Fluorescent detection of lipid droplets and associated proteins

Impaired fatty acid import or catabolism in macrophages restricts intracellular growth of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) infection of macrophages reprograms cellular metabolism to promote lipid retention. While it is clearly known that intracellular Mtb utilize host derived lipids to maintain infection, the role of macrophage lipid processing on the bacteria's ability to access the intracellular lipid pool remains undefined. We utilized a CRISPR-Cas9 genetic approach to assess the impact of sequential steps in fatty acid metabolism on the growth of intracellular Mtb. Our analyzes demonstrate that mutated macrophages that cannot either import, store or catabolize fatty acids restrict Mtb growth by both common and divergent anti-microbial mechanisms, including increased glycolysis, increased oxidative stress, production of pro-inflammatory cytokines, enhanced autophagy and nutrient limitation. We also show that impaired macrophage lipid droplet biogenesis is restrictive to Mtb replication, but increased induction fails to rescue Mtb growth. Our work expands our understanding of how host fatty acid homeostasis impacts Mtb growth in the macrophage.

The long-chain polyfluorinated alkyl substance perfluorohexane sulfonate (PFHxS) promotes bone marrow adipogenesis

Per- and polyfluoroalkyl substances (PFAS) bioaccumulate in different organ systems, including bone. While existing research highlights the adverse impact of PFAS on bone density, a critical gap remains in understanding the specific effects on the bone marrow microenvironment, especially the bone marrow adipose tissue (BMAT). Changes in BMAT have been linked to various health consequences, such as the development of osteoporosis and the progression of metastatic tumors in bone. Studies presented herein demonstrate that exposure to a mixture of five environmentally relevant PFAS compounds promotes marrow adipogenesis in vitro and in vivo. We show that among the components of the mixture, PFHxS, an alternative to PFOS, has the highest propensity to accumulate in bone and effectively promote marrow adipogenesis. Utilizing RNAseq approaches, we identified the peroxisome proliferator-activated receptor (PPAR) signaling as a top pathway modulated by PFHxS exposure. Furthermore, we provide results suggesting the activation and involvement of PPAR-gamma (PPARγ) in PFHxS-mediated bone marrow adipogenesis, especially in combination with high-fat diet. In conclusion, our findings demonstrate the potential impact of elevated PFHxS levels, particularly in occupational settings, on bone health, and specifically bone marrow adiposity. This study contributes new insights into the health risks of PFHxS exposure, urging further research on the relationship between environmental factors, diet, and adipose tissue dynamics.

A fluorescent perilipin 2 knock-in mouse model reveals a high abundance of lipid droplets in the developing and adult brain

Lipid droplets (LDs) are dynamic lipid storage organelles. They are tightly linked to metabolism and can exert protective functions, making them important players in health and disease. Most LD studies in vivo rely on staining methods, providing only a snapshot. We therefore developed a LD-reporter mouse by labelling the endogenous LD coat protein perilipin 2 (PLIN2) with tdTomato, enabling staining-free fluorescent LD visualisation in living and fixed tissues and cells. Here we validate this model under standard and high-fat diet conditions and demonstrate that LDs are highly abundant in various cell types in the healthy brain, including neurons, astrocytes, ependymal cells, neural stem/progenitor cells and microglia. Furthermore, we also show that LDs are abundant during brain development and can be visualized using live imaging of embryonic slices. Taken together, our tdTom-Plin2 mouse serves as a novel tool to study LDs and their dynamics under both physiological and diseased conditions in all tissues expressing Plin2.

The Role of Neutral Sphingomyelinase-2 (NSM2) in the Control of Neutral Lipid Storage in T Cells

The accumulation of lipid droplets (LDs) and ceramides (Cer) is linked to non-alcoholic fatty liver disease (NAFLD), regularly co-existing with type 2 diabetes and decreased immune function. Chronic inflammation and increased disease severity in viral infections are the hallmarks of the obesity-related immunopathology. The upregulation of neutral sphingomyelinase-2 (NSM2) has shown to be associated with the pathology of obesity in tissues. Nevertheless, the role of sphingolipids and specifically of NSM2 in the regulation of immune cell response to a fatty acid (FA) rich environment is poorly studied. Here, we identified the presence of the LD marker protein perilipin 3 (PLIN3) in the intracellular nano-environment of NSM2 using the ascorbate peroxidase APEX2-catalyzed proximity-dependent biotin labeling method. In line with this, super-resolution structured illumination microscopy (SIM) shows NSM2 and PLIN3 co-localization in LD organelles in the presence of increased extracellular concentrations of oleic acid (OA). Furthermore, the association of enzymatically active NSM2 with isolated LDs correlates with increased Cer levels in these lipid storage organelles. NSM2 enzymatic activity is not required for NSM2 association with LDs, but negatively affects the LD numbers and cellular accumulation of long-chain unsaturated triacylglycerol (TAG) species. Concurrently, NSM2 expression promotes mitochondrial respiration and fatty acid oxidation (FAO) in response to increased OA levels, thereby shifting cells to a high energetic state. Importantly, endogenous NSM2 activity is crucial for primary human CD4+ T cell survival and proliferation in a FA rich environment. To conclude, our study shows a novel NSM2 intracellular localization to LDs and the role of enzymatically active NSM2 in metabolic response to enhanced FA concentrations in T cells.

BODIPY-Based Molecules for Biomedical Applications

BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives have attracted attention as probes in applications like imaging and sensing due to their unique properties like (1) strong absorption and emission in the visible and near-infrared regions of the electromagnetic spectrum, (2) strong fluorescence and (3) supreme photostability. They have also been employed in areas like photodynamic therapy. Over the last decade, BODIPY-based molecules have even emerged as candidates for cancer treatments. Cancer remains a significant health issue world-wide, necessitating a continuing search for novel therapeutic options. BODIPY is a flexible fluorophore with distinct photophysical characteristics and is a fascinating drug development platform. This review provides a comprehensive overview of the most recent breakthroughs in BODIPY-based small molecules for cancer or disease detection and therapy, including their functional potential.

Application of synthetic lipid droplets in metabolic diseases

BACKGROUND

The study and synthesis of membrane organelles are becoming increasingly important, not only as simplified cellular models for corresponding molecular and metabolic studies but also for applications in synthetic biology of artificial cells and drug delivery vehicles. Lipid droplets (LDs) are central organelles in cellular lipid metabolism and are involved in almost all metabolic processes. Multiple studies have also demonstrated a high correlation between LDs and metabolic diseases. During these processes, LDs reveal a highly dynamic character, with their lipid fraction, protein composition and subcellular localisation constantly changing in response to metabolic demands. However, the molecular mechanisms underlying these functions have not been fully understood due to the limitations of cell biology approaches. Fortunately, developments in synthetic biology have provided a huge breakthrough for metabolism research, and methods for in vitro synthesis of LDs have been successfully established, with great advances in protein binding, lipid function, membrane dynamics and enzymatic reactions.

AIMS AND METHODS

In this review, we provide a comprehensive overview of the assembly and function of endogenous LDs, from the generation of lipid molecules to how they are assembled into LDs in the endoplasmic reticulum. In particular, we highlight two major classes of synthetic LD models for fabrication techniques and their recent advances in biology and explore their roles and challenges in achieving real applications of artificial LDs in the future.

Environmental gradients reveal stress hubs pre-dating plant terrestrialization

Plant terrestrialization brought forth the land plants (embryophytes). Embryophytes account for most of the biomass on land and evolved from streptophyte algae in a singular event. Recent advances have unravelled the first full genomes of the closest algal relatives of land plants; among the first such species was Mesotaenium endlicherianum. Here we used fine-combed RNA sequencing in tandem with a photophysiological assessment on Mesotaenium exposed to a continuous range of temperature and light cues. Our data establish a grid of 42 different conditions, resulting in 128 transcriptomes and ~1.5 Tbp (~9.9 billion reads) of data to study the combinatory effects of stress response using clustering along gradients. Mesotaenium shares with land plants major hubs in genetic networks underpinning stress response and acclimation. Our data suggest that lipid droplet formation and plastid and cell wall-derived signals have denominated molecular programmes since more than 600 million years of streptophyte evolution-before plants made their first steps on land.

Mycobacterium tuberculosis response to cholesterol is integrated with environmental pH and potassium levels via a lipid utilization regulator

How bacterial response to environmental cues and nutritional sources may be integrated in enabling host colonization is poorly understood. Exploiting a reporter-based screen, we discovered that overexpression of Mycobacterium tuberculosis (Mtb) lipid utilization regulators altered Mtb acidic pH response dampening by low environmental potassium (K+). Transcriptional analyses unveiled amplification of Mtb response to acidic pH in the presence of cholesterol, a major carbon source for Mtb during infection, and vice versa. Strikingly, deletion of the putative lipid regulator mce3R resulted in loss of augmentation of (i) cholesterol response at acidic pH, and (ii) low [K+] response by cholesterol, with minimal effect on Mtb response to each signal individually. Finally, the ∆mce3R mutant was attenuated for colonization in a murine model that recapitulates lesions with lipid-rich foamy macrophages. These findings reveal critical coordination between bacterial response to environmental and nutritional cues, and establish Mce3R as a crucial integrator of this process.

Mycobacterial formation of intracellular lipid inclusions is a dynamic process associated with rapid replication

Intracellular lipid inclusions (ILI) are triacylglyceride rich organelles produced by mycobacteria thought to serve as energy reservoirs. It is believed that ILI are formed as a result of a dosR mediated transition from replicative growth to non-replicating persistence (NRP). ILI rich Mycobacterium tuberculosis (Mtb) bacilli have been reported during infection and in sputum, establishing their importance in Mtb pathogenesis. Studies conducted in mycobacteria such as Mycobacterium smegmatis, Mycobacterium abscessus, or lab Mtb strains have demonstrated ILI formation in the presence of hypoxic, nitric oxide, nutrient limitation, or low nitrogen stress, conditions believed to emulate the host environment within which Mtb resides. Here, we show that M. marinum and clinical Mtb isolates make ILI during active replication in axenic culture independent of environmental stressors. By tracking ILI formation dynamics we demonstrate that ILI are quickly formed in the presence of fresh media or exogenous fatty acids but are rapidly depleted while bacteria are still actively replicating. We also show that the cell envelope is an alternate site for neutral lipid accumulation observed during stationary phase. In addition, we screen a panel of 60 clinical isolates and observe variation in ILI production during early log phase growth between and among Mtb lineages. Finally, we show that dosR expression level does not strictly correlate with ILI accumulation in fresh clinical isolates. Taken together, our data provide evidence of an active ILI formation pathway in replicating mycobacteria cultured in the absence of stressors, suggesting a decoupling of ILI formation from NRP.

Conservation of Markers and Stemness in Adipose Stem and Progenitor Cells between Cattle and Other Species

Adipose stem and progenitor cells (ASPCs) have been isolated from humans and animals for use in regenerative medicine and therapy. However, knowledge of ASPCs in other species is limited. Particularly, ASPCs in livestock are expected to enhance the fat content and meat composition. In this study, we isolated bovine ASPCs using cell surface markers. Specifically, we focused on ASPC markers in humans and experimental animals, namely CD26, CD146, and CD54. Stromal vascular fraction cells from bovine fat were separated using flow cytometry before primary culture. We evaluated the self-renewal and adipogenic potential of each fraction. We identified four cell populations: CD26-CD146+CD54+, CD26-CD146+CD54-, CD26-CD146-, and CD26+CD146-. Among them, the CD26-CD146+ fraction, particularly CD54+, demonstrated the properties of preadipocytes (PreAs), characterized by slow proliferation and a high adipogenic capacity. In conclusion, we could collect and characterize possible PreAs as CD26-CD146+CD54+ or CD26-CD146+CD54-, which are expected for in vitro bovine adipogenic assays in the future.

Multi-targeting TACE/ADAM17 and gamma-secretase of notch signalling pathway in TNBC via drug repurposing approach using Lomitapide

The aberrant expression of the Notch signalling pathway genes aids in potentiating the belligerent characteristics of numerous malignancies. Besides imparting abnormal proliferation and metastasis, the Notch also aids in the metabolic reprogramming of tumor cells. Since the activation of the Notch pathway is mediated via TACE/ADAM protease and the γ-secretase complex, hence it is crucial in determining a multi-targeted therapeutic approach to target these major proteases to downregulate the aberrant Notch signalling pathway. In this study, Lomitapide was chosen based on its binding score (-305.108 kJ/mol and - 173.174 kJ/mol) against the crucial proteases, TACE and γ-secretase, respectively. Further, the remarkable antitumor properties of Lomitapide were established on the TNBC cell lines (MDA-MB-231 and MDA-MB-468), along with the EMT-induced MDA-MB-468 cells. Apart from inducing ∼2 to 2.5-fold increase in the cellular ROS levels, Lomitapide treatment induced significant apoptosis, arrested cell cycle progression and reduced sphere and colony forming abilities of the TNBC cells. Differentiated epithelial phenotype with diminished CD44-stem cell marker was also observed upon treatment. Furthermore, reduction of migration potential, decrease in the gene expression profile of the EMT markers, along with downregulation of the Notch signalling genes were evident in the treated TNBC cells. Altogether, the present study attributes the repurposing of Lomitapide as an effective therapeutic agent against the major proteases of the Notch pathway to combat TNBC progression and dissemination.

Effect of oxidation and in vitro intestinal hydrolysis on phospholipid toxicity towards HT29 cell line serving as a model of human intestinal epithelium

Oxidation of food-derived phospholipids (PLs) can influence nutrient digestion and induce oxidative stress in gastrointestinal epithelium. In this study, hen egg yolk PL fraction was used to evaluate the effect of lipoxygenase (LOX)-induced PL oxidation on the rate of PL hydrolysis catalyzed by pancreatic phospholipase A₂ (PLA₂) in the presence of bile salts (BSs). Then, PL/BS solutions containing native or oxidized PLs were used in in vitro intestinal digestion to assess the effect of PL oxidation and hydrolysis on the toxicity towards HT29 cell line. Based on the obtained results, we suggest that hexanal and (E)-2-nonenal, formed by the decomposition of PL hydroperoxides, inhibited PLA₂ activity. The cell exposure to simulated intestinal fluid (SIF) containing BSs decreased HT29 cell viability and significantly damaged cellular DNA. However, the genotoxic effect was reversed in the presence of all tested PL samples, while the protective effect against the BS-induced cytotoxicity was observed for native non-hydrolyzed PLs, but was not clearly visible for other samples. This can result from an overlap of other toxic effects such as lipotoxicity or disturbance of cellular redox homeostasis. Taking into account the data obtained, it was proposed that the PLA₂ activity decline in the presence of PL oxidation products may be a kind of protective mechanism against rapid release of oxidized FAs characterized by high cytotoxic effect towards intestinal epithelium cells.

NSCLC Cells Resistance to PI3K/mTOR Inhibitors Is Mediated by Delta-6 Fatty Acid Desaturase (FADS2)

Hyperactivation of the phosphatidylinositol-3-kinase (PI3K) pathway is one of the most common events in human cancers. Several efforts have been made toward the identification of selective PI3K pathway inhibitors. However, the success of these molecules has been partially limited due to unexpected toxicities, the selection of potentially responsive patients, and intrinsic resistance to treatments. Metabolic alterations are intimately linked to drug resistance; altered metabolic pathways can help cancer cells adapt to continuous drug exposure and develop resistant phenotypes. Here we report the metabolic alterations underlying the non-small cell lung cancer (NSCLC) cell lines resistant to the usual PI3K-mTOR inhibitor BEZ235. In this study, we identified that an increased unsaturation degree of lipid species is associated with increased plasma membrane fluidity in cells with the resistant phenotype and that fatty acid desaturase FADS2 mediates the acquisition of chemoresistance. Therefore, new studies focused on reversing drug resistance based on membrane lipid modifications should consider the contribution of desaturase activity.

How to follow lipid droplets dynamics during adipocyte metabolism

Lipid droplets (LDs) are important cellular organelles due to their ability to accumulate and store lipids. LD dynamics are associated with various cellular and metabolic processes. Accurate monitoring of LD's size and shape is of prime importance as it indicates the metabolic status of the cells. Unintrusive continuous quantification techniques have a clear advantage in analyzing LDs as they measure and monitor the cells' metabolic function and droplets over time. Here, we present a novel machine-learning-based method for LDs analysis by segmentation of phase-contrast images of differentiated adipocytes (in vitro) and adipose tissue (in vivo). We developed a new workflow based on the ImageJ waikato environment for knowledge analysis segmentation plugin, which provides an accurate, label-free, live single-cell, and organelle quantification of LD-related parameters. By applying the new method on differentiating 3T3-L1 cells, the size of LDs was analyzed over time in differentiated adipocytes and their correlation with other morphological parameters. Moreover, we analyzed the LDs dynamics during catabolic changes such as lipolysis and lipophagy and demonstrated its ability to identify different cellular subpopulations based on their structural, numerical, and spatial variability. This analysis was also implemented on unstained ex vivo adipose tissues to measure adipocyte size, an important readout of the tissue's metabolism. The presented approach can be applied in different LD-related metabolic conditions to provide a better understanding of LD biogenesis and function in vivo and in vitro while serving as a new platform that enables rapid and accurate screening of data sets.

Precision Navigation of Hepatic Ischemia-Reperfusion Injury Guided by Lysosomal Viscosity-Activatable NIR-II Fluorescence

Hepatic ischemia-reperfusion injury (HIRI) is responsible for postoperative liver dysfunction and liver failure. Precise and rapid navigation of HIRI lesions is critical for early warning and timely development of pretreatment plans. Available methods for assaying liver injury fail to provide the exact location of lesions in real time intraoperatively. HIRI is intimately associated with oxidative stress which impairs lysosomal degradative function, leading to significant changes in lysosomal viscosity. Therefore, lysosomal viscosity is a potential biomarker for the precise targeting of HIRI. Hence, we developed a viscosity-activatable second near-infrared window fluorescent probe (NP-V) for the detection of lysosomal viscosity in hepatocytes and mice during HIRI. A reactive oxygen species-malondialdehyde-cathepsin B signaling pathway during HIRI was established. We further conducted high signal-to-background ratio NIR-II fluorescence imaging of HIRI mice. The contour and boundary of liver lesions were delineated, and as such the precise intraoperative resection of the lesion area was implemented. This research demonstrates the potential of NP-V as a dual-functional probe for the elucidation of HIRI pathogenesis and the direct navigation of HIRI lesions in clinical applications.

Label-free metabolic imaging of non-alcoholic-fatty-liver-disease (NAFLD) liver by volumetric dynamic optical coherence tomography

Label-free metabolic imaging of non-alcoholic fatty liver disease (NAFLD) mouse liver is demonstrated ex vivo by dynamic optical coherence tomography (OCT). The NAFLD mouse is a methionine choline-deficient (MCD)-diet model, and two mice fed the MCD diet for 1 and 2 weeks are involved in addition to a normal-diet mouse. The dynamic OCT is based on repeating raster scan and logarithmic intensity variance (LIV) analysis that enables volumetric metabolic imaging with a standard-speed (50,000 A-lines/s) OCT system. Metabolic domains associated with lipid droplet accumulation and inflammation are clearly visualized three-dimensionally. Particularly, the normal-diet liver exhibits highly metabolic vessel-like structures of peri-vascular hepatic zones. The 1-week MCD-diet liver shows ring-shaped highly metabolic structures formed with lipid droplets. The 2-week MCD-diet liver exhibits fragmented vessel-like structures associated with inflammation. These results imply that volumetric LIV imaging is useful for visualizing and assessing NAFLD abnormalities.

Development of a fluorescent nanoprobe based on an amphiphilic single-benzene-based fluorophore for lipid droplet detection and its practical applications

Lipid droplets (LDs) are crucial biological organelles connected with metabolic pathways in biological systems and diseases. To monitor the locations and accumulation of LDs in lipid-related diseases, the development of a visualization tool for LDs has gained importance. In particular, LD visualization using fluorescent probes has gained attention. Herein, a new fluorescent nanoprobe, BMeS-Ali, is developed that can sense LDs based on an amphiphilic single benzene-based fluorophore (SBBF). BMeS-Ali consists of hydrophilic (-NH₂) and hydrophobic (-C₁₂H₂₅) moieties and exists as a micelle nanostructure in aqueous media. BMeS-Ali has a weak fluorescence, but its emission was dramatically enhanced upon exposure to the LD components such as oleic acids (OA) by reassembling its nano-formulation. BMeS-Ali showed a selective LD staining ability and great biocompatibility in cells (cancer cells and stem cells). It also showed a practical sensing ability towards biologically derived lipids and can be applied to the visualization of human fingerprints. We found that the nanoprobe BMeS-Ali has significant potential to serve as a practical dye and sensor for lipids, especially for LD imaging in the biomedical research area and broader industrial applications.

MOSPD2 is an endoplasmic reticulum-lipid droplet tether functioning in LD homeostasis

Membrane contact sites between organelles are organized by protein bridges. Among the components of these contacts, the VAP family comprises ER-anchored proteins, such as MOSPD2, that function as major ER-organelle tethers. MOSPD2 distinguishes itself from the other members of the VAP family by the presence of a CRAL-TRIO domain. In this study, we show that MOSPD2 forms ER-lipid droplet (LD) contacts, thanks to its CRAL-TRIO domain. MOSPD2 ensures the attachment of the ER to LDs through a direct protein-membrane interaction. The attachment mechanism involves an amphipathic helix that has an affinity for lipid packing defects present at the surface of LDs. Remarkably, the absence of MOSPD2 markedly disturbs the assembly of lipid droplets. These data show that MOSPD2, in addition to being a general ER receptor for inter-organelle contacts, possesses an additional tethering activity and is specifically implicated in the biology of LDs via its CRAL-TRIO domain.

Squaraine probes for the bimodal staining of lipid droplets and endoplasmic reticulum imaging in live cells

We report the synthesis of a library of asymmetric squaraines and their application as superior bimodal “on-demand” fluorescence probes for lipid drolet and endoplasmic reticulum in cancer cells.

Lipid droplet availability affects neural stem/progenitor cell metabolism and proliferation

Neural stem/progenitor cells (NSPCs) generate new neurons throughout adulthood. However, the underlying regulatory processes are still not fully understood. Lipid metabolism plays an important role in regulating NSPC activity: build-up of lipids is crucial for NSPC proliferation, whereas break-down of lipids has been shown to regulate NSPC quiescence. Despite their central role for cellular lipid metabolism, the role of lipid droplets (LDs), the lipid storing organelles, in NSPCs remains underexplored. Here we show that LDs are highly abundant in adult mouse NSPCs, and that LD accumulation is significantly altered upon fate changes such as quiescence and differentiation. NSPC proliferation is influenced by the number of LDs, inhibition of LD build-up, breakdown or usage, and the asymmetric inheritance of LDs during mitosis. Furthermore, high LD-containing NSPCs have increased metabolic activity and capacity, but do not suffer from increased oxidative damage. Together, these data indicate an instructive role for LDs in driving NSPC behaviour.

Autophagy protects murine preputial glands against premature aging, and controls their sebum phospholipid and pheromone profile

Preputial glands are large lipid and hormone secreting sebaceous organs of mice, and present a convenient model for the investigation of biological processes in sebocytes. Suppression of ATG7-dependent macroautophagy/autophagy in epithelial cells of murine skin causes enlargement of hair follicle-associated sebaceous glands and alters the lipid profile of sebum. We have now extended these studies to the preputial glands and find that autophagy significantly delays the onset of age-related ductal ectasia, influences lipid droplet morphology and contributes to the complete dissolution of the mature sebocytes during holocrine secretion. Single cell RNA sequencing showed that many genes involved in lipid metabolism and oxidative stress response were downregulated in immature and mature epithelial cells of ATG7-deficient glands. When analyzing the lipid composition of control and mutant glands, we found that levels of all phospholipid classes, except choline plasmalogen, were decreased in the mutant glands, with a concomitant accumulation of diacyl glycerides. Mass spectrometric imaging (MSI) demonstrated that phospholipid species, specifically the dominant phosphatidylcholine (PC 34:1), were decreased in immature and mature sebocytes. In addition, we found a strong reduction in the amounts of the pheromone, palmityl acetate. Thus, autophagy in the preputial gland is not only important for homeostasis of the gland as a whole and an orderly breakdown of cells during holocrine secretion, but also regulates phospholipid and fatty acid metabolism, as well as pheromone production.AbbreviationsATG7: autophagy related 7; BODIPY: boron dipyrromethene; DAG: diacyl glycerides; DBI: diazepam binding inhibitor; GFP: green fluorescent protein; KRT14: keratin 14; HPLC-MS: high performance liquid chromatography-mass spectrometry; LD: lipid droplet; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MSI: mass spectrometric imaging; ORO: Oil Red O; PC: phosphatidylcholine; PE: phosphatidylethanolamine; PG: preputial gland; PLIN2: perilipin 2; PtdIns: phosphatidylinositol; PL: phospholipids; POPC: 1-palmitoyl-2-oleoyl-PC; PS: phosphatidylserine; qRT-PCR: quantitative reverse transcribed PCR; SG: sebaceous gland; scRNAseq: single-cell RNA sequencing; TAG: triacylglycerides; TLC: thin layer chromatography.

Cellular cholesterol and how to find it

Cholesterol is an essential component of eukaryotic cellular membranes. Information about its subcellular localization and transport pathways inside cells are key for the understanding and treatment of cholesterol-related diseases. In this review we give an overview over the most commonly used methods that contributed to our current understanding of subcellular cholesterol localization and transport routes. First, we discuss methods that provide insights into cholesterol metabolism based on readouts of downstream effects such as esterification. Subsequently, we focus on the use of cholesterol-binding molecules as probes that facilitate visualization and quantification of sterols inside of cells. Finally, we explore different analogues of cholesterol which, when taken up by living cells, are integrated and transported in a similar fashion as endogenous sterols. Taken together, we highlight the challenges and advantages of each method such that researchers studying aspects of cholesterol transport may choose the most pertinent approach for their problem.

WNT6/ACC2-induced storage of triacylglycerols in macrophages is exploited by Mycobacterium tuberculosis

In view of emerging drug-resistant tuberculosis (TB), host-directed adjunct therapies are urgently needed to improve treatment outcomes with currently available anti-TB therapies. One approach is to interfere with the formation of lipid-laden "foamy" macrophages in the host, as they provide a nutrient-rich host cell environment for Mycobacterium tuberculosis (Mtb). Here, we provide evidence that Wnt family member 6 (WNT6), a ligand of the evolutionarily conserved Wingless/Integrase 1 (WNT) signaling pathway, promotes foam cell formation by regulating key lipid metabolic genes including acetyl-CoA carboxylase 2 (ACC2) during pulmonary TB. Using genetic and pharmacological approaches, we demonstrated that lack of functional WNT6 or ACC2 significantly reduced intracellular triacylglycerol (TAG) levels and Mtb survival in macrophages. Moreover, treatment of Mtb-infected mice with a combination of a pharmacological ACC2 inhibitor and the anti-TB drug isoniazid (INH) reduced lung TAG and cytokine levels, as well as lung weights, compared with treatment with INH alone. This combination also reduced Mtb bacterial numbers and the size of mononuclear cell infiltrates in livers of infected mice. In summary, our findings demonstrate that Mtb exploits WNT6/ACC2-induced storage of TAGs in macrophages to facilitate its intracellular survival, a finding that opens new perspectives for host-directed adjunctive treatment of pulmonary TB.

TDP-43 mediates SREBF2-regulated gene expression required for oligodendrocyte myelination

Cholesterol metabolism operates autonomously within the central nervous system (CNS), where the majority of cholesterol resides in myelin. We demonstrate that TDP-43, the pathological signature protein for amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), influences cholesterol metabolism in oligodendrocytes. TDP-43 binds directly to mRNA of SREBF2, the master transcription regulator for cholesterol metabolism, and multiple mRNAs encoding proteins responsible for cholesterol biosynthesis and uptake, including HMGCR, HMGCS1, and LDLR. TDP-43 depletion leads to reduced SREBF2 and LDLR expression, and cholesterol levels in vitro and in vivo. TDP-43-mediated changes in cholesterol levels can be restored by reintroducing SREBF2 or LDLR. Additionally, cholesterol supplementation rescues demyelination caused by TDP-43 deletion. Furthermore, oligodendrocytes harboring TDP-43 pathology from FTD patients show reduced HMGCR and HMGCS1, and coaggregation of LDLR and TDP-43. Collectively, our results indicate that TDP-43 plays a role in cholesterol homeostasis in oligodendrocytes, and cholesterol dysmetabolism may be implicated in TDP-43 proteinopathies-related diseases.

Dissecting lipid droplet biology with coherent Raman scattering microscopy

Lipid droplets (LDs) are lipid-rich organelles universally found in most cells. They serve as a key energy reservoir, actively participate in signal transduction and dynamically communicate with other organelles. LD dysfunction has been associated with a variety of diseases. The content level, composition and mobility of LDs are crucial for their physiological and pathological functions, and these different parameters of LDs are subject to regulation by genetic factors and environmental inputs. Coherent Raman scattering (CRS) microscopy utilizes optical nonlinear processes to probe the intrinsic chemical bond vibration, offering label-free, quantitative imaging of lipids in vivo with high chemical specificity and spatiotemporal resolution. In this Review, we provide an overview over the principle of CRS microscopy and its application in tracking different parameters of LDs in live cells and organisms. We also discuss the use of CRS microscopy in genetic screens to discover lipid regulatory mechanisms and in understanding disease-related lipid pathology.

Mitochondria-dependent phase separation of disease-relevant proteins drives pathological features of age-related macular degeneration

Age-related macular degeneration (AMD) damages the retinal pigment epithelium (RPE), the tissue that safeguards photoreceptor health, leading to irreversible vision loss. Polymorphisms in cholesterol and complement genes are implicated in AMD, yet mechanisms linking risk variants to RPE injury remain unclear. We sought to determine how allelic variants in the apolipoprotein E cholesterol transporter modulate RPE homeostasis and function. Using live-cell imaging, we show that inefficient cholesterol transport by the AMD risk-associated ApoE2 increases RPE ceramide, leading to autophagic defects and complement-mediated mitochondrial damage. Mitochondrial injury drives redox state–sensitive cysteine-mediated phase separation of ApoE2, forming biomolecular condensates that could nucleate drusen. The protective ApoE4 isoform lacks these cysteines and is resistant to phase separation and condensate formation. In Abca^–/– Stargardt macular degeneration mice, mitochondrial dysfunction induces liquid-liquid phase separation of p62/SQSTM1, a multifunctional protein that regulates autophagy. Drugs that decrease RPE cholesterol or ceramide prevent mitochondrial injury and phase separation in vitro and in vivo. In AMD donor RPE, mitochondrial fragmentation correlates with ApoE and p62 condensates. Our studies demonstrate that major AMD genetic and biological risk pathways converge upon RPE mitochondria, and identify mitochondrial stress-mediated protein phase separation as an important pathogenic mechanism and promising therapeutic target in AMD.

Indolylbenzothiadiazoles as highly tunable fluorophores for imaging lipid droplet accumulation in astrocytes and glioblastoma cells

We present an extensive photophysical study of a series of fluorescent indolylbenzothiadiazole derivatives and their ability to specifically image lipid droplets in astrocytes and glioblastoma cells. All compounds in the series displayed positive solvatochromism together with large Stokes shifts, and π-extended derivatives exhibited elevated brightness. It was shown that the fluorescence properties were highly tunable by varying the electronic character or size of the N-substituent on the indole motif. Three compounds proved capable as probes for detecting small quantities of lipid deposits in healthy and cancerous brain cells. In addition, all twelve compounds in the series were predicted to cross the blood–brain barrier, which raises the prospect for future in vivo studies for exploring the role of lipid droplets in the central nervous system.

We present an extensive photophysical study of a series of fluorescent indolylbenzothiadiazole derivatives and their ability to specifically image lipid droplets in astrocytes and glioblastoma cells.

Divergence exists in the subcellular distribution of intramuscular triglyceride in human skeletal muscle dependent on the choice of lipid dye

Despite over 50 years of research, a comprehensive understanding of how intramuscular triglyceride (IMTG) is stored in skeletal muscle and its contribution as a fuel during exercise is lacking. Immunohistochemical techniques provide information on IMTG content and lipid droplet (LD) morphology on a fibre type and subcellular-specific basis, and the lipid dye Oil Red O (ORO) is commonly used to achieve this. BODIPY 493/503 (BODIPY) is an alternative lipid dye with lower background staining and narrower emission spectra. Here we provide the first quantitative comparison of BODIPY and ORO for investigating exercise-induced changes in IMTG content and LD morphology on a fibre type and subcellular-specific basis. Estimates of IMTG content were greater when using BODIPY, which was predominantly due to BODIPY detecting a larger number of LDs, compared to ORO. The subcellular distribution of intramuscular lipid was also dependent on the lipid dye used; ORO detects a greater proportion of IMTG in the periphery (5 μm below cell membrane) of the fibre, whereas IMTG content was higher in the central region using BODIPY. In response to 60 min moderate-intensity cycling exercise, IMTG content was reduced in both the peripheral (− 24%) and central region (− 29%) of type I fibres (P < 0.05) using BODIPY, whereas using ORO, IMTG content was only reduced in the peripheral region of type I fibres (− 31%; P < 0.05). As well as highlighting some methodological considerations herein, our investigation demonstrates that important differences exist between BODIPY and ORO for detecting and quantifying IMTG on a fibre type and subcellular-specific basis.

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.

A BODIPY-Based Fluorogenic Probe for Specific Imaging of Lipid Droplets

We developed an easily accessible boron-dipyrromethene (BODIPY)-based fluorogenic probe, which we named LD-TB. This probe emits bright fluorescence in oil; when compared with aqueous solution, a significant enhancement of fluorescence brightness is observed. Cellular experiments confirmed that the probe stains the lipid droplets (LDs) specifically in both live and fixed cells, providing background-free images. Compared with Nile Red dye, a commonly used LD marker, LD-TB showed superior photostability. The sharp absorption and emission bands enable its multicolor imaging with blue and green probes. Importantly, the probe has proved to have low toxicity and is compatible with cell fixation. Our research provides a promising new fluorogenic probe for specific imaging of LDs.

Live-cell imaging of lipid droplets using solvatochromic coumarin derivatives

Lipid droplets (LDs), the lipid-rich intracellular organelles were selectively detected using simple coumarin containing fluorophores.

Lipid Droplets Define a Sub-Population of Breast Cancer Stem Cells

Tumor recurrence is now the leading cause of breast cancer-related death. These recurrences are believed to arise from residual cancer stem cells that survive initial therapeutic intervention. Therefore, a comprehensive understanding of cancer stem cell biology is needed to generate more effective therapies. Here we investigate the association between dysregulation of lipid metabolism and breast cancer stem cells. Focusing specifically on lipid droplets, we found that the lipid droplet number correlates with stemness in a panel of breast cell lines. Using a flow cytometry-based method developed for this study, we establish a means to isolate cells with augmented lipid droplet loads from total populations and show that they are enriched in cancer stem cells. Furthermore, pharmacological targeting of fatty acid metabolism reveals a metabolic addiction in a subset of cell lines. Our results highlight a key role for the lipid metabolism in the maintenance of the breast cancer stem cell pool, and as such, suggest it as a potential therapeutic target.

Reversible solidification of fission yeast cytoplasm after prolonged nutrient starvation

Cells depend on a highly ordered organisation of their content and must develop strategies to maintain the anisotropic distribution of organelles during periods of nutrient shortage. One of these strategies is to solidify the cytoplasm, which was observed in bacteria and yeast cells with acutely interrupted energy production. Here, we describe a different type of cytoplasm solidification fission yeast cells switch to, after having run out of nutrients during multiple days in culture. It provides the most profound reversible cytoplasmic solidification of yeast cells described to date. Our data exclude the previously proposed mechanisms for cytoplasm solidification in yeasts and suggest a mechanism that immobilises cellular components in a size-dependent manner. We provide experimental evidence that, in addition to time, cells use intrinsic nutrients and energy sources to reach this state. Such cytoplasmic solidification may provide a robust means to protect cellular architecture in dormant cells.

Summary: After prolonged quiescence, fission yeast cell populations switch state to immobilise subcellular components much more profoundly than cells experiencing acute energy depletion.

Targeting of lipid metabolism with a metabolic inhibitor cocktail eradicates peritoneal metastases in ovarian cancer cells

Ovarian cancer is an intra-abdominal tumor in which the presence of ascites facilitates metastatic dissemination, and associated with poor prognosis. However, the significance of metabolic alterations in ovarian cancer cells in the ascites microenvironment remains unclear. Here we show ovarian cancer cells exhibited increased aggressiveness in ascites microenvironment via reprogramming of lipid metabolism. High lipid metabolic activities are found in ovarian cancer cells when cultured in the ascites microenvironment, indicating a metabolic shift from aerobic glycolysis to β-oxidation and lipogenesis. The reduced AMP-activated protein kinase (AMPK) activity due to the feedback effect of high energy production led to the activation of its downstream signaling, which in turn, enhanced the cancer growth. The combined treatment of low toxic AMPK activators, the transforming growth factor beta-activated kinase 1 (TAK1) and fatty acid synthase (FASN) inhibitors synergistically impair oncogenic augmentation of ovarian cancer. Collectively, targeting lipid metabolism signaling axis impede ovarian cancer peritoneal metastases.

Subcellular antibiotic visualization reveals a dynamic drug reservoir in infected macrophages

Tuberculosis, caused by the intracellular pathogen Mycobacterium tuberculosis, remains the world's deadliest infectious disease. Sterilizing chemotherapy requires at least 6 months of multidrug therapy. Difficulty visualizing the subcellular localization of antibiotics in infected host cells means that it is unclear whether antibiotics penetrate all mycobacteria-containing compartments in the cell. Here, we combined correlated light, electron, and ion microscopy to image the distribution of bedaquiline in infected human macrophages at submicrometer resolution. Bedaquiline accumulated primarily in host cell lipid droplets, but heterogeneously in mycobacteria within a variety of intracellular compartments. Furthermore, lipid droplets did not sequester antibiotic but constituted a transferable reservoir that enhanced antibacterial efficacy. Thus, strong lipid binding facilitated drug trafficking by host organelles to an intracellular target during antimicrobial treatment.

RDH1 suppresses adiposity by promoting brown adipose adaptation to fasting and re-feeding

RDH1 is one of the several enzymes that catalyze the first of the two reactions to convert retinol into all-trans-retinoic acid (atRA). Here, we show that Rdh1-null mice fed a low-fat diet gain more weight as adiposity (17% males, 13% females) than wild-type mice by 20 weeks old, despite neither consuming more calories nor decreasing activity. Glucose intolerance and insulin resistance develop following increased adiposity. Despite the increase in white fat pads, epididymal white adipose does not express Rdh1, nor does muscle. Brown adipose tissue (BAT) and liver express Rdh1 at relatively high levels compared to other tissues. Rdh1 ablation lowered body temperatures during ambient conditions. Given the decreased body temperature, we focused on BAT. A lack of differences in BAT adipogenic gene expression between Rdh1-null mice and wild-type mice, including Pparg, Prdm16, Zfp516 and Zfp521, indicated that the phenotype was not driven by brown adipose hyperplasia. Rather, Rdh1 ablation eliminated the increase in BAT atRA that occurs after re-feeding. This disruption of atRA homeostasis increased fatty acid uptake, but attenuated lipolysis in primary brown adipocytes, resulting in increased lipid content and larger lipid droplets. Rdh1 ablation also decreased mitochondrial proteins, including CYCS and UCP1, the mitochondria oxygen consumption rate, and disrupted the mitochondria membrane potential, further reflecting impaired BAT function, resulting in both BAT and white adipose hypertrophy. RNAseq revealed dysregulation of 424 BAT genes in null mice, which segregated predominantly into differences after fasting vs after re-feeding. Exceptions were Rbp4 and Gbp2b, which increased during both dietary conditions. Rbp4 encodes the serum retinol-binding protein-an insulin desensitizer. Gbp2b encodes a GTPase. Because Gbp2b increased several hundred-fold, we overexpressed it in brown adipocytes. This caused a shift to larger lipid droplets, suggesting that GBP2b affects signaling downstream of the β-adrenergic receptor during basal thermogenesis. Thus, Rdh1-generated atRA in BAT regulates multiple genes that promote BAT adaptation to whole-body energy status, such as fasting and re-feeding. These gene expression changes promote optimum mitochondria function and thermogenesis, limiting adiposity. Attenuation of adiposity and insulin resistance suggests that RDH1 mitigates metabolic syndrome.

Capsaicin Targets Lipogenesis in HepG2 Cells Through AMPK Activation, AKT Inhibition and PPARs Regulation

Obesity, a major risk factor for chronic diseases such as type 2 diabetes (T2D), represents a serious primary health problem worldwide. Dietary habits are of special interest to prevent and counteract the obesity and its associated metabolic disorders, including lipid steatosis. Capsaicin, a pungent compound of chili peppers, has been found to ameliorate diet-induced obesity in rodents and humans. The purpose of this study was to examine the effect of capsaicin on hepatic lipogenesis and to delineate the underlying signaling pathways involved, using HepG2 cells as an experimental model. Cellular neutral lipids, stained with BODIPY493/503, were quantified by flow cytometry, and the protein expression and activity were determined by immunoblotting. Capsaicin reduced basal neutral lipid content in HepG2 cells, as well that induced by troglitazone or by oleic acid. This effect of capsaicin was prevented by dorsomorphin and GW9662, pharmacological inhibitors of AMPK and PPARγ, respectively. In addition, capsaicin activated AMPK and inhibited the AKT/mTOR pathway, major regulators of hepatic lipogenesis. Furthermore, capsaicin blocked autophagy and increased PGC-1α protein. These results suggest that capsaicin behaves as an anti-lipogenic compound in HepG2 cells.

The Distinct Effects of Palmitic and Oleic Acid on Pancreatic Beta Cell Function: The Elucidation of Associated Mechanisms and Effector Molecules

In this study, we aimed to identify the mechanisms underlying the different effects of palmitic acid and oleic acid on human pancreatic beta cell function. To address this problem, the oxidative stress, endoplasmic reticulum stress, inflammation, apoptosis and their mediator molecules have been investigated in the insulin releasing beta cells exposed to palmitic and/or oleic acid. Herein, we have demonstrated that in cultured 1.1B4 beta cells oleic acid promotes neutral lipid accumulation and insulin secretion, whereas palmitic acid is poorly incorporated into triglyceride and it does not stimulate insulin secretion from human pancreatic islets at physiologically glucose concentrations. In addition, palmitic acid caused: (1) oxidative stress through a mechanism involving increases in ROS production and MMP-2 protein expression/gelatinolytic activity associated with down-regulation of SOD2 protein; (2) endoplasmic reticulum stress by up-regulation of chaperone BiP protein and unfolded protein response (UPR) transcription factors (eIF2α, ATF6, XBP1u proteins) and by PTP-1B down-regulation in both mRNA and protein levels; (3) inflammation through enhanced synthesis of proinflammatory cytokines (IL6, IL8 proteins); and (4) apoptosis by enforced proteic expression of CHOP multifunctional transcription factor. Oleic acid alone had opposite effects due to its different capacity of controlling these metabolic pathways, in particular by reduction of the ROS levels and MMP-2 activity, down-regulation of BiP, eIF2α, ATF6, XBP1u, CHOP, IL6, IL8 and by SOD2 and PTP-1B overexpression. The supplementation of saturated palmitic acid with the monounsaturated oleic acid reversed the negative effects of palmitic acid alone regulating insulin secretion from pancreatic beta cells through ROS, MMP-2, ATF6, XBP1u, IL8 reduction and SOD2, PTP-1B activation. Our findings have shown the protective action of oleic acid against palmitic acid on beta cell lipotoxicity through promotion of triglyceride accumulation and insulin secretion and regulation of some effector molecules involved in oxidative stress, endoplasmic reticulum stress, inflammation and apoptosis.

Monitoring Lipid Droplet Dynamics in Living Cells by Using Fluorescent Probes

We have developed three types of lipid droplet (LD)-specific fluorescent probes for live-cell imaging, Lipi-Blue, Lipi-Green, and Lipi-Red, which exhibit fluorescence upon being incorporated into LDs both of living and of fixed cells. These Lipi-probes are LD-specific probes that contain a pyrene or perylene group as a fluorescent scaffold and can be used to observe dynamics of LD in live cells and also interrelations with other organelles by simultaneous staining with multiple organelle-specific probes. Additionally, Lipi-Blue and Lipi-Green allow monitoring LDs in live cells even for 48 h after the staining. Here we show that newly formed LDs and previously existed LDs can be separately monitored in a single cell by using these probes and that intercellular transfer of whole LDs is observed in KB cells, but not in HepG2 cells under the same culturing condition. These findings indicate that newly developed LD-specific probes are useful to analyze the dynamics of LDs in live cells.

The long noncoding RNA CHROME regulates cholesterol homeostasis in primate

The human genome encodes thousands of long non-coding RNAs (lncRNAs), the majority of which are poorly conserved and uncharacterized. Here we identify a primate-specific lncRNA (CHROME), elevated in the plasma and atherosclerotic plaques of individuals with coronary artery disease, that regulates cellular and systemic cholesterol homeostasis. LncRNA CHROME expression is influenced by dietary and cellular cholesterol via the sterol-activated liver X receptor transcription factors, which control genes mediating responses to cholesterol overload. Using gain- and loss-of-function approaches, we show that CHROME promotes cholesterol efflux and HDL biogenesis by curbing the actions of a set of functionally related microRNAs that repress genes in those pathways. CHROME knockdown in human hepatocytes and macrophages increases levels of miR-27b, miR-33a, miR-33b and miR-128, thereby reducing expression of their overlapping target gene networks and associated biologic functions. In particular, cells lacking CHROME show reduced expression of ABCA1, which regulates cholesterol efflux and nascent HDL particle formation. Collectively, our findings identify CHROME as a central component of the non-coding RNA circuitry controlling cholesterol homeostasis in humans.

Tumor suppressor RARRES1- A novel regulator of fatty acid metabolism in epithelial cells

Retinoic acid receptor responder 1 (RARRES1) is silenced in many cancers and is differentially expressed in metabolism associated diseases, such as hepatic steatosis, hyperinsulinemia and obesity. Here we report a novel function of RARRES1 in metabolic reprogramming of epithelial cells. Using non-targeted LC-MS, we discovered that RARRES1 depletion in epithelial cells caused a global increase in lipid synthesis. RARRES1-depleted cells rewire glucose metabolism by switching from aerobic glycolysis to glucose-dependent de novo lipogenesis (DNL). Treatment with fatty acid synthase (FASN) inhibitor, C75, reversed the effects of RARRES1 depletion. The increased DNL in RARRES1-depleted normal breast and prostate epithelial cells proved advantageous to the cells during starvation, as the increase in fatty acid availability lead to more oxidized fatty acids (FAO), which were used for mitochondrial respiration. Expression of RARRES1 in several common solid tumors is also contextually correlated with expression of fatty acid metabolism genes and fatty acid-regulated transcription factors. Pathway enrichment analysis led us to determine that RARRES1 is regulated by peroxisome proliferating activated receptor (PPAR) signaling. These findings open up a new avenue for metabolic reprogramming and identify RARRES1 as a potential target for cancers and other diseases with impaired fatty acid metabolism.

Recent Advances in Fluorescent Probes for Lipid Droplets

Lipid droplets (LDs) are organelles that serve as the storage of intracellular neutral lipids. LDs regulate many physiological processes. They recently attracted attention after extensive studies showed their involvement in metabolic disorders and diseases such as obesity, diabetes, and cancer. Therefore, it is of the highest importance to have reliable imaging tools. In this review, we focus on recent advances in the development of selective fluorescent probes for LDs. Their photophysical properties are described, and their advantages and drawbacks in fluorescence imaging are discussed. At last, we review the reported applications using these probes including two-photon excitation, in vivo and tissue imaging, as well as LDs tracking.

Inactivation of autophagy leads to changes in sebaceous gland morphology and function

We have reported recently that inactivation of the essential autophagy-related gene 7 (Atg7) in keratinocytes has little or no impact on morphology and function of the epidermal barrier in experimental animals. When these mice aged, mutant males, (Atg7 ΔKC), developed an oily coat. As the keratin 14 promoter driven cre/LoxP system inactivates floxed Atg7 in all keratin 14 (K14) expressing cells, including sebocytes, we investigated whether the oily hair phenotype was the consequence of changes in function of the skin sebaceous glands. Using an antibody to the GFP-LC3 fusion protein, autophagosomes were detected at the border of sebocyte disintegration in control but not in mutant animals, suggesting that autophagy was (a) active in normal sebaceous glands and (b) was inactivated in the mutant mice. Detailed analysis established that dorsal sebaceous glands were about twice as large in all Atg7 ΔKC mice compared to those of controls (Atg7 F/F), and their rate of sebocyte proliferation was increased. In addition, male mutant mice yielded twice as much lipid per unit hair as age-matched controls. Analysis of sebum lipids by thin layer chromatography revealed a 40% reduction in the proportion of free fatty acids (FFA) and cholesterol, and a 5-fold increase in the proportion of fatty acid methyl esters (FAME). In addition, the most common diester wax species (58-60 carbon atoms) were increased, while shorter species (54-55 carbon atoms) were under-represented in mutant sebum. Our data show that autophagy contributes to sebaceous gland function and to the control of sebum composition.

Autophagy gene overexpression in Saccharomyces cerevisiae perturbs subcellular organellar function and accumulates ROS to accelerate cell death with relevance to sparkling wine production

Traditional sparkling wines are produced by the refermentation of a base wine with yeast in the bottle followed by a critical period of aging. During the often lengthy aging process, yeast undergoes cell death and autolysis to release cellular compounds that over time ultimately contribute to the flavor and appearance of the product. While accelerating yeast autolysis for sparkling wine production has been the focus of several studies, employing overexpressed native yeast alleles for this purpose remains poorly explored. Here, we show that the overexpression of native yeast genes, specifically selected autophagic genes, results in accelerated cell death in nitrogen starvation and base wine refermentation. We show ATG3 or ATG4 overexpression has pleiotropic intracellular ramifications including reduced turnover of autophagic cargo, vacuolar fragmentation, abnormal accumulation of lipids, and accelerated accumulation of reactive oxygen species (ROS), all of which precede accelerated cell death. Our findings suggest that the increased expression of autophagy-related genes, such as ATG3 and ATG4, in industrial wine yeast can serve as a suitable marker or breeding strategy to accelerate the cell death and autolysis of wine yeast during sparkling wine production.

Energy metabolic capacities of human adipose-derived mesenchymal stromal cells in vitro and their adaptations in osteogenic and adipogenic differentiation

Mesenchymal stromal/stem cells (MSC) are important in tissue homeostasis and regeneration due to their ability for self-renewal and multipotent differentiation. Differentiation, as well as proliferation, requires adaptations in the cell metabolism. However, only few data exist concerning the energy metabolism of non-differentiating and differentiating MSC. In this study we compared capacities of major energy metabolic pathways of MSC from human adipose tissue (adMSC) in vitro in the non-differentiated state with those of osteogenically or adipogenically differentiating adMSC. To this end we quantified the proliferation and differentiation status of adMSC and analyzed maximum enzyme capacities and several enzyme isoforms of major energy metabolic pathways regarding their activity and gene expression. We could show that non-differentiating and osteogenic cultivation conditions induced proliferation and showed increasing capacities of the glycolytic marker enzyme phosphofructokinase as well as the marker enzyme of the pentose phosphate pathway glucose-6-phosphate dehydrogenase. Adipogenic stimulation, which was accompanied by the absence of proliferation, reduced the glycolytic capacity (e.g. decreased glyceraldehyde 3-phosphate dehydrogenase capacity) and induced an increase in mitochondrial enzyme capacities. These changes in energy metabolism might represent an adaptation of adMSC to the high energy demand during proliferation and to the specific cellular functions during osteogenic or adipogenic differentiation respectively.

Impact of delipidated estrous sheep serum supplementation on in vitro maturation, cryotolerance and endoplasmic reticulum stress gene expression of sheep oocytes

High lipid content of oocytes and embryos in domestic animals is one of the well-known factors associated with poor cryosurvival. Herein, we wanted to determine whether the use of delipidated estrous sheep serum during in vitro maturation (IVM) of ovine oocytes reduces the cytoplasmic lipid droplets content and improves embryo development and cryotolerance after vitrification. Cumulus oocytes complexes (COCs) were matured in vitro for 24 h in medium supplemented with whole or delipidated estrous sheep serum prior to vitrification. Neutral lipid present in lipid droplets of COCs, cleavage rate, embryo development rate on Day 6 and Day 8, and hatching rate on Day 8, were compared among experimental groups. Endoplasmic reticulum stress genes were evaluated in in vitro matured COCs under different lipid conditions prior to vitrification. The lipid droplets’ content (mean fluorescence intensity) of oocytes cultured with IVM media supplemented with delipidated serum was lower than COCs matured with whole serum (7.6 ± 1.7 vs. 22.8 ± 5.0 arbitrary units, respectively; P< 0.05). Despite IVM treatment, oocytes subjected to vitrification showed impaired competence compared with the non-vitrified groups (P<0.05). No significant differences in embryo production were observed in non-vitrified COCs after maturation in delipidated or whole serum (33.4±4.9 vs 31.9 ±4.2). COCs matured in delipidated serum and subjected to vitrification showed increased expression of ATF4, ATF6, GRP78, and CHOP10 genes (ER stress markers). Collectively, our results demonstrate that although supplementation of IVM medium with delipidated estrous sheep serum reduces the presence of cytoplasmic lipid droplets in oocytes after maturation, oocyte cryotolerance is not improved. Notably, the expression of genes associated with the unfolded protein response (UPR) was increased in COCs, with fewer lipid droplets subjected to vitrification, suggesting that oocyte cryopreservation is associated with ER stress and activation of adaptive responses.