Autophagic flux and autophagosome morphogenesis require the participation of sphingolipids

A Near-Infrared Fluorogenic Probe for Rapid, Specific, and Ultrasensitive Detection of Sphingosine in Living Cells and In Vivo

Sphingosine (Sph) plays important roles in various complex biological processes. Abnormalities in Sph metabolism can result in various diseases, including neurodegenerative disorders. However, due to the lack of rapid and accurate detection methods, understanding sph metabolic in related diseases is limited. Herein, a series of near-infrared fluorogenic probes DMS-X (X = 2F, F, Cl, Br, and I) are designed and synthesized. The fast oxazolidinone ring formation enables the DMS-2F to detect Sph selectively and ultrasensitively, and the detection limit reaches 9.33 ± 0.41 nm. Moreover, it is demonstrated that DMS-2F exhibited a dose- and time-dependent response to Sph and can detect sph in living cells. Importantly, for the first time, the changes in Sph levels induced by Aβ42 oligomers and H2 O2 are assessed through a fluorescent imaging approach, and further validated the physiological processes by which Aβ42 oligomers and reactive oxygen species (ROS)-induce changes in intracellular Sph levels. Additionally, the distribution of Sph in living zebrafish is successfully mapped by in vivo imaging of a zebrafish model. This work provides a simple and efficient method for probing Sph in living cells and in vivo, which will facilitate investigation into the metabolic process of Sph and the connection between Sph and disease pathologies.

Perturbations of Glutathione and Sphingosine Metabolites in Port Wine Birthmark Patient-Derived Induced Pluripotent Stem Cells

Port Wine Birthmarks (PWBs) are a congenital vascular malformation on the skin, occurring in 1-3 per 1000 live births. We have recently generated PWB-derived induced pluripotent stem cells (iPSCs) as clinically relevant disease models. The metabolites associated with the pathological phenotypes of PWB-derived iPSCs are unknown, and so we aim to explore them in this study. Metabolites were separated by ultra-performance liquid chromatography and screened with electrospray ionization mass spectrometry. Orthogonal partial least-squares discriminant, multivariate, and univariate analyses were used to identify differential metabolites (DMs). KEGG analysis was used to determine the enrichment of metabolic pathways. A total of 339 metabolites was identified. There were 22 DMs, among which nine were downregulated-including sphingosine-and 13 were upregulated, including glutathione in PWB iPSCs, as compared to controls. Pathway enrichment analysis confirmed the upregulation of glutathione and the downregulation of sphingolipid metabolism in PWB-derived iPSCs as compared to normal ones. We next examined the expression patterns of the key molecules associated with glutathione metabolism in PWB lesions. We found that hypoxia-inducible factor 1α (HIF1α), glutathione S-transferase Pi 1 (GSTP1), γ-glutamyl transferase 7 (GGT7), and glutamate cysteine ligase modulatory subunit (GCLM) were upregulated in PWB vasculatures as compared to blood vessels in normal skin. Other significantly affected metabolic pathways in PWB iPSCs included pentose and glucuronate interconversions; amino sugar and nucleotide sugars; alanine, aspartate, and glutamate; arginine, purine, D-glutamine, and D-glutamate; arachidonic acid, glyoxylate, and dicarboxylate; nitrogen, aminoacyl-tRNA biosynthesis, pyrimidine, galactose, ascorbate, and aldarate; and starch and sucrose. Our data demonstrated that there were perturbations in sphingolipid and cellular redox homeostasis in PWB vasculatures, which could facilitate cell survival and pathological progression. Our data implied that the upregulation of glutathione could contribute to laser-resistant phenotypes in some PWB vasculatures.

Perturbations of glutathione and sphingosine metabolites in Port Wine Birthmark patient-derived induced pluripotent stem cells

Port Wine Birthmark (PWB) is a congenital vascular malformation in the skin, occurring in 1-3 per 1,000 live births. We recently generated PWB-derived induced pluripotent stem cells (iPSCs) as clinically relevant disease models. The metabolites associated with the pathological phenotypes of PWB-derived iPSCs are unknown, which we aimed to explore in this study. Metabolites were separated by ultra-performance liquid chromatography and were screened with electrospray ionization mass spectrometry. Orthogonal partial least-squares discriminant analysis, multivariate and univariate analysis were used to identify differential metabolites (DMs). KEGG analysis was used for the enrichment of metabolic pathways. A total of 339 metabolites were identified. There were 22 DMs confirmed with 9 downregulated DMs including sphingosine and 13 upregulated DMs including glutathione in PWB iPSCs as compared to controls. Pathway enrichment analysis confirmed the upregulation of glutathione and downregulation of sphingolipid metabolism in PWB-derived iPSCs as compared to normal ones. We next examined the expression patterns of the key factors associated with glutathione metabolism in PWB lesions. We found that hypoxia-inducible factor 1α (HIF1α), glutathione S-transferase Pi 1 (GSTP1), γ-glutamyl transferase 7 (GGT7), and glutamate cysteine ligase modulatory subunit (GCLM) were upregulated in PWB vasculatures as compared to blood vessels in normal skins. Our data demonstrate that there are perturbations in sphingolipid and cellular redox homeostasis in the PWB vasculature, which may facilitate cell survival and pathological progression. Our data imply that upregulation of glutathione may contribute to laser-resistant phenotypes in the PWB vasculature.

The ER calcium channel Csg2 integrates sphingolipid metabolism with autophagy

Sphingolipids are ubiquitous components of membranes and function as bioactive lipid signaling molecules. Here, through genetic screening and lipidomics analyses, we find that the endoplasmic reticulum (ER) calcium channel Csg2 integrates sphingolipid metabolism with autophagy by regulating ER calcium homeostasis in the yeast Saccharomyces cerevisiae. Csg2 functions as a calcium release channel and maintains calcium homeostasis in the ER, which enables normal functioning of the essential sphingolipid synthase Aur1. Under starvation conditions, deletion of Csg2 causes increases in calcium levels in the ER and then disturbs Aur1 stability, leading to accumulation of the bioactive sphingolipid phytosphingosine, which specifically and completely blocks autophagy and induces loss of starvation resistance in cells. Our findings indicate that calcium homeostasis in the ER mediated by the channel Csg2 translates sphingolipid metabolism into autophagy regulation, further supporting the role of the ER as a signaling hub for calcium homeostasis, sphingolipid metabolism and autophagy.

Phospholipids, the Masters in the Shadows during Healing after Acute Myocardial Infarction

Phospholipids are major components of cell membranes with complex structures, high heterogeneity and critical biological functions and have been used since ancient times to treat cardiovascular disease. Their importance and role were shadowed by the difficulty or incomplete available research methodology to study their biological presence and functionality. This review focuses on the current knowledge about the roles of phospholipids in the pathophysiology and therapy of cardiovascular diseases, which have been increasingly recognized. Used in singular formulation or in inclusive combinations with current drugs, phospholipids proved their positive and valuable effects not only in the protection of myocardial tissue, inflammation and fibrosis but also in angiogenesis, coagulation or cardiac regeneration more frequently in animal models as well as in human pathology. Thus, while mainly neglected by the scientific community, phospholipids present negligible side effects and could represent an ideal target for future therapeutic strategies in healing myocardial infarction. Acknowledging and understanding their mechanisms of action could offer a new perspective into novel therapeutic strategies for patients suffering an acute myocardial infarction, reducing the burden and improving the general social and economic outcome.

rTFPI Protects Cardiomyocytes from Hypoxia/Reoxygenation Injury through Inhibiting Autophagy and the Class III PI3K/Beclin-1 Pathway

Autophagy plays various roles at different stages of ischemia reperfusion (I/R) injury in cardiomyocytes. It has been reported that tissue factor pathway inhibitor (TFPI) has a protective effect on I/R injury. This study aimed to determine the roles of TFPI in autophagy during the I/R injury process in cardiomyocytes and the possible mechanisms. An isolated hypoxia/reoxygenation (H/R) pattern of cardiomyocytes was established by the MIC101 system. The cell viability and oxidative stress of cardiomyocytes were detected by an MTT assay and ROS assay, respectively. The autophagy level was measured by Ad-mCherry-GFP-LC3B and MDC. We detected the expression levels of autophagy-related proteins by western blotting. After 2 h of hypoxia and 12 h of reoxygenation, the cardiomyocyte viability in the H/R group was significantly lower than that in the control group (p < 0.05) than in the H/R group. According to intracellular ROS production, the fluorescence intensity in the H/R group was enhanced compared with that in the negative control group, and it was weaker in the H/R + rTFPI group compared with the H/R group. The level of autophagy and the expression levels of autophagy-related proteins (LC3-II/LC3-I, Beclin-1 and PI3K) were markedly increased in the H/R group compared to the control group (p < 0.05) whereas the levels were markedly decreased in the H/R + rTFPI group compared to the H/R group (p < 0.05). TFPI could relieve cardiomyocyte injury by inhibiting the Class III PI3K/Beclin-1 pathway and oxidative stress; thus, TFPI decreased autophagy and protected cardiomyocytes induced by H/R injury. In conclusion, TFPI may be a new direction for the prevention of myocardial I/R injury.

Neurological Consequences of Sphingosine Phosphate Lyase Insufficiency

In 2017, an inborn error of metabolism caused by recessive mutations in SGPL1 was discovered. The disease features steroid-resistant nephrotic syndrome, adrenal insufficiency, and neurological defects. The latter can include sensorineural hearing loss, cranial nerve defects, peripheral neuropathy, abnormal brain development, seizures and/or neurodegeneration. SGPL1 encodes the pyridoxal-5’-phosphate (PLP) dependent enzyme sphingosine phosphate lyase (SPL), and the condition is now referred to as SPL insufficiency syndrome (SPLIS). SPL catalyzes the final step in the degradative pathway of sphingolipids in which the bioactive sphingolipid sphingosine-1-phosphate (S1P) is irreversibly degraded to a long chain aldehyde and phosphoethanolamine (PE). SPL guards the only exit point for sphingolipid metabolism, and its inactivation leads to accumulation of various types of sphingolipids which have biophysical roles in plasma membrane rafts and myelin, and signaling roles in cell cycle progression, vesicular trafficking, cell migration, and programmed cell death. In addition, the products of the SPL reaction have biological functions including regulation of autophagic flux, which is important in axonal and neuronal integrity. In this review, the neurological manifestations of SPLIS will be described, and insights regarding the neurological consequences of SPL insufficiency from the study of brain-specific SPL knockout mice and Drosophila SPL mutants will be summarized.

Role of apolipoprotein O in autophagy via the p38 mitogen-activated protein kinase signaling pathway in myocardial infarction

OBJECTIVE

To explore the role and possible mechanisms of action of apolipoprotein O (APOO) in autophagy in Myocardial Infarction (MI) in vivo and in vitro.

METHODS

Differential gene expression and single Gene Set Enrichment Analysis (GSEA) were used to evaluate MI-related candidate genes. Animal and cell MI models were established. Sh-APOO, si-APOO, and SB203580 were used to inhibit the expression of APOO or p38MAPK. Western blot and qRT-PCR were used to analyze the expression levels of the target protein or mRNA. Apoptosis was observed using the TUNEL assay. The plasma concentrations of CK-MB and cTn-I in humans and mice were determined.

RESULTS

In the GSE23294 dataset, APOO mRNA was highly expressed in the left ventricle of mice with MI; GSEA revealed that APOO was positively correlated with p38MAPK, autophagy, and apoptosis. The plasma concentration of APOO in patients with MI was significantly higher than that in healthy subjects. The expression of APOO, Beclin-1, LC3, and Bax in mouse and AC16 cell MI models increased, while the level of Bcl-2 decreased. After silencing the APOO gene, the expression of APOO was downregulated; meanwhile, changes in autophagy, apoptosis and myocardial cell injury were reversed in vivo and in vitro. Furthermore, autophagy was alleviated after AC16 cells were treated with SB203580.

CONCLUSIONS

The increased APOO expression in mouse and cell MI models may activate autophagy and apoptosis by regulating the p38MAPK signaling pathway, thus aggravating the myocardial injury.

Chronic activation of cardiac Atg-5 and pancreatic Atg-7 by intermittent fasting alleviates acute myocardial infarction in old rats

BACKGROUND

Aging is associated with cardiovascular and metabolic changes, increasing the susceptibility to acute myocardial infarction (AMI). Intermittent fasting (IF) has a beneficial effect on the age-associated cardiovascular diseases. The present study was planned to investigate the possible protective effect of IF against acute AMI induced by isoproterenol (ISO) in old rats and its possible underlying mechanisms mediated by heart and pancreatic autophagy. Thirty Male Wistar rats were divided into four groups: adult; old; Old-ISO (rats subjected to AMI by ISO) and Old-F-ISO groups (rats were subjected to IF for 4 weeks and AMI by ISO).

RESULTS

IF significantly increased the mRNA expression of cardiac Atg-5 and pancreatic Atg-7 in Old-F-ISO versus old and adult groups. This was associated with a significant decrease in serum troponin-I, serum creatine kinase (CK-MB), cardiac malondialdehyde and cardiac TNF-α, fasting plasma glucose, and HOMA-IR in Old-F-ISO compared to Old-ISO group. Also, IF significantly decreased the age-related overall and visceral obesity in Old-F-ISO versus old and Old-ISO groups. Histological studies revealed attenuation of the local inflammatory response in Old-F-ISO versus Old-ISO group. Pancreatic Atg-7 and heart Atg-5 were significantly increased in Old-ISO versus old rats.

CONCLUSIONS

IF protects against acute AMI in old rats, possibly, via chronic activation of heart Atg-5 and pancreatic Atg-7, and alleviation of age-related overall and visceral obesity. Thus, IF could be a dietary lifestyle modification for attenuation of the susceptibility to acute AMI in aged population. On the other hand, acute activation of heart and pancreatic autophagy by ISO might augment cardiac injury.

Thymoquinone dose-dependently attenuates myocardial injury induced by isoproterenol in rats via integrated modulations of oxidative stress, inflammation, apoptosis, autophagy, and fibrosis

As rats develop myocardial infarction (MI) like lesions when injected with large doses of isoproterenol (ISO), this investigation was designed to evaluate the dose-dependent effects of thymoquinone (TQ) on ISO-induced myocardial injury in rats. Adult male rats were divided into negative control, TQ20 (20 mg/kg/day), TQ50 (50 mg/kg/day), ISO positive control, TQ20 + ISO, and TQ50 + ISO groups. In these rats, biochemical, immunobiochemical, and histopathological studies were carried out to evaluate myocardial oxidative stress, inflammation, apoptosis, fibrosis, and autophagy, and the changes in serum cardiac biomarkers. The results showed that TQ pretreatment in ISO-administered rats produced a dose-dependent significant reduction of the myocardial infarct size, markedly reduced the ISO-induced elevation in serum cardiac markers and demonstrated several other important findings related to the cardioprotective efficacy of TQ. First, this study is the first reported research work showing that TQ treatment could increase the myocardial reduced glutathione baseline level, adding an indirect antioxidant effect to its known direct free radical scavenging effect. Second, pretreatment with TQ significantly reduced the markers of myocardial oxidative stress, inflammation, fibrosis, and apoptosis. Third, TQ acted as an autophagy enhancer ameliorating myocardial cell damage and dysfunction. Thus, the morphological and biochemical changes associated with ISO-induced myocardial injury were ameliorated with TQ pretreatment. The extent of this improvement was significantly greater in the TQ50 + ISO group than in the TQ20 + ISO group. The present study, for the first time, demonstrates these dose-dependent effects of TQ in experimentally induced myocardial injury. These findings raise the possibility that TQ may serve as a promising prophylactic cardioprotective therapy for patients who are at risk of developing myocardial injury and against the progression of existent myocardial injury as in cases of MI.

The Anti-Infectious Role of Sphingosine in Microbial Diseases

Sphingolipids are important structural membrane components and, together with cholesterol, are often organized in lipid rafts, where they act as signaling molecules in many cellular functions. They play crucial roles in regulating pathobiological processes, such as cancer, inflammation, and infectious diseases. The bioactive metabolites ceramide, sphingosine-1-phosphate, and sphingosine have been shown to be involved in the pathogenesis of several microbes. In contrast to ceramide, which often promotes bacterial and viral infections (for instance, by mediating adhesion and internalization), sphingosine, which is released from ceramide by the activity of ceramidases, kills many bacterial, viral, and fungal pathogens. In particular, sphingosine is an important natural component of the defense against bacterial pathogens in the respiratory tract. Pathologically reduced sphingosine levels in cystic fibrosis airway epithelial cells are normalized by inhalation of sphingosine, and coating plastic implants with sphingosine prevents bacterial infections. Pretreatment of cells with exogenous sphingosine also prevents the viral spike protein of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) from interacting with host cell receptors and inhibits the propagation of herpes simplex virus type 1 (HSV-1) in macrophages. Recent examinations reveal that the bactericidal effect of sphingosine might be due to bacterial membrane permeabilization and the subsequent death of the bacteria.

Alteration in the Cerebrospinal Fluid Lipidome in Parkinson's Disease: A Post-Mortem Pilot Study

Lipid metabolism is clearly associated to Parkinson's disease (PD). Although lipid homeostasis has been widely studied in multiple animal and cellular models, as well as in blood derived from PD individuals, the cerebrospinal fluid (CSF) lipidomic profile in PD remains largely unexplored. In this study, we characterized the post-mortem CSF lipidomic imbalance between neurologically intact controls (n = 10) and PD subjects (n = 20). The combination of dual extraction with ultra-performance liquid chromatography-electrospray ionization quadrupole-time-of-flight mass spectrometry (UPLC-ESI-qToF-MS/MS) allowed for the monitoring of 257 lipid species across all samples. Complementary multivariate and univariate data analysis identified that glycerolipids (mono-, di-, and triacylglycerides), saturated and mono/polyunsaturated fatty acids, primary fatty amides, glycerophospholipids (phosphatidylcholines, phosphatidylethanolamines), sphingolipids (ceramides, sphingomyelins), N-acylethanolamines and sterol lipids (cholesteryl esters, steroids) were significantly increased in the CSF of PD compared to the control group. Interestingly, CSF lipid dyshomeostasis differed depending on neuropathological staging and disease duration. These results, despite the limitation of being obtained in a small population, suggest extensive CSF lipid remodeling in PD, shedding new light on the deployment of CSF lipidomics as a promising tool to identify potential lipid markers as well as discriminatory lipid species between PD and other atypical parkinsonisms.

Shared genetic etiology between Parkinson's disease and blood levels of specific lipids

Parkinson’s disease (PD) is characterized by the degeneration of dopaminergic neurons in the substantia nigra and the formation of Lewy bodies. The mechanisms underlying these molecular and cellular effects are largely unknown. Previously, based on genetic and other data, we built a molecular landscape of PD that highlighted a central role for lipids. To explore which lipid species may be involved in PD pathology, we used published genome-wide association study (GWAS) data to conduct polygenic risk score-based analyses to examine putative genetic sharing between PD and blood levels of 370 lipid species and lipid-related molecules. We found a shared genetic etiology between PD and blood levels of 25 lipids. We then used data from a much-extended GWAS of PD to try and corroborate our findings. Across both analyses, we found genetic overlap between PD and blood levels of eight lipid species, namely two polyunsaturated fatty acids (PUFA 20:3n3-n6 and 20:4n6), four triacylglycerols (TAG 44:1, 46:1, 46:2, and 48:0), phosphatidylcholine aa 32:3 (PC aa 32:3) and sphingomyelin 26:0 (SM 26:0). Analysis of the concordance—the agreement in genetic variant effect directions across two traits—revealed a significant negative concordance between PD and blood levels of the four triacylglycerols and PC aa 32:3 and a positive concordance between PD and blood levels of both PUFA and SM 26:0. Taken together, our analyses imply that genetic variants associated with PD modulate blood levels of a specific set of lipid species supporting a key role of these lipids in PD etiology.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

Gangliosides in the Brain: Physiology, Pathophysiology and Therapeutic Applications

Gangliosides are glycosphingolipids highly abundant in the nervous system, and carry most of the sialic acid residues in the brain. Gangliosides are enriched in cell membrane microdomains ("lipid rafts") and play important roles in the modulation of membrane proteins and ion channels, in cell signaling and in the communication among cells. The importance of gangliosides in the brain is highlighted by the fact that loss of function mutations in ganglioside biosynthetic enzymes result in severe neurodegenerative disorders, often characterized by very early or childhood onset. In addition, changes in the ganglioside profile (i.e., in the relative abundance of specific gangliosides) were reported in healthy aging and in common neurological conditions, including Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), stroke, multiple sclerosis and epilepsy. At least in HD, PD and in some forms of epilepsy, experimental evidence strongly suggests a potential role of gangliosides in disease pathogenesis and potential treatment. In this review, we will summarize ganglioside functions that are crucial to maintain brain health, we will review changes in ganglioside levels that occur in major neurological conditions and we will discuss their contribution to cellular dysfunctions and disease pathogenesis. Finally, we will review evidence of the beneficial roles exerted by gangliosides, GM1 in particular, in disease models and in clinical trials.

Lysosomal proteome analysis reveals that CLN3-defective cells have multiple enzyme deficiencies associated with changes in intracellular trafficking

Numerous lysosomal enzymes and membrane proteins are essential for the degradation of proteins, lipids, oligosaccharides, and nucleic acids. The CLN3 gene encodes a lysosomal membrane protein of unknown function, and CLN3 mutations cause the fatal neurodegenerative lysosomal storage disorder CLN3 (Batten disease) by mechanisms that are poorly understood. To define components critical for lysosomal homeostasis that are affected by this disease, here we quantified the lysosomal proteome in cerebellar cell lines derived from a CLN3 knock-in mouse model of human Batten disease and control cells. We purified lysosomes from SILAC-labeled, and magnetite-loaded cerebellar cells by magnetic separation and analyzed them by MS. This analysis identified 70 proteins assigned to the lysosomal compartment and 3 lysosomal cargo receptors, of which most exhibited a significant differential abundance between control and CLN3-defective cells. Among these, 28 soluble lysosomal proteins catalyzing the degradation of various macromolecules had reduced levels in CLN3-defective cells. We confirmed these results by immunoblotting and selected protease and glycosidase activities. The reduction of 11 lipid-degrading lysosomal enzymes correlated with reduced capacity for lipid droplet degradation and several alterations in the distribution and composition of membrane lipids. In particular, levels of lactosylceramides and glycosphingolipids were decreased in CLN3-defective cells, which were also impaired in the recycling pathway of the exocytic transferrin receptor. Our findings suggest that CLN3 has a crucial role in regulating lysosome composition and their function, particularly in degrading of sphingolipids, and, as a consequence, in membrane transport along the recycling endosome pathway.

Fifty years of lyase and a moment of truth: sphingosine phosphate lyase from discovery to disease

Sphingosine phosphate lyase (SPL) is the final enzyme in the sphingolipid degradative pathway, catalyzing the irreversible cleavage of long-chain base phosphates (LCBPs) to yield a long-chain aldehyde and ethanolamine phosphate (EP). SPL guards the sole exit point of sphingolipid metabolism. Its inactivation causes product depletion and accumulation of upstream sphingolipid intermediates. The main substrate of the reaction, sphingosine-1-phosphate (S1P), is a bioactive lipid that controls immune-cell trafficking, angiogenesis, cell transformation, and other fundamental processes. The products of the SPL reaction contribute to phospholipid biosynthesis and programmed cell-death activation. The main features of SPL enzyme activity were first described in detail by Stoffel et al. in 1969. The first SPL-encoding gene was cloned from budding yeast in 1997. Reverse and forward genetic strategies led to the rapid identification of other genes in the pathway and their homologs in other species. Genetic manipulation of SPL-encoding genes in model organisms has revealed the contribution of sphingolipid metabolism to development, physiology, and host-pathogen interactions. In 2017, recessive mutations in the human SPL gene SGPL1 were identified as the cause of a novel inborn error of metabolism associated with nephrosis, endocrine defects, immunodeficiency, acanthosis, and neurological problems. We refer to this condition as SPL insufficiency syndrome (SPLIS). Here, we share our perspective on the 50-year history of SPL from discovery to disease, focusing on insights provided by model organisms regarding the pathophysiology of SPLIS and how SPLIS raises the possibility of a hidden role for sphingolipids in other disease conditions.

The Role of Lipids in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disease characterized by a progressive loss of dopaminergic neurons from the nigrostriatal pathway, formation of Lewy bodies, and microgliosis. During the past decades multiple cellular pathways have been associated with PD pathology (i.e., oxidative stress, endosomal-lysosomal dysfunction, endoplasmic reticulum stress, and immune response), yet disease-modifying treatments are not available. We have recently used genetic data from familial and sporadic cases in an unbiased approach to build a molecular landscape for PD, revealing lipids as central players in this disease. Here we extensively review the current knowledge concerning the involvement of various subclasses of fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and lipoproteins in PD pathogenesis. Our review corroborates a central role for most lipid classes, but the available information is fragmented, not always reproducible, and sometimes differs by sex, age or PD etiology of the patients. This hinders drawing firm conclusions about causal or associative effects of dietary lipids or defects in specific steps of lipid metabolism in PD. Future technological advances in lipidomics and additional systematic studies on lipid species from PD patient material may improve this situation and lead to a better appreciation of the significance of lipids for this devastating disease.

Sphingolipids in neurodegeneration (with focus on ceramide and S1P)

For many decades, research on sphingolipids associated with neurodegenerative disease focused on alterations in glycosphingolipids, particularly glycosylceramides (cerebrosides), sulfatides, and gangliosides. This seemed quite natural since many of these glycolipids are constituents of myelin and accumulated in lipid storage diseases (sphingolipidoses) resulting from enzyme deficiencies in glycolipid metabolism. With the advent of recognizing ceramide and its derivative, sphingosine-1-phosphate (S1P), as key players in lipid cell signaling and regulation of cell death and survival, research focus shifted toward these two sphingolipids. Ceramide and S1P are invoked in a plethora of cell biological processes participating in neurodegeneration such as ER stress, autophagy, dysregulation of protein and lipid transport, exosome secretion and neurotoxic protein spreading, neuroinflammation, and mitochondrial dysfunction. Hence, it is timely to discuss various functions of ceramide and S1P in neurodegenerative disease and to define sphingolipid metabolism and cell signaling pathways as potential targets for therapy.

Chemosensitivity of human colon cancer cells is influenced by a p53-dependent enhancement of ceramide synthase 5 and induction of autophagy

Resistance against chemotherapy is a life-threatening complication in colon cancer therapy. To increase response rate, new additional targets that contribute to chemoresistance are still needed to be explored. Ceramides, which belong to the group of sphingolipids, are well-known regulators of cell death and survival, respectively. Here, we show that in human wild-type (^wt) p53 HCT-116 colon cancer cells treatment with oxaliplatin or 5-fluorouracil (5-FU) leads to a strong increase in ceramide synthase 5 (CerS5) expression and C_16:0-ceramide levels, which was not shown in HCT-116 lacking p53 expression (HCT-116 p53^-/-). The increase in CerS5 expression occurs by stabilizing CerS5 mRNA at the 3'-UTR. By contrast, in the p53-deficient cells CerS2 expression and CerS2-related C_24:0- and C_24:1-ceramide levels were elevated which is possibly related to enhanced polyadenylation of the CerS2 transcript in these cells. Stable knockdown of CerS5 expression using CerS5-targeting shRNA led to an increased sensitivity of HCT-116 p53^wt cells, but not of p53^-/- cells, to oxaliplatin and 5-FU. Enhanced sensitivity was accompanied by an inhibition of autophagy and inhibition of mitochondrial respiration in these cells. However, knockdown of CerS2 had no significant effects on chemosensitivity of both cell lines. In conclusion, in p53^wt colon cancer cells chemosensitivity against oxaliplatin or 5-FU could be enhanced by downregulation of CerS5 expression leading to reduced autophagy and mitochondrial respiration.

Inflammation, Autophagy, and Apoptosis After Myocardial Infarction

Background

There is evidence for inflammation, autophagy, and apoptosis in the ischemic heart. Autophagy is a physiologic process for tissue survival. Apoptosis, on the other hand, is a mechanism that serves to clear the debris in the setting of tissue injury. The balance between autophagy and apoptosis may be important in cell survival and cardiac function.

Methods and Results

We examined the interplay of inflammation and myocyte autophagy and apoptosis during the ischemic process. We subjected mice to total left coronary artery ligation and studied these animals for up to 4 weeks. The inflammatory (tumor necrosis factor [TNF]‐α, monocyte chemoattractant protein‐1, interleukin‐6, and interleukin‐1β) and autophagic signals (light chain‐3 and beclin‐1) were strongest during the first week and then began to decline. However, the apoptotic signals peaked at week 2 after left coronary artery ligation, and the elevated levels persisted until the end of the fourth week. To elucidate the role of inflammation in the regulation of myocyte autophagy and apoptosis, we administered TNF‐α inhibitor (CAS1049741‐03‐8, Millipore, Burlington, MA) to the mice daily during the first week of myocardial infarction. Anti‐TNF‐α therapy reduced the levels of inflammatory cytokines and the inflammatory cell infiltration in and around the infarct area. However, cardiac function measured by echocardiography (fractional shortening and ejection fraction) worsened with anti‐TNF‐α therapy. More importantly, application of TNF‐α inhibitor markedly inhibited autophagy and promoted myocyte apoptosis in the border zone.

Conclusions

These observations suggest that inflammatory response may be protective in the early stage of the myocardial infarction through stimulation of myocyte autophagy. Anti‐inflammatory treatment early after coronary occlusion may have an adverse effect.

CPTP: A sphingolipid transfer protein that regulates autophagy and inflammasome activation

The macroautophagy/autophagy and inflammasome pathways are linked through their roles in innate immunity and chronic inflammatory disease. Ceramide-1-phosphate (C1P) is a bioactive sphingolipid that regulates pro-inflammatory eicosanoid production. Whether C1P also regulates autophagy and inflammasome assembly/activation is not known. Here we show that CPTP (a protein that traffics C1P from its site of phosphorylation in the trans-Golgi to target membranes) regulates both autophagy and inflammasome activation. In human epithelial cells, knockdown of CPTP (but not GLTP [glycolipid transfer protein]) or expression of C1P binding-site point mutants, stimulated an 8- to 10-fold increase in autophagosomes and altered endogenous LC3-II and SQSTM1/p62 protein expression levels. CPTP depletion-induced autophagy elevated early markers of autophagosome formation (Golgi-derived ATG9A-vesicles, WIPI1), required key phagophore assembly and elongation factors (ATG5, ATG7, ULK1), and suppressed MTOR phosphorylation and that of its downstream target, RPS6KB1/p70S6K. Wild-type CPTP overexpression exerted a protective effect against starvation-induced autophagy. In THP-1 macrophage-like surveillance cells, CPTP knockdown induced not only autophagy but also elevated CASP1/caspase-1 levels, and strongly increased IL1B/interleukin-1β and IL18 release via a NLRP3 (but not NLRC4) inflammasome-based mechanism, while only moderately increasing inflammatory (pyroptotic) cell death. Inflammasome assembly and activation stimulated by CPTP depletion were autophagy dependent. Elevation of intracellular C1P by exogenous C1P treatment (instead of CPTP inhibition) also induced autophagy and IL1B release. Our findings identify human CPTP as an endogenous regulator of early-stage autophagosome assembly and inflammasome-driven, pro-inflammatory cytokine generation and release.

Dihydroceramide Desaturase 1 Inhibitors Reduce Amyloid-β Levels in Primary Neurons from an Alzheimer's Disease Transgenic Model

PURPOSE

The induction of autophagy has recently been explored as a promising therapeutic strategy to combat Alzheimer's disease. Among many other factors, there is evidence that ceramides/dihydroceramides act as mediators of autophagy, although the exact mechanisms underlying such effects are poorly understood. Here, we describe how two dihydroceramide desaturase inhibitors (XM461 and XM462) trigger autophagy and reduce amyloid secretion by neurons.

METHODS

Neurons isolated from wild-type and APP/PS1 transgenic mice were exposed to the two dihydroceramide desaturase inhibitors to assess their effect on these cell's protein and lipid profiles.

RESULTS

Both dihydroceramide desaturase inhibitors increased the autophagic vesicles in wild-type neurons, reflected as an increase in LC3-II, and this was correlated with the accumulation of dihydroceramides and dihydrosphingomyelins. Exposing APP/PS1 transgenic neurons to these inhibitors also produced a 50% reduction in amyloid secretion and/or production. The lipidomic defects triggered by these dihydroceramide desaturase inhibitors were correlated with a loss of S6K activity, witnessed by the changes in S6 phosphorylation, which strongly suggested a reduction of mTORC1 activity.

CONCLUSIONS

The data obtained strongly suggest that dihydroceramide desaturase 1 activity may modulate autophagy and mTORC1 activity in neurons, inhibiting amyloid secretion and S6K activity. As such, it is tantalizing to propose that dihydroceramide desaturase 1 may be an important therapeutic target to combat amyloidosis.

Essential role for acid sphingomyelinase-inhibited autophagy in melanoma response to cisplatin

The sphingolipid metabolising enzyme Acid Sphingomyelinase (A-SMase) has been recently shown to inhibit melanoma progression and correlate inversely to tumour grade. In this study we have investigated the role of A-SMase in the chemo-resistance to anticancer treatmentusing mice with melanoma allografts and melanoma cells differing in terms of expression/activity of A-SMase. Since autophagy is emerging as a key mechanism in tumour growth and chemo-resistance, we have also investigated whether an action of A-SMase in autophagy can explain its role. Melanoma sensitivity to chemotherapeutic agent cisplatin in terms of cell viability/apoptosis, tumour growth, and animal survival depended directly on the A-SMase levels in tumoural cells. A-SMase action was due to inhibition of autophagy through activation of Akt/mammalian target of rapamycin (mTOR) pathway. Treatment of melanoma-bearing mice with the autophagy inhibitor chloroquine restored sensitivity to cisplatin of tumours expressing low levels of A-SMase while no additive effects were observed in tumours characterised by sustained A-SMase levels. The fact that A-SMase in melanomas affects mTOR-regulated autophagy and plays a central role in cisplatin efficacy encourages pre-clinical testing on the modulation of A-SMase levels/activity as possible novel anti-neoplastic strategy.

Lithium improves cell viability in psychosine-treated MO3.13 human oligodendrocyte cell line via autophagy activation

Globoid cell leukodystrophy (GLD) is a rare, rapidly progressing childhood leukodystrophy triggered by deficit of the lysosomal enzyme galactosylceramidase (GALC) and characterized by the accumulation of galactosylsphingosine (psychosine; PSY) in the nervous system. PSY is a cytotoxic sphingolipid, which leads to widespread degeneration of oligodendrocytes and Schwann cells, causing demyelination. Here we report on autophagy in the human oligodendrocyte cell line MO3.13 treated with PSY and exploitation of Li as an autophagy modulator to rescue cell viability. We demonstrate that PSY causes upregulation of the autophagic flux at the level of autophagosome and autolysosome formation and LC3-II expression. We show that pretreatment with Li, a drug clinically used to treat bipolar disorders, can further stimulate autophagy, improving cell tolerance to PSY. This Li protective effect is found not to be linked to reduction of PSY-induced oxidative stress and might not stem from a reduction of PSY accumulation. These data provide novel information on the intracellular pathways activated during PSY-induced toxicity and suggest the autophagy pathway as a promising novel therapeutic target for ameliorating the GLD phenotype. © 2016 Wiley Periodicals, Inc.

Dihydroceramide desaturase inhibitors induce autophagy via dihydroceramide-dependent and independent mechanisms

BACKGROUND

Autophagy consists on the delivery of cytoplasmic material and organelles to lysosomes for degradation. Research on autophagy is a growing field because deciphering the basic mechanisms of autophagy is key to understanding its role in health and disease, and to paving the way to discovering novel therapeutic strategies. Studies with chemotherapeutic drugs and pharmacological tools support a role for dihydroceramides as mediators of autophagy. However, their effect on the autophagy outcome (cell survival or death) is more controversial.

METHODS

We have examined the capacity of structurally varied Des1 inhibitors to stimulate autophagy (LC3-II analysis), to increase dihydroceramides (mass spectrometry) and to reduce cell viability (SRB) in T98G and U87MG glioblastoma cells under different experimental conditions.

RESULTS

The compounds activity on autophagy induction took place concomitantly with accumulation of dihydroceramides, which occurred by both stimulation of ceramide synthesis de novo and reduction of Des1 activity. However, autophagy was also induced by the test compounds after preincubation with myriocin and in cells with a reduced capacity to produce dihydroceramides (U87DND). Autophagy inhibition with 3-methyladenine in the de novo dihydroceramide synthesis competent U87MG cells increased cytotoxicity, while genetic inhibition of autophagy in U87DND cells, poorly efficient at synthesizing dihydroceramides, augmented resistance to the test compounds.

CONCLUSION

Dihydroceramide desaturase 1 inhibitors activate autophagy via both dihydroceramide-dependent and independent pathways and the balance between the two pathways influences the final cell fate.

GENERAL SIGNIFICANCE

The cells capacity to biosynthesize dihydroceramides must be taken into account in proautophagic Des1 inhibitors-including therapies.

The roles of phosphoinositides in mammalian autophagy

Autophagy is an evolutionarily conserved cellular process for lysosomal degradation, which is involved in various physiological processes within cells. Its dysfunction is associated with many human diseases, such as cancer, liver diseases, heart diseases, and infectious diseases, including neurodegenerative diseases. Autophagy involves the formation of a double-membrane bound autophagosome and the degradation of cytosolic components via its fusion and maturation with the lysosome. One of the most important steps in the process of autophagy is membrane biogenesis during autophagosome formation/maturation from different membrane sources within cells. However, there is limited knowledge regarding: (1) how the core autophagy machinery is recruited to the initial site to initiate the formation of the isolation membrane and (2) how the autophagosome matures into the functional autolysosome. Lipid supply for nucleation/elongation of the autophagosome has been proposed as one possible mechanism. Accumulating evidence suggests the important role of phosphoinositides as phospholipids, which represent key membrane-localized signals in the regulation of fundamental cellular processes, in autophagosome formation and maturation. This review focuses on how phosphoinositides influence autophagy induction or autophagosome biogenesis/maturation, because the way they are altered by autophagy might contribute to the pathogenesis of human diseases.

IL10 inhibits starvation-induced autophagy in hypertrophic scar fibroblasts via cross talk between the IL10-IL10R-STAT3 and IL10-AKT-mTOR pathways

Hypertrophic scar (HS) is a serious skin fibrotic disease characterized by excessive hypercellularity and extracellular matrix (ECM) component deposition. Autophagy is a tightly regulated physiological process essential for cellular maintenance, differentiation, development, and homeostasis. Previous studies show that IL10 has potential therapeutic benefits in terms of preventing and reducing HS formation. However, no studies have examined IL10-mediated autophagy during the pathological process of HS formation. Here, we examined the effect of IL10 on starvation-induced autophagy and investigated the molecular mechanism underlying IL10-mediated inhibition of autophagy in HS-derived fibroblasts (HSFs) under starvation conditions. Immunostaining and PCR analysis revealed that a specific component of the IL10 receptor, IL10 alpha-chain (IL10Rα), is expressed in HSFs. Transmission electron microscopy and western blot analysis revealed that IL10 inhibited starvation-induced autophagy and induced the expression of p-AKT and p-STAT3 in HSFs in a dose-dependent manner. Blocking IL10R, p-AKT, p-mTOR, and p-STAT3 using specific inhibitors (IL10RB, LY294002, rapamycin, and cryptotanshinone, respectively) showed that IL10 inhibited autophagy via IL10Rα-mediated activation of STAT3 (the IL10R-STAT3 pathway) and by directly activating the AKT-mTOR pathway. Notably, these results suggest that IL10-mediated inhibition of autophagy is facilitated by the cross talk between STAT3, AKT, and mTOR; in other words, the IL10-IL10R-STAT3 and IL10-AKT-mTOR pathways. Finally, the results also indicate that mTOR-p70S6K is the molecule upon which these two pathways converge to induce IL10-mediated inhibition of autophagy in starved HSFs. In summary, the findings reported herein shed light on the molecular mechanism underlying IL10-mediated inhibition of autophagy and suggest that IL10 is a potential therapeutic agent for the treatment of HS.

Legionella pneumophila S1P-lyase targets host sphingolipid metabolism and restrains autophagy

Autophagy is an essential component of innate immunity, enabling the detection and elimination of intracellular pathogens. Legionella pneumophila, an intracellular pathogen that can cause a severe pneumonia in humans, is able to modulate autophagy through the action of effector proteins that are translocated into the host cell by the pathogen's Dot/Icm type IV secretion system. Many of these effectors share structural and sequence similarity with eukaryotic proteins. Indeed, phylogenetic analyses have indicated their acquisition by horizontal gene transfer from a eukaryotic host. Here we report that L. pneumophila translocates the effector protein sphingosine-1 phosphate lyase (LpSpl) to target the host sphingosine biosynthesis and to curtail autophagy. Our structural characterization of LpSpl and its comparison with human SPL reveals high structural conservation, thus supporting prior phylogenetic analysis. We show that LpSpl possesses S1P lyase activity that was abrogated by mutation of the catalytic site residues. L. pneumophila triggers the reduction of several sphingolipids critical for macrophage function in an LpSpl-dependent and -independent manner. LpSpl activity alone was sufficient to prevent an increase in sphingosine levels in infected host cells and to inhibit autophagy during macrophage infection. LpSpl was required for efficient infection of A/J mice, highlighting an important virulence role for this effector. Thus, we have uncovered a previously unidentified mechanism used by intracellular pathogens to inhibit autophagy, namely the disruption of host sphingolipid biosynthesis.