Roles and regulation of secretory and lysosomal acid sphingomyelinase

Multicentric investigations of the role in the disease severity of accelerated phospholipid changes in COVID-19 patient airway

CONTEXT

The changes in host membrane phospholipids are crucial in airway infection pathogenesis. Phospholipase A2 hydrolyzes host cell membranes, producing lyso-phospholipids and free fatty acids, including arachidonic acid (AA), which contributes significantly to lung inflammation.

AIM

Follow these changes and their evolution from day 1, day 3 to day 7 in airway aspirates of 89 patients with COVID-19-associated acute respiratory distress syndrome and examine whether they correlate with the severity of the disease. The patients were recruited in three French intensive care units. The analysis was conducted from admission to the intensive care unit until the end of the first week of mechanical ventilation.

RESULTS

In the airway aspirates, we found significant increases in the levels of host cell phospholipids, including phosphatidyl-serine and phosphatidyl-ethanolamine, and their corresponding lyso-phospholipids. This was accompanied by increased levels of AA and its inflammatory metabolite prostaglandin E2 (PGE2). Additionally, enhanced levels of ceramides, sphingomyelin, and free cholesterol were observed in these aspirates. These lipids are known to be involved in cell death and/or apoptosis, whereas free cholesterol plays a role in virus entry and replication in host cells. However, there were no significant changes in the levels of dipalmitoyl-phosphatidylcholine, the major surfactant phospholipid. A correlation analysis revealed an association between mortality risk and levels of AA and PGE2, as well as host cell phospholipids.

CONCLUSION

Our findings indicate a correlation between heightened cellular phospholipid modifications and variations in AA and PGE2 with the severity of the disease in patients. Nevertheless, there is no indication of surfactant alteration in the initial phases of the illness.

Ceramide-mediated orchestration of oxidative stress response through filopodia-derived small extracellular vesicles

Extracellular vesicles (EVs) are shed from the plasma membrane, but the regulation and function of these EVs remain unclear. We found that oxidative stress induced by H2O2 in Hela cells stimulated filopodia formation and the secretion of EVs. EVs were small (150 nm) and labeled for CD44, indicating that they were derived from filopodia. Filopodia-derived small EVs (sEVs) were enriched with the sphingolipid ceramide, consistent with increased ceramide in the plasma membrane of filopodia. Ceramide was colocalized with neutral sphingomyelinase 2 (nSMase2) and acid sphingomyelinase (ASM), two sphingomyelinases generating ceramide at the plasma membrane. Inhibition of nSMase2 and ASM prevented oxidative stress-induced sEV shedding but only nSMase2 inhibition prevented filopodia formation. nSMase2 was S-palmitoylated and interacted with ASM in filopodia to generate ceramide for sEV shedding. sEVs contained nSMase2 and ASM and decreased the level of these two enzymes in oxidatively stressed Hela cells. A novel metabolic labeling technique for EVs showed that oxidative stress induced secretion of fluorescent sEVs labeled with NBD-ceramide. NBD-ceramide-labeled sEVs transported ceramide to mitochondria, ultimately inducing cell death in a proportion of neuronal (N2a) cells. In conclusion, using Hela cells we provide evidence that oxidative stress induces interaction of nSMase2 and ASM at filopodia, which leads to shedding of ceramide-rich sEVs that target mitochondria and propagate cell death.

Overview of clinical, molecular, and therapeutic features of Niemann-Pick disease (types A, B, and C): Focus on therapeutic approaches

Niemann-Pick disease (NPD) is another type of metabolic disorder that is classified as lysosomal storage diseases (LSDs). The main cause of the disease is mutation in the SMPD1 (type A and B) or NPC1 or NPC2 (type C) genes, which lead to the accumulation of lipid substrates in the lysosomes of the liver, brain, spleen, lung, and bone marrow cells. This is followed by multiple cell damage, dysfunction of lysosomes, and finally dysfunction of body organs. So far, about 346, 575, and 30 mutations have been reported in SMPD1, NPC1, and NPC2 genes, respectively. Depending on the type of mutation and the clinical symptoms of the disease, the treatment will be different. The general aim of the current study is to review the clinical and molecular characteristics of patients with NPD and study various treatment methods for this disease with a focus on gene therapy approaches.

Normal and Dysregulated Sphingolipid Metabolism: Contributions to Podocyte Injury and Beyond

Podocyte health is vital for maintaining proper glomerular filtration in the kidney. Interdigitating foot processes from podocytes form slit diaphragms which regulate the filtration of molecules through size and charge selectivity. The abundance of lipid rafts, which are ordered membrane domains rich in cholesterol and sphingolipids, near the slit diaphragm highlights the importance of lipid metabolism in podocyte health. Emerging research shows the importance of sphingolipid metabolism to podocyte health through structural and signaling roles. Dysregulation in sphingolipid metabolism has been shown to cause podocyte injury and drive glomerular disease progression. In this review, we discuss the structure and metabolism of sphingolipids, as well as their role in proper podocyte function and how alterations in sphingolipid metabolism contributes to podocyte injury and drives glomerular disease progression.

Acid sphingomyelinase as a pathological and therapeutic target in neurological disorders: focus on Alzheimer's disease

Over the past decade, numerous studies have highlighted the importance of acid sphingomyelinase (ASM) in disease treatment in humans. This enzyme functions primarily to generate ceramide, maintain the cellular membrane, and regulate cellular function. However, in the blood and brain of patients with neurological disorders, including major depression, ischemic stroke, amyotrophic lateral sclerosis, multiple sclerosis, and Alzheimer's disease (AD), elevated ASM levels significantly suggest disease onset or progression. In these diseases, increased ASM is profoundly involved in neuronal death, abnormal autophagy, neuroinflammation, blood-brain barrier disruption, hippocampal neurogenesis loss, and immune cell dysfunction. Moreover, genetic and pharmacological inhibition of ASM can prevent or ameliorate various diseases. The therapeutic effects of ASM inhibition have prompted the urgent need to develop ASM inhibitors, and several ASM inhibitors have been identified. In this review, we summarize the current knowledge on the critical roles and mechanisms of ASM in brain cells and blood that are associated with different neuropathological features, especially those observed in AD. Furthermore, we elucidate the potential possibility and limitations of existing ASM-targeting drugs according to experimental studies in neurological disorder mouse models.

Mysterious sphingolipids: metabolic interrelationships at the center of pathophysiology

Metabolic pathways are complex and intertwined. Deficiencies in one or more enzymes in a given pathway are directly linked with genetic diseases, most of them having devastating manifestations. The metabolic pathways undertaken by sphingolipids are diverse and elaborate with ceramide species serving as the hubs of sphingolipid intermediary metabolism and function. Sphingolipids are bioactive lipids that serve a multitude of cellular functions. Being pleiotropic in function, deficiency or overproduction of certain sphingolipids is associated with many genetic and chronic diseases. In this up-to-date review article, we strive to gather recent scientific evidence about sphingolipid metabolism, its enzymes, and regulation. We shed light on the importance of sphingolipid metabolism in a variety of genetic diseases and in nervous and immune system ailments. This is a comprehensive review of the state of the field of sphingolipid biochemistry.

Factor VIIa releases phosphatidylserine-enriched extracellular vesicles from endothelial cells by activating acid sphingomyelinase

BACKGROUND

Our recent studies showed that activated factor (F) VII (FVIIa) releases extracellular vesicles (EVs) from the endothelium. FVIIa-released EVs were found to be enriched with phosphatidylserine (PS) and contribute to the hemostatic effect of FVIIa in thrombocytopenia and hemophilia.

OBJECTIVE

To investigate mechanisms by which FVIIa induces EV biogenesis and enriches EVs with PS.

METHODS

FVIIa activation of acid sphingomyelinase (aSMase) was evaluated by its translocation to the cell surface. The role of aSMase in the biogenesis of FVIIa-induced EVs and their enrichment with PS was investigated using specific siRNAs and inhibitors of aSMase and its downstream metabolites. Wild-type and aSMase-/- mice were injected with a control vehicle or FVIIa. EVs released into circulation were quantified by nanoparticle tracking analysis. EVs hemostatic potential was assessed in a murine thrombocytopenia model.

RESULTS

FVIIa activation of aSMase is responsible for both the externalization of PS and the release of EVs in endothelial cells. FVIIa-induced aSMase activation led to ceramide generation and de novo expression of transmembrane protein 16F. Inhibitors of ceramidases, sphingosine kinase, or sphingosine-1-phosphate receptor modulator blocked FVIIa-induced expression of transmembrane protein 16F and PS externalization without interfering with FVIIa release of EVs. In vivo, FVIIa release of EVs was markedly impaired in aSMase-/- mice compared with wild-type mice. Administration of a low dose of FVIIa, sufficient to induce EVs release, corrected bleeding associated with thrombocytopenia in wild-type mice but not in aSMase-/- mice.

CONCLUSION

Our study identifies a novel mechanism by which FVIIa induces PS externalization and releases PS-enriched EVs.

The therapeutic potential of sphingolipids for cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide and Inflammation plays a critical role in the development of CVD. Despite considerable progress in understanding the underlying mechanisms and various treatment options available, significant gaps in therapy necessitate the identification of novel therapeutic targets. Sphingolipids are a family of lipids that have gained attention in recent years as important players in CVDs and the inflammatory processes that underlie their development. As preclinical studies have shown that targeting sphingolipids can modulate inflammation and ameliorate CVDs, targeting sphingolipids has emerged as a promising therapeutic strategy. This review discusses the current understanding of sphingolipids' involvement in inflammation and cardiovascular diseases, the existing therapeutic approaches and gaps in therapy, and explores the potential of sphingolipids-based drugs as a future avenue for CVD treatment.

Immunotherapy targeting plasma ASM is protective in a mouse model of Alzheimer's disease

Acid sphingomyelinase (ASM) has been implicated in neurodegenerative disease pathology, including Alzheimer's disease (AD). However, the specific role of plasma ASM in promoting these pathologies is poorly understood. Herein, we explore plasma ASM as a circulating factor that accelerates neuropathological features in AD by exposing young APP/PS1 mice to the blood of mice overexpressing ASM, through parabiotic surgery. Elevated plasma ASM was found to enhance several neuropathological features in the young APP/PS1 mice by mediating the differentiation of blood-derived, pathogenic Th17 cells. Antibody-based immunotherapy targeting plasma ASM showed efficient inhibition of ASM activity in the blood of APP/PS1 mice and, interestingly, led to prophylactic effects on neuropathological features by suppressing pathogenic Th17 cells. Our data reveals insights into the potential pathogenic mechanisms underlying AD and highlights ASM-targeting immunotherapy as a potential strategy for further investigation.

Horse-Derived Ceramide Accentuates Glucosylceramide Synthase and Ceramide Synthase 3 by Activating PPARβ/δ and/or PPARγ to Stimulate Ceramide Synthesis

Horse-derived ceramide (HC), which contains galactosylceramides as its main component, significantly improves skin symptoms when applied topically to patients with atopic dermatitis. We speculated that efficacy resulted from the amelioration of epidermal ceramide metabolism, and we characterized those effects using reconstructed human epidermal equivalents. Lipid analysis, RT-PCR and Western blotting revealed that HC significantly increased the total ceramide content of the stratum corneum (SC), accompanied by significantly increased gene and/or protein expression levels of ceramide synthase (CERS) 3, fatty acid elongase (ELOVL) 4, glucosylceramide synthase (GCS), β-glucocerebrosidase, sphingomyelin synthase and acid sphingomyelinase. Mechanistic analyses using cultures of primary human keratinocytes revealed the marked stimulatory effects of HC on the mRNA expression levels of CERS3, ELOVL4 and GCS under high calcium-derived differentiation conditions. Signaling analyses demonstrated that an antagonist of PPARβ/δ significantly abrogated the HC-stimulated mRNA expression levels of GCS, CERS3 and ELOVL4. GW9662, an antagonist of PPARγ, significantly abolished the HC-up-regulated mRNA expression levels of GCS and ELOVL4, but not of CERS3. These findings suggest that HC has the distinct potential to accentuate the expression of GCS, CERS3 and ELOVL4 via the activation of PPARβ/δ and/or PPARγ to accelerate ceramide synthesis in the SC.

The lipidomes of C. elegans with mutations in asm-3/acid sphingomyelinase and hyl-2/ceramide synthase show distinct lipid profiles during aging

Lipid metabolism affects cell and physiological functions that mediate animal healthspan and lifespan. Lipidomics approaches in model organisms have allowed us to better understand changes in lipid composition related to age and lifespan. Here, using the model C. elegans, we examine the lipidomes of mutants lacking enzymes critical for sphingolipid metabolism; specifically, we examine acid sphingomyelinase (asm-3), which breaks down sphingomyelin to ceramide, and ceramide synthase (hyl-2), which synthesizes ceramide from sphingosine. Worm asm-3 and hyl-2 mutants have been previously found to be long- and short-lived, respectively. We analyzed longitudinal lipid changes in wild type animals compared to mutants at 1-, 5-, and 10-days of age. We detected over 700 different lipids in several lipid classes. Results indicate that wildtype animals exhibit increased triacylglycerols (TAG) at 10-days compared to 1-day, and decreased lysophoshatidylcholines (LPC). We find that 10-day hyl-2 mutants have elevated total polyunsaturated fatty acids (PUFA) and increased LPCs compared to 10-day wildtype animals. These changes mirror another short-lived model, the daf-16/FOXO transcription factor that is downstream of the insulin-like signaling pathway. In addition, we find that hyl-2 mutants have poor oxidative stress response, supporting a model where mutants with elevated PUFAs may accumulate more oxidative damage. On the other hand, 10-day asm-3 mutants have fewer TAGs. Intriguingly, asm-3 mutants have a similar lipid composition as the long-lived, caloric restriction model eat-2/mAChR mutant. Together, these analyses highlight the utility of lipidomic analyses to characterize metabolic changes during aging in C. elegans.

Alterations to Sphingomyelin Metabolism Affect Hemostasis and Thrombosis

BACKGROUND

Our recent studies suggest that sphingomyelin levels in the plasma membrane influence TF (tissue factor) procoagulant activity. The current study was performed to investigate how alterations to sphingomyelin metabolic pathway would affect TF procoagulant activity and thereby affect hemostatic and thrombotic processes.

METHODS

Macrophages and endothelial cells were transfected with specific siRNAs or infected with adenoviral vectors to alter sphingomyelin levels in the membrane. TF activity was measured in factor X activation assay. Saphenous vein incision-induced bleeding and the inferior vena cava ligation-induced flow restriction mouse models were used to evaluate hemostasis and thrombosis, respectively.

RESULTS

Overexpression of SMS (sphingomyelin synthase) 1 or SMS2 in human monocyte-derived macrophages suppresses ATP-stimulated TF procoagulant activity, whereas silencing SMS1 or SMS2 increases the basal cell surface TF activity to the same level as of ATP-decrypted TF activity. Consistent with the concept that sphingomyelin metabolism influences TF procoagulant activity, silencing of acid sphingomyelinase or neutral sphingomyelinase 2 or 3 attenuates ATP-induced enhanced TF procoagulant activity in macrophages and endothelial cells. Niemann-Pick disease fibroblasts with a higher concentration of sphingomyelin exhibited lower TF activity compared with wild-type fibroblasts. In vivo studies revealed that LPS+ATP-induced TF activity and thrombin generation were attenuated in ASMase^-/- mice, while their levels were increased in SMS2^-/- mice. Further studies revealed that acid sphingomyelinase deficiency leads to impaired hemostasis, whereas SMS2 deficiency increases thrombotic risk.

CONCLUSIONS

Overall, our data indicate that alterations in sphingomyelin metabolism would influence TF procoagulant activity and affect hemostatic and thrombotic processes.

Acid sphingomyelinase inhibition improves motor behavioral deficits and neuronal loss in an amyotrophic lateral sclerosis mouse model

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease characterized by the degeneration of motor neurons in the spinal cord. Main symptoms are manifested as weakness, muscle loss, and muscle atrophy. Some studies have reported that alterations in sphingolipid metabolism may be intimately related to neurodegenerative diseases, including ALS. Acid sphingomyelinase (ASM), a sphingolipid-metabolizing enzyme, is considered an important mediator of neurodegenerative diseases. Herein, we show that ASM activity increases in samples from patients with ALS and in a mouse model. Moreover, genetic inhibition of ASM improves motor function impairment and spinal neuronal loss in an ALS mouse model. Therefore, these results suggest the role of ASM as a potentially effective target and ASM inhibition may be a possible therapeutic approach for ALS. [BMB Reports 2022; 55(12): 621-626].

Comparative Study on Epidermal Moisturizing Effects and Hydration Mechanisms of Rice-Derived Glucosylceramides and Ceramides

Ceramide (Cer) plays an important role in skin barrier functions in the stratum corneum (SC). The ingestion of food-derived glucosylceramides (GlcCer) attenuates transepidermal water loss (TEWL). However, the moisturizing effects of single molecules of GlcCer and Cer remain unclear. Therefore, we herein purified 13 GlcCer and 6 Cer, including elasticamide, which has the same structure as human Cer[AP], from rice and compared their epidermal moisturizing effects in a reconstructed human epidermal keratinization model. The results obtained showed that 10 µM of 5 GlcCer[d18:2] with a 4E,8Z sphingadienine and C18 to C26 fatty acids and 10 µg/mL of 3 Cer with C23 or C24 fatty acids significantly reduced TEWL. The moisturizing effects of these GlcCer were dependent on the length of fatty acids. Furthermore, 10 µg/mL of elasticamide increased the SC Cer contents by promoting the expression of GlcCer synthase. Electron microscopic observations revealed that 1 µM of GlcCer[d18:2(4E,8Z)/26:0] increased the number of keratohyalin granules and desmosomes. Immunostaining and Western blotting indicated that 1 µM of GlcCer[d18:2(4E,8Z)/26:0] up-regulated the expression of filaggrin and corneodesmosin, which contribute to epidermal hydration. This comparative study on epidermal moisturization by GlcCer and Cer isolated from rice revealed differences in their hydration mechanisms.

Acid sphingomyelinase inhibition improves motor behavioral deficits and neuronal loss in an amyotrophic lateral sclerosis mouse model

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease characterized by the degeneration of motor neurons in the spinal cord. Main symptoms are manifested as weakness, muscle loss, and muscle atrophy. Some studies have reported that alterations in sphingolipid metabolism may be intimately related to neurodegenerative diseases, including ALS. Acid sphingomyelinase (ASM), a sphingolipid-metabolizing enzyme, is considered an important mediator of neurodegenerative diseases. Herein, we show that ASM activity increases in samples from patients with ALS and in a mouse model. Moreover, genetic inhibition of ASM improves motor function impairment and spinal neuronal loss in an ALS mouse model. Therefore, these results suggest the role of ASM as a potentially effective target and ASM inhibition may be a possible therapeutic approach for ALS. [BMB Reports 2022; 55(12): 621-626].

Advancements on the Multifaceted Roles of Sphingolipids in Hematological Malignancies

Dysregulation of sphingolipid metabolism plays a complex role in hematological malignancies, beginning with the first historical link between sphingolipids and apoptosis discovered in HL-60 leukemic cells. Numerous manuscripts have reviewed the field including the early discoveries that jumpstarted the studies. Many studies discussed here support a role for sphingolipids, such as ceramide, in combinatorial therapeutic regimens to enhance anti-leukemic effects and reduce resistance to standard therapies. Additionally, inhibitors of specific nodes of the sphingolipid pathway, such as sphingosine kinase inhibitors, significantly reduce leukemic cell survival in various types of leukemias. Acid ceramidase inhibitors have also shown promising results in acute myeloid leukemia. As the field moves rapidly, here we aim to expand the body of literature discussed in previously published reviews by focusing on advances reported in the latter part of the last decade.

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.

The Lard Works in Mysterious Ways: Ceramides in Nutrition-Linked Chronic Disease

Diet influences onset, progression, and severity of several chronic diseases, including heart failure, diabetes, steatohepatitis, and a subset of cancers. The prevalence and clinical burden of these obesity-linked diseases has risen over the past two decades. These metabolic disorders are driven by ectopic lipid deposition in tissues not suited for fat storage, leading to lipotoxic disruption of cell function and survival. Sphingolipids such as ceramides are among the most deleterious and bioactive metabolites that accrue, as they participate in selective insulin resistance, dyslipidemia, oxidative stress and apoptosis. This review discusses our current understanding of biochemical pathways controlling ceramide synthesis, production and action; influences of diet on ceramide levels; application of circulating ceramides as clinical biomarkers of metabolic disease; and molecular mechanisms linking ceramides to altered metabolism and survival of cells. Development of nutritional or pharmacological strategies to lower ceramides could have therapeutic value in a wide range of prevalent diseases.

FTY720 decreases ceramides levels in the brain and prevents memory impairments in a mouse model of familial Alzheimer's disease expressing APOE4

The protection mediated by the bioactive sphingolipid sphingosine-1-phosphate (S1P) declines during Alzheimer's disease (AD) progression, especially in patients carrying the apolipoprotein E ε4 (APOE4) isoform. The drug FTY720 mimics S1P bioactivity, but its efficacy in treating AD is unclear. Two doses of FTY720 (0.1 mg / kg and 0.5 mg / kg daily) were given by oral gavage for 15 weeks to transgenic mouse models of familial AD carrying human apolipoprotein E (APOE) APOE3 (E3FAD) or APOE4 (E4FAD). After 12 weeks of treatment, animals were subjected to behavioral tests for memory, locomotion, and anxiety. Blood was withdrawn at different time points and brains were collected for sphingolipids analysis by mass spectrometry, gene expression by RT-PCR and Aβ quantification by ELISA. We discovered that low levels of S1P in the plasma is associated with a higher probability of failing the memory test and that FTY720 prevents memory impairments in E4FAD. The beneficial effect of FTY720 was induced by a shift of the sphingolipid metabolism in the brain towards a lower production of toxic metabolites, like ceramide d18:1/16:0 and d18:1/22:0, and reduction of amyloid-β burden and inflammation. In conclusion, we provide further evidence of the druggability of the sphingolipid system in AD.

Relationships between ocular surface sphingomyelinases, Meibum and Tear Sphingolipids, and clinical parameters of meibomian gland dysfunction

PURPOSE

Sphingolipids (SPL) are a class of lipid molecules that play important functional and structural roles in our body and are a component of meibum. Sphingomyelinases (SMases) are key enzymes in sphingolipid metabolism that hydrolyze sphingomyelin (SM) and generate ceramide (Cer). The purpose of this study was to examine relationships between ocular surface SMases, SPL composition, and parameters of Meibomian gland dysfunction (MGD).

METHODS

Individuals were grouped by meibum quality (n = 25 with poor-quality, MGD, and n = 25 with good-quality, control). Meibum and tears were analyzed with LC-MS to quantify SPL classes: Cer, Hexosyl-Ceramide (Hex-Cer), SM, Sphingosine (Sph), and sphingosine 1-phosphate (S1P). SMase activity in tears were quantified using a commercially available 'SMase assay'. Statistical analysis included multiple linear regression analyses to assess the impact of SMase activity on lipid composition, as well as ocular surface symptoms and signs of MGD.

RESULTS

Demographic characteristics were similar between the two groups. nSMase and aSMase levels were lower in the poor vs good quality group. aSMase activity in tears negatively correlated with SM in meibum and tears and positively with Sph in meibum and S1P in tears. Lower SMase activity were associated with signs of MGD, most notably Meibomian gland dropout.

CONCLUSION

This study suggests that individuals with MGD have reduced enzymatic activity of SMases in tears. Specifically, individuals with poor vs good meibum quality were noted to have alterations in SMase activity and SPL composition of meibum and tears which may reflect deviations from normal lipid metabolism in individuals with MGD.

Increased acid sphingomyelinase levels in pediatric patients with obesity

The level of secretory acid sphingomyelinase (S-ASM), a key enzyme in the sphingolipid metabolism, is elevated in a variety of human diseases, including in the serum of obese adults. Alterations in S-ASM were also found to induce morphological changes in erythrocytes. Consequently, the inhibition of S-ASM by functional Inhibitors of ASM (FIASMA) may have broad clinical implications. The purpose of this study was to assess S-ASM activity in pediatric patients with obesity and healthy matched controls, as well as to investigate the erythrocyte morphology using transmission electron microscopy. We recruited 46 obese patients (mean age 11 ± 2.9 years) and 44 controls (mean age 10.8 ± 2.9 years). S-ASM activity was significantly higher (Wilcoxon signed-rank test p-value: 0.004) in obese patients (mean 396.4 ± 49.7 pmol/ml/h) than in controls (mean 373.7 ± 23.1 pmol/ml/h). No evidence of morphological differences in erythrocytes was found between the two populations. We then carried out a case–control study based on the spontaneous reporting system database to compare FIASMAs with NON-FIASMAs in terms of weight gain risk. Children who received FIASMA had a significantly lower frequency of weight gain reports than patients who took NON-FIASMA agents (p < 0.001). Our findings suggest there is an intriguing possibility that S-ASM may play a role in pediatric obesity. This pilot study could serve as the basis for future studies in this interesting field of research.

Acid sphingomyelinase/ceramide system in schizophrenia: implications for therapeutic intervention as a potential novel target

Schizophrenia is a severe mental illness, as the efficacies of current antipsychotic medications are far from satisfactory. An improved understanding of the signaling molecules involved in schizophrenia may provide novel therapeutic targets. Acid sphingomyelinase (ASM) catalyzes cellular membrane sphingomyelin into ceramide, which is further metabolized into sphingosine-1-phophate (S1P). ASM, ceramide, and S1P at the cell surface exert critical roles in the regulation of biophysical processes that include proliferation, apoptosis, and inflammation, and are thereby considered important signaling molecules. Although research on the ASM/ceramide system is still in its infancy, structural and metabolic abnormalities have been demonstrated in schizophrenia. ASM/ceramide system dysfunction is linked to the two important models of schizophrenia, the dopamine (DA) hypothesis through affecting presynaptic DA signaling, and the vulnerability-stress-inflammation model that includes the contribution of stress on the basis of genetic predisposition. In this review, we highlight the current knowledge of ASM/ceramide system dysfunction in schizophrenia gained from human and animal studies, and formulate future directions from the biological landscape for the development of new treatments. Collectively, these discoveries suggest that aberrations in the ASM/ceramide system, especially in ASM activity and levels of ceramide and S1P, may alter cerebral microdomain structure and neuronal metabolism, leading to neurotransmitter (e.g., DA) dysfunction and neuroinflammation. As such, the ASM/ceramide system may offer therapeutic targets for novel medical interventions. Normalization of the aberrant ASM/ceramide system or ceramide reduction by using approved functional inhibitors of ASM, such as fluvoxamine and rosuvastatin, may improve clinical outcomes of patients with schizophrenia. These transformative findings of the ASM/ceramide system in schizophrenia, although intriguing and exciting, may pose scientific questions and challenges that will require further studies for their resolution.

Involvement of Ceramide Signalling in Radiation-Induced Tumour Vascular Effects and Vascular-Targeted Therapy

Sphingolipids are well-recognized critical components in several biological processes. Ceramides constitute a class of sphingolipid metabolites that are involved in important signal transduction pathways that play key roles in determining the fate of cells to survive or die. Ceramide accumulated in cells causes apoptosis; however, ceramide metabolized to sphingosine promotes cell survival and angiogenesis. Studies suggest that vascular-targeted therapies increase endothelial cell ceramide resulting in apoptosis that leads to tumour cure. Specifically, ultrasound-stimulated microbubbles (USMB) used as vascular disrupting agents can perturb endothelial cells, eliciting acid sphingomyelinase (ASMase) activation accompanied by ceramide release. This phenomenon results in endothelial cell death and vascular collapse and is synergistic with other antitumour treatments such as radiation. In contrast, blocking the generation of ceramide using multiple approaches, including the conversion of ceramide to sphingosine-1-phosphate (S1P), abrogates this process. The ceramide-based cell survival "rheostat" between these opposing signalling metabolites is essential in the mechanotransductive vascular targeting following USMB treatment. In this review, we aim to summarize the past and latest findings on ceramide-based vascular-targeted strategies, including novel mechanotransductive methodologies.

Complexities of JC Polyomavirus Receptor-Dependent and -Independent Mechanisms of Infection

JC polyomavirus (JCPyV) is a small non-enveloped virus that establishes lifelong, persistent infection in most of the adult population. Immune-competent patients are generally asymptomatic, but immune-compromised and immune-suppressed patients are at risk for the neurodegenerative disease progressive multifocal leukoencephalopathy (PML). Studies with purified JCPyV found it undergoes receptor-dependent infectious entry requiring both lactoseries tetrasaccharide C (LSTc) attachment and 5-hydroxytryptamine type 2 entry receptors. Subsequent work discovered the major targets of JCPyV infection in the central nervous system (oligodendrocytes and astrocytes) do not express the required attachment receptor at detectable levels, virus could not bind these cells in tissue sections, and viral quasi-species harboring recurrent mutations in the binding pocket for attachment. While several research groups found evidence JCPyV can use novel receptors for infection, it was also discovered that extracellular vesicles (EVs) can mediate receptor independent JCPyV infection. Recent work also found JCPyV associated EVs include both exosomes and secretory autophagosomes. EVs effectively present a means of immune evasion and increased tissue tropism that complicates viral studies and anti-viral therapeutics. This review focuses on JCPyV infection mechanisms and EV associated and outlines key areas of study necessary to understand the interplay between virus and extracellular vesicles.

Ars moriendi: Proteases as sculptors of cellular suicide

The Ars moriendi, which translates to "The Art of Dying," encompasses two Latin texts that gave advice on how to die well and without fear according to the Christian precepts of the late Middle Ages. Given that ten to hundred billion cells die in our bodies every day, it is obvious that the concept of a well and orderly ("regulated") death is also paramount at the cellular level. In apoptosis, as the most well-studied form of regulated cell death, proteases of the caspase family are the central mediators. However, caspases are not the only proteases that act as sculptors of cellular suicide, and therefore, we here provide an overview of the impact of proteases in apoptosis and other forms of regulated cell death.

Discovery of a dual-action small molecule that improves neuropathological features of Alzheimer's disease mice

Since Alzheimer’s disease (AD) is a multifaceted neurodegenerative disease, multitargeted therapeutic approaches are likely required for effective AD treatment. The importance of acid sphingomyelinase (ASM) activation in the various neuropathological features of AD is well-known. Therefore, in this study, we focused on identifying an efficient, direct inhibitor of ASM activity. We found that KARI 201 was a highly selective ASM activity inhibitor without any off-target effects. Through RNA-sequencing analysis in brains of AD mice, we also unexpectedly uncovered the role of KARI 201 as a ghrelin receptor agonist. This dual role of KARI 201 in neurons led to improvement of Aβ accumulation, neuroinflammation, synapse loss, hippocampal neurogenesis, and memory dysfunction in AD mice.

Alzheimer’s disease (AD) is characterized by complex, multifactorial neuropathology, suggesting that small molecules targeting multiple neuropathological factors are likely required to successfully impact clinical progression. Acid sphingomyelinase (ASM) activation has been recognized as an important contributor to these neuropathological features in AD, leading to the concept of using ASM inhibitors for the treatment of this disorder. Here we report the identification of KARI 201, a direct ASM inhibitor evaluated for AD treatment. KARI 201 exhibits highly selective inhibition effects on ASM, with excellent pharmacokinetic properties, especially with regard to brain distribution. Unexpectedly, we found another role of KARI 201 as a ghrelin receptor agonist, which also has therapeutic potential for AD treatment. This dual role of KARI 201 in neurons efficiently rescued neuropathological features in AD mice, including amyloid beta deposition, autophagy dysfunction, neuroinflammation, synaptic loss, and decreased hippocampal neurogenesis and synaptic plasticity, leading to an improvement in memory function. Our data highlight the possibility of potential clinical application of KARI 201 as an innovative and multifaceted drug for AD treatment.

Conformational dynamics of free and membrane-bound human Hsp70 in model cytosolic and endo-lysosomal environments

The binding of the major stress-inducible human 70-kDa heat shock protein (Hsp70) to the anionic phospholipid bis-(monoacylglycero)-phosphate (BMP) in the lysosomal membrane is crucial for its impact on cellular pathology in lysosomal storage disorders. However, the conformational features of this protein-lipid complex remain unclear. Here, we apply hydrogen-deuterium exchange mass spectrometry (HDX-MS) to describe the dynamics of the full-length Hsp70 in the cytosol and its conformational changes upon translocation into lysosomes. Using wild-type and W90F mutant proteins, we also map and discriminate the interaction of Hsp70 with BMP and other lipid components of the lysosomal membrane. We identify the N-terminal of the nucleotide binding domain (residues 87-118) as the primary orchestrator of BMP interaction. We show that the conformation of this domain is significantly reorganized in the W90F mutant, explaining its inability to stabilize lysosomal membranes. Overall, our results reveal important new molecular details of the protective effect of Hsp70 in lysosomal storage diseases, which, in turn, could guide future drug development.

Mapping the serum proteome to neurological diseases using whole genome sequencing

Despite the increasing global burden of neurological disorders, there is a lack of effective diagnostic and therapeutic biomarkers. Proteins are often dysregulated in disease and have a strong genetic component. Here, we carry out a protein quantitative trait locus analysis of 184 neurologically-relevant proteins, using whole genome sequencing data from two isolated population-based cohorts (N = 2893). In doing so, we elucidate the genetic landscape of the circulating proteome and its connection to neurological disorders. We detect 214 independently-associated variants for 107 proteins, the majority of which (76%) are cis-acting, including 114 variants that have not been previously identified. Using two-sample Mendelian randomisation, we identify causal associations between serum CD33 and Alzheimer's disease, GPNMB and Parkinson's disease, and MSR1 and schizophrenia, describing their clinical potential and highlighting drug repurposing opportunities.

Transcriptional Differences in Lipid-Metabolizing Enzymes in Murine Sebocytes Derived from Sebaceous Glands of the Skin and Preputial Glands

Sebaceous glands are adnexal structures, which critically contribute to skin homeostasis and the establishment of a functional epidermal barrier. Sebocytes, the main cell population found within the sebaceous glands, are highly specialized lipid-producing cells. Sebaceous gland-resembling tissue structures are also found in male rodents in the form of preputial glands. Similar to sebaceous glands, they are composed of lipid-specialized sebocytes. Due to a lack of adequate organ culture models for skin sebaceous glands and the fact that preputial glands are much larger and easier to handle, previous studies used preputial glands as a model for skin sebaceous glands. Here, we compared both types of sebocytes, using a single-cell RNA sequencing approach, to unravel potential similarities and differences between the two sebocyte populations. In spite of common gene expression patterns due to general lipid-producing properties, we found significant differences in the expression levels of genes encoding enzymes involved in the biogenesis of specialized lipid classes. Specifically, genes critically involved in the mevalonate pathway, including squalene synthase, as well as the sphingolipid salvage pathway, such as ceramide synthase, (acid) sphingomyelinase or acid and alkaline ceramidases, were significantly less expressed by preputial gland sebocytes. Together, our data revealed tissue-specific sebocyte populations, indicating major developmental, functional as well as biosynthetic differences between both glands. The use of preputial glands as a surrogate model to study skin sebaceous glands is therefore limited, and major differences between both glands need to be carefully considered before planning an experiment.

Actin Cytoskeletal Dynamics in Single-Cell Wound Repair

The plasma membrane protects the eukaryotic cell from its surroundings and is essential for cell viability; thus, it is crucial that membrane disruptions are repaired quickly to prevent immediate dyshomeostasis and cell death. Accordingly, cells have developed efficient repair mechanisms to rapidly reseal ruptures and reestablish membrane integrity. The cortical actin cytoskeleton plays an instrumental role in both plasma membrane resealing and restructuring in response to damage. Actin directly aids membrane repair or indirectly assists auxiliary repair mechanisms. Studies investigating single-cell wound repair have often focused on the recruitment and activation of specialized repair machinery, despite the undeniable need for rapid and dynamic cortical actin modulation; thus, the role of the cortical actin cytoskeleton during wound repair has received limited attention. This review aims to provide a comprehensive overview of membrane repair mechanisms directly or indirectly involving cortical actin cytoskeletal remodeling.

Lycoperoside H, a Tomato Seed Saponin, Improves Epidermal Dehydration by Increasing Ceramide in the Stratum Corneum and Steroidal Anti-Inflammatory Effect

Tomatoes are widely consumed, however, studies on tomato seeds are limited. In this study, we isolated 11 compounds including saponins and flavonol glycosides from tomato seeds and evaluated their effects on epidermal hydration. Among the isolated compounds, tomato seed saponins (10 µM) significantly increased the mRNA expression of proteins related to epidermal hydration, including filaggrin, involucrin, and enzymes for ceramide synthesis, by 1.32- to 1.91-fold compared with the control in HaCaT cells. Tomato seed saponins (10 µM) also decreased transepidermal water loss by 7 to 13 g/m²·h in the reconstructed human epidermal keratinization (RHEK) models. Quantitative analysis of the ceramide content in the stratum corneum (SC) revealed that lycoperoside H (1–10 µM) is a promising candidate to stimulate ceramide synthesis via the upregulation of ceramide synthase-3, glucosylceramide synthase, and β-glucocerebrosidase, which led to an increase in the total SC ceramides (approximately 1.5-fold) in concert with ceramide (NP) (approximately 2-fold) in the RHEK models. Evaluation of the anti-inflammatory and anti-allergic effects of lycoperoside H demonstrated that lycoperoside H is suggested to act as a partial agonist of the glucocorticoid receptor and exhibits anti-inflammatory effects (10 mg/kg in animal test). These findings indicate that lycoperoside H can improve epidermal dehydration and suppress inflammation by increasing SC ceramide and steroidal anti-inflammatory activity.

Evaluation of the relationship between intravascular hemolysis and clinical manifestations in sickle cell disease: decreased hemopexin during vaso-occlusive crises and increased inflammation in acute chest syndrome

The aims of this study were to determine the possible relationships between the levels of hemin, hemopexin, acid sphingomyelinase, nitrite/nitrate (NOx), and other parameters in patients with SCD and to assess whether they were associated with vaso-occlusive crises (VOCs) or acute chest syndrome (ACS). Patients with SCD (homozygous or sickle beta-thalassemia) who were confirmed to have VOC or ACS were included. Blood samples were obtained at admission, on the third day of hospitalization, and at steady state. Demographic characteristics, pain (visual analog scale), complication history, complete blood count, lactate dehydrogenase, and C-reactive protein levels were recorded. Hemin, hemopexin, acid sphingomyelinase, and NOx were measured via ELISA. A total of 31 patients (22 VOC, 9 ACS) were included. Mean age was 16.4 ± 4.7 years. Admission white blood cell count and C-reactive protein levels were significantly higher in the ACS group. Patients with ACS also demonstrated a significant decreasing trend of LDH and an increasing trend of NOx values from admission to steady state. Notably, hemopexin levels were significantly lower on the third day of hospitalization compared to steady-state levels. Despite limited patient count in the ACS group, these patients appear to have strikingly greater inflammatory activation at admission, and the progression of ACS may be associated with LDH and NOx levels. Lower hemopexin levels during hospitalization versus steady state appear to support a role for the administration of hemopexin therapy during crises.

Role of ceramide/sphingomyelin (SM) balance regulated through "SM cycle" in cancer

Sphingomyelin synthase (SMS), which comprises of two isozymes, SMS1 and SMS2, is the only enzyme that generates sphingomyelin (SM) by transferring phosphocholine of phosphatidylcholine to ceramide in mammals. Conversely, ceramide is generated from SM hydrolysis via sphingomyelinases (SMases), ceramide de novo synthesis, and the salvage pathway. The biosynthetic pathway for SM and ceramide content by SMS and SMase, respectively, is called "SM cycle." SM forms a SM-rich microdomain on the cell membrane to regulate signal transduction, such as proliferation/survival, migration, and inflammation. On the other hand, ceramide acts as a lipid mediator by forming a ceramide-rich platform on the membrane, and ceramide exhibits physiological actions such as cell death, cell cycle arrest, and autophagy induction. Therefore, the regulation of ceramide/SM balance by SMS and SMase is responsible for diverse cell functions not only in physiological cells but also in cancer cells. This review outlines the implications of ceramide/SM balance through "SM cycle" in cancer progression and prevention. In addition, the possible involvement of "SM cycle" is introduced in anti-cancer tumor immunity, which has become a hot topic to innovate a more effective and safer way to conquer cancer in recent years.

Functional characterization of novel variants in SMPD1 in Indian patients with acid sphingomyelinase deficiency

Pathogenic variations in SMPD1 lead to acid sphingomyelinase deficiency (ASMD), that is, Niemann-Pick disease (NPD) type A and B (NPA, NPB), which is a recessive lysosomal storage disease. The knowledge of variant spectrum in Indian patients is crucial for early and accurate NPD diagnosis and genetic counseling of families. In this study, we recruited 40 unrelated pediatric patients manifesting symptoms of ASMD and subnormal ASM enzyme activity. Variations in SMPD1 were studied using Sanger sequencing for all exons, followed by interpretation of variants based on American College of Medical Genetics and Genomics & Association for Molecular Pathology (ACMG/AMP) criteria. We identified 18 previously unreported variants and 21 known variants, including missense, nonsense, deletions, duplications, and splice site variations with disease-causing potential. Eight missense variants were functionally characterized using in silico molecular dynamic simulation and in vitro transient transfection in HEK293T cells, followed by ASM enzyme assay, immunoblot, and immunofluorescence studies. All the variants showed reduced ASM activity in transfected cells confirming their disease-causing potential. The study provides data for efficient prenatal diagnosis and genetic counseling of families with NPD type A and B.

Synthesis and characterization of a new two photon excitable acid sphingomyelinase FRET probe

Recently, FRET probes for acid sphingomyelinase (ASM) have enabled the observation of enzyme activity in intact cells for the first time. Here we present an ASM FRET probe specifically optimized for 2-photon excitation. To facilitate probe characterization and comparison to the previous probe, we mixed the two intact probes with defined amounts of the probes' ceramide cleavage products and mounted them on lipid beads. Directly excited NBD FRET acceptor fluorescene proved to be a useful means of reference and showed that the new probe is brighter, albeit only moderately, than the previous one. The new probe was then used to detect inhibition by various ASM inhibitors microscopically for the first time. Also in cells, directly excited acceptor fluorescence proved to be a useful parameter in addition to FRET to visualize inhibition of ASM.

Sphingomyelinases in a journey to combat arthropod-borne pathogen transmission

Ixodes scapularis ticks feed on humans and other vertebrate hosts and transmit several pathogens of public health concern. Tick saliva is a complex mixture of bioactive proteins, lipids and immunomodulators, such as I. scapularis sphingomyelinase (IsSMase)-like protein, an ortholog of dermonecrotoxin SMase D found in the venom of Loxosceles spp. of spiders. IsSMase modulates the host immune response towards Th2, which suppresses Th1-mediated cytokines to facilitate pathogen transmission. Arboviruses utilize exosomes for their transmission from tick to the vertebrate host, and exosomes derived from tick saliva/salivary glands suppress C-X-C motif chemokine ligand 12 and interleukin-8 immune response(s) in human skin to delay wound healing and repair processes. IsSMase affects also viral replication and exosome biogenesis, thereby inhibiting tick-to-vertebrate host transmission of pathogenic exosomes. In this review, we elaborate on exosomes and their biogenesis as potential candidates for developing novel control measure(s) to combat tick-borne diseases. Such targets could help with the development of an efficient anti-tick vaccine for preventing the transmission of tick-borne pathogens.

Enzyme Replacement Therapy for Genetic Disorders Associated with Enzyme Deficiency

Mutations in human genes might lead to loss of functional proteins, causing diseases. Among these genetic disorders, a large class is associated with the deficiency in metabolic enzymes, resulting in both an increase in the concentration of substrates and a loss in the metabolites produced by the catalyzed reactions. The identification of therapeutic actions based on small molecules represents a challenge to medicinal chemists because the target is missing. Alternative approaches are biology-based, ranging from gene and stem cell therapy, CRISPR/Cas9 technology, distinct types of RNAs, and enzyme replacement therapy (ERT). This review will focus on the latter approach that since the 1990s has been successfully applied to cure many rare diseases, most of them being lysosomal storage diseases or metabolic diseases. So far, a dozen enzymes have been approved by FDA/EMA for lysosome storage disorders and only a few for metabolic diseases. Enzymes for replacement therapy are mainly produced in mammalian cells and some in plant cells and yeasts and are further processed to obtain active, highly bioavailable, less degradable products. Issues still under investigation for the increase in ERT efficacy are the optimization of enzymes interaction with cell membrane and internalization, the reduction in immunogenicity, and the overcoming of blood-brain barrier limitations when neuronal cells need to be targeted. Overall, ERT has demonstrated its efficacy and safety in the treatment of many genetic rare diseases, both saving newborn lives and improving patients' life quality, and represents a very successful example of targeted biologics.

Physiological functions and therapeutic applications of neutral sphingomyelinase and acid sphingomyelinase

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

In Silico Analysis of the Molecular-Level Impact of SMPD1 Variants on Niemann-Pick Disease Severity

Sphingomyelin phosphodiesterase (SMPD1) is a key enzyme in the sphingolipid metabolism. Genetic SMPD1 variants have been related to the Niemann-Pick lysosomal storage disorder, which has different degrees of phenotypic severity ranging from severe symptomatology involving the central nervous system (type A) to milder ones (type B). They have also been linked to neurodegenerative disorders such as Parkinson and Alzheimer. In this paper, we leveraged structural, evolutionary and stability information on SMPD1 to predict and analyze the impact of variants at the molecular level. We developed the SMPD1-ZooM algorithm, which is able to predict with good accuracy whether variants cause Niemann-Pick disease and its phenotypic severity; the predictor is freely available for download. We performed a large-scale analysis of all possible SMPD1 variants, which led us to identify protein regions that are either robust or fragile with respect to amino acid variations, and show the importance of aromatic-involving interactions in SMPD1 function and stability. Our study also revealed a good correlation between SMPD1-ZooM scores and in vitro loss of SMPD1 activity. The understanding of the molecular effects of SMPD1 variants is of crucial importance to improve genetic screening of SMPD1-related disorders and to develop personalized treatments that restore SMPD1 functionality.

Targeting the Sphingosine Kinase/Sphingosine-1-Phosphate Signaling Axis in Drug Discovery for Cancer Therapy

Sphingolipid metabolites have emerged as critical players in the regulation of various physiological processes. Ceramide and sphingosine induce cell growth arrest and apoptosis, whereas sphingosine-1-phosphate (S1P) promotes cell proliferation and survival. Here, we present an overview of sphingolipid metabolism and the compartmentalization of various sphingolipid metabolites. In addition, the sphingolipid rheostat, a fine metabolic balance between ceramide and S1P, is discussed. Sphingosine kinase (SphK) catalyzes the synthesis of S1P from sphingosine and modulates several cellular processes and is found to be essentially involved in various pathophysiological conditions. The regulation and biological functions of SphK isoforms are discussed. The functions of S1P, along with its receptors, are further highlighted. The up-regulation of SphK is observed in various cancer types and is also linked to radio- and chemoresistance and poor prognosis in cancer patients. Implications of the SphK/S1P signaling axis in human pathologies and its inhibition are discussed in detail. Overall, this review highlights current findings on the SphK/S1P signaling axis from multiple angles, including their functional role, mechanism of activation, involvement in various human malignancies, and inhibitor molecules that may be used in cancer therapy.

Lipid presentation by the protein C receptor links coagulation with autoimmunity

Antiphospholipid antibodies (aPLs) cause severe autoimmune disease characterized by vascular pathologies and pregnancy complications. Here, we identify endosomal lysobisphosphatidic acid (LBPA) presented by the CD1d-like endothelial protein C receptor (EPCR) as a pathogenic cell surface antigen recognized by aPLs for induction of thrombosis and endosomal inflammatory signaling. The engagement of aPLs with EPCR-LBPA expressed on innate immune cells sustains interferon- and toll-like receptor 7-dependent B1a cell expansion and autoantibody production. Specific pharmacological interruption of EPCR-LBPA signaling attenuates major aPL-elicited pathologies and the development of autoimmunity in a mouse model of systemic lupus erythematosus. Thus, aPLs recognize a single cell surface lipid-protein receptor complex to perpetuate a self-amplifying autoimmune signaling loop dependent on the cooperation with the innate immune complement and coagulation pathways.

β-Sitosterol 3-O-D-glucoside increases ceramide levels in the stratum corneum via the up-regulated expression of ceramide synthase-3 and glucosylceramide synthase in a reconstructed human epidermal keratinization model

β-Sitosterol 3-O-d-glucoside (BSG) is known to act as an agonist by binding to estrogen receptors, and estrogen has been reported to enhance the activity of β-glucocerebrosidase, an epidermal ceramide metabolizing enzyme. In this study, we determined whether BSG up-regulates ceramide levels in the stratum corneum (SC) of a reconstructed human epidermal keratinization (RHEK) model. Treatment with BSG significantly increased the total ceramide content by 1.2-fold compared to that in the control in the SC of the RHEK model, accompanied by a significant increase of the ceramide species, Cer[EOS] by 2.1-fold compared to that in the control. RT-PCR analysis demonstrated that BSG significantly up-regulated the mRNA expression levels of serine palmitoyltransferase (SPT)2, ceramide synthase (CerS)3, glucosylceramide synthase (GCS) and acid sphingomyelinase by 1.41-1.89, 1.35-1.44, 1.19 and 2.06-fold, respectively, compared to that in the control in the RHEK model. Meanwhile, BSG significantly down-regulated the mRNA expression levels of sphingomyelin synthase (SMS)2 by 0.87-0.89-fold. RT-PCR analysis also demonstrated that BSG significantly up-regulated the mRNA expression levels of CerS3 and GCS by 1.19-1.55 and 1.20-fold, respectively, but not of SPT2 and significantly down-regulated that of SMS2 by 0.74-fold in HaCaT keratinocytes. Western blotting analysis revealed that BSG significantly increased the protein expression levels of CerS3 and GCS by 1.78 and 1.28-1.32-fold, respectively, compared to that in the control in HaCaT cells. These findings indicate that BSG stimulates ceramide synthesis via the up-regulated expression levels of CerS3 and GCS in the glucosylceramide pathway, which results in a significantly increased level of total ceramides in the SC accompanied by significantly increased levels of acylceramide species such as Cer[EOS].

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.

Role of ceramides in the pathogenesis of diabetes mellitus and its complications

Diabetes mellitus (DM) is a systemic metabolic disease that affects 463 million adults worldwide and is a leading cause of cardiovascular disease, blindness, nephropathy, peripheral neuropathy, and lower-limb amputation. Lipids have long been recognized as contributors to the pathogenesis and pathophysiology of DM and its complications, but recent discoveries have highlighted ceramides, a class of bioactive sphingolipids with cell signaling and second messenger capabilities, as particularly important contributors to insulin resistance and the underlying mechanisms of DM complications. Besides their association with insulin resistance and pathophysiology of type 2 diabetes, evidence is emerging that certain species of ceramides are mediators of cellular mechanisms involved in the initiation and progression of microvascular and macrovascular complications of DM. Advances in our understanding of these associations provide unique opportunities for exploring ceramide species as potential novel therapeutic targets and biomarkers. This review discusses the links between ceramides and the pathogenesis of DM and diabetic complications and identifies opportunities for novel discoveries and applications.

The Role of Sphingolipids and Specialized Pro-Resolving Mediators in Alzheimer's Disease

Alzheimer’s disease (AD) is the leading cause of dementia worldwide giving rise to devastating forms of cognitive decline, which impacts patients’ lives and that of their proxies. Pathologically, AD is characterized by extracellular amyloid deposition, neurofibrillary tangles and chronic neuroinflammation. To date, there is no cure that prevents progression of AD. In this review, we elaborate on how bioactive lipids, including sphingolipids (SL) and specialized pro-resolving lipid mediators (SPM), affect ongoing neuroinflammatory processes during AD and how we may exploit them for the development of new biomarker panels and/or therapies. In particular, we here describe how SPM and SL metabolism, ranging from ω-3/6 polyunsaturated fatty acids and their metabolites to ceramides and sphingosine-1-phosphate, initiates pro- and anti-inflammatory signaling cascades in the central nervous system (CNS) and what changes occur therein during AD pathology. Finally, we discuss novel therapeutic approaches to resolve chronic neuroinflammation in AD by modulating the SPM and SL pathways.

Keep Your Friends Close, but Your Enemies Closer: Role of Acid Sphingomyelinase During Infection and Host Response

Breakdown of the inert and constitutive membrane building block sphingomyelin to the highly active lipid mediator ceramide by extracellularly active acid sphingomyelinase is tightly regulated during stress response and opens the gate for invading pathogens, triggering the immune response, development of remote organ failure, and tissue repair following severe infection. How do one enzyme and one mediator manage all of these affairs? Under physiological conditions, the enzyme is located in the lysosomes and takes part in the noiseless metabolism of sphingolipids, but following stress the protein is secreted into circulation. When secreted, acid sphingomyelinase (ASM) is able to hydrolyze sphingomyelin present at the outer leaflet of membranes to ceramide. Its generation troubles the biophysical context of cellular membranes resulting in functional assembly and reorganization of proteins and receptors, also embedded in highly conserved response mechanisms. As a consequence of cellular signaling, not only induction of cell death but also proliferation, differentiation, and fibrogenesis are affected. Here, we discuss the current state of the art on both the impact and function of the enzyme during host response and damage control. Also, the potential role of lysosomotropic agents as functional inhibitors of this upstream alarming cascade is highlighted.

Methods to Characterize Synthesis and Degradation of Sphingomyelin at the Plasma Membrane and Its Impact on Lipid Raft Dynamics

This chapter will discuss methods for analyses of the rates of sphingomyelin synthesis and turnover associated with lipid rafts or plasma membrane. These methods involve the use of fluorescently (NBD-C6-ceramide or NBD-C6-Sphingomyelin)) or radioactively labeled substrates ([³H-methyl]-phosphatidylcholine, [³H-acyl]-ceramide, [¹⁴C-methyl]-sphingomyelin) to quantify in vitro the activity of the sphingomyelin synthase (SMS) (also known as phosphatidylcholine:ceramide phosphocholine transferase), acid sphingomyelinase (the endosomal/lysosomal (L-SMase) and the secretory (S-SMase) forms) and neutral sphingomyelinase-2 (nSMase-2). These methods allow to quantify changes in the activity of enzymes that affect the SM-to-ceramide ratio on the plasma membrane, and consequently, the lipid rafts biophysical properties, dynamics, and raft-associated receptor clustering and signaling events. Specific attention is paid to challenges caused by the fact that SMS and nSMase-2 are integral/membrane bound proteins and how to avoid the use of detergent that suppress their specific activities.

In Vitro Anti-Inflammatory and Skin Moisturizing Propertiesof Pilea martini(Levl.) Hand.-Mazz. Extracts

The in vitro anti-inflammatory and skin moisturizing activities of Pilea martini (Levl.) Hand.-Mazz. were investigated on lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages and human immortalized keratinocytes. Chromatographic analysis was performed to identify the chemical composition of the extracts. Pilea martini extracts significantly suppressed LPS-induced nitric oxide, prostaglandin E2, interleukin 6, and tumor necrosis factor α production in dose-dependent manners. In addition, the extracts inhibited LPS-induced inducible nitric oxide synthase and cyclooxygenase-2 proteins and their mRNA expression through causing a downregulation of nuclear factor-κB, activator protein 1, and mitogen-activated protein kinase signaling cascades. The extracts increased the production of hyaluronic acid levels and enhanced the expression levels of both filaggrin and serine palmitoyltransferase regulation. Liquid chromatography-mass spectroscopy analysis showed that the extracts contained 6 different compounds (malic acid, tryptophan, chlorogenic acid, caffeic acid, p-coumaric acid, and isoquercetin) that may contribute to their bioactivities. Taken together, Pilea martini extract showed remarkable promise as an anti-inflammatory and moisturizing agent.