Tumor Necrosis Factor-α (TNFα)-induced Ceramide Generation via Ceramide Synthases Regulates Loss of Focal Adhesion Kinase (FAK) and Programmed Cell Death

Enzymes of sphingolipid metabolism as transducers of metabolic inputs

Sphingolipids (SLs) constitute a discrete subdomain of metabolism, and they display both structural and signaling functions. Accumulating evidence also points to intimate connections between intermediary metabolism and SL metabolism. Given that many SLs exhibit bioactive properties (i.e. transduce signals), these raise the possibility that an important function of SLs is to relay information on metabolic changes into specific cell responses. This could occur at various levels. Some metabolites are incorporated into SLs, whereas others may initiate regulatory or signaling events that, in turn, modulate SL metabolism. In this review, we elaborate on the former as it represents a poorly appreciated aspect of SL metabolism, and we develop the hypothesis that the SL network is highly sensitive to several specific metabolic changes, focusing on amino acids (serine and alanine), various fatty acids, choline (and ethanolamine), and glucose.

Heat shock protein (Hsp27)-ceramide synthase (Cers1) protein-protein interactions provide a new avenue for unexplored anti-cancer mechanism and therapy

Hsp27 is a member of the small heat-shock proteins (sHSPs) - the known cellular line of defence against abnormal protein folding behaviors. Nevertheless, its upregulation is linked to a variety of pathological disorders, including several types of cancers. The ceramide synthases (CerS) mediate the synthesis of ceramide, a critical structural and signaling lipid. Functionally, downstream ceramide metabolites are implicated in the apoptosis process and their abnormal functionality has been linked to anticancer resistance. Studies showed that CerS1 are possibly inhibited by Hsp27 leading to biochemical anticancer effects in vitro. Nevertheless, the nature of such protein-protein interaction (PPI) has not been considerably investigated in molecular terms, hence, we present the first description of the dynamics CerS1-Hsp27 interaction landscapes using molecular dynamics simulations. Time-scale molecular dynamics simulation analysis indicated a system-wide conformational events of decreased stability, increased flexibility, reduced compactness, and decreased folding of CerS1. Analysis of binding energy showed a favorable interaction entailing 56 residues at the interface and a total stabilizing energy of -158 KJ/mol. The CerS1 catalytic domain experienced an opposite trend compared to the protein backbone. Yet, these residues adopted a highly compact conformation as per DCCM and DSSP analysis. Furthermore, conserved residues (SER 212, ASP 213, ALA 240, GLY 243, ASP 319) comprising the substrate shuttling machinery showed notable rigidity implying a restrained ceramide precursor access and assembly; hence, a possible inhibitory mechanism. Findings from this report would streamline a better molecular understanding of CerS1-Hsp27 interactions and decipher its potential avenue toward unexplored anti-cancer mechanisms and therapy.

Unveiling enigmatic essence of Sphingolipids: A promising avenue for glaucoma treatment

Treatment of glaucoma, the leading cause of irreversible blindness, remains challenging. The apoptotic loss of retinal ganglion cells (RGCs) in glaucoma is the pathological hallmark. Current treatments often remain suboptimal as they aim to halt RGC loss secondary to reduction of intraocular pressure. The pathophysiological targets for exploring direct neuroprotective approaches, therefore are highly relevant. Sphingolipids have emerged as significant target molecules as they are not only the structural components of various cell constituents, but they also serve as signaling molecules that regulate molecular pathways involved in cell survival and death. Investigations have shown that a critical balance among various sphingolipid species, particularly the ceramide and sphingosine-1-phosphate play a role in deciding the fate of the cell. In this review we briefly discuss the metabolic interconversion of sphingolipid species to get an insight into "sphingolipid rheostat", the dynamic balance among metabolites. Further we highlight the role of sphingolipids in the key pathophysiological mechanisms that lead to glaucomatous loss of RGCs. Lastly, we summarize the potential drug candidates that have been investigated for their neuroprotective effects in glaucoma via their effects on sphingolipid axis.

Sphingolipid-Induced Bone Regulation and Its Emerging Role in Dysfunction Due to Disease and Infection

The human skeleton is a metabolically active system that is constantly regenerating via the tightly regulated and highly coordinated processes of bone resorption and formation. Emerging evidence reveals fascinating new insights into the role of sphingolipids, including sphingomyelin, sphingosine, ceramide, and sphingosine-1-phosphate, in bone homeostasis. Sphingolipids are a major class of highly bioactive lipids able to activate distinct protein targets including, lipases, phosphatases, and kinases, thereby conferring distinct cellular functions beyond energy metabolism. Lipids are known to contribute to the progression of chronic inflammation, and notably, an increase in bone marrow adiposity parallel to elevated bone loss is observed in most pathological bone conditions, including aging, rheumatoid arthritis, osteoarthritis, and osteomyelitis. Of the numerous classes of lipids that form, sphingolipids are considered among the most deleterious. This review highlights the important primary role of sphingolipids in bone homeostasis and how dysregulation of these bioactive metabolites appears central to many chronic bone-related diseases. Further, their contribution to the invasion, virulence, and colonization of both viral and bacterial host cell infections is also discussed. Many unmet clinical needs remain, and data to date suggest the future use of sphingolipid-targeted therapy to regulate bone dysfunction due to a variety of diseases or infection are highly promising. However, deciphering the biochemical and molecular mechanisms of this diverse and extremely complex sphingolipidome, both in terms of bone health and disease, is considered the next frontier in the field.

Drug Targeting of Acyltransferases in the Triacylglyceride and 1-O-AcylCeramide Biosynthetic Pathways

Acyltransferase enzymes (EC 2.3.) are a large group of enzymes that transfer acyl groups to a variety of substrates. This review focuses on fatty acyltransferases involved in the biosynthetic pathways of glycerolipids and sphingolipids and how these enzymes have been pharmacologically targeted in their biologic context. Glycerolipids and sphingolipids, commonly treated independently in their regulation and biologic functions, are put together to emphasize the parallelism in their metabolism and bioactive roles. Furthermore, a newly considered signaling molecule, 1-O-acylceramide, resulting from the acylation of ceramide by DGAT2 enzyme, is discussed. Finally, the implications of DGAT2 as a putative ceramide acyltransferase (CAT) enzyme, with a putative dual role in TAG and 1-O-acylceramide generation, are explored. SIGNIFICANCE STATEMENT: This manuscript reviews the current status of drug development in lipid acyltransferases. These are current targets in metabolic syndrome and other diseases, including cancer. A novel function for a member in this group of lipids has been recently reported in cancer cells. The responsible enzyme and biological implications of this added member are discussed.

GIMAP5 deficiency reveals a mammalian ceramide-driven longevity assurance pathway

Preserving cells in a functional, non-senescent state is a major goal for extending human healthspans. Model organisms reveal that longevity and senescence are genetically controlled, but how genes control longevity in different mammalian tissues is unknown. Here, we report a new human genetic disease that causes cell senescence, liver and immune dysfunction, and early mortality that results from deficiency of GIMAP5, an evolutionarily conserved GTPase selectively expressed in lymphocytes and endothelial cells. We show that GIMAP5 restricts the pathological accumulation of long-chain ceramides (CERs), thereby regulating longevity. GIMAP5 controls CER abundance by interacting with protein kinase CK2 (CK2), attenuating its ability to activate CER synthases. Inhibition of CK2 and CER synthase rescues GIMAP5-deficient T cells by preventing CER overaccumulation and cell deterioration. Thus, GIMAP5 controls longevity assurance pathways crucial for immune function and healthspan in mammals.

Biological function, topology, and quantification of plasma membrane Ceramide

Over the past 30 years, a growing body of evidence has revealed the regulatory role of the lipid ceramide in various cellular functions. The structural diversity of ceramide, resulting in numerous species, and its distinct distribution within subcellular compartments may account for its wide range of functions. However, our ability to study the potential role of ceramide in specific subcellular membranes has been limited. Several works have shown mitochondrial, Golgi, and plasma membrane ceramide to mediate signaling pathways independently. These results have started to shift the focus on ceramide signaling research toward specific membrane pools. Nonetheless, the challenge arises from the substantial intracellular ceramide content, hindering efforts to quantify its presence in particular membranes. Recently, we have developed the first method capable of detecting and quantifying ceramide in the plasma membrane, leading to unexpected results such as detecting different pools of ceramide responding to drug concentration or time. This review summarizes the historical context that defined the idea of pools of ceramide, the studies on plasma membrane ceramide as a bioactive entity, and the tools available for its study, especially the new method to detect and, for the first time, quantify plasma membrane ceramide. We believe this method will open new avenues for researching sphingolipid signaling and metabolism.

Independent association of hypovitaminosis d with non-alcoholic fatty liver disease in people with chronic spinal cord injury: a cross-sectional study

PURPOSE

Non-alcoholic fatty liver disease (NAFLD) and hypovitaminosis D are highly prevalent in people with spinal cord injury (SCI) and could exert an unfavorable influence on cardiovascular profile and rehabilitation outcomes. We aimed to assess the independent association between low 25-hydroxy vitamin D (25(OH)D) levels and NAFLD in people with chronic (> 1 year) SCI.

METHODS

One hundred seventy-three consecutive patients with chronic SCI (132 men and 41 women) admitted to a rehabilitation program underwent clinical/biochemical evaluations and liver ultrasonography.

RESULTS

NAFLD was found in 105 patients (60.7% of the study population). They were significantly older and exhibited a poorer leisure time physical activity (LTPA) and functional independence in activities of daily living, a greater number of comorbidities and a higher prevalence of metabolic syndrome (MetS) and its correlates, including lower HDL and higher values of body mass index (BMI), systolic blood pressure, HOMA-index of insulin resistance and triglycerides. 25(OH)D levels were significantly lower in NAFLD (median: 10.6 ng/ml, range: 2.0-31.0) than in non-NAFLD group (22.5 ng/ml, 4.2-51.6). When all these variables were included in a multiple logistic regression analysis, a significant independent association with NAFLD only persisted for lower 25(OH)D levels, a greater number of comorbidities and a poorer LTPA. The ROC analysis revealed that 25(OH)D levels < 18.25 ng/ml discriminated patients with NAFLD with a sensitivity of 89.0% and a specificity of 73.0% (AUC: 85.7%; 95%CI: 79.6-91.7%). NAFLD was exhibited by 83.9% of patients with 25(OH)D levels < 18.25 ng/ml and by 18% of those with 25(OH)D levels ≥ 18.25 ng/ml (p < 0.0001).

CONCLUSION

In people with chronic SCI, 25(OH)D levels < 18.25 ng/ml may represent a marker of NAFLD independent of MetS-related features. Further studies are warranted to define the cause-effect relationships of this association.

Mitochondrial Lipid Metabolism Genes as Diagnostic and Prognostic Indicators in Hepatocellular Carcinoma

Background

Due to the heterogeneity of Hepatocellular carcinoma (HCC), there is an urgent need for reliable diagnosis and prognosis. Mitochondria-mediated abnormal lipid metabolism affects the occurrence and progression of HCC.

Objective

This study aims to investigate the potential of mitochondrial lipid metabolism (MTLM) genes as diagnostic and independent prognostic biomarkers for HCC.

Methods

MTLM genes were screened from the Gene Expression Omnibus (GEO) and Gene Set Enrichment Analysis (GSEA) databases, followed by an evaluation of their diagnostic values in both The Cancer Genome Atlas Program (TCGA) and the Affiliated Cancer Hospital of Guangxi Medical University (GXMU) cohort. The TCGA dataset was utilized to construct a gene signature and investigate the prognostic significance, immune infiltration, and copy number alterations. The validity of the prognostic signature was confirmed through GEO, International Cancer Genome Consortium (ICGC), and GXMU cohorts.

Results

The diagnostic receiver operating characteristic (ROC) curve revealed that eight MTLM genes have excellent diagnostic of HCC. A prognostic signature comprising 5 MTLM genes with robust predictive value was constructed using the lasso regression algorithm based on TCGA data. The results of the Stepwise regression model showed that the combination of signature and routine clinical parameters had a higher area under the curve (AUC) compared to a single risk score. Further, a nomogram was constructed to predict the survival probability of HCC, and the calibration curves demonstrated a perfect predictive ability. Finally, the risk score also unveiled the different immune and mutation statuses between the two different risk groups.

Conclusion

MTLT-related genes may serve as diagnostic and prognostic biomarkers for HCC as well as novel therapeutic targets, which may be beneficial for facilitating further understanding the molecular pathogenesis and providing potential therapeutic strategies for HCC.

The heat shock protein Hsp27 controls mitochondrial function by modulating ceramide generation

Sphingolipids have key functions in membrane structure and cellular signaling. Ceramide is the central molecule of the sphingolipid metabolism and is generated by ceramide synthases (CerS) in the de novo pathway. Despite their critical function, mechanisms regulating CerS remain largely unknown. Using an unbiased proteomics approach, we find that the small heat shock protein 27 (Hsp27) interacts specifically with CerS1 but not other CerS. Functionally, our data show that Hsp27 acts as an endogenous inhibitor of CerS1. Wild-type Hsp27, but not a mutant deficient in CerS1 binding, inhibits CerS1 activity. Additionally, silencing of Hsp27 enhances CerS1-generated ceramide accumulation in cells. Moreover, phosphorylation of Hsp27 modulates Hsp27-CerS1 interaction and CerS1 activity in acute stress-response conditions. Biologically, we show that Hsp27 knockdown impedes mitochondrial function and induces lethal mitophagy in a CerS1-dependent manner. Overall, we identify an important mode of CerS1 regulation and CerS1-mediated mitophagy through protein-protein interaction with Hsp27.

Natural Products and Small Molecules Targeting Cellular Ceramide Metabolism to Enhance Apoptosis in Cancer Cells

Molecular targeting strategies have been used for years in order to control cancer progression and are often based on targeting various enzymes involved in metabolic pathways. Keeping this in mind, it is essential to determine the role of each enzyme in a particular metabolic pathway. In this review, we provide in-depth information on various enzymes such as ceramidase, sphingosine kinase, sphingomyelin synthase, dihydroceramide desaturase, and ceramide synthase which are associated with various types of cancers. We also discuss the physicochemical properties of well-studied inhibitors with natural product origins and their related structures in terms of these enzymes. Targeting ceramide metabolism exhibited promising mono- and combination therapies at preclinical stages in preventing cancer progression and cemented the significance of sphingolipid metabolism in cancer treatments. Targeting ceramide-metabolizing enzymes will help medicinal chemists design potent and selective small molecules for treating cancer progression at various levels.

Long- and very long-chain ceramides are predictors of acute kidney injury in patients with acute coronary syndrome: the PEACP study

BACKGROUND

Acute kidney injury (AKI) can be caused by multiple factors/events, including acute coronary syndrome (ACS). Ceramides are involved in atherosclerosis progression, cardiovascular events, and renal damage. Almost no studies have been conducted on the relationship between ceramide concentrations and AKI events. Therefore, we evaluated the association between plasma ceramide level at admission and AKI in patients with ACS undergoing percutaneous coronary intervention.

METHODS

We enrolled 842 ACS patients from the Prospective Multicenter Study for Early Evaluation of Acute Chest Pain. AKI was defined using the criteria from the 2012 Kidney Disease: Improving Global Outcomes. Eleven C16-C26 ceramides were measured using the high-performance liquid chromatography interfaced to tandem mass spectrometer procedure. Logistic regression models were used to evaluate relationships between ceramides and AKI risk. The area under the receiver operating characteristic curves (AUC) was used to evaluate differences between ceramides.

RESULTS

Overall, 139 (16.5%) patients developed AKI during hospitalisation. Patients who developed AKI had higher levels of Cer(d18:1/16:0), Cer(d18:1/18:0), Cer(d18:1/20:0), Cer(d18:1/21:0), Cer(d18:1/24:1), and Cer(d18:1/24:2) than patients who did not (P < 0.05). In risk-factor adjusted logistic regression models, these ceramides were independently associated with AKI risk (P < 0.05). Cer(d18:1/24:2) had the highest odds ratio of 3.503 (Q4 vs. Q1, 95% confidence interval: 1.743-7.040, P < 0.001). Ceramides had AUCs of 0.581-0.661 (P < 0.001) for AKI. Each ceramide combined with the Mehran risk score (AUC: 0.780) had AUCs of 0.802-0.808, greater than the Mehran risk score alone.

CONCLUSION

Long-chain and very-long-chain ceramide levels may help determine the high AKI risk beyond traditional assessments.

BCAA insufficiency leads to premature ovarian insufficiency via ceramide-induced elevation of ROS

Premature ovarian insufficiency (POI) is a disease featured by early menopause before 40 years of age, accompanied by an elevation of follicle-stimulating hormone. Though POI affects many aspects of women's health, its major causes remain unknown. Many clinical studies have shown that POI patients are generally underweight, indicating a potential correlation between POI and metabolic disorders. To understand the pathogenesis of POI, we performed metabolomics analysis on serum and identified branch-chain amino acid (BCAA) insufficiency-related metabolic disorders in two independent cohorts from two clinics. A low BCAA diet phenotypically reproduced the metabolic, endocrine, ovarian, and reproductive changes of POI in young C57BL/6J mice. A mechanism study revealed that the BCAA insufficiency-induced POI is associated with abnormal activation of the ceramide-reactive oxygen species (ROS) axis and consequent impairment of ovarian granulosa cell function. Significantly, the dietary supplement of BCAA prevented the development of ROS-induced POI in female mice. The results of this pathogenic study will lead to the development of specific therapies for POI.

The Critical Impact of Sphingolipid Metabolism in Breast Cancer Progression and Drug Response

Breast cancer is the second leading cause of cancer-related death in women in the world, and its management includes a combination of surgery, radiation therapy, chemotherapy, and immunotherapy, whose effectiveness depends largely, but not exclusively, on the molecular subtype (Luminal A, Luminal B, HER2+ and Triple Negative). All breast cancer subtypes are accompanied by peculiar and substantial changes in sphingolipid metabolism. Alterations in sphingolipid metabolite levels, such as ceramides, dihydroceramide, sphingosine, sphingosine-1-phosphate, and sphingomyelin, as well as in their biosynthetic and catabolic enzymatic pathways, have emerged as molecular mechanisms by which breast cancer cells grow, respond to or escape therapeutic interventions and could take on diagnostic and prognostic value. In this review, we summarize the current landscape around two main themes: 1. sphingolipid metabolites, enzymes and transport proteins that have been found dysregulated in human breast cancer cells and/or tissues; 2. sphingolipid-driven mechanisms that allow breast cancer cells to respond to or evade therapies. Having a complete picture of the impact of the sphingolipid metabolism in the development and progression of breast cancer may provide an effective means to improve and personalize treatments and reduce associated drug resistance.

Ceramide Metabolism in Cardiovascular Disease: A Network With High Therapeutic Potential

Growing evidence suggests that ceramides play an important role in the development of atherosclerotic and valvular heart disease. Ceramides are biologically active sphingolipids that are produced by a complex network of enzymes. Lowering cellular and tissue levels of ceramide by inhibiting the ceramide-producing enzymes counteracts atherosclerotic and valvular heart disease development in animal models. In vascular tissues, ceramides are produced in response to hyperglycemia and TNF (tumor necrosis factor)-α signaling and are involved in NO-signaling and inflammation. In humans, elevated blood ceramide levels are associated with cardiovascular events. Furthermore, important cardiovascular risk factors, such as obesity and diabetes, have been linked to ceramide accumulation. This review summarizes the basic mechanisms of how ceramides drive cardiovascular disease locally and links these findings to the intriguing results of human studies on ceramides as biomarkers for cardiovascular events. Moreover, we discuss the current state of interventions to therapeutically influence vascular ceramide metabolism, both locally and systemically.

Contribution of specific ceramides to obesity-associated metabolic diseases

Ceramides are a heterogeneous group of bioactive membrane sphingolipids that play specialized regulatory roles in cellular metabolism depending on their characteristic fatty acyl chain lengths and subcellular distribution. As obesity progresses, certain ceramide molecular species accumulate in metabolic tissues and cause cell-type-specific lipotoxic reactions that disrupt metabolic homeostasis and lead to the development of cardiometabolic diseases. Several mechanisms for ceramide action have been inferred from studies in vitro, but only recently have we begun to better understand the acyl chain length specificity of ceramide-mediated signaling in the context of physiology and disease in vivo. New discoveries show that specific ceramides affect various metabolic pathways and that global or tissue-specific reduction in selected ceramide pools in obese rodents is sufficient to improve metabolic health. Here, we review the tissue-specific regulation and functions of ceramides in obesity, thus highlighting the emerging concept of selectively inhibiting production or action of ceramides with specific acyl chain lengths as novel therapeutic strategies to ameliorate obesity-associated diseases.

Comprehensive analysis of LASS6 expression and prognostic value in ovarian cancer

BACKGROUND

Ceramide plays an important role in the occurrence and development of tumor. The synthesis of ceramide needs the participation of LASS. Current studies have shown that different LASS family members play different functions in tumors, especially LASS6, has been proved to play a key role in breast cancer, gastric cancer, melanoma and so on, but the research on ovarian cancer is very limited.

METHODS

Bioinformatics web resources, including Oncomine, UALCAN, Kaplan-Meier Plotter and TIMER were used to analyze the expression profile, prognostic value and immune infiltration of LASS6. The related genes of LASS6 in ovarian cancer were mined by Regulome Explorer and LinkedOmics database, and cluster analysis was done by DAVID. The PPI network involving LASS6 was constructed by STRING database. Finally, the correlation between 10 genes and LASS6 was analyzed by GEPIA database, and their prognostic value in ovarian cancer was analyzed by Kaplan-Meier plotter.

RESULTS

The expression of LASS6 was up-regulated in ovarian cancer, which was related to the progression and poor prognosis of ovarian cancer. Through GO/KEGG cluster analysis, we also found that LASS6 may affect calcium ion channel and its transport pathways. The analysis of regulatory network involved in LASS6 showed that the high mRNAs of 7 key genes were associated with poor prognosis of OS in patients with ovarian cancer, among which DEGS1 was the most significant.

CONCLUSIONS

LASS6 may play an important role in the regulation of calcium pathway and become a new therapeutic target and potential prognostic marker in ovarian cancer.

Ceramide synthase 6 mediates sex-specific metabolic response to dietary folic acid in mice

Folic acid-fortified foods and multi-vitamin supplements containing folic acid (FA) are widely used around the world, but the exact mechanisms/metabolic effects of FA are not precisely identified. We have demonstrated that Ceramide Synthase 6 (CerS6) and C_16:0-ceramide mediate response to folate stress in cultured cells. Here we investigated the dietary FA effects on mouse liver metabolome, with a specific focus on sphingolipids, CerS6 and C_16:0-ceramide. Wild-type and CerS6^-/- mice were fed FA-deficient, control, or FA over-supplemented diets for 4 weeks. After dietary treatment, liver concentrations of ceramides, sphingomyelins and hexosylceramides were measured by LC-MS/MS and complemented by untargeted metabolomic characterization of mouse livers. Our study shows that alterations in dietary FA elicit multiple sphingolipid responses mediated by CerS6 in mouse livers. Folic acid-deficient diet elevated C_14:0-, C_18:0- and C_20:0- but not C_16:0-ceramide in WT male and female mice. Additionally, FA over-supplementation increased multiple sphingomyelin species, including total sphingomyelins, in both sexes. Of note, concentrations of C_14:0- and C_16:0-ceramides and hexosylceramides were significantly higher in female livers than in male. The latter were increased by FD diet, with no difference between sexes in total pools of these sphingolipid classes. Untargeted liver metabolomic analysis concurred with the targeted measurements and showed broad effects of dietary FA and CerS6 status on multiple lipid classes including sex-specific effects on phosphatidylethanolamines and diacylglycerols. Our study demonstrates that both dietary FA and CerS6 status exhibit pleiotropic and sex-dependent effects on liver metabolism, including hepatic sphingolipids, diacylglycerols, long chain fatty acids, and phospholipids.

Ceramides and sphingosine-1-phosphate mediate the distinct effects of M1/M2-macrophage infusion on liver recovery after hepatectomy

Post-hepatectomy liver dysfunction is a life-threatening morbidity that lacks efficient therapy. Bioactive lipids involved in macrophage polarization crucially regulate tissue injury and regeneration. Herein, we investigate the key bioactive lipids that mediate the cytotherapeutic potential of polarized-macrophage for post-hepatectomy liver dysfunction. Untargeted lipidomics identified elevation of ceramide (CER) metabolites as signature lipid species relevant to M1/M2 polarization in mouse bone-marrow-derived-macrophages (BMDMs). M1 BMDMs expressed a CER-generation-metabolic pattern, leading to elevation of CER; M2 BMDMs expressed a CER-breakdown-metabolic pattern, resulting in upregulation of sphingosine-1-phosphate (S1P). After infusing M1- or M2-polarized BMDMs into the mouse liver after hepatectomy, we found that M1-BMDM infusion increased M1 polarization and CER accumulation, resulting in exaggeration of hepatocyte apoptosis and liver dysfunction. Conversely, M2-BMDM infusion enhanced M2 polarization and S1P generation, leading to alleviation of liver dysfunction with improved hepatocyte proliferation. Treatment of exogenous CER and S1P or inhibition CER and S1P synthesis by siRNA targeting relevant enzymes further revealed that CER induced apoptosis while S1P promoted proliferation in post-hepatectomy primary hepatocytes. In conclusion, CER and S1P are uncovered as critical lipid mediators for M1- and M2-polarized BMDMs to promote injury and regeneration in the liver after hepatectomy, respectively. Notably, the upregulation of hepatic S1P induced by M2-BMDM infusion may have therapeutic potential for post-hepatectomy liver dysfunction.

Real-time lipid patterns to classify viable and necrotic liver tumors

Real-time tissue classifiers based on molecular patterns are emerging tools for fast tumor diagnosis. Here, we used rapid evaporative ionization mass spectrometry (REIMS) and multivariate statistical analysis (principal component analysis-linear discriminant analysis) to classify tissues with subsequent comparison to gold standard histopathology. We explored whether REIMS lipid patterns can identify human liver tumors and improve the rapid characterization of their underlying metabolic features. REIMS-based classification of liver parenchyma (LP), hepatocellular carcinoma (HCC), and metastatic adenocarcinoma (MAC) reached an accuracy of 98.3%. Lipid patterns of LP were more similar to those of HCC than to those of MAC and allowed clear distinction between primary and metastatic liver tumors. HCC lipid patterns were more heterogeneous than those of MAC, which is consistent with the variation seen in the histopathological phenotype. A common ceramide pattern discriminated necrotic from viable tumor in MAC with 92.9% accuracy and in other human tumors. Targeted analysis of ceramide and related sphingolipid mass features in necrotic tissues may provide a new classification of tumor cell death based on metabolic shifts. Real-time lipid patterns may have a role in future clinical decision-making in cancer precision medicine.

Ceramide synthases: Reflections on the impact of Dr. Lina M. Obeid

Sphingolipids are a family of lipids that are critical to cell function and survival. Much of the recent work done on sphingolipids has been performed by a closely-knit family of sphingolipid researchers, which including our colleague, Dr. Lina Obeid, who recently passed away. We now briefly review where the sphingolipid field stands today, focusing in particular on areas of sphingolipid research to which Dr. Obeid made valued contributions. These include the 'many-worlds' view of ceramides and the role of a key enzyme in the sphingolipid biosynthetic pathway, namely the ceramide synthases (CerS). The CerS contain a number of functional domains and also interact with a number of other proteins in lipid metabolic pathways, fulfilling Dr. Obeid's prophecy that ceramides, and the enzymes that generate ceramides, form the critical hub of the sphingolipid metabolic pathway.

Sphingolipids as critical players in retinal physiology and pathology

Sphingolipids have emerged as bioactive lipids involved in the regulation of many physiological and pathological processes. In the retina, they have been established to participate in numerous processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Dysregulation of sphingolipids is therefore crucial in the onset and progression of retinal diseases. This review examines the involvement of sphingolipids in retinal physiology and diseases. Ceramide (Cer) has emerged as a common mediator of inflammation and death of neuronal and retinal pigment epithelium cells in animal models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. Sphingosine-1-phosphate (S1P) has opposite roles, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1-phosphate may also contribute to uveitis. Notably, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), preserves neuronal viability and retinal function. These findings underscore the relevance of alterations in the sphingolipid metabolic network in the etiology of multiple retinopathies and highlight the potential of modulating their metabolism for the design of novel therapeutic approaches.

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

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

Therapeutic Efficacy of Antioxidants in Ameliorating Obesity Phenotype and Associated Comorbidities

Obesity has been a worldwide epidemic for decades. Despite the abundant increase in knowledge regarding the etiology and pathogenesis of obesity, the prevalence continues to rise with estimates predicting considerably higher numbers by the year 2030. Obesity is characterized by an abnormal lipid accumulation, however, the physiological consequences of obesity are far more concerning. The development of the obesity phenotype constitutes dramatic alterations in adipocytes, along with several other cellular mechanisms which causes substantial increase in systemic oxidative stress mediated by reactive oxygen species (ROS). These alterations promote a chronic state of inflammation in the body caused by the redox imbalance. Together, the systemic oxidative stress and chronic inflammation plays a vital role in maintaining the obese state and exacerbating onset of cardiovascular complications, Type II diabetes mellitus, dyslipidemia, non-alcoholic steatohepatitis, and other conditions where obesity has been linked as a significant risk factor. Because of the apparent role of oxidative stress in the pathogenesis of obesity, there has been a growing interest in attenuating the pro-oxidant state in obesity. Hence, this review aims to highlight the therapeutic role of antioxidants, agents that negate pro-oxidant state of cells, in ameliorating obesity and associated comorbidities. More specifically, this review will explore how various antioxidants target unique and diverse pathways to exhibit an antioxidant defense mechanism.

Ceramide-Induced Cell Death Depends on Calcium and Caspase-Like Activity in Rice

Ceramide sphingolipids are major components of membranes. C2 and C6 ceramides induce programmed cell death (PCD) in animals and plants, and we previously showed that C2 and C6 ceramides induce PCD in rice (Oryza sativa) protoplasts. However, the mechanistic link between sphingolipids and PCD in rice remains unclear. Here, we observed that calcium levels increased rapidly after ceramide treatment. Moreover, the calcium channel inhibitor LaCl₃ and the intracellular calcium chelator acetoxymethyl-1, 2-bis (2-aminophenoxy) ethic acid (BAPTA-AM) inhibited this calcium increase and prevented ceramide-induced PCD. Moreover, caspase-3-like protease activity increased significantly in C6 ceramide-treated protoplasts, and a caspase-specific inhibitor prevented C6 ceramide-induced cell death. We also detected the other typical PCD events including ATP loss. DIDS (4, 49-diisothiocyanatostilbene- 2, 29-disulfonic acid), an inhibitor of voltage-dependent anion channels (VDACs), decreased C6 ceramide-induced cell death. Together, this evidence suggests that mitochondria played an important role in C6 ceramide-induced PCD.

Rotten to the Cortex: Ceramide-Mediated Lipotoxicity in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a prevalent and progressive comorbidity of diabetes mellitus that increases one's risk of developing renal failure. Progress toward development of better DKD therapeutics is limited by an incomplete understanding of forces driving and connecting the various features of DKD, which include renal steatosis, fibrosis, and microvascular dysfunction. Herein we review the literature supporting roles for bioactive ceramides as inducers of local and systemic DKD pathology. In rodent models of DKD, renal ceramides are elevated, and genetic and pharmacological ceramide-lowering interventions improve kidney function and ameliorate DKD histopathology. In humans, circulating sphingolipid profiles distinguish human DKD patients from diabetic controls. These studies highlight the potential for ceramide to serve as a central and therapeutically tractable lipid mediator of DKD.

Elevated ceramides 18:0 and 24:1 with aging are associated with hip fracture risk through increased bone resorption

We assessed whether circulating ceramides, which play a role in a number of degenerative changes with aging, significantly differed according to fragility hip fracture (HF) status. We also performed a human study using bone marrow (BM) aspirates, directly reflecting the bone microenvironment, in addition to in vitro experiments. Peripheral blood and BM samples were simultaneously collected from 74 patients 65 years or older at hip surgery for either HF (n = 28) or for other causes (n = 46). Ceramides were measured by liquid chromatography-tandem mass spectrometry. Age was correlated positively with circulating C16:0, C18:0, and C24:1 ceramide levels. Patients with fragility HF had 21.3%, 49.5%, 34.3%, and 22.5% higher plasma C16:0, C18:0, C18:1, and C24:1 ceramide levels, respectively, than those without HF. Higher C16:0, C18:0, C18:1, and C24:1 ceramide levels were positively related to bone resorption markers in both blood and BM samples. Furthermore, in vitro studies showed that C18:0 and C24:1 ceramides directly increased osteoclastogenesis, bone resorption, and expression levels of osteoclast differentiation markers. These results suggested that the association of increased ceramides, especially C18:0 and C24:1, with adverse bone phenotypes in elderly people could be explained mainly by the increase in osteoclastogenesis and bone resorption.

Sphingolipids as Emerging Mediators in Retina Degeneration

The sphingolipids ceramide (Cer), sphingosine-1-phosphate (S1P), sphingosine (Sph), and ceramide-1-phosphate (C1P) are key signaling molecules that regulate major cellular functions. Their roles in the retina have gained increasing attention during the last decade since they emerge as mediators of proliferation, survival, migration, neovascularization, inflammation and death in retina cells. As exacerbation of these processes is central to retina degenerative diseases, they appear as crucial players in their progression. This review analyzes the functions of these sphingolipids in retina cell types and their possible pathological roles. Cer appears as a key arbitrator in diverse retinal pathologies; it promotes inflammation in endothelial and retina pigment epithelium (RPE) cells and its increase is a common feature in photoreceptor death in vitro and in animal models of retina degeneration; noteworthy, inhibiting Cer synthesis preserves photoreceptor viability and functionality. In turn, S1P acts as a double edge sword in the retina. It is essential for retina development, promoting the survival of photoreceptors and ganglion cells and regulating proliferation and differentiation of photoreceptor progenitors. However, S1P has also deleterious effects, stimulating migration of Müller glial cells, angiogenesis and fibrosis, contributing to the inflammatory scenario of proliferative retinopathies and age related macular degeneration (AMD). C1P, as S1P, promotes photoreceptor survival and differentiation. Collectively, the expanding role for these sphingolipids in the regulation of critical processes in retina cell types and in their dysregulation in retina degenerations makes them attractive targets for treating these diseases.

Intricate role of mitochondrial lipid in mitophagy and mitochondrial apoptosis: its implication in cancer therapeutics

The efficacy of chemotherapy is mostly restricted by the drug resistance developed during the course of cancer treatment. Mitophagy, as a pro-survival mechanism, crucially maintains mitochondrial homeostasis and it is one of the mechanisms that cancer cells adopt for their progression. On the other hand, mitochondrial apoptosis, a precisely regulated form of cell death, acts as a tumor-suppressive mechanism by targeting cancer cells. Mitochondrial lipids, such as cardiolipin, ceramide, and sphingosine-1-phosphate, act as a mitophageal signal for the clearance of damaged mitochondria by interacting with mitophagic machinery as well as activate mitochondrial apoptosis via the release of cytochrome c into the cytoplasm. In the recent time, the lipid-mediated lethal mitophagy has also been used as an alternative approach to abolish the survival role of lipid in cancer. Therefore, by targeting mitochondrial lipids in cancer cells, the detailed mechanism linked to drug resistance can be unraveled. In this review, we precisely discuss the current knowledge about the multifaceted role of mitochondrial lipid in regulating mitophagy and mitochondrial apoptosis and its application in effective cancer therapy.

Advances in determining signaling mechanisms of ceramide and role in disease

Ceramide is a critical bioactive lipid involved in diverse cellular processes. It has been proposed to regulate cellular processes by influencing membrane properties and by directly interacting with effector proteins. Advances over the past decade have improved our understanding of ceramide as a bioactive lipid. Generation and characterization of ceramide-metabolizing enzyme KO mice, development of specific inhibitors and ceramide-specific antibodies, use of advanced microscopy and mass spectrometry, and design of synthetic ceramide derivatives have all provided insight into the signaling mechanisms of ceramide and its implications in disease. As a result, the role of ceramide in biological functions and disease are now better understood, with promise for development of therapeutic strategies to treat ceramide-regulated diseases.

Approaches for probing and evaluating mammalian sphingolipid metabolism

Sphingolipid metabolism plays a critical role in regulating processes that control cellular fate. This dynamic pathway can generate and degrade the central players: ceramide, sphingosine and sphingosine-1-phosphate in almost any membrane in the cell, adding an unexpected level of complexity in deciphering signaling events. While in vitro assays have been developed for most enzymes in SL metabolism, these assays are setup for optimal activity conditions and can fail to take into account regulatory components such as compartmentalization, substrate limitations, and binding partners that can affect cellular enzymatic activity. Therefore, many in-cell assays have been developed to derive results that are authentic to the cellular situation which may give context to alteration in SL mass. This review will discuss approaches for utilizing probes for mammalian in-cell assays to interrogate most enzymatic steps central to SL metabolism. The use of inhibitors in conjunction with these probes can verify the specificity of cellular assays as well as provide valuable insight into flux in the SL network. The use of inhibitors specific to each of the central sphingolipid enzymes are also discussed to assist researchers in further interrogation of these pathways.

The role of dihydrosphingolipids in disease

Dihydrosphingolipids refer to sphingolipids early in the biosynthetic pathway that do not contain a C4-trans-double bond in the sphingoid backbone: 3-ketosphinganine (3-ketoSph), dihydrosphingosine (dhSph), dihydrosphingosine-1-phosphate (dhS1P) and dihydroceramide (dhCer). Recent advances in research related to sphingolipid biochemistry have shed light on the importance of sphingolipids in terms of cellular signalling in health and disease. However, dihydrosphingolipids have received less attention and research is lacking especially in terms of their molecular mechanisms of action. This is despite studies implicating them in the pathophysiology of disease, for example dhCer in predicting type 2 diabetes in obese individuals, dhS1P in cardiovascular diseases and dhSph in hepato-renal toxicity. This review gives a comprehensive summary of research in the last 10-15 years on the dihydrosphingolipids, 3-ketoSph, dhSph, dhS1P and dhCer, and their relevant roles in different diseases. It also highlights gaps in research that could be of future interest.

Very Long-Chain C24:1 Ceramide Is Increased in Serum Extracellular Vesicles with Aging and Can Induce Senescence in Bone-Derived Mesenchymal Stem Cells

Extracellular vesicles (EVs), including exosomes and microvesicles, function in cell-to-cell communication through delivery of proteins, lipids and microRNAs to target cells via endocytosis and membrane fusion. These vesicles are enriched in ceramide, a sphingolipid associated with the promotion of cell senescence and apoptosis. We investigated the ceramide profile of serum exosomes from young (24⁻40 yrs.) and older (75⁻90 yrs.) women and young (6⁻10 yrs.) and older (25⁻30 yrs.) rhesus macaques to define the role of circulating ceramides in the aging process. EVs were isolated using size-exclusion chromatography. Proteomic analysis was used to validate known exosome markers from Exocarta and nanoparticle tracking analysis used to characterize particle size and concentration. Specific ceramide species were identified with lipidomic analysis. Results show a significant increase in the average amount of C24:1 ceramide in EVs from older women (15.4 pmol/sample) compared to those from younger women (3.8 pmol/sample). Results were similar in non-human primate serum samples with increased amounts of C24:1 ceramide (9.3 pmol/sample) in older monkeys compared to the younger monkeys (1.8 pmol/sample). In vitro studies showed that primary bone-derived mesenchymal stem cells (BMSCs) readily endocytose serum EVs, and serum EVs loaded with C24:1 ceramide can induce BMSC senescence. Elevated ceramide levels have been associated with poor cardiovascular health and memory impairment in older adults. Our data suggest that circulating EVs carrying C24:1 ceramide may contribute directly to cell non-autonomous aging.

Contribution of Adipose Tissue Inflammation to the Development of Type 2 Diabetes Mellitus

The objective of this comprehensive review is to summarize and discuss the available evidence of how adipose tissue inflammation affects insulin sensitivity and glucose tolerance. Low-grade, chronic adipose tissue inflammation is characterized by infiltration of macrophages and other immune cell populations into adipose tissue, and a shift toward more proinflammatory subtypes of leukocytes. The infiltration of proinflammatory cells in adipose tissue is associated with an increased production of key chemokines such as C-C motif chemokine ligand 2, proinflammatory cytokines including tumor necrosis factor α and interleukins 1β and 6 as well as reduced expression of the key insulin-sensitizing adipokine, adiponectin. In both rodent models and humans, adipose tissue inflammation is consistently associated with excess fat mass and insulin resistance. In humans, associations with insulin resistance are stronger and more consistent for inflammation in visceral as opposed to subcutaneous fat. Further, genetic alterations in mouse models of obesity that reduce adipose tissue inflammation are-almost without exception-associated with improved insulin sensitivity. However, a dissociation between adipose tissue inflammation and insulin resistance can be observed in very few rodent models of obesity as well as in humans following bariatric surgery- or low-calorie-diet-induced weight loss, illustrating that the etiology of insulin resistance is multifactorial. Taken together, adipose tissue inflammation is a key factor in the development of insulin resistance and type 2 diabetes in obesity, along with other factors that likely include inflammation and fat accumulation in other metabolically active tissues. © 2019 American Physiological Society. Compr Physiol 9:1-58, 2019.

Early postoperative changes of sphingomyelins and ceramides after laparoscopic sleeve gastrectomy

Background

This study aimed to determine early postoperative changes of serum sphingomyelin (SM) and ceramide (CER) species following laparoscopic sleeve gastrectomy (LSG).

Methods

Twenty obese patients [mean body mass index (BMI) 45,64 ± 6,10 kg/m²] underwent LSG and normal weight control patients (mean BMI 31,51 ± 6,21 kg/m²) underwent laparoscopic cholecystectomy. Fasting blood samples were collected prior to surgery, at day 1 and day 30 after surgery. Circulating levels of C16-C24 SMs, C16-C24 CERs and sphingosine-1-phosphate (S1P) were determined by an optimized multiple reaction monitoring (MRM) method using ultra fast-liquid chromatography (UFLC) coupled with tandem mass spectrometry (MS/MS). Serum activity of neutral sphingomyelinase (N-SMase) was assayed by standard kit methods, and ceramide-1-phosphate (C1P) levels were determined by enzyme-linked immunosorbent assay (ELISA). Lipid profile, routine biochemical and hormone parameters were assayed by standard kit methods. Insulin sensitivity was evaluated using homeostatic model assessment for insulin resistance (HOMA IR).

Results

A significant decrease was observed in serum levels of very-long-chain C24 SM, very-long-chain C22-C24 CERs, HOMA-IR, N-SMase and C1P in LSG patients after postoperation day 1 and day 30 compared to preoperation levels. At 30 days postsurgery, BMI was reduced by 11%, fasting triglycerides were significantly decreased, and insulin sensitivity was increased compared to presurgery values. A significant positive correlation was found between HOMA-IR and serum levels of C22-C24 CERs in LSG patients.

Conclusion

We conclude that very long chain CERs may mediate improved insulin sensitivity after LSG.

Ceramide Synthase 6: Comparative Analysis, Phylogeny and Evolution

Ceramide synthase 6 (CerS6, also known as LASS6) is one of the six members of ceramide synthase gene family in humans. Comparisons of CerS6 amino acid sequences and structures as well as of CerS6 gene structures/locations were conducted using data from several vertebrate genome projects. A specific role for the CerS6 gene and protein has been identified as the endoplasmic reticulum C₁₄- and C₁₆-ceramide synthase. Mammalian CerS6 proteins share 90⁻100% similarity among different species, but are only 22⁻63% similar to other CerS family members, suggesting that CerS6 is a distinct gene family. Sequence alignments, predicted transmembrane, lumenal and cytoplasmic segments and N-glycosylation sites were also investigated, resulting in identification of the key conserved residues, including the active site as well as C-terminus acidic and serine residues. Mammalian CerS6 genes contain ten exons, are primarily located on the positive strands and transcribed as two major isoforms. The human CERS6 gene promoter harbors a large CpG island (94 CpGs) and multiple transcription factor binding sites (TFBS), which support precise transcriptional regulation and signaling functions. Additional regulation is conferred by 15 microRNA (miRNA) target sites identified in the CERS6 3'-UTR region. Phylogenetic analysis of the vertebrate CerS1⁻6 gene families relationships supports a major role for the CerS6 enzyme that is strongly conserved throughout vertebrate evolution.

Visualizing bioactive ceramides

In the last 30 years, ceramides have been found to mediate a myriad of biological processes. Ceramides have been recognized as bioactive molecules and their metabolizing enzymes are attractive targets in cancer therapy and other diseases. The molecular mechanism of action of cellular ceramides are still not fully established, with insights into roles through modification of lipid rafts, creation of ceramide platforms, ceramide channels, or through regulation of direct protein effectors such as protein phosphatases and kinases. Recently, the 'Many Ceramides' hypothesis focuses on distinct pools of subcellular ceramides and ceramide species as potential defined bioactive entities. Traditional methods that measure changes in ceramide levels in the whole cell, such as mass spectrometry, fluorescent ceramide analogues, and ceramide antibodies, fail to differentiate specific bioactive species at the subcellular level. However, a few ceramide binding proteins have been reported, and a smaller subgroup within these, have been shown to translocate to ceramide-enriched membranes, revealing these localized pools of bioactive ceramides. In this review we want to discuss and consolidate these works and explore the possibility of defining these binding proteins as new tools are emerging to visualize bioactive ceramides in cells. Our goal is to encourage the scientific community to explore these ceramide partners, to improve techniques to refine the list of these binding partners, making possible the identification of specific domains that recognize and bind ceramides to be used to visualize the 'Many Ceramides' in the cell.

Functions of neutral ceramidase in the Golgi apparatus

Ceramidases hydrolyze ceramides into sphingosine and fatty acids, with sphingosine being further metabolized into sphingosine-1-phosphate (S1P); thus, ceramidases control the levels of these bioactive sphingolipids in cells and tissues. Neutral ceramidase (nCDase) is highly expressed in colorectal tissues, and a recent report showed that nCDase activity is involved in Wnt/β-catenin signaling. In addition, the inhibition of nCDase decreases the development and progression of colorectal tumor growth. Here, to determine the action of nCDase in colorectal cancer cells, we focused on the subcellular localization and metabolic functions of this enzyme in HCT116 cells. nCDase was found to be located in both the plasma membrane and in the Golgi apparatus, but it had minimal effects on basal levels of ceramide, sphingosine, or S1P. Cells overexpressing nCDase were protected from the cell death and Golgi fragmentation induced by C6-ceramide, and they showed reduced levels of C6-ceramide and higher levels of S1P and sphingosine. Furthermore, compartment-specific metabolic functions of the enzyme were probed using C6-ceramide and Golgi-targeted bacterial SMase (bSMase) and bacterial ceramidase (bCDase). The results showed that Golgi-specific bCDase also demonstrated resistance against the cell death stimulated by C6-ceramide, and it catalyzed the metabolism of ceramides and produced sphingosine in the Golgi. Targeting bSMase to the Golgi resulted in increased levels of ceramide that were attenuated by the expression of nCDase, also supporting its ability to metabolize Golgi-generated ceramide. These results are critical in understanding the functions of nCDase actions in colorectal cancer cells as well as the compartmentalized pathways of sphingolipid metabolism.

Flupirtine derivatives as potential treatment for the neuronal ceroid lipofuscinoses

Objective

Neuronal Ceroid Lipofuscinoses (NCL) are fatal inherited neurodegenerative diseases with established neuronal cell death and increased ceramide levels in brain, hence, a need for disease‐modifying drug candidates, with potential to enhance growth, reduce apoptosis and lower ceramide in neuronal precursor PC12 cells and human NCL cell lines using enhanced flupirtine aromatic carbamate derivatives in vitro.

Methods

Aromatic carbamate derivatives were tested by establishing growth curves under pro‐apoptotic conditions and activity evaluated by trypan blue and JC‐1 staining, as well as a drop in pro‐apoptotic ceramide in neuronal precursor PC12 cells following siRNA knockdown of the CLN3 gene, and CLN1‐/CLN2‐/CLN3‐/CLN6‐/CLN8 patient‐derived lymphoblasts. Ceramide levels were determined in CLN1‐/CLN2‐/CLN3‐/CLN6‐/CLN8 patient‐derived lymphoblasts before and after treatment. Expression of BCL‐2, ceramide synthesis enzymes (CERS2/CERS6/SMPD1/DEGS2) and Caspases 3/8/9 levels were compared in treated versus untreated CLN3‐deficient PC12 cells by qRT‐PCR.

Results

Retigabine, the benzyl‐derivatized carbamate and an allyl carbamate derivative were neuroprotective in CLN3‐defective PC12 cells and rescued CLN1‐/CLN2‐/CLN3‐/CLN6‐/CLN8 patient‐derived lymphoblasts from diminished growth and accelerated apoptosis. All drugs decreased ceramide in CLN1‐/CLN2‐/CLN3‐/CLN6‐/CLN8 patient‐derived lymphoblasts. Increased BCL‐2 and decreased ceramide synthesis enzyme expression were established in CLN3‐derived PC12 cells treated with the benzyl and allyl carbamate derivatives. They down‐regulated Caspase 3/Caspase 8 expression. Caspase 9 expression was reduced by the benzyl‐derivatized carbamate.

Interpretation

These findings establish that compounds analogous to flupirtine demonstrate anti‐apoptotic activity with potential for treatment of NCL disease and use of ceramide as a marker for these diseases.

Sphingosine-1-Phosphate Signaling and Metabolism Gene Signature in Pediatric Inflammatory Bowel Disease: A Matched-case Control Pilot Study

GOAL

The aim of this study was to investigate gene expression levels of proteins involved in sphingosine-1-phosphate (S1P) metabolism and signaling in a pediatric inflammatory bowel disease (IBD) patient population.

BACKGROUND

IBD is a debilitating disease affecting 0.4% of the US population. The incidence of IBD in childhood is rising. Identifying effective targeted therapies that can be used safely in young patients and developing tools for selecting specific candidates for targeted therapies are important goals. Clinical IBD trials now underway target S1PR1, a receptor for the pro-inflammatory sphingolipid S1P. However, circulating and tissue sphingolipid levels and S1P-related gene expression have not been characterized in pediatric IBD.

METHODS

Pediatric IBD patients and controls were recruited in a four-site study. Patients received a clinical score using PUCAI or PCDAI evaluation. Colon biopsies were collected during endoscopy. Gene expression was measured by qRT-PCR. Plasma and gut tissue sphingolipids were measured by LC-MS/MS.

RESULTS

Genes of S1P synthesis (SPHK1, SPHK2), degradation (SGPL1), and signaling (S1PR1, S1PR2, and S1PR4) were significantly upregulated in colon biopsies of IBD patients with moderate/severe symptoms compared with controls or patients in remission. Tissue ceramide, dihydroceramide, and ceramide-1-phosphate (C1P) levels were significantly elevated in IBD patients compared with controls.

CONCLUSIONS

A signature of elevated S1P-related gene expression in colon tissues of pediatric IBD patients correlates with active disease and normalizes in remission. Biopsied gut tissue from symptomatic IBD patients contains high levels of pro-apoptotic and pro-inflammatory sphingolipids. A combined analysis of gut tissue sphingolipid profiles with this S1P-related gene signature may be useful for monitoring response to conventional therapy.

Myristate-induced endoplasmic reticulum stress requires ceramide synthases 5/6 and generation of C14-ceramide in intestinal epithelial cells

Saturated fatty acids (SFAs) have been shown to induce endoplasmic reticulum (ER) stress and chronic inflammatory responses, as well as alter sphingolipid metabolism. Disruptions in ER stress and sphingolipid metabolism have also been implicated in intestinal inflammation. Therefore, to elucidate the roles of SFAs in ER stress and inflammation in intestinal epithelial cells, we examined myristate (C14:0) and palmitate (C16:0). Myristate, but not palmitate, induced ER stress signaling, including activation of inositol-requiring enzyme 1 (IRE1) and X-box binding protein 1 (XBP1) signaling. Myristate significantly increased C14-ceramide levels, whereas palmitate increased several long-chain ceramides. To define the role of ceramide synthases (CerSs) in myristate-induced ER stress, we used the pharmacologic inhibitor, fumonisin B1 (FB1), and small interfering RNA (siRNA) for CerS5 and 6, the primary isoforms that are involved in C14-ceramide generation. FB1 and siRNA for CerS5 or 6 suppressed myristate-induced C14-ceramide generation and XBP1 splicing (XBP1s). Moreover, increased XBP1s induced the downstream expression of IL-6 in a CerS5/6-dependent manner. In addition, a myristate-enriched milk fat-based diet, but not a lard-based diet, increased C14-ceramide, XBP1s, and IL-6 expression in vivo. Taken together, our data suggest that myristate modulates ER stress and cytokine production in the intestinal epithelium via CerS5/6 and C14-ceramide generation.-Choi, S., Snider, J. M., Olakkengil, N., Lambert, J. M., Anderson, A. K., Ross-Evans, J. S., Cowart, L. A., Snider, A. J. Myristate-induced endoplasmic reticulum stress requires ceramide synthases 5/6 and generation of C14-ceramide in intestinal epithelial cells.

Decreased ceramide underlies mitochondrial dysfunction in Charcot-Marie-Tooth 2F

Charcot-Marie-Tooth (CMT) disease is the most commonly inherited neurologic disorder, but its molecular mechanisms remain unclear. One variant of CMT, 2F, is characterized by mutations in heat shock protein 27 (Hsp27). As bioactive sphingolipids have been implicated in neurodegenerative diseases, we sought to determine if their dysregulation is involved in CMT. Here, we show that Hsp27 knockout mice demonstrated decreases in ceramide in peripheral nerve tissue and that the disease-associated Hsp27 S135F mutant demonstrated decreases in mitochondrial ceramide. Given that Hsp27 is a chaperone protein, we examined its role in regulating ceramide synthases (CerSs), an enzyme family responsible for catalyzing generation of the sphingolipid ceramide. We determined that CerSs colocalized with Hsp27, and upon the presence of S135F mutants, CerS1 lost its colocalization with mitochondria suggesting that decreased mitochondrial ceramides result from reduced mitochondrial CerS localization rather than decreased CerS activity. Mitochondria in mutant cells appeared larger with increased interconnectivity. Furthermore, mutant cell lines demonstrated decreased mitochondrial respiratory function and increased autophagic flux. Mitochondrial structural and functional changes were recapitulated by blocking ceramide generation pharmacologically. These results suggest that mutant Hsp27 decreases mitochondrial ceramide levels, producing structural and functional changes in mitochondria leading to neuronal degeneration.-Schwartz, N. U., Linzer, R. W., Truman, J.-P., Gurevich, M., Hannun, Y. A., Senkal, C. E., Obeid, L. M. Decreased ceramide underlies mitochondrial dysfunction in Charcot-Marie-Tooth 2F.

Dietary and Endogenous Sphingolipid Metabolism in Chronic Inflammation

Chronic inflammation is a common underlying factor in many major metabolic diseases afflicting Western societies. Sphingolipid metabolism is pivotal in the regulation of inflammatory signaling pathways. The regulation of sphingolipid metabolism is in turn influenced by inflammatory pathways. In this review, we provide an overview of sphingolipid metabolism in mammalian cells, including a description of sphingolipid structure, biosynthesis, turnover, and role in inflammatory signaling. Sphingolipid metabolites play distinct and complex roles in inflammatory signaling and will be discussed. We also review studies examining dietary sphingolipids and inflammation, derived from in vitro and rodent models, as well as human clinical trials. Dietary sphingolipids appear to influence inflammation-related chronic diseases through inhibiting intestinal lipid absorption, altering gut microbiota, activation of anti-inflammatory nuclear receptors, and neutralizing responses to inflammatory stimuli. The anti-inflammatory effects observed with consuming dietary sphingolipids are in contrast to the observation that most cellular sphingolipids play roles in augmenting inflammatory signaling. The relationship between dietary sphingolipids and low-grade chronic inflammation in metabolic disorders is complex and appears to depend on sphingolipid structure, digestion, and metabolic state of the organism. Further research is necessary to confirm the reported anti-inflammatory effects of dietary sphingolipids and delineate their impacts on endogenous sphingolipid metabolism.

Micron rhubarb charcoal plus Bletilla striata gelatin protects against gastric mucosal injury in rats

AIM

To investigate whether micron rhubarb charcoal plus Bletilla striata gelatin can protect against gastric mucosal injury by regulating the expression of focal adhesion kinase (FAK), vinculin, and kindlin-2.

METHODS

Eighty SD rats were randomly divided into four groups: control group, model group, micron rhubarb charcoal group, micron rhubarb charcoal plus Bletilla striata gelatin group. After treatment for 14 days, the area of mucosal lesions was detected. Radioimmunoassay was used to detect the contents of prostaglandin E₂ (PGE₂) and gastrin (GAS) in serum, and interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α) in the gastric mucosa. RT-PCR and Western blot were used to detect the mRNA and protein expression of FAK, vinculin and kindlin-2.

RESULTS

Compared with the control group, the injury area in the gastric mucosa was significantly increased (P < 0.01), the content of GAS in serum and the levels of TNF-α and IL-8 in the gastric mucosa (P < 0.01) were significantly increased, the content of PGE₂ in serum and the mRNA and protein expression of FAK, vinculin, and kindlin-2 were significantly decreased in the model group (P < 0.01). Compared with the model group, the area of gastric mucosal lesions was significantly decreased (P < 0.01), the content of GAS in serum and the levels of TNF-α and IL-8 in the gastric mucosa were significantly decreased (P < 0.01), the content of PGE₂ in serum and the mRNA and protein expression of FAK, vinculin, and kindlin-2 were significantly increased in the two treatment groups (P < 0.01). The changes in the above indexes were more significant in the micron rhubarb charcoal plus Bletilla striata gelatin group than in the micron rhubarb charcoal group.

CONCLUSION

Micron rhubarb charcoal plus Bletilla striata gelatin can significantly improve gastric mucosal injury in rats, and the protective effect may be related to un-regulating the expression of FAK, vinculin, and kindlin-2.

Augmented trophoblast cell death in preeclampsia can proceed via ceramide-mediated necroptosis

Preeclampsia, a serious hypertensive disorder of pregnancy, is characterized by elevated ceramide (CER) content that is responsible for heightened trophoblast cell death rates via apoptosis and autophagy. Whether trophoblast cells undergo necroptosis, a newly characterized form of regulated necrosis, and the potential role of CER in this process remain to be established. Herein, we report that exposure of both JEG3 cells and primary isolated cytotrophoblasts to C16:0 CER in conjunction with a caspase-8 inhibitor (Q-VD-OPh) promoted necroptotic cell death, as evidenced by increased expression and association of receptor-interacting protein kinases RIP1 and RIP3, as well as phosphorylation of mixed lineage kinase domain-like (MLKL) protein. MLKL activation and oligomerization could be abrogated by pretreatment with the necroptosis inhibitor necrostatin-1 (Nec-1). CER+Q-VD-OPH-treated primary trophoblasts displayed striking necrotic morphology along with disrupted fusion processes as evidenced by maintenance of E-cadherin-stained membrane boundaries and reduced glial cell missing-1 expression, but these events were effectively reversed using Nec-1. Of clinical relevance, we established an increased susceptibility to necroptotic cell death in preeclamptic placentae relative to normotensive controls. In preeclampsia, increased necrosome (RIP1/RIP3) protein levels, as well as MLKL activation and oligomerization associated with necrotic cytotrophoblast morphology. In addition, caspase-8 activity was reduced in severe early-onset preeclampsia cases. This study is the first to report that trophoblast cells undergo CER-induced necroptotic cell death, thereby contributing to the increased placental dysfunction and cell death found in preeclampsia.

Sphingolipids in mitochondria

Sphingolipids are bioactive lipids found in cell membranes that exert a critical role in signal transduction. In recent years, it has become apparent that sphingolipids participate in growth, senescence, differentiation and apoptosis. The anabolism and catabolism of sphingolipids occur in discrete subcellular locations and consist of a strictly regulated and interconnected network, with ceramide as the central hub. Altered sphingolipid metabolism is linked to several human diseases. Hence, an advanced knowledge of how and where sphingolipids are metabolized is of paramount importance in order to understand the role of sphingolipids in cellular functions. In this review, we provide an overview of sphingolipid metabolism. We focus on the distinct pathways of ceramide synthesis, highlighting the mitochondrial ceramide generation, transport of ceramide to mitochondria and its role in the regulation of mitochondrial-mediated apoptosis, mitophagy and implications to disease. We will discuss unanswered questions and exciting future directions. This article is part of a Special Issue entitled: Lipids of Mitochondria edited by Guenther Daum.