Regulation of CC ligand 5/RANTES by acid sphingomyelinase and acid ceramidase

Acid sphingomyelinase modulates anxiety-like behavior likely through toll-like receptor signaling pathway

Recent studies have shown that abnormal activity of acid sphingomyelinase (Asm) has been associated with a range of psychiatric disorders including schizophrenia and depression. However, the role of Asm in the regulation of anxiety remains unclear. In the present study, we employed Asm-knockout (Asm KO) mice to investigate the association between Asm and anxiety using behavioral tests, RNA sequencing, q-PCR, immunohistochemical staining, and other methods. The behavioral results showed that Asm KO mice exhibit enhanced anxiety-like behaviors, such as restricted activity, reduced cumulative times in the central area, diminished exploratory interest, delayed latency to feed, through behavioral tests including open field, novelty-suppressed feeding test, elevated plus maze test, ect. Transcriptional profiling combined with bioinformatics analysis revealed the upregulation of Toll-like receptor signaling pathway related gene including Tlr1/2, Ccl3, Ccl4, Ccl5 and Cd86 in Asm KO mice, which was further confirmed by the detection of activated microglia and astrocytes through iba-1 and GFAP immunohistochemical staining. Collectively, our findings uncover a role for Asm in regulating anxiety-like behavior and suggest that it may be essential for the maintenance of emotional stability, indicating its potential as a promising target for treating anxiety disorders.

Fish ELOVL7a is involved in virus replication via lipid metabolic reprogramming

The elongation of very long chain fatty acids (ELOVL) proteins are key rate-limiting enzymes that catalyze fatty acid synthesis to form long chain fatty acids. ELOVLs also play regulatory roles in the lipid metabolic reprogramming induced by mammalian viruses. However, little is known about the roles of fish ELOVLs during virus infection. Here, a homolog of ELOVL7 was cloned from Epinephelus coioides (EcELOVL7a), and its roles in red-spotted grouper nervous necrosis virus (RGNNV) and Singapore grouper iridovirus (SGIV) infection were investigated. The transcription level of EcELOVL7a was significantly increased upon RGNNV and SGIV infection or other pathogen-associated molecular patterns stimulation in grouper spleen (GS) cells. Subcellular localization analysis showed that EcELOVL7a encoded an endoplasmic reticulum (ER) related protein. Overexpression of EcELOVL7a promoted the viral production and virus release during SGIV and RGNNV infection. Furthermore, the lipidome profiling showed that EcELOVL7a overexpression reprogrammed cellular lipid components in vitro, evidenced by the increase of glycerophospholipids, sphingolipids and glycerides components. In addition, VLCFAs including FFA (20:2), FFA (20:4), FFA (22:4), FFA (22:5) and FFA (24:0), were enriched in EcELOVL7a overexpressed cells. Consistently, EcELOVL7a overexpression upregulated the transcription level of the key lipid metabolic enzymes, including fatty acid synthase (FASN), phospholipase A 2α (PLA 2α), and cyclooxygenases -2 (COX-2), LPIN1, and diacylglycerol acyltransferase 1α (DGAT1α). Together, our results firstly provided the evidence that fish ELOVL7a played an essential role in SGIV and RGNNV replication by reprogramming lipid metabolism.

Tricarboxylic acid (TCA) cycle, sphingolipid, and phosphatidylcholine metabolism are dysregulated in T. gondii infection-induced cachexia

Cachexia is a life-threatening disease characterized by chronic, inflammatory muscle wasting and systemic metabolic impairment. Despite its high prevalence, there are no efficacious therapies for cachexia. Mice chronically infected with the protozoan parasite Toxoplasma gondii represent a novel animal model recapitulating the chronic kinetics of cachexia. To understand how perturbations to metabolic tissue homeostasis influence circulating metabolite availability we used mass spectrometry analysis. Despite the significant reduction in circulating triacylglycerides, non-esterified fatty acids, and glycerol, sphingolipid long-chain bases and a subset of phosphatidylcholines (PCs) were significantly increased in the sera of mice with T. gondii infection-induced cachexia. In addition, the TCA cycle intermediates α-ketoglutarate, 2-hydroxyglutarate, succinate, fumarate, and malate were highly depleted in cachectic mouse sera. Sphingolipids and their de novo synthesis precursors PCs are the major components of the mitochondrial membrane and regulate mitochondrial function consistent with a causal relationship in the energy imbalance driving T. gondii-induced chronic cachexia.

Sphingolipids and impaired hypoxic stress responses in Huntington disease

Huntington disease (HD) is a debilitating, currently incurable disease. Protein aggregation and metabolic deficits are pathological hallmarks but their link to neurodegeneration and symptoms remains debated. Here, we summarize alterations in the levels of different sphingolipids in an attempt to characterize sphingolipid patterns specific to HD, an additional molecular hallmark of the disease. Based on the crucial role of sphingolipids in maintaining cellular homeostasis, the dynamic regulation of sphingolipids upon insults and their involvement in cellular stress responses, we hypothesize that maladaptations or blunted adaptations, especially following cellular stress due to reduced oxygen supply (hypoxia) contribute to the development of pathology in HD. We review how sphingolipids shape cellular energy metabolism and control proteostasis and suggest how these functions may fail in HD and in combination with additional insults. Finally, we evaluate the potential of improving cellular resilience in HD by conditioning approaches (improving the efficiency of cellular stress responses) and the role of sphingolipids therein. Sphingolipid metabolism is crucial for cellular homeostasis and for adaptations following cellular stress, including hypoxia. Inadequate cellular management of hypoxic stress likely contributes to HD progression, and sphingolipids are potential mediators. Targeting sphingolipids and the hypoxic stress response are novel treatment strategies for HD.

Ceramide Transfer Protein (CERT): An Overlooked Molecular Player in Cancer

Sphingolipids are a class of essential lipids implicated in constructing cellular membranes and regulating nearly all cellular functions. Sphingolipid metabolic network is centered with the ceramide-sphingomyelin axis. Ceramide is well-recognized as a pro-apoptotic signal; while sphingomyelin, as the most abundant type of sphingolipids, is required for cell growth. Therefore, the balance between these two sphingolipids can be critical for cancer cell survival and functioning. Ceramide transfer protein (CERT) dictates the ratio of ceramide to sphingomyelin within the cell. It is the only lipid transfer protein that specifically delivers ceramide from the endoplasmic reticulum to the Golgi apparatus, where ceramide serves as the substrate for sphingomyelin synthesis. In the past two decades, an increasing body of evidence has suggested a critical role of CERT in cancer, but much more intensive efforts are required to draw a definite conclusion. Herein, we review all research findings of CERT, focusing on its molecular structure, cellular functions and implications in cancer. This comprehensive review of CERT will help to better understand the molecular mechanism of cancer and inspire to identify novel druggable targets.

Physiological functions and therapeutic applications of neutral sphingomyelinase and acid sphingomyelinase

Sphingomyelin (SM) can be converted into ceramide (Cer) by neutral sphingomyelinase (NSM) and acid sphingomyelinase (ASM). Cer is a second messenger of lipids and can regulate cell growth and apoptosis. Increasing evidence shows that NSM and ASM play key roles in many processes, such as apoptosis, immune function and inflammation. Therefore, NSM and ASM have broad prospects in clinical treatments, especially in cancer, cardiovascular diseases (such as atherosclerosis), nervous system diseases (such as Alzheimer's disease), respiratory diseases (such as chronic obstructive pulmonary disease) and the phenotype of dwarfisms in adolescents, playing a complex regulatory role. This review focuses on the physiological functions of NSM and ASM and summarizes their roles in certain diseases and their potential applications in therapy.

Ceramide launches an acute anti-adhesion pro-migration cell signaling program in response to chemotherapy

Chemotherapy has been reported to upregulate sphingomylinases and increase cellular ceramide, often linked to the induction to cell death. In this work, we show that sublethal doses of doxorubicin and vorinostat still increased cellular ceramide, which was located predominantly at the plasma membrane. To interrogate possible functions of this specific pool of ceramide, we used recombinant enzymes to mimic physiological levels of ceramide at the plasma membrane upon chemotherapy treatment. Using mass spectrometry and network analysis, followed by experimental confirmation, the results revealed that this pool of ceramide acutely regulates cell adhesion and cell migration pathways with weak connections to commonly established ceramide functions (eg, cell death). Neutral sphingomyelinase 2 (nSMase2) was identified as responsible for the generation of plasma membrane ceramide upon chemotherapy treatment, and both ceramide at the plasma membrane and nSMase2 were necessary and sufficient to mediate these "side" effects of chemotherapy on cell adhesion and migration. This is the first time a specific pool of ceramide is interrogated for acute signaling functions, and the results define plasma membrane ceramide as an acute signaling effector necessary and sufficient for regulation of cell adhesion and cell migration under chemotherapeutical stress.

Identification of an acid sphingomyelinase ceramide kinase pathway in the regulation of the chemokine CCL5

Acid sphingomyelinase (ASM) hydrolyzes sphingomyelin to produce the biologically active lipid ceramide. Previous studies have implicated ASM in the induction of the chemokine CCL5 in response to TNF-α however, the lipid mediator of this effect was not established. In the present study, we identified a novel pathway connecting ASM and ceramide kinase (CERK). The results show that TNF-α induces the formation of ceramide 1-phosphate (C-1-P) in a CERK-dependent manner. Silencing of CERK blocks CCL5 production in response to TNF-α. Interestingly, cells lacking ASM have decreased C-1-P production following TNF-α treatment, suggesting that ASM may be acting upstream of CERK. Functionally, ASM and CERK induce a highly concordant program of cytokine production and both are required for migration of breast cancer cells. Taken together, these data suggest ASM can produce ceramide which is then converted to C-1-P by CERK, and that C-1-P is required for production of CCL5 and several cytokines and chemokines, with roles in cell migration. These results highlight the diversity in action of ASM through more than one bioactive sphingolipid.

Sphingolipids and their metabolism in physiology and disease

Studies of bioactive lipids in general and sphingolipids in particular have intensified over the past several years, revealing an unprecedented and unanticipated complexity of the lipidome and its many functions, which rivals, if not exceeds, that of the genome or proteome. These results highlight critical roles for bioactive sphingolipids in most, if not all, major cell biological responses, including all major cell signalling pathways, and they link sphingolipid metabolism to key human diseases. Nevertheless, the fairly nascent field of bioactive sphingolipids still faces challenges in its biochemical and molecular underpinnings, including defining the molecular mechanisms of pathway and enzyme regulation, the study of lipid-protein interactions and the development of cellular probes, suitable biomarkers and therapeutic approaches.

Ceramide activates lysosomal cathepsin B and cathepsin D to attenuate autophagy and induces ER stress to suppress myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are immune suppressive cells that are hallmarks of human cancer. MDSCs inhibit cytotoxic T lymphocytes (CTLs) and NK cell functions to promote tumor immune escape and progression, and therefore are considered key targets in cancer immunotherapy. Recent studies determined a key role of the apoptosis pathways in tumor-induced MDSC homeostasis and it is known that ceramide plays a key role in regulation of mammalian cell apoptosis. In this study, we aimed to determine the efficacy and underlying molecular mechanism of ceramide in suppression of MDSCs. Treatment of tumor-bearing mice with LCL521, a lysosomotropic inhibitor of acid ceramidase, significantly decreased MDSC accumulation in vivo. Using a MDSC-like myeloid cell model, we determined that LCL521 targets lysosomes and increases total cellular C16 ceramide level. Although MDSC-like cells have functional apoptosis pathways, LCL521-induced MDSC death occurs in an apoptosis- and necroptosis-independent mechanism. LCL521 treatment resulted in an increase in the number of autophagic vesicles, heterolysosomes and swollen ERs. Finally, concomitant inhibition of cathepsin B and cathepsin D was required to significantly decrease LCL521-induced cell death. Our observations indicate that LCL521 targets lysosomes to activate cathepsin B and cathepsin D, resulting in interrupted autophagy and ER stress that culminates in MDSC death. Therefore, a ceramidase inhibitor is potentially an effective adjunct therapeutic agent for suppression of MDSCs to enhance the efficacy of CTL-based cancer immunotherapy.

Loss of acid ceramidase in myeloid cells suppresses intestinal neutrophil recruitment

Bioactive sphingolipids are modulators of immune processes and their metabolism is often dysregulated in ulcerative colitis, a major category of inflammatory bowel disease (IBD). While multiple axes of sphingolipid metabolism have been investigated to delineate mechanisms regulating ulcerative colitis, the role of acid ceramidase (AC) in intestinal inflammation is yet to be characterized. Here we demonstrate that AC expression is elevated selectively in the inflammatory infiltrate in human and murine colitis. To probe for mechanistic insight into how AC up-regulation can impact intestinal inflammation, we investigated the selective loss of AC expression in the myeloid population. Using a model of intestinal epithelial injury, we demonstrate that myeloid AC conditional knockout mice exhibit impairment of neutrophil recruitment to the colon mucosa as a result of defective cytokine and chemokine production. Furthermore, the loss of myeloid AC protects from tumor incidence in colitis-associated cancer (CAC) and inhibits the expansion of neutrophils and granulocytic myeloid-derived suppressor cells in the tumor microenvironment. Collectively, our results demonstrate a tissue-specific role for AC in regulating neutrophilic inflammation and cytokine production. We demonstrate novel mechanisms of how granulocytes are recruited to the colon that may have therapeutic potential in intestinal inflammation, IBD, and CAC.-Espaillat, M. P., Snider, A. J., Qiu, Z., Channer, B., Coant, N., Schuchman, E. H., Kew, R. R., Sheridan, B. S., Hannun, Y. A., Obeid, L. M. Loss of acid ceramidase in myeloid cells suppresses intestinal neutrophil recruitment.

Comparative Proteomics of Purified Pathogen Vacuoles Correlates Intracellular Replication of Legionella pneumophila with the Small GTPase Ras-related protein 1 (Rap1)

Legionella pneumophila is an opportunistic bacterial pathogen that causes a severe lung infection termed "Legionnaires' disease." The pathogen replicates in environmental protozoa as well as in macrophages within a unique membrane-bound compartment, the Legionella-containing-vacuole (LCV). LCV formation requires the bacterial Icm/Dot type IV secretion system, which translocates ca. 300 "effector proteins" into host cells, where they target distinct host factors. The L. pneumophila "pentuple" mutant (Δpentuple) lacks 5 gene clusters (31% of the effector proteins) and replicates in macrophages but not in Dictyostelium discoideum amoeba. To elucidate the host factors defining a replication-permissive compartment, we compare here the proteomes of intact LCVs isolated from D. discoideum or macrophages infected with Δpentuple or the parental strain Lp02. This analysis revealed that the majority of host proteins are shared in D. discoideum or macrophage LCVs containing the mutant or the parental strain, respectively, whereas some proteins preferentially localize to distinct LCVs. The small GTPase Rap1 was identified on D. discoideum LCVs containing strain Lp02 but not the Δpentuple mutant and on macrophage LCVs containing either strain. The localization pattern of active Rap1 on D. discoideum or macrophage LCVs was confirmed by fluorescence microscopy and imaging flow cytometry, and the depletion of Rap1 by RNA interference significantly reduced the intracellular growth of L. pneumophila Thus, comparative proteomics identified Rap1 as a novel LCV host component implicated in intracellular replication of L. pneumophila.

Cadmium attenuates the macrophage response to LPS through inhibition of the NF-κB pathway

Chronic obstructive pulmonary disease (COPD) in the U.S. is primarily caused by cigarette smoking. COPD patients are highly susceptible to respiratory infections in part due to alveolar macrophage dysfunction despite a substantial increase in macrophages in the lung. Cadmium (Cd) is a toxic metal that is concentrated within tobacco and accumulates in the lung of smokers. We hypothesized that Cd uptake into macrophages alters immune function thereby impairing the macrophage response to invading pathogens. Our hypothesis was tested by comparing primary human monocytes and macrophages, primary mouse bronchoalveolar lavage myeloid cells, and related cell lines. Strikingly, Cd exposure followed by LPS stimulation resulted in a dose-dependent, significant decrease in nuclear p65 activity in macrophages that was not observed in monocytes. This corresponded with Cd-mediated inhibition of IKKβ and an impaired ability to transcribe and release cytokines in response to LPS challenge in vivo. These findings provide novel evidence that Cd has the capacity to disrupt macrophage immune function compared with monocytes. Importantly, Cd results in immune dysfunction in macrophages through inhibition of the NF-κB signaling pathway. Based on these findings, we provide new evidence that Cd contributes to immune dysfunction in the lung of COPD subjects and may increase susceptibility to infection.

Lack of Acid Sphingomyelinase Induces Age-Related Retinal Degeneration

Background

Mutations of acid sphingomyelinase (ASMase) cause Niemann–Pick diseases type A and B, which are fatal inherited lipid lysosomal storage diseases, characterized with visceral organ abnormalities and neurodegeneration. However, the effects of suppressing retinal ASMase expression are not understood. The goal of this study was to determine if the disruption of ASMase expression impacts the retinal structure and function in the mouse, and begin to investigate the mechanisms underlying these abnormalities.

Methods

Acid sphingomyelinase knockout (ASMase KO) mice were utilized to study the roles of this sphingolipid metabolizing enzyme in the retina. Electroretinogram and morphometric analysis were used to assess the retinal function and structure at various ages. Sphingolipid profile was determined by liquid chromatography-mass spectrometry. Western blots evaluated the level of the autophagy marker LC3-II.

Results

When compared to control animals, ASMase KO mice exhibited significant age-dependent reduction in ERG a- and b-wave amplitudes. Associated with these functional deficits, morphometric analysis revealed progressive thinning of retinal layers; however, the most prominent degeneration was observed in the photoreceptor and outer nuclear layer. Additional analyses of ASMase KO mice revealed early reduction in ERG c-wave amplitudes and increased lipofuscin accumulation in the retinal pigment epithelium (RPE). Sphingolipid analyses showed abnormal accumulation of sphingomyelin and sphingosine in ASMase KO retinas. Western blot analyses showed a higher level of the autophagosome marker LC3-II.

Conclusions

These studies demonstrate that ASMase is necessary for the maintenance of normal retinal structure and function. The early outer retinal dysfunction, outer segment degeneration, accumulation of lipofuscin and autophagosome markers provide evidence that disruption of lysosomal function contributes to the age-dependent retinal degeneration exhibited by ASMase KO mice.

S1P-induced airway smooth muscle hyperresponsiveness and lung inflammation in vivo: molecular and cellular mechanisms

BACKGROUND AND PURPOSE

Sphingosine-1-phosphate (S1P) has been shown to be involved in the asthmatic disease as well in preclinical mouse experimental models of this disease. The aim of this study was to understand the mechanism(s) underlying S1P effects on the lung.

EXPERIMENTAL APPROACH

BALB/c, mast cell-deficient and Nude mice were injected with S1P (s.c.) on days 0 and 7. Functional, molecular and cellular studies were performed.

KEY RESULTS

S1P administration to BALB/c mice increased airway smooth muscle reactivity, mucus production, PGD2 , IgE, IL-4 and IL-13 release. These features were associated to a higher recruitment of mast cells to the lung. Mast cell-deficient Kit (W) (-sh/) (W) (-sh) mice injected with S1P did not display airway smooth muscle hyper-reactivity. However, lung inflammation and IgE production were still present. Treatment in vivo with the anti-CD23 antibody B3B4, which blocks IgE production, inhibited both S1P-induced airway smooth muscle reactivity in vitro and lung inflammation. S1P administration to Nude mice did not elicit airway smooth muscle hyper-reactivity and lung inflammation. Naïve (untreated) mice subjected to the adoptive transfer of CD4+ T-cells harvested from S1P-treated mice presented all the features elicited by S1P in the lung.

CONCLUSIONS AND IMPLICATIONS

S1P triggers a cascade of events that sequentially involves T-cells, IgE and mast cells reproducing several asthma-like features. This model may represent a useful tool for defining the role of S1P in the mechanism of action of currently-used drugs as well as in the development of new therapeutic approaches for asthma-like diseases.

Sphingolipid metabolites in inflammatory disease

Sphingolipids are ubiquitous building blocks of eukaryotic cell membranes. Progress in our understanding of sphingolipid metabolism, state-of-the-art sphingolipidomic approaches and animal models have generated a large body of evidence demonstrating that sphingolipid metabolites, particularly ceramide and sphingosine-1-phosphate, are signalling molecules that regulate a diverse range of cellular processes that are important in immunity, inflammation and inflammatory disorders. Recent insights into the molecular mechanisms of action of sphingolipid metabolites and new perspectives on their roles in regulating chronic inflammation have been reported. The knowledge gained in this emerging field will aid in the development of new therapeutic options for inflammatory disorders.

Defining a role for acid sphingomyelinase in the p38/interleukin-6 pathway

Acid sphingomyelinase (ASM) is one of the key enzymes involved in regulating the metabolism of the bioactive sphingolipid ceramide in the sphingolipid salvage pathway, yet defining signaling pathways by which ASM exerts its effects has proven difficult. Previous literature has implicated sphingolipids in the regulation of cytokines such as interleukin-6 (IL-6), but the specific sphingolipid pathways and mechanisms involved in inflammatory signaling need to be further elucidated. In this work, we sought to define the role of ASM in IL-6 production because our previous work showed that a parallel pathway of ceramide metabolism, acid β-glucosidase 1, negatively regulates IL-6. First, silencing ASM with siRNA abrogated IL-6 production in response to the tumor promoter, 4β-phorbol 12-myristate 13-acetate (PMA), in MCF-7 cells, in distinction to acid β-glucosidase 1 and acid ceramidase, suggesting specialization of the pathways. Moreover, treating cells with siRNA to ASM or with the indirect pharmacologic inhibitor desipramine resulted in significant inhibition of TNFα- and PMA-induced IL-6 production in MDA-MB-231 and HeLa cells. Knockdown of ASM was found to significantly inhibit PMA-dependent IL-6 induction at the mRNA level, probably ruling out mechanisms of translation or secretion of IL-6. Further, ASM knockdown or desipramine blunted p38 MAPK activation in response to TNFα, revealing a key role for ASM in activating p38, a signaling pathway known to regulate IL-6 induction. Last, knockdown of ASM dramatically blunted invasion of HeLa and MDA-MB-231 cells through Matrigel. Taken together, these results demonstrate that ASM plays a critical role in p38 signaling and IL-6 synthesis with implications for tumor pathobiology.

Acid sphingomyelinase determines melanoma progression and metastatic behaviour via the microphtalmia-associated transcription factor signalling pathway

Melanoma is a rapidly growing and highly metastatic cancer with high mortality rates, for which a resolutive treatment is lacking. Identification of novel therapeutic strategies and biomarkers of tumour stage is thus of particular relevance. We report here on a novel biomarker and possible candidate therapeutic target, the sphingolipid metabolising enzyme acid sphingomyelinase (A-SMase). A-SMase expression correlates inversely with tumour stage in human melanoma biopsies. Studies in a mouse model of melanoma and on cell lines derived from mouse and human melanomas demonstrated that A-SMase levels of expression actually determine the malignant phenotype of melanoma cells in terms of pigmentation, tumour progression, invasiveness and metastatic ability. The action of A-SMase is mediated by the activation of the extracellular signal-regulated kinase, the subsequent proteasomal degradation of the Microphtalmia-associated transcription factor (Mitf) and inhibition of cyclin-dependent kinase 2, Bcl-2 and c-Met, downstream targets of Mitf involved in tumour cell proliferation, survival and metastatisation.

Evaluation of the role of secretory sphingomyelinase and bioactive sphingolipids as biomarkers in hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a rare systemic inflammatory syndrome that results from unrestrained immune cell activation. Despite significant advances in the understanding of the pathophysiology of HLH, interventions remain limited for this often-fatal condition. Secretory sphingomyelinase (S-SMase) is a pro-inflammatory lipid hydrolase that is upregulated in several inflammatory conditions, including HLH. S-SMase promotes the formation of ceramide, a bioactive lipid implicated in several human disease states. However, the role of the S-SMase/ceramide pathway in HLH remains unexplored. To further evaluate the role of S-SMase upregulation in HLH, we tested the serum of patients with HLH (n = 16; primary = 3, secondary = 13) and healthy control patients (n = 25) for serum S-SMase activity with tandem sphingolipid metabolomic profiling. Patients with HLH exhibited elevated levels of serum S-SMase activity, with concomitant elevations in several ceramide species and sphingosine, while levels of sphingosine-1-phosphate were significantly decreased. Importantly, the ratio of C16 -ceramide:sphingosine was uniquely elevated in HLH patients that died despite appropriate treatment, but remained low in HLH patients that survived, suggesting that this ratio may be of prognostic significance. Together, these results demonstrate upregulation of the S-SMase/ceramide pathway in HLH, and suggest that the balance of ceramide and sphingosine determine clinical outcomes in HLH. .

Sphingosine kinase 1 regulates tumor necrosis factor-mediated RANTES induction through p38 mitogen-activated protein kinase but independently of nuclear factor κB activation

Sphingosine kinase 1 (SK1) produces the pro-survival sphingolipid sphingosine 1-phosphate and has been implicated in inflammation, proliferation, and angiogenesis. Recent studies identified TRAF2 as a sphingosine 1-phosphate target, implicating SK1 in activation of the NF-κB pathway, but the functional consequences of this connection on gene expression are unknown. Here, we find that loss of SK1 potentiates induction of the chemokine RANTES (regulated on activation, normal T cell expressed and secreted; also known as CCL5) in HeLa cells stimulated with TNF-α despite RANTES induction being highly dependent on the NF-κB pathway. Additionally, we find that SK1 is not required for TNF-induced IKK phosphorylation, IκB degradation, nuclear translocation of NF-κB subunits, and transcriptional NF-κB activity. In contrast, loss of SK1 prevented TNF-induced phosphorylation of p38 MAPK, and inhibition of p38 MAPK, like SK1 knockdown, also potentiates RANTES induction. Finally, in addition to RANTES, loss of SK1 also potentiated the induction of multiple chemokines and cytokines in the TNF response. Taken together, these data identify a potential and novel anti-inflammatory function of SK1 in which chemokine levels are suppressed through SK1-mediated activation of p38 MAPK. Furthermore, in this system, activation of NF-κB is dissociated from SK1, suggesting that the interaction between these pathways may be more complex than currently thought.

Safety study of adeno-associated virus serotype 2-mediated human acid sphingomyelinase expression in the nonhuman primate brain

Niemann-Pick disease is a lysosomal storage disorder resulting from inherited deficiency in acid sphingomyelinase (ASM). Use of adeno-associated virus serotype 2 (AAV2) to deliver human acid sphingomyelinase (hASM) is currently being explored as a means to treat the devastating neurological features of NPD, which are refractory to traditional enzyme replacement therapy. In this study, we evaluated the long-term efficacy and safety of AAV2-hASM after direct infusion into the CNS of nonhuman primates. First, we confirmed the efficacy of AAV2-hASM in naive rats, which exhibited increased ASM expression and enzyme activity after infusion, without evidence of local or systemic toxicity. Next, the model was adapted to naive nonhuman primates (NHPs) with various doses of AAV2-hASM or saline delivered into the brainstem and both thalami. Strikingly, NHPs that received a high dose of AAV2-hASM displayed significant motor deficits that were not seen in low-dose animals in both the short-term (3-month) and long-term (9-month) treatment groups. In treated NHPs, ASM expression and activity were elevated with associated alterations in the sphingolipidomic profile in brain regions transduced with AAV2-hASM. Initial histological analysis indicated marked inflammatory reactions, and immunohistochemical analysis confirmed a robust inflammatory response. Importantly, pronounced upregulation of the chemokine CCL5, a target of ASM-mediated inflammatory signaling, was detected that correlated with the inflammatory response, providing a possible mechanism for hASM-associated toxicity. This study defines dose-dependent and dose-independent toxicities of AAV2-hASM in the naive primate brain, and reveals potential challenges in the design of a clinical trial.

Sphingosine 1-phosphate induces filopodia formation through S1PR2 activation of ERM proteins

Previously we demonstrated that the sphingolipids ceramide and S1P (sphingosine 1-phosphate) regulate phosphorylation of the ERM (ezrin/radixin/moesin) family of cytoskeletal proteins [Canals, Jenkins, Roddy, Hernande-Corbacho, Obeid and Hannun (2010) J. Biol. Chem. 285, 32476-3285]. In the present article, we show that exogenously applied or endogenously generated S1P (in a sphingosine kinase-dependent manner) results in significant increases in phosphorylation of ERM proteins as well as filopodia formation. Using phosphomimetic and non-phosphorylatable ezrin mutants, we show that the S1P-induced cytoskeletal protrusions are dependent on ERM phosphorylation. Employing various pharmacological S1PR (S1P receptor) agonists and antagonists, along with siRNA (small interfering RNA) techniques and genetic knockout approaches, we identify the S1PR2 as the specific and necessary receptor to induce phosphorylation of ERM proteins and subsequent filopodia formation. Taken together, the results demonstrate a novel mechanism by which S1P regulates cellular architecture that requires S1PR2 and subsequent phosphorylation of ERM proteins.

Regulation of the sphingosine kinase/sphingosine 1-phosphate pathway

Sphingolipids have emerged as pleiotropic signaling molecules with roles in numerous cellular and biological functions. Defining the regulatory mechanisms governing sphingolipid metabolism is crucial in order to develop a complete understanding of the biological functions of sphingolipid metabolites. The sphingosine kinase/ sphingosine 1-phosphate pathway was originally thought to function in the irreversible breakdown of sphingoid bases; however, in the last few decades it has materialized as an extremely important signaling pathway involved in a plethora of cellular events contributing to both normal and pathophysiological events. Recognition of the SK/S1P pathway as a second messaging system has aided in the identification of many mechanisms of its regulation; however, a cohesive, global understanding of the regulatory mechanisms controlling the SK/S1P pathway is lacking. In this chapter, the role of the SK/S1P pathway as a second messenger is discussed, and its role in mediating TNF-α- and EGF-induced biologies is examined. This work provides a comprehensive look into the roles and regulation of the sphingosine kinase/ sphingosine 1-phosphate pathway and highlights the potential of the pathway as a therapeutic target.

Identification and characterization of protein phosphatase 2C activation by ceramide

Ceramide is a bioactive sphingolipid with many associated biological outcomes, yet there is a significant gap in our current understanding of how ceramide mediates these processes. Previously, ceramide has been shown to activate protein phosphatase (PP) 1 and 2A. While continuing this line of work, a late fraction from a Mono-Q column was consistently observed to be activated by ceramide, yet PP1 and PP2A were undetectable in this fraction. Proteomic analysis of this fraction revealed the identity of the phosphatase to be PP2Cγ/PPM1G. This was consistent with our findings that PP2Cγ 1-eluted in a high salt fraction due to its strongly acidic domain, and 2-was insensitive to okadaic acid. Further characterization was performed with PP2Cα, which showed robust activation by C(6)-ceramide. Activation was specific for the erythro conformation of ceramide and the presence of the acyl chain and hydroxyl group at the first carbon. In order to demonstrate more physiological activation of PP2Cα by ceramide, phospho-p38δ was utilized as substrate. Indeed, PP2Cα induced the dephosphorylation of p38δ only in the presence of C(16)-ceramide. Taken together, these results show that the PP2C family of phosphatases is activated by ceramide, which may have important consequences in mediating the biological effects of ceramide.

Acid sphingomyelinase in macrophage biology

Macrophages play a central role in innate immune responses, in disposal of cholesterol, and in tissue homeostasis and remodeling. To perform these vital functions macrophages display high endosomal/lysosomal activities. Recent studies have highlighted that acid sphingomyelinase (ASMase), which generates ceramide from sphingomyelin, is involved in modulation of membrane structures and signal transduction in addition to its metabolic role in the lysosome. In this review, we bring together studies on ASMase, its different forms and locations that are necessary for the macrophage to accomplish its diverse functions. We also address the importance of ASMase to several disease processes that are mediated by activated macrophages.