The ins and outs of endoplasmic reticulum-controlled lipid biosynthesis

Disrupted maxillofacial, cardiovascular, and nervous development in washc5 knockout Zebrafish: Insights into 3C syndrome

3C syndrome features craniofacial, nervous, and cardiovascular malformations. WASHC5 gene mutations may underline this syndrome, but the pathogenicity and underlying mechanism remain undetermined. We analyzed the expression pattern of the washc5 gene in zebrafish using whole-body in situ hybridization and generated a zebrafish model with washc5 gene knockout using CRISPR/Cas9 technology. Homozygous zebrafish exhibited high mortality, retarded growth, lighter stripes, and reduced pigmentation around the pupils. In the maxillofacial region, homozygotes displayed a shortened and tilted maxilla and delayed ossification of bones. In the heart, homozygous zebrafish showed a decreased heart rate, increased ventricular area, disorganized ventricular muscle fibers, mitochondrial swelling, Golgi lysis, and endoplasmic reticulum (ER) lysis in ventricular myocytes. The mRNA levels of nppb and myh7 were significantly increased. In the nervous system, homozygotes displayed bradykinesia and impaired neuronal development. qRT-PCR analysis revealed downregulation of col1a2, col1a1a, col1a1b, sp7, and msx2b (osteogenic factors and regulators of maxillofacial skeletal development) and abnormal expression of alpk2, alpk3b, actc2 (cardiac development factors), as well as tsen54, exosc8, and exosc9 (cerebellar development factors). Enrichment analysis of differentially expressed genes and proteins indicated involvement in ER-related processes. The washc5 knockout zebrafish model exhibits phenotypic similarities to human 3C syndrome, suggesting that mutations of this gene may play a pathogenic role in the syndrome. The mechanism of the washc5 gene in 3C syndrome may be associated with disturbances in ER homeostasis, providing insights into potential gene therapy strategies.

Unraveling the link between cholesterol and immune system in cancer: From biological mechanistic insights to clinical evidence. A narrative review

Cholesterol and its metabolism seem to be involved not only in cancer progression but also in immune cells activity. In this comprehensive review, we summarize preclinical, translational, and clinical evidence regarding the crucial role of cholesterol and its metabolism in regulating the immune response against cancer cells, shedding light on the multifaceted mechanisms by which cholesterol influences immune cell function and anti-tumor immunity. By synthesizing findings from preclinical studies, we have elucidated the impact of cholesterol on immune cell activation, differentiation, and effector functions. These investigations have revealed that cholesterol metabolism plays a pivotal role in shaping the immune response, with alterations in cholesterol levels directly impacting immune cell behavior and anti-tumor activity. All the steps related to cholesterol metabolism, including its de-novo synthesis, its influx and efflux mechanisms, as well as its metabolites, have a distinct impact on immune cells function and activity, which, if altered, might influence tumor progression. In addition, we have reviewed clinical studies investigating the role of circulating cholesterol on outcomes of patients with advanced tumors treated with immune checkpoint inhibitors, highlighting again in a clinical scenario the correlation between cholesterol and the immune system. Overall, our review emphasizes the importance of cholesterol and its metabolism in orchestrating the immune response against cancer cells. Herein we have provided a comprehensive overview of this emerging field by illustrating the intricate interplay between cholesterol and immune system.

Targeting polyunsaturated fatty acids desaturase FADS1 inhibits renal cancer growth via ATF3-mediated ER stress response

OBJECTIVE

Fatty Acid Desaturase 1 (FADS1) is a rate-limiting enzyme controlling the bioproduction of long-chain polyunsaturated fatty acids (PUFAs). Increasing studies suggest that FADS1 is a potential cancer target. Our previous research has demonstrated the significant role of FADS1 in cancer biology and patient survival, especially in kidney cancers. We aim to explore the underlying mechanism in this study.

METHOD AND RESULTS

We found that pharmacological inhibition or knockdown of the expression of FADS1 significantly reduced the intracellular conversion of long-chain PUFAs, effectively inhibits renal cancer cell proliferation, and induces cell cycle arrest. The stable knockdown of FADS1 also significantly inhibits tumor formation in vivo. Mechanistically, we showed that while FADS1 inhibition induces endoplasmic reticulum (ER) stress, FADS1 expression is augmented by ER-stress inducer, suggesting a necessary role of PUFA production in response to ER stress. FADS1-inhibition sensitized cellular response to ER stress inducers, leading to cell apoptosis. Also, FADS1 inhibition-induced ER stress leads to activation of the PERK/eIF2α/ATF4/ATF3 pathway. Inhibiting PERK or knockdown of ATF3 rescued FADS1 inhibition-induced ER stress and cell growth suppression, while ATF3-overexpression aggravates the FADS1 inhibition-induced cell growth suppression and leads to cell death. Metabolomic analysis revealed that FADS1 inhibition results in decreased level of UPD-N-Acetylglucosamine, a critical mediator of the unfolded protein response, as well as impaired biosynthesis of nucleotides, possibly accounting for the cell cycle arrest.

CONCLUSION

Our findings suggest that PUFA desaturation is crucial for rescuing cancer cells from persistent ER stress, supporting FADS1 as a new therapeutic target.

Immunity responses as checkpoints for efficient transmission of begomoviruses by whiteflies

Begomoviruses are a group of single stranded DNA plant viruses exclusively transmitted by the sweet potato whitefly Bemisia tabaci in a persistent, circulative manner. After acquisition from plant phloem, this group of viruses circulate and are retained within the whitefly, interacting with tissues, cells and molecular pathways for maintaining the safety of the infective intact virions, by exploiting cellular mechanisms and avoiding degradation by the insect immune responses. During retention, the virions are internalized in the midgut cells, exit and spend hours-days in the hemolymph and cross into salivary gland cells, before transmission. Destroying this group of viruses by the insect immune system seems inefficient for the most part, by examining their very efficient transmission. Thus, within the various sites along the transmission pathway especially in the midgut, it is thought that the immune system with its various layers is activated for avoiding the damage caused by the viruses on one hand, and for ensuring their safe circulation and transmission on the other hand. Begomoviruses have evolved mechanisms for counteracting and exploiting the activated immune system for their safe translocation within the whitefly. In this review, we discuss the various levels of immunity activated against begomoviruses in B. tabaci, taking other pathogen-vector systems as examples and reflecting relevant components on the interactions between B. tabaci and Begomoviruses.

Alterations in ether phospholipids metabolism activate the conserved UPR-Xbp1- PDIA3/ERp60 signaling to maintain intestinal homeostasis

Intestinal epithelium regeneration and homeostasis must be tightly regulated. Alteration of epithelial homeostasis is a major contributing factor to diseases such as colorectal cancer and inflammatory bowel diseases. Many pathways involved in epithelial regeneration have been identified, but more regulators remain undiscovered. Metabolism has emerged as an overlooked regulator of intestinal epithelium homeostasis. Using the model organism Drosophila melanogaster, we found that ether lipids metabolism is required to maintain intestinal epithelial homeostasis. Its dysregulation in intestinal progenitors causes the activation of the unfolded protein response of the endoplasmic reticulum (UPR) that triggers Xbp1 and upregulates the conserved disulfide isomerase PDIA3/ERp60. Activation of the Xbp1-ERp60 signaling causes Jak/Stat-mediated increase in progenitor cells, compromising epithelial barrier function and survival in males but not females. This study identified ether lipids-PDIA3/ERp60 as a key regulator of intestinal progenitor homeostasis in health that, if altered, causes pathological conditions in the intestinal epithelium.

SEL1L-HRD1 ER-Associated Degradation Facilitates Prohormone Convertase 2 Maturation and Glucagon Production in Islet α Cells

Proteolytic cleavage of proglucagon by prohormone convertase 2 (PC2) is required for islet α cells to generate glucagon. However, the regulatory mechanisms underlying this process remain largely unclear. Here, we report that SEL1L-HRD1 endoplasmic reticulum (ER)-associated degradation (ERAD), a highly conserved protein quality control system responsible for clearing misfolded proteins from the ER, plays a key role in glucagon production by regulating turnover of the nascent proform of the PC2 enzyme (proPC2). Using a mouse model with SEL1L deletion in proglucagon-expressing cells, we observed a progressive decline in stimulated glucagon secretion and a reduction in pancreatic glucagon content. Mechanistically, we found that endogenous proPC2 is a substrate of SEL1L-HRD1 ERAD, and that degradation of misfolded proPC2 ensures the maturation of activation-competent proPC2 protein. These findings identify ERAD as a novel regulator of PC2 biology and an essential mechanism for maintaining α cell function.

Identification of Key Fatty Acid Metabolism-Related Genes in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, and the role of fatty acid metabolism in its pathogenesis remains incompletely understood. Using AD transcriptome sequencing data from the GEO database, we initially screened for differentially expressed genes and applied Weighted Gene Correlation Network Analysis (WGCNA) to identify crucial gene modules. By intersecting these genes with fatty acid metabolism-related genes (FAMRGs), we obtained AD-related fatty acid metabolism genes (AD-FAMRGs). Subsequently, we conducted KEGG, GO, and Single-sample Gene Set Enrichment Analysis (ssGSEA). Furthermore, we employed three machine learning algorithms to determine the key AD-FAMRGs. Risk genes were thus identified, leading to the construction of a risk model which was subsequently validated through receiver operating characteristic (ROC) curve analysis. Additionally, protein docking studies were performed to assess interactions between key AD-FAMRGs and Tau as well as amyloid beta (Aβ) proteins. To explore potential therapeutic avenues, we searched the DrugBank database for agents targeting these AD-FAMRGs, followed by molecular docking and dynamics simulations. Our investigations highlighted three key AD-FAMRGs: DLD, ELOVL5, and HMGCS1. Functional enrichment analysis indicated their association with metabolism, oxidative stress, and AD pathogenesis. ZDOCK analysis further suggested their interactions with Tau and Aβ proteins, pointing to their possible involvement in AD's pathological processes. ROC analysis demonstrated the predictive accuracy of these AD-FAMRGs, with AUC values ranging from 0.764 to 0.876. Molecular docking and dynamic simulations confirmed the favorable binding of predicted therapeutic agents to these key AD-FAMRGs. Our findings suggest that fatty acid metabolism may be involved in AD pathogenesis, and DLD, ELOVL5, and HMGCS1 may serve as potential therapeutic targets for AD.

Acute diacylglycerol production activates critical membrane-shaping proteins leading to mitochondrial tubulation and fission

Mitochondrial dynamics are orchestrated by protein assemblies that directly remodel membrane structure, however the influence of specific lipids on these processes remains poorly understood. Here, using an inducible heterodimerization system to selectively modulate the lipid composition of the outer mitochondrial membrane (OMM), we show that local production of diacylglycerol (DAG) directly leads to transient tubulation and rapid fragmentation of the mitochondrial network, which are mediated by isoforms of endophilin B (EndoB) and dynamin-related protein 1 (Drp1), respectively. Reconstitution experiments on cardiolipin-containing membrane templates mimicking the planar and constricted OMM topologies reveal that DAG facilitates the membrane binding and remodeling activities of both EndoB and Drp1, thereby independently potentiating membrane tubulation and fission events. EndoB and Drp1 do not directly interact with each other, suggesting that DAG production activates multiple pathways for membrane remodeling in parallel. Together, our data emphasizes the importance of OMM lipid composition in regulating mitochondrial dynamics.

Lipid metabolic reprograming: the unsung hero in breast cancer progression and tumor microenvironment

Aberrant lipid metabolism is a well-recognized hallmark of cancer. Notably, breast cancer (BC) arises from a lipid-rich microenvironment and depends significantly on lipid metabolic reprogramming to fulfill its developmental requirements. In this review, we revisit the pivotal role of lipid metabolism in BC, underscoring its impact on the progression and tumor microenvironment. Firstly, we delineate the overall landscape of lipid metabolism in BC, highlighting its roles in tumor progression and patient prognosis. Given that lipids can also act as signaling molecules, we next describe the lipid signaling exchanges between BC cells and other cellular components in the tumor microenvironment. Additionally, we summarize the therapeutic potential of targeting lipid metabolism from the aspects of lipid metabolism processes, lipid-related transcription factors and immunotherapy in BC. Finally, we discuss the possibilities and problems associated with clinical applications of lipid‑targeted therapy in BC, and propose new research directions with advances in spatiotemporal multi-omics.

The ELOVL proteins: Very and ultra long-chain fatty acids at the crossroads between metabolic and neurodegenerative disorders

In lipid metabolism, the fatty acid (FA) elongation system synthesises a wide array of FAs, crucial for various biological functions. The role of this system is to lengthen FA carbon chains to produce FAs with ≥C16, and notably, very long-chain FAs (VLCFAs, C24-C26) and ultra long-chain FAs (ULCFAs, C28 to ≥C36). Elongation occurs in the endoplasmic reticulum (ER) through the actions of a complex of four ER-embedded enzymes, which includes the ELOVL proteins. Together with desaturases that introduce double bonds, these processes significantly increase the variety of FAs. VLCFAs and ULCFAs are required for the biosynthesis of complex lipids, notably glycero(phospho)lipids, ether(phospho)lipids and sphingolipids. The FA elongation system is therefore fundamental for membrane biogenesis and lipid homeostasis, and also for signalling pathways associated with inflammation and cell proliferation. This review focuses on the elongase enzymes, encoded by the ELOVL genes, which catalyze the first and rate-limiting step of the FA elongation cycle. We summarize the physiological roles of the elongase system, with emphasis on the less-characterized ULCFAs, their biological functions, and the functional tools, biomarkers and lipidomic studies used to study them. Additionally, we discuss how ELOVL enzyme defects contribute to disorders at the intersection of metabolic and neurodegenerative conditions, driven by disrupted lipid metabolism and misfolded enzymes in the ER and Golgi.

Whole-Genome Identification of the Flax Fatty Acid Desaturase Gene Family and Functional Analysis of the LuFAD2.1 Gene Under Cold Stress Conditions

Fatty acid desaturase (FAD) is essential for plant growth and development and plant defence response. Although flax (Linum usitatissimum L.) is an important oil and fibre crop, but its FAD gene remains understudied. This study identified 43 LuFAD genes in the flax genome. The phylogenetic analysis divided the FAD genes into seven subfamilies. LuFAD is unevenly distributed on 15 chromosomes, and fragment duplication is the only driving force for the amplification of the LuFAD gene family. In the LuFAD gene promoter region, most elements respond to plant hormones (MeJA, ABA) and abiotic stresses (anaerobic and low temperature). The expression pattern analysis showed that the temporal and spatial expression patterns of all LuFAD genes in different tissues and the response patterns to abiotic stresses (heat and salt) were identified. Subcellular localisation showed that all LuFAD2-GFP were expressed in the endoplasmic reticulum membrane. RT-qPCR analysis revealed that LuFAD2 was significantly upregulated under cold, salt and drought stress, and its overexpression in Arabidopsis thaliana enhanced cold tolerance genes and reduced ROS accumulation. This study offers key insights into the FAD gene family's role in flax development and stress adaptation.

Synthetic Lipid Biology

Cells contain thousands of different lipids. Their rapid and redundant metabolism, dynamic movement, and many interactions with other biomolecules have justly earned lipids a reputation as a vexing class of molecules to understand. Further, as the cell's hydrophobic metabolites, lipids assemble into supramolecular structures─most commonly bilayers, or membranes─from which they carry out myriad biological functions. Motivated by this daunting complexity, researchers across disciplines are bringing order to the seeming chaos of biological lipids and membranes. Here, we formalize these efforts as "synthetic lipid biology". Inspired by the idea, central to synthetic biology, that our abilities to understand and build biological systems are intimately connected, we organize studies and approaches across numerous fields to create, manipulate, and analyze lipids and biomembranes. These include construction of lipids and membranes from scratch using chemical and chemoenzymatic synthesis, editing of pre-existing membranes using optogenetics and protein engineering, detection of lipid metabolism and transport using bioorthogonal chemistry, and probing of lipid-protein interactions and membrane biophysical properties. What emerges is a portrait of an incipient field where chemists, biologists, physicists, and engineers work together in proximity─like lipids themselves─to build a clearer description of the properties, behaviors, and functions of lipids and membranes.

The emerging roles of the endoplasmic reticulum in mechanosensing and mechanotransduction

Cells are continuously subjected to physical and chemical cues from the extracellular environment, and sense and respond to mechanical cues via mechanosensation and mechanotransduction. Although the role of the cytoskeleton in these processes is well known, the contribution of intracellular membranes has been long neglected. Recently, it has become evident that various organelles play active roles in both mechanosensing and mechanotransduction. In this Review, we focus on mechanosensitive roles of the endoplasmic reticulum (ER), the functions of which are crucial for maintaining cell homeostasis. We discuss the effects of mechanical stimuli on interactions between the ER, the cytoskeleton and other organelles; the role of the ER in intracellular Ca2+ signalling via mechanosensitive channels; and how the unfolded protein response and lipid homeostasis contribute to mechanosensing. The expansive structure of the ER positions it as a key intracellular communication hub, and we additionally explore how this may be leveraged to transduce mechanical signals around the cell. By synthesising current knowledge, we aim to shed light on the emerging roles of the ER in cellular mechanosensing and mechanotransduction.

Tubular ER structures shaped by ER-phagy receptors engage in stress-induced Golgi bypass

Cellular stresses, particularly endoplasmic reticulum (ER) stress induced by ER-to-Golgi transport blockade, trigger Golgi-independent secretion of cytosolic and transmembrane proteins. However, the molecular mechanisms underlying this unconventional protein secretion (UPS) remain largely elusive. Here, we report that an ER tubulovesicular structure (ER tubular body [ER-TB]), shaped by the tubular ER-phagy receptors ATL3 and RTN3L, plays an important role in stress-induced UPS of transmembrane proteins such as cystic fibrosis transmembrane conductance regulator (CFTR) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Correlative light-electron microscopy analyses demonstrate the formation of ER-TB under UPS-inducing conditions in HEK293 and HeLa cells. Individual gene knockdowns of ATL3 and RTN3 inhibit ER-TB formation and the UPS of trafficking-deficient ΔF508-CFTR. Combined supplementation of ATL3 and RTN3L induces ER-TB formation and UPS. ATL3 also participates in the SARS-CoV-2-associated convoluted membrane formation and Golgi-independent trafficking of SARS-CoV-2 spike protein. These findings suggest that ER-TB serves a common function in mediating stress-induced UPS, which participates in various physiological and pathophysiological processes.

Molecular mechanisms of mitochondrial dynamics

Mitochondria not only synthesize energy required for cellular functions but are also involved in numerous cellular pathways including apoptosis, calcium homoeostasis, inflammation and immunity. Mitochondria are dynamic organelles that undergo cycles of fission and fusion, and these transitions between fragmented and hyperfused networks ensure mitochondrial function, enabling adaptations to metabolic changes or cellular stress. Defects in mitochondrial morphology have been associated with numerous diseases, highlighting the importance of elucidating the molecular mechanisms regulating mitochondrial morphology. Here, we discuss recent structural insights into the assembly and mechanism of action of the core mitochondrial dynamics proteins, such as the dynamin-related protein 1 (DRP1) that controls division, and the mitofusins (MFN1 and MFN2) and optic atrophy 1 (OPA1) driving membrane fusion. Furthermore, we provide an updated view of the complex interplay between different proteins, lipids and organelles during the processes of mitochondrial membrane fusion and fission. Overall, we aim to present a valuable framework reflecting current perspectives on how mitochondrial membrane remodelling is regulated.

Type I IFN induces long-chain acyl-CoA synthetase 1 to generate a phosphatidic acid reservoir for lipotoxic saturated fatty acids

Long-chain acyl-CoA synthetase 1 (ACSL1) catalyzes the conversion of long-chain fatty acids to acyl-CoAs. ACSL1 is required for β-oxidation in tissues that rely on fatty acids as fuel, but no consensus exists on why ACSL1 is induced by inflammatory mediators in immune cells. We used a comprehensive and unbiased approach to investigate the role of ACSL1 induction by interferon type I (IFN-I) in myeloid cells in vitro and in a mouse model of IFN-I overproduction. Our results show that IFN-I induces ACSL1 in macrophages via its interferon-α/β receptor, and consequently that expression of ACSL1 is increased in myeloid cells from individuals with systemic lupus erythematosus (SLE), an autoimmune condition characterized by increased IFN production. Taking advantage of a myeloid cell-targeted ACSL1-deficient mouse model and a series of lipidomics, proteomics, metabolomics and functional analyses, we show that IFN-I leverages induction of ACSL1 to increase accumulation of fully saturated phosphatidic acid species in macrophages. Conversely, ACSL1 induction is not needed for IFN-I's ability to induce the prototypical IFN-stimulated protein signature or to suppress proliferation or macrophage metabolism. Loss of ACSL1 in IFN-I stimulated myeloid cells enhances apoptosis and secondary necrosis in vitro, especially in the presence of increased saturated fatty acid load, and in a mouse model of atherosclerosis associated with IFN overproduction, resulting in larger lesion necrotic cores. We propose that ACSL1 induction is a mechanism used by IFN-I to increase phosphatidic acid saturation while protecting the cells from saturated fatty acid-induced cell death.

In vitro characteristics of purified recombinant hepatitis C virus core protein

In our previous study, we established a method for purifying bacterially expressed HCV core 1-164 under non-denaturing conditions. In the present study, we elucidated the characteristics of the purified core. The purified HCV core exhibited a notable affinity for HCV RNA, with a Kd of 3 nM, as determined by a filter binding assay. Electron microscopy analysis revealed that the purified HCV core self-assembled with RNA into spherical structures approximately 50 nm in diameter. Additionally, we demonstrated the direct binding of the purified HCV core to the purified endoplasmic reticulum (ER). Moreover, lipid strip assays revealed specific binding of the purified HCV core to specific phospholipids, suggesting that the core plays a role in specific ER membrane domains. These studies reveal the biochemical characteristics of the HCV core that significantly advance our understanding of its role as a capsid protein in the viral lifecycle and pathogenesis.

How lipid transfer proteins and the mitochondrial membrane shape the kinetics of β-oxidation the liver

The mitochondrial fatty acid β-oxidation (mFAO) is important for producing ATP under conditions of energetic stress, such as fasting and cold exposure. The regulation of this pathway is dependent on the kinetic properties of the enzymes involved. To better understand pathway behaviour, accurate enzyme kinetics is required. Setting up and interpreting such proper assays requires a good understanding of what influences the enzymes' kinetics. Often, knowing the buffer composition, pH, and temperature is considered to be sufficient. Many mFAO enzymes are membrane-bound, however, and their kinetic properties depend on the composition and curvature of the mitochondrial membranes. These properties are, in turn, affected by metabolite concentrations, but are rarely accounted for in kinetic assays. Especially for carnitine palmitoyltransferase 1 (CPT1), this has been shown to be of great consequence. Moreover, the enzymes of the mFAO metabolise water-insoluble acyl-CoA derivatives, which become toxic at high concentrations. In vivo, these are carried across the cytosol by intracellular lipid transfer proteins (iLTPs), such as the fatty-acid and acyl-CoA-binding proteins (FABP and ACBP, respectively). In vitro, this is often mimicked by using bovine serum albumin (BSA), which differs from the iLPTs in terms of its binding behaviour and subcellular localisation patterns. In this review, we argue that the iLTPs and membrane properties cannot be ignored when measuring or interpreting the kinetics of mFAO enzymes. They should be considered fundamental to the activity of mFAO enzymes just as pH, buffer composition, and temperature are.

Endoplasmic reticulum stress induced autophagy in cancer and its potential interactions with apoptosis and ferroptosis

The endoplasmic reticulum (ER) is a dynamic organelle that is a site of the synthesis of proteins and lipids, contributing to the regulation of proteostasis, lipid metabolism, redox balance, and calcium storage/-dependent signaling events. The disruption of ER homeostasis due to the accumulation of misfolded proteins in the ER causes ER stress which activates the unfolded protein response (UPR) system through the activation of IRE1, PERK, and ATF6. Activation of UPR is observed in various cancers and therefore, its association with process of carcinogenesis has been of importance. Tumor cells effectively utilize the UPR system to overcome ER stress. Moreover, ER stress and autophagy are the stress response mechanisms operating together to maintain cellular homeostasis. In human cancers, ER stress-driven autophagy can function as either pro-survival or pro-death in a context-dependent manner. ER stress-mediated autophagy can have crosstalk with other types of cell death pathways including apoptosis and ferroptosis. In this connection, the present review has evaluated the role of ER stress in the regulation of autophagy-mediated tumorigenesis and its interactions with other cell death mechanisms such as apoptosis and ferroptosis. We have also comprehensively discussed the effect of ER stress-mediated autophagy on cancer progression and chemotherapeutic resistance.

Exploiting lipid droplet metabolic pathway to foster lipid production: oleosin in focus

In the past decade, there has been an emerging gap between the demand and supply of vegetable oils globally for both edible and industrial use. Lipids are important biomolecules with enormous applications in the industrial sector and a major source of energy for animals and plants. Hence, to elevate the lipid content through metabolic engineering, new strategies have come up for triacylglycerol (TAG) accumulation and in raising the lipid or oil yield in crop plants. Increased levels of energy density can be achieved by single and multiple gene strategies that re-orient the carbon flux into TAG. Transcription factors and enzymes of the metabolic pathways have been targeted to foster lipid production. Oleosin, a structural protein of the lipid droplet plays a vital role in its stabilization and subsequently in its mobilization for seed germination and seedling growth. Maintenance of increased lipid content with optimal composition is a major target. Knowledge gained from genetic engineering strategies suggests that oleosin co-expression can result in a significant shift in carbon allocation to LDs. In this review, we present a detailed analysis of the recent advancements in metabolic engineering of plant lipids with emphasis on oleosin with its distinct patterns and functions in plants.

Folic Acid Prevents High-Fat Diet-Induced Postpartum Weight Retention in Rats, Which Is Associated with a Reduction in Endoplasmic Reticulum Stress-Mediated Hepatic Lipogenesis

BACKGROUND

Proactively preventing postpartum weight retention (PPWR) is one of the effective intervention strategies to reduce the occurrence of obesity in women. Population studies have shown that serum folate levels are closely related to body weight. The regulation of folic acid on lipid metabolism has been fully confirmed in both in vivo and in vitro studies. For many years, folic acid supplementation has been widely used in periconceptional women due to its role in preventing fetal neural tube defects. However, whether folic acid supplementation prior to and throughout pregnancy exerts preventive effects on PPWR remains uncertain. This study aims to investigate the preventive effect of folic acid on PPWR in rats and further explore the underlying mechanisms.

METHODS

In this study, pregnant rats were administered one of the dietary schedules: control diet (CON), high-fat diet (HF), control diet combined with folic acid (FA) and high-fat diet combined with folic acid (HF + FA).

RESULTS

We discovered that folic acid supplementation inhibited high-fat diet-induced elevations in body weight, visceral fat weight, liver weight, hepatic lipid levels and serum lipid levels at 1 week post-weaning (PW). Western blot analysis showed that folic acid supplementation inhibited the expression of endoplasmic reticulum (ER) stress-specific proteins including GRP78, PERK, eIF2α, IRE1α, XBP1 and ATF6, subsequently decreasing the expression of proteins related to lipid synthesis including SREBP-1c, ACC1 and FAS.

CONCLUSIONS

In conclusion, folic acid supplementation prior to and throughout pregnancy exerts preventive effects on high-fat diet-induced PPWR in rats, and the mechanism is associated with the inhibition of ER stress-mediated lipogenesis signaling pathways in the liver. Folic acid supplementation may serve as a potential strategy for preventing PPWR. In the future, the effectiveness of folic acid in PPWR prevention can be further verified by population studies.

Stress on the Endoplasmic Reticulum Impairs the Photosynthetic Efficiency of Chlamydomonas

Stress on the Endoplasmic reticulum (ER) can severely disrupt cellular function by impairing protein folding and post-translational modifications, thereby leading to the accumulation of poor-quality proteins. However, research on its impact on photosynthesis remains limited. In this study, we investigated the impact of ER stress on the photosynthetic efficiency of Chlamydomonas reinhardtii using pharmacological inducers, tunicamycin (TM) and brefeldin A (BFA), which specifically target the ER. Our measurements of photosynthetic parameters showed that these ER stress-inducing compounds caused a significant decline in photosynthetic efficiency. A proteomic analysis confirmed that TM and BFA effectively induce ER stress, as evidenced by the upregulation of ER stress-related proteins. Furthermore, we observed a widespread downregulation of photosynthesis-related proteins, which is consistent with the results obtained from our measurements of photosynthetic parameters. These findings suggest that the stress on ER has a profound impact on chloroplast function, disrupting photosynthetic processes. This study highlights the critical interdependence between the ER and chloroplasts, and it underscores the broader implications of ER stress on the cellular metabolism and energy efficiency of photosynthetic organisms.

Behind the stoNE wall: A fervent activity for nuclear lipids

The four main types of biomolecules are nucleic acids, proteins, carbohydrates and lipids. The knowledge about their respective interactions is as important as the individual understanding of each of them. However, while, for example, the interaction of proteins with the other three groups is extensively studied, that of nucleic acids and lipids is, in comparison, very poorly explored. An iconic paradigm of physical (and likely functional) proximity between DNA and lipids is the case of the genomic DNA in eukaryotes: enclosed within the nucleus by two concentric lipid bilayers, the wealth of implications of this interaction, for example in genome stability, remains underassessed. Nuclear lipid-related phenotypes have been observed for 50 years, yet in most cases kept as mere anecdotical descriptions. In this review, we will bring together the evidence connecting lipids with both the nuclear envelope and the nucleoplasm, and will make critical analyses of these descriptions. Our exploration establishes a scenario in which lipids irrefutably play a role in nuclear homeostasis.

From sensing to acclimation: The role of membrane lipid remodeling in plant responses to low temperatures

Low temperatures pose a dramatic challenge to plant viability. Chilling and freezing disrupt cellular processes, forcing metabolic adaptations reflected in alterations to membrane compositions. Understanding the mechanisms of plant cold tolerance is increasingly important due to anticipated increases in the frequency, severity, and duration of cold events. This review synthesizes current knowledge on the adaptive changes of membrane glycerolipids, sphingolipids, and phytosterols in response to cold stress. We delve into key mechanisms of low-temperature membrane remodeling, including acyl editing and headgroup exchange, lipase activity, and phytosterol abundance changes, focusing on their impact at the subcellular level. Furthermore, we tabulate and analyze current gycerolipidomic data from cold treatments of Arabidopsis, maize, and sorghum. This analysis highlights congruencies of lipid abundance changes in response to varying degrees of cold stress. Ultimately, this review aids in rationalizing observed lipid fluctuations and pinpoints key gaps in our current capacity to fully understand how plants orchestrate these membrane responses to cold stress.

Interplay between membranes and biomolecular condensates in the regulation of membrane-associated cellular processes

Liquid‒liquid phase separation (LLPS) has emerged as a key mechanism for organizing cellular spaces independent of membranes. Biomolecular condensates, which assemble through LLPS, exhibit distinctive liquid droplet-like behavior and can exchange constituents with their surroundings. The regulation of condensate phases, including transitions from a liquid state to gel or irreversible aggregates, is important for their physiological functions and for controlling pathological progression, as observed in neurodegenerative diseases and cancer. While early studies on biomolecular condensates focused primarily on those in fluidic environments such as the cytosol, recent discoveries have revealed their existence in close proximity to, on, or even comprising membranes. The aim of this review is to provide an overview of the properties of membrane-associated condensates in a cellular context and their biological functions in relation to membranes.

Biogenesis of omegasomes and autophagosomes in mammalian autophagy

Autophagy is a highly conserved catabolic pathway that maintains cellular homeostasis by promoting the degradation of damaged or superfluous cytoplasmic material. A hallmark of autophagy is the generation of membrane cisternae that sequester autophagic cargo. Expansion of these structures allows cargo to be engulfed in a highly selective and exclusive manner. Cytotoxic stress or starvation induces the formation of autophagosomes that sequester bulk cytoplasm instead of selected cargo. This rather nonselective pathway is essential for maintaining vital cellular functions during adverse conditions and is thus a major stress response pathway. Both selective and nonselective autophagy rely on the same molecular machinery. However, due to the different nature of cargo to be sequestered, the involved molecular mechanisms are fundamentally different. Although intense research over the past decades has advanced our understanding of autophagy, fundamental questions remain to be addressed. This review will focus on molecular principles and open questions regarding the formation of omegasomes and phagophores in nonselective mammalian autophagy.

The dynamic regulatory network of phosphatidic acid metabolism: a spotlight on substrate cycling between phosphatidic acid and diacylglycerol

Mammalian cells utilize over 1000 different lipid species to maintain cell and organelle membrane properties, control cell signaling and processes, and store energy. Lipid synthesis and metabolism are mediated by highly interconnected and spatiotemporally regulated networks of lipid-metabolizing enzymes and supported by vesicle trafficking and lipid-transfer at membrane contact sites. However, the regulatory mechanisms that achieve lipid homeostasis are largely unknown. Phosphatidic acid (PA) serves as the central hub for phospholipid biosynthesis, acting as a key intermediate in both the Kennedy pathway and the CDP-DAG pathway. Additionally, PA is a potent signaling molecule involved in various cellular processes. This dual role of PA, both as a critical intermediate in lipid biosynthesis and as a significant signaling molecule, suggests that it is tightly regulated within cells. This minireview will summarize the functional diversity of PA molecules based on their acyl tail structures and subcellular localization, highlighting recent tools and findings that shed light on how the physical, chemical, and spatial properties of PA species contribute to their differential metabolic fates and functions. Dysfunctional effects of altered PA metabolism as well as the strategies cells employ to maintain PA regulation and homeostasis will also be discussed. Furthermore, this review will explore the differential regulation of PA metabolism across distinct subcellular membranes. Our recent proximity labeling studies highlight the possibility that substrate cycling between PA and DAG may be location-dependent and have functional significance in cell signaling and lipid homeostasis.

Endoplasmic Reticulum Stress in Bronchopulmonary Dysplasia: Contributor or Consequence?

Bronchopulmonary dysplasia (BPD) is the most common complication of prematurity. Oxidative stress (OS) and inflammation are the major contributors to BPD. Despite aggressive treatments, BPD prevalence remains unchanged, which underscores the urgent need to explore more potential therapies. The endoplasmic reticulum (ER) plays crucial roles in surfactant and protein synthesis, assisting mitochondrial function, and maintaining metabolic homeostasis. Under OS, disturbed metabolism and protein folding transform the ER structure to refold proteins and help degrade non-essential proteins to resume cell homeostasis. When OS becomes excessive, the endogenous chaperone will leave the three ER stress sensors to allow subsequent changes, including cell death and senescence, impairing the growth potential of organs. The contributing role of ER stress in BPD is confirmed by reproducing the BPD phenotype in rat pups by ER stress inducers. Although chemical chaperones attenuate BPD, ER stress is still associated with cellular senescence. N-acetyl-lysyltyrosylcysteine amide (KYC) is a myeloperoxidase inhibitor that attenuates ER stress and senescence as a systems pharmacology agent. In this review, we describe the role of ER stress in BPD and discuss the therapeutic potentials of chemical chaperones and KYC, highlighting their promising role in future therapeutic interventions.

The endoplasmic reticulum as an active liquid network

The peripheral endoplasmic reticulum (ER) forms a dense, interconnected, and constantly evolving network of membrane-bound tubules in eukaryotic cells. While individual structural elements and the morphogens that stabilize them have been described, a quantitative understanding of the dynamic large-scale network topology remains elusive. We develop a physical model of the ER as an active liquid network, governed by a balance of tension-driven shrinking and new tubule growth. This minimalist model gives rise to steady-state network structures with density and rearrangement timescales predicted from the junction mobility and tubule spawning rate. Several parameter-independent geometric features of the liquid network model are shown to be representative of ER architecture in live mammalian cells. The liquid network model connects the timescales of distinct dynamic features such as ring closure and new tubule growth in the ER. Furthermore, it demonstrates how the steady-state network morphology on a cellular scale arises from the balance of microscopic dynamic rearrangements.

Mechanisms for assembly of the nucleoplasmic reticulum

The nuclear envelope consists of an outer membrane connected to the endoplasmic reticulum, an inner membrane facing the nucleoplasm and a perinuclear space separating the two bilayers. The inner and outer nuclear membranes are physically connected at nuclear pore complexes that mediate selective communication and transfer of materials between the cytoplasm and nucleus. The spherical shape of the nuclear envelope is maintained by counterbalancing internal and external forces applied by cyto- and nucleo-skeletal networks, and the nuclear lamina and chromatin that underly the inner nuclear membrane. Despite its apparent rigidity, the nuclear envelope can invaginate to form an intranuclear membrane network termed the nucleoplasmic reticulum (NR) consisting of Type-I NR contiguous with the inner nuclear membrane and Type-II NR containing both the inner and outer nuclear membranes. The NR extends deep into the nuclear interior potentially facilitating communication and exchanges between the nuclear interior and the cytoplasm. This review details the evidence that NR intrusions that regulate cytoplasmic communication and genome maintenance are the result of a dynamic interplay between membrane biogenesis and remodelling, and physical forces exerted on the nuclear lamina derived from the cyto- and nucleo-skeletal networks.

Cytosolic FKBPL and ER-resident CKAP4 co-regulates ER-phagy and protein secretion

Endoplasmic reticulum quality control is crucial for maintaining cellular homeostasis and adapting to stress conditions. Although several ER-phagy receptors have been identified, the collaboration between cytosolic and ER-resident factors in ER fragmentation and ER-phagy regulation remains unclear. Here, we perform a phenotype-based gain-of-function screen and identify a cytosolic protein, FKBPL, functioning as an ER-phagy regulator. Overexpression of FKBPL triggers ER fragmentation and ER-phagy. FKBPL has multiple protein binding domains, can self-associate and might act as a scaffold connecting CKAP4 and LC3/GABARAPs. CKAP4 serves as a bridge between FKBPL and ER-phagy cargo. ER-phagy-inducing conditions increase FKBPL-CKAP4 interaction followed by FKBPL oligomerization at the ER, leading to ER-phagy. In addition, FKBPL-CKAP4 deficiency leads to Golgi disassembly and lysosome impairment, and an increase in ER-derived secretory vesicles and enhances cytosolic protein secretion via microvesicle shedding. Taken together, FKBPL with the aid of CKAP4 induces ER fragmentation and ER-phagy, and FKBPL-CKAP4 deficiency facilitates protein secretion.

The regulation of the thermal stability and affinity of the HSPA5 (Grp78/BiP) by clients and nucleotides is modulated by domains coupling

The HSPA5 protein (BiP/Grp78) serves as a pivotal chaperone in maintaining cellular protein quality control. As a member of the human HSP70 family, HSPA5 comprises two distinct domains: a nucleotide-binding domain (NBD) and a peptide-binding domain (PBD). In this study, we investigated the interdomain interactions of HSPA5, aiming to elucidate how these domains regulate its function as a chaperone. Our findings revealed that HSPA5-FL, HSPA5-T, and HSPA5-N exhibit varying affinities for ATP and ADP, with a noticeable dependency on Mg2+ for optimal interactions. Interestingly, in ADP assays, the presence of the metal ion seems to enhance NBD binding only for HSPA5-FL and HSPA5-T. Moreover, while the truncation of the C-terminus does not significantly impact the thermal stability of HSPA5, experiments involving MgATP underscore its essential role in mediating interactions and nucleotide hydrolysis. Thermal stability assays further suggested that the NBD-PBD interface enhances the stability of the NBD, more pronounced for HSPA5 than for the orthologous HSPA1A, and prevents self-aggregation through interdomain coupling. Enzymatic analyses indicated that the presence of PBD enhances NBD ATPase activity and augments its nucleotide affinity. Notably, the intrinsic chaperone activity of the PBD is dependent on the presence of the NBD, potentially due to the propensity of the PBD for self-oligomerization. Collectively, our data highlight the pivotal role of allosteric mechanisms in modulating thermal stability, nucleotide interaction, and ATPase activity of HSPA5, underscoring its significance in protein quality control within cellular environments.

Selective delivery of imaging probes and therapeutics to the endoplasmic reticulum or Golgi apparatus: Current strategies and beyond

To maximize therapeutic effects and minimize unwanted effects, the interest in drug targeting to the endoplasmic reticulum (ER) or Golgi apparatus (GA) has been recently growing because two organelles are distributing hubs of cellular building/signaling components (e.g., proteins, lipids, Ca2+) to other organelles and the plasma membrane. Their structural or functional damages induce organelle stress (i.e., ER or GA stress), and their aggravation is strongly related to diseases (e.g., cancers, liver diseases, brain diseases). Many efforts have been developed to image (patho)physiological functions (e.g., oxidative stress, protein/lipid-related processing) and characteristics (e.g., pH, temperature, biothiols, reactive oxygen species) in the target organelles and to deliver drugs for organelle disruption using organelle-targeting moieties. Therefore, this review will overview the structure, (patho)physiological functions/characteristics, and related diseases of the organelles of interest. Future direction on ER or GA targeting will be discussed by understanding current strategies and investigations on targeting, imaging/sensing, and therapeutic systems.

The triglyceride-synthesizing enzyme diacylglycerol acyltransferase 2 modulates the formation of the hepatitis C virus replication organelle

The replication organelle of hepatitis C virus (HCV), called membranous web, is derived from the endoplasmic reticulum (ER) and mainly comprises double membrane vesicles (DMVs) that concentrate the viral replication complexes. It also tightly associates with lipid droplets (LDs), which are essential for virion morphogenesis. In particular acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), a rate-limiting enzyme in triglyceride synthesis, promotes early steps of virus assembly. The close proximity between ER membranes, DMVs and LDs therefore permits the efficient coordination of the HCV replication cycle. Here, we demonstrate that exaggerated LD accumulation due to the excessive expression of the DGAT1 isozyme, DGAT2, dramatically impairs the formation of the HCV membranous web. This effect depended on the enzymatic activity and ER association of DGAT2, whereas the mere LD accumulation was not sufficient to hamper HCV RNA replication. Our lipidomics data indicate that both HCV infection and DGAT2 overexpression induced membrane lipid biogenesis and markedly increased phospholipids with long chain polyunsaturated fatty acids, suggesting a dual use of these lipids and their possible competition for LD and DMV biogenesis. On the other hand, overexpression of DGAT2 depleted specific phospholipids, particularly oleyl fatty acyl chain-containing phosphatidylcholines, which, in contrast, are increased in HCV-infected cells and likely essential for viral infection. In conclusion, our results indicate that lipid exchanges occurring during LD biogenesis regulate the composition of intracellular membranes and thereby affect the formation of the HCV replication organelle. The potent antiviral effect observed in our DGAT2 overexpression system unveils lipid flux that may be relevant in the context of steatohepatitis, a hallmark of HCV infection, but also in physiological conditions, locally in specific subdomains of the ER membrane. Thus, LD formation mediated by DGAT1 and DGAT2 might participate in the spatial compartmentalization of HCV replication and assembly factories within the membranous web.

Dyslipidemia-induced renal fibrosis related to ferroptosis and endoplasmic reticulum stress

Dyslipidemia may induce chronic kidney disease and trigger both ferroptosis and endoplasmic reticulum (ER) stress, but the instigating factors are incompletely understood. We tested the hypothesis that different models of dyslipidemia engage distinct kidney injury mechanisms. Wild-type (WT) or proprotein-convertase subtilisin/kexin type-9 (PCSK9)-gain-of-function (GOF) Ossabaw pigs were fed with a 6-month normal diet (ND) or high-fat diet (HFD) (n = 5-6 each). Renal function and fat deposition were studied in vivo using CT, and blood and kidney tissue studied ex-vivo for lipid profile, systemic and renal vein FFAs levels, and renal injury mechanisms including lipid peroxidation, ferroptosis, and ER stress. Compared with WT-ND pigs, both HFD and PCSK9-GOF elevated triglyceride levels, which were highest in WT-HFD, whereas total and LDL cholesterol levels rose only in PCSK9-GOF pigs, particularly in PCSK9-GOF/HFD. The HFD groups had worse kidney function than the ND groups. The WT-HFD kidneys retained more FFA than other groups, but all kidneys developed fibrosis. Furthermore, HFD-induced ferroptosis in WT-HFD indicated by increased free iron, lipid peroxidation, and decreased glutathione peroxidase-4 mRNA expression, while PCSK9-GOF induced ER stress with upregulated GRP94 and CHOP protein expression. In vitro, pig kidney epithelial cells treated with palmitic acid and oxidized LDL to mimic HFD and PCSK9-GOF showed similar trends to those observed in vivo. Taken together, HFD-induced hypertriglyceridemia promotes renal FFA retention and ferroptosis, whereas PCSK9-GOF-induced hypercholesterolemia elicits ER stress, both resulting in renal fibrosis. These observations suggest different targets for preventing and treating renal fibrosis in subjects with specific types of dyslipidemia.

The Role of ATG9 Vesicles in Autophagosome Biogenesis

Autophagy mediates the degradation and recycling of cellular material in the lysosomal system. Dysfunctional autophagy is associated with a plethora of diseases including uncontrolled infections, cancer and neurodegeneration. In macroautophagy (hereafter autophagy) this material is encapsulated in double membrane vesicles, the autophagosomes, which form upon induction of autophagy. The precursors to autophagosomes, referred to as phagophores, first appear as small flattened membrane cisternae, which gradually enclose the cargo material as they grow. The assembly of phagophores during autophagy initiation has been a major subject of investigation over the past decades. A special focus has been ATG9, the only conserved transmembrane protein among the core machinery. The majority of ATG9 localizes to small Golgi-derived vesicles. Here we review the recent advances and breakthroughs regarding our understanding of how ATG9 and the vesicles it resides in serve to assemble the autophagy machinery and to establish membrane contact sites for autophagosome biogenesis. We also highlight open questions in the field that need to be addressed in the years to come.

Effect of Lipid Bilayer Anchoring on the Conformational Properties of the Cytochrome P450 2D6 Binding Site

Human cytochrome P450 (CYP) proteins metabolize 75% of small-molecule pharmaceuticals, which makes structure-based modeling of CYP metabolism and inhibition, bolstered by the current availability of X-ray crystal structures of CYP globular catalytic domains, an attractive prospect. Accounting for this broad metabolic capacity is a combination of the existence of multiple different CYP proteins and the capacity of a single CYP protein to metabolize multiple different small molecules. It is thought that structural plasticity and flexibility contribute to this latter property; therefore, incorporating diverse conformational states of a particular CYP is likely an important consideration in structure-based CYP metabolism and inhibition modeling. While all-atom explicit-solvent molecular dynamics simulations can be used to generate conformational ensembles under biologically relevant conditions, existing CYP crystal structures are of the globular domain only, whereas human CYPs contain N-terminal transmembrane and linker peptides that anchor the globular catalytic domain to the endoplasmic reticulum. To determine whether this can cause significant differences in the sampled binding site conformations, microsecond scale all-atom explicit-solvent molecular dynamics simulations of the CYP2D6 globular domain in an aqueous environment were compared with those of the full-length protein anchored in a POPC lipid bilayer. While bilayer-anchoring damped some structural fluctuations in the globular domain relative to the aqueous simulations, none of the affected residues included binding site pocket residues. Furthermore, clustering of molecular dynamics snapshots based on either pairwise binding site pocket RMSD or volume differences demonstrated a lack of separation of snapshots from the two simulation conditions into different clusters. These results suggest the substantially simpler and computationally cheaper aqueous simulation approach can be used to generate a relevant conformational ensemble of the CYP2D6 binding site for structure-based metabolism and inhibition modeling.

StaufenC facilitates utilization of the ERAD pathway to transport dsRNA through the endoplasmic reticulum to the cytosol

RNA interference (RNAi) is more efficient in coleopteran insects than other insects. StaufenC (StauC), a coleopteran-specific double-stranded RNA (dsRNA)-binding protein, is required for efficient RNAi in coleopterans. We investigated the function of StauC in the intracellular transport of dsRNA into the cytosol, where dsRNA is digested by Dicer enzymes and recruited by Argonauts to RNA-induced silencing complexes. Confocal microscopy and cellular organelle fractionation studies have shown that dsRNA is trafficked through the endoplasmic reticulum (ER) in coleopteran Colorado potato beetle (CPB) cells. StauC is localized to the ER in CPB cells, and StauC-knockdown caused the accumulation of dsRNA in the ER and a decrease in the cytosol, suggesting that StauC plays a key role in the intracellular transport of dsRNA through the ER. Using immunoprecipitation, we showed that StauC is required for dsRNA interaction with ER proteins in the ER-associated protein degradation (ERAD) pathway, and these interactions are required for RNAi in CPB cells. These results suggest that StauC works with the ERAD pathway to transport dsRNA through the ER to the cytosol. This information could be used to develop dsRNA delivery methods aimed at improving RNAi.

Broad-Spectrum Antiviral Effect of Cannabidiol Against Enveloped and Nonenveloped Viruses

Introduction: Cannabidiol (CBD), the main non-psychoactive cannabinoid of the Cannabis sativa plant, is a powerful antioxidant compound that in recent years has increased interest due to causes effects in a wide range of biological functions. Zika virus (ZIKV) is a virus transmitted mainly by the Aedes aegypti mosquitoes, which causes neurological diseases, such as microcephaly and Guillain-Barre syndrome. Although the frequency of viral outbreaks has increased recently, no vaccinations or particular chemotherapeutic treatments are available for ZIKV infection. Objectives: The major aim of this study was to explore the in vitro antiviral activity of CBD against ZIKV, expanding also to other dissimilar viruses. Materials and Methods: Cell cultures were infected with enveloped and nonenveloped viruses and treated with non-cytotoxic concentrations of CBD and then, viral titers were determined. Additionally, the mechanism of action of the compound during ZIKV in vitro infections was studied. To study the possible immunomodulatory role of CBD, infected and uninfected Huh-7 cells were exposed to 10 μM CBD during 48 h and levels of interleukins 6 and 8 and interferon-beta (IFN-β) expression levels were measured. On the other hand, the effect of CBD on cellular membranes was studied. For this, an immunofluorescence assay was performed, in which cell membranes were labeled with wheat germ agglutinin. Finally, intracellular cholesterol levels were measured. Results: CBD exhibited a potent antiviral activity against all the tested viruses in different cell lines with half maximal effective concentration values (CE50) ranging from 0.87 to 8.55 μM. Regarding the immunomodulatory effect of CBD during ZIKV in vitro infections, CBD-treated cells exhibited significantly IFN-β increased levels, meanwhile, interleukins 6 and 8 were not induced. Furthermore, it was determined that CBD affects cellular membranes due to the higher fluorescence intensity that was observed in CBD-treated cells and lowers intracellular cholesterol levels, thus affecting the multiplication of ZIKV and other viruses. Conclusions: It was demonstrated that CBD inhibits structurally dissimilar viruses, suggesting that this phytochemical has broad-spectrum antiviral effect, representing a valuable alternative in emergency situations during viral outbreaks, like the one caused by severe acute respiratory syndrome coronavirus 2 in 2020.

Loss of dihydroceramide desaturase drives neurodegeneration by disrupting endoplasmic reticulum and lipid droplet homeostasis in glial cells

Dihydroceramide desaturases convert dihydroceramides to ceramides, the precursors of all complex sphingolipids. Reduction of DEGS1 dihydroceramide desaturase function causes pediatric neurodegenerative disorder hypomyelinating leukodystrophy-18 (HLD-18). We discovered that infertile crescent (ifc), the Drosophila DEGS1 homolog, is expressed primarily in glial cells to promote CNS development by guarding against neurodegeneration. Loss of ifc causes massive dihydroceramide accumulation and severe morphological defects in cortex glia, including endoplasmic reticulum (ER) expansion, failure of neuronal ensheathment, and lipid droplet depletion. RNAi knockdown of the upstream ceramide synthase schlank in glia of ifc mutants rescues ER expansion, suggesting dihydroceramide accumulation in the ER drives this phenotype. RNAi knockdown of ifc in glia but not neurons drives neuronal cell death, suggesting that ifc function in glia promotes neuronal survival. Our work identifies glia as the primary site of disease progression in HLD-18 and may inform on juvenile forms of ALS, which also feature elevated dihydroceramide levels.

Futile lipid cycling: from biochemistry to physiology

In the healthy state, the fat stored in our body isn't just inert. Rather, it is dynamically mobilized to maintain an adequate concentration of fatty acids (FAs) in our bloodstream. Our body tends to produce excess FAs to ensure that the FA availability is not limiting. The surplus FAs are actively re-esterified into glycerides, initiating a cycle of breakdown and resynthesis of glycerides. This cycle consumes energy without generating a new product and is commonly referred to as the 'futile lipid cycle' or the glyceride/FA cycle. Contrary to the notion that it's a wasteful process, it turns out this cycle is crucial for systemic metabolic homeostasis. It acts as a control point in intra-adipocyte and inter-organ cross-talk, a metabolic rheostat, an energy sensor and a lipid diversifying mechanism. In this Review, we discuss the metabolic regulation and physiological implications of the glyceride/FA cycle and its mechanistic underpinnings.

Mechanism of Decision Making between Autophagy and Apoptosis Induction upon Endoplasmic Reticulum Stress

Dynamic regulation of the cellular proteome is mainly controlled in the endoplasmic reticulum (ER). Accumulation of misfolded proteins due to ER stress leads to the activation of unfolded protein response (UPR). The primary role of UPR is to reduce the bulk of damages and try to drive back the system to the former or a new homeostatic state by autophagy, while an excessive level of stress results in apoptosis. It has already been proven that the proper order and characteristic features of both surviving and self-killing mechanisms are controlled by negative and positive feedback loops, respectively. The new results suggest that these feedback loops are found not only within but also between branches of the UPR, fine-tuning the response to ER stress. In this review, we summarize the recent knowledge of the dynamical characteristic of endoplasmic reticulum stress response mechanism by using both theoretical and molecular biological techniques. In addition, this review pays special attention to describing the mechanism of action of the dynamical features of the feedback loops controlling cellular life-and-death decision upon ER stress. Since ER stress appears in diseases that are common worldwide, a more detailed understanding of the behaviour of the stress response is of medical importance.

D-Allulose Reduces Hypertrophy and Endoplasmic Reticulum Stress Induced by Palmitic Acid in Murine 3T3-L1 Adipocytes

Natural rare sugars are an alternative category of sweeteners with positive physiologic and metabolic effects both in in vitro and animal models. D-allulose is a D-fructose epimer that combines 70% sucrose sweetness with the advantage of an extremely low energy content. However, there are no data about the effect of D-allulose against adipose dysfunction; thus, it remains to be confirmed whether D-allulose is useful in the prevention and in treatment of adipose tissue alterations. With this aim, we evaluated D-allulose's preventive effects on lipid accumulation in 3T3-L1 murine adipocytes exposed to palmitic acid (PA), a trigger for hypertrophic adipocytes. D-allulose in place of glucose prevented adipocyte hypertrophy and the activation of adipogenic markers C/EBP-β and PPARγ induced by high PA concentrations. Additionally, D-allulose pretreatment inhibited the NF-κB pathway and endoplasmic reticulum stress caused by PA, through activation of the Nrf2 pathway. Interestingly, these effects were also observed as D-allulose post PA treatment. Although our data need to be confirmed through in vivo models, our findings suggest that incorporating D-allulose as a glucose substitute in the diet might have a protective role in adipocyte function and support a unique mechanism of action in this sugar as a preventive or therapeutic compound against PA lipotoxicity through the modulation of pathways connected to lipid transport and metabolism.

Ultralow Background Membrane Editors for Spatiotemporal Control of Phosphatidic Acid Metabolism and Signaling

Phosphatidic acid (PA) is a multifunctional lipid with important metabolic and signaling functions, and efforts to dissect its pleiotropy demand strategies for perturbing its levels with spatiotemporal precision. Previous membrane editing approaches for generating local PA pools used light-mediated induced proximity to recruit a PA-synthesizing enzyme, phospholipase D (PLD), from the cytosol to the target organelle membrane. Whereas these optogenetic PLDs exhibited high activity, their residual activity in the dark led to undesired chronic lipid production. Here, we report ultralow background membrane editors for PA wherein light directly controls PLD catalytic activity, as opposed to localization and access to substrates, exploiting a light-oxygen-voltage (LOV) domain-based conformational photoswitch inserted into the PLD sequence and enabling their stable and nonperturbative targeting to multiple organelle membranes. By coupling organelle-targeted LOVPLD activation to lipidomics analysis, we discovered different rates of metabolism for PA and its downstream products depending on the subcellular location of PA production. We also elucidated signaling roles for PA pools on different membranes in conferring local activation of AMP-activated protein kinase signaling. This work illustrates how membrane editors featuring acute, optogenetic conformational switches can provide new insights into organelle-selective lipid metabolic and signaling pathways.

Targeting Fatty Acid Desaturase I Inhibits Renal Cancer Growth Via ATF3-mediated ER Stress Response

Monounsaturated fatty acids (MUFAs) play a pivotal role in maintaining endoplasmic reticulum (ER) homeostasis, an emerging hallmark of cancer. However, the role of polyunsaturated fatty acid (PUFAs) desaturation in persistent ER stress driven by oncogenic abnormalities remains elusive. Fatty Acid Desaturase 1 (FADS1) is a rate-limiting enzyme controlling the bioproduction of long-chain PUFAs. Our previous research has demonstrated the significant role of FADS1 in cancer survival, especially in kidney cancers. We explored the underlying mechanism in this study. We found that pharmacological inhibition or knockdown of the expression of FADS1 effectively inhibits renal cancer cell proliferation and induces cell cycle arrest. The stable knockdown of FADS1 also significantly inhibits tumor formation in vivo. Mechanistically, we show that while FADS1 inhibition induces ER stress, its expression is also augmented by ER-stress inducers. Notably, FADS1-inhibition sensitized cellular response to ER stress inducers, providing evidence of FADS1's role in modulating the ER stress response in cancer cells. We show that, while FADS1 inhibition-induced ER stress leads to activation of ATF3, ATF3-knockdown rescues the FADS1 inhibition-induced ER stress and cell growth suppression. In addition, FADS1 inhibition results in the impaired biosynthesis of nucleotides and decreases the level of UPD-N-Acetylglucosamine, a critical mediator of the unfolded protein response. Our findings suggest that PUFA desaturation is crucial for rescuing cancer cells from persistent ER stress, supporting FADS1 as a new therapeutic target.

LipidSIM: Inferring mechanistic lipid biosynthesis perturbations from lipidomics with a flexible, low-parameter, Markov modeling framework

Lipid metabolism is a complex and dynamic system involving numerous enzymes at the junction of multiple metabolic pathways. Disruption of these pathways leads to systematic dyslipidemia, a hallmark of many pathological developments, such as nonalcoholic steatohepatitis and diabetes. Recent advances in computational tools can provide insights into the dysregulation of lipid biosynthesis, but limitations remain due to the complexity of lipidomic data, limited knowledge of interactions among involved enzymes, and technical challenges in standardizing across different lipid types. Here, we present a low-parameter, biologically interpretable framework named Lipid Synthesis Investigative Markov model (LipidSIM), which models and predicts the source of perturbations in lipid biosynthesis from lipidomic data. LipidSIM achieves this by accounting for the interdependency between the lipid species via the lipid biosynthesis network and generates testable hypotheses regarding changes in lipid biosynthetic reactions. This feature allows the integration of lipidomics with other omics types, such as transcriptomics, to elucidate the direct driving mechanisms of altered lipidomes due to treatments or disease progression. To demonstrate the value of LipidSIM, we first applied it to hepatic lipidomics following Keap1 knockdown and found that changes in mRNA expression of the lipid pathways were consistent with the LipidSIM-predicted fluxes. Second, we used it to study lipidomic changes following intraperitoneal injection of CCl4 to induce fast NAFLD/NASH development and the progression of fibrosis and hepatic cancer. Finally, to show the power of LipidSIM for classifying samples with dyslipidemia, we used a Dgat2-knockdown study dataset. Thus, we show that as it demands no a priori knowledge of enzyme kinetics, LipidSIM is a valuable and intuitive framework for extracting biological insights from complex lipidomic data.

Rapid simulation of glycoprotein structures by grafting and steric exclusion of glycan conformer libraries

Most membrane proteins are modified by covalent addition of complex sugars through N- and O-glycosylation. Unlike proteins, glycans do not typically adopt specific secondary structures and remain very mobile, shielding potentially large fractions of protein surface. High glycan conformational freedom hinders complete structural elucidation of glycoproteins. Computer simulations may be used to model glycosylated proteins but require hundreds of thousands of computing hours on supercomputers, thus limiting routine use. Here, we describe GlycoSHIELD, a reductionist method that can be implemented on personal computers to graft realistic ensembles of glycan conformers onto static protein structures in minutes. Using molecular dynamics simulation, small-angle X-ray scattering, cryoelectron microscopy, and mass spectrometry, we show that this open-access toolkit provides enhanced models of glycoprotein structures. Focusing on N-cadherin, human coronavirus spike proteins, and gamma-aminobutyric acid receptors, we show that GlycoSHIELD can shed light on the impact of glycans on the conformation and activity of complex glycoproteins.

Mechanism and cellular function of direct membrane binding by the ESCRT and ERES-associated Ca2+-sensor ALG-2

Apoptosis linked Gene-2 (ALG-2) is a multifunctional intracellular Ca2+ sensor and the archetypal member of the penta-EF hand protein family. ALG-2 functions in the repair of damage to both the plasma and lysosome membranes and in COPII-dependent budding at endoplasmic reticulum exit sites (ERES). In the presence of Ca2+, ALG-2 binds to ESCRT-I and ALIX in membrane repair and to SEC31A at ERES. ALG-2 also binds directly to acidic membranes in the presence of Ca2+ by a combination of electrostatic and hydrophobic interactions. By combining giant unilamellar vesicle-based experiments and molecular dynamics simulations, we show that charge-reversed mutants of ALG-2 at these locations disrupt membrane recruitment. ALG-2 membrane binding mutants have reduced or abrogated ERES localization in response to Thapsigargin-induced Ca2+ release but still localize to lysosomes following lysosomal Ca2+ release. In vitro reconstitution shows that the ALG-2 membrane-binding defect can be rescued by binding to ESCRT-I. These data thus reveal the nature of direct Ca2+-dependent membrane binding and its interplay with Ca2+-dependent protein binding in the cellular functions of ALG-2.

SHMT2 reduces fatty liver but is necessary for liver inflammation and fibrosis in mice

Non-alcoholic fatty liver disease is associated with an irregular serine metabolism. Serine hydroxymethyltransferase 2 (SHMT2) is a liver enzyme that breaks down serine into glycine and one-carbon (1C) units critical for liver methylation reactions and overall health. However, the contribution of SHMT2 to hepatic 1C homeostasis and biological functions has yet to be defined in genetically modified animal models. We created a mouse strain with targeted SHMT2 knockout in hepatocytes to investigate this. The absence of SHMT2 increased serine and glycine levels in circulation, decreased liver methylation potential, and increased susceptibility to fatty liver disease. Interestingly, SHMT2-deficient mice developed simultaneous fatty liver, but when fed a diet high in fat, fructose, and cholesterol, they had significantly less inflammation and fibrosis. This study highlights the critical role of SHMT2 in maintaining hepatic 1C homeostasis and its stage-specific functions in the pathogenesis of NAFLD.

Increased fatty acid synthesis and disturbed lipid metabolism in Neuro2a cells after repeated cocaine exposure: A preliminary study

Chronic use of cocaine prompts neurodegeneration and neuroinflammation. Lipids play pivotal roles in neuronal function and pathology. Although evidence correlates cocaine use with the alteration of lipid metabolism in blood and brain, the precise mechanism remains to be elucidated. In this study, we explore the effect of cocaine on neuronal fatty acid profiles in vitro. Neuro2a cells following seven days of repeated exposure to cocaine (0, 600, 800, 1000 μM) showed apoptosis-irrelevant cell death, dysregulated autophagy, activation of atypical endoplasmic reticulum stress response, increased saturated and unsaturated fatty acid synthesis, and disrupted lipid metabolism. These preliminary findings indicated the association between lipid metabolism and cocaine-induced neurotoxicity, which should be beneficial for understanding the neurotoxicity of cocaine.