Overlapping Signaling Pathways of Sphingosine 1-Phosphate and TGF-β in the Murine Langerhans Cell Line XS52

Potentiation of Sphingolipids and TGF-β in the human corneal stroma reveals intricate signaling pathway crosstalks

Corneal haze brought on by fibrosis due to insult can lead to partial or complete vision loss. Currently, corneal transplantation is the gold standard for treating severe corneal fibrosis, which comes with the risk of rejection and the issue of donor tissue shortages. Sphingolipids (SPLs) are known to be associated with fibrosis in various tissues and organs, including the cornea. We previously reported that SPLs are tightly related to Transforming Growth Factor β (TGF-β) signaling and corneal fibrogenesis. This study aimed to elucidate the interplay of SPLs, specifically sphingosine-1-phosphate (S1P) signaling, and its' interactions with TGF-β signaling through detailed analyses of the corresponding downstream signaling targets in the context of corneal fibrosis, in vitro. Healthy human corneal fibroblasts (HCFs) were isolated, plated on polycarbonate membranes, and stimulated with a stable Vitamin C derivative. The 3D constructs were treated with either 5 μM sphingosine-1-phosphate (S1P), 5 μM SPHK I₂ (I₂; inhibitor of sphingosine kinase 1, one of the two enzymes responsible for generating S1P in mammalian cells), 0.1 ng/mL TGF-β1, or 0.1 ng/mL TGF-β3. Cultures with control medium-only served as controls. All 3D constructs were examined for protein expression of fibrotic markers, SPLs, TGF-βs, and relevant downstream signaling pathways. This data revealed no significant changes in any LTBP (latent TGF-β binding proteins) expression when stimulated with S1P or I₂. However, LTBP1 was significantly upregulated via stimulation of TGF-β1 and TGF-β3, whereas LTBP2 was significantly upregulated only with TGF-β3 stimulation. Significant downregulation of TGF-β receptor II (TGF-βRII) following S1P stimulation but significant upregulation following I₂ stimulation was observed. Following TGF-β1, S1P, and I₂ stimulation, phospho-SMAD2 (pSMAD2) was significantly downregulated. Furthermore, I₂ stimulation led to significant downregulation of SMAD4. Adhesion/proliferation/transcription regulation targets, SRC, FAK, and pERK 1/2 were all significantly downregulated by exogenous S1P, whereas I₂ only significantly downregulated FAK. Exogenous TGF-β3 caused significant upregulation of AKT. Interestingly, both I₂ and TGF-β3 caused significant downregulation of JNK expression. Lastly, TGF-β1 led to significant upregulation of sphingosine kinase 1 (SphK1) and sphingosine-1-phosphate receptor 3 (S1PR3), whereas TGF-β3 caused significant upregulation of only SphK1. Together with previously published work from our group and others, S1P inhibition exhibits great potential as an efficacious anti-fibrotic modality in human corneal stromal ECM. The current findings shed further light on a very complex and rather incompletely investigated mechanism, and cement the intricate crosstalk between SPLs and TGF-β in corneal fibrogenesis. Future studies will dictate the potential of utilizing SPLs/TGF-β signaling modulators as novel therapeutics in corneal fibrosis.

Pathogenic sphingosine 1-phosphate pathway in psoriasis: a critical review of its pathogenic significance and potential as a therapeutic target

Sphingosine-1-phosphate (S1P) is a sphingolipid mediator that exerts a variety of biological functions, including immune, cardiovascular, and neurological regulation as well as tumor promotion, through high-affinity G protein-coupled receptors (S1P_1-5). It has been reported that circulating S1P levels remain higher in patients with psoriasis than in healthy individuals and that circulating S1P levels do not decrease after anti-TNF-α treatment in those patients. The S1P-S1PR signaling system plays an important role in inhibiting keratinocyte proliferation, regulating lymphocyte migration, and promoting angiogenesis, thus contributing to the regulation of psoriasis pathogenesis. Here, we review the mechanisms by which S1P-S1PR signaling affects the development of psoriasis and the available clinical/preclinical evidence for targeting S1P-S1PR in psoriasis. S1P-S1PR signaling mechanisms may partially explain the link between psoriasis and its comorbidities. Although the detailed mechanisms remain to be elucidated, S1P may be a new target for future psoriasis remission.

Backstage players of fibrosis: NOX4, mTOR, HDAC, and S1P; companions of TGF-β

The fibrotic process could be easily defined as a pathological excess of extracellular matrix deposition, leading to disruption of tissue architecture and eventually loss of function; however, this process involves a complex network of several signal transduction pathways. Virtually almost all organs could be affected by fibrosis, the most affected are the liver, lung, skin, kidney, heart, and eyes; in all of them, the transforming growth factor-beta (TGF-β) has a central role. The canonical and non-canonical signal pathways of TGF-β impact the fibrotic process at the cellular and molecular levels, inducing the epithelial-mesenchymal transition (EMT) and the induction of profibrotic gene expression with the consequent increase in proteins such as alpha-smooth actin (α-SMA), fibronectin, collagen, and other extracellular matrix proteins. Recently, it has been reported that some molecules that have not been typically associated with the fibrotic process, such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4), mammalian target of rapamycin (mTOR), histone deacetylases (HDAC), and sphingosine-1 phosphate (S1P); are critical in its development. In this review, we describe and discuss the role of these new players of fibrosis and the convergence with TGF-β signaling pathways, unveiling new insights into the panorama of fibrosis that could be useful for future therapeutic targets.

New Insights into the Role of Sphingolipid Metabolism in Melanoma

Cutaneous melanoma is a deadly skin cancer whose aggressiveness is directly linked to its metastatic potency. Despite remarkable breakthroughs in term of treatments with the emergence of targeted therapy and immunotherapy, the prognosis for metastatic patients remains uncertain mainly because of resistances. Better understanding the mechanisms responsible for melanoma progression is therefore essential to uncover new therapeutic targets. Interestingly, the sphingolipid metabolism is dysregulated in melanoma and is associated with melanoma progression and resistance to treatment. This review summarises the impact of the sphingolipid metabolism on melanoma from the initiation to metastatic dissemination with emphasis on melanoma plasticity, immune responses and resistance to treatments.

Sphingosine-1-Phosphate Receptor 5 Modulates Early-Stage Processes during Fibrogenesis in a Mouse Model of Systemic Sclerosis: A Pilot Study

Systemic sclerosis (SSc) is a rare multi-organ autoimmune disease characterized by progressive skin fibrosis. Inflammation, type 2 immunity, and fibrogenic processes are involved in disease development and may be affected by sphingolipids. However, details about early-stage pathophysiological mechanisms and implicated mediators remain elusive. The sphingolipid sphingosine-1-phosphate (S1P) is elevated in the sera of SSc patients, and its receptor S1P5 is expressed in skin tissue. Nevertheless, almost nothing is known about the dermatological contribution of S1P5 to inflammatory and pro-fibrotic processes leading to the pathological changes seen in SSc. In this study, we observed a novel effect of S1P5 on the inflammatory processes during low-dose bleomycin (BLM)-induced fibrogenesis in murine skin. By comparing 2-week-treated skin areas of wild-type (WT) and S1P5-deficient mice, we found that S1P5 is important for the transcriptional upregulation of the Th2 characteristic transcription factor GATA-3 under treatment-induced inflammatory conditions, while T-bet (Th1) and FoxP3 (Treg) mRNA expression was regulated independently of S1P5. Additionally, treatment caused a regulation of S1P receptor 1 and S1P receptor 3 mRNA as well as a regulation of long-chain ceramide profiles, which both differ significantly between the genotypes. Despite S1P5-dependent differences regarding inflammatory processes, similar macroscopic evidence of fibrosis was detected in the skin histology of WT and S1P5-deficient mice after 4 weeks of subcutaneous BLM treatment. However, at the earlier 2-week point in time, the mRNA data of pro-collagen type 1 and SMAD7 indicate a pro-fibrotic S1P5 contribution in the applied SSc mouse model. In conclusion, we propose that S1P5 plays a role as a novel modulator during the early phase of BLM-caused fibrogenesis in murine skin. An immediate relationship between dermal S1P5 expression and fibrotic processes leading to skin alterations, such as formative for SSc pathogenesis, is indicated but should be studied more profound in further investigations. Therefore, this study is an initial step in understanding the role of S1P5-mediated effects during early stages of fibrogenesis, which may encourage the ongoing search for new therapeutic options for SSc patients.

Unravelling the interplay of sphingolipids and TGF-β signaling in the human corneal stroma

Purpose

To delineate the role of Sphingolipids (SPLs) in the human cornea and their cross-talks with transforming growth factor beta (TGF-β) in order to develop novel, non-invasive therapies.

Methods

Human corneal fibroblasts (HCFs) were harvested from healthy donors, stimulated with Vitamin C to promote extracellular matrix assembly, treated with exogenous sphingosine-1-phosphate (S1P) or sphingosine kinase inhibitor 2 (SPHK I₂) and isolated after 4 weeks for further analysis.

Results

Data showed that S1P led to a significant decrease in cellular migration where SPHK I₂ just delayed it for 24h. Significant modulation of the sphingolipid pathway was also noted. Sphingosine kinase-1 (SphK1) was significantly downregulated upon exogenous stimulation with S1P at a concentration of 5μM and Sphingosine kinase-2 (SphK2) was also significantly downregulated at concentrations of 0.01μM, 0.1μM, and 5μM; whereas no effects were observed upon stimulation with SPHK I_2. S1PR3 was significantly downregulated by 0.1μM and 5μM S1P and upregulated by 5μM and 10μM SPHK I₂. Furthermore, both S1P and SPHK I₂ regulated corneal fibrosis markers such as alpha-smooth muscle actin, collagen I, III, and V. We also investigated the interplay between two TGF-β isoforms and S1P/SPHK I₂ treatments and found that TGF-β1 and TGF-β3 were both significantly upregulated with the 0.1μM S1P but were significantly downregulated with the 5μM S1P concentration. When TGF-β1 was compared directly to TGF-β3 expression, we observed that TGF-β3 was significantly downregulated compared to TGF-β1 in the 5μM concentration of S1P. No changes were observed upon SPHK I₂ treatment.

Conclusion

Our study delineates the role of sphingolipids in the human cornea and highlights their different activities based on the cell/tissue type.

An unbiased in vivo functional genomics screening approach in mice identifies novel tumor cell-based regulators of immune rejection

The clinical successes of immune checkpoint therapies for cancer make it important to identify mechanisms of resistance to anti-tumor immune responses. Numerous resistance mechanisms have been identified employing studies of single genes or pathways, thereby parsing the tumor microenvironment complexity into tractable pieces. However, this limits the potential for novel gene discovery to in vivo immune attack. To address this challenge, we developed an unbiased in vivo genome-wide RNAi screening platform that leverages host immune selection in strains of immune-competent and immunodeficient mice to select for tumor cell-based genes that regulate in vivo sensitivity to immune attack. Utilizing this approach in a syngeneic triple-negative breast cancer (TNBC) model, we identified 709 genes that selectively regulated adaptive anti-tumor immunity and focused on five genes (CD47, TGFβ1, Sgpl1, Tex9 and Pex14) with the greatest impact. We validated the mechanisms that underlie the immune-related effects of expression of these genes in different TNBC lines, as well as tandem synergistic interactions. Furthermore, we demonstrate the impact of different genes with previously unknown immune functions (Tex9 and Pex14) on anti-tumor immunity. Thus, this innovative approach has utility in identifying unknown tumor-specific regulators of immune recognition in multiple settings to reveal novel targets for future immunotherapies.

Sphingosine metabolism as a therapeutic target in cutaneous melanoma

Melanoma is by far the most aggressive type of skin cancer with a poor prognosis in its advanced stages. Understanding the mechanisms involved in melanoma pathogenesis, response, and resistance to treatment has gained a lot of attention worldwide. Recently, the role of sphingolipid metabolism has been studied in cutaneous melanoma. Sphingolipids are bioactive lipid effector molecules involved in the regulation of various cellular signaling pathways such as inflammation, cancer cell proliferation, death, senescence, and metastasis. Recent studies suggest that sphingolipid metabolism impacts melanoma pathogenesis and is a potential therapeutic target. This review focuses on defining the role of sphingolipid metabolism in melanoma carcinogenesis, discussing sphingolipid-based therapeutic approaches, and highlighting the areas that require more extensive research.

Sphingolipids in neutrophil function and inflammatory responses: Mechanisms and implications for intestinal immunity and inflammation in ulcerative colitis

Bioactive sphingolipids are regulators of immune cell function and play critical roles in inflammatory conditions including ulcerative colitis. As one of the major forms of inflammatory bowel disease, ulcerative colitis pathophysiology is characterized by an aberrant intestinal inflammatory response that persists causing chronic inflammation and tissue injury. Innate immune cells play an integral role in normal intestinal homeostasis but their dysregulation is thought to contribute to the pathogenesis of ulcerative colitis. In particular, neutrophils are key effector cells and are first line defenders against invading pathogens. While the activity of neutrophils in the intestinal mucosa is required for homeostasis, regulatory mechanisms are equally important to prevent unnecessary activation. In ulcerative colitis, unregulated neutrophil inflammatory mechanisms promote tissue injury and loss of homeostasis. Aberrant neutrophil function represents an early checkpoint in the detrimental cycle of chronic intestinal inflammation; thus, dissecting the mechanisms by which these cells are regulated both before and during disease is essential for understanding the pathogenesis of ulcerative colitis. We present an analysis of the role of sphingolipids in the regulation of neutrophil function and the implication of this relationship in ulcerative colitis.

MPL W515L expression induces TGFβ secretion and leads to an increase in chemokinesis via phosphorylation of THOC5

The thrombopoietin receptor (MPL) has been shown to be mutated (MPL W515L) in myelofibrosis and thrombocytosis yet new approaches to treat this disorder are still required. We have previously shown that transcriptome and proteomic effects do not correlate well in oncogene-mediated leukemogenesis. We therefore investigated the effects of MPL W515L using proteomics. The consequences of MPL W515L expression on over 3300 nuclear and 3500 cytoplasmic proteins were assessed using relative quantification mass spectrometry. We demonstrate that MPL W515L expression markedly modulates the CXCL12/CXCR4/CD45 pathway associated with stem and progenitor cell chemotactic movement. We also demonstrated that MPL W515L expressing cells displayed increased chemokinesis which required the MPL W515L-mediated dysregulation of MYC expression via phosphorylation of the RNA transport protein THOC5 on tyrosine 225. In addition MPL W515L expression induced TGFβ secretion which is linked to sphingosine 1-phosphate production and the increased chemokinesis. These studies identify several pathways which offer potential targets for therapeutic intervention in the treatment of MPL W515L-driven malignancy. We validate our approach by showing that CD34+ cells from MPL W515L positive patients display increased chemokinesis and that treatment with a combination of MYC and sphingosine kinase inhibitors leads to the preferential killing of MPL W515L expressing cells.

TGFβ-Mediated induction of SphK1 as a potential determinant in human MDA-MB-231 breast cancer cell bone metastasis

Mechanistic understanding of the preferential homing of circulating tumor cells to bone and their perturbation on bone metabolism within the tumor-bone microenvironment remains poorly understood. Alteration in both transforming growth factor β (TGFβ) signaling and sphingolipid metabolism results in the promotion of tumor growth and metastasis. Previous studies using MDA-MB-231 human breast cancer-derived cell lines of variable metastatic potential were queried for changes in sphingolipid metabolism genes to explore correlations between TGFβ dependence and bone metastatic behavior. Of these genes, only sphingosine kinase-1 (SPHK1) was identified to be significantly increased following TGFβ treatment. Induction of SPHK1 expression correlated to the degree of metastatic capacity in these MDA-MB-231-derived cell lines. We demonstrate that TGFβ mediates the regulation of SPHK1 gene expression, protein kinase activity and is critical to MDA-MB-231 cell viability. Furthermore, a bioinformatic analysis of human breast cancer gene expression supports SPHK1 as a hallmark TGFβ target gene that also bears the genetic fingerprint of the basal-like/triple-negative breast cancer molecular subtype. These data suggest a potential new signaling axis between TGFβ/SphK1 that may have a role in the development, prognosis or the clinical phenotype associated with tumor-bone metastasis.

Sphingosine-1-phosphate as signaling molecule in the skin: Relevance in atopic dermatitis

Sphingolipids are essential molecules of the mammalian epidermis. Keratinocytes generate and secrete huge amounts of ceramide-precursors to the extracellular domain of the stratum corneum, where they are further metabolized to specific ceramide species. The arrangement of ceramides to well-organized lipid lamellae is essential to form the epidermal barrier. Besides their role as structural components sphingolipids are also critical molecules involved in the modulation of epidermal cells. Sphingosine-1-phosphate (S1P) has been identified as a prominent signaling molecule which regulates fundamental functions of keratinocytes and skin dendritic cells. Thus, S1P inhibits proliferation of keratinocytes and induces their differentiation. Moreover, antigen uptake, migration and cytokine production of dendritic cells are under the control of this sphingolipid. A dysregulation of the sphingolipid metabolism has been discussed in inflammatory skin disorders like atopic dermatitis. Animal models of contact dermatitis provide evidence that topical treatment with S1P is connected with an anti-inflammatory action suggesting a novel approach for the treatment of atopic dermatitis.

Inflammatory lipid sphingosine-1-phosphate upregulates C-reactive protein via C/EBPβ and potentiates breast cancer progression

A crucial role of the inflammatory lipid sphingosine-1-phosphate (S1P) in breast cancer aggressiveness has been reported. Recent clinical studies have suggested that C-reactive protein (CRP) has a role in breast cancer development. However, limited information is available on the molecular basis for the expression of CRP and its functional significance in breast cell invasion. The present study aimed to elucidate the molecular link between S1P and CRP during the invasive process of breast epithelial cells. This is the first report showing that transcription of CRP was markedly activated by S1P in breast cells. Our data suggest that not only S1P treatment but also the endogenously produced S1P may upregulate CRP in breast carcinoma cells. Transcription factors CCAAT/enhancer-binding protein beta and c-fos were required for S1P-induced CRP expression. Coupling of S1P3 to heterotrimeric Gαq triggered the expression of CRP, utilizing signaling pathways involving reactive oxygen species (ROS), Ca(2+) and extracellular signal-related kinases (ERKs). S1P-induced CRP expression was crucial for the transcriptional activation of matrix metalloproteinase-9 through ERKs, ROS and c-fos, leading to breast cell invasion. Using a xenograft mice tumor model, we demonstrated that S1P induced CRP expression both in vitro and in vivo. Taken together, our findings have revealed a molecular basis for S1P-induced transcriptional activation of CRP and its functional significance in the acquisition of the invasive phenotype of human breast epithelial cells under inflammatory conditions. Our findings may provide useful information on the identification of useful therapeutic targets for inflammatory breast cancer.

The impact of sphingosine kinase-1 in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) has a high reoccurrence rate and an extremely low survival rate. There is limited availability of effective therapies to reduce the rate of recurrence, resulting in high morbidity and mortality of advanced cases. Late presentation, delay in detection of lesions, and a high rate of metastasis make HNSCC a devastating disease. This review offers insight into the role of sphingosine kinase-1 (SphK1), a key enzyme in sphingolipid metabolism, in HNSCC. Sphingolipids not only play a structural role in cellular membranes, but also modulate cell signal transduction pathways to influence biological outcomes such as senescence, differentiation, apoptosis, migration, proliferation, and angiogenesis. SphK1 is a critical regulator of the delicate balance between proliferation and apoptosis. The highest expression of SphK1 is found in the advanced stage of disease, and there is a positive correlation between SphK1 expression and recurrent tumors. On the other hand, silencing SphK1 reduces HNSCC tumor growth and sensitizes tumors to radiation-induced death.  Thus, SphK1 plays an important and influential role in determining HNSCC proliferation and metastasis. We discuss roles of SphK1 and other sphingolipids in HNSCC development and therapeutic strategies against HNSCC.

Sphingolipids and inflammatory diseases of the skin

Mammalian skin protects our body against external assaults due to a well-organized skin barrier. The formation of the skin barrier is a complex process, in which basal keratinocytes lose their mitotic activity and differentiate to corneocytes. These corneocytes are embedded in intercellular lipid lamellae composed of ceramides, cholesterol, fatty acids, and cholesterol esters. Ceramides are the dominant lipid molecules and their reduction is connected with a transepidermal water loss and an epidermal barrier dysfunction resulting in inflammatory skin diseases. Moreover, bioactive sphingolipid metabolites like ceramide-1-phosphate, sphingosylphosphorylcholine, and sphingosine-1-phosphate are also involved in the biological modulation of keratinocytes and immune cells of the skin. Therefore, it is not astonishing that a dysregulation of sphingolipid metabolism has been identified in inflammatory skin diseases such as atopic dermatitis and psoriasis vulgaris. This chapter will describe not only the specific sphingolipid species and their skin functions but also the dysregulation of sphingolipid metabolism in inflammatory skin diseases.

Sphingosine 1-phosphate modulates antigen capture by murine Langerhans cells via the S1P2 receptor subtype

Dendritic cells (DCs) play a pivotal role in the development of cutaneous contact hypersensitivity (CHS) and atopic dermatitis as they capture and process antigen and present it to T lymphocytes in the lymphoid organs. Recently, it has been indicated that a topical application of the sphingolipid sphingosine 1-phosphate (S1P) prevents the inflammatory response in CHS, but the molecular mechanism is not fully elucidated. Here we indicate that treatment of mice with S1P is connected with an impaired antigen uptake by Langerhans cells (LCs), the initial step of CHS. Most of the known actions of S1P are mediated by a family of five specific G protein-coupled receptors. Our results indicate that S1P inhibits macropinocytosis of the murine LC line XS52 via S1P₂ receptor stimulation followed by a reduced phosphatidylinositol 3-kinase (PI3K) activity. As down-regulation of S1P₂ not only diminished S1P-mediated action but also enhanced the basal activity of LCs on antigen capture, an autocrine action of S1P has been assumed. Actually, S1P is continuously produced by LCs and secreted via the ATP binding cassette transporter ABCC1 to the extracellular environment. Consequently, inhibition of ABCC1, which decreased extracellular S1P levels, markedly increased the antigen uptake by LCs. Moreover, stimulation of sphingosine kinase activity, the crucial enzyme for S1P formation, is connected not only with enhanced S1P levels but also with diminished antigen capture. These results indicate that S1P is essential in LC homeostasis and influences skin immunity. This is of importance as previous reports suggested an alteration of S1P levels in atopic skin lesions.

Sphingosine-1-phosphate: a Janus-faced mediator of fibrotic diseases

Sphingosine-1-phosphate (S1P) is a pleiotropic lipid mediator that acts either on G protein-coupled S1P receptors on the cell surface or via intracellular target sites. In addition to the well established effects of S1P in angiogenesis, carcinogenesis and immunity, evidence is now continuously accumulating which demonstrates that S1P is an important regulator of fibrosis. The contribution of S1P to fibrosis is of a Janus-faced nature as S1P exhibits both pro- and anti-fibrotic effects depending on its site of action. Extracellular S1P promotes fibrotic processes in a S1P receptor-dependent manner, whereas intracellular S1P has an opposite effect and dampens a fibrotic reaction by yet unidentified mechanisms. Fibrosis is a result of chronic irritation by various factors and is defined by an excess production of extracellular matrix leading to tissue scarring and organ dysfunction. In this review, we highlight the general effects of extracellular and intracellular S1P on the multistep cascade of pathological fibrogenesis including tissue injury, inflammation and the action of pro-fibrotic cytokines that stimulate ECM production and deposition. In a second part we summarize the current knowledge about the involvement of S1P signaling in the development of organ fibrosis of the lung, kidney, liver, heart and skin. Altogether, it is becoming clear that targeting the sphingosine kinase-1/S1P signaling pathway offers therapeutic potential in the treatment of various fibrotic processes. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Sphingolipid regulation of tissue fibrosis

Bioactive sphingolipids, such as sphingosine 1-phosphate (S1P), dihydrosphingosine 1-phosphate (dhS1P) and ceramide, regulate a diverse array of cellular processes. Many of these processes are important components of wound-healing responses to tissue injury, including cellular apoptosis, vascular leak, fibroblast migration, and TGF-β signaling. Since over-exuberant or aberrant wound-healing responses to repetitive injury have been implicated in the pathogenesis of tissue fibrosis, these signaling sphingolipids have the potential to influence the development and progression of fibrotic diseases. Here we review accumulating in vitro and in vivo data indicating that these lipid mediators can in fact influence fibrogenesis in numerous organ systems, including the lungs, skin, liver, heart, and eye. Targeting these lipids, their receptors, or the enzymes involved in their metabolism consequently now appears to hold great promise for the development of novel therapies for fibrotic diseases.

Sphingosine 1-phosphate regulates matrix metalloproteinase-9 expression and breast cell invasion through S1P3-Gαq coupling

Recent evidence suggests that inflammation is involved in malignant progression of breast cancer. Sphingosine 1-phosphate (S1P), acting on the G-protein-coupled receptors, is known as a potent inflammatory mediator. In this study, the effect of the inflammatory lipid S1P on the regulation of invasive/migratory phenotypes of MCF10A human breast epithelial cells was investigated to elucidate a causal relationship between inflammation and the control of invasiveness of breast cells. We show that S1P causes induction of matrix metalloproteinase-9 (MMP-9) in vitro and in vivo, and thus enhances invasion and migration. We also show that fos plays a crucial role in the transcriptional activation of MMP-9 by S1P. In addition, activation of extracellular-signal-regulated kinases 1 and 2 (ERK1/2), p38 and alpha serine/threonine-protein kinase (Akt) are involved in the process of S1P-mediated induction of MMP-9 expression and invasion. Activation of the S1P receptor S1P₃ and G(αq) are required for S1P-induced invasive/migratory responses, suggesting that the enhancement of S1P-mediated invasiveness is triggered by the specific coupling of S1P₃ to the heterotrimeric G(αq) subunit. Activation of phospholipase C-β₄ and intracellular Ca²⁺ release are required for S1P-induced MMP-9 upregulation. Taken together, this study demonstrated that S1P regulates MMP-9 induction and invasiveness through coupling of S1P₃ and G(αq) in MCF10A cells, thus providing a molecular basis for the crucial role of S1P in promoting breast cell invasion.

Sphingosine 1-phosphate induces differentiation of mesoangioblasts towards smooth muscle. A role for GATA6

Different cells can contribute to repair following vascular injury by differentiating into smooth muscle (SM) cells; however the extracellular signals involved are presently poorly characterized. Mesoangioblasts are progenitor cells capable of differentiating into various mesoderm cell types including SM cells. In this study the biological action exerted by the pleiotropic sphingolipid sphingosine 1-phosphate (S1P) in human mesoangioblasts has been initially investigated by cDNA microarray analysis. Obtained data confirmed the anti-apoptotic action of this sphingolipid and identified for the first time a strong differentiating action toward SM cells. Quantitative mRNA and protein analysis corroborated the microarray results demonstrating enhanced expression of myogenic marker proteins and regulation of the expression of transcription factor GATA6 and its co-regulator, LMCD1. Importantly, GATA6 up-regulation induced by S1P was responsible for the enhanced expression of SM-specific contractile proteins. Moreover, by specific gene silencing experiments GATA6 was critical in the pro-differentiating activity of the cytokine TGFβ. Finally, the pharmacological inhibition of endogenous S1P formation in response to TGFβ abrogated GATA6 up-regulation, supporting the view that the S1P pathway plays a physiological role in mediating the pro-myogenic effect of TGFβ. This study individuates GATA6 as novel player in the complex transcriptional regulation of mesoangioblast differentiation into SM cells and highlights a role for S1P to favour vascular regeneration.

Translational aspects of sphingosine 1-phosphate biology

Sphingosine 1-phosphate (S1P) is a bioactive lipid that has both physiological and pathophysiological roles. It regulates cellular processes such as proliferation, migration, survival and differentiation and affects all organ systems. S1P not only activates S1P-specific receptors to initiate cellular signalling pathways but also directly regulates specific intracellular target proteins. The therapeutic opportunities surrounding S1P signalling are numerous and exemplified by the recent approval of FTY720 (a sphingosine analogue, Gilenya™) for the treatment of relapsing multiple sclerosis. A major focus of research is to develop small-molecule antagonists/agonists/inhibitors that are specific to the different S1P receptor subtypes and the enzymes that regulate S1P levels. This review describes fundamental aspects of S1P biology with an emphasis on the translational potential of intervention therapeutics.

Sphingosine 1-phosphate-induced motility and endocytosis of dendritic cells is regulated by SWAP-70 through RhoA

The phospholipid mediator sphingosine 1-phosphate (S1P) enhances motility and endocytosis of mature dendritic cells (DCs). We show that in vitro migration of Swap-70(-/-) bone marrow-derived DCs (BMDCs) in response to S1P and S1P-induced upregulation of endocytosis are significantly reduced. S1P-stimulated movement of Swap-70(-/-) BMDCs, specifically retraction of their trailing edge, in a collagen three-dimensional environment is impaired. These in vitro observations correlate with delayed entry into lymphatic vessels and migration to lymph nodes of skin DCs in Swap-70(-/-) mice. Expression of S1P receptors (S1P(1-3)) by wild-type and Swap-70(-/-) BMDCs is similar, but Swap-70(-/-) BMDCs fail to activate RhoA and to localize Rac1 and RhoA into areas of actin polymerization after S1P stimulus. The Rho-activating G protein Gα(i) interacts with SWAP-70, which also supports the localization of Gα(13) to membrane rafts in BMDCs. LPS-matured Swap-70(-/-) BMDCs contain significantly more active RhoA than wild-type DCs. Preinhibition of Rho activation restored migration to S1P, S1P-induced upregulation of endocytosis in mature Swap-70(-/-) BMDCs, and localization of Gα(13) to membrane rafts. These data demonstrate SWAP-70 as a novel regulator of S1P signaling necessary for DC motility and endocytosis.

Connective tissue growth factor induction by lysophosphatidic acid requires transactivation of transforming growth factor type β receptors and the JNK pathway

Transforming growth factor β (TGF-β) is a very strong pro-fibrotic factor which mediates its action, at least in part, through the expression of connective tissue growth factor (CTGF/CCN2). Along with these cytokines, the involvement of phospholipids in wound healing and the development of fibrosis has been revealed. Among them, lysophosphatidic acid (LPA) is a novel, potent regulator of wound healing and fibrosis that has diverse effects on many types of cells. We decided to evaluate the effect of LPA together with TGF-β on CTGF expression. We found that myoblasts treated with LPA and TGF-β1 produced an additive effect on CTGF expression. In the absence of TGF-β, the induction of CTGF expression by LPA was abolished by a dominant negative form of the TGF-β receptor type II (TGF-βRII) and by the use of SB 431542, a specific inhibitor of the serine/threonine kinase activity of TGF-βRI, suggesting that CTGF induction is dependent on LPA and requires active TGF-βRs. Moreover, we show that LPA requires Smad-2/3 proteins for the induction of CTGF expression, but not their phosphorylation or their nuclear translocation. The requirement of TGF-βRI for LPA mediated-effects is differential, since treatment of myoblasts with LPA in the presence of SB 431542 abolished the induction of stress fibers but not the induction of proliferation. Finally, we demonstrated that CTGF induction in response to LPA requires the activation of JNK, but not ERK, signaling pathways. The JNK requirement is independent of TGF-βRI-mediated activity. These novel results for the mechanism of action of LPA and TGF-β are important for understanding the role of pro-fibrotic growth factors and phospholipids involved in wound healing and related diseases.

New insights into the mechanism of fibroblast to myofibroblast transformation and associated pathologies

Myofibroblasts are a differentiated cell type essential for wound healing, participating in tissue remodeling following insult. Myofibroblasts are typically activated fibroblasts, although they can also be derived from other cell types, including epithelial cells, endothelial cells, and mononuclear cells. In most organ systems, cell signals initiated following tissue-specific insult or during the metastatic process lead to differentiation of fibroblasts or other precursor cells to the myofibroblast phenotype. In addition to their beneficial and necessary role in wound healing, myofibroblasts also contribute to a number of pathologies, primarily fibrotic processes and tumor invasiveness. This review explores both traditional and nontraditional concepts of myofibroblast differentiation in the cornea, skin, heart, and other tissues, as well as some of the pathologies associated with myofibroblast activities.

Lipids as targets for novel anti-inflammatory therapies

Lipids serve important functions as membrane constituents and also as energy storing molecules. Besides these functions certain lipid species have now been recognized as signalling molecules that regulate a multitude of cellular responses including cell growth and death, and also inflammatory reactions. Bioactive lipids are generated by hydrolysis from membrane lipids mainly by phospholipases giving rise to fatty acids and lysophospholipids that either directly exert their function or are further converted to active mediators. This review will summarize the present knowledge about bioactive lipids that either promote or attenuate inflammatory reactions. These lipids include polyunsaturated fatty acids (PUFA), eicosanoids including the epoxyeicosatrienoic acids (EET), peroxisome proliferation activating receptor (PPAR) activators, cannabinoids and the sphingolipids ceramide, sphingosine 1-phosphate and sphingosylphosphorylcholine.

Topical application of sphingosine-1-phosphate and FTY720 attenuate allergic contact dermatitis reaction through inhibition of dendritic cell migration

Migration of Langerhans cells (LCs) from the skin to the lymph node is an essential step in the pathogenesis of allergic contact dermatitis (ACD). Therefore, inhibition of LC-migration could be a promising strategy to improve this skin disease. Effects of sphingosine-1-phosphate (S1P) and the immunomodulator FTY720 on LC trafficking is not well defined, yet. Thus, we investigated the action of topically administered S1P and FTY720 in a murine model of ACD. Most interestingly, FTY720 as well as S1P inhibited the inflammatory reaction in the elicitation phase of ACD. In the sensitization phase, FTY720, and S1P reduced the weight and cell count of the draining auricular lymph node, as well as immigrated dendritic cells provoked by repetitive topical administration of the hapten. Correspondingly, the density of LCs in the epidermis was higher in FTY720- and S1P-treated mice compared to vehicle treatment. A skin dendritic cell migration assay confirmed the significant inhibition of dendritic cell migration by FTY720 and S1P. These data supply conclusive evidence that the strategy of targeting the migratory response of LCs with locally acting S1P or FTY720 represents an emerging option in the treatment of allergic skin diseases like contact hypersensitivity and atopic dermatitis.

Involvement of the lysophosphatidic acid-generating enzyme autotaxin in lymphocyte-endothelial cell interactions

Autotaxin (ATX) is a secreted protein with lysophospholipase D activity that generates lysophosphatidic acid (LPA) from lysophosphatidylcholine. Here we report that functional ATX is selectively expressed in high endothelial venules (HEVs) of both lymph nodes and Peyer's patches. ATX expression was developmentally regulated and coincided with lymphocyte recruitment to the lymph nodes. In adults, ATX expression was independent of HEV-expressed chemokines such as CCL21 and CXCL13, innate immunity signals including those via TLR4 or MyD88, and of the extent of lymphocyte trafficking across the HEVs. ATX expression was induced in venules at sites of chronic inflammation. Receptors for the ATX enzyme product LPA were constitutively expressed in HEV endothelial cells (ECs). In vitro, LPA induced strong morphological changes in HEV ECs. Forced ATX expression caused cultured ECs to respond to lysophosphatidylcholine, up-regulating lymphocyte binding to the ECs in a LPA receptor-dependent manner under both static and flow conditions. Although in vivo depletion of circulating ATX did not affect lymphocyte trafficking into the lymph nodes, we surmise, based on the above data, that ATX expressed by HEVs acts on HEVs in situ to facilitate lymphocyte binding to ECs and that ATX in the general circulation does not play a major role in this process. Tissue-specific inactivation of ATX will verify this hypothesis in future studies of its mechanism of action.

Sphingosine 1-phosphate receptor agonism impairs skin dendritic cell migration and homing to secondary lymphoid tissue: association with prolonged allograft survival

The novel immunomodulator FTY720 is a prototypic sphingosine-1-phosphate (S1P) receptor agonist that regulates lymphocyte migration and prolongs allograft survival. Skin dendritic cells (DC) play important roles in cutaneous immunity. We investigated the migration and function of skin DC exposed to FTY720 in vivo, or to its metabolite FTY720 phosphate (P) in vitro. C57BL/10 (H2(b)) recipient (but not donor) FTY720 treatment prolonged median skin C3H (H2(k)) allograft survival significantly, from 12 to 34.5 days. Non-transplanted, FTY720-treated mice revealed a marked increase in skin DC, although total DC in skin-draining lymph nodes (DLN) were unchanged compared with controls. Fewer allogeneic donor DC migrated to DLN of FTY720-treated graft recipients. DC that migrated from the skin of FTY720-treated mice showed reduced MHC class II, CD86 and CCR7 expression, suggesting impaired migratory potential to secondary lymphoid tissue, that correlated with DC retention in skin, and reduced T cell stimulatory activity. Fewer DC migrated from normal skin explants exposed to the FTY720 metabolite, FTY720P than to control medium. DC that did migrate expressed lower levels of MHC class II, CD86 and CCR7, and inferior T cell stimulatory ability. These data demonstrate S1P signaling regulates skin DC trafficking and modulates MHC class II, costimulatory, and homing receptor molecule expression that impairs their ability to elicit allogeneic T cell responses.

Sphingosine-1-phosphate receptor type-1 agonism impairs blood dendritic cell chemotaxis and skin dendritic cell migration to lymph nodes under inflammatory conditions

SEW2871 is a potent sphingosine-1-phosphate receptor type-1 (S1P(1))-selective agonist that induces peripheral lymphopenia through sequestration of lymphocytes into secondary lymphoid organs, similar to the non-selective sphingosine-1-phosphate (S1P) receptor agonist FTY720. FTY720 has been reported to interfere with human dendritic cell (DC) effector functions and both FTY720 and SEW2871 have been shown to modulate murine DC trafficking in vivo. Little is known about the possible effects of SEW2871 on human and murine DC functions. Here, we demonstrate that in contrast to FTY720, SEW2871 does not induce down-regulation of S1P(1) in human DCs and thus does not exert a functional antagonism at S1P(1). Notably, the compound was found to impair chemotaxis of immature and mature human DCs in vitro, possibly by interfering with the activation of p44/p42 and p38 mitogen-activated protein kinase signaling pathways. Comparative FACS analyses show that SEW2871 mediates CD18 down-regulation on mature human DCs. The influence on DC migration could be confirmed with in vivo assays using BALB/c mice in which SEW2871 impairs the migration of CD11c+ DC and CD207+ Langerhans cells (LC) to the draining lymph nodes (LNs) under inflammatory conditions. These results suggest that the S1P-S1P(1) axis might not only control lymphocyte trafficking but also play a pivotal role in DC migration from the skin to LN.

Sphingosine kinases and sphingosine-1-phosphate are critical for transforming growth factor beta-induced extracellular signal-regulated kinase 1 and 2 activation and promotion of migration and invasion of esophageal cancer cells

Transforming growth factor beta (TGFbeta) plays a dual role in oncogenesis, acting as both a tumor suppressor and a tumor promoter. These disparate processes of suppression and promotion are mediated primarily by Smad and non-Smad signaling, respectively. A central issue in understanding the role of TGFbeta in the progression of epithelial cancers is the elucidation of the mechanisms underlying activation of non-Smad signaling cascades. Because the potent lipid mediator sphingosine-1-phosphate (S1P) has been shown to transactivate the TGFbeta receptor and activate Smad3, we examined its role in TGFbeta activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and promotion of migration and invasion of esophageal cancer cells. Both S1P and TGFbeta activate ERK1/2, but only TGFbeta activates Smad3. Both ligands promoted ERK1/2-dependent migration and invasion. Furthermore, TGFbeta rapidly increased S1P, which was required for TGFbeta-induced ERK1/2 activation, as well as migration and invasion, since downregulation of sphingosine kinases, the enzymes that produce S1P, inhibited these responses. Finally, our data demonstrate that TGFbeta activation of ERK1/2, as well as induction of migration and invasion, is mediated at least in part by ligation of the S1P receptor, S1PR2. Thus, these studies provide the first evidence that TGFbeta activation of sphingosine kinases and formation of S1P contribute to non-Smad signaling and could be important for progression of esophageal cancer.

Cross-talk at the crossroads of sphingosine-1-phosphate, growth factors, and cytokine signaling

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that mediates a wide array of biologic effects through its interaction with a family of five G protein-coupled receptors. Cytokines and growth factors interact with this signaling pathway in a variety of ways, including both activation and regulation of the expression of the enzymes that regulate synthesis and degradation of S1P. Not only do many growth factors and cytokines stimulate S1P production, leading to transactivation of S1P receptors, ligation of S1P receptors by S1P can also transactivate growth factor tyrosine kinase receptors and stimulate growth factor and cytokine signaling cascades. This review discusses the mechanisms involved in cross-talk between S1P, cytokines, and growth factors and the impact of that cross-talk on cell signaling and cell biology.

Anti-apoptotic effect of sphingosine-1-phosphate and platelet-derived growth factor in human embryonic stem cells

Human embryonic stem (hES) cells hold great promise for use in regenerative medicine. However, technologies first need to be established to maintain hES cells efficiently in vitro. Understanding the signaling networks involved in hES cell maintenance will prove to be essential to the development of such culture systems. Previously, we described a serum-free medium capable of supporting prolonged hES cell maintenance using sphingosine-1-phosphate (S1P) and platelet-derived growth factor (PDGF). Here, we describe an anti-apoptotic effect of S1P and PDGF in hES cells and demonstrate a direct effect of S1P in preventing hES cell apoptosis. Western blot analysis shows that S1P stimulates the phosphorylation of the mitogen-activated protein (MAP) kinases Erk1/2 but not of Akt, whereas PDGF stimulates both Erk1/2 and Akt phosphorylation. Moreover, our study suggests that the Erk1/2 and PI3K/Akt signaling pathways act independently of each other. Furthermore, neither S1P nor PDGF modify intracellular calcium concentration ([Ca(2+)]( i )) and Smad2 phosphorylation. Using pharmacological inhibitors of Erk1/2 and PI3K, our results demonstrate a critical role of the Erk1/2 and PI3K/Akt signaling pathways in mediating the anti-apoptotic effect of S1P and PDGF on hES cells. However, inhibition of the mammalian target of rapamycin (mTOR), a common downstream effector of Erk1/2 and PI3K/Akt, has no effect on hES cell apoptosis.

Sphingosine kinase 1 regulates differentiation of human and mouse lung fibroblasts mediated by TGF-beta1

Transforming growth factor beta (TGF-beta) contributes to the progression of pulmonary fibrosis through up-regulation of alpha-smooth muscle actin (alpha-SMA) as lung myofibroblast differentiation. Bioactive sphingosine 1-phosphate (S1P) has been shown to mimic TGF-beta signals; however, the function of S1P in lung fibrotic process has not been well documented. We found, in a mouse model of bleomycin lung fibrosis, that SPHK1 and alpha-SMA were colocalized within lung fibrotic foci and that these expressions were significantly increased in primary cultured fibroblasts. Using human lung fibroblasts WI-38, we explored the rationale of sphingosine kinase (SPHK) with TGF-beta1 stimulation. SPHK inhibitors and small interference RNA (siRNA) targeted SPHK1 decreased alpha-SMA and fibronectin expression up-regulated by TGF-beta1. In the meantime, SPHK1 inhibition did not affect smad2 phosphorylation in response to TGF-beta1. Then we examined whether S1P receptors transactivation may affect TGF-beta signals. siRNA against S1P(2) and S1P(3), but not S1P(1), reduced alpha-SMA expression as well as Y-27632, Rho kinase inhibitor. We also detected activation of Rho GTPase upon stimulation of TGF-beta1 on the cell membrane where S1P(2) or S1P(3) was overexpressed. These data suggested that SPHK1 activation by TGF-beta1 leads to Rho-associated myofibroblasts differentiation mediated by transactivated S1P receptors in the lung fibrogenic process.

Migration of CD4 T cells and dendritic cells toward sphingosine 1-phosphate (S1P) is mediated by different receptor subtypes: S1P regulates the functions of murine mature dendritic cells via S1P receptor type 3

Dendritic cells (DCs) and lymphocytes are known to show a migratory response to the phospholipid mediator, sphingosine 1-phosphate (S1P). However, it is unclear whether the same S1P receptor subtype mediates the migration of lymphocytes and DCs toward S1P. In this study, we investigated the involvement of S1P receptor subtypes in S1P-induced migration of CD4 T cells and bone marrow-derived DCs in mice. A potent S1P receptor agonist, the (S)-enantiomer of FTY720-phosphate [(S)-FTY720-P], at 0.1 nM or higher and a selective S1P receptor type 1 (S1P(1)) agonist, SEW2871, at 0.1 muM or higher induced a dose-dependent down-regulation of S1P(1). The pretreatment with these compounds resulted in a significant inhibition of mouse CD4 T cell migration toward S1P. Thus, it is revealed that CD4 T cell migration toward S1P is highly dependent on S1P(1). Mature DCs, when compared with CD4 T cells or immature DCs, expressed a relatively higher level of S1P(3) mRNA. S1P at 10-1000 nM induced a marked migration and significantly enhanced the endocytosis of FITC-dextran in mature but not immature DCs. Pretreatment with (S)-FTY720-P at 0.1 microM or higher resulted in a significant inhibition of S1P-induced migration and endocytosis in mature DCs, whereas SEW2871 up to 100 microM did not show any clear effect. Moreover, we found that S1P-induced migration and endocytosis were at an extremely low level in mature DCs prepared from S1P(3)-knockout mice. These results indicate that S1P regulates migration and endocytosis of murine mature DCs via S1P(3) but not S1P(1).

Diverse signaling pathways regulate fibroblast differentiation and transformation through Rho kinase activation

This study examined the role of agonist-induced Rho kinase (ROCK) involvement in the morphological outcome of pulmonary-derived fibroblasts. Normal human lung fibroblasts (NHLF) spontaneously differentiate into network-like structures in a two-dimensional growth factor reduced Matrigel matrix-based assay. Sphingosine 1-phosphate (SPP), a bioactive phospholipid that regulates angiogenesis, inhibited fibroblast morphogenesis in a dose-dependent manner, virtually eliminating the presence of multi-cellular structures at 500 nM. Pretreatment with the Rho kinase-specific inhibitor, H1152, eradicated the high dose SPP-induced inhibition. Similarly, NHLFs transfected with Rho kinase siRNA prevented SPP-induced inhibition of the fibroblast morphogenesis. Alternatively, transforming growth factor-beta1 (TGF-beta1), a cytokine recognized as a key mediator of wound healing, terminally differentiates NHLF into myofibroblasts as evidenced by the expression of the smooth muscle cell isoform of alpha-actin (alpha-SMA). H1152 suppressed TGF-beta1-induced alpha-SMA expression in a dose-dependent manner. Similarly, treatment with Rho kinase siRNA reduced alpha-SMA expression by greater than 50%. SPP treatment had no effect on TGF-beta1-induced transformation into myofibroblasts, and TGF-beta1 treatment did not alter fibroblast morphogenesis. This study suggests a dual regulatory role for Rho kinase in cellular regulation of fibroblasts in which SPP-induced Rho kinase activation via a G-protein coupled receptor suppresses fibroblast morphogenesis while TGF-beta1-induced Rho kinase activation through a serine/threonine kinase receptor culminates in transformation into myofibroblasts.

FTY720 ameliorates Th1-mediated colitis in mice by directly affecting the functional activity of CD4+CD25+ regulatory T cells

Following the present concepts, the synthetic sphingosine analog of myriocin FTY720 alters migration and homing of lymphocytes via sphingosine 1-phosphate receptors. However, several studies indicate that the immunosuppressive properties of FTY720 may alternatively be due to tolerogenic activities via modulation of dendritic cell differentiation or based on direct effects on CD4(+)CD25(+) regulatory T cells (Treg). As Treg play an important role for the cure of inflammatory colitis, we used the Th1-mediated 2,4,6-trinitrobenzene sulfonic acid (TNBS) colitis model to address the therapeutic potential of FTY720 in vivo. A rectal enema of TNBS was given to BALB/c mice. FTY720 was administered i.p. from days 0 to 3 or 3 to 5. FTY720 substantially reduced all clinical, histopathologic, macroscopic, and microscopic parameters of colitis analyzed. The therapeutic effects of FTY720 were associated with a down-regulation of IL-12p70 and subsequent Th1 cytokines. Importantly, FTY720 treatment resulted in a prominent up-regulation of FoxP3, IL-10, TGFbeta, and CTLA4. Supporting the hypothesis that FTY720 directly affects functional activity of CD4(+)CD25(+) Treg, we measured a significant increase of CD25 and FoxP3 expression in isolated lamina propria CD4(+) T cells of FTY720-treated mice. The impact of FTY720 on Treg induction was further confirmed by concomitant in vivo blockade of CTLA4 or IL-10R which significantly abrogated its therapeutic activity. In conclusion, our data provide clear evidence that in addition to its well-established effects on migration FTY720 leads to a specific down-regulation of proinflammatory signals while simultaneously inducing functional activity of CD4(+)CD25(+) Treg. Thus, FTY720 may offer a promising new therapeutic strategy for the treatment of IBD.

FTY720 suppresses interleukin-1beta-induced secretory phospholipase A2 expression in renal mesangial cells by a transcriptional mechanism

BACKGROUND AND PURPOSE

FTY720 is a potent immunomodulatory prodrug that is converted to its active phosphorylated form by a sphingosine kinase. Here we have studied whether FTY720 mimicked the action of sphingosine-1-phosphate (S1P) and exerted an anti-inflammatory potential in renal mesangial cells.

EXPERIMENTAL APPROACH

Prostaglandin E(2) (PGE(2)) was quantified by an enzyme-linked immunosorbent-assay. Secretory phospholipase A(2) (sPLA(2)) protein was detected by Western blot analyses. mRNA expression was determined by Northern blot analysis and sPLA(2)-promoter activity was measured by a luciferase-reporter-gene assay.

KEY RESULTS

Stimulation of cells for 24 h with interleukin-1beta (IL-1beta) is known to trigger increased PGE(2) formation which coincides with an induction of the mRNA for group-IIA-sPLA(2) and protein expression. FTY720 dose-dependently suppressed IL-1beta-induced IIA-sPLA(2) protein secretion and activity in the supernatant. This effect is due to a suppression of cytokine-induced sPLA(2) mRNA expression which results from a reduced promoter activity. As a consequence of suppressed sPLA(2) activity, PGE(2) formation is also reduced by FTY720. Mechanistically, the FTY720-suppressed sPLA(2) expression results from an activation of the TGFbeta/Smad signalling cascade since inhibition of the TGFbeta receptor type I by a specific kinase inhibitor reverses the FTY720-mediated decrease of sPLA(2) protein expression and sPLA(2) promoter activity.

CONCLUSIONS AND IMPLICATIONS

In summary, our data show that FTY720 was able to mimic the anti-inflammatory activity of TGFbeta and blocked cytokine-triggered sPLA(2) expression and subsequent PGE(2) formation. Thus, FTY720 may exert additional in vivo effects besides the well reported immunomodulation and its anti-inflammatory potential should be considered.

Immunomodulator FTY720 induces myofibroblast differentiation via the lysophospholipid receptor S1P3 and Smad3 signaling

The novel immunomodulator FTY720 is an effective immunosuppressive agent in experimental models of transplantation and autoimmunity and is currently undergoing phase III clinical trials for multiple sclerosis. Phosphorylated FTY720 is a structural analogue of sphingosine 1-phosphate (S1P) and therefore acts as a high-affinity agonist at four of the five G protein-coupled S1P receptors. It has been well established that there exists a crosstalk between S1P and transforming growth factor (TGF)-beta signaling. Because TGF-beta is the most prominent inductor of fibrosis and myofibroblasts are primarily responsible for excessive matrix protein formation, we examined whether FTY720, in analogy to TGF-beta, induces differentiation of fibroblasts into myofibroblasts. Indeed, FTY720 provoked myofibroblast differentiation comparable with that of TGF-beta. For biological efficacy, FTY720 required endogenous phosphorylation because inhibition of sphingosine kinase completely prevented FTY720 from inducing the differentiation process. Moreover, we identified the lysophospholipid receptor S1P3 as the crucial receptor subtype for FTY720-induced myofibroblast differentiation because the effect was abolished in fibroblasts isolated from S1P3 knockout mice. Finally, we determined that downstream of S1P3 signaling Smad3 activation is essential for myofibroblast differentiation in response to FTY720. Thus, FTY720 may have adverse fibrotic effects related to its activity on S1P3 signaling.

The immunomodulator FTY720 and its phosphorylated derivative activate the Smad signalling cascade and upregulate connective tissue growth factor and collagen type IV expression in renal mesangial cells

1.--The immunomodulating agent FTY720 is a substrate for the sphingosine kinase and the phosphorylated form is able to bind to sphingosine 1-phosphate (S1P) receptors. In this study, we show that exposure of renal mesangial cells to phospho-FTY720 leads to a rapid and transient activation of several protein kinase cascades, including the mitogen- and stress-activated protein kinases. The nonphosphorylated FTY720 also increased MAPK phosphorylation, but with a reduced potency and a more delayed time course. In addition, phospho-FTY720 and FTY720 are able to increase phosphorylation of Smad proteins which are classical members of the transforming growth factor-beta (TGF-beta) signalling device, thus suggesting a crosstalk between FTY720 and TGF-beta signalling. 2.--Pretreatment with the S1P(3) receptor antagonist suramin inhibits FTY720 and phospho-FTY720-induced Smad phosphorylation, whereas pertussis toxin pretreatment, which blocks G(i/0) proteins, has no effect on Smad phosphorylation. 3.--Since TGF-beta is a potent profibrotic cytokine in mesangial cells and upregulates the connective tissue growth factor (CTGF) and collagen as important hallmarks in the fibrotic sequelae, we investigated whether FTY720 and phospho-FTY720 are able to mimic these effects of TGF-beta. Indeed, FTY720 and phospho-FTY720 markedly upregulate CTGF and collagen type IV protein expressions. In addition, the tissue inhibitor of metalloproteinase-1 is transcriptionally activated by FTY720, whereas cytokine-induced matrix metalloproteinase-9 is down-regulated by FTY720. 4.--Depletion of the TGF-beta receptor type II by the siRNA transfection technique blocks not only Smad phosphorylation but also CTGF upregulation. Similarly, Smad-4 depletion by siRNA transfection also abrogates CTGF upregulation induced by FTY720 and phospho-FTY720. 5.--In summary, our data show that FTY720 and phospho-FTY720 not only activate the Smad signalling cascade in mesangial cells, but also upregulate the expression of CTGF and collagen. These findings suggest that FTY720 may have additional effects besides the established immunomodulatory action and, importantly, a profibrotic activity has to be considered in future experimental approaches.

TLR-ligand stimulated interleukin-23 subunit expression and assembly is regulated differentially in murine plasmacytoid and myeloid dendritic cells

Interleukin-23 (IL-23) is a heterodimeric cytokine composed of the p40 and p19 subunits, the first of which is also part of the IL-12 heterodimer. IL-23 induces a unique T helper cell subset to produce IL-17, which plays a critical and IL-12/IFN-gamma-independent role in autoimmunity. Plasmacytoid dendritic cells (pDC), as opposed to myeloid DC (mDC) and the closely related epidermal Langerhans cells (LC), exhibit a specific and broad range of pro-inflammatory cytokine secretion, with type I interferons representing a typical difference to classical mDC and LC. In this study we show that upon treatment with a selection of ligands for Toll-like receptor (TLR) 3, 4, 7, and 9, only mDC and LC but not pDC secreted IL-23. While pDC produced both mRNA and protein of the p40 subunit, the lack of bioactive heterodimeric IL-23 protein release was related to the fact that in these cells only the p19 mRNA was expressed which was not translated into protein. In addition to these differential findings in both DC subsets a novel p19 splice variant was identified. This analysis of transcriptional and/or post-transcriptional regulation of the IL-23 subunits p40 and p19 may help to understand the complex regulation of heterodimeric cytokines and the overlapping but distinct functions of IL-12 and IL-23. It supports the hypothesis of a coordinated adaptive immune response based on a finely tuned contribution of these cytokines by different mouse DC subsets.