Fluorescent high-content imaging allows the discrimination and quantitation of E-LDL-induced lipid droplets and Ox-LDL-generated phospholipidosis in human macrophages

Two protocols for the detection of oleaginous bacteria using Oil Red O

The selection of oleaginous bacteria, potentially applicable to biotechnological approaches, is usually carried out by different expensive and time-consuming techniques. In this study, we used Oil Red O (ORO) as an useful dye for staining of neutral lipids (triacylglycerols and wax esters) on thin-layer chromatography plates. ORO could detect minimal quantities of both compounds (detection limit, 0.0025 mg of tripalmitin or 0.005 mg of cetylpalmitate). In addition, we developed a specific, rapid, and inexpensive screening methodology to detect triacylglycerol-accumulating microorganisms grown on the agar plate. This staining methodology detected 9/13 strains with a triacylglycerol content higher than 20% by cellular dry weight. ORO did not stain polyhydroxyalkanoates-producing bacteria. The four oleaginous strains not detected by this screening methodology exhibited a mucoid morphology of their colonies. Apparently, an extracellular polymeric substance produced by these strains hampered the entry of the lipophilic dye into cells. The utilization of the developed screening methodology would allow selecting of oleaginous bacteria in a simpler and faster way than techniques usually used nowadays, based on unspecific staining protocols and spectrophotometric or chromatographic methods. Furthermore, the use of ORO as a staining reagent would easily characterize the neutral lipids accumulated by microorganisms as reserve compounds. KEY POINTS: • Oil Red O staining is specific for triacylglycerols • Oil Red O staining is useful to detect oleaginous bacteria • Fast and inexpensive staining to isolate oleaginous bacteria from the environment.

Beneficial Effects of Carvacrol on In Vitro Models of Metabolically-Associated Liver Steatosis and Endothelial Dysfunction: A Role for Fatty Acids in Interfering with Carvacrol Binding to Serum Albumin

Background:

Carvacrol, a plant phenolic monoterpene, is largely employed as food additive and phytochemical.

Objective:

We aimed to assess the lipid lowering and protective effects of carvacrol in vitro using cellular models of hepatic steatosis and endothelial dysfunction. We also investigated if and how the binding of carvacrol to albumin, the physiological transporter for small compounds in the blood, might be altered by the presence of high levels of fatty acids (FAs).

Methods:

Hepatic FaO cells treated with exogenous FAs mimic hepatosteatosis; endothelial HECV cells exposed to hydrogen peroxide are a model of endothelial dysfunction. In these models, we measured spectrophotometrically lipid accumulation and release, lipoperoxidation, free radical production, and nitric oxide release before and after treatment with carvacrol. The carvacrol binding to albumin in the presence or absence of high levels of FAs was assessed by absorption and emission spectroscopies.

Results:

Carvacrol counteracted lipid accumulation and oxidative stress in hepatocytes and protected endothelial cells from oxidative stress and dysfunction. Moreover, high levels of FAs reduced the binding of carvacrol to albumin.

Conclusion:

The results suggest the good potential of carvacrol in ameliorating dysfunction of hepatic and endothelial cells in vitro. High levels of circulating FAs might compete with carvacrol for binding to albumin thus influencing its transport and bio-distribution.

Synthesis, Photoisomerization, Antioxidant Activity, and Lipid-Lowering Effect of Ferulic Acid and Feruloyl Amides

The Ugi four-component reaction employing naturally occurred ferulic acid (FA) is proposed as a convenient method to synthesize feruloyl tertiary amides. Applying this strategy, a peptoid-like derivative of ferulic acid (FEF77) containing 2 additional hydroxy-substituted aryl groups, has been synthesized. The influence of the configuration of the double bond of ferulic acid and feruloyl amide on the antioxidant activity has been investigated thanks to light-mediated isomerization studies. At the cellular level, both FA, trans and cis isomers of FEF77 were able to protect human endothelial cord vein (HECV) cells from the oxidative damage induced by exposure to hydrogen peroxide, as measured by cell viability and ROS production assays. Moreover, in steatotic FaO rat hepatoma cells, an in vitro model resembling non-alcoholic fatty liver disease (NAFLD), the molecules exhibited a lipid-lowering effect, which, along with the antioxidant properties, points to consider feruloyl amides for further investigations in a therapeutic perspective.

Different Sensitivity of Macrophages to Phospholipidosis Induction by Amphiphilic Cationic Drugs

Phospholipidosis (PLD), the intracellular accumulation of phospholipids, is an adaptive response to toxic stimuli and serves as an important parameter in the biological assessment of compounds. Cationic amphiphilic drugs are the main inducers of PLD and may impair the function of alveolar macrophages. In vivo and in vitro models are used for PLD screening but the choice of the cellular model may be important because PLD develops in a cell- and species-specific manner. In this study, a panel of different staining (LysoSensor, Acridine Orange, Nile Red, HCS LipidTOX, LysoID) was evaluated in murine (DMBM-2, J774, RAW264.7) and human (THP-1, monocyte-derived macrophages from peripheral blood) cells to identify the most sensitive and easy to analyze staining method and to detect species-specific differences in the reaction pattern. Amiodarone and chloroquine served as inducers of PLD. High content screening was used to compare number, area, and intensity of the staining. Due to the fast staining protocol and the sensitivity of the detection, LysoID proved to be the most suitable dye of the testing. The lower induction of PLD by chloroquine reported in vivo was also seen in this study. THP-1 macrophages, followed by DMBM-2 cells, produced the most similar reaction pattern to human monocyte-derived macrophages.

Smooth Muscle Cells Contribute the Majority of Foam Cells in ApoE (Apolipoprotein E)-Deficient Mouse Atherosclerosis

Objective- Smooth muscle cells (SMCs) are the most abundant cells in human atherosclerotic lesions and are suggested to contribute at least 50% of atheroma foam cells. In mice, SMCs contribute fewer total lesional cells. The purpose of this study was to determine the contribution of SMCs to total foam cells in apolipoprotein E-deficient (ApoE^-/-) mice, and the utility of these mice to model human SMC foam cell biology and interventions. Approach and Results- Using flow cytometry, foam cells in the aortic arch of ApoE^-/- mice were characterized based on the expression of leukocyte-specific markers. Nonleukocyte foam cells increased from 37% of total foam cells in 27-week-old to 75% in 57-week-old male ApoE^-/- mice fed a chow diet and were ≈70% in male and female ApoE^-/- mice following 6 weeks of Western diet feeding. A similar contribution to total foam cells by SMCs was found using SMC-lineage tracing ApoE^-/- mice fed the Western diet for 6 or 12 weeks. Nonleukocyte foam cells contributed a similar percentage of total atheroma cholesterol and exhibited lower expression of the cholesterol exporter ABCA1 (ATP-binding cassette transporter A1) when compared with leukocyte-derived foam cells. Conclusions- Consistent with previous studies of human atheromas, we present evidence that SMCs contribute the majority of atheroma foam cells in ApoE^-/- mice fed a Western diet and a chow diet for longer periods. Reduced expression of ABCA1, also seen in human intimal SMCs, suggests a common mechanism for formation of SMC foam cells across species, and represents a novel target to enhance atherosclerosis regression.

Cholesterol sulfate alters astrocyte metabolism and provides protection against oxidative stress

Cholesterol sulfate (CS) is one of the most important known sterol sulfates in human plasma and it is present as a normal constituent in a variety of human tissues. In both the brain and periphery, CS serves as a substrate for the synthesis of sulfonated adrenal steroids such as pregnenolone sulfate and dehydroepiandrosterone (DHEA) sulfate and as a constituent of many biological membranes including red blood cells where it functions as a stabilizing agent. It also acts as an endogenous regulator of cholesterol synthesis. However, the role of CS in brain metabolism and neurological disorder is unclear. In the current study we investigated the neuroprotective action of CS as well as its role in brain energy metabolism. The neuroprotective effect of CS and its role on cell metabolism were determined in primary astrocyte prepared from the cortex of postnatal day 0-2 C57BL/6 pups and a hippocampal HT-22 cell line using Calcein AM and MTT cell viability assay, flow cytometry, Seahorse extracellular flux analysis, and metabolism assay kits. We found that CS attenuates glutamate and rotenone induced cell death in HT-22 cells, decrease glutamate induced mitochondria membrane potential collapse, and reactive oxygen species production. Additionally, CS activates the Akt/Bcl₂ pathway. We observed that CS impacts astrocyte metabolism by increasing mitochondrial phosphorylation, ATP, and glycogen contents. Our study demonstrated that CS modulates brain energy metabolism and its neuroprotective effects might be due to the activation of Akt signaling or its ability to decrease reactive oxygen species production.

Association of tamoxifen resistance and lipid reprogramming in breast cancer

Background

Tamoxifen treatment of estrogen receptor (ER)-positive breast cancer reduces mortality by 31%. However, over half of advanced ER-positive breast cancers are intrinsically resistant to tamoxifen and about 40% will acquire the resistance during the treatment.

Methods

In order to explore mechanisms underlying endocrine therapy resistance in breast cancer and to identify new therapeutic opportunities, we created tamoxifen-resistant breast cancer cell lines that represent the luminal A or the luminal B. Gene expression patterns revealed by RNA-sequencing in seven tamoxifen-resistant variants were compared with their isogenic parental cells. We further examined those transcriptomic alterations in a publicly available patient cohort.

Results

We show that tamoxifen resistance cannot simply be explained by altered expression of individual genes, common mechanism across all resistant variants, or the appearance of new fusion genes. Instead, the resistant cell lines shared altered gene expression patterns associated with cell cycle, protein modification and metabolism, especially with the cholesterol pathway. In the tamoxifen-resistant T-47D cell variants we observed a striking increase of neutral lipids in lipid droplets as well as an accumulation of free cholesterol in the lysosomes. Tamoxifen-resistant cells were also less prone to lysosomal membrane permeabilization (LMP) and not vulnerable to compounds targeting the lipid metabolism. However, the cells were sensitive to disulfiram, LCS-1, and dasatinib.

Conclusion

Altogether, our findings highlight a major role of LMP prevention in tamoxifen resistance, and suggest novel drug vulnerabilities associated with this phenotype.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4757-z) contains supplementary material, which is available to authorized users.

Ratiometric Raman imaging reveals the new anti-cancer potential of lipid targeting drugs

De novo lipid synthesis is upregulated in cancer cells and inhibiting these pathways has displayed anti-tumour activity. Here we use Raman spectroscopy, focusing solely on high wavenumber spectra, to detect changes in lipid composition in single cells in response to drugs targeting de novo lipid synthesis. Unexpectedly, the beta-blocker propranolol showed selectively towards cancerous PC3 compared to non-cancerous PNT2 prostate cells, demonstrating the potential of this approach to identify new anti-cancer drug leads. A unique and simple ratiometric approach for intracellular lipid investigation is reported using statistical analysis to create phenotypic 'barcodes', a globally applicable strategy for Raman drug-cell studies. High wavenumber spectral analysis is compatible with low cost glass substrates, easily translatable into the cytological work stream. The analytical strength of this technique could have a significant impact on cancer treatment through vastly improved understanding of cancer cell metabolism, and thus guide drug design and enhance personalised medicine strategies.

Effects of chlorogenic acid on intracellular calcium regulation in lysophosphatidylcholine-treated endothelial cells

Lysophosphatidylcholine (LPC) is a major phospholipid component of oxidized low-density lipoprotein (ox-LDL) and is implicated in its atherogenic activity. This study investigated the effects of LPC on cell viability, intracellular calcium homeostasis, and the protective mechanisms of chlorogenic acid (CGA) in human umbilical vein endothelial cells (HUVECs). LPC increased intracellular calcium ([Ca²⁺]_i) by releasing Ca²⁺ from intracellular stores and via Ca²⁺ influx through store-operated channels (SOCs). LPC also increased the generation of reactive oxygen species (ROS) and decreased cell viability. The mRNA expression of Transient receptor potential canonical (TRPC) channel 1 was increased significantly by LPC treatment and suppressed by CGA. CGA inhibited LPC-induced Ca²⁺ influx and ROS generation, and restored cell viability. These results suggested that CGA inhibits SOC-mediated Ca²⁺ influx and ROS generation by attenuating TRPC1 expression in LPC-treated HUVECs. Therefore, CGA might protect endothelial cells against LPC injury, thereby inhibiting atherosclerosis.

The Nutraceutic Silybin Counteracts Excess Lipid Accumulation and Ongoing Oxidative Stress in an In Vitro Model of Non-Alcoholic Fatty Liver Disease Progression

Non-alcoholic fatty liver disease (NAFLD) is a major cause of liver-related morbidity and mortality. Oxidative stress and release of pro-inflammatory cytokines, such as tumor necrosis factor α (TNFα), are major consequences of hepatic lipid overload, which can contribute to progression of NAFLD to non-alcoholic steatohepatitis (NASH). Also, mitochondria are involved in the NAFLD pathogenesis for their role in hepatic lipid metabolism. Definitive treatments for NAFLD/NASH are lacking so far. Silybin, the extract of the milk thistle seeds, has previously shown beneficial effects in NAFLD. Sequential exposure of hepatocytes to high concentrations of fatty acids (FAs) and TNFα resulted in fat overload and oxidative stress, which mimic in vitro the progression of NAFLD from simple steatosis (SS) to steatohepatitis (SH). The exposure to 50 µM silybin for 24 h reduced fat accumulation in the model of NAFLD progression. The in vitro progression of NAFLD from SS to SH resulted in reduced hepatocyte viability, increased apoptosis and oxidative stress, reduction in lipid droplet size, and up-regulation of IκB kinase β-interacting protein and adipose triglyceride lipase expressions. The direct action of silybin on SS or SH cells and the underlying mechanisms were assessed. Beneficial action of silybin was sustained by changes in expression/activity of peroxisome proliferator-activated receptors and enzymes for FA oxidation. Moreover, silybin counteracted the FA-induced mitochondrial damage by acting on complementary pathways: (i) increased the mitochondrial size and improved the mitochondrial cristae organization; (ii) stimulated mitochondrial FA oxidation; (iii) reduced basal and maximal respiration and ATP production in SH cells; (iv) stimulated ATP production in SS cells; and (v) rescued the FA-induced apoptotic signals and oxidative stress in SH cells. We provide new insights about the direct protective effects of the nutraceutic silybin on hepatocytes mimicking in vitro NAFLD progression.

Metabolic injury-induced NLRP3 inflammasome activation dampens phospholipid degradation

The collateral effects of obesity/metabolic syndrome include inflammation and renal function decline. As renal disease in obesity can occur independently of hypertension and diabetes, other yet undefined causal pathological pathways must be present. Our study elucidate novel pathological pathways of metabolic renal injury through LDL-induced lipotoxicity and metainflammation. Our in vitro and in vivo analysis revealed a direct lipotoxic effect of metabolic overloading on tubular renal cells through a multifaceted mechanism that includes intralysosomal lipid amassing, lysosomal dysfunction, oxidative stress, and tubular dysfunction. The combination of these endogenous metabolic injuries culminated in the activation of the innate immune NLRP3 inflammasome complex. By inhibiting the sirtuin-1/LKB1/AMPK pathway, NLRP3 inflammasome dampened lipid breakdown, thereby worsening the LDL-induced intratubular phospholipid accumulation. Consequently, the presence of NLRP3 exacerbated tubular oxidative stress, mitochondrial damage and malabsorption during overnutrition. Altogether, our data demonstrate a causal link between LDL and tubular damage and the creation of a vicious cycle of excessive nutrients-NLRP3 activation-catabolism inhibition during metabolic kidney injury. Hence, this study strongly highlights the importance of renal epithelium in lipid handling and recognizes the role of NLRP3 as a central hub in metainflammation and immunometabolism in parenchymal non-immune cells.

oxLDL and eLDL Induced Membrane Microdomains in Human Macrophages

Background

Extravasation of macrophages and formation of lipid-laden foam cells are key events in the development and progression of atherosclerosis. The degradation of atherogenic lipoproteins subsequently leads to alterations in cellular lipid metabolism that influence inflammatory signaling. Especially sphingolipids and ceramides are known to be involved in these processes. We therefore analyzed monocyte derived macrophages during differentiation and after loading with enzymatically (eLDL) and oxidatively (oxLDL) modified low-density lipoproteins (LDL).

Methods

Primary human monocytes were isolated from healthy, normolipidemic blood donors using leukapheresis and counterflow elutriation. On the fourth day of MCSF-induced differentiation eLDL (40 μg/ml) or oxLDL (80 μg/ml) were added for 48h. Lipid species were analyzed by quantitative tandem mass spectrometry. Taqman qPCR was performed to investigate transcriptional changes in enzymes involved in sphingolipid metabolism. Furthermore, membrane lipids were studied using flow cytometry and confocal microscopy.

Results

MCSF dependent phagocytic differentiation of blood monocytes had only minor effects on the sphingolipid composition. Levels of total sphingomyelin and total ceramide remained unchanged, while lactosylceramides, cholesterylesters and free cholesterol decreased. At the species level most ceramide species showed a reduction upon phagocytic differentiation. Loading with eLDL preferentially increased cellular cholesterol while loading with oxLDL increased cellular ceramide content. Activation of the salvage pathway with a higher mRNA expression of acid and neutral sphingomyelinase, neutral sphingomyelinase activation associated factor and glucosylceramidase as well as increased surface expression of SMPD1 were identified as potentially underlying mechanisms. Moreover, flow-cytometric analysis revealed a higher cell-surface-expression of ceramide, lactosylceramide (CDw17), globotriaosylceramide (CD77), dodecasaccharide-ceramide (CD65s) and GM1 ganglioside upon oxLDL loading. ApoE in contrast to apoA-I preferentially bound to the ceramide enriched surfaces of oxLDL loaded cells. Confocal microscopy showed a co-localization of acid sphingomyelinase with ceramide rich membrane microdomains.

Conclusion

eLDL leads to the formation of lipid droplets and preferentially induces cholesterol/sphingomyelin rich membrane microdomains while oxLDL promotes the development of cholesterol/ceramide rich microdomains via activation of the salvage pathway.

Novel flow cytometric approach for the detection of adipocyte subpopulations during adipogenesis

The ability of mesenchymal stromal cells (MSCs) to differentiate into adipocytes provides a cellular model of human origin to study adipogenesis in vitro. One of the major challenges in studying adipogenesis is the lack of tools to identify and monitor the differentiation of various subpopulations within the heterogeneous pool of MSCs. Cluster of differentiation (CD)36 plays an important role in the formation of intracellular lipid droplets, a key characteristic of adipocyte differentiation/maturation. The objective of this study was to develop a reproducible quantitative method to study adipocyte differentiation by comparing two lipophilic dyes [Nile Red (NR) and Bodipy 493/503] in combination with CD36 surface marker staining. We identified a subpopulation of adipose-derived stromal cells that express CD36 at intermediate/high levels and show that combining CD36 cell surface staining with neutral lipid-specific staining allows us to monitor differentiation of adipose-derived stromal cells that express CD36^{intermediate/high} during adipocyte differentiation in vitro. The gradual increase of CD36^{intermediate/high/}NR^positive cells during the 21 day adipogenesis induction period correlated with upregulation of adipogenesis-associated gene expression.

YC-1 induces lipid droplet formation in RAW 264.7 macrophages

BACKGROUND

3-(5'-Hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1) is a potential anticancer drug that may activate soluble guanylyl cyclase (sGC) and increase the level of cyclic guanosine monophosphate (cGMP). The aim of this study was to explore the effects of YC-1 on lipid droplet accumulation and foam cell formation in macrophages.

RESULTS

Human-oxidized low density lipoprotein (ox-LDL) was used to induce accumulation of lipid droplets in a murine macrophage cell line, RAW 264.7. Oil red O staining showed that treatment with 20 μM YC-1 for 24 h increased the area of intracellular lipid droplets in macrophages. The results of high content screening (HCS) with the AdipoRed™ assay further revealed that YC-1 enhanced ox-LDL-induced foam cell formation. This was evidenced by an increase in the total area of lipid droplets and the mean fluorescence intensity per cell. Inhibition of cGMP-dependent protein kinase (PKG) using KT5823 significantly reduced YC-1-enhanced lipid droplet formation in ox-LDL-induced macrophage foam cells.

CONCLUSION

YC-1 induces lipid droplet formation in macrophages, possibly through the sGC/cGMP/PKG signaling pathway. This chemical should be tested with caution in future clinical trials.

In Situ Characterization of Splenic Brucella melitensis Reservoir Cells during the Chronic Phase of Infection in Susceptible Mice

Brucella are facultative intracellular Gram-negative coccobacilli that chronically infect humans as well as domestic and wild-type mammals, and cause brucellosis. Alternatively activated macrophages (M2a) induced by IL-4/IL-13 via STAT6 signaling pathways have been frequently described as a favorable niche for long-term persistence of intracellular pathogens. Based on the observation that M2a-like macrophages are induced in the spleen during the chronic phase of B. abortus infection in mice and are strongly infected in vitro, it has been suggested that M2a macrophages could be a potential in vivo niche for Brucella. In order to test this hypothesis, we used a model in which infected cells can be observed directly in situ and where the differentiation of M2a macrophages is favored by the absence of an IL-12-dependent Th1 response. We performed an in situ analysis by fluorescent microscopy of the phenotype of B. melitensis infected spleen cells from intranasally infected IL-12p40^-/- BALB/c mice and the impact of STAT6 deficiency on this phenotype. Most of the infected spleen cells contained high levels of lipids and expressed CD11c and CD205 dendritic cell markers and Arginase1, but were negative for the M2a markers Fizz1 or CD301. Furthermore, STAT6 deficiency had no effect on bacterial growth or the reservoir cell phenotype in vivo, leading us to conclude that, in our model, the infected cells were not Th2-induced M2a macrophages. This characterization of B. melitensis reservoir cells could provide a better understanding of Brucella persistence in the host and lead to the design of more efficient therapeutic strategies.

Apoc2 loss-of-function zebrafish mutant as a genetic model of hyperlipidemia

Apolipoprotein C-II (APOC2) is an obligatory activator of lipoprotein lipase. Human patients with APOC2 deficiency display severe hypertriglyceridemia while consuming a normal diet, often manifesting xanthomas, lipemia retinalis and pancreatitis. Hypertriglyceridemia is also an important risk factor for development of cardiovascular disease. Animal models to study hypertriglyceridemia are limited, with no Apoc2-knockout mouse reported. To develop a genetic model of hypertriglyceridemia, we generated an apoc2 mutant zebrafish characterized by the loss of Apoc2 function. apoc2 mutants show decreased plasma lipase activity and display chylomicronemia and severe hypertriglyceridemia, which closely resemble the phenotype observed in human patients with APOC2 deficiency. The hypertriglyceridemia in apoc2 mutants is rescued by injection of plasma from wild-type zebrafish or by injection of a human APOC2 mimetic peptide. Consistent with a previous report of a transient apoc2 knockdown, apoc2 mutant larvae have a minor delay in yolk consumption and angiogenesis. Furthermore, apoc2 mutants fed a normal diet accumulate lipid and lipid-laden macrophages in the vasculature, which resemble early events in the development of human atherosclerotic lesions. In addition, apoc2 mutant embryos show ectopic overgrowth of pancreas. Taken together, our data suggest that the apoc2 mutant zebrafish is a robust and versatile animal model to study hypertriglyceridemia and the mechanisms involved in the pathogenesis of associated human diseases.

Highlighted Article: Apoc2 loss-of-function zebrafish display severe hypertriglyceridemia, which is characteristic of human patients with defective lipoprotein lipase activity.

Monocyte activation from interferon-α in HIV infection increases acetylated LDL uptake and ROS production

Atherosclerosis is an inflammatory disease that is accelerated in human immunodeficiency virus (HIV) infection. Individuals with HIV infection have an activated type I interferon (IFN) monocyte phenotype, which may enhance uptake of modified low-density lipoprotein (LDL) thereby initiating a prefoam cell pathology and recruitment into atherosclerotic plaques. In a sampling of HIV-infected subjects, an increase in monocyte activation genes, MX1 and CXCL10, correlated with monocyte expression of the scavenger receptor A (SR-A), a major receptor for lipid uptake and foam cell formation. Monocytes from HIV-infected subjects accumulated more lipid than control uninfected subjects. We modeled increased activation in HIV infection by priming human monocytes with IFNα followed by exposure to acetylated LDL (acLDL). Exposure to IFNα increased acLDL uptake, which generated increased cellular reactive oxygen species (ROS). We posit that HIV infection augments formation of arterial plaques by triggering monocyte activation with a type I IFN profile, which induces SR-A expression, lipid uptake, and subsequent ROS production. These findings may explain in part why HIV-infected individuals with chronic immune activation have an increased risk of atherosclerosis.

The evolutionarily conserved protein CG9186 is associated with lipid droplets, required for their positioning and for fat storage

Lipid droplets (LDs) are specialized cell organelles for the storage of energy-rich lipids. Although lipid storage is a conserved feature of all cells and organisms, little is known about fundamental aspects of the cell biology of LDs, including their biogenesis, structural assembly and subcellular positioning, and the regulation of organismic energy homeostasis. We identified a novel LD-associated protein family, represented by the Drosophila protein CG9186 and its murine homolog MGI:1916082. In the absence of LDs, both proteins localize at the endoplasmic reticulum (ER). Upon lipid storage induction, they translocate to LDs using an evolutionarily conserved targeting mechanism that acts through a 60-amino-acid targeting motif in the center of the CG9186 protein. Overexpression of CG9186, and MGI:1916082, causes clustering of LDs in both tissue culture and salivary gland cells, whereas RNAi knockdown of CG9186 results in a reduction of LDs. Organismal RNAi knockdown of CG9186 results in a reduction in lipid storage levels of the fly. The results indicate that we identified the first members of a novel and evolutionarily conserved family of lipid storage regulators, which are also required to properly position LDs within cells.

The mitochondrial H(+)-ATP synthase and the lipogenic switch: new core components of metabolic reprogramming in induced pluripotent stem (iPS) cells

Induced pluripotent stem (iPS) cells share some basic properties, such as self-renewal and pluripotency, with cancer cells, and they also appear to share several metabolic alterations that are commonly observed in human tumors. The cancer cells' glycolytic phenotype, first reported by Otto Warburg, is necessary for the optimal routing of somatic cells to pluripotency. However, how iPS cells establish a Warburg-like metabolic phenotype and whether the metabolic pathways that support the bioenergetics of iPS cells are produced by the same mechanisms that are selected during the tumorigenic process remain largely unexplored. We recently investigated whether the reprogramming-competent metabotype of iPS cells involves changes in the activation/expression status of the H(+)-ATPase, which is a core component of mitochondrial oxidative phosphorylation that is repressed at both the activity and protein levels in human carcinomas, and of the lipogenic switch, which refers to a marked overexpression and hyperactivity of the acetyl-CoA carboxylase (ACACA) and fatty acid synthase (FASN) lipogenic enzymes that has been observed in nearly all examined cancer types. A comparison of a starting population of mouse embryonic fibroblasts and their iPS cell progeny revealed that somatic cell reprogramming involves a significant increase in the expression of ATPase inhibitor factor 1 (IF1), accompanied by extremely low expression levels of the catalytic β-F1-ATPase subunit. The pharmacological inhibition of ACACA and FASN activities markedly decreases reprogramming efficiency, and ACACA and FASN expression are notably upregulated in iPS cells. Importantly, iPS cells exhibited a significant intracellular accumulation of neutral lipid bodies; however, these bodies may be a reflection of intense lysosomal/autophagocytic activity rather than bona fide lipid droplet formation in iPS cells, as they were largely unresponsive to pharmacological modulation of PPARgamma and FASN activities. The AMPK agonist metformin, which endows somatic cells with a bioenergetic infrastructure that is protected against reprogramming, was found to drastically elongate fibroblast mitochondria, fully reverse the high IF1/β-F1-ATPase ratio and downregulate the ACACA/FASN lipogenic enzymes in iPS cells. The mitochondrial H(+)-ATP synthase and the ACACA/FASN-driven lipogenic switch are newly characterized as instrumental metabolic events that, by coupling the Warburg effect to anabolic metabolism, enable de-differentiation during the reprogramming of somatic cells to iPS cells.

Transcriptomic signature of Leishmania infected mice macrophages: a metabolic point of view

We analyzed the transcriptional signatures of mouse bone marrow-derived macrophages at different times after infection with promastigotes of the protozoan parasite Leishmania major. Ingenuity Pathway Analysis revealed that the macrophage metabolic pathways including carbohydrate and lipid metabolisms were among the most altered pathways at later time points of infection. Indeed, L. major promastiogtes induced increased mRNA levels of the glucose transporter and almost all of the genes associated with glycolysis and lactate dehydrogenase, suggesting a shift to anaerobic glycolysis. On the other hand, L. major promastigotes enhanced the expression of scavenger receptors involved in the uptake of Low-Density Lipoprotein (LDL), inhibited the expression of genes coding for proteins regulating cholesterol efflux, and induced the synthesis of triacylglycerides. These data suggested that Leishmania infection disturbs cholesterol and triglycerides homeostasis and may lead to cholesterol accumulation and foam cell formation. Using Filipin and Bodipy staining, we showed cholesterol and triglycerides accumulation in infected macrophages. Moreover, Bodipy-positive lipid droplets accumulated in close proximity to parasitophorous vacuoles, suggesting that intracellular L. major may take advantage of these organelles as high-energy substrate sources. While the effect of infection on cholesterol accumulation and lipid droplet formation was independent on parasite development, our data indicate that anaerobic glycolysis is actively induced by L. major during the establishment of infection.

Leishmania are obligated intracellular pathogens that develop almost exclusively in macrophages. Experimental leishmaniasis in mice is one of the most extensively studied models of intracellular infections both at the level of the parasite and host immune responses. We took advantage of Balb/c mice model to investigate gene expression profile through Affymetrix oligonucleotide arrays. In order to have a general and dynamic picture of the complex biological events that are acting in the context of Leishmania intracellular parasitism, we investigated the mouse macrophage response to initial invasion of L. major over a time course that extended from one to 24 hours post-infection. Our results reveal the alteration of several biological processes and metabolic changes. Indeed, similarly to different other pathogens, Leishmania induces cholesterol accumulation and foam cell formation that have been confirmed by confocal microscopy experiments. Whether Leishmania parasites take advantage of this high-energy source is now under investigation. Our findings provided further understandings in host responses to Leishmania infection.

STARD4 abundance regulates sterol transport and sensing

The expression of a small sterol transport protein, STARD4, is regulated by cholesterol levels. We show that the abundance of STARD4 regulates the sensitivity of the SREBP-2 system to changes in cholesterol, providing an additional layer of regulation in the cholesterol homeostatic mechanism.

Nonvesicular transport of cholesterol plays an essential role in the distribution and regulation of cholesterol within cells, but it has been difficult to identify the key intracellular cholesterol transporters. The steroidogenic acute regulatory-related lipid-transfer (START) family of proteins is involved in several pathways of nonvesicular trafficking of sterols. Among them, STARD4 has been shown to increase intracellular cholesteryl ester formation and is controlled at the transcriptional level by sterol levels in cells. We found that STARD4 is very efficient in transporting sterol between membranes in vitro. Cholesterol levels are increased in STARD4-silenced cells, while sterol transport to the endocytic recycling compartment (ERC) and to the endoplasmic reticulum (ER) are enhanced upon STARD4 overexpression. STARD4 silencing attenuates cholesterol-mediated regulation of SREBP-2 activation, while its overexpression amplifies sterol sensing by SCAP/SREBP-2. To analyze STARD4's mode of action, we compared sterol transport mediated by STARD4 with that of a simple sterol carrier, methyl-β-cyclodextrin (MCD), when STARD4 and MCD were overexpressed or injected into cells. Interestingly, STARD4 and cytosolic MCD act similarly by increasing the rate of transfer of sterol to the ERC and to the ER. Our results suggest that cholesterol transport mediated by STARD4 is an important component of the cholesterol homeostasis regulatory machinery.

Small molecules targeting hepatitis C virus-encoded NS5A cause subcellular redistribution of their target: insights into compound modes of action

The current standard of care for hepatitis C virus (HCV)-infected patients consists of lengthy treatment with interferon and ribavirin. To increase the effectiveness of HCV therapy, future regimens will incorporate multiple direct-acting antiviral (DAA) drugs. Recently, the HCV-encoded NS5A protein has emerged as a promising DAA target. Compounds targeting NS5A exhibit remarkable potency in vitro and demonstrate early clinical promise, suggesting that NS5A inhibitors could feature in future DAA combination therapies. Since the mechanisms through which these molecules operate are unknown, we have used NS5A inhibitors as tools to investigate their modes of action. Analysis of replicon-containing cells revealed dramatic phenotypic alterations in NS5A localization following treatment with NS5A inhibitors; NS5A was redistributed from the endoplasmic reticulum to lipid droplets. The NS5A relocalization did not occur in cells treated with other classes of HCV inhibitors, and NS5A-targeting molecules did not cause similar alterations in the localization of other HCV-encoded proteins. Time course analysis of the redistribution of NS5A revealed that the transfer of protein to lipid droplets was concomitant with the onset of inhibition, as judged by the kinetic profiles for these compounds. Furthermore, analysis of the kinetic profile of inhibition for a panel of test molecules permitted the separation of compounds into different kinetic classes based on their modes of action. Results from this approach suggested that NS5A inhibitors perturbed the function of new replication complexes, rather than acting on preformed complexes. Taken together, our data reveal novel biological consequences of NS5A inhibition, which may help enable the development of future assay platforms for the identification of new and/or different NS5A inhibitors.