Sphingosine-1-phosphate receptor 2

Insight into modulators of sphingosine-1-phosphate receptor and implications for cardiovascular therapeutics

Cardiovascular disease is the leading cause of death worldwide, and it's of great importance to understand its underlying mechanisms and find new treatments. Sphingosine 1-phosphate (S1P) is an active lipid that exerts its effects through S1P receptors on the cell surface or intracellular signal, and regulates many cellular processes such as cell growth, cell proliferation, cell migration, cell survival, and so on. S1PR modulators are a class of modulators that can interact with S1PR subtypes to activate receptors or block their activity, exerting either agonist or functional antagonist effects. Many studies have shown that S1P plays a protective role in the cardiovascular system and regulates cardiac physiological functions mainly through interaction with cell surface S1P receptors (S1PRs). Therefore, S1PR modulators may play a therapeutic role in cardiovascular diseases. Here, we review five S1PRs and their functions and the progress of S1PR modulators. In addition, we focus on the effects of S1PR modulators on atherosclerosis, myocardial infarction, myocardial ischaemia/reperfusion injury, diabetic cardiovascular diseases, and myocarditis, which may provide valuable insights into potential therapeutic strategies for cardiovascular disease.

FAM19A5 in vascular aging and osteoporosis: Mechanisms and the "calcification paradox"

Aging induces a progressive decline in the vasculature's structure and function. Vascular aging is a determinant factor for vascular ailments in the elderly. FAM19A5, a recently identified adipokine, has demonstrated involvement in multiple vascular aging-related pathologies, including atherosclerosis, cardio-cerebral vascular diseases and cognitive deficits. This review summarizes the current understanding of FAM19A5' role and explores its putative regulatory mechanisms in various aging-related disorders, including cardiovascular diseases (CVDs), metabolic diseases, neurodegenerative diseases and malignancies. Importantly, we provide novel insights into the underlying therapeutic value of FAM19A5 in osteoporosis. Finally, we outline future perspectives on the diagnostic and therapeutic potential of FAM19A5 in vascular aging-related diseases.

Signaling controversy and future therapeutical perspectives of targeting sphingolipid network in cancer immune editing and resistance to tumor necrosis factor-α immunotherapy

Anticancer immune surveillance and immunotherapies trigger activation of cytotoxic cytokine signaling, including tumor necrosis factor-α (TNF-α) and TNF-related apoptosis-inducing ligand (TRAIL) pathways. The pro-inflammatory cytokine TNF-α may be secreted by stromal cells, tumor-associated macrophages, and by cancer cells, indicating a prominent role in the tumor microenvironment (TME). However, tumors manage to adapt, escape immune surveillance, and ultimately develop resistance to the cytotoxic effects of TNF-α. The mechanisms by which cancer cells evade host immunity is a central topic of current cancer research. Resistance to TNF-α is mediated by diverse molecular mechanisms, such as mutation or downregulation of TNF/TRAIL receptors, as well as activation of anti-apoptotic enzymes and transcription factors. TNF-α signaling is also mediated by sphingosine kinases (SphK1 and SphK2), which are responsible for synthesis of the growth-stimulating phospholipid, sphingosine-1-phosphate (S1P). Multiple studies have demonstrated the crucial role of S1P and its transmembrane receptors (S1PR) in both the regulation of inflammatory responses and progression of cancer. Considering that the SphK/S1P/S1PR axis mediates cancer resistance, this sphingolipid signaling pathway is of mechanistic significance when considering immunotherapy-resistant malignancies. However, the exact mechanism by which sphingolipids contribute to the evasion of immune surveillance and abrogation of TNF-α-induced apoptosis remains largely unclear. This study reviews mechanisms of TNF-α-resistance in cancer cells, with emphasis on the pro-survival and immunomodulatory effects of sphingolipids. Inhibition of SphK/S1P-linked pro-survival branch may facilitate reactivation of the pro-apoptotic TNF superfamily effects, although the role of SphK/S1P inhibitors in the regulation of the TME and lymphocyte trafficking should be thoroughly assessed in future studies.

Bile acid profiles and mRNA abundance of bile acid-related genes in adipose tissue of dairy cows with high versus normal body condition

Besides their lipid-digestive role, bile acids (BA) influence overall energy homeostasis, such as glucose and lipid metabolism. We hypothesized that BA along with their receptors, regulatory enzymes, and transporters are present in subcutaneous adipose tissue (scAT). In addition, we hypothesized that their mRNA abundance varies with the body condition of dairy cows around calving. Therefore, we analyzed BA in serum and scAT as well as the mRNA abundance of BA -related enzymes, transporters, and receptors in scAT during the transition period in cows with different body conditions around calving. In a previously established animal model, 38 German Holstein cows were divided into either a high (HBCS; n = 19) or normal BCS (NBCS; n = 19) group based on their body condition score (BCS) and back fat thickness (BFT). Cows were fed different diets to achieve the targeted differences in BCS and BFT (NBCS: BCS <3.5, BFT <1.2 cm; HBCS: BCS >3.75, BFT >1.4 cm) until dry-off at 7 wk ante partum. During the dry period and subsequent lactation, both groups were fed the same diets regarding their demands. Using a targeted metabolomics approach via LC-ESI-MS /MS, BA were analyzed in serum and scAT at wk -7, 1, 3, and 12 relative to parturition. In serum, 15 BA (cholic acid (CA), chenodeoxycholic acid (CDCA), glycocholic acid (GCA), taurocholic acid (TCA), glycochenodeoxycholic acid (GCDCA), taurochenodeoxycholic acid (TCDCA), deoxycholic acid (DCA), lithocholic acid (LCA), glycodeoxycholic acid (GDCA), glycolithocholic acid (GLCA), taurodeoxycholic acid (TDCA), taurolithocholic acid (TLCA), β-muricholic acid (MCA(b)), tauromuricholic acid (sum of α and β) (TMCA (a+b)), glycoursodeoxycholic acid (GUDCA)) were observed, whereas in scAT 7 BA (CA, GCA, TCA, GCDCA, TCDCA, GDCA, TDCA) were detected. In serum and scAT samples, the primary BA CA and its conjugate GCA were predominantly detected. Increasing serum concentrations of CA, CDCA, TCA, GCA, GCDCA, DCA, and MCA(b) with the onset of lactation might be related to the increasing DMI after parturition. Furthermore, serum concentrations of CA, CDCA, GCA, DCA, GCDCA, TCA, LCA, and GDCA were lower in HBCS cows compared with NBCS cows, concomitant with increased lipolysis in HBCS cows. The correlation between CA in serum and scAT may point to the transport of CA across cell membranes. Overall, the findings of the present study suggest a potential role of BA in lipid metabolism depending on the body condition of periparturient dairy cows.

Sphingolipids: From structural components to signaling hubs

In late November 2019, Prof. Lina M. Obeid passed away from cancer, a disease she spent her life researching and studying its intricate molecular underpinnings. Along with her husband, Prof. Yusuf A. Hannun, Obeid laid down the foundations of sphingolipid biochemistry and oversaw its remarkable evolution over the years. Lipids are a class of macromolecules that are primarily associated with cellular architecture. In fact, lipids constitute the perimeter of the cell in such a way that without them, there cannot be cells. Hence, much of the early research on lipids identified the function of this class of biological molecules as merely structural. Nevertheless, unlike proteins, carbohydrates, and nucleic acids, lipids are elaborately diverse as they are not made up of monomers in polymeric forms. This diversity in structure is clearly mirrored by functional pleiotropy. In this chapter, we focus on a major subset of lipids, sphingolipids, and explore their historic rise from merely inert structural components of plasma membranes to lively and necessary signaling molecules that transmit various signals and control many cellular processes. We will emphasize the works of Lina Obeid since she was an integral pillar of the sphingolipid research world.

Characterization of a S1PR2 specific 11C-labeled radiotracer in streptozotocin-induced diabetic murine model

BACKGROUND

Diabetes mellitus is a chronic progressive metabolic disorder that affects millions of people worldwide. Emerging evidence suggests the important roles of sphingolipid metabolism in diabetes. In particular, sphingosine-1-phosphate (S1P) and S1P receptor 2 (S1PR2) have important metabolic functions and are involved in several metabolic diseases. In diabetes, S1PR2 can effectively preserve β cells and improve glucose/insulin tolerance in high-fat diet induced and streptozotocin (STZ)-induced diabetic mouse models. We previously developed a group of potent and selective S1PR2 ligands and radioligands.

METHODS

In this study, we continued our efforts and characterized our leading S1PR2 radioligand, [11C]TZ34125, in a STZ-induced diabetic mouse model. [11C]TZ34125 was radiosynthesized in an automated synthesis module and in vitro saturation binding assay was performed using recombinant human S1PR2 membrane. In vitro saturation autoradiography analysis was also performed to determine the binding affinity of [11C]TZ34125 against mouse tissues. Type-1 diabetic mouse model was developed following a single high dose of STZ in C57BL/6 mice. Ex vivo biodistribution was performed to evaluate the distribution and amount of [11C]TZ34125 in tissues. In vitro autoradiography analysis was performed to compare the uptake of [11C]TZ34125 between diabetic and control animals in mouse spleen and pancreas.

RESULTS

Our in vitro saturation binding assay using [11C]TZ34125 confirmed [11C]TZ34125 is a potent radioligand to recombinant human S1PR2 membrane with a Kd value of 0.9 nM. Saturation autoradiographic analysis showed [11C]TZ34125 has a Kd of 67.5, 45.9, and 25.0 nM to mouse kidney, spleen, and liver tissues respectively. Biodistribution study in STZ-induced diabetic mice showed the uptake of [11C]TZ34125 was significantly elevated in the spleen (~2 fold higher) and pancreas (~1.4 fold higher) compared to normal controls. The increased uptake of [11C]TZ34125 was further confirmed using autoradiographic analysis in the spleen and pancreases of STZ-induced diabetic mice, indicating S1PR2 can potentially act as a biomarker of diabetes in pancreases and inflammation in spleen. Future mechanistic analysis and in vivo quantitative assessment using non-invasive PET imaging in large animal model of diabetes is worthwhile.

CONCLUSIONS

Overall, our data showed an increased uptake of our lead S1PR2-specific radioligand, [11C]TZ34125, in the spleen and pancreases of STZ-induced diabetic mice, and demonstrated [11C]TZ34125 has a great potential for preclinical and clinical usage for assessment of S1PR2 in diabetes and inflammation.

Bile Acids and Biliary Fibrosis

Biliary fibrosis is the driving pathological process in cholangiopathies such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Cholangiopathies are also associated with cholestasis, which is the retention of biliary components, including bile acids, in the liver and blood. Cholestasis may worsen with biliary fibrosis. Furthermore, bile acid levels, composition and homeostasis are dysregulated in PBC and PSC. In fact, mounting data from animal models and human cholangiopathies suggest that bile acids play a crucial role in the pathogenesis and progression of biliary fibrosis. The identification of bile acid receptors has advanced our understanding of various signaling pathways involved in regulating cholangiocyte functions and the potential impact on biliary fibrosis. We will also briefly review recent findings linking these receptors with epigenetic regulatory mechanisms. Further detailed understanding of bile acid signaling in the pathogenesis of biliary fibrosis will uncover additional therapeutic avenues for cholangiopathies.

Sphingosine-1-phosphate receptor 2 plays a dual role depending on the stage of cell differentiation in renal epithelial cells

Epithelial renal cells have the ability to adopt different cellular phenotypes through epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET). These processes are increasingly recognized as important repair factors following acute renal tubular injury. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid with impact on proliferation, growth, migration, and differentiation which has significant implication in various diseases including cancer and kidney fibrosis. Here we demonstrated that S1P can exert by activating S1P receptor 2 (S1PR2) different functions depending on the stage of cell differentiation. We observed that the differences in the migratory profile of Madin-Darby canine kidney (MDCK) cells depend both on their stage of cell differentiation and the activity of S1PR2, a receptor that can either promote or inhibit the migratory process. Meanwhile in non-differentiated cells S1PR2 activation avoids migration, it is essential on fully differentiated cells. This is the first time that an antagonist effect of S1PR2 was reported for the same cell type. Moreover, in fully differentiated cells, S1PR2 activation is crucial for the progression of EMT - characterized by adherent junctions disassembly, β-catenin and SNAI2 nuclear translocation and vimentin expression- and depends on ERK 1/2 activation and nuclear translocation. These findings provide a new perspective about the different S1PR2 functions depending on the stage of cell differentiation that can be critical to the modulation of renal epithelial cell plasticity, potentially paving the way for innovative research with pathophysiologic relevance.

S1PR2 is Important for Cigarette Smoke-induced Pyroptosis in Human Bronchial Epithelial Cells

BACKGROUND

Chronic obstructive pulmonary disease and other respiratory inflammatory diseases are often associated with cigarette smoke exposure. However, the underlying molecular mechanism remains unclear.

AIM OF THE STUDY

This study aimed to investigate the role of sphingosine-1-phosphate receptor 2 (S1PR2) in cigarette smoke extract (CSE)-induced inflammation and pyroptosis in human bronchial epithelial (HBE) cells.

METHODS

CSE was administered to HBE cells and inflammation and pyroptosis were assessed. The mRNA levels of S1PR2, NLRP3, IL-1β, and IL-18 in HBE cells were detected by quantitative RT-PCR. Secreted protein levels of IL-1β and IL-18 in the culture supernatants were detected using enzyme-linked immunosorbent assay. Western blotting was used to measure the levels of S1PR2 and pyroptosis-related proteins (NLRP3, ASC, caspase-1, GSDMD, IL-1β, and IL-18).

RESULTS

Our study revealed an upregulated expression of S1PR2, NLRP3, ASC, caspase-1, GSDMD, IL-1β, and regulated IL-18 in HBE cells after CSE exposure. Genetic blockage of S1PR2 could reverse the increased expression of these proteins related to CSE-induced pyroptosis. Conversely, S1PR2 overexpression increased CSE-induced pyroptosis by upregulating the expression of NLRP3, ASC, caspase-1, GSDMD, IL-1β, and IL-18 in HBE cells.

CONCLUSIONS

Our results revealed that a novel S1PR2 signaling pathway may be involved in the pathogenesis of CSE-induced inflammation and pyroptosis in HBE cells. Thus, S1PR2 inhibitors could be an effective treatment for cigarette smoke-induced airway inflammation and injury.

Adverse effect of FTY720P on colonic Na+ /K+ ATPase is mediated via ERK, p38MAPK, PKC, and PI3K

FTY720P, an analogue of sphingosine 1-phosphate, has emerged lately as a potential causative agent of inflammatory bowel disease, in which electrolytes movements driven by the sodium gradient established by the Na⁺ /K⁺ ATPase are altered. We showed previously in Caco-2 cells, a 50% FTY720P-induced decrease in the ATPase activity, mediated via S1PR2 and PGE2. This work aims at delineating the mechanism underlying PGE2 release and at investigating if the ATPase inhibition is due to changes in its abundance. The activity of the ATPase and the localization of a GFP-tagged Na⁺ /K⁺ -ATPase α₁ -subunit were assessed in cells treated with 7.5 nM FTY720P. The involvement of ERK, p38 MAPK, PKC, and PI3K was studied in cells treated with 7.5 nM FTY720P or 1 nM PGE2 in presence of their inhibitors, or by determining changes in the protein expression of their activated phosphorylated forms. Imaging data showed ∼30% reduction in the GFP-tagged Na⁺ /K⁺ ATPase at the plasma membrane. Both FTY720P and PGE2 showed, respectively, 50% and 60% reduction in ATPase activity that disappeared when p38 MAPK, PKC, and PI3K were inhibited individually but not with ERK inhibition. The effect of FTY720P was imitated by PMA, an activator of PKC. Western blotting revealed inhibition of ERK by FTY720P. It was concluded that FTY720P, through activation of S1PR2, downregulates the Na⁺ /K⁺ ATPase by inhibiting ERK, which in turn activates p38 MAPK leading to the sequential activation of PKC and PI3K, PGE2 release, and a decrease in the Na⁺ /K⁺ ATPase activity and membrane abundance.

Sphingosine 1-phosphate receptor 2 promotes the onset and progression of non-alcoholic fatty liver disease-related hepatocellular carcinoma through the PI3K/AKT/mTOR pathway

PURPOSE

Recent studies have revealed an increase in the incidence rate of non-alcoholic fatty liver disease-related hepatocellular carcinoma (NAFLD-HCC). Furthermore, the association of Sphingosine 1-phosphate receptor 2 (S1PR2) with various types of tumours is identified, and the metabolism of conjugated bile acids (CBAs) performs an essential function in the onset and development of HCC. However, the association of CBA and S1PR2 with NAFLD-HCC is unclear.

METHODS

The relationship between the expression of S1PR2 and the prognosis of patients suffering from NAFLD-HCC was investigated by bioinformatics techniques. Subsequently, the relationship between S1PR2 and the biological behaviours of HCC cell lines Huh 7 and HepG2 was explored by conducting molecular biology assays. Additionally, several in vivo animal experiments were carried out for the elucidation of the biological impacts of S1PR2 inhibitors on HCC cells. Finally, We used Glycodeoxycholic acid (GCDA) of CBA to explore the biological effects of CBA on HCC cell and its potential mechanism.

RESULTS

High S1PR2 expression was linked to poor prognosis of the NAFLD-HCC patients. According to cellular assay results, S1PR2 expression could affect the proliferation, invasion, migration, and apoptosis of Huh 7 and HepG2 cells, and was closely associated with the G1/G2 phase of the cell cycle. The experiments conducted in the In vivo conditions revealed that the overexpression of S1PR2 accelerated the growth of subcutaneous tumours. In addition, JTE-013, an antagonist of S1PR2, effectively inhibited the migration and proliferation of HCC cells. Furthermore, the bioinformatics analysis highlighted a correlation between S1PR2 and the PI3K/AKT/mTOR pathway. GCDA administration further enhanced the expression levels of p-AKT, p-mTOR, VEGF, SGK1, and PKCα. Moreover, both the presence and absence of GCDA did not reveal any significant change in the levels of S1PR2, p-AKT, p-mTOR, VEGF, SGK1, and PKCα proteins under S1PR2 knockdown, indicating that CBA may regulates the PI3K/AKT/mTOR pathway by mediating S1PR2 expression.

CONCLUSION

S1PR2 is a potential prognostic biomarker in NAFLD-HCC. In addition, We used GCDA in CBAs to treat HCC cell and found that the expression of S1PR2 was significantly increased, and the expression of PI3K/AKT/mTOR signalling pathway-related signal molecules was also significantly enhanced, indicating that GCDA may activate PI3K/AKT/mTOR signalling pathway by up-regulating the expression of S1PR2, and finally affect the activity of hepatocellular carcinoma cells. S1PR2 can be a candidate therapeutic target for NAFLD-HCC. Collectively, the findings of this research offer novel perspectives on the prevention and treatment of NAFLD-HCC.

Clonorchis sinensis infection induces hepatobiliary injury via disturbing sphingolipid metabolism and activating sphingosine 1-phosphate receptor 2

Clonorchis sinensis (C. sinensis) infection induces severe hepatobiliary injuries, which can cause inflammation, periductal fibrosis, and even cholangiocarcinoma. Sphingolipid metabolic pathways responsible for the generation of sphingosine-1-phosphate (S1P) and its receptor S1P receptors (S1PRs) have been implicated in many liver-related diseases. However, the role of S1PRs in C. sinensis-mediated biliary epithelial cells (BECs) proliferation and hepatobiliary injury has not been elucidated. In the present study, we found that C. sinensis infection resulted in alteration of bioactive lipids and sphingolipid metabolic pathways in mice liver. Furthermore, S1PR2 was predominantly activated among these S1PRs in BECs both in vivo and in vitro. Using JTE-013, a specific antagonist of S1PR2, we found that the hepatobiliary pathological injuries, inflammation, bile duct hyperplasia, and periductal fibrosis can be significantly inhibited in C. sinensis-infected mice. In addition, both C. sinensis excretory-secretory products (CsESPs)- and S1P-induced activation of AKT and ERK1/2 were inhibited by JTE-013 in BECs. Therefore, the sphingolipid metabolism pathway and S1PR2 play an important role, and may serve as potential therapeutic targets in hepatobiliary injury caused by C. sinensis-infection.

Intrahepatic cholestasis of pregnancy can increase the risk of metabolic disorders: A meta-analysis

BACKGROUND

Gestational diabetes mellitus (GDM) and preeclampsia (PE) are common complications during pregnancy. Studies indicated that abnormal bile acid metabolism is related to its pathogenesis. Intrahepatic cholestasis of pregnancy (ICP) is the most common pregnancy-specific liver disease, which classic symptoms include generalized pruritus that commonly and biochemical evidence of elevated bile acids. Our study aimed to explore the correlation between the ICP presence and risk of GDM, PE incident in pregnant women.

METHODS

A meta-analysis, which included 10 eligible studies including 17,688 ICP cases and 1,386,771 controls, was performed to assess the correlation of ICP with preeclampsia (PE) and gestational diabetes mellitus (GDM). There were 7 studies investigating the relationship between ICP and PE, and 9 studies that evaluated the relationship between ICP and GDM. All eligible studies were screened from Pubmed, Web of Science and EBSCO databases.

RESULTS

The results of this meta-analysis indicate that ICP significantly increase the risk for both PE (pooled odds ratio OR: 2.56 95%CI: 2.27 2.88, I2 heterogeneity = 35%, p heterogeneity = 0.16) and GDM (pooled OR: 2.28 95%CI: 1.69 3.07, I2 heterogeneity = 81%, p heterogeneity < 0.001). In the sensitivity analysis of GDM, excluding the largest heterogeneity study cannot change the result (pooled OR: 2.86 95%CI: 2.59 3.16, I2 heterogeneity = 0%, p heterogeneity = 0.56).

CONCLUSIONS

This meta-analysis shows that ICP is closely associated with ICP increased risk of PE and GDM) during pregnancy.

Sphk1-induced autophagy in microglia promotes neuronal injury following cerebral ischaemia-reperfusion

Microglial hyperactivation mediated by sphingosine kinase 1/sphingosine-1-phosphate (SphK1/S1P) signalling and the consequent inflammatory mediator production serve as the key drivers of cerebral ischaemia-reperfusion injury (CIRI). Although SphK1 reportedly controls autophagy and microglial activation, it remains uncertain as to whether SphK1 is similarly capable of regulating damage mediated by CIRI-activated microglia. In the current study, we adopted both in vitro oxygen-glucose deprivation reperfusion (OGDR) models and in vivo rat models of focal CIRI to ascertain this possibility. It was found that CIRI upregulated SphK1 and induced autophagy in microglia, while inhibiting these changes significantly impaired to prevented neuronal apoptosis. Results of mechanistic investigation revealed that SphK1 promoted autophagy via the tumour necrosis factor receptor associated factor 2 (TRAF2) pathway. Altogether, our findings unfolded to reveal a novel mechanism, whereby SphK1-induced autophagy in microglia contributed to the pathogenesis of CIRI, potentially highlighting novel avenues for future therapeutic intervention in ischaemic stroke patients.

Gut microbiota, bile acids, and nature compounds

Natural compounds (NPs) have historically made a major contribution to pharmacotherapy in various diseases and drug discovery. In the past decades, studies on gut microbiota have shown that the efficacy of NPs can be affected by the interactions between gut microbiota and NPs. On one hand, gut microbiota can metabolize NPs. On the other hand, NPs can influence the metabolism and composition of gut microbiota. Among gut microbiota metabolites, bile acids (BAs) have attracted widespread attention due to their effects on the body homeostasis and the development of diseases. Studies have also confirmed that NPs can regulate the metabolism of BAs and ultimately regulate the physiological function of the body and disease progresses. In this review, we comprehensively summarize the interactions among NPs, gut microbiota, and BAs. In addition, we also discuss the role of microbial BAs metabolism in understanding the toxicity and efficacy of NPs. Furthermore, we present personal insights into the future research directions of NPs and BAs.

Specific Gut Microbial Environment in Lard Diet-Induced Prostate Cancer Development and Progression

Lard diet (LD) is a risk factor for prostate cancer (PCa) development and progression. Two immunocompetent mouse models fed with isocaloric specific fat diets (LD) enriched in saturated and monounsaturated fatty acid (SMFA), showed significanftly enhanced PCa progression with weight gain compared with a fish oil diet (FOD). High gut microbial divergency resulted from difference in diets, and the abundance of several bacterial species, such as in the orders Clostridiales and Lactobacillales, was markedly altered in the feces of LD- or FOD-fed mice. The proportion of the order Lactobacillales in the gut was negatively involved in SMFA-induced body weight gain and PCa progression. We found the modulation of lipid metabolism and cholesterol biosynthesis pathways with three and seven commonly up- and downregulated genes in PCa tissues, and some of them correlated with the abundance of the order Lactobacillales in mouse gut. The expression of sphingosine 1-phosphate receptor 2, which is associated with the order Lactobacillales and cancer progression in mouse models, was inversely associated with aggressive phenotype and weight gain in patients with PCa using the NCBI Gene Expression Omnibus database. Therefore, SMFA may promote PCa progression with the abundance of specific gut microbial species and overexpression of lipogenic genes in PCa. Therapeutics with alteration of gut microbiota and candidate genes involved in diet-induced PCa progression may be attractive in PCa.

Signaling through the S1P-S1PR Axis in the Gut, the Immune and the Central Nervous System in Multiple Sclerosis: Implication for Pathogenesis and Treatment

Sphingosine 1-phosphate (S1P) is a signaling molecule with complex biological functions that are exerted through the activation of sphingosine 1-phosphate receptors 1–5 (S1PR1–5). S1PR expression is necessary for cell proliferation, angiogenesis, neurogenesis and, importantly, for the egress of lymphocytes from secondary lymphoid organs. Since the inflammatory process is a key element of immune-mediated diseases, including multiple sclerosis (MS), S1PR modulators are currently used to ameliorate systemic immune responses. The ubiquitous expression of S1PRs by immune, intestinal and neural cells has significant implications for the regulation of the gut–brain axis. The dysfunction of this bidirectional communication system may be a significant factor contributing to MS pathogenesis, since an impaired intestinal barrier could lead to interaction between immune cells and microbiota with a potential to initiate abnormal local and systemic immune responses towards the central nervous system (CNS). It appears that the secondary mechanisms of S1PR modulators affecting the gut immune system, the intestinal barrier and directly the CNS, are coordinated to promote therapeutic effects. The scope of this review is to focus on S1P−S1PR functions in the cells of the CNS, the gut and the immune system with particular emphasis on the immunologic effects of S1PR modulation and its implication in MS.

Bile Acid Receptors and the Gut-Liver Axis in Nonalcoholic Fatty Liver Disease

The prevalence of nonalcoholic fatty liver disease (NAFLD) has been significantly increased due to the global epidemic of obesity. The disease progression from simple steatosis (NAFL) to nonalcoholic steatohepatitis (NASH) is closely linked to inflammation, insulin resistance, and dysbiosis. Although extensive efforts have been aimed at elucidating the pathological mechanisms of NAFLD disease progression, current understanding remains incomplete, and no effective therapy is available. Bile acids (BAs) are not only important physiological detergents for the absorption of lipid-soluble nutrients in the intestine but also metabolic regulators. During the last two decades, BAs have been identified as important signaling molecules involved in lipid, glucose, and energy metabolism. Dysregulation of BA homeostasis has been associated with NAFLD disease severity. Identification of nuclear receptors and G-protein-coupled receptors activated by different BAs not only significantly expanded the current understanding of NAFLD/NASH disease progression but also provided the opportunity to develop potential therapeutics for NAFLD/NASH. In this review, we will summarize the recent studies with a focus on BA-mediated signaling pathways in NAFLD/NASH. Furthermore, the therapeutic implications of targeting BA-mediated signaling pathways for NAFLD will also be discussed.

Sphingolipids in Lung Pathology in the Coronavirus Disease Era: A Review of Sphingolipid Involvement in the Pathogenesis of Lung Damage

Sphingolipids are bioactive lipids involved in the regulation of cell survival, proliferation, and the inflammatory response. The SphK/S1P/S1PR pathway (S1P pathway) is a driver of many anti-apoptotic and proliferative processes. Pro-survival sphingolipid sphingosine-1-phosphate (S1P) initiates its signaling cascade by interacting with various sphingosine-1-phosphate receptors (S1PR) through which it is able to exert its pro-survival or inflammatory effects. Whereas sphingolipids, including ceramides and sphingosines are pro-apoptotic. The pro-apoptotic lipid, ceramide, can be produced de novo by ceramide synthases and converted to sphingosine by way of ceramidases. The balance of these antagonistic lipids and how this balance manifests is the essence of the sphingolipid rheostat. Recent studies on SARS-CoV-2 have implicated the S1P pathway in the pathogenesis of novel coronavirus disease COVID-19-related lung damage. Accumulating evidence indicates that an aberrant inflammatory process, known as "cytokine storm" causes lung injury in COVID-19, and studies have shown that the S1P pathway is involved in signaling this hyperinflammatory response. Beyond the influence of this pathway on cytokine storm, over the last decade the S1P pathway has been investigated for its role in a wide array of lung pathologies, including pulmonary fibrosis, pulmonary arterial hypertension (PAH), and lung cancer. Various studies have used S1P pathway modulators in models of lung disease; many of these efforts have yielded results that point to the potential efficacy of targeting this pathway for future treatment options. Additionally, they have emphasized S1P pathway's significant role in inflammation, fibrosis, and a number of other endothelial and epithelial changes that contribute to lung damage. This review summarizes the S1P pathway's involvement in COVID-19 and chronic lung diseases and discusses the potential for targeting S1P pathway as a therapeutic option for these diseases.

Compartmentalization of Sphingolipid metabolism: Implications for signaling and therapy

Sphingolipids (SLs) are a family of bioactive lipids implicated in a variety of cellular processes, and whose levels are controlled by an interlinked network of enzymes. While the spatial distribution of SL metabolism throughout the cell has been understood for some time, the implications of this for SL signaling and biological outcomes have only recently begun to be fully explored. In this review, we outline the compartmentalization of SL metabolism and describe advances in tools for investigating and probing compartment-specific SL functions. We also briefly discuss the implications of SL compartmentalization for cell signaling and therapeutic approaches to targeting the SL network.

TUDCA receptors and their role on pancreatic beta cells

Bile acids have received increasing attention over the past years as their multiple alternative roles became clearer. Tauroursodeoxycholic Acid (TUDCA) in specific has generated special interest due to its ability to promote pancreatic survival and function, as well as reduce endoplasmic reticulum stress. However, there are few studies explaining the molecular mechanisms behind TUDCA's beneficial actions on pancreatic beta cells. In this review, we decided to review the literature in order to craft a primer for researchers on what is known about TUDCA's receptors and the molecular pathways involved in this bile acid's function in the endocrine pancreas. We review the studies that focused on G protein-coupled bile acid receptor (TGR5), Sphingosine-1-phosphate receptor 2 (S1PR2) and α5β1 Integrin function in pancreatic cells. Our hope is to provide a basis for future studies to expand upon, especially considering the current lack of studies focusing on the importance of these receptors, either through TUDCA signaling or other signaling molecules.

S1P2-Gα12 Signaling Controls Astrocytic Glutamate Uptake and Mitochondrial Oxygen Consumption

Glutamate is the principal excitatory neurotransmitter in the human brain. Following neurotransmission, astrocytes remove excess extracellular glutamate to prevent neurotoxicity. Glutamate neurotoxicity has been reported in multiple neurologic diseases including multiple sclerosis (MS), representing a shared neurodegenerative mechanism. A potential modulator of glutamate neurotoxicity is the bioactive lysophospholipid sphingosine 1-phosphate (S1P) that signals through five cognate G-protein-coupled receptors, S1P₁-S1P₅; however, a clear link between glutamate homeostasis and S1P signaling has not been established. Here, S1P receptor knock-out mice, primary astrocyte cultures, and receptor-selective chemical tools were used to examine the effects of S1P on glutamate uptake. S1P inhibited astrocytic glutamate uptake in a dose-dependent manner and increased mitochondrial oxygen consumption, primarily through S1P₂ Primary cultures of wild-type mouse astrocytes expressed S1P_1,2,3 transcripts, and selective deletion of S1P₁ and/or S1P₃ in cerebral cortical astrocytes, did not alter S1P-mediated, dose-dependent inhibition of glutamate uptake. Pharmacological antagonists, S1P₂-null astrocytes, and Gα₁₂ hemizygous-null astrocytes indicated that S1P₂-Gα₁₂-Rho/ROCK signaling was primarily responsible for the S1P-dependent inhibition of glutamate uptake. In addition, S1P exposure increased mitochondrial oxygen consumption rates (OCRs) in wild-type astrocytes and reduced OCRs in S1P₂-null astrocytes, implicating receptor selective metabolic consequences of S1P-mediated glutamate uptake inhibition. Astrocytic S1P-S1P₂ signaling increased extracellular glutamate, which could contribute to neurotoxicity. This effect was not observed with the FDA-approved S1P receptor modulators, siponimod and fingolimod. Development and use of S1P₂-selective antagonists may provide a new approach to reduce glutamate neurotoxicity in neurologic diseases.

A Novel Role of Nogo Proteins: Regulating Macrophages in Inflammatory Disease

Nogo proteins, also known as Reticulon-4, have been identified as myelin-derived inhibitors of neurite outgrowth in the central nervous system (CNS). There are three Nogo variants, Nogo-A, Nogo-B and Nogo-C. Recent studies have shown that Nogo-A/B is abundant in macrophages and may have a wider effect on inflammation. In this review, we focus mainly on the possible roles of Nogo-A/B on polarization and recruitment of macrophages and their involvement in a variety of inflammatory diseases. We then discuss the Nogo receptor1 (NgR1), a common receptor for Nogo proteins that is also abundant in microglia/macrophage in the CNS. Interaction of Nogo and NgR1 in microglia/macrophage may affect the adhesion and polarization of macrophages that are involved in multiple neurodegenerative diseases, including Alzheimer's disease and multiple sclerosis. Overall, this review provides insights into the roles of Nogo proteins in regulating macrophage functions and suggests that, potentially, Nogo proteins maybe a new target in the treatment of inflammatory diseases.

Sphingosine 1-Phosphate Receptor 2 Is Central to Maintaining Epidermal Barrier Homeostasis

The outer layer of the epidermis composes the skin barrier, a sophisticated filter constituted by layers of corneocytes in a lipid matrix. The matrix lipids, especially the ceramide-generated sphingosine 1-phosphate, are the messengers that the skin barrier uses to communicate with the basal layer of the epidermis where replicating keratinocytes are located. Sphingosine 1-phosphate is a bioactive sphingolipid mediator involved in various cellular functions through S1PR1‒5, expressed by keratinocytes. We discovered that the S1pr2 absence is linked to an impairment in the skin barrier function. Although S1pr2^-/- mouse skin has no difference in its phenotype and barrier function compared with that of wild-type mouse, after tape stripping, S1pr2^-/- mouse showed significantly higher transepidermal water loss and required another 24 hours to normalize their transepidermal water loss levels. Moreover, after epicutaneous Staphylococcus aureus application, impaired S1pr2^-/- mouse epidermal barrier function allowed deeper bacterial penetration and denser neutrophil infiltration in the dermis. Microarray and RNA sequence of S1pr2^-/- mouse epidermis linked the barrier dysfunction with a decrease in FLG2 and tight junction components. In conclusion, S1pr2^-/- mice have compromised skin barrier function and increased bacteria permeability, making them a suitable model for diseases that present similar characteristics, such as atopic dermatitis.

Sphingosine-1-phosphate receptor 3 signaling

Sphingosine-1-phosphate (S1P) is a bioactive lipid which regulates a series of physiological and pathological processes via binding to five S1P receptors (S1PR1-5). Although S1PR1-3 are widely expressed, the study of S1PRs, however, mainly addressed S1PR1 and S1PR2, and few studies focus on S1PR3-5. In recent years, a growing number of studies have shown that S1PR3 plays an important role in cell proliferation, differentiation, apoptosis, and migration, but its function is still controversial. This is the first comprehensive review paper about the role of S1PR3 signaling in cardiovascular function, tissue fibrosis, cancer, immune response, and neurological function. In addition, existing S1PR3 agonists and antagonists are listed at the end of the article, and we also put forward our opinion on the dispute of S1PR3 function.

FAM19A5/S1PR1 signaling pathway regulates the viability and proliferation of mantle cell lymphoma

Several intracellular pathological processes have been reported to be regulated by the FAM19A5/S1PR1 signaling pathway. However, the role of FAM19A5/S1PR1 signaling pathway in the viability and proliferation of mantle cell lymphoma is not been completely understood. The task of this study is to explore the influence of FAM19A5/S1PR1 signaling pathway in affecting the survival and growth of mantle cell lymphoma. shRNAs against FAM19A5 or S1PR1 were transfected into mantle cell lymphom. Cell viability and proliferation were measured through MTT assay and CCK8 assay, respectively. Our results demonstrated that loss of FAM19A5 significantly reduced the viability of mantle cell lymphom, an effect that was followed by a drop in cell proliferation capacity. Besides, inhibition of S1PR1 also impairs cell survival and interrupt mantle cell lymphom proliferation in vitro. Taken together, our results illustrate that FAM19A5/S1PR1 signaling pathway is associated with the regulation of mantle cell lymphom viability and proliferation. This finding will provide a potential target for the treatment of malignant lymphoma in the clinical practice.

An Insight into Molecular Mechanisms and Novel Therapeutic Approaches in Epileptogenesis

Epilepsy is the second most common neurological disease with abnormal neural activity involving the activation of various intracellular signalling transduction mechanisms. The molecular and system biology mechanisms responsible for epileptogenesis are not well defined or understood. Neuroinflammation, neurodegeneration and Epigenetic modification elicit epileptogenesis. The excessive neuronal activities in the brain are associated with neurochemical changes underlying the deleterious consequences of excitotoxicity. The prolonged repetitive excessive neuronal activities extended to brain tissue injury by the activation of microglia regulating abnormal neuroglia remodelling and monocyte infiltration in response to brain lesions inducing axonal sprouting contributing to neurodegeneration. The alteration of various downstream transduction pathways resulted in intracellular stress responses associating endoplasmic reticulum, mitochondrial and lysosomal dysfunction, activation of nucleases, proteases mediated neuronal death. The recently novel pharmacological agents modulate various receptors like mTOR, COX-2, TRK, JAK-STAT, epigenetic modulators and neurosteroids are used for attenuation of epileptogenesis. Whereas the various molecular changes like the mutation of the cell surface, nuclear receptor and ion channels focusing on repetitive episodic seizures have been explored by preclinical and clinical studies. Despite effective pharmacotherapy for epilepsy, the inadequate understanding of precise mechanisms, drug resistance and therapeutic failure are the current fundamental problems in epilepsy. Therefore, the novel pharmacological approaches evaluated for efficacy on experimental models of epilepsy need to be identified and validated. In addition, we need to understand the downstream signalling pathways of new targets for the treatment of epilepsy. This review emphasizes on the current state of novel molecular targets as therapeutic approaches and future directions for the management of epileptogenesis. Novel pharmacological approaches and clinical exploration are essential to make new frontiers in curing epilepsy.

Stimulation of hepatocarcinogenesis by activated cholangiocytes via Il17a/f1 pathway in kras transgenic zebrafish model

It has been well known that tumor progression is dependent on secreted factors not only from tumor cells but also from other surrounding non-tumor cells. In the current study, we investigated the role of cholangiocytes during hepatocarcinogenesis following induction of oncogenic kras^V12 expression in hepatocytes using an inducible transgenic zebrafish model. Upon induction of carcinogenesis in hepatocytes, a progressive cell proliferation in cholangiocytes was observed. The proliferative response in cholangiocytes was induced by enhanced lipogenesis and bile acids secretion from hepatocytes through activation of Sphingosine 1 phosphate receptor 2 (S1pr2), a known cholangiocyte receptor involving in cholangiocyte proliferation. Enhancement and inhibition of S1pr2 could accelerate or inhibit cholangiocyte proliferation and hepatocarcinogenesis respectively. Gene expression analysis of hepatocytes and cholangiocytes showed that cholangiocytes stimulated carcinogenesis in hepatocytes via an inflammatory cytokine, Il17a/f1, which activated its receptor (Il17ra1a) on hepatocytes and enhanced hepatocarcinogenesis via an ERK dependent pathway. Thus, the enhancing effect of cholangiocytes on hepatocarcinogenesis is likely via an inflammatory loop.

ABCA8-mediated efflux of taurocholic acid contributes to gemcitabine insensitivity in human pancreatic cancer via the S1PR2-ERK pathway

The development of resistance to anticancer drugs is believed to cause chemotherapy failure in pancreatic cancer (PC). The efflux of anticancer drugs mediated by ATP-binding cassette (ABC) transporters is a widely accepted mechanism for chemoresistance, but for ABCA subfamily members, which are characterized by their ability to transport lipids and cholesterol, its role in chemoresistance remains unknown. Here we found that the expression of ABCA8, a member of ABCA subfamily transporters, was significantly increased in human PC cells after gemcitabine (GEM) treatment, as well as in established GEM-resistant (Gem-R) PC cells. Importantly, ABCA8 knockdown reversed the chemoresistance phenotype of Gem-R cells, whereas ABCA8 overexpression significantly decreased the sensitivity of human PC cells to GEM, both in vitro and in vivo, demonstrating an important role of ABCA8 in regulating chemosensitivity. Moreover, our results showed that treatment with taurocholic acid (TCA), an endogenous substrate of ABCA8, also induced GEM insensitivity in PC cells. We further demonstrated that ABCA8 mediates the efflux of TCA out of PC cells, and that extracellular TCA activates extracellular signal-regulated kinase (ERK) signaling via the sphingosine 1-phosphate receptor 2 (S1PR2), which is responsible for ABCA8-induced GEM ineffectiveness. Together, these findings reveal a novel TCA-related mechanism of ABCA subfamily transporter-mediated chemoresistance that goes beyond the role of a drug pump and suggest ABCA8 or the TCA-S1RP2-ERK pathway as potential targets for improving the effectiveness of and overcoming the resistance to chemotherapy in PC.

The noncanonical chronicles: Emerging roles of sphingolipid structural variants

Sphingolipids (SPs) are structurally diverse and represent one of the most quantitatively abundant classes of lipids in mammalian cells. In addition to their structural roles, many SP species are known to be bioactive mediators of essential cellular processes. Historically, studies have focused on SP species that contain the canonical 18‑carbon, mono-unsaturated sphingoid backbone. However, increasingly sensitive analytical technologies, driven by advances in mass spectrometry, have facilitated the identification of previously under-appreciated, molecularly distinct SP species. Many of these less abundant species contain noncanonical backbones. Interestingly, a growing number of studies have identified clinical associations between these noncanonical SPs and disease, suggesting that there is functional significance to the alteration of SP backbone structure. For example, associations have been found between SP chain length and cardiovascular disease, pain, diabetes, and dementia. This review will provide an overview of the processes that are known to regulate noncanonical SP accumulation, describe the clinical correlations reported for these molecules, and review the experimental evidence for the potential functional implications of their dysregulation. It is likely that further scrutiny of noncanonical SPs may provide new insight into pathophysiological processes, serve as useful biomarkers for disease, and lead to the design of novel therapeutic strategies.

Sphingosine-1-phosphate in acute exercise and training

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid found in all eukaryotic cells. Although it may function as an intracellular second messenger, most of its effects are induced extracellularly via activation of a family of five specific membrane receptors. Sphingosine-1-phosphate is enriched in plasma, where it is transported by high-density lipoprotein and albumin, as well as in erythrocytes and platelets which store and release large amounts of this sphingolipid. Sphingosine-1-phosphate regulates a host of cellular processes such as growth, proliferation, differentiation, migration, and apoptosis suppression. It was also shown to play an important role in skeletal muscle physiology and pathophysiology. In recent years, S1P metabolism in both muscle and blood was found to be modulated by exercise. In this review, we summarize the current knowledge on the effect of acute exercise and training on S1P metabolism, highlighting the role of this sphingolipid in skeletal muscle adaptation to physical effort.

Bioactive sphingolipids: Advancements and contributions from the laboratory of Dr. Lina M. Obeid

Sphingolipids and their synthetic enzymes have emerged as critical mediators in numerous diseases including inflammation, aging, and cancer. One enzyme in particular, sphingosine kinase (SK) and its product sphingosine-1-phosphate (S1P), has been extensively implicated in these processes. SK catalyzes the phosphorylation of sphingosine to S1P and exists as two isoforms, SK1 and SK2. In this review, we will discuss the contributions from the laboratory of Dr. Lina M. Obeid that have defined the roles for several bioactive sphingolipids in signaling and disease with an emphasis on her work defining SK1 in cellular fates and pathobiologies including proliferation, senescence, apoptosis, and inflammation.

Bile Acids: A Communication Channel in the Gut-Brain Axis

Bile acids are signalling hormones involved in the regulation of several metabolic pathways. The ability of bile acids to bind and signal through their receptors is modulated by the gut microbiome, since the microbiome contributes to the regulation and synthesis of bile acids as well to their physiochemical properties. From the gut, bacteria have been shown to send signals to the central nervous system via their metabolites, thus affecting the behaviour and brain function of the host organism. In the last years it has become increasingly evident that bile acids affect brain function, during normal physiological and pathological conditions. Although bile acids may be synthesized locally in the brain, the majority of brain bile acids are taken up from the systemic circulation. Since the composition of the brain bile acid pool may be regulated by the action of intestinal bacteria, it is possible that bile acids function as a communication bridge between the gut microbiome and the brain. However, little is known about the molecular mechanisms and the physiological roles of bile acids in the central nervous system. The possibility that bile acids may be a direct link between the intestinal microbiome and the brain is also an understudied subject. Here we review the influence of gut bacteria on the bile acid pool composition and properties, as well as striking evidence showing the role of bile acids as neuroactive molecules.

Post-translational modifications of S1PR1 and endothelial barrier regulation

Sphingosine-1-phosphate receptor-1 (S1PR1), a G-protein coupled receptor that is expressed in endothelium and activated upon ligation by the bioactive lipid sphingosine-1-phosphate (S1P), is an important vascular-barrier protective mechanism at the level of adherens junctions (AJ). Loss of endothelial barrier function is a central factor in the pathogenesis of various inflammatory conditions characterized by protein-rich lung edema formation, such as acute respiratory distress syndrome (ARDS). While several S1PR1 agonists are available, the challenge of arresting the progression of protein-rich edema formation remains to be met. In this review, we discuss the role of S1PRs, especially S1PR1, in regulating endothelial barrier function. We review recent findings showing that replenishment of the pool of cell-surface S1PR1 may be crucial to the effectiveness of S1P in repairing the endothelial barrier. In this context, we discuss the S1P generating machinery and mechanisms that regulate S1PR1 at the cell surface and their impact on endothelial barrier function.

S1PR2 Knockdown Promotes Migration and Invasion in Multiple Myeloma Cells via NF-κB Activation

Background

The presence of circulating plasma cells (cPCs) was associated with a worse prognosis in multiple myeloma patients. However, the underlying mechanisms involved in the migration and invasion of bone marrow myeloma cells (BMMCs) to cPCs remains unclear. Here, we investigate the possible factors related to hematogenous myeloma cell dissemination and potential regulatory mechanisms.

Methods

BMMCs and cPCs of five extramedullary plasmacytoma (EMP) patients were selected for single cell RNA sequencing, We found that the expression level of sphingosine-1-phosphate receptor 2 (S1RP2) was lower in cPCs compared with that in BMMCs. Then, we investigated the effect of S1PR2 in cell migration and invasion through pharmacologic inhibition with a S1PR2-selective antagonist JTE-013 or knockdown of S1PR2 expression in MM cell line U266.

Results

The results showed that S1PR2 inhibition with JTE-013 or S1PR2-shRNA significantly promoted cell migration and invasion in U266 cells. We measured the expression of invasion-related proteins by Western blot and found that knockdown of S1PR2 could reduce MMP-9 expression in U266 cells. Furthermore, we found NF-κB pathway may mediate the inhibition effects of S1PR2 on cell migration and invasion in MM cells.

Conclusion

Our findings demonstrated that S1PR2 downregulation may contribute to the initial extramedullary translocation by promoting cell migration and invasion through NF-κB pathway activation.

Lipid Players of Cellular Senescence

Lipids are emerging as key players of senescence. Here, we review the exciting new findings on the diverse roles of lipids in cellular senescence, most of which are enabled by the advancements in omics approaches. Senescence is a cellular process in which the cell undergoes growth arrest while retaining metabolic activity. At the organismal level, senescence contributes to organismal aging and has been linked to numerous diseases. Current research has documented that senescent cells exhibit global alterations in lipid composition, leading to extensive morphological changes through membrane remodeling. Moreover, senescent cells adopt a secretory phenotype, releasing various components to their environment that can affect the surrounding tissue and induce an inflammatory response. All of these changes are membrane and, thus, lipid related. Our work, and that of others, has revealed that fatty acids, sphingolipids, and glycerolipids are involved in the initiation and maintenance of senescence and its associated inflammatory components. These studies opened up an exciting frontier to investigate the deeper mechanistic understanding of the regulation and function of these lipids in senescence. In this review, we will provide a comprehensive snapshot of the current state of the field and share our enthusiasm for the prospect of potential lipid-related protein targets for small-molecule therapy in pathologies involving senescence and its related inflammatory phenotypes.

Blocking sphingosine 1-phosphate receptor 2 accelerates hepatocellular carcinoma progression in a mouse model of NASH

The role of sphingosine 1-phosphate (S1P) and its sphingosine-1-phosphate receptors (S1PRs) in non-alcoholic steatohepatitis (NASH) is unclear. We aimed to analyze the role of S1P/S1PRs in a Melanocortin-4 receptor (Mc4r)-deficient NASH murine model using FTY720, the functional antagonist of S1PR1, S1PR3, S1PR4, and S1PR5, and JTE-013, the antagonist of S1PR2. We observed that, compared to that in the control, the mRNA of S1pr1 tended to decrease, whereas those of S1pr2 and S1pr3 significantly increased in Mc4r-knockout (KO) mice subjected to a Western diet (WD). While the fat area did not differ, fibrosis progression differed significantly between control mice and mice in which liver S1PRs were blocked. Lipidomic and metabolomic analysis of liver tissues showed that JTE-013-administered mice showed elevation of S-adenosyl-l-methionine level, which can induce aberrant methylation due to reduction in glycine N-methyltransferase (GNMT) and elevation in diacylglycerol (DG) and triacylglycerol (TG) levels, leading to increased susceptibility to hepatocellular carcinoma (HCC). These phenotypes are similar to those of Gnmt-KO mice, suggesting that blocking the S1P/S1PR2 axis triggers aberrant methylation, which may increase DG and TG, and hepatocarcinogenesis. Our observations that the S1P/S1PR2 axis averts HCC occurrence may assist in HCC prevention in NASH.

Sphingosine-1-Phosphate: Its Pharmacological Regulation and the Treatment of Multiple Sclerosis: A Review Article

Sphingosine-1-phosphate (S1P), via its G-protein-coupled receptors, is a signaling molecule with important regulatory properties on numerous, widely varied cell types. Five S1P receptors (S1PR1-5) have been identified, each with effects determined by their unique G-protein-driven downstream pathways. The discovery that lymphocyte egress from peripheral lymphoid organs is promoted by S1P via S1PR-1 stimulation led to the development of pharmacological agents which are S1PR antagonists. These agents promote lymphocyte sequestration and reduce lymphocyte-driven inflammatory damage of the central nervous system (CNS) in animal models, encouraging their examination of efficacy in the treatment of multiple sclerosis (MS). Preclinical research has also demonstrated direct protective effects of S1PR antagonists within the CNS, by modulation of S1PRs, particularly S1PR-1 and S1PR-5, and possibly S1PR-2, independent of effects upon lymphocytes. Three of these agents, fingolimod, siponimod and ozanimod have been approved, and ponesimod has been submitted for regulatory approval. In patients with MS, these agents reduce relapse risk, sustained disability progression, magnetic resonance imaging markers of disease activity, and whole brain and/or cortical and deep gray matter atrophy. Future opportunities in the development of more selective and intracellular S1PR-driven downstream pathway modulators may expand the breadth of agents to treat MS.

Pulsatilla chinensis saponins cause liver injury through interfering ceramide/sphingomyelin balance that promotes lipid metabolism dysregulation and apoptosis

BACKGROUND

P. chinensis saponins (PRS) are pentacyclic triterpenoid bioactive constituents from Pulsatilla chinensis (Bunge) Regel. In our previous study, PRS caused chronic liver injury (CLI) with the significant changes of lipid metabolites including sphingomyelin (SM) in serum after long-term administration. The SM in the hepatocytes membrane plays an indispensable role in maintaining cell membrane stability and regulating the extracellular and intracellular signal transduction. However, it is still unknown the pathway related to SM and the mechanism of CLI on hepatocyte.

PURPOSE

The purpose of this study was to explore the hepatotoxicity mechanism of PRS in vivo and in vitro, to reveal the action of mechanism of SM and the pathway related to liver injury.

METHODS

SD rats were orally administered with PRS for 240 days and liver injury was evaluated by histological examinations. Metabolomics analysis was used to explore the liver metabolic pathway affected by PRS, and the expressions of related proteins were evaluated by western blots. To discover and elucidate the underlying mechanisms of metabolites changes induced by PRS at the cellular level, cellular morphology, MTT assays, western blots and cell membrane potential measurements were carried out using LO2 cells. Furthermore, the roles of SM and cholesterol (Chol) in hepatocyte injury were investigated individually in overload Chol and SM groups. Sphingolipid metabolic pathway related with ceramide/sphingomyelin (Cer/SM) balance was explored using cellular lipidomics and RT-PCR.

RESULTS

PRS gradually damaged the rat's liver in a time-dependent manner. The analysis of liver metabolism profiles showed that lipids metabolites were changed, including sphingolipid, bile acid, linoleic acid and fatty acid. We found that PRS induced apoptosis by interfering with bile acid-mediated sphingolipid metabolic pathway and Cer/SM balance in CLI. In in vitro experiments, PRS led to the increase of LDH leakage, depolarized cell membrane potential and caused cell membrane toxicity. Furthermore, PRS inducedG0/G1 phase cell cycle arrest in LO2 cells, simultaneously activated cellular extrinsic and intrinsic apoptosis pathways. PRS acted on SM and interfered with Cer/SM balance, which promote lipid metabolism dysregulation and apoptosis.

CONCLUSION

PRS acted on SM to interfere Cer/SM balance on LO2 cell. Both in vivo and in vitro, PRS induced Cer/SM imbalance which promoted lipid metabolism disorder and apoptosis. Apoptosis and lipids changes gradually damaged the rats liver, and ultimately developed into CLI.

La sclérose en plaques et les médicaments immuno-modulateurs des récepteurs de la sphingosine 1-phosphate

La sclérose en plaques (SEP) est une maladie du système nerveux central à composante inflammatoire, très invalidante qui atteint généralement de jeunes adultes (20 à 40 ans). Cette maladie se caractérise par la destruction progressive, par les cellules du système immunitaire, de la gaine de myéline des axones, ce qui aboutit à une dégénérescence neuronale. Les lymphocytes T et B sont les acteurs principaux de cette maladie qui peut être rémittente ou progressive. Parmi les médicaments utilisés dans le cadre de son traitement, le fingolimod, un immunosuppresseur dont les cibles sont les récepteurs de la sphingosine 1-phosphate, administré par voie orale, agit en empêchant les lymphocytes de quitter le thymus et les ganglions lymphatiques, et de rejoindre les foyers inflammatoires cérébraux. Une recherche intense pour développer des traitements et des médicaments curatifs est actuellement en cours et d’autres immunosuppresseurs interagissant avec les récepteurs de sphingosine 1-phosphate sont en cours de développement.

The role of the sphingolipid pathway in liver fibrosis: an emerging new potential target for novel therapies

Sphingolipids (SL) are a family of bioactive lipids and a major cellular membrane structural component. SLs include three main compounds: ceramide (Cer), sphingosine (Sp), and sphingosine-1-phosphate (S-1P), all of which have emerging roles in biological functions in cells, especially in the liver. They are under investigation in various liver diseases, including cirrhosis and end-stage liver disease. In this review, we provide an overview on the role of SLs in liver pathobiology and focus on their potential role in the development of hepatic fibrosis. We describe recent evidence and suggest SLs are a promising potential therapeutic target for the treatment of liver disease and fibrosis.

Unbalanced Sphingolipid Metabolism and Its Implications for the Pathogenesis of Psoriasis

Sphingolipids (SLs), which have structural and biological responsibilities in the human epidermis, are importantly involved in the maintenance of the skin barrier and regulate cellular processes, such as the proliferation, differentiation and apoptosis of keratinocytes (KCs). As many dermatologic diseases, including psoriasis (PsO), intricately characterized by perturbations in these cellular processes, are associated with altered composition and unbalanced metabolism of epidermal SLs, more education to precisely determine the role of SLs, especially in the pathogenesis of skin disorders, is needed. PsO is caused by a complex interplay between skin barrier disruption, immune dysregulation, host genetics and environmental triggers. The contribution of particular cellular compartments and organelles in SL metabolism, a process related to dysfunction of lysosomes in PsO, seems to have a significant impact on lysosomal signalling linked to a modulation of the immune-mediated inflammation accompanying this dermatosis and is not fully understood. It is also worth noting that a prominent skin disorder, such as PsO, has diminished levels of the main epidermal SL ceramide (Cer), reflecting altered SL metabolism, that may contribute not only to pathogenesis but also to disease severity and/or progression. This review provides a brief synopsis of the implications of SLs in PsO, aims to elucidate the roles of these molecules in complex cellular processes deregulated in diseased skin tissue and highlights the need for increased research in the field. The significance of SLs as structural and signalling molecules and their actions in inflammation, in which these components are factors responsible for vascular endothelium abnormalities in the development of PsO, are discussed.

Evaluating the antitumor activity of sphingosine-1-phosphate against human triple-negative breast cancer cells with basal-like morphology

Sphingosine-1-phosphate (S1P) is an important sphingolipid metabolite that regulates a wide range of physiological and pathophysiological processes. Our previous studies show that S1P selectively induces cell apoptosis in human breast cancer luminal A subtype cell line MCF7. In addition, S1P exhibits synergistic effects with chemotherapy drugs against both MCF7 and luminal B subtype cell line MDA-MB-361 at concentration in the high nM to low μM range. In the current study, we evaluated the effect of S1P on proliferation, apoptosis and cytotoxicity towards a panel of nine triple-negative breast cancer with basal-like morphology (TNBC-BL) cell lines (HCC1599, HCC1937, HCC1143, MDA-MB-468, HCC38, HCC70, HCC1806, HCC1187 and DU4475) in the same concentration range. S1P exhibited mild to moderate effects (<20% increase comparted to control) towards the TNBC-BL cell lines except HCC38, HCC70 and HCC1806. Furthermore, it increased cell apoptosis by ~15-20% in all the cell lines compared to the control, and elicited moderate to strong cytotoxic effect towards all cell lines except MDA-MB-468 and HCC1806. However, no synergistic/additive effect was observed between S1P and chemotherapy drug docetaxel for any TNBC-BL cell line.

Endothelial sphingosine 1-phosphate receptors promote vascular normalization and antitumor therapy

Tumor progression is dependent on angiogenesis, which supplies nutrients and enables gas exchange and metastatic dissemination. However, tumor vessels are dysfunctional and immature, which hinders the effectiveness of various therapeutics. Sphingosine 1-phosphate receptors in endothelial cells are essential for developmental angiogenesis and physiological functions such as the maintenance of the vascular barrier and vascular tone. This study shows that endothelial sphingosine 1-phosphate receptors determine the tumor vascular phenotype and maturation and that function of S1P receptor-1 is needed for tumor vascular normalization, which allows better blood circulation and enhances antitumor therapeutic efficacy in mouse models.

Sphingosine 1-phosphate receptor-1 (S1PR1) is essential for embryonic vascular development and maturation. In the adult, it is a key regulator of vascular barrier function and inflammatory processes. Its roles in tumor angiogenesis, tumor growth, and metastasis are not well understood. In this paper, we show that S1PR1 is expressed and active in tumor vessels. Murine tumor vessels that lack S1PR1 in the vascular endothelium (S1pr1 ECKO) show excessive vascular sprouting and branching, decreased barrier function, and poor perfusion accompanied by loose attachment of pericytes. Compound knockout of S1pr1, 2, and 3 genes further exacerbated these phenotypes, suggesting compensatory function of endothelial S1PR2 and 3 in the absence of S1PR1. On the other hand, tumor vessels with high expression of S1PR1 (S1pr1 ECTG) show less branching, tortuosity, and enhanced pericyte coverage. Larger tumors and enhanced lung metastasis were seen in S1pr1 ECKO, whereas S1pr1 ECTG showed smaller tumors and reduced metastasis. Furthermore, antitumor activity of a chemotherapeutic agent (doxorubicin) and immune checkpoint inhibitor blocker (anti-PD-1 antibody) were more effective in S1pr1 ECTG than in the wild-type counterparts. These data suggest that tumor endothelial S1PR1 induces vascular normalization and influences tumor growth and metastasis, thus enhancing antitumor therapies in mouse models. Strategies to enhance S1PR1 signaling in tumor vessels may be an important adjunct to standard cancer therapy of solid tumors.

Activation of sphingosine 1-phosphate receptor 2 attenuates chemotherapy-induced neuropathy

Platinum-based therapeutics are used to manage many forms of cancer, but frequently result in peripheral neuropathy. Currently, the only option available to attenuate chemotherapy-induced neuropathy is to limit or discontinue this treatment. Sphingosine 1-phosphate (S1P) is a lipid-based signaling molecule involved in neuroinflammatory processes by interacting with its five cognate receptors: S1P_1-5 In this study, using a combination of drug pharmacodynamic analysis in human study participants, disease modeling in rodents, and cell-based assays, we examined whether S1P signaling may represent a potential target in the treatment of chemotherapy-induced neuropathy. To this end, we first investigated the effects of platinum-based drugs on plasma S1P levels in human cancer patients. Our analysis revealed that oxaliplatin treatment specifically increases one S1P species, d16:1 S1P, in these patients. Although d16:1 S1P is an S1P₂ agonist, it has lower potency than the most abundant S1P species (d18:1 S1P). Therefore, as d16:1 S1P concentration increases, it is likely to disproportionately activate proinflammatory S1P₁ signaling, shifting the balance away from S1P₂ We further show that a selective S1P₂ agonist, CYM-5478, reduces allodynia in a rat model of cisplatin-induced neuropathy and attenuates the associated inflammatory processes in the dorsal root ganglia, likely by activating stress-response proteins, including ATF3 and HO-1. Cumulatively, the findings of our study suggest that the development of a specific S1P₂ agonist may represent a promising therapeutic approach for the management of chemotherapy-induced neuropathy.

Sphingosine-1-phosphate receptor 2 modulates pain sensitivity by suppressing the ROS-RUNX3 pathway in a rat model of neuropathy

Neuropathic pain correlates with a lesion or other dysfunction in the nervous system. Sphingosine-1-phosphate receptor 2 (S1P2) is expressed in the central nervous system and modulates synaptic plasticity. The present study aimed to investigate the role of S1P2 in neuropathic pain caused by chronic constriction injury (CCI). Sprague-Dawley rats were allocated into eight groups (n = 15 for each group): sham, CCI, CCI + green fluorescent protein, CCI + S1P2, CCI + Ctrl-short hairpin RNA (shRNA), CCI + S1P2 shRNA, CCI + S1P2 + CYM-5442, and CCI + S1P2 shRNA + CYM-5442. The CCI model was established via sciatic nerve ligation. S1P2 was overexpressed or knocked down by intrathecal injection of adeno-associated virus-S1P2 (AAV-S1P2) or AAV-S1P2 shRNA. The S1P1 agonist, CYM-5442 (1 mg/kg), was injected intraperitoneally after surgery. S1P2 expression, pain thresholds, apoptosis signaling, inflammation, and oxidative stress in rats were then examined. We found that sciatic nerve injury downregulated S1P2 expression in the spinal cords of rats. S1P2 overexpression enhanced pain thresholds. In contrast, S1P2 knockdown decreased pain thresholds in rats exposed to CCI. CCI and S1P2 silencing increased secretion of interleukin-1β (IL-1β), IL-6, and CCL2, whereas S1P2 overexpression decreased. S1P2 impeded CCI-induced reactive oxygen species (ROS) production and runt-related transcription factors 3 (RUNX3) downregulation, and S1P2 knockdown had the opposite effect. S1P2 overexpression suppressed Bax and active caspase 3 expression and promoted Bcl-2 expression, whereas loss of S1P2 reversed their expression. Additionally, S1P1 activation counteracted the effect of S1P2 on pain sensitivity. In conclusion, S1P2 is downregulated in CCI rats and may help modulate neuropathic pain via the ROS/RUNX3 pathway.