Sphingolipids: the nexus between Gaucher disease and insulin resistance

GBA Regulates EMT/MET and Chemoresistance in Squamous Cell Carcinoma Cells by Modulating the Cellular Glycosphingolipid Profile

Glycosphingolipids (GSL) are plasma membrane components that influence molecular processes involved in cancer initiation, progression, and therapeutic responses. They also modulate receptor tyrosine kinases involved in EMT. Therefore, understanding the mechanisms that regulate GSLs in cancer has important therapeutic potential. One critical regulator of GSLs is the lysosomal glucosylceramidase β1 (GBA) that catalyzes the last step in GSL degradation. We show that, in cancer, GBA copy number amplifications and increased expression are widespread. We show that depleting GBA in squamous cell carcinoma cell lines results in a mesenchymal-to-epithelial shift, decreased invasion and migration, increased chemotherapeutic sensitivity, and decreased activation of receptor tyrosine kinases that are involved in regulating EMT. Untargeted lipidomics shows that GBA depletion had significant effects on sphingolipids and GSLs, suggesting that increased GBA activity in cancer sustains EMT and chemoresistance by modulating receptor tyrosine kinase activity and signaling via effects on the cellular lipid profile.

Evaluation of endocrinological involvement and metabolic status in patients with Gaucher disease Type 1 and Fabry disease under enzyme replacement therapy

OBJECTIVES

Gaucher disease type 1 (GD1) and Fabry disease (FD) are the two most common lysosomal storage diseases. For over three decades, effective enzyme replacement therapies (ERTs) have changed the fate of patients and offered a longer chance of survival and improve their quality of life.

METHODS

The clinical and molecular findings, endocrinological features and metabolic status of 26 patients (16 with FD, and 10 with GD1) were evaluated. The results were compared to age- and gender-matched healthy individuals.

RESULTS

Patients with GD1 and FD were followed for 7.2 ± 4.7 and 6.4 ± 4.3 years, respectively. Calcium and magnesium levels in patients with GD1 were lower than in controls (p=0.01; p=0.002). Osteoporosis was detected in 20% (n=2) of GD1 patients and 12.5% (n=2) of FD patients. The HbA1c value of GD1 patients was significantly lower than both in control and Fabry patients (p=0.004; and p=0.007, respectively). There was a negative correlation between LysoGb3 and female gender (p=0.04; r=-0.49), but no correlation was found with any other biochemical parameters. There was a negative correlation between the LysoGb1 level and the neutrophil (p=0.03; r=-0.711) and thrombocyte levels (p=0.02; r=-0.767), and a positive correlation with ferritin levels (p<0.001; r=0.867).

CONCLUSION

Long time effective ERT seems to have beneficial effects on metabolic and hormonal status as well as primary target organs in both FD and GD1 patients.

Disruption of morphogenic and growth pathways in lysosomal storage diseases

The lysosome achieved a new protagonism that highlights its multiple cellular functions, such as in the catabolism of complex substrates, nutrient sensing, and signaling pathways implicated in cell metabolism and growth. Lysosomal storage diseases (LSDs) cause lysosomal accumulation of substrates and deficiency in trafficking of macromolecules. The substrate accumulation can impact one or several pathways which contribute to cell damage. Autophagy impairment and immune response are widely studied, but less attention is paid to morphogenic and growth pathways and its impact on the pathophysiology of LSDs. Hedgehog pathway is affected with abnormal expression and changes in distribution of protein levels, and a reduced number and length of primary cilia. Moreover, growth pathways are identified with delay in reactivation of mTOR that deregulate termination of autophagy and reformation of lysosomes. Insulin resistance caused by changes in lipids rafts has been described in different LSDs. While the genetic and biochemical bases of deficient proteins in LSDs are well understood, the secondary molecular mechanisms that disrupt wider biological processes associated with LSDs are only now becoming clearer. Therefore, we explored how specific signaling pathways can be related to specific LSDs, showing that a system medicine approach could be a valuable tool for the better understanding of LSD pathogenesis. This article is categorized under: Metabolic Diseases > Molecular and Cellular Physiology.

Nutrition in adult patients with selected lysosomal storage diseases

Lysosomal storage disorders (LSDs) are a group of clinically heterogeneous disorders affecting the function of lysosomes and are characterized by an accumulation of undigested substrates within several cell types. In recent years there have been substantial advances in supportive care and drug treatment for some LSDs, leading to improved patient survival, as seen in Gaucher, Pompe and Fabry disease and some Mucopolysaccharidoses; however, many symptoms still persist. Thus it is now even more important to improve patients' quality of life and reduce symptoms and comorbidities. One potential way of achieving this goal is through adjunct nutritional therapy, which is challenging as patients may be overweight with associated consequences, or malnourished, or underweight. Furthermore, drugs used to treat LSDs can modify the metabolic status and needs of patients. There are currently not enough data to make specific dietary recommendations for individual LSDs; however, suggestions can be made for managing clinical manifestations of the diseases, as well as treatment-associated adverse events. The metabolic and nutritional status of adult patients must be regularly assessed and individualized dietary plans may be created to cater to a patient's specific needs. Damage to the autophagic process is a common feature in LSDs that is potentially sensitive to dietary manipulation and needs to be assessed in clinical studies.

Metabolic syndrome does not influence the phenotype of LRRK2 and GBA related Parkinson's disease

In order toevaluate the influence of the metabolic syndrome (MS) (obesity, hypertension, elevated triglycerides, reduced levels of HDL cholesterol and glucose impairment) on the phenotype of LRRK2 and GBA Parkinson’s disease (PD), and on the prevalence of prodromal features among individuals at risk, we collected, laboratory test results, blood pressure, demographic, cognitive, motor, olfactory and affective information enabling the assessment of each component of MS and the construction of the MDS prodromal probability score. The number of metabolic components and their levels were compared between participants who were separated based on disease state and genetic status. One hundred and four idiopathic PD, 40 LRRK2-PD, 70 GBA-PD, 196 healthy non-carriers, 55 LRRK2-NMC and 97 GBA-NMC participated in this study. PD groups and non manifesting carriers (NMC) did not differ in the number of metabolic components (p = 0.101, p = 0.685, respectively). LRRK2-PD had higher levels of triglycerides (p = 0.015) and higher rates of prediabetes (p = 0.004), while LRRK2-NMC had higher triglyceride levels (p = 0.014). NMC with probability rates for prodromal PD above 50% had higher frequencies of hypertriglyceridemia and prediabetes (p < 0.005, p = 0.023 respectively). While elevated triglycerides and prediabetes were more frequent among LRRK2 carriers, MS does not seem to influence GBA and LRRK2-PD phenotype.

Endocrine and metabolic disorders in patients with Gaucher disease type 1: a review

Background

Gaucher disease (GD) is one of the most prevalent lysosomal storage diseases and is associated with hormonal and metabolic abnormalities, including nutritional status disorders, hypermetabolic state with high resting energy expenditures, peripheral insulin resistance, hypoadiponectinaemia, leptin and ghrelin impairments, hypolipidaemia, linear growth deceleration and growth hormone deficiency, delayed puberty, hypocalcaemia and vitamin D deficiency. Specific treatments for GD such as enzyme replacement therapy and substrate reduction therapy display significant effects on the metabolic profile of GD patients.

Main body of the abstract

Hormonal and metabolic disturbances observed in both adult and paediatric patients with Gaucher disease type 1 (GD1) are discussed in this review. The PubMed database was used to identify articles on endocrine and metabolic disorders in GD1. GD1 appears to facilitate the development of disorders of nutrition, glucose metabolism and vitamin D insufficiency. Metabolic and hormonal diseases may have a significant impact on the course of the underlying disease and patient quality of life.

Conclusions

Conditions relating to hormones and metabolism can be wide-ranging in GD1. Obtained findings were intrinsic to GD either as a deleterious process or a compensatory response and some changes detected may represent co-morbidities. Actively seeking and diagnosing endocrine and metabolic disorders are strongly recommended in GD1 patients to optimize healthcare.

Sphingolipids as Potential Therapeutic Targets against Enveloped Human RNA Viruses

Several notable human diseases are caused by enveloped RNA viruses: influenza, AIDS, hepatitis C, dengue hemorrhagic fever, microcephaly, and Guillain-Barré Syndrome. Being enveloped, the life cycle of this group of viruses is critically dependent on host lipid biosynthesis. Viral binding and entry involve interactions between viral envelope glycoproteins and cellular receptors localized to lipid-rich regions of the plasma membrane. Subsequent infection by these viruses leads to reorganization of cellular membranes and lipid metabolism to support the production of new viral particles. Recent work has focused on defining the involvement of specific lipid classes in the entry, genome replication assembly, and viral particle formation of these viruses in hopes of identifying potential therapeutic targets for the treatment or prevention of disease. In this review, we will highlight the role of host sphingolipids in the lifecycle of several medically important enveloped RNA viruses.

Dual targeting of PTP1B and glucosidases with new bifunctional iminosugar inhibitors to address type 2 diabetes

The diffusion of type 2 diabetes (T2D) throughout the world represents one of the most important health problems of this century. Patients suffering from this disease can currently be treated with numerous oral anti-hyperglycaemic drugs, but none is capable of reproducing the physiological action of insulin and, in several cases, they induce severe side effects. Developing new anti-diabetic drugs remains one of the most urgent challenges of the pharmaceutical industry. Multi-target drugs could offer new therapeutic opportunities for the treatment of T2D, and the reported data on type 2 diabetic mice models indicate that these drugs could be more effective and have fewer side effects than mono-target drugs. α-Glucosidases and Protein Tyrosine Phosphatase 1B (PTP1B) are considered important targets for the treatment of T2D: the first digest oligo- and disaccharides in the gut, while the latter regulates the insulin-signaling pathway. With the aim of generating new drugs able to target both enzymes, we synthesized a series of bifunctional compounds bearing both a nitro aromatic group and an iminosugar moiety. The results of tests carried out both in vitro and in a cell-based model, show that these bifunctional compounds maintain activity on both target enzymes and, more importantly, show a good insulin-mimetic activity, increasing phosphorylation levels of Akt in the absence of insulin stimulation. These compounds could be used to develop a new generation of anti-hyperglycemic drugs useful for the treatment of patients affected by T2D.

Retention time bracketing for targeted sphingolipidomics by liquid chromatography-tandem mass spectrometry

Aim: In complex biological matrixes, many sphingolipids are present with multiple reaction monitoring traces or lack of standard for verification, potentially leading to inaccurate identification and quantitation. Results/methodology: Based on these retention times of available standards, we devised a retention time bracketing approach to identify and predict sphingolipids of the same homologous series. Excellent concordance of predicted and observed retention times (<0.1 min) of sphingolipids were demonstrated. We also showed that many odd- and/or short-chain sphingolipids, commonly used as internal standards, are present in biological matrices including human serum, peritoneal fluid and cells. Conclusion: A retention time table, and a list of appropriate standards are presented, which are expected to be useful resources in targeted sphingolipidomics.

Lipid profiling of parkin-mutant human skin fibroblasts

Parkin mutations are a major cause of early-onset Parkinson's disease (PD). The impairment of protein quality control system together with defects in mitochondria and autophagy process are consequences of the lack of parkin, which leads to neurodegeneration. Little is known about the role of lipids in these alterations of cell functions. In the present study, parkin-mutant human skin primary fibroblasts have been considered as cellular model of PD to investigate on possible lipid alterations associated with the lack of parkin protein. Dermal fibroblasts were obtained from two unrelated PD patients with different parkin mutations and their lipid compositions were compared with that of two control fibroblasts. The lipid extracts of fibroblasts have been analyzed by combined matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF/MS) and thin-layer chromatography (TLC). In parallel, we have performed direct MALDI-TOF/MS lipid analyses of intact fibroblasts by skipping lipid extraction steps. Results show that the proportions of some phospholipids and glycosphingolipids were altered in the lipid profiles of parkin-mutant fibroblasts. The detected higher level of gangliosides, phosphatidylinositol, and phosphatidylserine could be linked to dysfunction of autophagy and mitochondrial turnover; in addition, the lysophosphatidylcholine increase could represent the marker of neuroinflammatory state, a well-known component of PD.

Compounds of the sphingomyelin-ceramide-glycosphingolipid pathways as secondary messenger molecules: new targets for novel therapies for fatty liver disease and insulin resistance

The compounds of sphingomyelin-ceramide-glycosphingolipid pathways have been studied as potential secondary messenger molecules in various systems, along with liver function and insulin resistance. Secondary messenger molecules act directly or indirectly to affect cell organelles and intercellular interactions. Their potential role in the pathogenesis of steatohepatitis and diabetes has been suggested. Data samples collected from patients with Gaucher's disease, who had high levels of glucocerebroside, support a role for compounds from these pathways as a messenger molecules in the pathogenesis of fatty liver disease and diabetes. The present review summarizes some of the recent data on the role of glycosphingolipid molecules as messenger molecules in various physiological and pathological conditions, more specifically including insulin resistance and fatty liver disease.

Comorbidities and pharmacotherapies in patients with Gaucher disease type 1: The potential for drug-drug interactions

PURPOSE

Clinical care for patients with rare diseases may be complicated by comorbidities. Administration of medications to treat comorbidities may elicit potentially harmful drug-drug interactions (DDIs). Genetic background may also influence DDI occurrence. We investigated the range of comorbid conditions in patients with Gaucher disease type I (GD1), the pharmacotherapies prescribed and the potential for DDI with enzyme replacement and substrate reduction therapies and additional medications, specifically cytochrome P450 (CYP) metabolizing medications.

METHODS

A literature review examined comorbid conditions and pharmacotherapies reported in GD1. Analysis of two national databases reported real-world prescription practices in patients with GD1 (Germany, N=87; US, N=374). Prescribed drugs were assessed for known interactions with isoenzymes from the hepatic CYP enzyme family.

RESULTS

The literature reported GD1 symptomatology and comorbid conditions in broad agreement with the known clinical picture. German patients received 86 different medications whereas US patients received 329 different medications. An average of 3.2 medications (Germany) and 7 medications (US) per patient were prescribed. Moderate/strong inhibitors of CYP isoenzymes were prescribed to 20% and 57% of patients in the US and Germany, respectively.

CONCLUSION

This study describes the extensive number of comorbid conditions and drugs prescribed to patients with GD1, and the importance of determining CYP isoenzyme interaction to reduce DDI risk.

Ceramides - Lipotoxic Inducers of Metabolic Disorders

In obesity and dyslipidemia, the oversupply of fat to tissues not suited for lipid storage induces cellular dysfunction that underlies diabetes and cardiovascular disease (i.e., lipotoxicity). Of the myriad lipids that accrue under these conditions, sphingolipids such as ceramide or its metabolites are amongst the most deleterious because they disrupt insulin sensitivity, pancreatic β cell function, vascular reactivity, and mitochondrial metabolism. Remarkably, inhibiting ceramide biosynthesis or catalyzing ceramide degradation in rodents ameliorates many metabolic disorders including diabetes, cardiomyopathy, insulin resistance, atherosclerosis, and steatohepatitis. Herein we discuss and critically assess studies that identify sphingolipids as major contributors to the tissue dysfunction underlying metabolic pathologies, highlighting the need to further decipher the full array of benefits elicited by ceramide depletion.

AMP-activated Protein Kinase Suppresses Biosynthesis of Glucosylceramide by Reducing Intracellular Sugar Nucleotides

The membrane glycolipid glucosylceramide (GlcCer) plays a critical role in cellular homeostasis. Its intracellular levels are thought to be tightly regulated. How cells regulate GlcCer levels remains to be clarified. AMP-activated protein kinase (AMPK), which is a crucial cellular energy sensor, regulates glucose and lipid metabolism to maintain energy homeostasis. Here, we investigated whether AMPK affects GlcCer metabolism. AMPK activators (5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside and metformin) decreased intracellular GlcCer levels and synthase activity in mouse fibroblasts. AMPK inhibitors or AMPK siRNA reversed these effects, suggesting that GlcCer synthesis is negatively regulated by an AMPK-dependent mechanism. Although AMPK did not affect the phosphorylation or expression of GlcCer synthase, the amount of UDP-glucose, an activated form of glucose required for GlcCer synthesis, decreased under AMPK-activating conditions. Importantly, the UDP-glucose pyrophosphatase Nudt14, which degrades UDP-glucose, generating UMP and glucose 1-phosphate, was phosphorylated and activated by AMPK. On the other hand, suppression of Nudt14 by siRNA had little effect on UDP-glucose levels, indicating that mammalian cells have an alternative UDP-glucose pyrophosphatase that mainly contributes to the reduction of UDP-glucose under AMPK-activating conditions. Because AMPK activators are capable of reducing GlcCer levels in cells from Gaucher disease patients, our findings suggest that reducing GlcCer through AMPK activation may lead to a new strategy for treating diseases caused by abnormal accumulation of GlcCer.

Dysregulated sphingolipid metabolism in endometriosis

BACKGROUND

In endometriosis, the establishment and subsistence of ectopic lesions outside the endometrium suggest an altered cellular state for pathological hyperplasia. Sphingolipids are bioactive compounds, and their biosynthesis and metabolism modulate a range of cellular processes including proliferation, migration and apoptosis. We demonstrate that aberrations in sphingolipid metabolism occur in women with endometriosis.

METHODS

Targeted mass spectrometry on >120 sphingolipids were measured in the sera (n = 62), peritoneal fluid (n = 63), and endometrial tissue (n = 14) of women with and without endometriosis. Quantitative RT-PCR and immunohistochemistry were performed on endometrial tissues determine the expression levels of sphingolipid enzymes.

RESULTS

Sphingolipidomics identified the in vivo accumulation of numerous sphingolipids, including the functionally antagonistic glucosylceramides and ceramides in the serum and PF of women with endometriosis. We found upregulation of specific sphingolipid enzymes, namely sphingomyelin synthase 1 (SMS1), sphingomyelinase 3 (SMPD3), and glucosylceramide synthase (GCS) in the endometrium of endometriotic women with corresponding increased GlcCer, decreased sphingomyelin levels, and decreased apoptosis in the endometrium.

CONCLUSIONS

Our sphingolipidomics approach provided evidence of altered sphingolipid metabolism flux in serum, peritoneal fluid, and endometrial tissue in women with endometriosis. The results provide new information on how sphingolipids and eutopic endometrium may contribute to the pathophysiology of endometriosis. The results also have implications for the use of sphingolipids as potential biomarkers.

Bioactives of Artemisia dracunculus L. enhance insulin sensitivity by modulation of ceramide metabolism in rat skeletal muscle cells

OBJECTIVE

An increase in ectopic lipids in peripheral tissues has been implicated in attenuating insulin action. The botanical extract of Artemisia dracunculus L. (PMI 5011) improves insulin action, yet the precise mechanism is unknown. The aim of this study was to determine whether the mechanism by which the bioactive compounds in PMI 5011 improve insulin signaling is through regulation of ceramide metabolism.

METHODS

L6 Myotubes were separately preincubated with 250 μM palmitic acid with or without PMI 5011 or four bioactive compounds isolated from PMI 5011 and postulated to be responsible for the effect. The effects on insulin signaling, ceramide, and glucosylceramide profiles were determined.

RESULTS

Treatment of L6 myotubes with palmitic acid resulted in increased levels of total ceramides and glucosylceramides, and cell surface expression of gangliosides. Palmitic acid also inhibited insulin-stimulated phosphorylation of protein kinase B/Akt and reduced glycogen accumulation. Bioactives from PMI 5011 had no effect on ceramide formation but one active compound (DMC-2) and its synthetic analog significantly reduced glucosylceramide accumulation and increased insulin sensitivity via restoration of Akt phosphorylation.

CONCLUSIONS

The observations suggest that insulin sensitization by PMI 5011 is partly mediated through moderation of glycosphingolipid accumulation.

Reduced glucosylceramide in the mouse model of Fabry disease: correction by successful enzyme replacement therapy

Fabry disease is an X-linked lysosomal storage disease (LSD) caused by deficient activity of α-Galactosidase A (α-Gal A). As a result, glycosphingolipids, mainly globotriaosylceramide (Gb3), progressively accumulate in body fluids and tissues. Studies aiming at the identification of secondary lipid alterations in Fabry disease may be potentially useful for the monitorization of the response to enzyme replacement therapy (ERT) and development of future therapies. The focus of this study was to evaluate if α-Gal A deficiency has an effect on two key groups of molecules of sphingolipids metabolism: glucosylceramides (GlucCers) and ceramides (Cers). Studies performed in a mouse model of Fabry disease showed reduced level of GlucCer and normal level of Cer in plasma, liver, spleen, kidney and heart. Moreover, analysis of GlucCer isoforms in Fabry knockout mice showed that GlucCer isoforms are unequally reduced in different tissues of these animals. ERT had a specific effect on the liver's GlucCer levels of Fabry knockout mice, increasing hepatic GlucCer to the levels observed in wild type mice. In contrast to Fabry knockout mice, plasma of Fabry patients had normal GlucCer and Cer but an increased GlucCer/Cer ratio. This alteration showed a positive correlation with plasma globotriaosylsphingosine (lyso-Gb3) concentration. In conclusion, this work reveals novel secondary lipid imbalances caused by α-Gal A deficiency.

New insights on glucosylated lipids: metabolism and functions

Ceramide, cholesterol, and phosphatidic acid are major basic structures for cell membrane lipids. These lipids are modified with glucose to generate glucosylceramide (GlcCer), cholesterylglucoside (ChlGlc), and phosphatidylglucoside (PtdGlc), respectively. Glucosylation dramatically changes the functional properties of lipids. For instance, ceramide acts as a strong tumor suppressor that causes apoptosis and cell cycle arrest, while GlcCer has an opposite effect, downregulating ceramide activities. All glucosylated lipids are enriched in lipid rafts or microdomains and play fundamental roles in a variety of cellular processes. In this review, we discuss the biological functions and metabolism of these three glucosylated lipids.

Cell cycle arrest in Batten disease lymphoblast cells

Batten disease is an inherited neurodegenerative disorder caused by a CLN3 gene mutation. Batten disease is characterized by blindness, seizures, cognitive decline, and early death. Although apoptotic cell death is one of the pathological hallmarks of Batten disease, little is known about the regulatory mechanism of apoptosis in this disease. Since the CLN3 gene is suggested to be involved in the cell cycle in a yeast model, we investigated the cell cycle profile and its regulatory factors in lymphoblast cells from Batten disease patients. We found G1/G0 cell cycle arrest in Batten disease cells, with overexpression of p21, sphingosine, glucosylceramide, and sulfatide as possible cell cycle regulators.

Annexins as organizers of cholesterol- and sphingomyelin-enriched membrane microdomains in Niemann-Pick type C disease

Growing evidence suggests that membrane microdomains enriched in cholesterol and sphingomyelin are sites for numerous cellular processes, including signaling, vesicular transport, interaction with pathogens, and viral infection, etc. Recently some members of the annexin family of conserved calcium and membrane-binding proteins have been recognized as cholesterol-interacting molecules and suggested to play a role in the formation, stabilization, and dynamics of membrane microdomains to affect membrane lateral organization and to attract other proteins and signaling molecules onto their territory. Furthermore, annexins were implicated in the interactions between cytosolic and membrane molecules, in the turnover and storage of cholesterol and in various signaling pathways. In this review, we focus on the mechanisms of interaction of annexins with lipid microdomains and the role of annexins in membrane microdomains dynamics including possible participation of the domain-associated forms of annexins in the etiology of human lysosomal storage disease called Niemann-Pick type C disease, related to the abnormal storage of cholesterol in the lysosome-like intracellular compartment. The involvement of annexins and cholesterol/sphingomyelin-enriched membrane microdomains in other pathologies including cardiac dysfunctions, neurodegenerative diseases, obesity, diabetes mellitus, and cancer is likely, but is not supported by substantial experimental observations, and therefore awaits further clarification.

Lipid metabolism in skeletal muscle: generation of adaptive and maladaptive intracellular signals for cellular function

Fatty acids derived from adipose tissue lipolysis, intramyocellular triacylglycerol lipolysis, or de novo lipogenesis serve a variety of functions in skeletal muscle. The two major fates of fatty acids are mitochondrial oxidation to provide energy for the myocyte and storage within a variety of lipids, where they are stored primarily in discrete lipid droplets or serve as important structural components of membranes. In this review, we provide a brief overview of skeletal muscle fatty acid metabolism and highlight recent notable advances in the field. We then 1) discuss how lipids are stored in and mobilized from various subcellular locations to provide adaptive or maladaptive signals in the myocyte and 2) outline how lipid metabolites or metabolic byproducts derived from the actions of triacylglycerol metabolism or β-oxidation act as positive and negative regulators of insulin action. We have placed an emphasis on recent developments in the lipid biology field with respect to understanding skeletal muscle physiology and discuss unanswered questions and technical limitations for assessing lipid signaling in skeletal muscle.

Sphingolipid and ceramide homeostasis: potential therapeutic targets

Sphingolipids are ubiquitous in eukaryotic cells where they have been attributed a plethora of functions from the formation of structural domains to polarized cellular trafficking and signal transduction. Recent research has identified and characterised many of the key enzymes involved in sphingolipid metabolism and this has led to a heightened interest in the possibility of targeting these processes for therapies against cancers, Alzheimer's disease, and numerous important human pathogens. In this paper we outline the major pathways in eukaryotic sphingolipid metabolism and discuss these in relation to disease and therapy for both chronic and infectious conditions.

Effect of glycosphingolipids on osteoclastogenesis and osteolytic bone diseases

Alterations in glycosphingolipid (GSL) production results in lysosomal storage disorders associated with neurodegenerative changes. In Gaucher's disease, the patients also develop osteoporosis that is ameliorated upon treatment for the underlying defect in GSL metabolism. The role of GSLs in osteoclast and osteoblast formation is discussed here as well as the potential therapeutic uses of already approved drugs that limit GSL production in bone loss disorders such as multiple myeloma and periodontal disease.

Origins of metabolic complications in obesity: ectopic fat accumulation. The importance of the qualitative aspect of lipotoxicity

PURPOSE OF REVIEW

This study highlights two aspects of the concept of lipotoxicity. First, the metabolic consequences following ectopic fat accumulation are not only determined by the amount of lipid accumulated, but also the quality of lipid species. Second, the existence of allostatic mechanisms operating at cellular and tissue levels, which counterbalance the negative effects of lipid overload.

RECENT FINDINGS

The development of lipidomics has allowed the isolation and identification of a wide range of lipid species. Some are highly reactive and capable of inducing undesirable toxic effects. Here we focus on recent information related to pathways involved in the production of these reactive lipid species, their sites of generation and tropism for specific organelles and the molecular mechanisms through which they exert toxic effects. We describe how cell membranes and the lipid species forming their bilayer constitute the main platform from which reactive lipid species are generated. We propose that strategies aimed at maintaining membrane lipid homeostasis are fundamental to preventing the initiation of metabolically relevant lipotoxicity.

SUMMARY

It is essential to understand the qualitative component of lipid species involved in cellular toxicity and the molecular mechanisms mediating these toxic effects to identify new therapeutic targets.

Reprint of: chip-based nanoelectrospray mass spectrometry of brain gangliosides

In the past few years, a considerable effort was invested in interfacing mass spectrometry (MS) to microfluidics-based systems for electrospray ionization (ESI). Since its first introduction in biological mass spectrometry, chip-based ESI demonstrated a high potential to discover novel structures of biomarker value. Therefore, recently, microfluidics for electrospray in conjunction with advanced MS instruments able to perform multistage fragmentation were introduced also in glycolipid research. This review is focused on the strategies, which allowed a successful application of chip technology for ganglioside mapping and sequencing by ESI MS and tandem MS (MS/MS). The first part of the review is dedicated to the progress of MS methods in brain ganglioside research, which culminated with the introduction of two types of microfluidic devices: the NanoMate robot and a polymer microchip for electrospray. In the second part a systematic description of most relevant results obtained by using MS in combination with the two chip systems is presented. Chip-based ESI accomplishments for determination of ganglioside expression and structure in normal brain regions and brain pathologies such as neurodegenerative diseases and primary brain tumors are described together with some considerations upon the perspectives of microfluidics-MS to be routinely introduced in biomedical investigation.

Gaucher disease and cancer: concept and controversy

Gaucher disease is an inherited disorder caused by a deficiency in the lysosomal hydrolase glucocerebrosidase. There is a wide spectrum of clinical presentations, with the most common features being hepatosplenomegaly, skeletal disease, and cytopenia. Gaucher disease has been classified into three broad phenotypes based upon the presence or absence of neurological involvement: Type 1 (nonneuronopathic), Type 2 (acute neuronopathic), and Type 3 (subacute neuronopathic). The two main treatment options include enzyme replacement therapy and substrate reduction therapy. Recently, discussion has escalated around the association of Gaucher disease and cancer, with conflicting reports as to whether Gaucher patients have an increased risk of malignancy. In this review, we present both the concept and controversy surrounding the association of Gaucher disease with cancer.

A view on sphingolipids and disease

Sphingolipid and glycosphingolipid levels and expression of sphingolipid metabolizing enzymes are altered in a variety of diseases or in response to drug treatment. Inherited defects of enzymes and other proteins required for the lysosomal degradation of these lipids lead to human sphingolipidoses. Also genetic defects that affect sphingolipid biosynthesis are known. Although the molecular details are often far from clear, (glyco)sphingolipids have been implicated to play a role in atherosclerosis, insulin resistance, cancer, and infections by pathogens. More general aspects of selected diseases are discussed.

Function and comorbidities of apolipoprotein e in Alzheimer's disease

Alzheimer's disease (AD)—the most common type of dementia among the elderly—represents one of the most challenging and urgent medical mysteries affecting our aging population. Although dominant inherited mutation in genes involved in the amyloid metabolism can elicit familial AD, the overwhelming majority of AD cases, dubbed sporadic AD, do not display this Mendelian inheritance pattern. Apolipoprotein E (APOE), the main lipid carrier protein in the central nervous system, is the only gene that has been robustly and consistently associated with AD risk. The purpose of the current paper is thus to highlight the pleiotropic roles and the structure-function relationship of APOE to stimulate both the functional characterization and the identification of novel lipid homeostasis-related molecular targets involved in AD.