Exogenous S1P via S1P receptor 2 induces CTGF expression through Src-RhoA-ROCK-YAP pathway in hepatic stellate cells.

BACKGROUND: Hepatic fibrosis, a prevalent chronic liver condition, involves excessive extracellular matrix production associated with aberrant wound healing. Hepatic stellate cells (HSCs) play a pivotal role in liver fibrosis, activated by inflammatory factors such as sphingosine 1-phosphate (S1P). Despite S1P's involvement in fibrosis, its specific role and downstream pathway in HSCs remain controversial. METHODS: In this study, we investigated the regulatory role of S1P/S1P receptor (S1PR) in Hippo-YAP activation in both LX-2 cell lines and primary HSCs. Real-time PCR, western blot, pharmacological inhibitors, siRNAs, and Rho activity assays were adopted to address the molecular mechanisms of S1P mediated YAP activation. RESULTS: Serum and exogenous S1P significantly increased the expression of YAP target genes in HSCs. Pharmacologic inhibitors and siRNA-mediated knockdowns of S1P receptors showed S1P receptor 2 (S1PR2) as the primary mediator for S1P-induced CTGF expression in HSCs. Results using siRNA-mediated knockdown, Verteporfin, and Phospho-Tag immunoblots showed that S1P-S1PR2 signaling effectively suppressed the Hippo kinases cascade, thereby activating YAP. Furthermore, S1P increased RhoA activities in cells and ROCK inhibitors effectively blocked CTGF induction. Cytoskeletal-perturbing reagents were shown to greatly modulate CTGF induction, suggesting the important role of actin cytoskeleton in S1P-induced YAP activation. Exogeneous S1P treatment was enough to increase the expression of COL1A1 and α-SMA, that were blocked by YAP specific inhibitor. CONCLUSIONS: Our data demonstrate that S1P/S1PR2-Src-RhoA-ROCK axis leads to Hippo-YAP activation, resulting in the up-regulation of CTGF, COL1A1 and α-SMA expression in HSCs. Therefore, S1PR2 may represent a potential therapeutic target for hepatic fibrosis.

miR-495 promotes intestinal epithelial cell apoptosis through downregulation of Sphingosine-1-phosphate.

Many pathological conditions lead to defects in intestinal epithelial integrity and loss of barrier function; Sphingosine-1-phosphate (S1P) has been shown to augment intestinal barrier integrity, though the exact mechanisms are not completely understood. We have previously shown that overexpression of Sphingosine Kinase 1 (SphK1), the rate limiting enzyme for S1P synthesis, significantly increased S1P production and cell proliferation. Here we show that microRNA 495 (miR-495) upregulation led to decreased levels of SphK1 resultant from a direct effect at the SphK1 mRNA. Increasing expression of miR-495 in intestinal epithelial cells resulted in decreased proliferation and increased susceptibility to apoptosis. Transgenic expression of miR-495 inhibited mucosal growth, as well as decreased proliferation in the crypts. The intestinal villi also expressed decreased levels of barrier proteins and exaggerated damage upon exposure to cecal ligation-puncture. These results implicate miR-495 as a critical negative regulator of intestinal epithelial protection and proliferation through direct regulation of SphK1, the rate limiting enzyme critical for production of S1P.

Sphingosine-1-phosphate receptor 1-mediated odontogenic differentiation of mouse apical papilla-derived stem cells.

Background/purpose: Sphingosine-1-phosphate (S1P) exhibits receptor-mediated physiological effects by facilitating the differentiation of mesenchymal stem cells toward the osteoblast lineage. This study aimed to determine the effect of S1P on odontogenic differentiation of mouse immortalized stem cells of dental apical papilla (iSCAP) and assess the distribution of the S1P receptor 1 (S1PR1) in the apical papilla and the root canal wall of immature rat molars. Materials and methods: Immunostaining for S1PR1 was conducted at the apex of the rat mandibular first molar and within the root canal wall. The iSCAP was treated with S1P and bone morphogenetic protein (BMP)-9 (for comparison), and the expression levels of the odontogenic differentiation marker were evaluated via real-time reverse-transcriptase quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Mineralization and lipid droplet formation were evaluated via Alizarin red and Oil red O staining. Results: S1PR1-positive cells were expressed in areas of both apical papilla and dentin-pulp interface of root canal wall. During the odontogenic differentiation of iSCAP, S1P and BMP-9 increased the expression of the differentiation marker mRNA and secreted proteins including dentin sialophosphoprotein, dentin matrix phosphoprotein 1, and matrix extracellular phosphoglycoprotein. The S1PR1 signaling pathway is involved in the action of S1P, but not that of BMP-9. S1PR1 signaling also facilitated mineralization in iSCAP and suppressed the differentiation of these cells into adipocytes. Conclusion: S1P induced odontogenic differentiation of iSCAP through S1PR1. Furthermore, S1PR1-positive cells were expressed in the apical papilla of immature rat molars and in the dentin-pulp interface where odontoblast-like cells exist.

Atypical sphingosine-1-phosphate metabolites-biological implications of alkyl chain length.

Sphingosine-1-phosphate (S1P) is a bioactive lipid signaling molecule with pleiotropic implications by both auto- and paracrine signaling. Signaling occurs by engaging five G protein-coupled receptors (S1P1-5) or intracellular pathways. While the extensively studied S1P with a chain length of 18 carbon atoms (d18:1 S1P) affects lymphocyte trafficking, immune cell survival and inflammatory responses, the biological implication of atypical S1Ps such as d16:1 or d20:1 remains elusive. As S1P lipids have far-reaching implications in health and disease states in mammalian organisms, the previous contrasting results may be attributed to differences in S1P's alkyl chain length. Current research is beginning to appreciate these less abundant atypical S1P moieties. This review provides an up-to-date foundation of recent findings on the biological implications of atypical S1P chain lengths and offers a perspective on future research endeavors on S1P alkyl chain length-influenced signaling and its implications for drug discovery.

Effect of Phospholipid Transfer Protein on Plasma Sphingosine-1-Phosphate.

Plasma phospholipid transfer protein (PLTP) is a risk factor for human coronary artery disease (CAD). Sphingosine-1-phosphate (S1P), carried by high-density lipoprotein (HDL), is a potent lipid mediator and is also associated with CAD. Previous studies indicate that Pltp knockout (KO) (germline) mice have decreased circulating S1P without influencing apoM, a major S1P carrier on HDL. We then hypothesized that, like apoM, PLTP is another S1P carrier. We established inducible Pltp-KO, germline Apom-KO, and Pltp/Apom double KO mice and measured plasma lipoprotein and S1P levels under chow and a Western diet. We found that PLTP deficiency and the double deficiency have a similar effect on HDL reduction, while apoM deficiency has no such effect. Importantly, we found that all mice have about 50% reduction in plasma S1P levels, compared to wild type mice, and PLTP deficiency significantly reduces apoM levels (about 40%), while apoM deficiency has no effect on PLTP activity, indicating that PLTP depletion reduces S1P through HDL reduction and there is no additive effect with the double deficiency. To further evaluate this HDL-reduction-mediated effect, we overexpressed PLTP which also caused a reduction of HDL. We found that the overexpression significantly reduces S1P and apoM as well as apoA-I, a major apolipoprotein on HDL. Furthermore, we found that albumin (another reported S1P carrier) deficiency in mice has no effect on plasma S1P. We also found that the influence of PLTP on HDL may not require its direct binding to the particle. In conclusion, PLTP is not a direct S1P carrier. PLTP depletion or overexpression in adulthood dramatically reduces plasma S1P through HDL reduction. ApoM, but not albumin, deficiency reduces plasma S1P levels.

Serum S1P level in interstitial lung disease (ILD) is a potential biomarker reflecting the severity of pulmonary function.

BACKGROUND: sphingosine-1-phosphate (S1P), a naturally occurring sphingolipid, has been involved in pulmonary interstitial remodeling signaling. However, no study has examined its clinical merits for interstitial lung disease (ILD). This study aimed to investigate the serum level of S1P in ILD patients and its clinical correlation with the severity of disease in the two main types of ILDs: the IPF and the CTD-ILD patients. METHODS: This retrospective observational pilot study included 67 ILD patients and 26 healthy controls. These patients were stratified into the IPF group (35) and the CTD-ILD group (32). The severity of ILD was evaluated through pulmonary function indicators and the length of hospital stay. RESULTS: Serum S1P level was statistically higher in ILD patients than in health control (p = 0.002), while the Serum S1P levels in CTD-ILD and IPF patients were comparable. Serum S1P level further showed statistically negative correlation with pulmonary function indexes (TLC% pred, FVC% pred and FEV1% pred) and positive correlation with length of hospital stay (r = -0.38, p = 0.04; r = -0.41, p = 0.02, r = -0.37, p = 0.04; r = 0.42, p = 0.02, respectively) in CTD-ILD patients, although serum S1P level was not significantly correlated with inflammatory indexes. The IPF patients failed to exhibit a significant correlation of serum S1P level with pulmonary function and length of hospital stay. CONCLUSIONS: Serum S1P level might be a clinically useful biomarker in evaluating the severity of CTD-ILD patients rather than IPF patients.

The Species Effect: Differential Sphingosine-1-Phosphate Responses in the Bone in Human Versus Mouse.

The deterioration of osteoblast-led bone formation and the upregulation of osteoclast-regulated bone resorption are the primary causes of bone diseases, including osteoporosis. Numerous circulating factors play a role in bone homeostasis by regulating osteoblast and osteoclast activity, including the sphingolipid-sphingosine-1-phosphate (S1P). However, to date no comprehensive studies have investigated the impact of S1P activity on human and murine osteoblasts and osteoclasts. We observed species-specific responses to S1P in both osteoblasts and osteoclasts, where S1P stimulated human osteoblast mineralisation and reduced human pre-osteoclast differentiation and mineral resorption, thereby favouring bone formation. The opposite was true for murine osteoblasts and osteoclasts, resulting in more mineral resorption and less mineral deposition. Species-specific differences in osteoblast responses to S1P were potentially explained by differential expression of S1P receptor 1. By contrast, human and murine osteoclasts expressed comparable levels of S1P receptors but showed differential expression patterns of the two sphingosine kinase enzymes responsible for S1P production. Ultimately, we reveal that murine models may not accurately represent how human bone cells will respond to S1P, and thus are not a suitable model for exploring S1P physiology or potential therapeutic agents.

Sphingosine-1-Phosphate Shapes Healthy Monocytes into An Immunosuppressive Phenotype.

BACKGROUND/AIMS: The physiological phenotype of individuals can influence and shape real-life phenomena in that it can contribute to the development of specific characteristics that can affect the immune response to specific stimuli. In this study we aimed to understand whether the sphingosine/sphingosine-1-phoshate (S1P) axis can modulate the immunotype of circulating cells. METHODS: To pursue this goal, we performed bioinformatic analyses of public datasets. RESULTS: The transcriptomic profile of healthy subjects of GSE192829 dataset identified two clusters with different transcriptional repertoire. Cluster 1 expressed higher levels of enzymes for S1P formation than cluster 0 which was characterized by enzymes that lead to ceramide formation, which represent the opposite metabolic direction. Inference analysis showed that cluster 1 was higher populated by monocytes, CD4+ T and B cells than cluster 0. Of particular interest was the phenotype of the monocytes in cluster 1 which showed an immunosuppressive nature compared to those in cluster 0. The role of S1P signature in healthy PBMCs was confirmed with other dataset analyses, supporting that circulating monocytes positive to the ceramidase, unlike the negative ones, had an immunosuppressive phenotype characterized by hub immunosuppressive markers (i.e. TYROBP, FCER1G, SYK, SIRPA, CSF1R, AIF1, FCGR2A, CLEC7A, LYN, PLCG2, LILRs, HCK, GAB2). This hub genes well discriminated the immunotype of healthy subjects. CONCLUSION: In conclusion this study highlights that S1P-associated hub markers can be useful to discriminate subjects with pronounced immunosuppression.

Gene therapy with AAV9-SGPL1 in an animal model of lung fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a progressive scarring disease of the lung that leads rapidly to respiratory failure. Novel approaches to treatment are urgently needed. The bioactive lipid sphingosine-1-phosphate (S1P) is increased in IPF lungs and promotes proinflammatory and profibrotic TGF-ß signaling. Hence, decreasing lung S1P represents a potential therapeutic strategy for IPF. S1P is degraded by the intracellular enzyme S1P lyase (SPL). Here we find that a knock-in mouse with a missense SPL mutation mimicking human disease resulted in reduced SPL activity, increased S1P, increased TGF-ß signaling, increased lung fibrosis, and higher mortality after injury compared to wild type (WT). We then tested adeno-associated virus 9 (AAV9)-mediated overexpression of human SGPL1 (AAV-SPL) in mice as a therapeutic modality. Intravenous treatment with AAV-SPL augmented lung SPL activity, attenuated S1P levels within the lungs, and decreased injury-induced fibrosis compared to controls treated with saline or only AAV. We confirmed that AAV-SPL treatment led to higher expression of SPL in the epithelial and fibroblast compartments during bleomycin-induced lung injury. Additionally, AAV-SPL decreased expression of the profibrotic cytokines TNFα and IL1ß as well as markers of fibroblast activation, such as fibronectin (Fn1), Tgfb1, Acta2, and collagen genes in the lung. Taken together, our results provide proof of concept for the use of AAV-SPL as a therapeutic strategy for the treatment of IPF. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Heparan Sulfate Modulation Affects Breast Cancer Cell Adhesion and Transmigration across In Vitro Blood-Brain Barrier.

The disruption of endothelial heparan sulfate (HS) is an early event in tumor cell metastasis across vascular barriers, and the reinforcement of endothelial HS reduces tumor cell adhesion to endothelium. Our recent study showed that while vascular endothelial growth factor (VEGF) greatly reduces HS at an in vitro blood-brain barrier (BBB) formed by human cerebral microvascular endothelial cells (hCMECs), it significantly enhances HS on a breast cancer cell, MDA-MB-231 (MB231). Here, we tested that this differential effect of VEGF on the HS favors MB231 adhesion and transmigration. We also tested if agents that enhance endothelial HS may affect the HS of MB231 and reduce its adhesion and transmigration. To test these hypotheses, we generated an in vitro BBB by culturing hCMECs on either a glass-bottom dish or a Transwell filter. We first quantified the HS of the BBB and MB231 after treatment with VEGF and endothelial HS-enhancing agents and then quantified the adhesion and transmigration of MB231 across the BBB after pretreatment with these agents. Our results demonstrated that the reduced/enhanced BBB HS and enhanced/reduced MB231 HS increase/decrease MB231 adhesion to and transmigration across the BBB. Our findings suggest a therapeutic intervention by targeting the HS-mediated breast cancer brain metastasis.

Navigating the landscape of psoriasis therapy: novel targeted pathways and emerging trends.

INTRODUCTION: Psoriasis is a chronic, inflammatory, non-communicable skin disorder that affects a patient's social and emotional well-being. It is characterized by hyperproliferation of keratinocytes, irregular shedding of skin cells, and abnormal invasion of inflammatory mediators. The treatment strategy is designed based on the severity of the disease condition starting from topical, phototherapy, systemic, and biologics. In recent years, extensive research into the underlying mechanisms of psoriasis has led to significant advancement in treatment options from small molecules to biologics. AREA COVERED: This review focuses on intracellular and molecular mechanisms such as AhR, A3AR, RIP1, CGRP, and S1P that serve as novel pharmacological targets for psoriasis. Moreover, new molecules are approved or are under clinical investigation to interfere with these target mechanisms. EXPERT OPINION: A detailed understanding of signaling pathways provides potential targets and molecular mechanisms for the inflammatory cascade in psoriasis. This has led to the development of small molecules targeting specific pathways. Further, the combination of nanotechnology can assist in dose reduction leading to reduced adverse effects in the management of psoriasis.

Sphingolipid metabolism and complement signaling in cancer progression.

Cancer treatment options are limited due to therapeutic resistance; thus, understanding the tumor microenvironment (TME) is crucial. Sphingolipid metabolism and complement activation products have essential roles in promoting tumor survival. Emerging evidence shows that sphingolipid signaling can regulate intracellular complement activation to induce inflammasome-mediated metastasis, offering a promising strategy for cancer therapy.

S1P Lyase Deficiency in the Brain Promotes Astrogliosis and NLRP3 Inflammasome Activation via Purinergic Signaling.

Astrocytes are critical players in brain health and disease. Brain pathologies and lesions are usually accompanied by astroglial alterations known as reactive astrogliosis. Sphingosine 1-phosphate lyase (SGPL1) catalysis, the final step in sphingolipid catabolism, irreversibly cleaves its substrate sphingosine 1-phosphate (S1P). We have shown that neural ablation of SGPL1 causes accumulation of S1P and hence neuronal damage, cognitive deficits, as well as microglial activation. Moreover, the S1P/S1P-receptor signaling axis enhances ATP production in SGPL1-deficient astrocytes. Using immunohistochemical methods as well as RNA Seq and CUT&Tag we show how S1P signaling causes activation of the astrocytic purinoreceptor P2Y1 (P2Y1R). With specific pharmacological agonists and antagonists, we uncover the P2Y1R as the key player in S1P-induced astrogliosis, and DDX3X mediated the activation of the NLRP3 inflammasome, including caspase-1 and henceforward generation of interleukin-1ß (IL-1ß) and of other proinflammatory cytokines. Our results provide a novel route connecting S1P metabolism and signaling with astrogliosis and the activation of the NLRP3 inflammasome, a central player in neuroinflammation, known to be crucial for the pathogenesis of numerous brain illnesses. Thus, our study opens the door for new therapeutic strategies surrounding S1P metabolism and signaling in the brain.

Sex Differences in Sphingosine-1-Phosphate Levels Are Dependent on Ceramide Synthase 1 and Ceramidase in Lung Physiology and Tumor Conditions.

Sex is a biological variable that can reflect clinical outcomes in terms of quality of life, therapy effectiveness, responsiveness and/or toxicity. Sphingosine-1-phosphate (S1P) is a lipidic mediator whose activity can be influenced by sex. To evaluate whether the S1P axis underlies sex 'instructions' in the lung during physiological and oncological lung conditions, sphingosine and S1P were quantified in the blood of healthy (H) volunteers, lung adenocarcinoma (ADK) and squamous cell carcinoma (SCC) patients of both sexes. S1P receptors and their metabolic enzymes were evaluated in the tissues. Circulating levels of S1P were similar among H female and male subjects and female SCC patients. Instead, male and female ADK patients had lower circulating S1P levels. S1P receptor 3 (S1PR3) was physiologically expressed in the lung, but it was overexpressed in male SCC, and female and male ADK, but not in female SCC patients, who showed a significantly reduced ceramide synthase 1 (CERS1) mRNA and an overexpression of the ceramidase (ASAH1) precursor in lung tumor tissues, compared to male SCC and both male and female ADK patients. These findings highlighted sex differences in S1P rheostat in pathological conditions, but not in physiological conditions, identifying S1P as a prognostic mediator depending on lung cancer histotype.

Induction of Inflammation Disrupts the Negative Interplay between STING and S1P Axis That Is Observed during Physiological Conditions in the Lung.

The stimulator of interferon genes (STING) is a master regulator of innate immunity, involved in several inflammatory diseases. Our previous data showed that sphingosine-1-phosphate (S1P) is released during inflammatory conditions in the lung. The aim of this study was to understand the interplay between S1P and STING during both physiological and pathological conditions. The mRNA levels of ceramidase (ASAH1), S1P precursor enzyme, and STING were inversely correlated in healthy lung tissues, but positively correlated in tumor tissues. The activation of STING induced higher expression of ASAH1 and was accompanied by IFN-ß and IL-6 release. ASAH1 and sphingosine kinases (SPHK I/II) blockade significantly reduced IL-6, but not IFNß, after STING activation. In support of this, taking advantage of a mouse model, we found that inflamed lungs had higher levels of inactive ASAH1 when STING was inhibited. This confirmed the human data, where higher levels of STING promoted the activation of ASAH1. Lung cancer patients positive to STING and ASAH1 mRNA levels had a dismal prognosis in that the overall survival was reduced compared to STING/ASAH1 negative patients. These data highlight that during physiological conditions, STING and the S1P axis do not interfere, whereas in lung cancer patients their interplay is associated to poor prognosis.

Actin-binding protein filamin B regulates the cell-surface retention of endothelial sphingosine 1-phosphate receptor 1.

Sphingosine 1-phosphate receptor 1 (S1PR1) is a G protein-coupled receptor essential for vascular development and postnatal vascular homeostasis. When exposed to sphingosine 1-phosphate (S1P) in the blood of ∼1 µM, S1PR1 in endothelial cells retains cell-surface localization, while lymphocyte S1PR1 shows almost complete internalization, suggesting the cell-surface retention of S1PR1 is endothelial cell specific. To identify regulating factors that function to retain S1PR1 on the endothelial cell surface, here we utilized an enzyme-catalyzed proximity labeling technique followed by proteomic analyses. We identified Filamin B (FLNB), an actin-binding protein involved in F-actin cross-linking, as a candidate regulating protein. We show FLNB knockdown by RNA interference induced massive internalization of S1PR1 into early endosomes, which was partially ligand dependent and required receptor phosphorylation. Further investigation showed FLNB was also important for the recycling of internalized S1PR1 back to the cell surface. FLNB knockdown did not affect the localization of S1PR3, another S1P receptor subtype expressed in endothelial cells, nor did it affect localization of ectopically expressed ß2-adrenergic receptor. Functionally, we show FLNB knockdown in endothelial cells impaired S1P-induced intracellular phosphorylation events and directed cell migration and enhancement of the vascular barrier. Taken together, our results demonstrate that FLNB is a novel regulator critical for S1PR1 cell-surface localization and thereby proper endothelial cell function.

Therapeutic activation of endothelial sphingosine-1-phosphate receptor 1 by chaperone-bound S1P suppresses proliferative retinal neovascularization.

Sphingosine-1-phosphate (S1P), the circulating HDL-bound lipid mediator that acts via S1P receptors (S1PR), is required for normal vascular development. The role of this signaling axis in vascular retinopathies is unclear. Here, we show in a mouse model of oxygen-induced retinopathy (OIR) that endothelial overexpression of S1pr1 suppresses while endothelial knockout of S1pr1 worsens neovascular tuft formation. Furthermore, neovascular tufts are increased in Apom-/- mice which lack HDL-bound S1P while they are suppressed in ApomTG mice which have more circulating HDL-S1P. These results suggest that circulating HDL-S1P activation of endothelial S1PR1 suppresses neovascular pathology in OIR. Additionally, systemic administration of ApoM-Fc-bound S1P or a small-molecule Gi-biased S1PR1 agonist suppressed neovascular tuft formation. Circulating HDL-S1P activation of endothelial S1PR1 may be a key protective mechanism to guard against neovascular retinopathies that occur not only in premature infants but also in diabetic patients and aging people.

The role of sphingosine 1-phosphate metabolism in brain health and disease.

Lipids are essential structural and functional components of the central nervous system (CNS). Sphingolipids are ubiquitous membrane components which were discovered in the brain in the late 19th century. In mammals, the brain contains the highest concentration of sphingolipids in the body. Sphingosine 1-phosphate (S1P) derived from membrane sphingolipids evokes multiple cellular responses which, depending on its concentration and localization, make S1P a double-edged sword in the brain. In the present review we highlight the role of S1P in brain development and focus on the often contrasting findings regarding its contributions to the initiation, progression and potential recovery of different brain pathologies, including neurodegeneration, multiple sclerosis (MS), brain cancers, and psychiatric illnesses. A detailed understanding of the critical implications of S1P in brain health and disease may open the door for new therapeutic options. Thus, targeting S1P-metabolizing enzymes and/or signaling pathways might help overcome, or at least ameliorate, several brain illnesses.

S1P Released by SGPL1-Deficient Astrocytes Enhances Astrocytic ATP Production via S1PR2,4, Thus Keeping Autophagy in Check: Potential Consequences for Brain Health.

Astrocytes are critical players in brain health and disease. Sphingosine-1-phosphate (S1P), a bioactive signaling lipid, is involved in several vital processes, including cellular proliferation, survival, and migration. It was shown to be crucial for brain development. Its absence is embryonically lethal, affecting, inter alia, the anterior neural tube closure. However, an excess of S1P due to mutations in S1P-lyase (SGPL1), the enzyme responsible for its constitutive removal, is also harmful. Of note, the gene SGPL1 maps to a region prone to mutations in several human cancers and also in S1P-lyase insufficiency syndrome (SPLIS) characterized by several symptoms, including peripheral and central neurological defects. Here, we investigated the impact of S1P on astrocytes in a mouse model with the neural-targeted ablation of SGPL1. We found that SGPL1 deficiency, and hence the accumulation of its substrate, S1P, causes the elevated expression of glycolytic enzymes and preferentially directs pyruvate into the tricarboxylic acid (TCA) cycle through its receptors (S1PR2,4). In addition, the activity of TCA regulatory enzymes was increased, and consequently, so was the cellular ATP content. The high energy load activates the mammalian target of rapamycin (mTOR), thus keeping astrocytic autophagy in check. Possible consequences for the viability of neurons are discussed.