Dropping in on lipid droplets: insights into cellular stress and cancer.Biosci Rep. 2018;38. [PMID: 30111611 DOI: 10.1042/BSR20180764]

HIG-2 promotes glioma stemness and radioresistance mediated by IGFBP2-rich microparticles in hypoxia

Hypoxia can weaken the efficacy of radiotherapy and decrease tumor immunogenicity leading to immune escape. Thus, a thorough understanding of the key signaling pathways regulated by hypoxia is vitally important to enhance the radiosensitivity and improve immunosuppressive microenvironment of glioma. In this study, we verified the crucial role of hypoxia-inducible gene 2 (HIG-2) in lipid droplet (LD) accumulation and demonstrated that HIG-2 binding to frizzled class receptor 10 (FZD10) activated Wnt/β-catenin signaling pathway and increased its downstream insulin-like growth factor binding protein 2 (IGFBP2) level in microparticles (MPs) derived from glioma stem cells (GSCs), leading to decreased radiosensitivity and immunogenicity of MPs-receiving cells via the cross-talk between GSCs and non-stem glioma cells (GCs). These findings suggest that HIG-2 may be a promising target in glioma radiotherapy and/or immunotherapy.

Planarian Mucus: A Novel Source of Pleiotropic Cytotoxic and Cytostatic Agents against Cancer Cells

Biological evolution has generated a vast array of natural compounds produced by organisms across all domains. Among these, secondary metabolites, selected to enhance an organism's competitiveness in its natural environment, make them a reservoir for discovering new compounds with cytotoxic activity, potentially useful as novel anticancer agents. Slime secretions, the first barrier between epithelial surfaces and the surrounding environment, frequently contain cytotoxic molecules to limit the growth of parasitic organisms. Planarians, freshwater Triclads, continuously secrete a viscous mucus with multiple physiological functions. The chemical composition of planarian mucus has been only partially elucidated, and there are no studies reporting its cytotoxic or cytostatic effects. In this study, we developed a protocol for collecting mucus from Dugesia japonica specimens and we demonstrated that it inhibits the growth of cancer cells by activating cytostatic and ROS-dependent cytotoxic mechanisms inducing lipid droplet accumulation and mitochondrial membrane reorganization. Although further research is needed to identify the specific chemicals responsible for the anticancer activity of planarian mucus, this work opens up numerous research avenues aimed at better understanding the mechanisms of action of this product for potential therapeutic applications.

Push-Pull Fluorescent Dyes with Trifluoroacetyl Acceptor for High-Fidelity Sensing of Polarity and Heterogeneity of Lipid Droplets

Imaging and sensing of lipid droplets (LDs) attracted significant attention due to growing evidence for their important role in cell life. Solvatochromic dyes are promising tools to probe LDs' local polarity, but this analysis is biased by their non-negligible emission from intracellular membranes and capacity to emit from both the apolar core and polar interface of LDs. Here, we developed two push-pull solvatochromic dyes based on naphthalene and fluorene cores bearing an exceptionally strong electron acceptor, the trifluoroacetyl group. The latter was found to boost the optical properties of the dyes by shifting their absorption and emission to red and increasing their extinction coefficient, photostability, and sensitivity to solvent polarity (solvatochromism). In contrast to classical solvatochromic dyes, such as parent aldehydes and reference Nile Red, the new dyes exhibited strong fluorescence quenching by millimolar water concentrations in organic solvents. In live cells, the trifluoroacetyl dyes exhibited high specificity to LDs, whereas the parent aldehydes and Nile Red showed a detectable backgrounds from intracellular membranes. Experiments in model lipid membranes and nanoemulsion droplets confirmed the high selectivity of new probes to LDs in contrast to classical solvatochromic dyes. Moreover, the new probes were found to be selective to the LDs oil core, where they can sense lipid unsaturation and chain length. Their ratiometric imaging in cells revealed strong heterogeneity in polarity within LDs, which covered the range of polarities of unsaturated triglyceride oils, whereas Nile Red failed to properly estimate the local polarity of LDs. Finally, the probes revealed that LDs core polarity can be altered by fatty acid diets, which correlates with their chain length and unsaturation.

Multimodal Phasor Approach to study breast cancer cells invasion in 3D spheroid model

We implemented a multimodal set of functional imaging techniques optimized for deep-tissue imaging to investigate how cancer cells invade surrounding tissues and how their physiological properties change in the process. As a model for cancer invasion of the extracellular matrix, we created 3D spheroids from triple-negative breast cancer cells (MDA-MB-231) and non-tumorigenic breast epithelial cells (MCF-10A). We analyzed multiple hallmarks of cancer within the same spheroid by combining a number of imaging techniques, such as metabolic imaging of NADH by Fluorescence Lifetime Imaging Microscopy (NADH-FLIM), hyperspectral imaging of a solvatochromic lipophilic dye (Nile Red) and extracellular matrix imaging by Second Harmonic Generation (SHG). We included phasor-based bioimage analysis of spheroids at three different time points, tracking both morphological and biological properties, including cellular metabolism, fatty acids storage, and collagen organization. Employing this multimodal deep-imaging framework, we observed and quantified cancer cell plasticity in response to changes in the environment composition.

Exploring the impact of lipid droplets on the evolution and progress of hepatocarcinoma

Over the past 10 years, the biological role of lipid droplets (LDs) has gained significant attention in the context of both physiological and pathological conditions. Considerable progress has been made in elucidating key aspects of these organelles, yet much remains to be accomplished to fully comprehend the myriad functions they serve in the progression of hepatic tumors. Our current perception is that LDs are complex and active structures managed by a distinct set of cellular processes. This understanding represents a significant paradigm shift from earlier perspectives. In this review, we aim to recapitulate the function of LDs within the liver, highlighting their pivotal role in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) (Hsu and Loomba, 2024) and their contribution to the progression towards more advanced pathological stages up to hepatocellular carcinoma (HC) (Farese and Walther, 2009). We are aware of the molecular complexity and changes occurring in the neoplastic evolution of the liver. Our attempt, however, is to summarize the most important and recent roles of LDs across both healthy and all pathological liver states, up to hepatocarcinoma. For more detailed insights, we direct readers to some of the many excellent reviews already available in the literature (Gluchowski et al., 2017; Hu et al., 2020; Seebacher et al., 2020; Paul et al., 2022).

Fluorescent Probes Based on Charge and Proton Transfer for Probing Biomolecular Environment

Fluorescent probes for sensing fundamental properties of biomolecular environment, such as polarity and hydration, help to study assembly of lipids into biomembranes, sensing interactions of biomolecules and imaging physiological state of the cells. Here, we summarize major efforts in the development of probes based on two photophysical mechanisms: (i) an excited-state intramolecular charge transfer (ICT), which is represented by fluorescent solvatochromic dyes that shift their emission band maximum as a function of environment polarity and hydration; (ii) excited-state intramolecular proton transfer (ESIPT), with particular focus on 5-membered cyclic systems, represented by 3-hydroxyflavones, because they exhibit dual emission sensitive to the environment. For both ICT and ESIPT dyes, the design of the probes and their biological applications are summarized. Thus, dyes bearing amphiphilic anchors target lipid membranes and report their lipid organization, while targeting ligands direct them to specific organelles for sensing their local environment. The labels, amino acid and nucleic acid analogues inserted into biomolecules enable monitoring their interactions with membranes, proteins and nucleic acids. While ICT probes are relatively simple and robust environment-sensitive probes, ESIPT probes feature high information content due their dual emission. They constitute a powerful toolbox for addressing multitude of biological questions.

Spectroscopic imaging to assess biochemical alterations in liver carcinoma cells exposed to transition metals

Despite the invaluable role of transition metals in every living organism, it should be remembered that failure to maintain the proper balance and exceed the appropriate dose may have the opposite effect. In the era of such a popular and propagated need for supplementation in the media, one should bear in mind the harmful effects that may become the result of improper and excessive intake of transition metals. This article establishes the feasibility of Raman (RS) and Fourier-transform infrared (FT-IR) spectroscopic imaging at the single-cell level to investigate the cellular response to various transition metals. These two non-destructive and perfectly complementary methods allow for in-depth monitoring of changes taking place within the cell under the influence of the agent used. HepG2 liver carcinoma cells were exposed to chromium, iron, cobalt, molybdenum, and nickel at 1 and 2 mM concentrations. Spectroscopic results were further supported by biological evaluation of selected caspases concentration. The caspase- 3, 6, 8, 9, and 12 concentrations were determined with the use of the enzyme-linked immunosorbent assay (ELISA) method. This study shows the induction of apoptosis in the intrinsic pathway by all studied transition metals. Cellular metabolism alterations are induced by mitochondrial metabolism changes and endoplasmic reticulum (ER) metabolism variations. Moreover, nickel induces not only the intrinsic pathway of apoptosis but also the extrinsic pathway of this process.

Oxidative stress mediates the inhibitory effects of Manzamine A on uterine leiomyoma cell proliferation and extracellular matrix deposition via SOAT inhibition

Uterine fibroids, the most common benign tumors of the myometrium in women, are characterized by abnormal extracellular matrix deposition and uterine smooth muscle cell neoplasia, with high recurrence rates. Here, we investigated the potential of the marine natural product manzamine A (Manz A), which has potent anti-cancer effects, as a treatment for uterine fibroids. Manz A inhibited leiomyoma cell proliferation in vitro and in vivo by arresting cell cycle progression and inducing caspase-mediated apoptosis. We performed target prediction analysis and identified sterol o-acyltransferases (SOATs) as potential targets of Manz A. Cholesterol esterification and lipid droplet formation were reduced by Manz A, in line with reduced SOAT expression. As a downstream target of SOAT, Manz A also prevented extracellular matrix deposition by inhibiting the β-catenin/fibronectin/metalloproteinases axis and enhanced autophagy turnover. Excessive free fatty acid accumulation by SOAT inhibition led to reactive oxygen species to impair mitochondrial oxidative phosphorylation and trigger endoplasmic reticulum stress via PERK/eIF2α/CHOP signaling. The inhibitory effect of ManzA on cell proliferation was partially restored by PERK knockdown and eliminated by tauroursodeoxycholic acid, suggesting oxidative stress plays a critical role in the mechanism of action of Manz A. These findings suggest that targeting SOATs by Manz A may be a promising therapeutic approach for uterine fibroids.

Mammalian lipid droplets: structural, pathological, immunological and anti-toxicological roles

Mammalian lipid droplets (LDs) are specialized cytosolic organelles consisting of a neutral lipid core surrounded by a membrane made up of a phospholipid monolayer and a specific population of proteins that varies according to the location and function of each LD. Over the past decade, there have been significant advances in the understanding of LD biogenesis and functions. LDs are now recognized as dynamic organelles that participate in many aspects of cellular homeostasis plus other vital functions. LD biogenesis is a complex, highly-regulated process with assembly occurring on the endoplasmic reticulum although aspects of the underpinning molecular mechanisms remain elusive. For example, it is unclear how many enzymes participate in the biosynthesis of the neutral lipid components of LDs and how this process is coordinated in response to different metabolic cues to promote or suppress LD formation and turnover. In addition to enzymes involved in the biosynthesis of neutral lipids, various scaffolding proteins play roles in coordinating LD formation. Despite their lack of ultrastructural diversity, LDs in different mammalian cell types are involved in a wide range of biological functions. These include roles in membrane homeostasis, regulation of hypoxia, neoplastic inflammatory responses, cellular oxidative status, lipid peroxidation, and protection against potentially toxic intracellular fatty acids and lipophilic xenobiotics. Herein, the roles of mammalian LDs and their associated proteins are reviewed with a particular focus on their roles in pathological, immunological and anti-toxicological processes.

The Janus-Faced Role of Lipid Droplets in Aging: Insights from the Cellular Perspective

It is widely accepted that nine hallmarks-including mitochondrial dysfunction, epigenetic alterations, and loss of proteostasis-exist that describe the cellular aging process. Adding to this, a well-described cell organelle in the metabolic context, namely, lipid droplets, also accumulates with increasing age, which can be regarded as a further aging-associated process. Independently of their essential role as fat stores, lipid droplets are also able to control cell integrity by mitigating lipotoxic and proteotoxic insults. As we will show in this review, numerous longevity interventions (such as mTOR inhibition) also lead to strong accumulation of lipid droplets in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, and mammalian cells, just to name a few examples. In mammals, due to the variety of different cell types and tissues, the role of lipid droplets during the aging process is much more complex. Using selected diseases associated with aging, such as Alzheimer's disease, Parkinson's disease, type II diabetes, and cardiovascular disease, we show that lipid droplets are "Janus"-faced. In an early phase of the disease, lipid droplets mitigate the toxicity of lipid peroxidation and protein aggregates, but in a later phase of the disease, a strong accumulation of lipid droplets can cause problems for cells and tissues.

Ensheathing glia promote increased lifespan and healthy brain aging

Glia have an emergent role in brain aging and disease. In the Drosophila melanogaster brain, ensheathing glia function as phagocytic cells and respond to acute neuronal damage, analogous to mammalian microglia. We previously reported changes in glia composition over the life of ants and fruit flies, including a decline in the relative proportion of ensheathing glia with time. How these changes influence brain health and life expectancy is unknown. Here, we show that ensheathing glia but not astrocytes decrease in number during Drosophila melanogaster brain aging. The remaining ensheathing glia display dysregulated expression of genes involved in lipid metabolism and apoptosis, which may lead to lipid droplet accumulation, cellular dysfunction, and death. Inhibition of apoptosis rescued the decline of ensheathing glia with age, improved the neuromotor performance of aged flies, and extended lifespan. Furthermore, an expanded ensheathing glia population prevented amyloid-beta accumulation in a fly model of Alzheimer's disease and delayed the premature death of the diseased animals. These findings suggest that ensheathing glia play a vital role in regulating brain health and animal longevity.

Effects and Mechanisms of Action of Preussin, a Marine Fungal Metabolite, against the Triple-Negative Breast Cancer Cell Line, MDA-MB-231, in 2D and 3D Cultures

Triple-negative breast cancer (TNBC) represents an aggressive subtype of breast cancer (BC) with a typically poorer prognosis than other subtypes of BC and limited therapeutic options. Therefore, new drugs would be particularly welcome to help treat TNBC. Preussin, isolated from the marine sponge-associated fungus, Aspergillus candidus, has shown the potential to reduce cell viability and proliferation as well as to induce cell death and cell cycle arrest in 2D cell culture models. However, studies that better mimic the tumors in vivo, such as 3D cell cultures, are needed. Here, we studied the effects of preussin in the MDA-MB-231 cell line, comparing 2D and 3D cell cultures, using ultrastructural analysis and the MTT, BrdU, annexin V-PI, comet (alkaline and FPG modified versions), and wound healing assays. Preussin was found to decrease cell viability, both in 2D and 3D cell cultures, in a dose-dependent manner, impair cell proliferation, and induce cell death, therefore excluding the hypothesis of genotoxic properties. The cellular impacts were reflected by ultrastructural alterations in both cell culture models. Preussin also significantly inhibited the migration of MDA-MB-231 cells. The new data expanded the knowledge on preussin actions while supporting other studies, highlighting its potential as a molecule or scaffold for the development of new anticancer drugs against TNBC.

Exploiting directed self-assembly and disassembly for off-to-on fluorescence responsive live cell imaging

A bio-responsive nanoparticle was formed by the directed self-assembly (DSA) of a hydrophobic NIR-fluorophore with poloxamer P₁₈₈. Fluorophore emission was switched off when part of the nanoparticle, however upon stimulus induced nanoparticle dis-assembly the emission switched on. The emission quenching was shown to be due to fluorophore hydration and aggregation within the nanoparticle and the turn on response attributable to nanoparticle disassembly with embedding of the fluorophore within lipophilic environments. This was exploited for temporal and spatial live cell imaging with a measurable fluorescence response seen upon intracellular delivery of the fluorophore. The first dynamic response, seen within minutes, was from lipid droplets with other lipophilic regions such as the endoplasmic reticulum, nuclear membranes and secretory vacuoles imageable after hours. The high degree of fluorophore photostability facilitated continuous imaging for extended periods and the off to on switching facilitated the real-time observation of lipid droplet biogenesis as they emerged from the endoplasmic reticulum. With an in-depth understanding of the principles involved, further assembly controlling functional responses could be anticipated.

Repeated trans-arterial treatments of LDL-DHA nanoparticles induce multiple pathways of tumor cell death in hepatocellular carcinoma bearing rats

Introduction

Repeated hepatic arterial delivery of therapeutic agents to the liver by percutaneously implanted port-catheter systems has been widely used to treat unresectable liver cancer. This approach is applied to assess the therapeutic efficacy of repeated low-density lipoprotein-docosahexaenoic acid (LDL-DHA) nanoparticle treatments in a rat model of hepatocellular carcinoma.

Methods

N1S1 hepatoma bearing rats underwent placement of a percutaneously implanted hepatic artery port-catheter system and were allocated to untreated, control LDL-triolein (LDL-TO) or LDL-DHA nanoparticle infusions groups. Treatments were performed every three days over a nine day study period. MRI was performed at baseline and throughout the study. At the end of the study tissue samples were collected for analyses.

Results and Discussion

Implantation of the port catheters was successful in all rats. MRI showed that repeated infusions of LDL-DHA nanoparticles significantly impaired the growth of the rat hepatomas eventually leading to tumor regression. The tumors in the LDL-TO treated group showed delayed growth, while the untreated tumors grew steadily throughout the study. Histopathology and MRI support these findings demonstrating extensive tumor necrosis in LDL-DHA treated groups while the control groups displayed minor necrosis. Molecular and biochemical analyses also revealed that LDL-DHA treated tumors had increased levels of nuclear factor-kappa B and lipid peroxidation and depletion of glutathione peroxidase 4 relative to the control groups. Evidence of both ferroptosis and apoptosis tumor cell death was observed following LDL-DHA treatments. In conclusion repeated transarterial infusions of LDL-DHA nanoparticles provides sustained repression of tumor growth in a rat hepatoma model.

Stearoyl CoA Desaturase-1 Silencing in Glioblastoma Cells: Phospholipid Remodeling and Cytotoxicity Enhanced upon Autophagy Inhibition

Modulation of lipid metabolism is a well-established cancer hallmark, and SCD1 has been recognized as a key enzyme in promoting cancer cell growth, including in glioblastoma (GBM), the deadliest brain tumor and a paradigm of cancer resistance. The central goal of this work was to identify, by MS, the phospholipidome alterations resulting from the silencing of SCD1 in human GBM cells, in order to implement an innovative therapy to fight GBM cell resistance. With this purpose, RNAi technology was employed, and low serum-containing medium was used to mimic nutrient deficiency conditions, at which SCD1 is overexpressed. Besides the expected increase in the saturated to unsaturated fatty acid ratio in SCD1 silenced-GBM cells, a striking increase in polyunsaturated chains, particularly in phosphatidylethanolamine and cardiolipin species, was noticed and tentatively correlated with an increase in autophagy (evidenced by the increase in LC3BII/I ratio). The contribution of autophagy to mitigate the impact of SCD1 silencing on GBM cell viability and growth, whose modest inhibition could be correlated with the maintenance of energetically associated mitochondria, was evidenced by using autophagy inhibitors. In conclusion, SCD1 silencing could constitute an important tool to halt GBM resistance to the available treatments, especially when coupled with a mitochondria disrupter chemotherapeutic.

The uniformity and stability of cellular mass density in mammalian cell culture

Cell dry mass is principally determined by the sum of biosynthesis and degradation. Measurable change in dry mass occurs on a time scale of hours. By contrast, cell volume can change in minutes by altering the osmotic conditions. How changes in dry mass and volume are coupled is a fundamental question in cell size control. If cell volume were proportional to cell dry mass during growth, the cell would always maintain the same cellular mass density, defined as cell dry mass dividing by cell volume. The accuracy and stability against perturbation of this proportionality has never been stringently tested. Normalized Raman Imaging (NoRI), can measure both protein and lipid dry mass density directly. Using this new technique, we have been able to investigate the stability of mass density in response to pharmaceutical and physiological perturbations in three cultured mammalian cell lines. We find a remarkably narrow mass density distribution within cells, that is, significantly tighter than the variability of mass or volume distribution. The measured mass density is independent of the cell cycle. We find that mass density can be modulated directly by extracellular osmolytes or by disruptions of the cytoskeleton. Yet, mass density is surprisingly resistant to pharmacological perturbations of protein synthesis or protein degradation, suggesting there must be some form of feedback control to maintain the homeostasis of mass density when mass is altered. By contrast, physiological perturbations such as starvation or senescence induce significant shifts in mass density. We have begun to shed light on how and why cell mass density remains fixed against some perturbations and yet is sensitive during transitions in physiological state.

The Role of Lipid Metabolism in Gastric Cancer

Gastric cancer has been one of the most common cancers worldwide with extensive metastasis and high mortality. Chemotherapy has been found as a main treatment for metastatic gastric cancer, whereas drug resistance limits the effectiveness of chemotherapy and leads to treatment failure. Chemotherapy resistance in gastric cancer has a complex and multifactorial mechanism, among which lipid metabolism plays a vital role. Increased synthesis of new lipids or uptake of exogenous lipids can facilitate the rapid growth of cancer cells and tumor formation. Lipids form the structural basis of biofilms while serving as signal molecules and energy sources. It is noteworthy that lipid metabolism is capable of inducing drug resistance in gastric cancer cells by reshaping the tumor micro-environment. In this study, new mechanisms of lipid metabolism in gastric cancer and the metabolic pathways correlated with chemotherapy resistance are reviewed. In particular, we discuss the effects of lipid metabolism on autophagy, biomarkers treatment and drug resistance in gastric cancer from the perspective of lipid metabolism. In brief, new insights can be gained into the development of promising therapies through an in-depth investigation of the mechanism of lipid metabolism reprogramming and resensitization to chemotherapy in gastric cancer cells, and scientific treatment can be provided by applying lipid-key enzyme inhibitors as cancer chemical sensitizers in clinical settings.

The Complex Biology of the Obesity-Induced, Metastasis-Promoting Tumor Microenvironment in Breast Cancer

Breast cancer is one of the most prevalent cancers in women contributing to cancer-related death in the advanced world. Apart from the menopausal status, the trigger for developing breast cancer may vary widely from race to lifestyle factors. Epidemiological studies refer to obesity-associated metabolic changes as a critical risk factor behind the progression of breast cancer. The plethora of signals arising due to obesity-induced changes in adipocytes present in breast tumor microenvironment, significantly affect the behavior of adjacent breast cells. Adipocytes from white adipose tissue are currently recognized as an active endocrine organ secreting different bioactive compounds. However, due to excess energy intake and increased fat accumulation, there are morphological followed by secretory changes in adipocytes, which make the breast microenvironment proinflammatory. This proinflammatory milieu not only increases the risk of breast cancer development through hormone conversion, but it also plays a role in breast cancer progression through the activation of effector proteins responsible for the biological phenomenon of metastasis. The aim of this review is to present a comprehensive picture of the complex biology of obesity-induced changes in white adipocytes and demonstrate the relationship between obesity and breast cancer progression to metastasis.

Pt(ii) complex containing the 1R,2R enantiomer of trans-1,2-diamino-4-cyclohexene ligand effectively and selectively inhibits the viability of aggressive pancreatic adenocarcinoma cells and alters their lipid metabolism

New compounds structurally derived from oxaliplatin exhibit high potency in malignant pancreatic adenocarcinoma cells. Their mechanism of antiproliferative action in pancreatic cancer cells involves inhibition of de novo lipid synthesis.

Lipid droplets as metabolic determinants for stemness and chemoresistance in cancer

Previously regarded as simple fat storage particles, new evidence suggests that lipid droplets (LDs) are dynamic and functional organelles involved in key cellular processes such as membrane biosynthesis, lipid metabolism, cell signalling and inflammation. Indeed, an increased LD content is one of the most apparent features resulting from lipid metabolism reprogramming necessary to support the basic functions of cancer cells. LDs have been associated to different cellular processes involved in cancer progression and aggressiveness, such as tumorigenicity, invasion and metastasis, as well as chemoresistance. Interestingly, all of these processes are controlled by a subpopulation of highly aggressive tumoral cells named cancer stem cells (CSCs), suggesting that LDs may be fundamental elements for stemness in cancer. Considering the key role of CSCs on chemoresistance and disease relapse, main factors of therapy failure, the design of novel therapeutic approaches targeting these cells may be the only chance for long-term survival in cancer patients. In this sense, their biology and functional properties render LDs excellent candidates for target discovery and design of combined therapeutic strategies. In this review, we summarise the current knowledge identifying LDs and CSCs as main contributors to cancer aggressiveness, metastasis and chemoresistance.

Comprehensive Genetic Analysis of DGAT2 Mutations and Gene Expression Patterns in Human Cancers

DGAT2 is a transmembrane protein encoded by the DGAT2 gene that functions in lipid metabolism, triacylglycerol synthesis, and lipid droplet regulation. Cancer cells exhibit altered lipid metabolism and mutations in DGAT2 may contribute to this state. Using data from the Catalogue of Somatic Mutations in Cancer (COSMIC), we analyzed all cancer genetic DGAT2 alterations, including mutations, copy number variations and gene expression. We find that several DGAT2 mutations fall within the catalytic site of the enzyme. Using the Variant Effect Scoring Tool (VEST), we identify multiple mutations with a high likelihood of contributing to cellular transformation. We also found that D222V is a mutation hotspot neighboring a previously discovered Y223H mutation that causes Axonal Charcot-Marie-Tooth disease. Remarkably, Y223H has not been detected in cancers, suggesting that it is inhibitory to cancer progression. We also identify several single nucleotide polymorphisms (SNP) with high VEST scores, indicating that certain alleles in human populations have a pathogenic predisposition. Most mutations do not correlate with a change in gene expression, nor is gene expression dependent on high allele copy number. However, we did identify eight alleles with high expression levels, suggesting that at least in certain cases, the excess DGAT2 gene product is not inhibitory to cellular proliferation. This work uncovers unknown functions of DGAT2 in cancers and suggests that its role may be more complex than previously appreciated.

Fucoxanthin Holds Potential to Become a Drug Adjuvant in Breast Cancer Treatment: Evidence from 2D and 3D Cell Cultures

Fucoxanthin (Fx) is a carotenoid derived from marine organisms that exhibits anticancer activities. However, its role as a potential drug adjuvant in breast cancer (BC) treatment is still poorly explored. Firstly, this study investigated the cytotoxic effects of Fx alone and combined with doxorubicin (Dox) and cisplatin (Cis) on a panel of 2D-cultured BC cell lines (MCF7, SKBR3 and MDA-MB-231) and one non-tumoral cell line (MCF12A). Fucoxanthin induced cytotoxicity against all the cell lines and potentiated Dox cytotoxic effects towards the SKBR3 and MDA-MB-231 cells. The combination triggering the highest cytotoxicity (Fx 10 µM + Dox 1 µM in MDA-MB-231) additionally showed significant induction of cell death and genotoxic effects, relative to control. In sequence, the same combination was tested on 3D cultures using a multi-endpoint approach involving bioactivity assays and microscopy techniques. Similar to 2D cultures, the combination of Fx and Dox showed higher cytotoxic effects on 3D cultures compared to the isolated compounds. Furthermore, this combination increased the number of apoptotic cells, decreased cell proliferation, and caused structural and ultrastructural damages on the 3D models. Overall, our findings suggest Fx has potential to become an adjuvant for Dox chemotherapy regimens in BC treatment.

Emerging Solvatochromic Push-Pull Dyes for Monitoring the Lipid Order of Biomembranes in Live Cells

Solvatochromic dyes have emerged as a new class of fluorescent probes in the field of lipid membranes due to their ability to identify the lipid organization of biomembranes in live cells by changing the color of their fluorescence. This type of solvatochromic function is useful for studying the heterogeneous features of biomembranes caused by the uneven distribution of lipids and cholesterols in live cells and related cellular processes. Therefore, a variety of advanced solvatochromic dyes have been rapidly developed over the last decade. To provide an overview of the works recently developed solvatochromic dyes have enabled, we herein present some solvatochromic dyes, with a particular focus on those based on pyrene and Nile red. As these dyes exhibit preferable photophysical properties in terms of fluorescence microscopy applications and unique distribution/localization in cellular compartments, some have already found applications in cell biological and biophysical studies. The goal of this review is to provide information to researchers who have never used solvatochromic dyes or who have not discovered applications of such dyes in biological studies.

Proteomic Characterization of Cytoplasmic Lipid Droplets in Human Metastatic Breast Cancer Cells

One of the characteristic features of metastatic breast cancer is increased cellular storage of neutral lipid in cytoplasmic lipid droplets (CLDs). CLD accumulation is associated with increased cancer aggressiveness, suggesting CLDs contribute to metastasis. However, how CLDs contribute to metastasis is not clear. CLDs are composed of a neutral lipid core, a phospholipid monolayer, and associated proteins. Proteins that associate with CLDs regulate both cellular and CLD metabolism; however, the proteome of CLDs in metastatic breast cancer and how these proteins may contribute to breast cancer progression is unknown. Therefore, the purpose of this study was to identify the proteome and assess the characteristics of CLDs in the MCF10CA1a human metastatic breast cancer cell line. Utilizing shotgun proteomics, we identified over 1500 proteins involved in a variety of cellular processes in the isolated CLD fraction. Interestingly, unlike other cell lines such as adipocytes or enterocytes, the most enriched protein categories were involved in cellular processes outside of lipid metabolism. For example, cell-cell adhesion was the most enriched category of proteins identified, and many of these proteins have been implicated in breast cancer metastasis. In addition, we characterized CLD size and area in MCF10CA1a cells using transmission electron microscopy. Our results provide a hypothesis-generating list of potential players in breast cancer progression and offers a new perspective on the role of CLDs in cancer.

Vitamin D regulation of energy metabolism in cancer

Vitamin D exerts anti-cancer effects in recent clinical trials and preclinical models. The actions of vitamin D are primarily mediated through its hormonal form, 1,25-dihydroxyvitamin D (1,25(OH)₂ D). Previous literature describing in vitro studies has predominantly focused on the anti-tumourigenic effects of the hormone, such as proliferation and apoptosis. However, recent evidence has identified 1,25(OH)₂ D as a regulator of energy metabolism in cancer cells, where requirements for specific energy sources at different stages of progression are dramatically altered. The literature suggests that 1,25(OH)₂ D regulates energy metabolism, including glucose, glutamine and lipid metabolism during cancer progression, as well as oxidative stress protection, as it is closely associated with energy metabolism. Mechanisms involved in energy metabolism regulation are an emerging area in which vitamin D may inhibit multiple stages of cancer progression.

Caveolin-1 function at the plasma membrane and in intracellular compartments in cancer

Caveolin-1 (CAV1) is commonly considered to function as a cell surface protein, for instance in the genesis of caveolae. Nonetheless, it is also present in many intracellular organelles and compartments. The contributions of these intracellular pools to CAV1 function are generally less well understood, and this is also the case in the context of cancer. This review will summarize literature available on the role of CAV1 in cancer, highlighting particularly our understanding of the canonical (CAV1 in the plasma membrane) and non-canonical pathways (CAV1 in organelles and exosomes) linked to the dual role of the protein as a tumor suppressor and promoter of metastasis. With this in mind, we will focus on recently emerging concepts linking CAV1 function to the regulation of intracellular organelle communication within the same cell where CAV1 is expressed. However, we now know that CAV1 can be released from cells in exosomes and generate systemic effects. Thus, we will also elaborate on how CAV1 participates in intracellular communication between organelles as well as signaling between cells (non-canonical pathways) in cancer.

Polarization-sensitive stimulated Raman scattering imaging resolves amphotericin B orientation in Candida membrane

Ergosterol-targeting amphotericin B (AmB) is the first line of defense for life-threatening fungal infections. Two models have been proposed to illustrate AmB assembly in the cell membrane; one is the classical ion channel model in which AmB vertically forms transmembrane tunnel and the other is a recently proposed sterol sponge model where AmB is laterally adsorbed onto the membrane surface. To address this controversy, we use polarization-sensitive stimulated Raman scattering from fingerprint C═C stretching vibration to visualize AmB, ergosterol, and lipid in single fungal cells. Intracellular lipid droplet accumulation in response to AmB treatment is found. AmB is located in membrane and intracellular droplets. In the 16 strains studied, AmB residing inside cell membrane was highly ordered, and its orientation is primarily parallel to phospholipid acyl chains, supporting the ion channel model. Label-free imaging of AmB and chemical contents offers an analytical platform for developing low-toxicity, resistance-refractory antifungal agents.

Bringing naturally-occurring saturated fatty acids into biomedical research

This review introduces naturally-occurring saturated fatty acids (NSFAs) and their biomedical applications, including controlled drug release, targeted drug delivery, cancer therapy, antibacterial treatment, and tissue engineering.

Neutral lipids regulate amphipathic helix affinity for model lipid droplets

Cellular lipid droplets (LDs) have a neutral lipid core shielded from the aqueous environment by a phospholipid monolayer containing proteins. These proteins define the biological functions of LDs, and most of them bear amphipathic helices (AH), which can selectively target to LDs, or to LD subsets. How such binding preference happens remains poorly understood. Here, we found that artificial LDs made of different neutral lipids but presenting equal phospholipid packing densities differentially recruit AHs. Varying the phospholipid density shifts the binding levels, but the differential recruitment is unchanged. We found that the binding level of AHs is defined by their interaction preference with neutral lipids and ability to decrease surface tension. The phospholipid packing level regulates mainly the amount of neutral lipid accessible. Therefore, it is the hydrophobic nature of the phospholipid packing voids that controls the binding level of AHs. Our data bring us a major step closer to understanding the binding selectivity of AHs to lipid membranes.

Multiplex coherent anti-Stokes Raman scattering microspectroscopy detection of lipid droplets in cancer cells expressing TrkB

For many years, scientists have been looking for specific biomarkers associated with cancer cells for diagnosis purposes. These biomarkers mainly consist of proteins located at the cell surface (e.g. the TrkB receptor) whose activation is associated with specific metabolic modifications. Identification of these metabolic changes usually requires cell fixation and specific dye staining. MCARS microspectroscopy is a label-free, non-toxic, and minimally invasive method allowing to perform analyses of live cells and tissues. We used this method to follow the formation of lipid droplets in three colorectal cancer cell lines expressing TrkB. MCARS images of cells generated from signal integration of CH₂ stretching modes allow to discriminate between lipid accumulation in the endoplasmic reticulum and the formation of cytoplasmic lipid droplets. We found that the number of the latter was related to the TrkB expression level. This result was confirmed thanks to the creation of a HEK cell line which over-expresses TrkB. We demonstrated that BDNF-induced TrkB activation leads to the formation of cytoplasmic lipid droplets, which can be abolished by K252a, an inhibitor of TrkB. So, MCARS microspectroscopy proved useful in characterizing cancer cells displaying an aberrant lipid metabolism.

Lipid composition of the cancer cell membrane

Cancer cell possesses numerous adaptations to resist the immune system response and chemotherapy. One of the most significant properties of the neoplastic cells is the altered lipid metabolism, and consequently, the abnormal cell membrane composition. Like in the case of phosphatidylcholine, these changes result in the modulation of certain enzymes and accumulation of energetic material, which could be used for a higher proliferation rate. The changes are so prominent, that some lipids, such as phosphatidylserines, could even be considered as the cancer biomarkers. Additionally, some changes of biophysical properties of cell membranes lead to the higher resistance to chemotherapy, and finally to the disturbances in signalling pathways. Namely, the increased levels of certain lipids, like for instance phosphatidylserine, lead to the attenuation of the immune system response. Also, changes in lipid saturation prevent the cells from demanding conditions of the microenvironment. Particularly interesting is the significance of cell membrane cholesterol content in the modulation of metastasis. This review paper discusses the roles of each lipid type in cancer physiology. The review combined theoretical data with clinical studies to show novel therapeutic options concerning the modulation of cell membranes in oncology.

Detection and time-tracking activation of a photosensitiser on live single colorectal cancer cells using Raman spectroscopy

Raman spectroscopy has been used to observe uptake, metabolism and response of single-cells to drugs. Photodynamic therapy is based on the use of light, a photosensitiser and oxygen to destroy tumour tissue. Here, we used single-cell Raman spectroscopy to study the uptake and intracellular degradation of a novel photosensitiser with a diphenylacetylene structure, DC473, in live single-cells from colorectal adenocarcinoma cell lines SW480, HT29 and SW620. DC473 was seen to predominantly accumulate in lipid droplets, showing higher accumulation in HT29 and SW620 cells than in SW480 cells, with a broader DC473 peak shifted to higher wavenumbers. DC473 activation and effects were tracked on live single-cells for 5 minutes. Upon exposure to UV light, the DC473 signal intensity dropped, with remaining DC473 shifting towards higher wavenumbers and widening, with a lifetime of approximately 50 seconds. Morphologically, SW480 and SW620 cells showed changes upon photodynamic therapy, whereas HT29 cells showed no changes. Morphological changes correlated with higher remaining DC473 signal after UV exposure. Our research suggests that DC473 forms aggregates within the cells that disaggregate following activation, showing the potential of Raman spectroscopy for the study of time-dependent single-cell pharmacodynamics.

Involvement of activation of PLIN5-Sirt1 axis in protective effect of glycycoumarin on hepatic lipotoxicity

Licorice is a popular medicinal plant, and it has been used to treat various diseases, including liver diseases. Glycycoumarin (GCM) is a major coumarin compound isolated from licorice with favorable bioavailability property. Our previous studies have shown that GCM is capable of inhibiting lipoapoptosis in both cell culture and methionine-choline-defcient (MCD) diet-induced mouse model of non-alcoholic steatohepatitis (NASH) through mechanisms involving suppression of endoplasmic reticulum (ER) stress. Perilipin 5 (PLIN5), a newly identified lipid drop protein in the perilipin family, is highly expressed in oxidative tissues including the liver and is suggested to play an important role in protecting against hepatic lipotoxicity. Give the hepatoprotective role of PLIN5, we hypothesized that induction of PLIN5 might contribute to the hepatoprotective effect of GCM via mitigating ER stress and inflammatory responses. Results showed that PLIN5 and its downstream target Sirt1 were induced by GCM both in vitro and in vivo. Inhibition of either PLIN5 or Sirt1 led to significantly attenuated protective effect of GCM on palmitic acid (PA)-induced lipoapoptosis and inflammatory responses, supporting involvement of PLIN5-Sirt1 axis in the protective effect of GCM on hepatic lipotoxicity. The findings of the present study provide novel insight into the understanding of mechanisms underlying the hepatoprotective effect of GCM.

CDP-diacylglycerol, a critical intermediate in lipid metabolism

The roles of lipids expand beyond the basic building blocks of biological membranes. In addition to forming complex and dynamic barriers, the thousands of different lipid species in the cell contribute to essentially all the processes of life. Specific lipids are increasingly identified in cellular processes, including signal transduction, membrane trafficking, metabolic control and protein regulation. Tight control of their synthesis and degradation is essential for homeostasis. Most of the lipid molecules in the cell originate from a small number of critical intermediates. Thus, regulating the synthesis of intermediates is essential for lipid homeostasis and optimal biological functions. Cytidine diphosphate diacylglycerol (CDP-DAG) is an intermediate which occupies a branch point in lipid metabolism. CDP-DAG is incorporated into different synthetic pathways to form distinct phospholipid end-products depending on its location of synthesis. Identification and characterization of CDP-DAG synthases which catalyze the synthesis of CDP-DAG has been hampered by difficulties extracting these membrane-bound enzymes for purification. Recent developments have clarified the cellular localization of the CDP-DAG synthases and identified a new unrelated CDP-DAG synthase enzyme. These findings have contributed to a deeper understanding of the extensive synthetic and signaling networks stemming from this key lipid intermediate.

Multiplex Stimulated Raman Scattering Imaging Cytometry Reveals Lipid-Rich Protrusions in Cancer Cells under Stress Condition

In situ measurement of cellular metabolites is still a challenge in biology. Conventional methods, such as mass spectrometry or fluorescence microscopy, would either destroy the sample or introduce strong perturbations to target molecules. Here, we present multiplex stimulated Raman scattering (SRS) imaging cytometry as a label-free single-cell analysis platform with chemical specificity and high-throughput capabilities. Using SRS imaging cytometry, we studied the metabolic responses of human pancreatic cancer cells under stress by starvation and chemotherapeutic drug treatments. We unveiled protrusions containing lipid droplets as a metabolic marker for stress-resistant cancer cells. Furthermore, by spectroscopic SRS mapping, we unveiled that triglyceride in lipid droplets are used for local energy production through lipolysis, autophagy, and β-oxidation. Our findings demonstrate the potential of targeting lipid metabolism for selective treatment of stress-resistant cancers. Collectively, these results highlight SRS imaging cytometry as a powerful label-free tool for biological discoveries with a high-throughput, high-content capacity.

Decreased Efficacy of Doxorubicin Corresponds With Modifications in Lipid Metabolism Markers and Fatty Acid Profiles in Breast Tumors From Obese vs. Lean Mice

Breast cancer cells modulate lipid and fatty acid metabolism to sustain proliferation. The role of adipocytes in cancer treatment efficacy remains, however, to be fully elucidated. We investigated whether diet-induced obesity (DIO) affects the efficacy of doxorubicin treatment in a breast tumor-bearing mouse model. Female C57BL6 mice were fed a high fat or low fat diet for the full duration of the study (12 weeks). After 8 weeks, mice were inoculated with E0771 triple-negative breast cancer cells in the fourth mammary gland to develop breast tumor allographs. Tumor-bearing mice received either vehicle (Hank's balanced salt solution) or doxorubicin (chemotherapy). Plasma inflammatory markers, tumor, and mammary adipose tissue fatty acid composition, as well as protein expression of lipid metabolism markers were determined. The high fat diet (HFD) attenuated the treatment efficacy of doxorubicin. Both leptin and resistin concentrations were significantly increased in the HFD group treated with doxorubicin. Suppressed lipogenesis (decreased stearoyl CoA-desaturase-1) and lipolysis (decreased hormone-sensitive lipase) were observed in mammary adipose tissue of the DIO animals, whereas increased expression was observed in the tumor tissue of doxorubicin treated HFD mice. Obesogenic conditions induced altered tissue fatty acid (FA) compositions, which reduced doxorubicin's treatment efficacy. In mammary adipose tissue breast cancer cells suppressed the storage of FAs, thereby increasing the availability of free FAs and favored inflammation under obesogenic conditions.

Visualization of Lipid Droplets in Living Cells and Fatty Livers of Mice Based on the Fluorescence of π-Extended Coumarin Using Fluorescence Lifetime Imaging Microscopy

Lipid droplets (LDs) are closely related to lipid metabolism in living cells and are highly associated with diverse diseases such as fatty liver, diabetes, and cancer. Herein we describe a π-extended fluorescent coumarin (PC6S) for visualizing LDs in living cells and in the tissues of living mice using confocal fluorescence lifetime imaging microscopy (FLIM). PC6S showed a large positive solvatochromic shift and high fluorescence quantum yield (>0.80) in both nonpolar and polar solvents. Additionally, the fluorescence lifetimes of PC6S were largely dependent on solvent polarity. The excellent spectral and photophysical properties of PC6S allowed its selective staining of LDs in living and fixed cells, and multicolor imaging. Fluorescence lifetime measurements of PC6S allowed estimation of the apparent polarity of LDs. The high photostability and long intracellular retention of PC6S supported in situ visualization of the formation processes of LDs resulting from the accumulation of fatty acid. Furthermore, intravenous administration of PC6S and use of the FLIM system allowed the imaging of LDs in hepatocytes in living normal mice and the growth of LDs resulting from the excess accumulation of lipids in high-fat-diet-fed mice (fatty liver model mice). Taking advantage of the high selectivity and sensitivity of PC6S for LDs in liver, we could visualize the adipocytes of lipid-rich tissues and LDs in kidney peritubular cells by PC6S fluorescence. These results demonstrated that PC6S combined with a FLIM system can be useful for monitoring and tracking the formation of LDs in both cultured cells and specific tissues and organs.

AdipoRon Attenuates Wnt Signaling by Reducing Cholesterol-Dependent Plasma Membrane Rigidity

The increasing prevalence of adult and adolescent obesity and its associated risk of colorectal cancer reinforces the urgent need to elucidate the underlying mechanisms contributing to the promotion of colon cancer in obese individuals. Adiponectin is an adipose tissue-derived adipokine, whose levels are reduced during obesity. Both epidemiological and preclinical data indicate that adiponectin suppresses colon tumorigenesis. We have previously demonstrated that both adiponectin and AdipoRon, a small-molecule adiponectin receptor agonist, suppress colon cancer risk in part by reducing the number of Lgr5+ stem cells in mouse colonic organoids. However, the mechanism by which the adiponectin signaling pathway attenuates colon cancer risk remains to be addressed. Here, we have hypothesized that adiponectin signaling supports colonic stem cell maintenance through modulation of the biophysical properties of the plasma membrane (PM). Specifically, we investigated the effects of adiponectin receptor activation by AdipoRon on the biophysical perturbations linked to the attenuation of Wnt-driven signaling and cell proliferation as determined by LEF luciferase reporter assay and colonic organoid proliferation, respectively. Using physicochemical sensitive dyes, Di-4-ANEPPDHQ and C-laurdan, we demonstrated that AdipoRon decreased the rigidity of the colonic cell PM. The decrease in membrane rigidity was associated with a reduction in PM free cholesterol levels and the intracellular accumulation of free cholesterol in lysosomes. These results suggest that adiponectin signaling plays a role in modulating cellular cholesterol homeostasis, PM biophysical properties, and Wnt-driven signaling. These findings are noteworthy because they may in part explain how obesity drives colon cancer progression.

Aggregation-Induced Emission Photosensitizers: From Molecular Design to Photodynamic Therapy

Photodynamic therapy (PDT) has emerged as a promising noninvasive treatment option for cancers and other diseases. The key factor that determines the effectiveness of PDT is the photosensitizers (PSs). Upon light irradiation, the PSs would be activated, produce reactive oxygen species (ROS), and induce cell death. One of the challenges is that traditional PSs adopt a large flat disc-like structure, which tend to interact with the adjacent molecules through strong π-π stacking that reduces their ROS generation ability. Aggregation-induced emission (AIE) molecules with a twisted configuration to suppress strong intermolecular interactions represent a new class of PSs for image-guided PDT. In this Miniperspective, we summarize the recent progress on the design rationale of AIE-PSs and the strategies to achieve desirable theranostic applications in cancers. Subsequently, approaches of combining AIE-PS with other imaging and treatment modalities, challenges, and future directions are addressed.

In Steatotic Cells, ATP-Citrate Lyase mRNA Is Efficiently Translated through a Cap-Independent Mechanism, Contributing to the Stimulation of De Novo Lipogenesis

Non-alcoholic fatty liver disease (NAFLD) is a chronic disease in which excessive amount of lipids is accumulated as droplets in hepatocytes. Recently, cumulative evidences suggested that a sustained de novo lipogenesis can play an important role in NAFLD. Dysregulated expression of lipogenic genes, including ATP-citrate lyase (ACLY), has been found in liver diseases associated with lipid accumulation. ACLY is a ubiquitous cytosolic enzyme positioned at the intersection of nutrients catabolism and cholesterol and fatty acid biosyntheses. In the present study, the molecular mechanism of ACLY expression in a cell model of steatosis has been reported. We identified an internal ribosome entry site (IRES) in the 5' untranslated region of the ACLY mRNA, that can support an efficient mRNA translation through a Cap-independent mechanism. In steatotic HepG2 cells, ACLY expression was up-regulated through IRES-mediated translation. Since it has been demonstrated that lipid accumulation in cells induces endoplasmic reticulum (ER) stress, the involvement of this cellular pathway in the translational regulation of ACLY has been also evaluated. Our results showed that ACLY expression was increased in ER-stressed cells, through IRES-mediated translation of ACLY mRNA. A potential role of the Cap-independent translation of ACLY in NAFLD has been discussed.

The Acidic Tumor Microenvironment as a Driver of Cancer

Acidic metabolic waste products accumulate in the tumor microenvironment because of high metabolic activity and insufficient perfusion. In tumors, the acidity of the interstitial space and the relatively well-maintained intracellular pH influence cancer and stromal cell function, their mutual interplay, and their interactions with the extracellular matrix. Tumor pH is spatially and temporally heterogeneous, and the fitness advantage of cancer cells adapted to extracellular acidity is likely particularly evident when they encounter less acidic tumor regions, for instance, during invasion. Through complex effects on genetic stability, epigenetics, cellular metabolism, proliferation, and survival, the compartmentalized pH microenvironment favors cancer development. Cellular selection exacerbates the malignant phenotype, which is further enhanced by acid-induced cell motility, extracellular matrix degradation, attenuated immune responses, and modified cellular and intercellular signaling. In this review, we discuss how the acidity of the tumor microenvironment influences each stage in cancer development, from dysplasia to full-blown metastatic disease.

Highly selective staining and quantification of intracellular lipid droplets with a compact push–pull fluorophore based on benzothiadiazole

A robust lipophilic dye, based on the structures of the benzothiadiazole heterocycle, was shown to be a potent fluorescent stain for the selective imaging of lipid droplets (LDs) within both live and fixed human cells.

Lipid droplet velocity is a microenvironmental sensor of aggressive tumors regulated by V-ATPase and PEDF

Lipid droplets (LDs) utilize microtubules (MTs) to participate in intracellular trafficking of cargo proteins. Cancer cells accumulate LDs and acidify their tumor microenvironment (TME) by increasing the proton pump V-ATPase. However, it is not known whether these two metabolic changes are mechanistically related or influence LD movement. We postulated that LD density and velocity are progressively increased with tumor aggressiveness and are dependent on V-ATPase and the lipolysis regulator pigment epithelium-derived factor (PEDF). LD density was assessed in human prostate cancer (PCa) specimens across Gleason scores (GS) 6-8. LD distribution and velocity were analyzed in low and highly aggressive tumors using live-cell imaging and in cells exposed to low pH and/or treated with V-ATPase inhibitors. The MT network was disrupted and analyzed by α-tubulin staining. LD density positively correlated with advancing GS in human tumors. Acidification promoted peripheral localization and clustering of LDs. Highly aggressive prostate, breast, and pancreatic cell lines had significantly higher maximum LD velocity (LDVmax) than less aggressive and benign cells. LDVmax was MT-dependent and suppressed by blocking V-ATPase directly or indirectly with PEDF. Upon lowering pH, LDs moved to the cell periphery and carried metalloproteinases. These results suggest that acidification of the TME can alter intracellular LD movement and augment velocity in cancer. Restoration of PEDF or blockade of V-ATPase can normalize LD distribution and decrease velocity. This study identifies V-ATPase and PEDF as new modulators of LD trafficking in the cancer microenvironment.

Naringenin Ameliorates Drosophila ReepA Hereditary Spastic Paraplegia-Linked Phenotypes

Defects in the endoplasmic reticulum (ER) membrane shaping and interaction with other organelles seem to be a crucial mechanism underlying Hereditary Spastic Paraplegia (HSP) neurodegeneration. REEP1, a transmembrane protein belonging to TB2/HVA22 family, is implicated in SPG31, an autosomal dominant form of HSP, and its interaction with Atlastin/SPG3A and Spastin/SPG4, the other two major HSP linked proteins, has been demonstrated to play a crucial role in modifying ER architecture. In addition, the Drosophila ortholog of REEP1, named ReepA, has been found to regulate the response to ER neuronal stress. Herein we investigated the role of ReepA in ER morphology and stress response. ReepA is upregulated under stress conditions and aging. Our data show that ReepA triggers a selective activation of Ire1 and Atf6 branches of Unfolded Protein Response (UPR) and modifies ER morphology. Drosophila lacking ReepA showed Atf6 and Ire1 activation, expansion of ER sheet-like structures, locomotor dysfunction and shortened lifespan. Furthermore, we found that naringenin, a flavonoid that possesses strong antioxidant and neuroprotective activity, can rescue the cellular phenotypes, the lifespan and locomotor disability associated with ReepA loss of function. Our data highlight the importance of ER homeostasis in nervous system functionality and HSP neurodegenerative mechanisms, opening new opportunities for HSP treatment.

Mechanisms by which PE21, an extract from the white willow Salix alba, delays chronological aging in budding yeast

We have recently found that PE21, an extract from the white willow Salix alba, slows chronological aging and prolongs longevity of the yeast Saccharomyces cerevisiae more efficiently than any of the previously known pharmacological interventions. Here, we investigated mechanisms through which PE21 delays yeast chronological aging and extends yeast longevity. We show that PE21 causes a remodeling of lipid metabolism in chronologically aging yeast, thereby instigating changes in the concentrations of several lipid classes. We demonstrate that such changes in the cellular lipidome initiate three mechanisms of aging delay and longevity extension. The first mechanism through which PE21 slows aging and prolongs longevity consists in its ability to decrease the intracellular concentration of free fatty acids. This postpones an age-related onset of liponecrotic cell death promoted by excessive concentrations of free fatty acids. The second mechanism of aging delay and longevity extension by PE21 consists in its ability to decrease the concentrations of triacylglycerols and to increase the concentrations of glycerophospholipids within the endoplasmic reticulum membrane. This activates the unfolded protein response system in the endoplasmic reticulum, which then decelerates an age-related decline in protein and lipid homeostasis and slows down an aging-associated deterioration of cell resistance to stress. The third mechanisms underlying aging delay and longevity extension by PE21 consists in its ability to change lipid concentrations in the mitochondrial membranes. This alters certain catabolic and anabolic processes in mitochondria, thus amending the pattern of aging-associated changes in several key aspects of mitochondrial functionality.

CDP-DAG synthase 1 and 2 regulate lipid droplet growth through distinct mechanisms

Lipid droplets (LDs) are evolutionarily conserved organelles that play critical roles in mammalian lipid storage and metabolism. However, the molecular mechanisms governing the biogenesis and growth of LDs remain poorly understood. Phosphatidic acid (PA) is a precursor of phospholipids and triacylglycerols and substrate of CDP-diacylglycerol (CDP-DAG) synthase 1 (CDS1) and CDS2, which catalyze the formation of CDP-DAG. Here, using siRNA-based gene knockdowns and CRISPR/Cas9-mediated gene knockouts, along with immunological, molecular, and fluorescence microscopy approaches, we examined the role of CDS1 and CDS2 in LD biogenesis and growth. Knockdown of either CDS1 or CDS2 expression resulted in the formation of giant or supersized LDs in cultured mammalian cells. Interestingly, down-regulation of cell death-inducing DFF45-like effector C (CIDEC), encoding a prominent regulator of LD growth in adipocytes, restored LD size in CDS1- but not in CDS2-deficient cells. On the other hand, reducing expression of two enzymes responsible for triacylglycerol synthesis, diacylglycerol O-acyltransferase 2 (DGAT2) and glycerol-3-phosphate acyltransferase 4 (GPAT4), rescued the LD phenotype in CDS2-deficient, but not CDS1-deficient, cells. Moreover, CDS2 deficiency, but not CDS1 deficiency, promoted the LD association of DGAT2 and GPAT4 and impaired initial LD maturation. Finally, although both CDS1 and CDS2 appeared to regulate PA levels on the LD surface, CDS2 had a stronger effect. We conclude that CDS1 and CDS2 regulate LD dynamics through distinct mechanisms.

Targeting Long Chain Acyl-CoA Synthetases for Cancer Therapy

The deregulation of cancer cell metabolic networks is now recognized as one of the hallmarks of cancer. Abnormal lipid synthesis and extracellular lipid uptake are advantageous modifications fueling the needs of uncontrolled cancer cell proliferation. Fatty acids are placed at the crossroads of anabolic and catabolic pathways, as they are implicated in the synthesis of phospholipids and triacylglycerols, or they can undergo β-oxidation. Key players to these decisions are the long-chain acyl-CoA synthetases, which are enzymes that catalyze the activation of long-chain fatty acids of 12-22 carbons. Importantly, the long-chain acyl-CoA synthetases are deregulated in many types of tumors, providing a rationale for anti-tumor therapeutic opportunities. The purpose of this review is to summarize the last up-to-date findings regarding their role in cancer, and to discuss the related emerging tumor targeting opportunities.