pathological hypertrophy. CDR132L is a synthetic lead-optimized oligonucleotide inhibitor with proven preclinical efficacy and safety in heart failure (HF) early after myocardial infarction (MI), and recently completed clinical evaluation in a Phase 1b study (NCT04045405). The aim of the current study was to assess safety and efficacy of CDR132L in a clinically relevant large animal (pig) model of chronic heart failure following MI.

Methods and results

In a chronic model of post-MI HF, slow-growing pigs underwent 90 min left anterior descending artery occlusion followed by reperfusion. Animals were randomized and treatment started 1-month post-MI. Monthly intravenous (IV) treatments of CDR132L over 3 or 5 months (3× or 5×) were applied in a blinded randomized placebo-controlled fashion. Efficacy was evaluated based on serial magnetic resonance imaging, haemodynamic, and biomarker analyses. The treatment regime provided sufficient tissue exposure and CDR132L was well tolerated. Overall, CDR132L treatment significantly improved cardiac function and reversed cardiac remodelling. In addition to the systolic recovery, diastolic function was also ameliorated in this chronic model of HF.

Conclusion

Monthly repeated dosing of CDR132L is safe and adequate to provide clinically relevant exposure and therapeutic efficacy in a model of chronic post-MI HF. CDR132L thus should be explored as treatment for the broad area of chronic heart failure.

Green Tea (Camellia sinensis) Extract Increased Topoisomerase IIβ, Improved Antioxidant Defense, and Attenuated Cardiac Remodeling in an Acute Doxorubicin Toxicity Model

Experimental studies have shown the action of green tea in modulating cardiac remodeling. However, the effects of green tea on the cardiac remodeling process induced by doxorubicin (DOX) are not known. Therefore, this study is aimed at evaluating whether green tea extract could attenuate DOX-induced cardiac remodeling, assessed by cardiac morphological and functional changes and associated with the evaluation of different modulators of cardiac remodeling. The animals were divided into four groups: the control group (C), the green tea group (GT), the DOX group (D), and the DOX and green tea group (DGT). Groups C and GT received intraperitoneal sterile saline injections, D and DGT received intraperitoneal injections of DOX, and GT and DGT were fed chow supplemented with green tea extract for 35 days prior to DOX injection. After forty-eight hours, we performed an echocardiogram and euthanasia and collected the materials for analysis. Green tea attenuated DOX-induced cardiotoxicity by increasing cardiac function and decreasing the concentric remodeling. Treatment with DOX increased oxidative stress in the heart, marked by a higher level of lipid hydroperoxide (LH) and lower levels of antioxidant enzymes. Treatment with green tea increased the antioxidant enzymes' activity and decreased the production of LH. Green tea extract increased the expression of Top2-β independent of DOX treatment. The activity of ATP synthase, citrate synthase, and complexes I and II decreased with DOX, without the effects of green tea. Both groups that received DOX presented with a lower ratio of P-akt/T-akt and a higher expression of CD45, TNFα, and intermediate MMP-2, without the effects of green tea. In conclusion, green tea attenuated cardiac remodeling induced by DOX and was associated with increasing the expression of Top2-β and lowering oxidative stress. However, energy metabolism and inflammation probably do not receive the benefits induced by green tea in this model.

Stretch-induced sarcoplasmic reticulum calcium leak is causatively associated with atrial fibrillation in pressure-overloaded hearts

AIMS

Despite numerous reports documenting an important role of hypertension in the development of atrial fibrillation (AF), the detailed mechanism underlying the pathological process remains incompletely understood. Here, we aim to test the hypothesis that diastolic sarcoplasmic reticulum (SR) Ca2+ leak in atrial myocytes, induced by mechanical stretch due to elevated pressure in the left atrium (LA), plays an essential role in the AF development in pressure-overloaded hearts.

METHODS AND RESULTS

Isolated mouse atrial myocytes subjected to acute axial stretch displayed an immediate elevation of SR Ca2+ leak. Using a mouse model of transverse aortic constriction (TAC), the relation between stretch, SR Ca2+ leak, and AF susceptibility was further tested. At 36 h post-TAC, SR Ca2+ leak in cardiomyocytes from the LA (with haemodynamic stress), but not right atrium (without haemodynamic stress), significantly increased, which was further elevated at 4 weeks post-TAC. Accordingly, AF susceptibility to atrial burst pacing in the 4-week TAC mice were also significantly increased, which was unaffected by inhibition of atrial fibrosis or inflammation via deletion of galectin-3. Western blotting revealed that type 2 ryanodine receptor (RyR2) in left atrial myocytes of TAC mice was oxidized due to activation and up-regulation of Nox2 and Nox4. Direct rescue of dysfunctional RyR2 with dantrolene or rycal S107 reduced diastolic SR Ca2+ leak in left atrial myocytes and prevented atrial burst pacing stimulated AF.

CONCLUSION

Our study demonstrated for the first time the increased SR Ca2+ leak mediated by enhanced oxidative stress in left atrial myocytes that is causatively associated with higher AF susceptibility in pressure-overloaded hearts.

Excess sarcoplasmic reticulum-mitochondria calcium transport induced by Sphingosine-1-phosphate contributes to cardiomyocyte hypertrophy

Sphingosine-1-phosphate (S1P) has been shown to possess pro-hypertrophic properties in the heart, but the detailed molecular mechanism that underlies the pathological process is rarely explored. In the present study, we aim to explore the role of S1P-mediated intracellular Ca²⁺ signaling, with a focus on sarcoplasmic reticulum (SR)-mitochondria communication, in cardiomyocyte hypertrophy. Cultured neonatal rat ventricular myocytes (NRVMs) displayed significantly hypertrophic growth after treatment with 1 μmol/L S1P for 48 h, as indicated by the cell surface area or mRNA expressions of hypertrophic marker genes (ANP, BNP and β-MHC). Importantly, mitochondrial Ca²⁺ and reactive oxygen species (ROS) levels were dramatically elevated upon S1P stimulation, and pharmacological blockage of which abolished NRVM hypertrophy. 0.5 Hz electrical pacing induced similar cytosolic Ca²⁺ kinetics to S1P stimulation, but unaffected the peak of mitochondrial [Ca²⁺]. With interference of the expression of type 2 inositol 1,4,5-trisphosphate receptors (IP₃R2), which are unemployed in electrical paced Ca²⁺ activity but may be activated by S1P, alteration in mitochondrial Ca²⁺ as well as the hypertrophic effect in NRVMs under S1P stimulation were attenuated. The hypertrophic effect of S1P can also be abolished by pharmacological block of S1PR1 or Gi signaling. Collectively, our study highlights the mechanistic role of IP₃R2-mediated excess SR-mitochondria Ca²⁺ transport in S1P-induced cardiomyocyte hypertrophy.

The antithetic role of ceramide and sphingosine-1-phosphate in cardiac dysfunction

Cardiovascular diseases (CVDs) are the leading cause of death globally and the number of cardiovascular patients, which is estimated to be over 30 million in 2018, represent a challenging issue for the healthcare systems worldwide. Therefore, the identification of novel molecular targets to develop new treatments is an ongoing challenge for the scientific community. In this context, sphingolipids (SLs) have been progressively recognized as potent bioactive compounds that play crucial roles in the modulation of several key biological processes, such as proliferation, differentiation, and apoptosis. Furthermore, SLs involvement in cardiac physiology and pathophysiology attracted much attention, since these molecules could be crucial in the development of CVDs. Among SLs, ceramide and sphingosine-1-phosphate (S1P) represent the most studied bioactive lipid mediators, which are characterized by opposing activities in the regulation of the fate of cardiac cells. In particular, maintaining the balance of the so-called ceramide/S1P rheostat emerged as an important novel therapeutical target to counteract CVDs. Thus, this review aims at critically summarizing the current knowledge about the antithetic roles of ceramide and S1P in cardiomyocytes dysfunctions, highlighting how the modulation of their metabolism through specific molecules, such as myriocin and FTY720, could represent a novel and interesting therapeutic approach to improve the management of CVDs.

Cardiac β-adrenergic receptor activation mediates distinct and cell type-dependent changes in the expression and distribution of connexin 43

Activation of the sympatho-β-adrenergic receptors (β-ARs) system is a hallmark of heart failure, leading to fibrosis and arrhythmias. Connexin 43 (Cx43) is the most abundant gap junctional protein in the myocardium. Current knowledge is limited regarding Cx43 remodelling in diverse cell types in the diseased myocardium and the underlying mechanism. We studied cell type-dependent changes in Cx43 remodelling due to β-AR overactivation and molecular mechanisms involved. Mouse models of isoproterenol stimulation or transgenic cardiomyocyte overexpression of β₂ -AR were used, which exhibited cardiac fibrosis and up-regulated total Cx43 abundance. In both models, whereas Cx43 expression in cardiomyocytes was reduced and more laterally distributed, fibroblasts exhibited elevated Cx43 expression and enhanced gap junction communication. Mechanistically, activation of β₂ -AR in fibroblasts in vitro elevated Cx43 expression, which was abolished by the β₂ -antagonist ICI-118551 or protein kinase A inhibitor H-89, but simulated by the adenylyl cyclase activator forskolin. Our in vitro and in vivo data showed that β-AR activation-induced production of IL-18 sequentially stimulated Cx43 expression in fibroblasts in a paracrine fashion. In summary, our findings demonstrate a pivotal role of β-AR in mediating distinct and cell type-dependent changes in the expression and distribution of Cx43, leading to pathological gap junction remodelling in the myocardium.

The S1P-S1PR Axis in Neurological Disorders-Insights into Current and Future Therapeutic Perspectives

Sphingosine 1-phosphate (S1P), derived from membrane sphingolipids, is a pleiotropic bioactive lipid mediator capable of evoking complex immune phenomena. Studies have highlighted its importance regarding intracellular signaling cascades as well as membrane-bound S1P receptor (S1PR) engagement in various clinical conditions. In neurological disorders, the S1P–S1PR axis is acknowledged in neurodegenerative, neuroinflammatory, and cerebrovascular disorders. Modulators of S1P signaling have enabled an immense insight into fundamental pathological pathways, which were pivotal in identifying and improving the treatment of human diseases. However, its intricate molecular signaling pathways initiated upon receptor ligation are still poorly elucidated. In this review, the authors highlight the current evidence for S1P signaling in neurodegenerative and neuroinflammatory disorders as well as stroke and present an array of drugs targeting the S1P signaling pathway, which are being tested in clinical trials. Further insights on how the S1P–S1PR axis orchestrates disease initiation, progression, and recovery may hold a remarkable potential regarding therapeutic options in these neurological disorders.

Sphingosine 1-phosphate receptor-1 specific agonist SEW2871 ameliorates ANIT-induced dysregulation of bile acid homeostasis in mice plasma and liver

Dysregulated bile acid (BA) homeostasis is an extremely significant pathological phenomenon of intrahepatic cholestasis, and the accumulated BA could further trigger hepatocyte injury. Here, we showed that the expression of sphingosine-1-phosphate receptor 1 (S1PR1) was down-regulated by α-naphthylisothiocyanate (ANIT) in vivo and in vitro. The up-regulated S1PR1 induced by SEW2871 (a specific agonist of S1PR1) could improve ANIT-induced deficiency of hepatocyte tight junctions (TJs), cholestatic liver injury and the disrupted BA homeostasis in mice. BA metabolic profiles showed that SEW2871 not only reversed the disruption of plasma BA homeostasis, but also alleviated BA accumulation in the liver of ANIT-treated mice. Further quantitative analysis of 19 BAs showed that ANIT increased almost all BAs in mice plasma and liver, all of which were restored by SEW2871. Our data demonstrated that the top performing BAs were taurine conjugated bile acids (T-), especially taurocholic acid (TCA). Molecular mechanism studies indicated that BA transporters, synthetase, and BAs nuclear receptors (NRs) might be the important factors that maintained BA homeostasis by SEW2871 in ANIT-induced cholestasis. In conclusion, these results demonstrated that S1PR1 selective agonists might be the novel and potential effective agents for the treatment of intrahepatic cholestasis by recovering dysregulated BA homeostasis.

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.

Sphingosine 1-phosphate: Lipid signaling in pathology and therapy

Sphingosine 1-phosphate (S1P), a metabolic product of cell membrane sphingolipids, is bound to extracellular chaperones, is enriched in circulatory fluids, and binds to G protein-coupled S1P receptors (S1PRs) to regulate embryonic development, postnatal organ function, and disease. S1PRs regulate essential processes such as adaptive immune cell trafficking, vascular development, and homeostasis. Moreover, S1PR signaling is a driver of multiple diseases. The past decade has witnessed an exponential growth in this field, in part because of multidisciplinary research focused on this lipid mediator and the application of S1PR-targeted drugs in clinical medicine. This has revealed fundamental principles of lysophospholipid mediator signaling that not only clarify the complex and wide ranging actions of S1P but also guide the development of therapeutics and translational directions in immunological, cardiovascular, neurological, inflammatory, and fibrotic diseases.

Endothelial Sphingolipid De Novo Synthesis Controls Blood Pressure by Regulating Signal Transduction and NO via Ceramide

Ceramides are sphingolipids that modulate a variety of cellular processes via 2 major mechanisms: functioning as second messengers and regulating membrane biophysical properties, particularly lipid rafts, important signaling platforms. Altered sphingolipid levels have been implicated in many cardiovascular diseases, including hypertension, atherosclerosis, and diabetes mellitus-related conditions; however, molecular mechanisms by which ceramides impact endothelial functions remain poorly understood. In this regard, we generated mice defective of endothelial sphingolipid de novo biosynthesis by deleting the Sptlc2 (long chain subunit 2 of serine palmitoyltransferase)-the first enzyme of the pathway. Our study demonstrated that endothelial sphingolipid de novo production is necessary to regulate (1) signal transduction in response to NO agonists and, mainly via ceramides, (2) resting eNOS (endothelial NO synthase) phosphorylation, and (3) blood pressure homeostasis. Specifically, our findings suggest a prevailing role of C16:0-Cer in preserving vasodilation induced by tyrosine kinase and GPCRs (G-protein coupled receptors), except for Gq-coupled receptors, while C24:0- and C24:1-Cer control flow-induced vasodilation. Replenishing C16:0-Cer in vitro and in vivo reinstates endothelial cell signaling and vascular tone regulation. This study reveals an important role of locally produced ceramides, particularly C16:0-, C24:0-, and C24:1-Cer in vascular and blood pressure homeostasis, and establishes the endothelium as a key source of plasma ceramides. Clinically, specific plasma ceramides ratios are independent predictors of major cardiovascular events. Our data also suggest that plasma ceramides might be indicative of the diseased state of the endothelium.

Sphingolipid Signature of Human Feto-Placental Vasculature in Preeclampsia

Bioactive sphingolipids are emerging as key regulators of vascular function and homeostasis. While most of the clinical studies have been devoted to profile circulating sphingolipids in maternal plasma, little is known about the role of the sphingolipid at the feto-placental vasculature, which is in direct contact with the offspring circulation. Our study aims to compare the sphingolipid profile of normal with preeclamptic (PE) placental chorionic arteries and isolated endothelial cells, with the goal of unveiling potential underlying pathomechanisms in the vasculature. Dihydrosphingosine and sphingomyelin (SM) concentrations (C16:0-, C18:0-, and C24:0- sphingomyelin) were significantly increased in chorionic arteries of preeclamptic placentas, whereas total ceramide, although showing a downward trend, were not statistically different. Moreover, RNA and immunofluorescence analysis showed impaired sphingosine-1-phosphate (S1P) synthesis and signaling in PE vessels. Our data reveal that the exposure to a deranged maternal intrauterine environment during PE alters the sphingolipid signature and gene expression on the fetal side of the placental vasculature. This pathological remodeling consists in increased serine palmitoyltransferase (SPT) activity and SM accrual in PE chorionic arteries, with concomitance impairment endothelial S1P signaling in the endothelium of these vessels. The increase of endothelial S1P phosphatase, lyase and S1PR2, and blunted S1PR1 expression support the onset of the pathological phenotype in chorionic arteries.

Sphingolipids in the Heart: From Cradle to Grave

Cardiovascular diseases are the leading cause of mortality worldwide and this has largely been driven by the increase in metabolic disease in recent decades. Metabolic disease alters metabolism, distribution, and profiles of sphingolipids in multiple organs and tissues; as such, sphingolipid metabolism and signaling have been vigorously studied as contributors to metabolic pathophysiology in various pathological outcomes of obesity, including cardiovascular disease. Much experimental evidence suggests that targeting sphingolipid metabolism may be advantageous in the context of cardiometabolic disease. The heart, however, is a structurally and functionally complex organ where bioactive sphingolipids have been shown not only to mediate pathological processes, but also to contribute to essential functions in cardiogenesis and cardiac function. Additionally, some sphingolipids are protective in the context of ischemia/reperfusion injury. In addition to mechanistic contributions, untargeted lipidomics approaches used in recent years have identified some specific circulating sphingolipids as novel biomarkers in the context of cardiovascular disease. In this review, we summarize recent literature on both deleterious and beneficial contributions of sphingolipids to cardiogenesis and myocardial function as well as recent identification of novel sphingolipid biomarkers for cardiovascular disease risk prediction and diagnosis.

Transplantation of HUVECs with genetically modified Nogo-B accelerates wound-healing in nude mice

Wound repair is an intractable problem in clinic, with limited treatment options. Previous studies have demonstrated the therapeutic potential of Nogo-B in tissue repairs. However, the therapeutic effect of Nogo-B in HUVEC is still unknown. In this study, we examined the benefit of genetically modified Human Umbilical Vein Endothelial Cells (HUVECs) and found that down regulation of Nogo-B significantly promoted secretion of growth factors involving in wound healing and greatly boosted the proliferation, migration of fibroblasts and epithelial cells. Moreover, using an excisional wound splinting model, we showed that injection of exogenous HUVEC-siNogo-B around the wound significantly enhanced angiogenesis and wound healing in nude mice. Thus, our data suggests that genetically modified HUVECs support microenvironment suitable for wound healing and systemically demonstrates the beneficial effect of HUVECs in wound healing.

Pressure overload leads to coronary plaque formation, progression, and myocardial events in ApoE-/- mice

Hypercholesterolemia and hypertension are two major risk factors for coronary artery diseases, which remain the major cause of mortality in the industrialized world. Current animal models of atherosclerosis do not recapitulate coronary plaque disruption, thrombosis, and myocardial infarction occurring in humans. Recently, we demonstrated that exposure of the heart to high pressure, by transverse aortic constriction (TAC), induced coronary lesions in ApoE-/- mice on chow diet. The aim of this study was to characterize the magnitude and location of coronary lesions in ApoE-/- mice after TAC and to assess the susceptibility of coronary plaque to disruption, leading to myocardial events. Here, we describe a reliable pathological condition in mice characterized by the development of coronary lesions and its progression, leading to myocardial infarction; this model better recapitulates human disease. Following TAC surgery, about 90% of ApoE-/- mice developed coronary lesions, especially in the left anterior descending artery, with 59% of the mice manifesting a different magnitude of LAD stenosis. Myocardial events, identified in 74% of the mice, were mainly due to coronary plaque thrombosis and occlusion. That TAC-induced development and progression of coronary lesions in ApoE-/- mice, leading to myocardial events, represents a potentially novel and important tool to investigate the development of coronary lesions and its sequelae in a setting that better resemble human conditions.

L-cysteine/cystathionine-β-synthase-induced relaxation in mouse aorta involves a L-serine/sphingosine-1-phosphate/NO pathway

BACKGROUND AND PURPOSE

Among the three enzymes involved in the transsulfuration pathway, only cystathionine β-synthase (CBS) converts L-cysteine into L-serine and H₂ S. L-serine is also involved in the de novo sphingolipid biosynthesis through a condensation with palmitoyl-CoA by the action of serine palmitoyltransferase (SPT). Here, we have investigated if L-serine contributes to the vasorelaxant effect.

EXPERIMENTAL APPROACH

The presence of CBS in mouse vascular endothelium was assessed by immunohistochemistry and immunofluorescence. The relaxant activity of L-serine (0.1-300 μM) and L-cysteine (0.1-300 μM) was estimated on mouse aorta rings, with or without endothelium. A pharmacological modulation study evaluated NO and sphingosine-1-phosphate (S1P) involvement. Levels of NO and S1P were also measured following incubation of aorta tissue with either L-serine (1, 10, and 100 μM) or L-cysteine (10, 100 μM, and 1 mM).

KEY RESULTS

L-serine relaxed aorta rings in an endothelium-dependent manner. The vascular effect was reduced by L-NG-nitro-arginine methyl ester and wortmaninn. A similar pattern was obtained with L-cysteine. The S1P1 receptor antagonist (W146) or the SPT inhibitor (myriocin) reduced either L-serine or L-cysteine relaxant effect. L-serine or L-cysteine incubation increased NO and S1P levels in mouse aorta.

CONCLUSIONS AND IMPLICATIONS

L-serine, a by-product formed within the transsulfuration pathway starting from L-cysteine via CBS, contributes to the vasodilator action of L-cysteine. The L-serine effect involves both NO and S1P. This mechanism could be involved in the marked dysregulation of vascular tone in hyperhomocysteinemic patients (CBS deficiency) and may represent a feasible therapeutic target.

LINKED ARTICLES

This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

ADAM10 controls the differentiation of the coronary arterial endothelium

The coronary vasculature is crucial for normal heart function, yet much remains to be learned about its development, especially the maturation of coronary arterial endothelium. Here, we show that endothelial inactivation of ADAM10, a key regulator of Notch signaling, leads to defects in coronary arterial differentiation, as evidenced by dysregulated genes related to Notch signaling and arterial identity. Moreover, transcriptome analysis indicated reduced EGFR signaling in A10ΔEC coronary endothelium. Further analysis revealed that A10ΔEC mice have enlarged dysfunctional hearts with abnormal myocardial compaction, and increased expression of venous and immature endothelium markers. These findings provide the first evidence for a potential role for endothelial ADAM10 in cardioprotective homeostatic EGFR signaling and implicate ADAM10/Notch signaling in coronary arterial cell specification, which is vital for normal heart development and function. The ADAM10/Notch signaling pathway thus emerges as a potential therapeutic target for improving the regenerative capacity and maturation of the coronary vasculature.

RTN4 Knockdown Dysregulates the AKT Pathway, Destabilizes the Cytoskeleton, and Enhances Paclitaxel-Induced Cytotoxicity in Cancers

Reticulon-4 (RTN4), commonly known as a neurite outgrowth inhibitor (Nogo), is emerging as an important player in human cancers. Clinically, we found lower RTN4 expression in patient-derived tumors was associated with significantly better survival in lung, breast, cervical, and renal cancer patients. To identify the role of RTN4 in cancer biology, we performed mass spectrometry-based quantitative proteomic analysis on cancer cells following RTN4 knockdown and found its link with pro-survival as well as cytoskeleton-related processes. Subsequent mechanistic investigations revealed that RTN4 regulates lipid homeostasis, AKT signaling, and cytoskeleton modulation. In particular, downregulation of RTN4 reduced sphingomyelin synthesis and impaired plasma membrane localization of AKT, wherein AKT phosphorylation, involved in many cancers, was significantly reduced without any comparable effect on AKT-related upstream kinases, in a sphingolipid-dependent manner. Furthermore, knockdown of RTN4 retarded proliferation of cancer cells in vitro as well as tumor xenografts in mice. Finally, RTN4 knockdown affected tubulin stability and promoted higher cytotoxic effects with chemotherapeutic paclitaxel in cancer cells both in vitro and in vivo. In summary, RTN4 is involved in carcinogenesis and represents a molecular candidate that may be targeted to achieve desired antitumor effects in clinics.

Nogo-C regulates post myocardial infarction fibrosis through the interaction with ER Ca2+ leakage channel Sec61α in mouse hearts

Cardiac fibrosis is an independent risk factor for heart failure and even the leading cause of death in myocardial infarction patients. However, molecular mechanisms associated with the pathogenesis of cardiac fibrosis following myocardial infarction are not yet fully understood. Nogo-C protein ubiquitously expresses in tissues including in the heart. Our previous study found that Nogo-C regulated cardiomyocyte apoptosis during myocardial infarction. In the present study, we found that Nogo-C was upregulated in fibrotic hearts after myocardial infarction and in Ang II- or TGF-β1-stimulated cardiac fibroblasts. Overexpression of Nogo-C in cardiac fibroblasts increased expression of pro-fibrogenic proteins, while knockdown of Nogo-C inhibited the fibrotic responses of cardiac fibroblasts to Ang II- or TGF-β1 stimulation. Functionally, Nogo-C deficiency suppressed pro-fibrogenic proteins in post-myocardial infarction hearts and ameliorated post-myocardial infarction cardiac function. Mechanistically, we found that Nogo-C increased intracellular Ca²⁺ concentration and buffering Ca²⁺ totally abolished Nogo-C-induced fibrotic responses. Moreover, overexpression of Nogo-C caused increased Sec61α, the Ca²⁺ leakage channel on endoplasmic reticulum membrane. Nogo-C interacted with Sec61α on endoplasmic reticulum and stabilized Sec61α protein by inhibiting its ubiquitination. Inhibition or knockdown of Sec61α blocked Nogo-C-induced increase of cytosolic Ca²⁺ concentration and inhibited Nogo-C- and TGF-β1-induced fibrotic responses in cardiac fibroblasts, suggesting that Nogo-C regulates cardiac fibrosis through interacting with Sec61α to mediate the Ca²⁺ leakage from endoplasmic reticulum. Thus, our results reveal a novel mechanism underlying cardiac fibrosis following myocardial infarction, and provide a therapeutic strategy for cardiac remodeling related heart diseases.

Inhibition of Nogo-B promotes cardiac hypertrophy via endoplasmic reticulum stress

AIMS

Nogo-B is a key endoplasmic reticulum (ER) protein that regulates ER stress signaling. However, its role in cardiac hypertrophy remains poorly understood. ER stress is interrelated with autophagy in the process of cardiac hypertrophy. Therefore, we aimed to test the hypothesis that both ER stress and autophagy signaling mediate the function of Nogo-B in cardiac hypertrophy.

MAIN METHODS

Rat models of transverse aortic constriction (TAC), neonatal rat cardiomyocytes (NRCMs) stimulated with norepinephrine (Ne) and primary cardiac fibroblasts treated with transforming growth factor β1 (TGF-β1) were used in this study. The expression of Nogo-B and markers of ER stress were determined by quantitative RT-PCR, western blotting and immunofluorescence. Autophagy was measured by monitoring autophagic flux. Specific small interfering RNA (siRNA) of Nogo-B was transfected to investigate the role of Nogo-B in regulating cardiac hypertrophy.

KEY FINDINGS

In TAC-induced hypertrophic heart tissues, Ne-treated hypertrophic cardiomyocytes and TGF-β1-stimulated cardiac fibroblasts, the expression of Nogo-B, and markers of ER stress were significantly elevated. Impairment of autophagic flux was observed in the activated cardiac fibroblasts. Down-regulation of Nogo-B by siRNA further exacerbated Ne-induced cardiomyocyte hypertrophy and TGF-β1-induced cardiac fibroblast activation. Gene silencing of Nogo-B promoted the activation of the ER stress pathway and the impairment of autophagic flux. Moreover, inhibition of Nogo-B activated the protein kinase RNA-like ER kinase (PERK)/activating transcriptional factor 4 (ATF4) and activating transcriptional factor 6 (ATF6) branches of ER stress pathways.

SIGNIFICANCE

These findings suggest that inhibition of Nogo-B promotes cardiomyocyte hypertrophy and cardiac fibroblast activation by activating the PERK/ATF4 signaling pathway and defects of autophagic flux.

Getting to the heart of the sphingolipid riddle

Obesity, Type 2 Diabetes, and Metabolic Syndrome induce dyslipidemia resulting in inundation of peripheral organs with fatty acids. These not only serve as substrates for energy production, but also contribute to aberrant production of bioactive lipids. Moreover, lipid metabolism is affected in many cardiac disorders including heart failure, ischemia reperfusion injury, and others. While lipids serve crucial homeostatic roles, perturbing biosynthesis of lipid mediators leads to aberrant cell signaling, which contributes to maladaptive cardiovascular programs. Bioactive sphingolipids, in particular, have been implicated in pathophysiology in the heart and vasculature by a variety of studies in cells, animal models, and humans. Because of the burgeoning interest in sphingolipid-driven biology in the cardiovascular system, it is necessary to discuss the experimental considerations for studying sphingolipid metabolism and signaling, emphasizing the caveats to some widely available experimental tools and approaches. Additionally, there is a growing appreciation for the diversity of ceramide structures generated via specific enzymes and bearing disparate cellular functions. While targeting these individual species and enzymes constitutes a major advance, studies show that sphingolipid synthesis readily adapts to compensate for experimental targeting of any individual pathway, thereby convoluting data interpretation. Furthermore, though some molecular mechanisms of sphingolipid action are known, signaling pathways impacted by sphingolipids remain incompletely understood. In this review, we discuss these issues and highlight recent studies as well as future directions that may extend our understanding of the metabolism and signaling actions of these enigmatic lipids in the cardiovascular context.

An engineered S1P chaperone attenuates hypertension and ischemic injury

Endothelial dysfunction, a hallmark of vascular disease, is restored by plasma high-density lipoprotein (HDL). However, a generalized increase in HDL abundance is not beneficial, suggesting that specific HDL species mediate protective effects. Apolipoprotein M-containing HDL (ApoM⁺HDL), which carries the bioactive lipid sphingosine 1-phosphate (S1P), promotes endothelial function by activating G protein-coupled S1P receptors. Moreover, HDL-bound S1P is limiting in several inflammatory, metabolic, and vascular diseases. We report the development of a soluble carrier for S1P, ApoM-Fc, which activated S1P receptors in a sustained manner and promoted endothelial function. In contrast, ApoM-Fc did not modulate circulating lymphocyte numbers, suggesting that it specifically activated endothelial S1P receptors. ApoM-Fc administration reduced blood pressure in hypertensive mice, attenuated myocardial damage after ischemia/reperfusion injury, and reduced brain infarct volume in the middle cerebral artery occlusion model of stroke. Our proof-of-concept study suggests that selective and sustained targeting of endothelial S1P receptors by ApoM-Fc could be a viable therapeutic strategy in vascular diseases.

S1PR1 (Sphingosine-1-Phosphate Receptor 1) Signaling Regulates Blood Flow and Pressure

Nitric oxide is one of the major endothelial-derived vasoactive factors that regulate blood pressure (BP), and the bioactive lipid mediator S1P (sphingosine-1-phosphate) is a potent activator of endothelial nitric oxide synthase through G protein-coupled receptors. Endothelial-derived S1P and the autocrine/paracrine activation of S1PR (S1P receptors) play an important role in preserving vascular functions and BP homeostasis. Furthermore, FTY720 (fingolimod), binding to 4 out of 5 S1PRs recently approved by the Food and Drug Administration to treat autoimmune conditions, induces a modest and transient decrease in heart rate in both animals and humans, suggesting that drugs targeting sphingolipid signaling affect cardiovascular functions in vivo. However, the role of specific S1P receptors in BP homeostasis remains unknown. The aim of this study is to determine the role of the key vascular S1P receptors, namely, S1PR1 and S1PR3, in BP regulation in physiological and hypertensive conditions. The specific loss of endothelial S1PR1 decreases basal and stimulated endothelial-derived nitric oxide and resets BP to a higher-than-normal value. Interestingly, we identified a novel and important role for S1PR1 signaling in flow-mediated mechanotransduction. FTY720, acting as functional antagonist of S1PR1, markedly decreases endothelial S1PR1, increases BP in control mice, and exacerbates hypertension in angiotensin II mouse model, underlining the antihypertensive functions of S1PR1 signaling. Our study identifies S1P-S1PR1-nitric oxide signaling as a new regulatory pathway in vivo of vascular relaxation to flow and BP homeostasis, providing a novel therapeutic target for the treatment of hypertension.

IP3R and RyR calcium channels are involved in neonatal rat cardiac myocyte hypertrophy induced by tumor necrosis factor-α

To investigate which calcium channels are involved in cardiac myocyte hypertrophy induced by TNF-α, cultured cardiomyocytes were treated with 100 μg/L TNF-α. In addition, three different calcium channel blockers (2-APB, ryanodine and nifedipine) were used, and the effects of each calcium channel blocker on cardiac hypertrophy induced by TNF-α were carefully observed. Measurements included cytosolic calcium transients ([Ca2+]i), the level of intracellular calcium in individual cells, cell protein content, cell protein synthesis and cell volume. We found that the IP3R inhibitor (2-APB) and RyR inhibitor (ryanodine) both had significant suppressive effects on the level of [Ca2+]i, calcium concentration, cell protein content, cell protein synthesis and cell volume of cardiomyocytes treated with TNF-α (P<0.01). Moreover, their combined effects were significantly enhanced compared with their single effects (P<0.01). However, the inhibitor of the L type Ca2+ channel nifedipine exhibited no significant suppressive effects on the increase in [Ca2+]i, calcium concentration, cell protein content, cell protein synthesis and cell volume of cardiomyocytes induced by TNF-α (P>0.05). Our results suggest that TNF-α probably induces cardiac myocyte hypertrophy by activating IP3R and RyR calcium channels, which control the release of calcium ions from the sarcoplasmic reticulum (SR) in cardiomyocytes. On the other hand, extracellular calcium influx, which is mainly regulated by the L type Ca2+ channel, may not be involved in cardiac myocyte hypertrophy induced by TNF-α.

Introduction: T Cell Trafficking in Inflammation and Immunity

T cell migration across vascular endothelium is essential for T cell responses, as through the expression of specific tissue-homing receptors, these cells then access peripheral tissues, with the goal of eliminating invading pathogens and/or tumor cells. However, aberrant trafficking of T cells to peripheral tissues contributes to the development of most chronic inflammatory diseases. Very little is known about the mechanisms by which T cell trafficking is regulated during inflammation, and it is thus difficult to target this aspect of pathology for the development of new therapies. It is therefore important to understand the pathways involved in regulating the recruitment of immune cells.

Sphingolipid De Novo Biosynthesis: A Rheostat of Cardiovascular Homeostasis

Sphingolipids (SL) are both fundamental structural components of the eukaryotic membranes and signaling molecules that regulate a variety of biological functions. The highly-bioactive lipids, ceramide and sphingosine-1-phosphate, have emerged as important regulators of cardiovascular function in health and disease. In this review we discuss recent insights into the role of SLs, particularly ceramide and sphingosine-1-phosphate, in the pathophysiology of the cardiovascular system. We also highlight advances into the molecular mechanisms regulating serine palmitoyltransferase, the first and rate-limiting enzyme of de novo SL biosynthesis, with an emphasis on the recently discovered inhibitors of serine palmitoyltransferase, ORMDL and NOGO-B proteins. Understanding the molecular mechanisms regulating this biosynthetic pathway may lead to the development of novel therapeutic approaches for the treatment of cardiovascular diseases.

Green tea (Cammellia sinensis) attenuates ventricular remodeling after experimental myocardial infarction

BACKGROUND

Considering the high morbidity and mortality after myocardial infarction (MI), the study of compounds with potential benefits for cardiac remodeling is reasonable. Green tea (GT) (Cammellia sinensis) is the most consumed beverage in the world. The potential action mechanisms of GT include anti-inflammatory, anti-apoptotic, antioxidant, and lipid-lowering properties.

OBJECTIVE

This study analyzed the effects of GT on cardiac remodeling following coronary occlusion in rats.

METHODS

Male Wistar rats were divided into four groups: control (C), control green tea (GT), myocardial infarction (MI), and myocardial infarction and green tea (MI-GT). GT and MI-GT were fed with standard chow with 0.25% Polyphenon 60 (Sigma-Aldrich Canada, Oakville, ON, Canada). After 3months of observation, echocardiographic and isolated heart study, oxidative stress, energy metabolism, serum lipids, extracellular matrix, and apoptosis were evaluated.

RESULTS

GT reduced cardiac hypertrophy and improved systolic and diastolic dysfunction. Concerning oxidative stress, GT reduced protein carbonyl, increased Nrf-2, and restored antioxidant enzyme activity to the control pattern. Energy metabolism was affected by MI that presented with lower fatty acid oxidation and accumulation of triacylglycerol, increased serum lipids, impairment of the citric acid cycle, and oxidative phosphorylation. GT stimulated the glucose pathway and mitochondrial function after MI by increasing pyruvate dehydrogenase, Complex I, ATP synthase, and glycogen storage. In addition, MI changed the extracellular matrix including MMP-2 and TIMP-1 activity and increased apoptosis by 3-caspase, all of which were attenuated by GT.

CONCLUSION

GT attenuated cardiac remodeling after MI, associated with improvement in systolic and diastolic dysfunction. Oxidative stress, energy metabolism, apoptosis, and extracellular matrix alterations are all potential mechanisms by which GT may take part.