Sphingosine 1-phosphate increases an intracellular Ca(2+) concentration via S1P3 receptor in cultured vascular smooth muscle cells

Ichthyosis linked to sphingosine 1-phosphate lyase insufficiency is due to aberrant sphingolipid and calcium regulation

Sphingosine 1-phosphate lyase (SGPL1) insufficiency (SPLIS) is a syndrome which presents with adrenal insufficiency, steroid-resistant nephrotic syndrome, hypothyroidism, neurological disease, and ichthyosis. Where a skin phenotype is reported, 94% had abnormalities such as ichthyosis, acanthosis, and hyperpigmentation. To elucidate the disease mechanism and the role SGPL1 plays in the skin barrier we established clustered regularly interspaced short palindromic repeats-Cas9 SGPL1 KO and a lentiviral-induced SGPL1 overexpression (OE) in telomerase reverse-transcriptase immortalised human keratinocytes (N/TERT-1) and thereafter organotypic skin equivalents. Loss of SGPL1 caused an accumulation of S1P, sphingosine, and ceramides, while its overexpression caused a reduction of these species. RNAseq analysis showed perturbations in sphingolipid pathway genes, particularly in SGPL1_KO, and our gene set enrichment analysis revealed polar opposite differential gene expression between SGPL1_KO and _OE in keratinocyte differentiation and Ca2+ signaling genesets. SGPL1_KO upregulated differentiation markers, while SGPL1_OE upregulated basal and proliferative markers. The advanced differentiation of SGPL1_KO was confirmed by 3D organotypic models that also presented with a thickened and retained stratum corneum and a breakdown of E-cadherin junctions. We conclude that SPLIS associated ichthyosis is a multifaceted disease caused possibly by sphingolipid imbalance and excessive S1P signaling, leading to increased differentiation and an imbalance of the lipid lamellae throughout the epidermis.

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.

Sphingosine-1-phosphate in mitochondrial function and metabolic diseases

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite. The past decade has witnessed exponential growth in the field of S1P research, partly attributed to drugs targeting its receptors or kinases. Accumulating evidence indicates that changes in the S1P axis (i.e., S1P production, transport, and receptors) may modify metabolism and eventually mediate metabolic diseases. Dysfunction of the mitochondria on a master monitor of cellular metabolism is considered the leading cause of metabolic diseases, with aberrations typically induced by abnormal biogenesis, respiratory chain complex disorders, reactive oxygen species overproduction, calcium deposition, and mitophagy impairment. Accordingly, we discuss decades of investigation into changes in the S1P axis and how it controls mitochondrial function. Furthermore, we summarize recent scientific advances in disorders associated with the S1P axis and their involvement in the pathogenesis of metabolic diseases in humans, including type 2 diabetes mellitus and cardiovascular disease, from the perspective of mitochondrial function. Finally, we review potential challenges and prospects for S1P axis application to the regulation of mitochondrial function and metabolic diseases; these data may provide theoretical guidance for the treatment of metabolic diseases.

An Insight into GPCR and G-Proteins as Cancer Drivers

G-protein-coupled receptors (GPCRs) are the largest family of cell surface signaling receptors known to play a crucial role in various physiological functions, including tumor growth and metastasis. Various molecules such as hormones, lipids, peptides, and neurotransmitters activate GPCRs that enable the coupling of these receptors to highly specialized transducer proteins, called G-proteins, and initiate multiple signaling pathways. Integration of these intricate networks of signaling cascades leads to numerous biochemical responses involved in diverse pathophysiological activities, including cancer development. While several studies indicate the role of GPCRs in controlling various aspects of cancer progression such as tumor growth, invasion, migration, survival, and metastasis through its aberrant overexpression, mutations, or increased release of agonists, the explicit mechanisms of the involvement of GPCRs in cancer progression is still puzzling. This review provides an insight into the various responses mediated by GPCRs in the development of cancers, the molecular mechanisms involved and the novel pharmacological approaches currently preferred for the treatment of cancer. Thus, these findings extend the knowledge of GPCRs in cancer cells and help in the identification of therapeutics for cancer patients.

Metabolomic profiles and pathways of praziquantel in crucian carp

Praziquantel (PZQ) is a drug commonly used to treat some parasitic infections in animals. This study aimed to apply a reliable and simple method to identify important biological metabolites relevant to PZQ in crucian carp (Carassius auratus) to decipher the metabolic pathways and provide a basis for developing new anti-parasite drugs. The experimental group of crucian carp was administered oral PZQ at a dose of 10 mg kg^-1 via a stomach feed tube. All biological blood samples were analysed using liquid chromatography electrospray ionization/quadrupole time-of-flight mass spectrometry (LC ESI/Q-TOF MS). MetPA analysis was used to identify relevant pathways for PZQ in crucian carp. Thirty-five potential metabolic pathways were revealed by MetPA network software. Furthermore, the chemical structures of the related metabolites and pathways were identified by comparison with data obtained from free online databases. Forty-four significantly differentially abundant endogenous metabolites were found in the PZQ-treated crucian carp. The changes in metabolomic profiles and pathways induced by PZQ played a role in inhibiting pathogenesis.

S1P induces pulmonary artery smooth muscle cell proliferation by activating calcineurin/NFAT/OPN signaling pathway

The upregulation of osteopontin(OPN) has been found to contribute to the proliferation of pulmonary artery smooth muscle cells(PASMCs), and activation of PPARγ has been shown to suppress OPN expression in THP-1 cells. However, the molecular mechanisms underlying the upregulation of OPN expression and PPARγ agonist modulation of OPN expression in PASMCs remain largely unclear. Here we found that S1P stimulated PASMCs proliferation and up-regulated OPN expression in rat PASMCs, which was accompanied with the activation of phospholipase C(PLC), calcineurin and translocation of NFATc3 to nucleus. Further study showed that inhibition of PLC by U73122, suppression of calcineurin activity by cyclosporine A(CsA) or knockdown of NFATc3 using small interfering RNA suppressed S1P-induced OPN up-regulation. Activation of PPARγ by pioglitazone suppressed S1P-induced activation of calcineurin/NFATc3 signaling pathway and followed OPN up-regulation. Taken together, our study indicates that S1P stimulates OPN expression by activation of PLC/calcineurin/NFATc3 signaling pathway, and activation of PPARγ suppresses calcineurin/NFATc3-mediated OPN expression in PASMCs.

The sphingosine analog fingolimod (FTY720) enhances tone and contractility of rat gastric fundus smooth muscle

BACKGROUND

Sphingosine and its metabolite sphingosine phosphate (S1P) regulate a multitude of biological functions, including the contractile state of smooth. Gastrointestinal side effects have been reported in patients treated with FTY720, a sphingosine analog that is approved for the treatment of multiple sclerosis. The aim of this study was to characterize the effects of FTY720 on rat gastric fundus smooth muscle under basal conditions and during activation induced by high-K⁺ solution.

METHODS

Isometric contractions of isolated circular strips of gastric fundus smooth muscle were recorded using the organ bath method. The effects of FTY720 or vehicle were recorded under control conditions and in the presence of indomethacin, L-NAME, HA-1100, nifedipine, JTE-013, and suramin. Tone and contractions recorded in the presence of FTY720 or vehicle are reported as % of the amplitude of an initial high-K⁺ contraction obtained under control conditions.

KEY RESULTS

From a concentration of 10 μmol L^-1 onwards, FTY720 increased the tone, reaching 8.9% ± 7.5% at 100 μmol L^-1 (P < .05). With indomethacin in the solution, the effects of FTY720 were enhanced (32.1% ± 7.7%; P < .001). The FTY720-induced increase in tone was abolished in the absence of extracellular Ca²⁺ and reduced by nifedipine, HA-1100, JTE-013, and suramin. Furthermore, FTY720 increased high-K⁺ contractions in the presence of indomethacin.

CONCLUSIONS & INFERENCES

FTY720 increases tone and contractile responses to depolarization in gastric fundus smooth muscle by triggering calcium entry and calcium sensitization in a S1P receptor-dependent manner. Taken together, the experimental results presented in this work suggest that FTY720 may increase gastric tone and contractility in patients.

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.

FTY720 elevates smooth muscle contraction of aorta and blood pressure in rats via ERK activation

Sphingosine 1‐phosphate (S1P) is an important signaling sphingolipid involved in the pathogenesis of various cardio cerebral vascular diseases such as ischemic stroke. In particular, the S1P mimetic FTY720 is protective for brain against ischemic conditions. However, whether and how FTY720 can modulate vascular tone and blood pressure remains to be determined. We showed that FTY720 (1 mg/kg) enhanced the contractile response of rat thoracic aortic rings induced by high potassium and phenylephrine, respectively. This enhancement involves the activation of extracellular signal‐regulated kinase (ERK) since ERK phosphorylation was also enhanced and application of PD98059 (10 μmol/L), an inhibitor of ERK activation abrogated the aforementioned enhanced response by FTY720. In parallel, FTY720 (1 mg/kg) led to a modest elevation of blood pressure in rats, effects also being prevented by PD98059. In contrast, FTY720 decreased the high potassium‐induced contractile response in basilarartery preparations from rabbits, an effect blocked by PD98059. Together, FTY720‐induced an enhanced response of artery contractility in aorta and in arterial pressure involving ERK activation, with an attenuation in basilarartery contractility. This action property of FTY720 would be endowed with a potential of facilitating more blood flow perfusion to the brain and improving blood supply to the ischemic brain region and could be useful as an adjuvant in the treatment of ischemic stroke in the clinics.

Chemerin-induced arterial contraction is Gi- and calcium-dependent

Chemerin is an adipokine associated with increased blood pressure, and may link obesity with hypertension. We tested the hypothesis that chemerin-induced contraction of the vasculature occurs via calcium flux in smooth muscle cells. Isometric contraction of rat aortic rings was performed in parallel with calcium kinetics of rat aortic smooth muscle cells to assess the possible signaling pathway. Chemerin-9 (nonapeptide of the chemerin S¹⁵⁷ isoform) caused a concentration-dependent contraction of isolated aorta (EC₅₀ 100nM) and elicited a concentration-dependent intracellular calcium response (EC₅₀ 10nM). Pertussis toxin (G_i inhibitor), verapamil (L-type Ca²⁺ channel inhibitor), PP1 (Src inhibitor), and Y27632 (Rho kinase inhibitor) reduced both calcium influx and isometric contraction to chemerin-9 but PD098059 (Erk MAPK inhibitor) and U73122 (PLC inhibitor) had little to no effect on either measure of chemerin signaling. Although our primary aim was to examine chemerin signaling, we also highlight differences in the mechanisms of chemerin-9 and recombinant chemerin S¹⁵⁷. These data support a chemerin-induced contractile mechanism in vascular smooth muscle that functions through G_i proteins to activate L-type Ca²⁺ channels, Src, and Rho kinase. There is mounting evidence linking chemerin to hypertension and this mechanism brings us closer to targeting chemerin as a form of therapy.

Cellular function and signaling pathways of vascular smooth muscle cells modulated by sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) plays important roles in cardiovascular pathophysiology. S1P₁ and/or S1P₃, rather than S1P₂ receptors, seem to be predominantly expressed in vascular endothelial cells, while S1P₂ and/or S1P₃, rather than S1P₁ receptors, seem to be predominantly expressed in vascular smooth muscle cells (VSMCs). S1P has multiple actions, such as proliferation, inhibition or stimulation of migration, and vasoconstriction or release of vasoactive mediators. S1P induces an increase of the intracellular Ca²⁺ concentration in many cell types, including VSMCs. Activation of S1P₃ seems to play an important role in Ca²⁺ mobilization. S1P induces cyclooxygenase-2 expression in VSMCs via both S1P₂ and S1P₃ receptors. S1P₂ receptor activation in VSMCs inhibits inducible nitric oxide synthase (iNOS) expression. At the local site of vascular injury, vasoactive mediators such as prostaglandins and NO produced by VSMCs are considered primarily as a defensive and compensatory mechanism for the lack of endothelial function to prevent further pathology. Therefore, selective S1P₂ receptor antagonists may have the potential to be therapeutic agents, in view of their antagonism of iNOS inhibition by S1P. Further progress in studies of the precise mechanisms of S1P may provide useful knowledge for the development of new S1P-related drugs for the treatment of cardiovascular diseases.

S1P3 receptor influences key physiological properties of fast-twitch extensor digitorum longus muscle

To examine the role of sphingosine 1-phosphate (S1P) receptor 3 (S1P3) in modulating muscle properties, we utilized transgenic mice depleted of the receptor. Morphological analyses of extensor digitorum longus (EDL) muscle did not show evident differences between wild-type and S1P3-null mice. The body weight of 3-mo-old S1P3-null mice and the mean cross-sectional area of transgenic EDL muscle fibers were similar to those of wild-type. S1P3 deficiency enhanced the expression level of S1P1 and S1P2 receptors mRNA in S1P3-null EDL muscle. The contractile properties of S1P3-null EDL diverge from those of wild-type, largely more fatigable and less able to recover. The absence of S1P3 appears responsible for a lower availability of calcium during fatigue. S1P supplementation, expected to stimulate residual S1P receptors and signaling, reduced fatigue development of S1P3-null muscle. Moreover, in the absence of S1P3, denervated EDL atrophies less than wild-type. The analysis of atrophy-related proteins in S1P3-null EDL evidences high levels of the endogenous regulator of mitochondria biogenesis peroxisome proliferative-activated receptor-γ coactivator 1α (PGC-1α); preserving mitochondria could protect the muscle from disuse atrophy. In conclusion, the absence of S1P3 makes the muscle more sensitive to fatigue and slows down atrophy development after denervation, indicating that S1P3 is involved in the modulation of key physiological properties of the fast-twitch EDL muscle.

G protein-coupled receptors as promising cancer targets

G protein-coupled receptors (GPCRs) regulate an array of fundamental biological processes, such as growth, metabolism and homeostasis. Specifically, GPCRs are involved in cancer initiation and progression. However, compared with the involvement of the epidermal growth factor receptor in cancer, that of GPCRs have been largely ignored. Recent findings have implicated many GPCRs in tumorigenesis, tumor progression, invasion and metastasis. Moreover, GPCRs contribute to the establishment and maintenance of a microenvironment which is permissive for tumor formation and growth, including effects upon surrounding blood vessels, signaling molecules and the extracellular matrix. Thus, GPCRs are considered to be among the most useful drug targets against many solid cancers. Development of selective ligands targeting GPCRs may provide novel and effective treatment strategies against cancer and some anticancer compounds are now in clinical trials. Here, we focus on tumor related GPCRs, such as G protein-coupled receptor 30, the lysophosphatidic acid receptor, angiotensin receptors 1 and 2, the sphingosine 1-phosphate receptors and gastrin releasing peptide receptor. We also summarize their tissue distributions, activation and roles in tumorigenesis and discuss the potential use of GPCR agonists and antagonists in cancer therapy.