Sphingomyelin Synthase 1 (SMS1) Downregulation Is Associated With Sphingolipid Reprogramming and a Worse Prognosis in Melanoma

Proteomic Analysis Highlights the Impact of the Sphingolipid Metabolizing Enzyme β-Galactosylceramidase on Mitochondrial Plasticity in Human Melanoma

Mitochondrial plasticity, marked by a dynamism between glycolysis and oxidative phosphorylation due to adaptation to genetic and microenvironmental alterations, represents a characteristic feature of melanoma progression. Sphingolipids play a significant role in various aspects of cancer cell biology, including metabolic reprogramming. Previous observations have shown that the lysosomal sphingolipid-metabolizing enzyme β-galactosylceramidase (GALC) exerts pro-oncogenic functions in melanoma. Here, mining the cBioPortal for a Cancer Genomics data base identified the top 200 nuclear-encoded genes whose expression is negatively correlated with GALC expression in human melanoma. Their categorization indicated a significant enrichment in Gene Ontology terms and KEGG pathways related to mitochondrial proteins and function. In parallel, proteomic analysis by LC-MS/MS of two GALC overexpressing human melanoma cell lines identified 98 downregulated proteins when compared to control mock cells. Such downregulation was confirmed at a transcriptional level by a Gene Set Enrichment Analysis of the genome-wide expression profiling data obtained from the same cells. Among the GALC downregulated proteins, we identified a cluster of 42 proteins significantly associated with GO and KEGG categorizations related to mitochondrion and energetic metabolism. Overall, our data indicate that changes in GALC expression may exert a significant impact on mitochondrial plasticity in human melanoma cells.

Differences in the phospholipid profile of melanocytes and melanoma cells irradiated with UVA and treated with cannabigerol and cannabidiol

UV radiation inducing mutations in melanocytes might cause melanoma. As changes in lipid composition and metabolism are associated with many types of cancer including skin cancer, we aimed to evaluate the effects of two phytocannabinoids cannabidiol (CBD) and cannabigerol (CBG), on changes in phospholipid and ceramide (CER) profiles induced by UVA irradiation in human melanocytes and melanoma. UVA radiation caused a significant up-regulation PC, PI and SM species and decrease of CERs content in both types of cells, while up-regulation of PEo was only observed in melanocytes. Exposure of UVA-irradiated melanocytes or melanoma cells to CBD and/or CBG led to significant decrease in relative content of PC, PI and SM specie; however, this effect was more pronounced in cancer cells. Interestingly, only in UVA-irradiated melanocytes and not in melanoma, PEo content was lowered after CBD treatment, while CBG led to additional up-regulation of PEo species. CBD and CBG used together caused decrease of zeta potential, inhibiting PS externalization, and different changes in relative contents of CER and SM species of irradiated and non-irradiated melanoma cells. Obtained results are quite promising due to CBD and CBG abilities to partial reverse pro-cancerogenic changes in phospholipid and CER profiles induced by UVA.

Sphingomyelin synthase 2 is a positive regulator of the CSF1R-STAT3 pathway in pancreatic cancer-associated macrophage

Background: Tumor-associated macrophages (TAMs) are one of the most abundant immune cells in the pancreatic cancer stroma and are related to the poor prognosis of pancreatic ductal adenocarcinoma (PDAC) patients. Therefore, targeting tumor-associated macrophages is a possible strategy for the treatment of pancreatic cancer.

Purpose: We would like to investigate the role of sphingomyelin synthase 2 (SMS2) and the effect of the synthase 2 selective inhibitor YE2 in TAMs and the pancreatic tumor microenvironment. In addition, we also would like to investigate the mechanism by which YE2 attenuates macrophage M2 polarization.

Methods: YE2 was utilized to treat macrophages (in vitro) and mice (in vivo). Western blotting and real-time PCR were used to detect the protein levels and mRNA levels of macrophage M2 polarization markers and their downstream signaling pathways. Sphingomyelin synthase 2 gene knockout (KO) mice and their controls were used to establish a PANC-02 orthotopic pancreatic cancer model, and immune cell infiltration in the tumor tissue was analyzed by immunohistochemistry (IHC).

Results: We found that sphingomyelin synthase 2 mRNA expression is positively correlated with tumor-associated macrophages, the immunosuppressive microenvironment, and poor prognosis in pancreatic ductal adenocarcinoma patients. Sphingomyelin synthase 2 deficiency was confirmed to have an inhibitory effect on the growth of orthotopic PANC-02 tumors in vivo. The deficiency not only reduced the infiltration of tumor-associated macrophages but also regulated other immune components in the tumor microenvironment. In tissue culture, YE2 inhibited M2 polarization in both bone marrow-derived macrophages (BMDMs) and THP-1 macrophages and eliminated the protumor effect of M2 macrophages. In the mouse model, YE2 treatment reduced the infiltration of TAMs and regulated other immune components in the tumor microenvironment, slowing the progression of PANC-02 tumors. In terms of mechanism, we found that the inhibition of sphingomyelin synthase 2 could downregulate the expression of IL4Rα and CSF1R, thereby attenuating M2 polarization.

Conclusion: The sphingomyelin synthase 2 inhibitor YE2 or sphingomyelin synthase 2 deficiency can prevent macrophage M2 polarization in pancreatic cancer, and sphingomyelin synthase 2 could be a new potential target for the treatment of pancreatic cancer.

Bioinformatic Analyses of Broad H3K79me2 Domains in Different Leukemia Cell Line Data Sets

A subset of expressed genes is associated with a broad H3K4me3 (histone H3 trimethylated at lysine 4) domain that extends throughout the gene body. Genes marked in this way in normal cells are involved in cell-identity and tumor-suppressor activities, whereas in cancer cells, genes driving the cancer phenotype (oncogenes) have this feature. Other histone modifications associated with expressed genes that display a broad domain have been less studied. Here, we identified genes with the broadest H3K79me2 (histone H3 dimethylated at lysine 79) domain in human leukemic cell lines representing different forms of leukemia. Taking a bioinformatic approach, we provide evidence that genes with the broadest H3K79me2 domain have known roles in leukemia (e.g., JMJD1C). In the mixed-lineage leukemia cell line MOLM-13, the HOXA9 gene is in a 100 kb broad H3K79me2 domain with other HOXA protein-coding and oncogenic long non-coding RNA genes. The genes in this domain contribute to leukemia. This broad H3K79me2 domain has an unstable chromatin structure, as was evident by enhanced chromatin accessibility throughout. Together, we provide evidence that identification of genes with the broadest H3K79me2 domain will aid in generating a panel of genes in the diagnosis and therapeutic treatment of leukemia in the future.

Genetic Variants Associated with Elevated Plasma Ceramides in Individuals with Metabolic Syndrome

Metabolic syndrome (MetS) is a complex condition of metabolic disorders and shows a steady onset globally. Ceramides are known as intracellular signaling molecules that influence key metabolism through various pathways such as MetS and insulin resistance. Therefore, it is important to identify novel genetic factors related to increased plasma ceramides in subjects with MetS. Here we first measured plasma ceramides levels in 37 subjects with MetS and in 38 healthy subjects by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Specifically, levels of C16 ceramide (Cer-16), C18 ceramide (Cer-18), C20 ceramide (Cer-20), C18 dihydroceramide (DhCer-18), C24 dihydroceramide (DhCer-24), and C24:1 dihydroceramide (DhCer-24:1) were significantly increased in MetS group (p < 5.0 × 10−2). We then performed single nucleotide polymorphism (SNP) genotyping to identify variants associated with elevated plasma ceramides in MetS group using Axiom® Korea Biobank Array v1.1 chip. We also performed linear regression analysis on genetic variants involved in ceramide synthesis and significantly elevated plasma ceramides and dihydroceramides. Ten variants (rs75397325, rs4246316, rs80165332, rs62106618, rs12358192, rs11006229, rs10826014, rs149162405, rs6109681, and rs3906631) across six genes (ACER1, CERS3, CERS6, SGMS1, SPTLC2, and SPTLC3) functionally involved in ceramide biosynthesis showed significant associations with the elevated levels of at least one of the ceramide species in MetS group at a statistically significant threshold of false discovery rate (FDR)-adjusted p < 5.0 × 10−2. Our findings suggest that the variants may be genetic determinants associated with increased plasma ceramides in individuals with MetS.

Ketogenic diets slow melanoma growth in vivo regardless of tumor genetics and metabolic plasticity

Background

Growing evidence supports the use of low-carbohydrate/high-fat ketogenic diets as an adjunctive cancer therapy. However, it is unclear which genetic, metabolic, or immunological factors contribute to the beneficial effect of ketogenic diets. Therefore, we investigated the effect of ketogenic diets on the progression and metabolism of genetically and metabolically heterogeneous melanoma xenografts, as well as on the development of melanoma metastases in mice with a functional immune system.

Methods

Mice bearing BRAF mutant, NRAS mutant, and wild-type melanoma xenografts as well as mice bearing highly metastatic melanoma allografts were fed with a control diet or ketogenic diets, differing in their triglyceride composition, to evaluate the effect of ketogenic diets on tumor growth and metastasis. We performed an in-depth targeted metabolomics analysis in plasma and xenografts to elucidate potential antitumor mechanisms in vivo.

Results

We show that ketogenic diets effectively reduced tumor growth in immunocompromised mice bearing genetically and metabolically heterogeneous human melanoma xenografts. Furthermore, the ketogenic diets exerted a metastasis-reducing effect in the immunocompetent syngeneic melanoma mouse model. Targeted analysis of plasma and tumor metabolomes revealed that ketogenic diets induced distinct changes in amino acid metabolism. Interestingly, ketogenic diets reduced the levels of alpha-amino adipic acid, a biomarker of cancer, in circulation to levels observed in tumor-free mice. Additionally, alpha-amino adipic acid was reduced in xenografts by ketogenic diets. Moreover, the ketogenic diets increased sphingomyelin levels in plasma and the hydroxylation of sphingomyelins and acylcarnitines in tumors.

Conclusions

Ketogenic diets induced antitumor effects toward melanoma regardless of the tumors´ genetic background, its metabolic signature, and the host immune status. Moreover, ketogenic diets simultaneously affected multiple metabolic pathways to create an unfavorable environment for melanoma cell proliferation, supporting their potential as a complementary nutritional approach to melanoma therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40170-022-00288-7.

New insights into genetics underlying of plumage color

Plumage color can be considered as a social signal in chickens and a breeding identification tool among breeders. The relationship between plumage color and trait groups of immunity, growth and fertility is still a controversial issue. This research aimed to determine the genome-wide additive and epistatic variants affecting plumage color variation in chickens using the chicken Illumina 60k high-density SNP array. Two scenarios of genome-wide additive association studies using all SNPs and independent SNPs were carried out. To perform epistatic association analysis, the LD pruning approach was used to reduce the complexity of the analysis. We detected seven novel significant loci using all of the SNPs in the model and 14 SNPs using the LD pruning approach associated with plumage color. Moreover, 89 significantly associated SNP-SNP interactions (P-value <10^-6 ) distributed in 25 chromosomes were identified, indicating that all of the signals together putatively influence the quantitative variation of plumage color. By annotating genes relevant to top SNPs, we have distinguished 18 potential candidate genes comprising HNF4beta, CKMT1B, TBC1D22A, RPL8, CACNA2D1, FZD4, SGMS1, IRF8, OPTN, LOC420362, TRABD, OvoDA1, DAD1, USP6, RBM12B, MIR1772, MIR1709 and MIR6696 and also 89 putative gene-gene combinations responsible for plumage color variation in chickens. Furthermore, several KEGG pathways including metabolic pathway, cytokine-cytokine receptor interaction, focal adhesion, melanogenesis, glycosaminoglycan biosynthesis-keratan sulfate and sphingolipid metabolism were enriched in the gene-set analysis. The results indicated that plumage color is a highly polygenic trait which, in turn, can be affected by multiple coding genes, regulatory genes and gene-gene epistasis interactions. In addition to genes with additive effects, epistatic genes with tiny individual effect sizes but significant effects in a pair have the potential to control plumage coloration in chickens.

Profile of sphingolipid-related genes and its association with prognosis highlights sphingolipid metabolism in oral cancer

BACKGROUND

Sphingolipids are bioactive lipids that play a role in cancer development. However, the clinical role of sphingolipid (SPL)-related genes in oral cancer (OC) remains not fully understood.

OBJECTIVE

This study, aimed to examine the mRNA expression of 14 sphingolipid-related genes in oral cancer patients and their implication with clinicopathological features and prognosis.

METHODS

qPCR analysis was performed in 50 OC tissues and their matched surgical margins. Next, Kaplan-Meier, Cox regression, and Receiver operating characteristics (ROC) analysis were applied to evaluate the impact of sphingolipid-related genes expression on the prognosis of OC.

RESULTS

The genes SET, ACER3, SK1 and S1PR5 were predominantly up-regulated, while ABCG2, S1PR1, ABCB1 and SPNS2 were down-regulated in OC patients. Analyzing the Cancer Genome Atlas Head-Neck Squamous Cell Carcinoma (TCGA-HNSC) data, which are predominantly composed of OC samples, these genes displayed a similar profile. In OC patients, high levels of SK1 were associated with lymph node metastasis, extracapsular invasion, desmoplasia, locoregional relapse, and disease status. Low levels of SPNS2 were associated with lymph node metastasis, perineural invasion, and disease status. Furthermore, OC and HNSC patients with higher SK1 expression demonstrated shorter disease-free survival (p= 0.0037; p= 0.0087), whereas those with lower SPNS2 expression exhibited shorter overall survival (p= 0.051; p= 0.0012). High levels of ACER3 and low levels of S1PR1 were associated with shorter disease-free and overall survival in HNSC patients.

CONCLUSION

Several sphingolipid-related genes are deregulated in OC at the mRNA level and are associated with clinicopathological features and presented potencial for the prediction of poor prognosis in OC patients.

Ceramide Metabolism Enzymes-Therapeutic Targets against Cancer

Sphingolipids are both structural molecules that are essential for cell architecture and second messengers that are involved in numerous cell functions. Ceramide is the central hub of sphingolipid metabolism. In addition to being the precursor of complex sphingolipids, ceramides induce cell cycle arrest and promote cell death and inflammation. At least some of the enzymes involved in the regulation of sphingolipid metabolism are altered in carcinogenesis, and some are targets for anticancer drugs. A number of scientific reports have shown how alterations in sphingolipid pools can affect cell proliferation, survival and migration. Determination of sphingolipid levels and the regulation of the enzymes that are implicated in their metabolism is a key factor for developing novel therapeutic strategies or improving conventional therapies. The present review highlights the importance of bioactive sphingolipids and their regulatory enzymes as targets for therapeutic interventions with especial emphasis in carcinogenesis and cancer dissemination.

Sphingomyelin synthase 2 but not sphingomyelin synthase 1 is upregulated in ovarian cancer and involved in migration, growth and survival via different mechanisms

Sphingomyelin synthase 1 (SMS1) and 2 (SMS2) are two enzymes required for sphingomyelin de novo synthesis, and their roles in tumor transformation and development have been recently recognized. In this work, we systematically evaluated the expression patterns of SMS1 and 2 in ovarian cancer patient samples and cell lines. Furthermore, we analyzed the functions of SMS2 and its underlying mechanisms. We observed a specific increase in SMS2 expression in ovarian cancer tissues compared to the adjacent normal ovary tissues in majority of patients' samples. This is regardless of their clinico-pathological characteristics. SMS1 expression was similar between ovarian cancer and its normal counterpart in 30 patients tested. The upregulation of SMS2 but not SMS1 was also reproducible in a panel of ovarian cancer cell lines. Functional analysis indicated that SMS2 plays a predominant role in promoting migration rather than proliferation in ovarian cancer. SMS2 depletion suppressed migration, growth and survival, and furthermore this was dependent on SMS2 baseline level in ovarian cancer cells. SMS2 inhibition significantly augmented cisplatin's efficacy. We further found that migration inhibition induced by SMS2 depletion was largely due to the suppression of RhoA/ROCK/LIMK/cofilin and RhoA/ROCK/FAK/paxillin pathways. In addition, lipid metabolism disruption, oxidative stress and damage, and impaired mitochondrial function contributed to the inhibitory effects of SMS2 depletion in ovarian cancer growth and survival. Our work demonstrates that SMS2 but not SMS1 is upregulated in ovarian cancer and involved in migration, growth and survival via different mechanisms. Our findings highlight the therapeutic value of SMS2 inhibition in the treatment of ovarian cancer.

Combined Analysis of RNA Sequence and Microarray Data Reveals a Competing Endogenous RNA Network as Novel Prognostic Markers in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a highly aggressive cancer with short survival time. Unbalanced competing endogenous RNAs (ceRNAs) have been shown to participate in the tumor pathogenesis and served as biomarkers for the clinical prognosis. However, the comprehensive analyses of the ceRNA network in the prognosis of MPM are still rarely reported. In this study, we obtained the transcriptome data of the MPM and the normal samples from TCGA, EGA, and GEO databases and identified the differentially expressed (DE) mRNAs, lncRNAs, and miRNAs. The functions of the prognostic genes and the overlapped DEmRNAs were further annotated by the multiple enrichment analyses. Then, the targeting relationships among lncRNA–miRNA and miRNA–mRNA were predicted and calculated, and a prognostic ceRNA regulatory network was established. We included the prognostic 73 mRNAs and 13 miRNAs and 26 lncRNAs into the ceRNA network. Moreover, 33 mRNAs, three miRNAs, and seven lncRNAs were finally associated with prognosis, and a model including seven mRNAs, two lincRNAs, and some clinical factors was finally established and validated by two independent cohorts, where CDK6 and SGMS1-AS1 were significant to be independent prognostic factors. In addition, the identified co-expressed modules associated with the prognosis were overrepresented in the ceRNA network. Multiple enrichment analyses showed the important roles of the extracellular matrix components and cell division dysfunction in the invasion of MPM potentially. In summary, the prognostic ceRNA network of MPM was established and analyzed for the first time and these findings shed light on the function of ceRNAs and revealed the potential prognostic and therapeutic biomarkers of MPM.

Neutral Sphingomyelinase 2 Heightens Anti-Melanoma Immune Responses and Anti-PD-1 Therapy Efficacy

Dysregulation of lipid metabolism affects the behavior of cancer cells, but how this happens is not completely understood. Neutral sphingomyelinase 2 (nSMase2), encoded by SMPD3, catalyzes the breakdown of sphingomyelin to produce the anti-oncometabolite ceramide. We found that this enzyme was often downregulated in human metastatic melanoma, likely contributing to immune escape. Overexpression of nSMase2 in mouse melanoma reduced tumor growth in syngeneic wild-type but not CD8-deficient mice. In wild-type mice, nSMase2-overexpressing tumors showed accumulation of both ceramide and CD8⁺ tumor-infiltrating lymphocytes, and this was associated with increased level of transcripts encoding IFNγ and CXCL9. Overexpressing the catalytically inactive nSMase2 failed to alter tumor growth, indicating that the deleterious effect nSMase2 has on melanoma growth depends on its enzymatic activity. In vitro, small extracellular vesicles from melanoma cells overexpressing wild-type nSMase2 augmented the expression of IL12, CXCL9, and CCL19 by bone marrow-derived dendritic cells, suggesting that melanoma nSMase2 triggers T helper 1 (Th1) polarization in the earliest stages of the immune response. Most importantly, overexpression of wild-type nSMase2 increased anti-PD-1 efficacy in murine models of melanoma and breast cancer, and this was associated with an enhanced Th1 response. Therefore, increasing SMPD3 expression in melanoma may serve as an original therapeutic strategy to potentiate Th1 polarization and CD8⁺ T-cell-dependent immune responses and overcome resistance to anti-PD-1.

Characteristics of the Tumor Microenvironment That Influence Immune Cell Functions: Hypoxia, Oxidative Stress, Metabolic Alterations

Immunotherapy (IMT) is now a core component of cancer treatment, however, many patients do not respond to these novel therapies. Investigating the resistance mechanisms behind this differential response is now a critical area of research. Immune-based therapies, particularly immune checkpoint inhibitors (ICI), rely on a robust infiltration of T-cells into the tumor microenvironment (TME) for an effective response. While early efforts relied on quantifying tumor infiltrating lymphocytes (TIL) in the TME, characterizing the functional quality and degree of TIL exhaustion correlates more strongly with ICI response. Even with sufficient TME infiltration, immune cells face a harsh metabolic environment that can significantly impair effector function. These tumor-mediated metabolic perturbations include hypoxia, oxidative stress, and metabolites of cellular energetics. Primarily through HIF-1-dependent processes, hypoxia invokes an immunosuppressive phenotype via altered molecular markers, immune cell trafficking, and angiogenesis. Additionally, oxidative stress can promote lipid peroxidation, ER stress, and Treg dysfunction, all associated with immune dysregulation. Finally, the metabolic byproducts of lipids, amino acids, glucose, and cellular energetics are associated with immunosuppression and ICI resistance. This review will explore these biochemical pathways linked to immune cell dysfunction in the TME and highlight potential adjunctive therapies to be used alongside current IMT.

Overriding sorafenib resistance via blocking lipid metabolism and Ras by sphingomyelin synthase 1 inhibition in hepatocellular carcinoma

BACKGROUND

The survival benefit of sorafenib, the most used drug for advanced hepatocellular carcinoma (HCC), is unsatisfactory due to the development of adaptive resistance. Exploring the mechanisms underlying sorafenib resistance is important to develop sensitizing strategy. Sphingomyelin synthase (SMS) plays a critical role in sphingolipid metabolism which is involved in oncogenesis and drug resistance.

METHODS

SMS1 and SMS2 levels in HCC cells in response to prolonged chemotherapy were analyzed using ELISA. mRNA and protein levels of SMS in HCC and adjacent normal tissues were analyzed by ELISA and real-time PCR. The roles of SMS and its downstream targets were investigated using cellular and biochemical assays and mass spectrometry.

RESULTS

SMS1, but not SMS2, was upregulated in HCC in response to sorafenib treatment, although HCC displayed similar RNA and protein level of SMS1 compared to adjacent normal liver tissues. Overexpression of SMS1 promoted HCC growth and migration, and alleviated sorafenib's toxicity. SMS1 inhibition via genetic and pharmacological approaches consistently resulted in inhibition of growth and migration, and apoptosis induction in sorafenib-resistance HCC cells. SMS1 inhibition also augmented the efficacy of sorafenib in sensitive HCC cells. SMS1 inhibition disrupted sphingolipid metabolism via accumulating ceramide and decreasing sphingomyelin, inducing mitochondrial dysfunction and oxidative stress, and decreasing Ras activity in resistant cells. Overexpression of constitutively active Ras reversed the inhibitory effects of SMS1 inhibition. Although SMS1 overexpression did not affect Ras expression and activity, Pearson correlation coefficient analysis of SMS1 and Ras expression demonstrated that there was positive correlation between SMS1 and RAS (NRAS, R = 0.55, p < 0.01; KRAS, R = 0.44, p < 0.01).

CONCLUSIONS

Our work is the first to suggest that SMS1 plays a more important role in sorafenib resistance than tumorigenesis, and provides preclinical evidence to overcome sorafenib resistance with SMS1 inhibition in HCC.

Lipid metabolic Reprogramming: Role in Melanoma Progression and Therapeutic Perspectives

Simple Summary

Melanoma is a devastating skin cancer characterized by an impressive metabolic plasticity. Melanoma cells are able to adapt to the tumor microenvironment by using a variety of fuels that contribute to tumor growth and progression. In this review, the authors summarize the contribution of the lipid metabolic network in melanoma plasticity and aggressiveness, with a particular attention to specific lipid classes such as glycerophospholipids, sphingolipids, sterols and eicosanoids. They also highlight the role of adipose tissue in tumor progression as well as the potential antitumor role of drugs targeting critical steps of lipid metabolic pathways in the context of melanoma.

Abstract

Metabolic reprogramming contributes to the pathogenesis and heterogeneity of melanoma. It is driven both by oncogenic events and the constraints imposed by a nutrient- and oxygen-scarce microenvironment. Among the most prominent metabolic reprogramming features is an increased rate of lipid synthesis. Lipids serve as a source of energy and form the structural foundation of all membranes, but have also emerged as mediators that not only impact classical oncogenic signaling pathways, but also contribute to melanoma progression. Various alterations in fatty acid metabolism have been reported and can contribute to melanoma cell aggressiveness. Elevated expression of the key lipogenic fatty acid synthase is associated with tumor cell invasion and poor prognosis. Fatty acid uptake from the surrounding microenvironment, fatty acid β-oxidation and storage also appear to play an essential role in tumor cell migration. The aim of this review is (i) to focus on the major alterations affecting lipid storage organelles and lipid metabolism. A particular attention has been paid to glycerophospholipids, sphingolipids, sterols and eicosanoids, (ii) to discuss how these metabolic dysregulations contribute to the phenotype plasticity of melanoma cells and/or melanoma aggressiveness, and (iii) to highlight therapeutic approaches targeting lipid metabolism that could be applicable for melanoma treatment.

β-Galactosylceramidase Promotes Melanoma Growth via Modulation of Ceramide Metabolism

Disturbance of sphingolipid metabolism may represent a novel therapeutic target in metastatic melanoma, the most lethal form of skin cancer. β-Galactosylceramidase (GALC) removes β-galactose from galactosylceramide and other sphingolipids. In this study, we show that downregulation of galcb, a zebrafish ortholog of human GALC, affects melanoblast and melanocyte differentiation in zebrafish embryos, suggesting a possible role for GALC in melanoma. On this basis, the impact of GALC expression in murine B16-F10 and human A2058 melanoma cells was investigated following its silencing or upregulation. Galc knockdown hampered growth, motility, and invasive capacity of B16-F10 cells and their tumorigenic and metastatic activity when grafted in syngeneic mice or zebrafish embryos. Galc-silenced cells displayed altered sphingolipid metabolism and increased intracellular levels of ceramide, paralleled by a nonredundant upregulation of Smpd3, which encodes for the ceramide-generating enzyme neutral sphingomyelinase 2. Accordingly, GALC downregulation caused SMPD3 upregulation, increased ceramide levels, and inhibited the tumorigenic activity of human melanoma A2058 cells, whereas GALC upregulation exerted opposite effects. In concordance with information from melanoma database mining, RNAscope analysis demonstrated a progressive increase of GALC expression from common nevi to stage IV human melanoma samples that was paralleled by increases in microphthalmia transcription factor and tyrosinase immunoreactivity inversely related to SMPD3 and ceramide levels. Overall, these findings indicate that GALC may play an oncogenic role in melanoma by modulating the levels of intracellular ceramide, thus providing novel opportunities for melanoma therapy. SIGNIFICANCE: Data from zebrafish embryos, murine and human cell melanoma lines, and patient-derived tumor specimens indicate that β-galactosylceramidase plays an oncogenic role in melanoma and may serve as a therapeutic target.

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.

Exogenous Flupirtine as Potential Treatment for CLN3 Disease

CLN3 disease is a fatal neurodegenerative disorder affecting children. Hallmarks include brain atrophy, accelerated neuronal apoptosis, and ceramide elevation. Treatment regimens are supportive, highlighting the importance of novel, disease-modifying drugs. Flupirtine and its new allyl carbamate derivative (compound 6) confer neuroprotective effects in CLN3-deficient cells. This study lays the groundwork for investigating beneficial effects in Cln3^Δex7/8 mice. WT/Cln3^Δex7/8 mice received flupirtine/compound 6/vehicle for 14 weeks. Short-term effect of flupirtine or compound 6 was tested using a battery of behavioral testing. For flupirtine, gene expression profiles, astrogliosis, and neuronal cell counts were determined. Flupirtine improved neurobehavioral parameters in open field, pole climbing, and Morris water maze tests in Cln3^Δex7/8 mice. Several anti-apoptotic markers and ceramide synthesis/degradation enzymes expression was dysregulated in Cln3^Δex7/8 mice. Flupirtine reduced astrogliosis in hippocampus and motor cortex of male and female Cln3^Δex7/8 mice. Flupirtine increased neuronal cell counts in male mice. The newly synthesized compound 6 showed promising results in open field and pole climbing. In conclusion, flupirtine improved behavioral, neuropathological and biochemical parameters in Cln3^Δex7/8 mice, paving the way for potential therapies for CLN3 disease.

Fingolimod Affects Transcription of Genes Encoding Enzymes of Ceramide Metabolism in Animal Model of Alzheimer's Disease

The imbalance in sphingolipid signaling may be critically linked to the upstream events in the neurodegenerative cascade of Alzheimer’s disease (AD). We analyzed the influence of mutant (V717I) amyloid β precursor protein (AβPP) transgene on sphingolipid metabolism enzymes in mouse hippocampus. At 3 months of age AβPP/Aβ presence upregulated enzymes of ceramide turnover on the salvage pathway: ceramide synthases (CERS2, CERS4, CERS6) and also ceramidase ACER3. At 6 months, only CERS6 was elevated, and no ceramide synthase was increased at 12 months. However, sphingomyelin synthases, which utilize ceramide on the sphingomyelinase pathway, were reduced (SGMS1 at 12 and SGMS2 at 6 months). mRNAs for sphingomyelin synthases SGMS1 and SGMS2 were also significantly downregulated in human AD hippocampus and neocortex when compared with age-matched controls. Our findings suggest early-phase deregulation of sphingolipid homeostasis in favor of ceramide signaling. Fingolimod (FTY720), a modulator of sphingosine-1-phosphate receptors countered the AβPP-dependent upregulation of hippocampal ceramide synthase CERS2 at 3 months. Moreover, at 12 months, FTY720 increased enzymes of ceramide-sphingosine turnover: CERS4, ASAH1, and ACER3. We also observed influence of fingolimod on the expression of the sphingomyelinase pathway enzymes. FTY720 counteracted the AβPP-linked reduction of sphingomyelin synthases SGMS1/2 (at 12 and 6 months, respectively) and led to elevation of sphingomyelinase SMPD2 (at 6 and 12 months). Therefore, our results demonstrate potentially beneficial, age-specific effects of fingolimod on transcription of sphingolipid metabolism enzymes in an animal model of AD.

Acid Sphingomyelinase Downregulation Enhances Mitochondrial Fusion and Promotes Oxidative Metabolism in a Mouse Model of Melanoma

Melanoma is the most severe type of skin cancer. Its unique and heterogeneous metabolism, relying on both glycolysis and oxidative phosphorylation, allows it to adapt to disparate conditions. Mitochondrial function is strictly interconnected with mitochondrial dynamics and both are fundamental in tumour progression and metastasis. The malignant phenotype of melanoma is also regulated by the expression levels of the enzyme acid sphingomyelinase (A-SMase). By modulating at transcriptional level A-SMase in the melanoma cell line B16-F1 cells, we assessed the effect of enzyme downregulation on mitochondrial dynamics and function. Our results demonstrate that A-SMase influences mitochondrial morphology by affecting the expression of mitofusin 1 and OPA1. The enhanced expression of the two mitochondrial fusion proteins, observed when A-SMase is expressed at low levels, correlates with the increase of mitochondrial function via the stimulation of the genes PGC-1alpha and TFAM, two genes that preside over mitochondrial biogenesis. Thus, the reduction of A-SMase expression, observed in malignant melanomas, may determine their metastatic behaviour through the stimulation of mitochondrial fusion, activity and biogenesis, conferring a metabolic advantage to melanoma cells.

LC-HRMS based approach to identify novel sphingolipid biomarkers in breast cancer patients

Perturbations in lipid metabolic pathways to meet the bioenergetic and biosynthetic requirements is a principal characteristic of cancer cells. Sphingolipids (SPLs) are the largest class of bioactive lipids associated to various aspects of tumorigenesis and have been extensively studied in cancer cell lines and experimental models. The clinical relevance of SPLs in human malignancies however is still poorly understood and needs further investigation. In the present study, we adopted a UHPLC-High resolution (orbitrap) Mass spectrometry (HRMS) approach to identify various sphingolipid species in breast cancer patients. A total of 49 SPLs falling into 6 subcategories have been identified. Further, integrating the multivariate analysis with metabolomics enabled us to identify an elevation in the levels of ceramide phosphates and sphingosine phosphates in tumor tissues as compared to adjacent normal tissues. The expression of genes involved in the synthesis of reported metabolites was also determined in local as well as TCGA cohort. A significant upregulation in the expression of CERK and SPHK1 was observed in tumor tissues in local and TCGA cohort. Sphingomyelin levels were found to be high in adjacent normal tissues. Consistent with the above findings, expression of SGMS1 in tumor tissues was downregulated in TCGA cohort only. Clinical correlations of the selected metabolites and their performance as biomarkers was also evaluated. Significant ROC and positive correlation with Ki67 index highlight the diagnostic potential and clinical relevance of ceramide phosphates in breast cancer.