Lysosomal degradation of membrane lipids

Regulation of cellular and systemic sphingolipid homeostasis

One hundred and fifty years ago, Johann Thudichum described sphingolipids as unusual "Sphinx-like" lipids from the brain. Today, we know that thousands of sphingolipid molecules mediate many essential functions in embryonic development and normal physiology. In addition, sphingolipid metabolism and signalling pathways are dysregulated in a wide range of pathologies, and therapeutic agents that target sphingolipids are now used to treat several human diseases. However, our understanding of sphingolipid regulation at cellular and organismal levels and their functions in developmental, physiological and pathological settings is rudimentary. In this Review, we discuss recent advances in sphingolipid pathways in different organelles, how secreted sphingolipid mediators modulate physiology and disease, progress in sphingolipid-targeted therapeutic and diagnostic research, and the trans-cellular sphingolipid metabolic networks between microbiota and mammals. Advances in sphingolipid biology have led to a deeper understanding of mammalian physiology and may lead to progress in the management of many diseases.

Design of Novel Saposin-like Bacteriocins Using a Hybrid Approach

A multitude of approaches will be required to respond to the threat posed by the emergence and spread of antibiotic resistant pathogens. Bacteriocins have gained increasing attention as a possible alternative to antibiotics, as such peptide antimicrobials have mechanisms of action different from antibiotics and are therefore equally potent against antibiotic resistant bacteria as their susceptible counterparts. A group of bacteriocins known as saposin-like bacteriocins is believed to act directly on the bacterial membrane. Based on seven saposin-like leaderless bacteriocins, we have constructed a library of hybrid peptides containing all combinations of the N- and C-terminal halves of the native bacteriocins. All hybrid peptides were synthesized using in vitro protein expression and assayed for antimicrobial activity towards several pathogens. Of the 42 hybrid peptides, antimicrobial activity was confirmed for 11 novel hybrid peptides. Furthermore, several of the hybrid peptides exhibited altered antimicrobial spectra and apparent increase in potency compared to the peptides from which they were derived. The most promising hybrid, termed ISP26, was then obtained synthetically and shown to inhibit most of the Gram-positive species tested, including opportunistic pathogens and food spoilage bacteria. Additionally, ISP26 was shown to inhibit Acinetobacter, a species of Gram-negative bacteria frequently isolated from nosocomial infections. The activity of the hybrid library provides valuable insights into the design and screening of new active bacteriocins.

A lipidome landscape of aging in mice

Understanding the molecular mechanisms of aging is crucial for enhancing healthy longevity. We conducted untargeted lipidomics across 13 biological samples from mice at various life stages (2, 12, 19 and 24 months) to explore the potential link between aging and lipid metabolism, considering sex (male or female) and microbiome (specific pathogen-free or germ-free) dependencies. By analyzing 2,704 molecules from 109 lipid subclasses, we characterized common and tissue-specific lipidome alterations associated with aging. For example, the levels of bis(monoacylglycero)phosphate containing polyunsaturated fatty acids increased in various organs during aging, whereas the levels of other phospholipids containing saturated and monounsaturated fatty acids decreased. In addition, we discovered age-dependent sulfonolipid accumulation, absent in germ-free mice, correlating with Alistipes abundance determined by 16S ribosomal RNA gene amplicon sequencing. In the male kidney, glycolipids such as galactosylceramides, galabiosylceramides (Gal2Cer), trihexosylceramides (Hex3Cer), and mono- and digalactosyldiacylglycerols were detected, with two lipid classes-Gal2Cer and Hex3Cer-being significantly enriched in aged mice. Integrated analysis of the kidney transcriptome revealed uridine diphosphate galactosyltransferase 8A (UGT8a), alkylglycerone phosphate synthase and fatty acyl-coenzyme A reductase 1 as potential enzymes responsible for the male-specific glycolipid biosynthesis in vivo, which would be relevant to sex dependency in kidney diseases. Inhibiting UGT8 reduced the levels of these glycolipids and the expression of inflammatory cytokines in the kidney. Our study provides a valuable resource for clarifying potential links between lipid metabolism and aging.

Differential patterns of lysosomal dysfunction are seen in the clinicopathological forms of primary progressive aphasia

Increasing evidence implicates endo-lysosomal dysfunction in frontotemporal dementia (FTD). 18 proteins were quantified using a mass spectrometry assay panel in the cerebrospinal fluid of 36 people with the language variant of FTD, primary progressive aphasia (PPA) (including 13 with non-fluent variant (nfvPPA), 11 with semantic variant (svPPA), and 12 with logopenic variant (lvPPA)) and 19 healthy controls. The concentrations of the cathepsins (B, D, F, L1, and Z) as well as AP-2 complex subunit beta, ganglioside GM2 activator, beta-hexosaminidase subunit beta, tissue alpha L-fucosidase, and ubiquitin were decreased in nfvPPA compared with controls. In contrast, the concentrations of amyloid beta A4 protein, cathepsin Z, and dipeptidyl peptidase 2 were decreased in svPPA compared with controls. No proteins were abnormal in lvPPA. These results indicate a differential alteration of lysosomal proteins in the PPA variants, suggesting those with non-Alzheimer's pathologies are more likely to show abnormal lysosomal function.

Cationic amphiphilic drugs induce accumulation of cytolytic lysoglycerophospholipids in the lysosomes of cancer cells and block their recycling into common membrane glycerophospholipids

Lysosomes are acidic organelles responsible for lipid catabolism, and their functions can be disrupted by cationic amphiphilic drugs that neutralize lumenal pH and thereby inhibit most lysosomal hydrolases. These drugs can also induce lysosomal membrane permeabilization and cancer cell death, but the underlying mechanism remains elusive. Here, we uncover that the cationic amphiphilic drugs induce a substantial accumulation of cytolytic lysoglycerophospholipids within the lysosomes of cancer cells, and thereby prevent the recycling of lysoglycerophospholipids to produce common membrane glycerophospholipids. Using quantitative mass spectrometry-based shotgun lipidomics, we demonstrate that structurally diverse cationic amphiphilic drugs, along with other types of lysosomal pH-neutralizing reagents, elevate the amounts of lysoglycerophospholipids in MCF7 breast carcinoma cells. Lysoglycerophospholipids constitute ∼11 mol% of total glycerophospholipids in lysosomes purified from MCF7 cells, compared with ∼1 mol% in the cell lysates. Treatment with cationic amphiphilic drug siramesine further elevates the lysosomal lysoglycerophospholipid content to ∼24 mol% of total glycerophospholipids. Exogenously added traceable lysophosphatidylcholine is rapidly acylated to form diacylphosphatidylcholine, but siramesine treatment sequesters the lysophosphatidylcholine in the lysosomes and prevents it from undergoing acylation. These findings shed light on the unexplored role of lysosomes in the recycling of lysoglycerophospholipids and uncover the mechanism of action of promising anticancer agents.

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.

An overview of the role of Niemann-pick C1 (NPC1) in viral infections and inhibition of viral infections through NPC1 inhibitor

Viruses communicate with their hosts through interactions with proteins, lipids, and carbohydrate moieties on the plasma membrane (PM), often resulting in viral absorption via receptor-mediated endocytosis. Many viruses cannot multiply unless the host's cholesterol level remains steady. The large endo/lysosomal membrane protein (MP) Niemann-Pick C1 (NPC1), which is involved in cellular cholesterol transport, is a crucial intracellular receptor for viral infection. NPC1 is a ubiquitous housekeeping protein essential for the controlled cholesterol efflux from lysosomes. Its human absence results in Niemann-Pick type C disease, a deadly lysosomal storage disorder. NPC1 is a crucial viral receptor and an essential host component for filovirus entrance, infection, and pathogenesis. For filovirus entrance, NPC1's cellular function is unnecessary. Furthermore, blocking NPC1 limits the entry and replication of the African swine fever virus by disrupting cholesterol homeostasis. Cell entrance of quasi-enveloped variants of hepatitis A virus and hepatitis E virus has also been linked to NPC1. By controlling cholesterol levels, NPC1 is also necessary for the effective release of reovirus cores into the cytoplasm. Drugs that limit NPC1's activity are effective against several viruses, including SARS-CoV and Type I Feline Coronavirus (F-CoV). These findings reveal NPC1 as a potential therapeutic target for treating viral illnesses and demonstrate its significance for several viral infections. This article provides a synopsis of NPC1's function in viral infections and a review of NPC1 inhibitors that may be used to counteract viral infections. Video Abstract.

Review of Eukaryote Cellular Membrane Lipid Composition, with Special Attention to the Fatty Acids

Biological membranes, primarily composed of lipids, envelop each living cell. The intricate composition and organization of membrane lipids, including the variety of fatty acids they encompass, serve a dynamic role in sustaining cellular structural integrity and functionality. Typically, modifications in lipid composition coincide with consequential alterations in universally significant signaling pathways. Exploring the various fatty acids, which serve as the foundational building blocks of membrane lipids, provides crucial insights into the underlying mechanisms governing a myriad of cellular processes, such as membrane fluidity, protein trafficking, signal transduction, intercellular communication, and the etiology of certain metabolic disorders. Furthermore, comprehending how alterations in the lipid composition, especially concerning the fatty acid profile, either contribute to or prevent the onset of pathological conditions stands as a compelling area of research. Hence, this review aims to meticulously introduce the intricacies of membrane lipids and their constituent fatty acids in a healthy organism, thereby illuminating their remarkable diversity and profound influence on cellular function. Furthermore, this review aspires to highlight some potential therapeutic targets for various pathological conditions that may be ameliorated through dietary fatty acid supplements. The initial section of this review expounds on the eukaryotic biomembranes and their complex lipids. Subsequent sections provide insights into the synthesis, membrane incorporation, and distribution of fatty acids across various fractions of membrane lipids. The last section highlights the functional significance of membrane-associated fatty acids and their innate capacity to shape the various cellular physiological responses.

Novel beta-glucocerebrosidase chaperone compounds identified from cell-based screening reduce pathologically accumulated glucosylsphingosine in iPS-derived neuronal cells

The beta-glucocerebrosidase (GBA1) gene encodes the lysosomal beta-glucocerebrosidase (GCase) that metabolizes the lipids glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph). Biallelic loss-of-function mutations in GBA1 such as L444P cause Gaucher disease (GD), which is the most prevalent lysosomal storage disease and is histopathologically characterized by abnormal accumulation of the GCase substrates GlcCer and GlcSph. GD with neurological symptoms is associated with severe mutations in the GBA1 gene, most of which cause impairment in the process of GCase trafficking to lysosomes. Given that recombinant GCase protein cannot cross the blood-brain barrier due to its high molecular weight, it is invaluable to develop a brain-penetrant small-molecule pharmacological chaperone as a viable therapeutic strategy to boost GCase activity in the central nervous system. Despite considerable efforts to screen potent GCase activators/chaperones, cell-free assays using recombinant GCase protein have yielded compounds with only marginal efficacy and micromolar EC50 that would not have sufficient clinical efficacy or an acceptable safety margin. Therefore, we utilized a fluorescence-labeled GCase suicide inhibitor, MDW933, to directly monitor lysosomal GCase activity and performed a cell-based screening in fibroblasts from a GD patient with homozygotic L444P mutations. Here, we identified novel compounds that increase the fluorescence signal from labeled GCase with L444P mutations in a dose-dependent manner. Secondary assays using an artificial cell-permeable lysosomal GCase substrate also demonstrated that the identified compounds augment lysosomal GCase L444P in the fibroblast. Moreover, those compounds increased the total GCase L444P protein levels, suggesting the pharmacological chaperone-like mechanism of action. To further elucidate the effect of the compounds on the endogenous GCase substrate GlcSph, we generated iPSC-derived dopaminergic neurons with a GBA1 L444P mutation that exhibit GlcSph accumulation in vitro. Importantly, the identified compounds reduce GlcSph in iPSC-derived dopaminergic neurons with a GBA1 L444P mutation, indicating that the increase in lysosomal GCase resulting from application of the compounds leads to the clearance of pathologically-accumulated GlcSph. Together, our findings pave the way for developing potent and efficacious GCase chaperone compounds as a potential therapeutic approach for neurological GD.

Cell entry and release of quasi-enveloped human hepatitis viruses

Infectious hepatitis type A and type E are caused by phylogenetically distinct single-stranded, positive-sense RNA viruses that were once considered to be non-enveloped. However, studies show that both are released nonlytically from hepatocytes as 'quasi-enveloped' virions cloaked in host membranes. These virion types predominate in the blood of infected individuals and mediate virus spread within the liver. They lack virally encoded proteins on their surface and are resistant to neutralizing anti-capsid antibodies induced by infection, yet they efficiently enter cells and initiate new rounds of virus replication. In this Review, we discuss the mechanisms by which specific peptide sequences in the capsids of these quasi-enveloped virions mediate their endosomal sorting complexes required for transport (ESCRT)-dependent release from hepatocytes through multivesicular endosomes, what is known about how they enter cells, and the impact of capsid quasi-envelopment on host immunity and pathogenesis.

Sphingolipids: From structural components to signaling hubs

In late November 2019, Prof. Lina M. Obeid passed away from cancer, a disease she spent her life researching and studying its intricate molecular underpinnings. Along with her husband, Prof. Yusuf A. Hannun, Obeid laid down the foundations of sphingolipid biochemistry and oversaw its remarkable evolution over the years. Lipids are a class of macromolecules that are primarily associated with cellular architecture. In fact, lipids constitute the perimeter of the cell in such a way that without them, there cannot be cells. Hence, much of the early research on lipids identified the function of this class of biological molecules as merely structural. Nevertheless, unlike proteins, carbohydrates, and nucleic acids, lipids are elaborately diverse as they are not made up of monomers in polymeric forms. This diversity in structure is clearly mirrored by functional pleiotropy. In this chapter, we focus on a major subset of lipids, sphingolipids, and explore their historic rise from merely inert structural components of plasma membranes to lively and necessary signaling molecules that transmit various signals and control many cellular processes. We will emphasize the works of Lina Obeid since she was an integral pillar of the sphingolipid research world.

Cellular transformation promotes the incorporation of docosahexaenoic acid into the endolysosome-specific lipid bis(monoacylglycerol)phosphate in breast cancer

Bis(monoacylglycero)phosphates (BMPs), a class of lipids highly enriched within endolysosomal organelles, are key components of the lysosomal intraluminal vesicles responsible for activating sphingolipid catabolic enzymes. While BMPs are understudied relative to other phospholipids, recent reports associate BMP dysregulation with a variety of pathological states including neurodegenerative diseases and lysosomal storage disorders. Since the dramatic lysosomal remodeling characteristic of cellular transformation could impact BMP abundance and function, we employed untargeted lipidomics approaches to identify and quantify BMP species in several in vitro and in vivo models of breast cancer and comparative non-transformed cells and tissues. We observed lower BMP levels within transformed cells relative to normal cells, and consistent enrichment of docosahexaenoic acid (22:6) fatty acyl chain-containing BMP species in both human- and mouse-derived mammary tumorigenesis models. Our functional analysis points to a working model whereby 22:6 BMPs serve as reactive oxygen species scavengers in tumor cells, protecting lysosomes from oxidant-induced lysosomal membrane permeabilization. Our findings suggest that breast tumor cells might divert polyunsaturated fatty acids into BMP lipids as part of an adaptive response to protect their lysosomes from elevated reactive oxygen species levels, and raise the possibility that BMP-mediated lysosomal protection is a tumor-specific vulnerability that may be exploited therapeutically.

Emerging roles of TFE3 in metabolic regulation

TFE3 is a member of the MiT family of the bHLH-leucine zipper transcription factor. We previously focused on the role of TFE3 in autophagy and cancer. Recently, an increasing number of studies have revealed that TFE3 plays an important role in metabolic regulation. TFE3 participates in the metabolism of energy in the body by regulating pathways such as glucose and lipid metabolism, mitochondrial metabolism, and autophagy. This review summarizes and discusses the specific regulatory mechanisms of TFE3 in metabolism. We determined both the direct regulation of TFE3 on metabolically active cells, such as hepatocytes and skeletal muscle cells, and the indirect regulation of TFE3 through mitochondrial quality control and the autophagy-lysosome pathway. The role of TFE3 in tumor cell metabolism is also summarized in this review. Understanding the diverse roles of TFE3 in metabolic processes can provide new avenues for the treatment of some metabolism-related disorders.

The role of sphingosine 1-phosphate metabolism in brain health and disease

Lipids are essential structural and functional components of the central nervous system (CNS). Sphingolipids are ubiquitous membrane components which were discovered in the brain in the late 19^th century. In mammals, the brain contains the highest concentration of sphingolipids in the body. Sphingosine 1-phosphate (S1P) derived from membrane sphingolipids evokes multiple cellular responses which, depending on its concentration and localization, make S1P a double-edged sword in the brain. In the present review we highlight the role of S1P in brain development and focus on the often contrasting findings regarding its contributions to the initiation, progression and potential recovery of different brain pathologies, including neurodegeneration, multiple sclerosis (MS), brain cancers, and psychiatric illnesses. A detailed understanding of the critical implications of S1P in brain health and disease may open the door for new therapeutic options. Thus, targeting S1P-metabolizing enzymes and/or signaling pathways might help overcome, or at least ameliorate, several brain illnesses.

Lipidomic profiling of rat hepatic stellate cells during activation reveals a two-stage process accompanied by increased levels of lysosomal lipids

Hepatic stellate cells (HSCs) are liver-resident cells best known for their role in vitamin A storage under physiological conditions. Upon liver injury, HSCs activate into myofibroblast-like cells, a key process in the onset of liver fibrosis. Lipids play an important role during HSC activation. Here, we provide a comprehensive characterization of the lipidomes of primary rat HSCs during 17 days of activation in vitro. For lipidomic data interpretation, we expanded our previously described Lipid Ontology (LION) and associated web application (LION/Web) with the LION-PCA heatmap module, which generates heatmaps of the most typical LION-signatures in lipidomic datasets. Furthermore, we used LION to perform pathway analysis to determine the significant metabolic conversions in lipid pathways. Together, we identify two distinct stages of HSC activation. In the first stage, we observe a decrease of saturated phosphatidylcholine, sphingomyelin, and phosphatidic acid and an increase in phosphatidylserine and polyunsaturated bis(monoacylglycero)phosphate (BMP), a lipid class typically localized at endosomes and lysosomes. In the second activation stage, BMPs, hexosylceramides, and ether-linked phosphatidylcholines are elevated, resembling a lysosomal lipid storage disease profile. The presence of isomeric structures of BMP in HSCs was confirmed ex vivo in MS-imaging datasets of steatosed liver sections. Finally, treatment with pharmaceuticals targeting the lysosomal integrity led to cell death in primary HSCs but not in HeLa cells. In summary, our combined data suggest that lysosomes play a critical role during a two-stage activation process of HSCs.

A novel antimicrobial peptide M1-8 targets the lysosomal pathway to inhibit autolysosome formation and promote apoptosis in liver cancer cells

Lysosomes, a central regulator of autophagy, play a critical role in tumour growth. Lysosomal protease cathepsin D can initiate apoptosis when released from lysosomes into the cytosol. In this study, we observed that Musca domestica cecropin (Mdc) 1-8 (M1-8), a small anti-tumour peptide derived from Mdc, inhibits hepatoma cell growth by blocking autophagy-lysosome fusion. This effect is likely achieved by targeting lysosomes to activate lysosomal protease D. Additionally, we examined whether lysosomal content and cathepsin D release were involved in M1-8-induced apoptosis. After exposure to M1-8, human hepatoma HepG2 cells rapidly co-localized with lysosomes, disrupted lysosomal integrity, caused leakage of lysosomal protease cathepsin D, caspase activation and mitochondrial membrane potential changes; and promoted cell apoptosis. Interestingly, in M1-8-treated HepG2 cells, autophagic protein content increased and the lysosome-autophagosome fusion was inhibited, suggesting that M1-8 can cause apoptosis through autophagy and lysosomes. This result indicates that a small accumulation of autophagy and autolysosome inhibition in cells can cause cell death. Taken together, these data suggest a novel insight into the regulatory mechanisms of M1-8 in autophagy and lysosomes, which may facilitate the development of M1-8 as a potential cancer therapeutic agent.

Ursolic Acid Impairs Cellular Lipid Homeostasis and Lysosomal Membrane Integrity in Breast Carcinoma Cells

Cancer is one of the leading causes of death worldwide, thus the search for new cancer therapies is of utmost importance. Ursolic acid is a naturally occurring pentacyclic triterpene with a wide range of pharmacological activities including anti-inflammatory and anti-neoplastic effects. The latter has been assigned to its ability to promote apoptosis and inhibit cancer cell proliferation by poorly defined mechanisms. In this report, we identify lysosomes as the essential targets of the anti-cancer activity of ursolic acid. The treatment of MCF7 breast cancer cells with ursolic acid elevates lysosomal pH, alters the cellular lipid profile, and causes lysosomal membrane permeabilization and leakage of lysosomal enzymes into the cytosol. Lysosomal membrane permeabilization precedes the essential hallmarks of apoptosis placing it as an initial event in the cascade of effects induced by ursolic acid. The disruption of the lysosomal function impairs the autophagic pathway and likely partakes in the mechanism by which ursolic acid kills cancer cells. Furthermore, we find that combining treatment with ursolic acid and cationic amphiphilic drugs can significantly enhance the degree of lysosomal membrane permeabilization and cell death in breast cancer cells.

Oleate restores altered autophagic flux to rescue palmitate lipotoxicity in hypothalamic neurons

Accumulation of excess lipids in non-adipose tissues, such as the hypothalamus, is termed lipotoxicity and causative of free fatty acid-mediated pathology in metabolic disease. This study aimed to elucidate the molecular mechanisms behind oleate (OA)- and palmitate (PA)-mediated changes in hypothalamic neurons. Using the well-characterized hypothalamic neuronal cell model, mHypoE-46, we assessed gene changes through qRT-PCR, cell death with quantitative imaging, PA metabolism using stable isotope labeling, and cellular mechanisms using pharmacological modulation of lipid metabolism and autophagic flux. Palmitate (PA) disrupts gene expression, including Npy, Grp78, and Il-6 mRNA in mHypoE-46 hypothalamic neurons. Blocking PA metabolism using triacsin-C prevented the increase of these genes, implying that these changes depend on PA intracellular metabolism. Co-incubation with oleate (OA) is also potently protective and prevents cell death induced by increasing concentrations of PA. However, OA does not decrease U-¹³C-PA incorporation into diacylglycerol and phospholipids. Remarkably, OA can reverse PA toxicity even after significant PA metabolism and cellular impairment. OA can restore PA-mediated impairment of autophagy to prevent or reverse the accumulation of PA metabolites through lysosomal degradation, and not through other reported mechanisms. The autophagic flux inhibitor chloroquine (CQ) mimics PA toxicity by upregulating autophagy-related genes, Npy, Grp78, and Il-6, an effect partially reversed by OA. CQ also prevented the OA defense against PA toxicity, whereas the autophagy inducer rapamycin provided some protection. Thus, PA impairment of autophagic flux significantly contributes to its lipotoxicity, and OA-mediated protection requires functional autophagy. Overall, our results suggest that impairment of autophagy contributes to hypothalamic lipotoxicity.

Current methods to analyze lysosome morphology, positioning, motility and function

Since the discovery of lysosomes more than 70 years ago, much has been learned about the functions of these organelles. Lysosomes were regarded as exclusively degradative organelles, but more recent research has shown that they play essential roles in several other cellular functions, such as nutrient sensing, intracellular signalling and metabolism. Methodological advances played a key part in generating our current knowledge about the biology of this multifaceted organelle. In this review, we cover current methods used to analyze lysosome morphology, positioning, motility and function. We highlight the principles behind these methods, the methodological strategies and their advantages and limitations. To extract accurate information and avoid misinterpretations, we discuss the best strategies to identify lysosomes and assess their characteristics and functions. With this review, we aim to stimulate an increase in the quantity and quality of research on lysosomes and further ground-breaking discoveries on an organelle that continues to surprise and excite cell biologists.

Evaluation of Liposome-Loaded Microbubbles as a Theranostic Tool in a Murine Collagen-Induced Arthritis Model

Rheumatoid arthritis (RA) is an autoimmune disease characterized by severe inflammation of the synovial tissue. Here, we assess the feasibility of liposome-loaded microbubbles as theranostic agents in a murine arthritis model. First, contrast-enhanced ultrasound (CEUS) was used to quantify neovascularization in this model since CEUS is well-established for RA diagnosis in humans. Next, the potential of liposome-loaded microbubbles and ultrasound (US) to selectively enhance liposome delivery to the synovium was evaluated with in vivo fluorescence imaging. This procedure is made very challenging by the presence of hard joints and by the limited lifetime of the microbubbles. The inflamed knee joints were exposed to therapeutic US after intravenous injection of liposome-loaded microbubbles. Loaded microbubbles were found to be quickly captured by the liver. This resulted in fast clearance of attached liposomes while free and long-circulating liposomes were able to accumulate over time in the inflamed joints. Our observations show that murine arthritis models are not well-suited for evaluating the potential of microbubble-mediated drug delivery in joints given: (i) restricted microbubble passage in murine synovial vasculature and (ii) limited control over the exact ultrasound conditions in situ given the much shorter length scale of the murine joints as compared to the therapeutic wavelength.

Genome-Wide CRISPR-Cas9 Screen Does Not Identify Host Factors Modulating Streptococcus agalactiae β-Hemolysin/Cytolysin-Induced Cell Death

Pore-forming toxins (PFTs) are commonly produced by pathogenic bacteria, and understanding them is key to the development of virulence-targeted therapies. Streptococcus agalactiae, or group B Streptococcus (GBS), produces several factors that enhance its pathogenicity, including the PFT β-hemolysin/cytolysin (βhc). Little is understood about the cellular factors involved in βhc pore formation. We conducted a whole-genome CRISPR-Cas9 forward genetic screen to identify host genes that might contribute to βhc pore formation and cell death. While the screen identified the established receptor, CD59, in control experiments using the toxin intermedilysin (ILY), no clear candidate genes were identified that were required for βhc-mediated lethality. Of the top targets from the screen, two genes involved in membrane remodeling and repair represented candidates that might modulate the kinetics of βhc-induced cell death. Upon attempted validation of the results using monoclonal cell lines with targeted disruption of these genes, no effect on βhc-mediated cell lysis was observed. The CRISPR-Cas9 screen results are consistent with the hypothesis that βhc does not require a single nonessential host factor to mediate target cell death. IMPORTANCE CRISPR-Cas9 forward genetic screens have been used to identify host cell targets required by bacterial toxins. They have been used successfully to both verify known targets and elucidate novel host factors required by toxins. Here, we show that this approach fails to identify host factors required for cell death due to βhc, a toxin required for GBS virulence. These data suggest that βhc may not require a host cell receptor for toxin function or may require a host receptor that is an essential gene and would not be identified using this screening strategy.

Cooperative Chikungunya Virus Membrane Fusion and Its Substoichiometric Inhibition by CHK-152 Antibody

Chikungunya virus (CHIKV) presents a major burden on healthcare systems worldwide, but specific treatment remains unavailable. Attachment and fusion of CHIKV to the host cell membrane is mediated by the E1/E2 protein spikes. We used an in vitro single-particle fusion assay to study the effect of the potent, neutralizing antibody CHK-152 on CHIKV binding and fusion. We find that CHK-152 shields the virions, inhibiting interaction with the target membrane and inhibiting fusion. The analysis of the ratio of bound antibodies to epitopes implied that CHIKV fusion is a highly cooperative process. Further, dissociation of the antibody at lower pH results in a finely balanced kinetic competition between inhibition and fusion, suggesting a window of opportunity for the spike proteins to act and mediate fusion, even in the presence of the antibody.

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.

GBA mutations, glucosylceramide and Parkinson's disease

Mutations in GBA, which encodes the lysosomal enzyme glucocerebrosidase, are the highest genetic risk factor for Parkinson's disease (PD), although the mechanistic link between GBA mutations and PD is unknown. An attractive hypothesis is that the lipid substrate of glucocerebrosidase, glucosylceramide, accumulates in patients with PD with a GBA mutation (PD-GBA). Despite the availability of new and accurate methods to quantitatively measure brain glucosylceramide levels, there is little evidence that glucosylceramide, or its deacetylated derivative, glucosylsphingosine, accumulates in human PD or PD-GBA brain or cerebrospinal fluid. Thus, a straightforward association between glucosylceramide levels and the development of PD does not appear valid, necessitating the involvement of other cellular pathways to explain this association, which could involve defects in lysosomal function.

Sphingolipid metabolism in the development and progression of cancer: one cancer's help is another's hindrance

Cancer development is a multistep process in which cells must overcome a series of obstacles before they can become fully developed tumors. First, cells must develop the ability to proliferate unchecked. Once this is accomplished, they must be able to invade the neighboring tissue, as well as provide themselves with oxygen and nutrients. Finally, they must acquire the ability to detach from the newly formed mass in order to spread to other tissues, all the while evading an immune system that is primed for their destruction. Furthermore, increased levels of inflammation have been shown to be linked to the development of cancer, with sites of chronic inflammation being a common component of tumorigenic microenvironments. In this Review, we give an overview of the impact of sphingolipid metabolism in cancers, from initiation to metastatic dissemination, as well as discussing immune responses and resistance to treatments. We explore how sphingolipids can either help or hinder the progression of cells from a healthy phenotype to a cancerous one.

SapC-DOPS as a Novel Therapeutic and Diagnostic Agent for Glioblastoma Therapy and Detection: Alternative to Old Drugs and Agents

Glioblastoma multiforme (GBM), the most common type of brain cancer, is extremely aggressive and has a dreadful prognosis. GBM comprises 60% of adult brain tumors and the 5 year survival rate of GBM patients is only 4.3%. Standard-of-care treatment includes maximal surgical removal of the tumor in combination with radiation and temozolomide (TMZ) chemotherapy. TMZ is the "gold-standard" chemotherapy for patients suffering from GBM. However, the median survival is only about 12 to 18 months with this protocol. Consequently, there is a critical need to develop new therapeutic options for treatment of GBM. Nanomaterials have unique properties as multifunctional platforms for brain tumor therapy and diagnosis. As one of the nanomaterials, lipid-based nanocarriers are capable of delivering chemotherapeutics and imaging agents to tumor sites by enhancing the permeability of the compound through the blood-brain barrier, which makes them ideal for GBM therapy and imaging. Nanocarriers also can be used for delivery of radiosensitizers to the tumor to enhance the efficacy of the radiation therapy. Previously, high-atomic-number element-containing particles such as gold nanoparticles and liposomes have been used as radiosensitizers. SapC-DOPS, a protein-based liposomal drug comprising the lipid, dioleoylphosphatidylserine (DOPS), and the protein, saposin C (SapC), has been shown to be effective for treatment of a variety of cancers in small animals, including GBM. SapC-DOPS also has the unique ability to be used as a carrier for delivery of radiotheranostic agents for nuclear imaging and radiotherapeutic purposes. These unique properties make tumor-targeting proteo-liposome nanocarriers novel therapeutic and diagnostic alternatives to traditional chemotherapeutics and imaging agents. This article reviews various treatment modalities including nanolipid-based delivery and therapeutic systems used in preclinical and clinical trial settings for GBM treatment and detection.

Drug triggered pruritus, rash, papules, and blisters - is AGEP a clash of an altered sphingolipid-metabolism and lysosomotropism of drugs accumulating in the skin?

Rash, photosensitivity, erythema multiforme, and the acute generalized exanthematous pustulosis (AGEP) are relatively uncommon adverse reactions of drugs. To date, the etiology is not well understood and individual susceptibility still remains unknown. Amiodarone, chlorpromazine, amitriptyline, and trimipramine are classified lysosomotropic as well as photosensitizing, however, they fail to trigger rash and pruritic papules in all individuals. Lysosomotropism is a common charcteristic of various drugs, but independent of individuals. There is evidence that the individual ability to respond to external oxidative stress is crosslinked with the elongation of long-chain fatty acids to very long-chain fatty acids by ELOVLs. ELOVL6 and ELOVL7 are sensitive to ROS induced depletion of cellular NADPH and insufficient regeneration via the pentose phosphate pathway and mitochondrial fatty acid oxidation. Deficiency of NADPH in presence of lysosomotropic drugs promotes the synthesis of C16-ceramide in lysosomes and may contribute to emerging pruritic papules of AGEP. However, independently from a lysosomomotropic drug, severe depletion of ATP and NAD(P)H, e.g., by UV radiation or a potent photosensitizer can trigger likewise the collapse of the lysosomal transmembrane proton gradient resulting in lysosomal C16-ceramide synthesis and pruritic papules. This kind of papules are equally present in polymorphous light eruption (PMLE/PLE) and acne aestivalis (Mallorca acne). The suggested model of a compartmentalized ceramide metabolism provides a more sophisticated explanation of cutaneous drug adverse effects and the individual sensitivity to UV radiation. Parameters such as pKa and ClogP of the triggering drug, cutaneous fatty acid profile, and ceramide profile enables new concepts in risk assessment and scoring of AGEP as well as prophylaxis outcome.

Lipid Nanodiscs for High-Resolution NMR Studies of Membrane Proteins

Membrane proteins (MPs) play essential roles in numerous cellular processes. Because around 70% of the currently marketed drugs target MPs, a detailed understanding of their structure, binding properties, and functional dynamics in a physiologically relevant environment is crucial for a more detailed understanding of this important protein class. We here summarize the benefits of using lipid nanodiscs for NMR structural investigations and provide a detailed overview of the currently used lipid nanodisc systems as well as their applications in solution-state NMR. Despite the increasing use of other structural methods for the structure determination of MPs in lipid nanodiscs, solution NMR turns out to be a versatile tool to probe a wide range of MP features, ranging from the structure determination of small to medium-sized MPs to probing ligand and partner protein binding as well as functionally relevant dynamical signatures in a lipid nanodisc setting. We will expand on these topics by discussing recent NMR studies with lipid nanodiscs and work out a key workflow for optimizing the nanodisc incorporation of an MP for subsequent NMR investigations. With this, we hope to provide a comprehensive background to enable an informed assessment of the applicability of lipid nanodiscs for NMR studies of a particular MP of interest.

Lipid Membrane Mimetics in Functional and Structural Studies of Integral Membrane Proteins

Integral membrane proteins (IMPs) fulfill important physiological functions by providing cell-environment, cell-cell and virus-host communication; nutrients intake; export of toxic compounds out of cells; and more. However, some IMPs have obliterated functions due to polypeptide mutations, modifications in membrane properties and/or other environmental factors-resulting in damaged binding to ligands and the adoption of non-physiological conformations that prevent the protein from returning to its physiological state. Thus, elucidating IMPs' mechanisms of function and malfunction at the molecular level is important for enhancing our understanding of cell and organism physiology. This understanding also helps pharmaceutical developments for restoring or inhibiting protein activity. To this end, in vitro studies provide invaluable information about IMPs' structure and the relation between structural dynamics and function. Typically, these studies are conducted on transferred from native membranes to membrane-mimicking nano-platforms (membrane mimetics) purified IMPs. Here, we review the most widely used membrane mimetics in structural and functional studies of IMPs. These membrane mimetics are detergents, liposomes, bicelles, nanodiscs/Lipodisqs, amphipols, and lipidic cubic phases. We also discuss the protocols for IMPs reconstitution in membrane mimetics as well as the applicability of these membrane mimetic-IMP complexes in studies via a variety of biochemical, biophysical, and structural biology techniques.

Who moves the sphinx? An overview of intracellular sphingolipid transport

Lipid bilayers function as boundaries that enclose their content from the surrounding media, and the composition of different membrane types is accurately and dynamically tailored so that they can perform their function. To achieve this balance, lipid biosynthetic machinery and lipid trafficking events are intertwined into an elegant network. In this review, we focus on the intracellular movement of sphingolipids mediated by sphingolipid transfer proteins. Additionally, we will focus on the best characterized and understood mammalian sphingolipid transfer proteins and provide an overview of how they are hypothesized to function. Some are already well understood, while others remain enigmatic. A few are actual lipid transfer proteins, moving lipids from membrane to membrane, while others may have more of a sensor role, possibly reacting to changes in the concentrations of their ligands. Considering the substrates available for cytosolic sphingolipid transfer proteins, one open question that is discussed is whether galactosylceramide is a target. Another question is the exact mechanics by which sphingolipid transfer proteins are targeted to different organelles, such as how four phosphate adapter protein-2, FAPP2 is targeted to the endoplasmic reticulum. The aim of this review is to discuss what is known within the field today and to provide a basic understanding of how these proteins may work.

Novel Approaches of Dysregulating Lysosome Functions in Cancer Cells by Specific Drugs and Its Nanoformulations: A Smart Approach of Modern Therapeutics

The smart strategy of cancer cells to bypass the caspase-dependent apoptotic pathway has led to the discovery of novel anti-cancer approaches including the targeting of lysosomes. Recent discoveries observed that lysosomes perform far beyond just recycling of cellular waste, as these organelles are metabolically very active and mediate several signalling pathways to sense the cellular metabolic status. These organelles also play a significant role in mediating the immune system functions. Thus, direct or indirect lysosome-targeting with different drugs can be considered a novel therapeutic approach in different disease including cancer. Recently, some anticancer lysosomotropic drugs (eg, nortriptyline, siramesine, desipramine) and their nanoformulations have been engineered to specifically accumulate within these organelles. These drugs can enhance lysosome membrane permeabilization (LMP) or disrupt the activity of resident enzymes and protein complexes, like v-ATPase and mTORC1. Other anticancer drugs like doxorubicin, quinacrine, chloroquine and DQ661 have also been used which act through multi-target points. In addition, autophagy inhibitors, ferroptosis inducers and fluorescent probes have also been used as novel theranostic agents. Several lysosome-specific drug nanoformulations like mixed charge and peptide conjugated gold nanoparticles (AuNPs), Au-ZnO hybrid NPs, TPP-PEG-biotin NPs, octadecyl-rhodamine-B and cationic liposomes, etc. have been synthesized by diverse methods. These nanoformulations can target cathepsins, glucose-regulated protein 78, or other lysosome specific proteins in different cancers. The specific targeting of cancer cell lysosomes with drug nanoformulations is quite recent and faces tremendous challenges like toxicity concerns to normal tissues, which may be resolved in future research. The anticancer applications of these nanoformulations have led them up to various stages of clinical trials. Here in this review article, we present the recent updates about the lysosome ultrastructure, its cross-talk with other organelles, and the novel strategies of targeting this organelle in tumor cells as a recent innovative approach of cancer management.

A pathogenic HEXA missense variant in wild boars with Tay-Sachs disease

Gangliosidoses are inherited lysosomal storage disorders caused by reduced or absent activity of either a lysosomal enzyme involved in ganglioside catabolism, or an activator protein required for the proper activity of a ganglioside hydrolase, which results in the intra-lysosomal accumulation of undegraded metabolites. We hereby describe morphological, ultrastructural, biochemical and genetic features of GM2 gangliosidosis in three captive bred wild boar littermates. The piglets were kept in a partially-free range farm and presented progressive neurological signs, starting at 6 months of age. Animals were euthanized at approximately one year of age due to their poor conditions. Neuropathogens were excluded as a possible cause of the signs. Gross examination showed a reduction of cerebral and cerebellar consistency. Central (CNS) and peripheral (PNS) nervous system neurons were enlarged and foamy, with severe and diffuse cytoplasmic vacuolization. Transmission electron microscopy (TEM) of CNS neurons demonstrated numerous lysosomes, filled by parallel or concentric layers of membranous electron-dense material, defined as membranous cytoplasmic bodies (MCB). Biochemical composition of gangliosides analysis from CNS revealed accumulation of GM2 ganglioside; furthermore, Hex A enzyme activity was less than 1% compared to control animals. These data confirmed the diagnosis of GM2 gangliosidosis. Genetic analysis identified, at a homozygous level, the presence of a missense nucleotide variant c.1495C > T (p Arg499Cys) in the hexosaminidase subunit alpha gene (HEXA), located within the GH20 hexosaminidase superfamily domain of the encoded protein. This specific HEXA variant is known to be pathogenic and associated with Tay-Sachs disease in humans, but has never been identified in other animal species. This is the first report of a HEXA gene associated Tay-Sachs disease in wild boars and provides a comprehensive description of a novel spontaneous animal model for this lysosomal storage disease.

Quantitative Proteomics Reveal an Altered Pattern of Protein Expression in Brain Tissue from Mice Lacking GPR37 and GPR37L1

GPR37 and GPR37L1 are glia-enriched G protein-coupled receptors that have been implicated in several neurological and neurodegenerative diseases. To gain insight into the potential molecular mechanisms by which GPR37 and GPR37L1 regulate cellular physiology, proteomic analyses of whole mouse brain tissue from wild-type (WT) versus GPR37/GPR37L1 double knockout (DKO) mice were performed in order to identify proteins regulated by the absence versus presence of these receptors (data are available via ProteomeXchange with identifier PXD015202). These analyses revealed a number of proteins that were significantly increased or decreased by the absence of GPR37 and GPR37L1. One of the most decreased proteins in the DKO versus WT brain tissue was S100A5, a calcium-binding protein, and the reduction of S100A5 expression in KO brain tissue was validated via Western blot. Coexpression of S100A5 with either GPR37 or GPR37L1 in HEK293T cells did not result in any change in S100A5 expression but did robustly increase secretion of S100A5. To dissect the mechanism by which S100A5 secretion was enhanced, cells coexpressing S100A5 with the receptors were treated with different pharmacological reagents. These studies revealed that calcium is essential for the secretion of S100A5 downstream of GPR37 and GPR37L1 signaling, as treatment with BAPTA-AM, an intracellular Ca²⁺ chelator, reduced S100A5 secretion from transfected HEK293T cells. Collectively, these findings provide a panoramic view of proteomic changes resulting from loss of GPR37 and GPR37L1 and also impart mechanistic insight into the regulation of S100A5 by these receptors, thereby shedding light on the functions of GPR37 and GPR37L1 in brain tissue.

The role of endolysosomal trafficking in anticancer drug resistance

Multidrug resistance (MDR) remains a major obstacle towards curative treatment of cancer. Despite considerable progress in delineating the basis of intrinsic and acquired MDR, the underlying molecular mechanisms remain to be elucidated. Emerging evidences suggest that dysregulation in endolysosomal compartments is involved in mediating MDR through multiple mechanisms, such as alterations in endosomes, lysosomes and autophagosomes, that traffic and biodegrade the molecular cargo through macropinocytosis, autophagy and endocytosis. For example, altered lysosomal pH, in combination with transcription factor EB (TFEB)-mediated lysosomal biogenesis, increases the sequestration of hydrophobic anti-cancer drugs that are weak bases, thereby producing an insufficient and off-target accumulation of anti-cancer drugs in MDR cancer cells. Thus, the use of well-tolerated, alkalinizing compounds that selectively block Vacuolar H⁺-ATPase (V-ATPase) may be an important strategy to overcome MDR in cancer cells and increase chemotherapeutic efficacy. Other mechanisms of endolysosomal-mediated drug resistance include increases in the expression of lysosomal proteases and cathepsins that are involved in mediating carcinogenesis and chemoresistance. Therefore, blocking the trafficking and maturation of lysosomal proteases or direct inhibition of cathepsin activity in the cytosol may represent novel therapeutic modalities to overcome MDR. Furthermore, endolysosomal compartments involved in catabolic pathways, such as macropinocytosis and autophagy, are also shown to be involved in the development of MDR. Here, we review the role of endolysosomal trafficking in MDR development and discuss how targeting endolysosomal pathways could emerge as a new therapeutic strategy to overcome chemoresistance in cancer.

Glucosylceramide and galactosylceramide, small glycosphingolipids with significant impact on health and disease

Numerous clinical observations and exploitation of cellular and animal models indicate that glucosylceramide (GlcCer) and galactosylceramide (GalCer) are involved in many physiological and pathological phenomena. In many cases, the biological importance of these monohexosylcermides has been shown indirectly as the result of studies on enzymes involved in their synthesis and degradation. Under physiological conditions, GalCer plays a key role in the maintenance of proper structure and stability of myelin and differentiation of oligodendrocytes. On the other hand, GlcCer is necessary for the proper functions of epidermis. Such an important lysosomal storage disease as Gaucher disease (GD) and a neurodegenerative disorder as Parkinson’s disease are characterized by mutations in the GBA1 gene, decreased activity of lysosomal GBA1 glucosylceramidase and accumulation of GlcCer. In contrast, another lysosomal disease, Krabbe disease, is associated with mutations in the GALC gene, resulting in deficiency or decreased activity of lysosomal galactosylceramidase and accumulation of GalCer and galactosylsphingosine. Little is known about the role of both monohexosylceramides in tumor progression; however, numerous studies indicate that GlcCer and GalCer play important roles in the development of multidrug-resistance by cancer cells. It was shown that GlcCer is able to provoke immune reaction and acts as a self-antigen in GD. On the other hand, GalCer was recognized as an important cellular receptor for HIV-1. Altogether, these two molecules are excellent examples of how slight differences in chemical composition and molecular conformation contribute to profound differences in their physicochemical properties and biological functions.

Sphingolipid lysosomal storage diseases: from bench to bedside

Johann Ludwig Wilhelm Thudicum described sphingolipids (SLs) in the late nineteenth century, but it was only in the past fifty years that SL research surged in importance and applicability. Currently, sphingolipids and their metabolism are hotly debated topics in various biochemical fields. Similar to other macromolecular reactions, SL metabolism has important implications in health and disease in most cells. A plethora of SL-related genetic ailments has been described. Defects in SL catabolism can cause the accumulation of SLs, leading to many types of lysosomal storage diseases (LSDs) collectively called sphingolipidoses. These diseases mainly impact the neuronal and immune systems, but other systems can be affected as well. This review aims to present a comprehensive, up-to-date picture of the rapidly growing field of sphingolipid LSDs, their etiology, pathology, and potential therapeutic strategies. We first describe LSDs biochemically and briefly discuss their catabolism, followed by general aspects of the major diseases such as Gaucher, Krabbe, Fabry, and Farber among others. We conclude with an overview of the available and potential future therapies for many of the diseases. We strive to present the most important and recent findings from basic research and clinical applications, and to provide a valuable source for understanding these disorders.

Iminosugar glucosidase inhibitors reduce hepatic inflammation in HAV-infected Ifnar1-/- mice

Iminosugar compounds are monosaccharide mimetics with broad but generally weak antiviral activities related to inhibition of enzymes involved in glycobiology. Miglustat (N-butyl-1-deoxynojirimycin), which is approved for treatment of lipid storage diseases in humans, and UV-4 (N-(9-methoxynonyl)-1-deoxynojirimycin), inhibit replication of hepatitis A virus (HAV) in cell culture (IC₅₀ 32.13 μM and 8.05 μM, respectively) by blocking the synthesis of gangliosides essential for HAV cell entry. We used a murine model of hepatitis A and targeted mass spectrometry to assess the capacity of these compounds to deplete hepatic gangliosides and modify the course of HAV infection in vivo Miglustat, given by gavage to Ifnar1^-/- mice (4800 mg/kg/day) depleted hepatic gangliosides by 69-75%, but caused substantial gastrointestinal toxicity and failed to prevent viral infection. UV-4, similarly administered in high doses (400 mg/kg/day), was well tolerated, but depleted hepatic gangliosides by only 20% after 14 days. UV-4 depletion of gangliosides varied by class. Several GM2 species were paradoxically increased, likely due to inhibition of β-glucosidases that degrade gangliosides. Both compounds enhanced, rather than reduced, virus replication. Nonetheless, both iminosugars had surprising anti-inflammatory effects, blocking the accumulation of inflammatory cells within the liver. UV-4 treatment also resulted in a decrease in serum alanine aminotransferase (ALT) elevations associated with acute hepatitis A. These anti-inflammatory effects may result from iminosugar inhibition of cellular α-glucosidases, leading to impaired maturation of glycan moieties of chemokine and cytokine receptors, and point to the potential importance of paracrine signaling in the pathogenesis of acute hepatitis A.IMPORTANCEHepatitis A virus (HAV) is a common cause of viral hepatitis. Iminosugar compounds block its replication in cultured cells by inhibiting synthesis of gangliosides required for HAV cell entry, but have not been tested for their ability to prevent or treat hepatitis A in vivo We show that high doses of the iminosugars miglustat and UV-4 fail to deplete gangliosides sufficiently to block HAV infection in mice lacking a key interferon receptor. These compounds nonetheless have striking anti-inflammatory effects on the HAV-infected liver, reducing the severity of hepatitis despite enhancing chemokine and cytokine expression resulting from hepatocyte-intrinsic antiviral responses. We propose that iminosugar inhibition of cellular α-glucosidases impairs maturation of glycan moieties of chemokine and cytokine receptors required for effective signaling. These data highlight the potential importance of paracrine signaling pathways in the inflammatory response to HAV, and add to our understanding of HAV pathogenesis in mice.

Podocyte Lipotoxicity in CKD

CKD represents the ninth most common cause of death in the United States but, despite this large health burden, treatment options for affected patients remain limited. To remedy this, several relevant pathways have been identified that may lead to novel therapeutic options. Among them, altered renal lipid metabolism, first described in 1982, has been recognized as a common pathway in clinical and experimental CKD of both metabolic and nonmetabolic origin. This observation has led many researchers to investigate the cause of this renal parenchyma lipid accumulation and its downstream effect on renal structure and function. Among key cellular components of the kidney parenchyma, podocytes are terminally differentiated cells that cannot be easily replaced when lost. Clinical and experimental evidence supports a role of reduced podocyte number in the progression of CKD. Given the importance of the podocytes in the maintenance of the glomerular filtration barrier and the accumulation of TG and cholesterol-rich lipid droplets in the podocyte and glomerulus in kidney diseases that cause CKD, understanding the upstream cause and downstream consequences of lipid accumulation in podocytes may lead to novel therapeutic opportunities. In this review, we hope to consolidate our understanding of the causes and consequences of dysregulated renal lipid metabolism in CKD development and progression, with a major focus on podocytes.

Sunitinib treatment promotes metastasis of drug-resistant renal cell carcinoma via TFE3 signaling pathway

Receptor tyrosine kinase (RTK) inhibitors, such as sunitinib and sorafenib, remain the first-line drugs for the treatment of mRCC. Acquired drug resistance and metastasis are the main causes of treatment failure. However, in the case of metastasis Renal Cell Cancer (mRCC), which showed a good response to sunitinib, we found that long-term treatment with sunitinib could promote lysosome biosynthesis and exocytosis, thereby triggering the metastasis of RCC. By constructing sunitinib-resistant cell lines in vivo, we confirmed that TFE3 plays a key role in the acquired resistance to sunitinib in RCC. Under the stimulation of sunitinib, TFE3 continued to enter the nucleus, promoting the expression of endoplasmic reticulum (ER) protein E-Syt1. E-Syt1 and the lysosomal membrane protein Syt7 form a heterodimer, which induces ER fragmentation, Ca2+ release, and lysosomal exocytosis. Lysosomal exocytosis has two functions: pumping sunitinib out from the cytoplasm, which promotes resistance to sunitinib in RCC, releasing cathepsin B (CTSB) into the extracellular matrix (ECM), which can degrade the ECM to enhance the invasion and metastasis ability of RCC. Our study found that although sunitinib is an effective drug for the treatment of mRCC, once RCC has acquired resistance to sunitinib, sunitinib treatment will promote metastasis.

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

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

A Tetrameric Assembly of Saposin A: Increasing Structural Diversity in Lipid Transfer Proteins

Saposins are lipid transfer proteins required for the degradation of sphingolipids in the lysosome. These small proteins bind lipids by transitioning from a closed, monomeric state to an open conformation exposing a hydrophobic surface that binds and shields hydrophobic lipid tails from the aqueous environment. Saposins form a range of multimeric assemblies to encompass these bound lipids and present them to hydrolases in the lysosome. This lipid-binding property of human saposin A has been exploited to form lipoprotein nanodiscs suitable for structural studies of membrane proteins. Here we present the crystal structure of a unique tetrameric assembly of murine saposin A produced serendipitously, following modifications of published protocols for making lipoprotein nanodiscs. The structure of this new saposin oligomer highlights the diversity of tertiary arrangement that can be adopted by these important lipid transfer proteins.

Membrane Protein Structure Determination and Characterisation by Solution and Solid-State NMR

Biological membranes define the interface of life and its basic unit, the cell. Membrane proteins play key roles in membrane functions, yet their structure and mechanisms remain poorly understood. Breakthroughs in crystallography and electron microscopy have invigorated structural analysis while failing to characterise key functional interactions with lipids, small molecules and membrane modulators, as well as their conformational polymorphism and dynamics. NMR is uniquely suited to resolving atomic environments within complex molecular assemblies and reporting on membrane organisation, protein structure, lipid and polysaccharide composition, conformational variations and molecular interactions. The main challenge in membrane protein studies at the atomic level remains the need for a membrane environment to support their fold. NMR studies in membrane mimetics and membranes of increasing complexity offer close to native environments for structural and molecular studies of membrane proteins. Solution NMR inherits high resolution from small molecule analysis, providing insights from detergent solubilised proteins and small molecular assemblies. Solid-state NMR achieves high resolution in membrane samples through fast sample spinning or sample alignment. Recent developments in dynamic nuclear polarisation NMR allow signal enhancement by orders of magnitude opening new opportunities for expanding the applications of NMR to studies of native membranes and whole cells.

Lysosomal sulfatases: a growing family

Sulfatases constitute a family of enzymes that specifically act in the hydrolytic degradation of sulfated metabolites by removing sulfate monoesters from various substrates, particularly glycolipids and glycosaminoglycans. A common essential feature of all known eukaryotic sulfatases is the posttranslational modification of a critical cysteine residue in their active site by oxidation to formylglycine (FGly), which is mediated by the FGly-generating enzyme in the endoplasmic reticulum and is indispensable for catalytic activity. The majority of the so far described sulfatases localize intracellularly to lysosomes, where they act in different catabolic pathways. Mutations in genes coding for lysosomal sulfatases lead to an accumulation of the sulfated substrates in lysosomes, resulting in impaired cellular function and multisystemic disorders presenting as lysosomal storage diseases, which also cover the mucopolysaccharidoses and metachromatic leukodystrophy. Bioinformatics analysis of the eukaryotic genomes revealed, besides the well described and long known disease-associated sulfatases, additional genes coding for putative enzymes with sulfatases activity, including arylsulfatase G as well as the arylsulfatases H, I, J and K, respectively. In this article, we review current knowledge about lysosomal sulfatases with a special focus on the just recently characterized family members arylsulfatase G and arylsulfatase K.

The Emerging and Diverse Roles of Bis(monoacylglycero) Phosphate Lipids in Cellular Physiology and Disease

Although understudied relative to many phospholipids, accumulating evidence suggests that bis(monoacylglycero)phosphate (BMP) is an important class of regulatory lipid that plays key roles in lysosomal integrity and function. BMPs are rare in most mammalian tissues, comprising only a few percent of total cellular lipid content, but are elevated in cell types such as macrophages that rely heavily on lysosomal function. BMPs are markedly enriched in endosomal and lysosomal vesicles compared to other organelles and membranous structures, and their unique sn-1:sn-1′ stereoconfiguration may confer stability within the hydrolytic lysosomal environment. BMP-enriched vesicles serve in endosomal-lysosomal trafficking and function as docking structures for the activation of lysosomal hydrolytic enzymes, notably those involved in the catabolic breakdown of sphingolipids. BMP levels are dysregulated in lysosomal storage disorders, phospholipidosis, metabolic diseases, liver and kidney diseases and neurodegenerative disorders. However, whether BMP alteration is a mediator or simply a marker of pathological states is unclear. Likewise, although BMP acyl chain composition may be altered with disease states, the functional significance of specific BMP species remains to be resolved. Newly developed tools for untargeted lipidomic analysis, together with a deeper understanding of enzymes mediating BMP synthesis and degradation, will help shed further light on the functional significance of BMPs in cellular physiology and pathology.

Cationic amphiphilic drugs induce elevation in lysoglycerophospholipid levels and cell death in leukemia cells

INTRODUCTION

Repurposing of cationic amphiphilic drugs (CADs) emerges as an attractive therapeutic solution against various cancers, including leukemia. CADs target lysosomal lipid metabolism and preferentially kill cancer cells via induction of lysosomal membrane permeabilization, but the exact effects of CADs on the lysosomal lipid metabolism remain poorly illuminated.

OBJECTIVES

We aimed to systematically monitor CAD-induced alterations in the quantitative lipid profiles of leukemia cell lines in order to chart effects of CADs on the metabolism of various lipid classes present in these cells.

METHODS

We conducted this study on eight cultured cell lines representing two leukemia types, acute lymphoblastic leukemia and acute myeloid leukemia. Mass spectrometry-based quantitative shotgun lipidomics was employed to quantify the levels of around 400 lipid species of 26 lipid classes in the leukemia cell lines treated or untreated with a CAD, siramesine.

RESULTS

The two leukemia types displayed high, but variable sensitivities to CADs and distinct profiles of cellular lipids. Treatment with siramesine rapidly altered the levels of diverse lipid classes in both leukemia types. These included sphingolipid classes previously reported to play key roles in CAD-induced cell death, but also lipids of other categories. We demonstrated that the treatment with siramesine additionally elevated the levels of numerous cytolytic lysoglycerophospholipids in positive correlation with the sensitivity of individual leukemia cell lines to siramesine.

CONCLUSIONS

Our study shows that CAD treatment alters balance in the metabolism of glycerophospholipids, and proposes elevation in the levels of lysoglycerophospholipids as part of the mechanism leading to CAD-induced cell death of leukemia cells.

Biotherapy of Brain Tumors with Phosphatidylserine-Targeted Radioiodinated SapC-DOPS Nanovesicles

Glioblastoma multiforme (GBM), a common type of brain cancer, has a very poor prognosis. In general, viable GBM cells exhibit elevated phosphatidylserine (PS) on their membrane surface compared to healthy cells. We have developed a drug, saposin C-dioleoylphosphatidylserine (SapC-DOPS), that selectively targets cancer cells by honing in on this surface PS. To examine whether SapC-DOPS, a stable, blood–brain barrier-penetrable nanovesicle, could be an effective delivery system for precise targeted therapy of radiation, we iodinated several carbocyanine-based fluorescent reporters with either stable iodine (¹²⁷I) or radioactive isotopes (¹²⁵I and ¹³¹I). While all of the compounds, when incorporated into the SapC-DOPS delivery system, were taken up by human GBM cell lines, we chose the two that best accumulated in the cells (DiI (22,3) and DiD (16,16)). Pharmacokinetics were conducted with ¹²⁵I-labeled compounds and indicated that DiI (22,3)-SapC-DOPS had a time to peak in the blood of 0.66 h and an elimination half-life of 8.4 h. These values were 4 h and 11.5 h, respectively, for DiD (16,16)-SapC-DOPS. Adult nude mice with GBM cells implanted in their brains were treated with ¹³¹I-DID (16,16)-SapC-DOPS. Mice receiving the radionuclide survived nearly 50% longer than the control groups. These data suggest a potential novel, personalized treatment for a devastating brain disease.

Lipophagy and Lipolysis Status in Lipid Storage and Lipid Metabolism Diseases

This review discusses how lipophagy and cytosolic lipolysis degrade cellular lipids, as well as how these pathway ys communicate, how they affect lipid metabolism and energy homeostasis in cells and how their dysfunction affects the pathogenesis of lipid storage and lipid metabolism diseases. Answers to these questions will likely uncover novel strategies for the treatment of aforementioned human diseases, but, above all, will avoid destructive effects of high concentrations of lipids-referred to as lipotoxicity-resulting in cellular dysfunction and cell death.