EDG1 receptor stimulation leads to cardiac hypertrophy in rat neonatal myocytes

Unique pharmacological properties of etrasimod among S1P receptor modulators

Etrasimod (ADP334) is an oral, once-daily, selective sphingosine 1-phosphate (S1P)1,4,5 receptor modulator for the treatment of moderately to severely active ulcerative colitis and in development for the treatment of immune-mediated inflammatory diseases. Interaction between S1P and its five receptor subtypes (S1P1-S1P5) plays a role in several physiologic systems, including the cardiovascular and immune systems. Since differences in S1PR binding and downstream intracellular signaling could contribute to distinct profiles of drug efficacy and safety, we directly compared the S1P1-5 selectivity profile of etrasimod to three marketed S1PR modulators: fingolimod, ozanimod, and siponimod. Using both heterologous expression systems and human umbilical vein endothelial cells that spontaneously express S1P1, we profiled key S1P1 downstream signaling pathways and found that etrasimod had similar potency to the other tested S1PR modulators in promoting β-arrestin recruitment and S1P1 internalization. However, etrasimod was notably less potent than other S1PR modulators in assays measuring S1P1-mediated G protein activation (GTPγS binding and cAMP inhibition). Relatively lower potency of etrasimod in inducing G protein signaling corresponded to significantly diminished activation of human cardiac G protein-coupled inwardly rectifying potassium channels when compared to ozanimod. Together with pharmacokinetic properties, this pharmacologic profile of etrasimod may contribute to the positive benefit risk profile of etrasimod observed during the phase III ELEVATE UC 52 and ELEVATE UC 12 trials in patients with moderately to severely active ulcerative colitis.

Deficiency of the sphingosine-1-phosphate (S1P) transporter Mfsd2b protects the heart against hypertension-induced cardiac remodeling by suppressing the L-type-Ca2+ channel

The erythrocyte S1P transporter Mfsd2b is also expressed in the heart. We hypothesized that S1P transport by Mfsd2b is involved in cardiac function. Hypertension-induced cardiac remodeling was induced by 4-weeks Angiotensin II (AngII) administration and assessed by echocardiography. Ca2+ transients and sarcomere shortening were examined in adult cardiomyocytes (ACM) from Mfsd2b+/+ and Mfsd2b-/- mice. Tension and force development were measured in skinned cardiac fibers. Myocardial gene expression was determined by real-time PCR, Protein Phosphatase 2A (PP2A) by enzymatic assay, and S1P by LC/MS, respectively. Msfd2b was expressed in the murine and human heart, and its deficiency led to higher cardiac S1P. Mfsd2b-/- mice had regular basal cardiac function but were protected against AngII-induced deterioration of left-ventricular function as evidenced by ~ 30% better stroke volume and cardiac index, and preserved ejection fraction despite similar increases in blood pressure. Mfsd2b-/- ACM exhibited attenuated Ca2+ mobilization in response to isoprenaline whereas contractility was unchanged. Mfsd2b-/- ACM showed no changes in proteins responsible for Ca2+ homeostasis, and skinned cardiac fibers exhibited reduced passive tension generation with preserved contractility. Verapamil abolished the differences in Ca2+ mobilization between Mfsd2b+/+ and Mfsd2b-/- ACM suggesting that S1P inhibits L-type-Ca2+ channels (LTCC). In agreement, intracellular S1P activated the inhibitory LTCC phosphatase PP2A in ACM and PP2A activity was increased in Mfsd2b-/- hearts. We suggest that myocardial S1P protects from hypertension-induced left-ventricular remodeling by inhibiting LTCC through PP2A activation. Pharmacologic inhibition of Mfsd2b may thus offer a novel approach to heart failure.

Sphingolipid Levels and Signaling via Resveratrol and Antioxidant Actions in Cardiometabolic Risk and Disease

Resveratrol (RSV) is a phenolic compound with strong antioxidant activity, which is generally associated with the beneficial effects of wine on human health. All resveratrol-mediated benefits exerted on different systems and pathophysiological conditions are possible through resveratrol's interactions with different biological targets, along with its involvement in several key cellular pathways affecting cardiometabolic (CM) health. With regard to its role in oxidative stress, RSV exerts its antioxidant activity not only as a free radical scavenger but also by increasing the activity of antioxidant enzymes and regulating redox genes, nitric oxide bioavailability and mitochondrial function. Moreover, several studies have demonstrated that some RSV effects are mediated by changes in sphingolipids, a class of biolipids involved in a number of cellular functions (e.g., apoptosis, cell proliferation, oxidative stress and inflammation) that have attracted interest as emerging critical determinants of CM risk and disease. Accordingly, this review aimed to discuss the available data regarding the effects of RSV on sphingolipid metabolism and signaling in CM risk and disease, focusing on oxidative stress/inflammatory-related aspects, and the clinical implications of this relationship.

Therapeutic potential of the sphingosine kinase 1 inhibitor, PF-543

PF-543 is a sphingosine kinase 1（SPHK1）inhibitor developed by Pfizer and is currently considered the most potent selective SPHK1 inhibitor. SPHK1 catalyses the production of sphingosine 1-phosphate (S1P) from sphingosine. It is the rate-limiting enzyme of S1P production, and there is substantial evidence to support a very important role for sphingosine kinase in health and disease. This review is the first to summarize the role and mechanisms of PF-543 as an SPHK1 inhibitor in anticancer, antifibrotic, and anti-inflammatory processes, providing new therapeutic leads and ideas for future research and clinical trials.

Sphingolipid metabolism and signaling in cardiovascular diseases

Sphingolipids are a structural component of the cell membrane, derived from sphingosine, an amino alcohol. Its sphingoid base undergoes various types of enzymatic transformations that lead to the formation of biologically active compounds, which play a crucial role in the essential pathways of cellular signaling, proliferation, maturation, and death. The constantly growing number of experimental and clinical studies emphasizes the pivotal role of sphingolipids in the pathophysiology of cardiovascular diseases, including, in particular, ischemic heart disease, hypertension, heart failure, and stroke. It has also been proven that altering the sphingolipid metabolism has cardioprotective properties in cardiac pathologies, including myocardial infarction. Recent studies suggest that selected sphingolipids may serve as valuable biomarkers useful in the prognosis of cardiovascular disorders in clinical practice. This review aims to provide an overview of the current knowledge of sphingolipid metabolism and signaling in cardiovascular diseases.

Sphingosine-1-phosphate and Sphingosine-1-phosphate receptors in the cardiovascular system: pharmacology and clinical implications

Sphingosine-1-phosphate (S1P) is a lipid that binds and activates five distinct receptor subtypes, S1P₁, S1P₂, S1P₃, S1P₄, S1P₅, widely expressed in different cells, tissues and organs. In the cardiovascular system these receptors have been extensively studied, but no drug acting on them has been approved so far for treating cardiovascular diseases. In contrast, a number of S1P receptor agonists are approved as immunomodulators, mainly for multiple sclerosis, because of their action on lymphocyte trafficking. This chapter summarizes the available information on S1P receptors in the cardiovascular system and discusses their potential for treating cardiovascular conditions and/or their role on the clinical pharmacology of drugs so far approved for non-cardiovascular conditions. Basic research has recently produced data useful to understand the molecular pharmacology of S1P and S1P receptors, regarding biased agonism, S1P storage, release and vehiculation and chaperoning by lipoproteins, paracrine actions, intracellular non-receptorial S1P actions. On the other hand, the approval of fingolimod and newer generation S1P receptor ligands as immunomodulators, provides information on a number of clinical observations on the impact of these drugs on cardiovascular system which need to be integrated with preclinical data. S1P receptors are potential targets for prevention and treatment of major cardiovascular conditions, including hypertension, myocardial infarction, heart failure and stroke.

Biomarkers in Fabry Disease. Implications for Clinical Diagnosis and Follow-up

Fabry disease (FD) is a lysosomal storage disorder caused by deficient alpha-galactosidase A activity in the lysosome due to mutations in the GLA gene, resulting in gradual accumulation of globotriaosylceramide and other derivatives in different tissues. Substrate accumulation promotes different pathogenic mechanisms in which several mediators could be implicated, inducing multiorgan lesions, mainly in the kidney, heart and nervous system, resulting in clinical manifestations of the disease. Enzyme replacement therapy was shown to delay disease progression, mainly if initiated early. However, a diagnosis in the early stages represents a clinical challenge, especially in patients with a non-classic phenotype, which prompts the search for biomarkers that help detect and predict the evolution of the disease. We have reviewed the mediators involved in different pathogenic mechanisms that were studied as potential biomarkers and can be easily incorporated into clinical practice. Some accumulation biomarkers seem to be useful to detect non-classic forms of the disease and could even improve diagnosis of female patients. The combination of such biomarkers with some response biomarkers, may be useful for early detection of organ injury. The incorporation of some biomarkers into clinical practice may increase the capacity of detection compared to that currently obtained with the established diagnostic markers and provide more information on the progression and prognosis of the disease.

Attenuating PI3K/Akt- mTOR pathway reduces dihydrosphingosine 1 phosphate mediated collagen synthesis and hypertrophy in primary cardiac cells

Cardiac fibrosis and myocyte hypertrophy play contributory roles in the progression of diseases such as heart Failure (HF) through what is collectively termed cardiac remodelling. The phosphoinositide 3- kinase (PI3K), protein kinase B (Akt) and mammalian target for rapamycin (mTOR) signalling pathway (PI3K/Akt- mTOR) is an important pathway in protein synthesis, cell growth, cell proliferation, and lipid metabolism. The sphingolipid, dihydrosphingosine 1 phosphate (dhS1P) has been shown to bind to high density lipids in plasma. Unlike its analog, spingosine 1 phosphate (S1P), the role of dhS1P in cardiac fibrosis is still being deciphered. This study was conducted to investigate the effect of dhS1P on PI3K/Akt signalling in primary cardiac fibroblasts and myocytes. Our findings demonstrate that inhibiting PI3K reduced collagen synthesis in neonatal cardiac fibroblasts (NCFs), and hypertrophy in neonatal cardiac myocytes (NCMs) induced by dhS1P, in vitro. Reduced activation of the PI3K/Akt- mTOR signalling pathway led to impaired translation of fibrotic proteins such as collagen 1 (Coll1) and transforming growth factor β (TGFβ) and inhibited the transcription and translation of tissue inhibitor of matrix metalloproteinase 1 (TIMP1). PI3K inhibition also affected the gene expression of S1P receptors and enzymes such as the dihydroceramide delta 4 desaturase (DEGS1) and sphingosine kinase 1 (SK1) in the de novo sphingolipid pathway. While in myocytes, PI3K inhibition reduced myocyte hypertrophy induced by dhS1P by reducing skeletal muscle α- actin (αSKA) mRNA expression, and protein translation due to increased glycogen synthase kinase 3β (GSK3β) mRNA expression. Our findings show a relationship between the PI3K/Akt- mTOR signalling cascade and exogenous dhS1P induced collagen synthesis and myocyte hypertrophy in primary neonatal cardiac cells.

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.

Higher Serum Lysophosphatidic Acids Predict Left Ventricular Reverse Remodeling in Pediatric Dilated Cardiomyopathy

Background: The prognosis of pediatric dilated cardiomyopathy (PDCM) is highly variable, ranging from death to cardiac function recovery. Left ventricular reverse remodeling (LVRR) represents a favorable prognosis in PDCM. Disturbance of lipid metabolism is associated with the change of cardiac function, but no studies have examined lipidomics data and LVRR. Methods: Discovery analyses were based on 540 targeted lipids in an observational, prospective China-AOCC (An Integrative-Omics Study of Cardiomyopathy Patients for Diagnosis and Prognosis in China) study. The OPLS-DA and random forest (RF) analysis were used to screen the candidate lipids. Associations of the candidate lipids were examined in Cox proportional hazards regression models. Furthermore, we developed a risk score comprising the significant lipids, with each attributed a score of 1 when the concentration was above the median. All significant findings were replicated in a validation set of the China-AOCC study. Results: There were 59 patients in the discovery set and 24 patients in the validation set. LVRR was observed in 27 patients (32.5%). After adjusting for age, left ventricular ejection fraction (LVEF), and left ventricular end-diastolic dimension (LVEDD) z-score, lysophosphatidic acids (LysoPA) 16:0, LysoPA 18:2, LysoPA 18:1, and LysoPA 18:0 were significantly associated with LVRR in the discovery set, and hazard ratios (HRs) were 2.793 (95% CI, 1.545-5.048), 2.812 (95% CI, 1.542-5.128), 2.831 (95% CI, 1.555-5.154), and 2.782 (95% CI, 1.548-5.002), respectively. We developed a LysoPA score comprising the four LysoPA. When the LysoPA score reached 4, LVRR was more likely to be observed in both sets. The AUC increased with the addition of the LysoPA score to the LVEDD z-score (from 0.693 to 0.875 in the discovery set, from 0.708 to 0.854 in the validation set) for prediction of LVRR. Conclusions: Serum LysoPA can predict LVRR in PDCM patients. When the LysoPA score was combined with the LVEDD z-score, it may help in ascertaining the prognosis and monitoring effects of anti-heart failure pharmacotherapy.

Exogenous dihydrosphingosine 1 phosphate mediates collagen synthesis in cardiac fibroblasts through JAK/STAT signalling and regulation of TIMP1

Cardiac fibrosis and myocyte hypertrophy are hallmarks of the cardiac remodelling process in cardiomyopathies such as heart failure (HF). Dyslipidemia or dysregulation of lipids contribute to HF. The dysregulation of high density lipoproteins (HDL) could lead to altered levels of other lipid metabolites that are bound to it such as sphingosine-1- phosphate (S1P). Recently, it has been shown that S1P and its analogue dihydrosphingosine-1-phosphate (dhS1P) are bound to HDL in plasma. The effects of dhS1P on cardiac cells have been obscure. In this study, we show that extracellular dhS1P is able to increase collagen synthesis in neonatal rat cardiac fibroblasts (NCFs) and cause hypertrophy of neonatal cardiac myocytes (NCMs). The janus kinase/signal transducer and activator (JAK/STAT) signalling pathway was involved in the increased collagen synthesis by dhS1P, through sustained increase of tissue inhibitor of matrix metalloproteinase 1 (TIMP1). Extracellular dhS1P increased phosphorylation levels of STAT1 and STAT3 proteins, also caused an early increase in gene expression of transforming growth factor-β (TGFβ), and sustained increase in TIMP1. Inhibition of JAKs led to inhibition of TIMP1 and TGFβ gene and protein expression. We also show that dhS1P is able to cause NCM hypertrophy through S1P-receptor-1 (S1PR1) signalling which is opposite to that of its analogue, S1P. Taken together, our results show that dhS1P increases collagen synthesis in cardiac fibroblasts causing fibrosis through dhS1P-JAK/STAT-TIMP1 signalling.

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.

Cardiovascular Effects of Pharmacological Targeting of Sphingosine Kinase 1

High blood pressure is a risk factor for cardiovascular diseases. Ang II (angiotensin II), a key pro-hypertensive hormone, mediates target organ consequences such as endothelial dysfunction and cardiac hypertrophy. S1P (sphingosine-1-phosphate), produced by Sphk1 (sphingosine kinase 1), plays a pivotal role in the pathogenesis of hypertension and downstream organ damage, as it controls vascular tone and regulates cardiac remodeling. Accordingly, we aimed to examine if pharmacological inhibition of Sphk1 using selective inhibitor PF543 can represent a useful vasoprotective and cardioprotective anti-hypertensive strategy in vivo. PF543 was administered intraperitoneally throughout a 14-day Ang II-infusion in C57BL6/J male mice. Pharmacological inhibition of Sphk1 improved endothelial function of arteries of hypertensive mice that could be mediated via decrease in eNOS (endothelial nitric oxide synthase) phosphorylation at T495. This effect was independent of blood pressure. Importantly, PF543 also reduced cardiac hypertrophy (heart to body weight ratio, 5.6±0.2 versus 6.4±0.1 versus 5.9±0.2 mg/g; P<0.05 for Sham, Ang II+placebo, and Ang II+PF543-treated mice, respectively). Mass spectrometry revealed that PF543 elevated cardiac sphingosine, that is, Sphk1 substrate, content in vivo. Mechanistically, RNA-Seq indicated a decreased expression of cardiac genes involved in actin/integrin organization, S1pr1 signaling, and tissue remodeling. Indeed, downregulation of Rock1 (Rho-associated coiled-coil containing protein kinase 1), Stat3 (signal transducer and activator of transcription 3), PKC (protein kinase C), and ERK1/2 (extracellular signal-regulated kinases 1/2) level/phosphorylation by PF543 was observed. In summary, pharmacological inhibition of Sphk1 partially protects against Ang II-induced cardiac hypertrophy and endothelial dysfunction. Therefore, it may represent a promising target for harnessing residual cardiovascular risk in hypertension.

Sphingolipid Mediators of Myocardial Pathology

Cardiomyopathy is the leading cause of mortality worldwide. While the causes of cardiomyopathy continue to be elucidated, current evidence suggests that aberrant bioactive lipid signaling plays a crucial role as a component of cardiac pathophysiology. Sphingolipids have been implicated in the pathophysiology of cardiovascular disease, as they regulate numerous cellular processes that occur in primary and secondary cardiomyopathies. Experimental evidence gathered over the last few decades from both in vitro and in vivo model systems indicates that inhibitors of sphingolipid synthesis attenuate a variety of cardiomyopathic symptoms. In this review, we focus on various cardiomyopathies in which sphingolipids have been implicated and the potential therapeutic benefits that could be gained by targeting sphingolipid metabolism.

Novel Insights into the Role of HDL-Associated Sphingosine-1-Phosphate in Cardiometabolic Diseases

Sphingolipids are key signaling molecules involved in the regulation of cell physiology. These species are found in tissues and in circulation. Although they only constitute a small fraction in lipid composition of circulating lipoproteins, their concentration in plasma and distribution among plasma lipoproteins appears distorted under adverse cardiometabolic conditions such as diabetes mellitus. Sphingosine-1-phosphate (S1P), one of their main representatives, is involved in regulating cardiomyocyte homeostasis in different models of experimental cardiomyopathy. Cardiomyopathy is a common complication of diabetes mellitus and represents a main risk factor for heart failure. Notably, plasma concentration of S1P, particularly high-density lipoprotein (HDL)-bound S1P, may be decreased in patients with diabetes mellitus, and hence, inversely related to cardiac alterations. Despite this, little attention has been given to the circulating levels of either total S1P or HDL-bound S1P as potential biomarkers of diabetic cardiomyopathy. Thus, this review will focus on the potential role of HDL-bound S1P as a circulating biomarker in the diagnosis of main cardiometabolic complications frequently associated with systemic metabolic syndromes with impaired insulin signaling. Given the bioactive nature of these molecules, we also evaluated its potential of HDL-bound S1P-raising strategies for the treatment of cardiometabolic disease.

Effect of sphingosine-1-phosphate on cryopreserved sheep testicular explants cultured in vitro

Complete spermatogenesis has been achieved in vitro in mouse testicular explants with resulting sperm used to produce pups after Intra Cytoplasm Sperm Injection and Embryo Transfer. In the present study, we evaluated the influence of sphingosine-1-phosphate (S1P) on spermatogenesis of frozen-thawed lamb testis explants in vitro. Thawed testicular pieces were cultured for 12 d on agarose blocks in serum-free growth medium containing 0, 2, 5 or 10 μM S1P. At the end of D6 and D12, some pieces were fixed and processed for histology. Other pieces were processed for RNA isolation and quantitation of proliferation (PCNA, Ki67) and differentiation (PLZF) markers and genes involved in S1P signaling (S1PR1, SGPL1, SGPP1, AKT1 and NFKBIA) by qPCR. Histology revealed an increase (P < 0.05) in seminiferous cord (SC) diameter under all culture conditions, except 5 and 10 μM S1P by D6. In the presence of 5 μM S1P, percentage of gonocytes decreased (P < 0.05) by D6 (control, 24.9% vs. S1P, 10.3%) with a concomitant increase (P < 0.05) in spermatogonia formation (control, 74.4% vs. S1P, 88.1%). S1P induced PCNA or Ki67 expression by D6, whereas PLZF was up-regulated (P < 0.05) by D6 in 2 μM S1P and D12 in 5 & 10 μM S1P. Expression of SGPL1 and SGPP1 increased 4-12-fold in tissues cultured in 10 μM S1P by D12 compared to D12 control. AKT1 and NFKBIA mRNA expression was low (P < 0.05) in 5 and or 10 μM S1P treatments on D6. These results demonstrate that S1P promotes germ cell proliferation during first week of culture and may exert an anti-apoptotic influence on the seminiferous cord in sheep testicular explants in vitro.

The Role of S1P and the Related Signaling Pathway in the Development of Tissue Fibrosis

Tissue fibrosis, including pulmonary fibrosis, hepatic fibrosis, and cardiac fibrosis, is an important stage in the development of many diseases. It can lead to structural damage and dysfunction and even severe carcinogenesis or death. There is currently no effective method for the treatment of fibrosis. At present, the molecular mechanism of tissue fibrosis has not yet been fully elucidated, but many studies have demonstrated that it is involved in conveying the complex messages between fibroblasts and various cytokines. Sphingosine 1-phosphate (S1P) is a naturally bioactive sphingolipid. S1P and the related signaling pathways are important intracellular metabolic pathways involved in many life activities, including cell proliferation, differentiation, apoptosis, and cellular signal transduction. Increasing evidence suggests that S1P and its signaling pathways play an important role in the development of tissue fibrosis; however, the mechanisms of these effects have not yet been fully elucidated, and even the role of S1P and its signaling pathways are still controversial. This article focuses on the role of S1P and the related signaling pathways in the development of fibrosis of lung, liver, heart, and other tissues, with emphasis on the application of inhibitors of some of molecules in the pathway in clinical treatment of fibrosis diseases.

Emerging roles of sphingosylphosphorylcholine in modulating cardiovascular functions and diseases

Sphingosylphosphorylcholine (SPC) is a bioactive sphingolipid in blood plasma that is metabolized from the hydrolysis of the membrane sphingolipid. SPC maintains low levels in the circulation under normal conditions, which makes studying its origin and action difficult. In recent years, however, it has been revealed that SPC may act as a first messenger through G protein-coupled receptors (S1P_1-5, GPR12) or membrane lipid rafts, or as a second messenger mediating intracellular Ca²⁺ release in diverse human organ systems. SPC is a constituent of lipoproteins, and the activation of platelets promotes the release of SPC into blood, both implying a certain effect of SPC in modulating the pathological process of the heart and vessels. A line of evidence indeed confirms that SPC exerts a pronounced influence on the cardiovascular system through modulation of the functions of myocytes, vein endothelial cells, as well as vascular smooth muscle cells. In this review we summarize the current knowledge of the potential roles of SPC in the development of cardiovascular diseases and discuss the possible underlying mechanisms.

ADAP1 limits neonatal cardiomyocyte hypertrophy by reducing integrin cell surface expression

The ArfGAP with dual PH domains 1 (ADAP1) regulates the activation of the hypertrophic mitogen-activated protein kinase ERK1/2 pathway in non-cardiomyocytes. However, its role in cardiomyocytes is unknown. Our aim was to characterize the role of ADAP1 in the hypertrophic process of cardiomyocytes. We assessed the expression of ADAP1 in the hearts of adult and neonatal rats by RT-qPCR and Western blotting and showed that it is preferentially expressed in cardiomyocytes. Adenoviral-mediated ADAP1 overexpression in cultured rat neonatal ventricular cardiomyocytes limited their serum-induced hypertrophic response as measured by immunofluorescence microscopy. Furthermore, ADAP1 overexpression completely blocked phenylephrine- and Mek1 constitutively active (Mek1ca) mutant-induced hypertrophy in these cells. The anti-hypertrophic effect of ADAP1 was not caused by a reduction in protein synthesis, interference with the Erk1/2 pathway, or disruption of the fetal gene program activation, as assessed by nascent protein labeling, Western blotting, and RT-qPCR, respectively. An analysis of cultured cardiomyocytes by confocal microscopy revealed that ADAP1 partially re-organizes α-actinin into dense puncta, a phenomenon that is synergized by Mek1ca overexpression. Biotin labeling of cell surface proteins from cardiomyocytes overexpressing ADAP1 revealed that it reduces the surface expression of β1-integrin, an effect that is strongly potentiated by Mek1ca overexpression. Our findings provide insights into the anti-hypertrophic function of ADAP1 in cardiomyocytes.

TGF-β/Smad3 pathway enhances the cardio-protection of S1R/SIPR1 in in vitro ischemia-reperfusion myocardial cell model

Ischemia-reperfusion (IR) injury is usually associated with a high risk of cardiomyocyte death in patients with acute myocardial infarction. Sphingosine 1-phosphate (S1P) and transforming growth factor (TGF)-β are thought to be involved in the protection of cardiomyocyte and heart function following IR-induced injury. However, the possible association of S1P and S1P receptor 1 (S1PR1) with the TGF-β/Smad3 pathway as the potential protective mechanism has remained to be investigated. In the present study, an in vitro ischemia/reperfusion injury model was established and evaluated by analysis of apoptosis, lactate dehydrogenase (LDH) release and caspase3 activity. The mRNA and protein levels of S1PR1, TGF-β and Smad3 after treatment with 1 µM S1P alone or combined with 0.4 µM W146 (a specific S1PR1 antagonist) were assessed. The mRNA expression of five S1PRs (S1PR1-5) and the protein levels of S1PR1 were also assayed following treatment with 1 ng/ml TGF-β for 0, 4 or 24 h. The mRNA expression of S1PR1 and the levels of S1P were further assessed following exposure to 10 µM SB4 (TGFβR1 inhibitor) plus 1 ng/ml TGF-β and 2 µM SIS3 (Smad3 inhibitor) plus 1 ng/ml TGF-β. The results indicated that apoptosis, LDH release and caspase3 activity were all increased in the established IR model. Exogenous S1P increased the mRNA and protein levels of S1PR1, TGF-β and Smad3, which was abolished by addition of W146. Extraneous TGF-β resulted in the stimulation of several S1PRs, most prominently of S1PR1, while supplementation with SB4 and SIS3 offset the stimulation by TGF-β. These results suggested that the TGF-β/Smad3 pathway was closely associated with S1P/S1PR1 in the protection of myocardial cells from IR injury.

Sphingosine-1-phosphate ameliorates the cardiac hypertrophic response through inhibiting the activity of histone deacetylase-2

Inhibition of histone deacetylase-2 (HDAC2), which is a prohypertrophic factor in the heart, can functionally attenuate cardiac hypertrophy. The present study aimed to investigate whether sphingosine‑1‑phosphate (S1P), which has recently been reported to suppress HDAC2 activity, could ameliorate the cardiac hypertrophic response and improve cardiac function in mice with transverse aortic constriction (TAC), as well as to determine the underlying mechanisms. Briefly, 8‑week‑old male C57BL/6 mice were randomly divided into sham, TAC and TAC + S1P groups; the results indicated that S1P treatment attenuated TAC‑induced cardiac dysfunction. In addition, heart size and the expression levels of fetal cardiac genes were reduced in the TAC + S1P group compared with in the TAC group. Furthermore, in cultured H9c2 cells exposed to phenylephrine, S1P was revealed to decrease cardiomyocyte size and the exaggerated expression of fetal cardiac genes. The present study also demonstrated that S1P had no effect on HDAC2 expression, but it did suppress its activity and increase acetylation of histone H3 in vivo and in vitro. Krüppel‑like factor 4 (KLF4) is an antihypertrophic transcriptional regulator, which mediates HDAC inhibitor‑induced prevention of cardiac hypertrophy; in the present study, KLF4 was upregulated by S1P. Finally, the results indicated that S1P receptor 2 (S1PR2) may be involved in the antihypertrophic effects, whereas the suppressive effects of S1P on HDAC2 activity were independent of S1PR2. In conclusion, the present study demonstrated that S1P treatment may ameliorate the cardiac hypertrophic response, which may be partly mediated by the suppression of HDAC2 activity and the upregulation of KLF4; it was suggested that S1PR2 may also be involved. Therefore, S1P may be considered a potential therapy for the treatment of heart diseases caused by cardiac hypertrophy.

Augmented sphingosine 1 phosphate receptor-1 signaling in cardiac fibroblasts induces cardiac hypertrophy and fibrosis through angiotensin II and interleukin-6

Background: Cardiac fibroblasts, together with cardiomyocytes, occupy the majority of cells in the myocardium and are involved in myocardial remodeling. The lysophospholipid mediator sphigosine-1-phosphate (S1P) regulates functions of cardiovascular cells through multiple receptors including S1PR1–S1PR3. S1PR1 but not other S1P receptors was upregulated in angiotensin II-induced hypertrophic hearts. Therefore, we investigated a role of S1PR1 in fibroblasts for cardiac remodeling by employing transgenic mice that overexpressed S1PR1 under the control of α-smooth muscle actin promoter. In S1PR1-transgenic mouse heart, fibroblasts and/or myofibroblasts were hyperplastic, and those cells as well as vascular smooth muscle cells overexpressed S1PR1. Transgenic mice developed bi-ventricular hypertrophy by 12-week-old and diffuse interstitial fibrosis by 24-week-old without hemodynamic stress. Cardiac remodeling in transgenic mice was associated with greater ERK phosphorylation, upregulation of fetal genes, and systolic dysfunction. Transgenic mouse heart showed increased mRNA expression of angiotensin-converting enzyme and interleukin-6 (IL-6). Isolated fibroblasts from transgenic mice exhibited enhanced generation of angiotensin II, which in turn stimulated IL-6 release. Either an AT1 blocker or angiotensin-converting enzyme inhibitor prevented development of cardiac hypertrophy and fibrosis, systolic dysfunction and increased IL-6 expression in transgenic mice. Finally, administration of anti-IL-6 antibody abolished an increase in tyrosine phosphorylation of STAT3, a major signaling molecule downstream of IL-6, in the transgenic mouse heart and prevented development of cardiac hypertrophy in transgenic mice. These results demonstrate a promoting role of S1PR1 in cardiac fibroblasts for cardiac remodeling, in which angiotensin II—AT1 and IL-6 are involved.

Chemical Tools for Studying Lipid-Binding Class A G Protein-Coupled Receptors

Cannabinoid, free fatty acid, lysophosphatidic acid, sphingosine 1-phosphate, prostanoid, leukotriene, bile acid, and platelet-activating factor receptor families are class A G protein-coupled receptors with endogenous lipid ligands. Pharmacological tools are crucial for studying these receptors and addressing the many unanswered questions surrounding expression of these receptors in normal and diseased tissues. An inherent challenge for developing tools for these lipid receptors is balancing the often lipophilic requirements of the receptor-binding pharmacophore with favorable physicochemical properties to optimize highly specific binding. In this study, we review the radioligands, fluorescent ligands, covalent ligands, and antibodies that have been used to study these lipid-binding receptors. For each tool type, the characteristics and design rationale along with in vitro and in vivo applications are detailed.

Sphingosine 1-Phosphate Receptors: Do They Have a Therapeutic Potential in Cardiac Fibrosis?

Sphingosine 1-phosphate (S1P) is a bioactive lipid that is characterized by a peculiar mechanism of action. In fact, S1P, which is produced inside the cell, can act as an intracellular mediator, whereas after its export outside the cell, it can act as ligand of specific G-protein coupled receptors, which were initially named endothelial differentiation gene (Edg) and eventually renamed sphingosine 1-phosphate receptors (S1PRs). Among the five S1PR subtypes, S1PR1, S1PR2 and S1PR3 isoforms show broad tissue gene expression, while S1PR4 is primarily expressed in immune system cells, and S1PR5 is expressed in the central nervous system. There is accumulating evidence for the important role of S1P as a mediator of many processes, such as angiogenesis, carcinogenesis and immunity, and, ultimately, fibrosis. After a tissue injury, the imbalance between the production of extracellular matrix (ECM) and its degradation, which occurs due to chronic inflammatory conditions, leads to an accumulation of ECM and, consequential, organ dysfunction. In these pathological conditions, many factors have been described to act as pro- and anti-fibrotic agents, including S1P. This bioactive lipid exhibits both pro- and anti-fibrotic effects, depending on its site of action. In this review, after a brief description of sphingolipid metabolism and signaling, we emphasize the involvement of the S1P/S1PR axis and the downstream signaling pathways in the development of fibrosis. The current knowledge of the therapeutic potential of S1PR subtype modulators in the treatment of the cardiac functions and fibrinogenesis are also examined.

Characterization and Expression of Sphingosine 1-Phosphate Receptors in Human and Rat Heart

Aim: Sphingosine 1-phosphate (S1P), sphingolipid derivatives are known anti-inflammatory, anti-apoptotic, and anti-oxidant agent. S1P have been demonstrated to have a role in the cardiovascular system. The purpose of this study was to understand the precise expression and distribution of S1P receptors (S1PRs) in human and rat cardiovascular tissues to know the significance and possible implementation of our experimental studies in rat models. Methods and Results: In this study, we investigated the localization of S1PRs in human heart samples from cardiac surgery department, University of Verona Hospital and rat samples. Immunohistochemical investigation of paraffin-embedded sections illustrated diffused staining of the myocardial samples from human and rat. The signals of the human heart were similar to those of the rat heart in all chambers of the heart. The immunohistochemical expression levels correlated well with the results of RT-PCR-based analysis and western blotting. We confirmed by all techniques that S1PR1 expressed strongly as compared to S1PR3, and are uniformly distributed in all chambers of the heart with no significant difference in human and rat myocardial tissue. S1PR2 expression was significantly weak while S1PR4 and S1PR5 were not detectable in RT-PCR results in both human and rat heart. Conclusion: These results indicate that experimental studies using S1PR agonists on rat models are more likely to have a potential for translation into clinical studies, and second important information revealed by this study is, S1P receptor agonist can be used for cardioprotection in global ischemia-reperfusion injury.

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.

Implication of sphingosin-1-phosphate in cardiovascular regulation

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite generated by phosphorylation of sphingosine catalyzed by sphingosine kinase. S1P acts mainly through its high affinity G-protein-coupled receptors and participates in the regulation of multiple systems, including cardiovascular system. It has been shown that S1P signaling is involved in the regulation of cardiac chronotropy and inotropy and contributes to cardioprotection as well as cardiac remodeling; S1P signaling regulates vascular function, such as vascular tone and endothelial barrier, and possesses an anti-atherosclerotic effect; S1P signaling is also implicated in the regulation of blood pressure. Therefore, manipulation of S1P signaling may offer novel therapeutic approaches to cardiovascular diseases. As several S1P receptor modulators and sphingosine kinase inhibitors have been approved or under clinical trials for the treatment of other diseases, it may expedite the test and implementation of these S1P-based drugs in cardiovascular diseases.

Sphingosine 1-phosphate signaling contributes to cardiac inflammation, dysfunction, and remodeling following myocardial infarction

Sphingosine 1-phosphate (S1P) mediates multiple pathophysiological effects in the cardiovascular system. However, the role of S1P signaling in pathological cardiac remodeling following myocardial infarction (MI) remains controversial. In this study, we found that cardiac S1P greatly increased post-MI, accompanied with a significant upregulation of cardiac sphingosine kinase-1 (SphK1) and S1P receptor 1 (S1PR1) expression. In MI-operated mice, inhibition of S1P production by using PF543 (the SphK1 inhibitor) ameliorated cardiac remodeling and dysfunction. Conversely, interruption of S1P degradation by inhibiting S1P lyase augmented cardiac S1P accumulation and exacerbated cardiac remodeling and dysfunction. In the cardiomyocyte, S1P directly activated proinflammatory responses via a S1PR1-dependent manner. Furthermore, activation of SphK1/S1P/S1PR1 signaling attributed to β1-adrenergic receptor stimulation-induced proinflammatory responses in the cardiomyocyte. Administration of FTY720, a functional S1PR1 antagonist, obviously blocked cardiac SphK1/S1P/S1PR1 signaling, ameliorated chronic cardiac inflammation, and then improved cardiac remodeling and dysfunction in vivo post-MI. In conclusion, our results demonstrate that cardiac SphK1/S1P/S1PR1 signaling plays an important role in the regulation of proinflammatory responses in the cardiomyocyte and targeting cardiac S1P signaling is a novel therapeutic strategy to improve post-MI cardiac remodeling and dysfunction.

Sphingosine-1-phosphate signalling as a therapeutic target for patients with abnormal glucose metabolism and ischaemic heart disease

Abnormalities of glucose metabolism in patients with ischaemic heart disease (IHD) are common and are associated with a poor outcome in patients with and without diabetes. Sphingosine-1-phosphate (S1P) is a bioactive lipid which has been shown to increase insulin sensitivity in rodents and to increase myocardial tolerance to ischaemia. In the present review, I explore the relevance of S1P signalling pathway to IHD and abnormalities in glucose tolerance, and its potential as a therapeutic target for patients with abnormal glucose metabolism and IHD.

Sphingosine 1-phosphate to p38 signaling via S1P1 receptor and Gαi/o evokes augmentation of capsaicin-induced ionic currents in mouse sensory neurons

The perception of painful thermal stimuli by sensory neurons is largely mediated by TRPV1. Upon tissue injury or inflammation, S1P is secreted by thrombocytes as part of an inflammatory cocktail, which sensitizes nociceptive neurons towards thermal stimuli. S1P acts on G-protein coupled receptors that are expressed in sensory neurons and sensitize TRPV1 channels towards thermal stimuli. In this study, the S1P mediated signaling pathway required for sensitization of TRPV1 channels was explored.The capsaicin induced peak inward current (ICAPS) of sensory neurons was significantly increased after S1P stimulation within minutes after application. The potentiation of ICAPS resulted from activation of Gαi through G-protein coupled receptors for S1P. Consequently, Gαi led to a signaling cascade, involving phosphoinositide-3-kinase (PI3K) and protein kinase C, which augmented ICAPS in nociceptive neurons. The S1P1 receptor agonist SEW2871 resulted in activation of the same signaling pathway and potentiation of ICAPS. Furthermore, the mitogen-activated protein kinase p38 was phosphorylated after S1P stimulation and inhibition of p38 signaling by SB203580 prevented the S1P-induced ICAPS potentiation. The current data suggest that S1P sensitized ICAPS through G-protein coupled S1P1 receptor activation of Gαi-PI3K-PKC-p38 signaling pathway in sensory neurons.

Granule cargo release from bone marrow-derived cells sustains cardiac hypertrophy

Bone marrow-derived inflammatory cells, including platelets, may contribute to the progression of pressure overload-induced left ventricular hypertrophy (LVH). However, the underlying mechanisms for this are still unclear. One potential mechanism is through release of granule cargo. Unc13-d(Jinx) (Jinx) mice, which lack Munc13-4, a limiting factor in vesicular priming and fusion, have granule secretion defects in a variety of hematopoietic cells, including platelets. In the current study, we investigated the role of granule secretion in the development of LVH and cardiac remodeling using chimeric mice specifically lacking Munc13-4 in marrow-derived cells. Pressure overload was elicited by transverse aortic constriction (TAC). Chimeric mice were created by bone marrow transplantation. Echocardiography, histology staining, immunohistochemistry, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and mass spectrometry were used to study LVH progression and inflammatory responses. Wild-type (WT) mice that were transplanted with WT bone marrow (WT→WT) and WT mice that received Jinx bone marrow (Jinx→WT) developed LVH and a classic fetal reprogramming response early (7 days) after TAC. However, at late times (5 wk), mice lacking Munc13-4 in bone marrow-derived cells (Jinx→WT) failed to sustain the cardiac hypertrophy observed in WT chimeric mice. No difference in cardiac fibrosis was observed at early or late time points. Reinjection of WT platelets or platelet releasate partially restored cardiac hypertrophy in Jinx chimeric mice. These results suggest that sustained LVH in the setting of pressure overload depends on one or more factors secreted from bone marrow-derived cells, possibly from platelets. Inhibiting granule cargo release may represent a novel target for preventing sustained LVH.

Dietary fatty acids alter left ventricular myocardial gene expression in Wistar rats

Obesity increases the risk for cardiomyopathy in the absence of comorbidities. Myocardial structure is modified by dietary fatty acids. Left ventricular hypertrophy is associated with Western (WES) diet consumption, whereas intake of n-3 polyunsaturated fatty acids is associated with antihypertrophic effects. We previously observed no attenuation of left ventricular thickening after 3 months of docosahexaenoic acid (DHA) supplementation of a WES diet, compared with WES diet intake alone, in rats that had similar weight, adiposity, and insulin sensitivity to control animals. The objective of this study was to define left ventricular gene expression in these animals to determine whether diet alone was associated with a physiologic or pathologic hypertrophic response. We hypothesized that WES diet consumption would favor a pathologic or maladaptive myocardial gene expression pattern and that DHA supplementation would favor a physiologic or adaptive response. Microarray analysis identified 64 transcripts that were differentially expressed (P ≤ .001) within one or more treatment comparisons. Using quantitative real-time polymerase chain reaction, 29 genes with fold change at least 1.74 were successfully validated; all but 3 had similar directionality to that observed using microarray, and 2 genes, connective tissue growth factor and cathepsin M, were differentially expressed according to diet. WES blot analysis was performed on 4 proteins relevant to myocardial hypertrophy and metabolism. Acyl-CoA thioesterase 1, B-cell translocation gene 2, and carbonic anhydrase III showed directional change consistent with gene expression. Retinol saturase (all-trans-retinol 13,14-reductase), although not consistent with gene expression, was different according to diet, with increased concentrations in WES-fed rats compared with control and DHA-supplemented animals. Diet did not distinguish a transcriptome reflecting physiologic or pathologic myocardial hypertrophy; furthermore, the modest changes observed suggest that obesity and associated comorbidities may play a larger role than mere dietary fatty acid composition in development of cardiomyopathy.

Sphingosine-1-phosphate as a potential target for the treatment of myocardial infarction

This review focuses on the role of sphingosine-1-phosphate (S1P) signaling in the heart, with particular emphasis on how it could be modulated therapeutically in the context of myocardial infarction (MI). After a brief general description of sphingolipid metabolism and signaling, this review will examine the relationship between S1P and the beneficial effects of high-density lipoprotein (HDL), and finally focus on the known actions of S1P on different mechanisms relevant to MI pathophysiology (cardiomyocyte protection, fibrosis, remodeling, arrhythmia, control of vascular tone and potential repair mechanisms). The potential of particular enzyme isoforms or receptor subtypes for the development of therapeutic agents for MI will also be explored. 

β1-adrenergic receptor and sphingosine-1-phosphate receptor 1 (S1PR1) reciprocal downregulation influences cardiac hypertrophic response and progression to heart failure: protective role of S1PR1 cardiac gene therapy

BACKGROUND

The sphingosine-1-phosphate receptor 1 (S1PR1) and β1-adrenergic receptor (β1AR) are G-protein-coupled receptors expressed in the heart. These 2 receptors have opposing actions on adenylyl cyclase because of differential G-protein coupling. Importantly, both of these receptors can be regulated by the actions of G-protein-coupled receptor kinase-2, which triggers desensitization and downregulation processes. Although classic signaling paradigms suggest that simultaneous activation of β1ARs and S1PR1s in a myocyte would simply result in opposing action on cAMP production, in this report we have uncovered a direct interaction between these 2 receptors, with regulatory involvement of G-protein-coupled receptor kinase-2.

METHODS AND RESULTS

In HEK (human embryonic kidney) 293 cells overexpressing both β1AR and S1PR1, we demonstrated that β1AR downregulation can occur after stimulation with sphingosine-1-phosphate (an S1PR1 agonist), whereas S1PR1 downregulation can be triggered by isoproterenol (a β-adrenergic receptor agonist) treatment. This cross talk between these 2 distinct G-protein-coupled receptors appears to have physiological significance, because they interact and show reciprocal regulation in mouse hearts undergoing chronic β-adrenergic receptor stimulation and in a rat model of postischemic heart failure.

CONCLUSIONS

We demonstrate that restoration of cardiac plasma membrane levels of S1PR1 produces beneficial effects that counterbalance the deleterious β1AR overstimulation in heart failure.

Increased sphingosine-1-phosphate improves muscle regeneration in acutely injured mdx mice

BACKGROUND

Presently, there is no effective treatment for the lethal muscle wasting disease Duchenne muscular dystrophy (DMD). Here we show that increased sphingosine-1-phoshate (S1P) through direct injection or via the administration of the small molecule 2-acetyl-4(5)-tetrahydroxybutyl imidazole (THI), an S1P lyase inhibitor, has beneficial effects in acutely injured dystrophic muscles of mdx mice.

METHODS

We treated mdx mice with and without acute injury and characterized the histopathological and functional effects of increasing S1P levels. We also tested exogenous and direct administration of S1P on mdx muscles to examine the molecular pathways under which S1P promotes regeneration in dystrophic muscles.

RESULTS

Short-term treatment with THI significantly increased muscle fiber size and extensor digitorum longus (EDL) muscle specific force in acutely injured mdx limb muscles. In addition, the accumulation of fibrosis and fat deposition, hallmarks of DMD pathology and impaired muscle regeneration, were lower in the injured muscles of THI-treated mdx mice. Furthermore, increased muscle force was observed in uninjured EDL muscles with a longer-term treatment of THI. Such regenerative effects were linked to the response of myogenic cells, since intramuscular injection of S1P increased the number of Myf5nlacz/+ positive myogenic cells and newly regenerated myofibers in injured mdx muscles. Intramuscular injection of biotinylated-S1P localized to muscle fibers, including newly regenerated fibers, which also stained positive for S1P receptor 1 (S1PR1). Importantly, plasma membrane and perinuclear localization of phosphorylated S1PR1 was observed in regenerating muscle fibers of mdx muscles. Intramuscular increases of S1P levels, S1PR1 and phosphorylated ribosomal protein S6 (P-rpS6), and elevated EDL muscle specific force, suggest S1P promoted the upregulation of anabolic pathways that mediate skeletal muscle mass and function.

CONCLUSIONS

These data show that S1P is beneficial for muscle regeneration and functional gain in dystrophic mice, and that THI, or other pharmacological agents that raise S1P levels systemically, may be developed into an effective treatment for improving muscle function and reducing the pathology of DMD.

Therapeutic potential of targeting SK1 in human cancers

Sphingosine kinase 1 (SK1) is a lipid enzyme with oncogenic properties that converts the proapoptotic lipids ceramide and sphingosine into the antiapoptotic lipid sphingosine-1-phosphate and activates the signal transduction pathways that lead to cell proliferation, migration, the activation of the inflammatory response, and the impairment of apoptosis. There is compelling evidence that SK1 activation contributes to cancer progression leading to increased oncogenic transformation, tumor growth, resistance to therapies, tumor neovascularization, and metastatic spread. High levels of SK1 expression or activity have been associated with a poor prognosis in several human cancers. Recent studies using cancer cell and mouse models demonstrate a significant potential for SK1-targeting therapies to synergize with the effects of chemotherapy and radiotherapy; however, until recently the absence of clinically applicable SK1 inhibitors has limited the translation of these findings into patients. With the recent discovery of SK1 inhibiting properties of a clinically approved drug FTY720 (Fingolimod), SK1 has gained significant attention from both clinicians and the pharmaceutical industry and it is hoped that trials of newly developed SK1 inhibitors may follow soon. This review provides an overview of the SK1 signaling, its relevance to cancer progression, and the potential clinical significance of targeting SK1 for improved local or systemic control of human cancers.

Cardiovascular effects of sphingosine-1-phosphate (S1P)

Sphingosine-1-phosphate (S1P) regulates important functions in cardiac and vascular homeostasis. It has been implied to play causal roles in the pathogenesis of many cardiovascular disorders such as coronary artery disease, atherosclerosis, myocardial infarction, and heart failure. The majority of S1P in plasma is associated with high-density lipoproteins (HDL), and their S1P content has been shown to be responsible, at least in part, for several of the beneficial effects of HDL on cardiovascular risk. The attractiveness of S1P-based drugs for potential cardiovascular applications is increasing in the wake of the clinical approval of FTY720, but answers to important questions on the effects of S1P in cardiovascular biology and medicine must still be found. This chapter focuses on the current understanding of the role of S1P and its receptors in cardiovascular physiology, pathology, and disease.

Sphingolipids in obesity, type 2 diabetes, and metabolic disease

Metabolic disease, including obesity and type 2 diabetes, constitutes a major emerging health crisis in Western nations. Although the symptoms and clinical pathology and physiology of these conditions are well understood, the molecular mechanisms underlying the disease process have largely remained obscure. Sphingolipids, a lipid class with both signaling and structural properties, have recently emerged as key players in most major tissues affected by diabetes and are required components in the molecular etiology of this disease. Indeed, sphingolipids have been shown to mediate loss of insulin sensitivity, to promote the characteristic diabetic proinflammatory state, and to induce cell death and dysfunction in important organs such as the pancreas and heart. Furthermore, plasma sphingolipid levels are emerging as potential biomarkers for the decompensation of insulin resistance to frank type 2 diabetes. Despite these discoveries, the roles of specific sphingolipid species and sphingolipid metabolic pathways remain obscure, and newly developed experimental approaches must be employed to elucidate the detailed molecular mechanisms necessary for rational drug development and other clinical applications.

Sphingosine kinase and sphingosine 1-phosphate in the heart: a decade of progress

Activation of sphingosine kinase/sphingosine 1-phosphate (SK/S1P)-mediated signaling has emerged as a critical cardioprotective pathway in response to acute ischemia/reperfusion injury. S1P is released in both ischemic pre- and post-conditioning. Application of exogenous S1P to cultured cardiac myocytes subjected to hypoxia or treatment of isolated hearts either before ischemia or at the onset of reperfusion exerts prosurvival effects. Synthetic congeners of S1P such as FTY720 mimic these responses. Gene targeted mice null for the SK1 isoform whose hearts are subjected to ischemia/reperfusion injury exhibit increased infarct size and respond poorly either to ischemic pre- or postconditioning. Measurements of cardiac SK activity and S1P parallel these observations. Experiments in SK2 knockout mice have revealed that this isoform is necessary for survival in the heart. High density lipoprotein (HDL) is a major carrier of S1P, and studies of hearts in which selected S1P receptors have been inhibited implicate the S1P cargo of HDL in cardioprotection. Inhibition of S1P lyase, an endogenous enzyme that degrades S1P, also leads to cardioprotection. These observations have considerable relevance for future therapeutic approaches to acute and chronic myocardial injury. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

The impact of bioactive lipids on cardiovascular development

Lysophospholipids comprise a group of bioactive molecules with multiple biological functions. The cardinal members of this signalling molecule group are sphingosylphosphorylcholine (SPC), lysophosphatidic acid (LPA), and sphingosine 1-phosphate (S1P) which are, at least in part, homologous to each other. Bioactive lipids usually act via G-protein coupled receptors (GPCRs), but can also function as direct intracellular messengers. Recently, it became evident that bioactive lipids play a role during cellular differentiation development. SPC induces mesodermal differentiation of mouse ES cells and differentiation of promyelocytic leukemia cells, by a mechanism being critically dependent on MEK-ERK signalling. LPA stimulates the clonal expansion of neurospheres from neural stem/progenitor cells and induces c-fos via activation of mitogen- and stress-activated protein kinase 1 (MSK1) in ES cells. S1P acts on hematopoietic progenitor cells as a chemotactic factor and has also been found to be critical for cardiac and skeletal muscle regeneration. Furthermore, S1P promotes cardiogenesis and similarly activates Erk signalling in mouse ES cells. Interestingly, S1P may also act to maintain human stem cell pluripotency. Both LPA and S1P positively regulate the proliferative capacity of murine ES cells. In this paper we will focus on the differential and developmental impact of lysophospholipids on cardiovascular development.

S1P, dihydro-S1P and C24:1-ceramide levels in the HDL-containing fraction of serum inversely correlate with occurrence of ischemic heart disease

Background

The lysosphingolipid sphingosine 1-phosphate (S1P) is carried in the blood in association with lipoproteins, predominantly high density lipoproteins (HDL). Emerging evidence suggests that many of the effects of HDL on cardiovascular function may be attributable to its S1P cargo.

Methods

Here we have evaluated how levels of S1P and related sphingolipids in an HDL-containing fraction of human serum correlate with occurrence of ischemic heart disease (IHD). To accomplish this we used liquid chromatography-mass spectrometry to measure S1P levels in the HDL-containing fraction of serum (depleted of LDL and VLDL) from 204 subjects in the Copenhagen City Heart Study (CCHS). The study group consisted of individuals having high serum HDL cholesterol (HDL-C) (females:≥73.5 mg/dL; males:≥61.9 mg/dL) and verified IHD; subjects with high HDL-C and no IHD; individuals with low HDL-C (females:≤38.7 mg/dL; males:≤34.1 mg/dL) and IHD, and subjects with low HDL-C and no IHD.

Results

The results show a highly significant inverse relationship between the level of S1P in the HDL-containing fraction of serum and the occurrence of IHD. Furthermore, an inverse relationship with IHD was also observed for two other sphingolipids, dihydro-S1P and C24:1-ceramide, in the HDL-containing fraction of serum. Additionally, we demonstrated that the amount of S1P on HDL correlates with the magnitude of HDL-induced endothelial cell barrier signaling.

Conclusions

These findings indicate that compositional differences of sphingolipids in the HDL-containing fraction of human serum are related to the occurrence of IHD, and may contribute to the putative protective role of HDL in IHD.

Rho-kinase mediates TNF-α-induced MCP-1 expression via p38 MAPK signaling pathway in mesangial cells

Macrophage accumulation has been implicated in the pathogenesis of inflammatory glomerular disease. Monocyte chemoattractant protein-1 (MCP-1) plays a central role in recruiting monocytes to the glomeruli. Tumor necrosis factor-α (TNF-α) has been shown to induce MCP-1 expression in mesangial cells, although the precise mechanisms remain unclear. We previously demonstrated that RhoA and its effector, Rho-kinase (Rho-associated coiled-coil containing protein kinase, ROCK), are involved in the pathogenesis of diabetic nephropathy. However, its role in MCP-1 induction by TNF-α has not been elucidated. In the present study, we investigated whether the Rho/Rho-kinase signaling pathway regulates the TNF-α-mediated induction of MCP-1 in mesangial cells. Exposure of mouse mesangial cells (MES-13) to TNF-α resulted in an increase of MCP-1 expression (by RT-PCR) and secretion into the medium (by ELISA). Pull down and Western blot analysis revealed that TNF-α activated RhoA and Rho-kinase. Based on these observations, we speculated that the Rho/Rho-kinase signaling pathway may be involved in MCP-1 induction by TNF-α. In agreement with this concept, Y-27632, a specific Rho-kinase inhibitor, attenuated TNF-α-mediated induction of MCP-1. We demonstrated that Y-27632 inhibited TNF-α-mediated monocyte migration and attenuated TNF-α-mediated p38 MAPK activation. Based on these data we infer that Y-27632 inhibits TNF-α-induced MCP-1 expression, secretion and function through inhibition of Rho-kinase and p38 MAPK activity. Our study suggests that Rho/Rho-kinase is an important therapeutic target of monocyte recruitment and accumulation within the glomerulus in inflammatory renal disease.

Native and reconstituted HDL protect cardiomyocytes from doxorubicin-induced apoptosis

AIMS

We analysed the impact of native and reconstituted HDL on doxorubicin-induced cardiomyocyte apoptosis. While it is an effective anti-cancer agent, doxorubicin has serious cardiotoxic side effects. HDL has been shown to protect cardiomyocytes, notably against oxidative stress.

METHODS AND RESULTS

Cultured neonatal rat ventricular cardiomyocytes were subjected to doxorubicin-induced stress, monitored as caspase3 activation, apoptotic DNA fragmentation and cell viability. The protective effects of HDL and sphingosine-1-phosphate (S1P) were investigated using native HDL, reconstituted HDL of varied composition and agonists and antagonists of S1P receptors. Anti-apoptotic signalling pathways were identified with specific inhibitors. Native and reconstituted HDL significantly decreased doxorubicin-induced cardiomyocyte apoptosis, essentially due to the S1P component of HDL. The latter was mediated by the S1P2 receptor, but not the S1P1 or S1P3 receptors. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) signalling pathway was required for the anti-apoptotic effects of HDL and S1P. The transcription factor Stat3 also played an important role, as inhibition of its activity compromised the protective effects of HDL and S1P on doxorubicin-induced apoptosis.

CONCLUSION

HDL and its sphingosine-1-phosphate component can protect cardiomyocytes against doxorubicin toxicity and may offer one means of reducing cardiotoxic side effects during doxorubicin therapy. The study identified anti-apoptotic pathways that could be exploited to improve cardiomyocyte survival.

Evidence for a role of sphingosine-1 phosphate in cardiovascular remodelling in Fabry disease

AIMS

A hallmark of Fabry disease is the concomitant development of left-ventricular hypertrophy and arterial intima-media thickening, the pathogenesis of which is thought to be related to the presence of a plasmatic circulating growth-promoting factor. We therefore characterized the plasma of patients with Fabry disease in order to identify this factor.

METHODS AND RESULTS

Using a classical biochemical strategy, we isolated and identified sphingosine-1 phosphate (S1P) as a proliferative factor present in the plasma of patients with Fabry disease. Plasma S1P levels were significantly higher in 17 patients with Fabry disease compared with 17 healthy controls (225 +/- 40 vs. 164 +/- 17 ng/mL; P = 0.005). There was a positive correlation between plasma S1P levels and both common carotid artery intima-media thickness and left-ventricular mass index (r(2) = 0.47; P = 0.006 and r(2) = 0.53; P = 0.0007, respectively). In an experimental model, mice treated with S1P developed cardiovascular remodelling similar to that observed in patients with Fabry disease.

CONCLUSION

Sphingosine-1 phosphate participates in cardiovascular remodelling in Fabry disease. Our findings have implications for the treatment of cardiovascular involvement in Fabry disease.

S1P3-mediated cardiac fibrosis in sphingosine kinase 1 transgenic mice involves reactive oxygen species

AIMS

Sphingosine kinase 1 (SPHK1), its product sphingosine-1-phosphate (S1P), and S1P receptor subtypes have been suggested to play protective roles for cardiomyocytes in animal models of ischaemic preconditioning and cardiac ischaemia/reperfusion injury. To get more insight into roles for SPHK1 in vivo, we have generated SPHK1-transgenic (TG) mice and analysed the cardiac phenotype.

METHODS AND RESULTS

SPHK1-TG mice overexpressed SPHK1 in diverse tissues, with a nearly 20-fold increase in enzymatic activity. The TG mice grew normally with normal blood chemistry, cell counts, heart rate, and blood pressure. Unexpectedly, TG mice with high but not low expression levels of SPHK1 developed progressive myocardial degeneration and fibrosis, with upregulation of embryonic genes, elevated RhoA and Rac1 activity, stimulation of Smad3 phosphorylation, and increased levels of oxidative stress markers. Treatment of juvenile TG mice with pitavastatin, an established inhibitor of the Rho family G proteins, or deletion of S1P3, a major myocardial S1P receptor subtype that couples to Rho GTPases and transactivates Smad signalling, both inhibited cardiac fibrosis with concomitant inhibition of SPHK1-dependent Smad-3 phosphorylation. In addition, the anti-oxidant N-2-mercaptopropyonylglycine, which reduces reactive oxygen species (ROS), also inhibited cardiac fibrosis. In in vivo ischaemia/reperfusion injury, the size of myocardial infarct was 30% decreased in SPHK1-TG mice compared with wild-type mice.

CONCLUSION

These results suggest that chronic activation of SPHK1-S1P signalling results in both pathological cardiac remodelling through ROS mediated by S1P3 and favourable cardioprotective effects.

Protective effects of sphingosine-1-phosphate receptor agonist treatment after myocardial ischaemia-reperfusion

AIMS

Several experimental studies have demonstrated protection against cardiac ischaemia-reperfusion injury achieved by pre-treatment with exogenous sphingosine-1-phosphate (S1P). We tested the hypothesis that pharmacological S1P receptor agonists improve recovery of function when applied with reperfusion.

METHODS AND RESULTS

Isolated rat cardiomyocytes were stimulated with exogenous S1P, the selective S1P1 receptor agonist SEW2871, or the S1P1/3 receptor agonist FTY720. Western blot analysis was performed to analyse downstream signalling pathways. Ischaemia-reperfusion studies were conducted in rat cardiomyocytes, isolated Langendorff-perfused rat hearts, and in human myocardial muscle strip preparations to evaluate the effect of S1P receptor agonists on cell death and recovery of mechanical function. All S1P receptor agonists were able to activate Akt. This was associated with transactivation of the epidermal growth factor receptor. In isolated cardiomyocytes, selective stimulation of the S1P1 receptor by SEW2871 induced protection against cell death when administered either before or after ischaemia-reperfusion. In isolated rat hearts, treatment with FTY720 during reperfusion attenuated the rise in left ventricular end-diastolic pressure (LVEDP) and improved the recovery of left ventricular developed pressure without limiting infarct size. However, selective S1P1 receptor stimulation did not improve functional recovery but rather increased LVEDP. Additional experiments employing a human myocardial ischaemia-reperfusion model also demonstrated improved functional recovery induced by FTY720 treatment during reperfusion.

CONCLUSION

Pharmacological S1P receptor agonists have distinct effects on ischaemia-reperfusion injury. Their efficacy when applied during reperfusion makes them potential candidates for pharmaceutical postconditioning therapy after cardiac ischaemia.

Nuclear and mitochondrial signalling Akts in cardiomyocytes

Biological actions resulting from phosphoinositide synthesis trigger multiple downstream signalling cascades by recruiting proteins with pleckstrin homology domains, including phosphoinositide-dependent kinase-1 and protein kinase B (also known as Akt). Retrospectively, more attention has been focused on the plasma membrane-associated interactions of these molecules and resulting cytoplasmic target activation. The complex biological activities exerted by Akt activation suggest, however, that more subtle and complex subcellular control mechanisms are involved. This review examines the regulation of Akt activity from the perspective of subcellular compartmentalization and focuses specifically upon the actions of Akt activation downstream from phosphoinositide synthesis that influence cell biology by altering nuclear signalling leading to Pim-1 kinase induction as well as hexokinase phosphorylation that, together with Akt, serves to preserve mitochondrial integrity.

Akt mediated mitochondrial protection in the heart: metabolic and survival pathways to the rescue

Cardiomyocyte death is now recognized as a critical factor in the development of heart disease. Mitochondria are not only responsible for energy production to ensure that cardiac output meets the body's energy demands, but they serve as critical integrators of cell survival signals. Numerous stressors are known to induce cell death by necrosis and/or apoptosis mediated through mitochondrial dysregulation. Anti- and pro-apoptotic Bcl-2 family proteins regulate apoptosis by controlling mitochondrial outer membrane permeability, whereas opening of the mitochondrial permeability transition pore (PT-pore) induces large amplitude permeability of the inner membrane and consequent rupture of the outer membrane. Akt is one of the best described survival kinases activated by receptor ligands and its activation preserves mitochondrial integrity and protects cardiomyocytes against necrotic and apoptotic death. The mechanisms responsible for Akt-mediated mitochondrial protection have not been fully elucidated. There is, however, accumulating evidence that multiple Akt target molecules, recruited through both transcriptional and post-transcriptional mechanisms, directly impinge upon and protect mitochondria. In this review we discuss mechanisms by which Akt activation can effect changes at the mitochondria that protect cardiomyocytes and attenuate pathophysiological responses of the heart.