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hGX-induced LD accumulation is associated with activation of AMPKα. (A) MDA-MB-231 cells were treated with OA (100 μM) and hGX (1 nM) in complete culture medium for 48 h in the presence of etomoxir (Eto; 20 μM), triacsin C (TrC; 2 μM), AICAR (500 μM) or bezafibrate (Bez; 500 μM). Free OA was incubated in complete culture medium for 1 h before addition to the cells. Cell lysates were analyzed for the presence of Thr172-phosphorylated AMPKα (p-AMPKα), total AMPKα and β-actin loading control by immunoblotting and densitometry. The amounts of p-AMPKα obtained from three separate experiments were normalized to total AMPKα protein levels and quantified relative to untreated controls (B). (C) Cells were treated as in (A). Prolonged incubation (48 h) of proliferating MDA-MB-231 cells with AICAR (500 μM) abolished the hGX-induced (1 nM) LD formation. Cellular LD content was determined by Nile red staining. (D, E) Serum-starved MDA-MB-231 cells were treated with hGX (10 nM) in serum-free medium containing 0.02% FAF BSA for 96 h in the presence or absence of AICAR (500 μM). After 96 h, cellular LD content was determined by Nile red staining, showing that AICAR prevented hGX-induced LD formation (D). Cell survival was assessed with the TMRM/YO-PRO-1 apoptosis assay, indicating that AICAR alone has a pro-survival effect in MDA-MB-231 cells, thus effectively masking the positive effect exerted by hGX. Values on the graphs are means ± SD of at least two experiments performed in duplicate and results that are statistically significant over control samples are indicated (*, P < 0.05; **, P < 0.01; ***, P < 0.001; one-way ANOVA with Bonferroni adjustment).
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Alterations in lipid metabolism are inherent to the metabolic transformations that support tumorigenesis. The relationship between the synthesis, storage and use of lipids and their importance in cancer is poorly understood. The human group X secreted phospholipase A2 (hGX sPLA2) releases fatty acids (FAs) from cell membranes and lipoproteins, but...
Contexts in source publication
Context 1
... AMPK in- creases cancer cell growth and survival during energy stress by altering FA metabolism [6,8,60]. An increase in the amount of Thr172-phosphorylated AMPKα (p-AMPKα) in proliferating MDA-MB-231 cells was observed after 48 h of growth in the presence of recombinant hGX sPLA 2 or exogenous OA (Figures 8A and 8B). This showed that the effects of hGX on LD formation and cell survival are associated with the activation of AMPK. ...Context 2
... substantiate this view, we asked whether prolonged ac- tivation of AMPK would prevent the LD formation induced by hGX. Activating AMPK with the AMP-analog 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) [6] (Figures 8A and 8B) completely abolished hGX- induced LD formation in both proliferating ( Figure 8C) and in starved MDA-MB-231 cells (Figure 8D), indicating that AMPK activation indeed blocks hGX-induced LD biogenesis. This is in line with the complete blockade of lipid synthesis caused by AICAR in MDA-MB-231 cells [64]. ...Context 3
... substantiate this view, we asked whether prolonged ac- tivation of AMPK would prevent the LD formation induced by hGX. Activating AMPK with the AMP-analog 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) [6] (Figures 8A and 8B) completely abolished hGX- induced LD formation in both proliferating ( Figure 8C) and in starved MDA-MB-231 cells (Figure 8D), indicating that AMPK activation indeed blocks hGX-induced LD biogenesis. This is in line with the complete blockade of lipid synthesis caused by AICAR in MDA-MB-231 cells [64]. ...Context 4
... substantiate this view, we asked whether prolonged ac- tivation of AMPK would prevent the LD formation induced by hGX. Activating AMPK with the AMP-analog 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) [6] (Figures 8A and 8B) completely abolished hGX- induced LD formation in both proliferating ( Figure 8C) and in starved MDA-MB-231 cells (Figure 8D), indicating that AMPK activation indeed blocks hGX-induced LD biogenesis. This is in line with the complete blockade of lipid synthesis caused by AICAR in MDA-MB-231 cells [64]. ...Context 5
... further raised the question as to whether the sup- pression of LD biogenesis by AICAR would abolish the positive effect of hGX on cancer cell survival during serum deprivation. We found that prolonged treatments with AICAR reduced the basal level of dying cells in the starving MDA-MB-231 cell population to a level similar to that observed with hGX itself (Figure 8E), thus effect- ively masking the positive effect of hGX. The effect of AICAR accords with the recently reported role for AMPK in enabling cancer cell survival during energy stress by suppressing lipogenesis and activating β-oxidation [6,8]. ...Context 6
... sPLA 2 is shown in the present work to stimulate cell proliferation and in- crease the survival of serum-deprived MDA-MB-231 cells (Figures 1A and 5C and 5D). Further, exogenous hGX and OA are both shown to activate AMPK in proliferating cells ( Figures 8A and 8B), strongly suggesting that OA is one of the major mediators of the pro-tumorigenic effects of hGX. Importantly, the effects of OA are not restricted to breast cancer cells, since there is ample evidence that OA feeds into the TAG synthesis pathway and stimulates LD formation, cell growth and survival in different non- adipose cells, even channeling saturated FAs to TAGs to prevent their apoptotic effects [31,55]. ...Context 7
... besides promoting TAG synthesis, OA also pre- vented palmitate-induced apoptosis in skeletal muscle cells by stimulating β-oxidation through elevation of the expression of CPT1, activation of AMPK and repression of the activity of ACC [72]. Similarly, hGX significantly in- creased the levels of two important β-oxidation enzymes, CPT1A and VLCAD, in MDA-MB-231 cells (Figure 7), in parallel with the high rate of LD formation, activation of AMPK ( Figures 8A and 8B) and suppression of the induc- tion of lipogenic enzymes, including ACC1 (Figure 7). Nevertheless, it is highly likely that, besides OA, other products of hGX phospholipid hydrolysis contribute to its effects in breast cancer cells, either by feeding metabolic pathways or by triggering cell signaling to various degrees [73]. ...Context 8
... this study, we show that the activity of hGX sPLA 2 in invasive breast cancer cells leads to the activation of AMPK, suggesting that the kin- ase supports the pro-tumorigenic metabolic alterations induced by hGX sPLA 2 . Elevated phosphorylation of AMPK was detected in hGX-treated cells after 48 h of cell proliferation (Figures 8A and 8B) when neutral lipid accumulation reached maximal levels ( Figure 2C) and the gene expression changes were significant ( Figure 7A). Furthermore, etomoxir and triacsin C, which both atten- uated hGX-induced LD formation, also prevented hGX- induced AMPK activation (Figures 8A and 8B). ...Context 9
... phosphorylation of AMPK was detected in hGX-treated cells after 48 h of cell proliferation (Figures 8A and 8B) when neutral lipid accumulation reached maximal levels ( Figure 2C) and the gene expression changes were significant ( Figure 7A). Furthermore, etomoxir and triacsin C, which both atten- uated hGX-induced LD formation, also prevented hGX- induced AMPK activation (Figures 8A and 8B). This suggests that the energy stress caused by rapid cell growth and proliferation combined with extensive FA activation, TAG synthesis and LD biogenesis in hGX- treated MDA-MB-231 cells leads to AMPK activation [29]. ...Context 10
... suggests that the energy stress caused by rapid cell growth and proliferation combined with extensive FA activation, TAG synthesis and LD biogenesis in hGX- treated MDA-MB-231 cells leads to AMPK activation [29]. Accordingly, by mimicking cellular low energy sta- tus and inducing a several-fold higher increase in the level of phosphorylated AMPK relative to hGX (Figures 8A and 8B), the AMPK activator AICAR completely pre- vented hGX-induced LD formation ( Figure 8C). This is consistent with the previously reported strong cytostatic effect of AICAR on MDA-MB-231 cells caused by sup- pression of DNA, protein and lipid synthesis [64]. ...Context 11
... it has been shown that acti- vation of AMPK in cancer cells during energy stress en- ables cell survival by blocking lipid synthesis through inactivation of ACC and elevating β-oxidation-dependent NADPH production to restore the redox balance [8]. Our results indicate that AMPK activation also supports sur- vival of MDA-MB-231 cells, since AICAR displayed a strong anti-apoptotic effect in these cells ( Figure 8E). Thus, the activation of AMPK by hGX in proliferating cells implicates AMPK in the coordination of the adapta- tion of MDA-MB-231 cell metabolism to the FAs de- rived from hGX membrane hydrolysis. ...Context 12
... FA/TAG cycling requires high ACS ac- tivity, at the expense of ATP, to provide a continuous sup- ply of FA-CoA, it may also contribute to the observed hGX-induced activation of AMPK [29]. In line with this, besides etomoxir, the ACS inhibitor triacsin C also par- tially blocked hGX-induced LD formation (Additional file 5: Figure S4) and AMPK activation ( Figures 8A and 8B) in proliferating cells. We may thus speculate that, by supplying FFAs, hGX stimulates β-oxidation that in turn supports the anabolic branch of FA/TAG cycling, resulting in net LD accumulation and thus filling the LD energy reserves that can be used to support cell sur- vival. ...Citations
... Increased accumulation of LDs in tumor cells involves several signaling pathways, such as activation of the epidermal growth factor receptor and PI3K/AKT/ mammalian target of the rapamycin (mTOR) pathways and inactivation of the FOXO3/SIRT6 pathway [24]. Other intracellular stimulations, including lipid overload, ER stress, hypoxia, acidic environment, mitochondrial damage, imbalances in energy metabolism and redox homeostasis, and treatment with chemotherapeutics are also reported to trigger the biosynthesis of LDs in tumor cells [84,[92][93][94]. Notably, cancer-associated fibroblasts (CAFs), an important component of the tumor microenvironment, also participate in the accumulation of LDs by upregulating the secretion of lactate, which subsequently provides acetyl moieties for histone acetylation and establishes a regulatory loop between lipid metabolism and epigenetic modification in prostate tumor cells. ...
Lipid metabolism is widely reprogrammed in tumor cells. Lipid droplet is a common organelle existing in most mammal cells, and its complex and dynamic functions in maintaining redox and metabolic balance, regulating endoplasmic reticulum stress, modulating chemoresistance, and providing essential biomolecules and ATP have been well established in tumor cells. The balance between lipid droplet formation and catabolism is critical to maintaining energy metabolism in tumor cells, while the process of energy metabolism affects various functions essential for tumor growth. The imbalance of synthesis and catabolism of fatty acids in tumor cells leads to the alteration of lipid droplet content in tumor cells. Diacylglycerol acyltransferase 1 and diacylglycerol acyltransferase 2, the enzymes that catalyze the final step of triglyceride synthesis, participate in the formation of lipid droplets in tumor cells and in the regulation of cell proliferation, migration and invasion, chemoresistance, and prognosis in tumor. Several diacylglycerol acyltransferase 1 and diacylglycerol acyltransferase 2 inhibitors have been developed over the past decade and have shown anti-tumor effects in preclinical tumor models and improvement of metabolism in clinical trials. In this review, we highlight key features of fatty acid metabolism and different paradigms of diacylglycerol acyltransferase 1 and diacylglycerol acyltransferase 2 activities on cell proliferation, migration, chemoresistance, and prognosis in tumor, with the hope that these scientific findings will have potential clinical implications.
... These cancer cells can modulate their metabolic and signalling pathways to match the growth rates with nutrient availability. For example, the absence of serum, which is the primary source of lipids during growth in nutrient-rich media, activates the metabolic pathways in the MDA-MB-231 cells that convert glucose to lipids (de novo lipogenesis) to compensate for the lack of lipids and maintain membrane homeostasis and cell survival [53,54]. Serum-free cell-culture media still contain enough glucose, amino acids and vitamins to support lipogenesis and cancer-cell survival under these conditions. ...
Magneto-mechanical actuation (MMA) using the low-frequency alternating magnetic fields (AMFs) of magnetic nanoparticles internalized into cancer cells can be used to irreparably damage these cells. However, nanoparticles in cells usually agglomerate, thus greatly augmenting the delivered force compared to single nanoparticles. Here, we demonstrate that MMA also decreases the cell viability, with the MMA mediated by individual, non-interacting nanoparticles. The effect was demonstrated with ferrimagnetic (i.e., permanently magnetic) barium-hexaferrite nanoplatelets (NPLs, ∼50 nm wide and 3 nm thick) with a unique, perpendicular orientation of the magnetization. Two cancer-cell lines (MDA-MB-231 and HeLa) are exposed to the NPLs in-vitro under different cell-culture conditions and actuated with a uniaxial AMF. TEM analyses show that only a small number of NPLs internalize in the cells, always situated in membrane-enclosed compartments of the endosomal-lysosomal system. Most compartments contain 1–2 NPLs and only seldom are the NPLs found in small groups, but never in close contact or mutually oriented. Even at low concentrations, the single NPLs reduce the cell viability when actuated with AMFs, which is further increased when the cells are in starvation conditions. These results pave the way for more efficient in-vivo MMA at very low particle concentrations.
... Interestingly, LD formation is driven by a variety of stressors, which are also characteristic for the tumor microenvironment, including both nutrient excess and deficiency, hypoxia and oxidative stress, as well as autophagy [14,19,20]. In addition to their primary role as energy depots, LDs also serve as buffers that can minimize lipotoxicity [21][22][23][24] and also support mitochondrial metabolism and cell survival during prolonged starvation [9,[25][26][27][28][29]. ...
... LD analysis was performed as described previously [27]. Briefly, cells were seeded in complete medium in 24-well culture plates at concentration of 3 × 10 4 cells/well (HeLa) or 6 × 10 4 cells/well (MDA-MB-231), left to adhere for 24 h, and then treated with a mixture of 20 µM T863 and 20 µM PF-06424439 (DGATi) inhibitors for blocking LD formation, or (MDA-MB-231), or 100 µM CQ for inhibition of autophagy for 4, 6, 16, or 24 h in serum-free or amino acid-free media. ...
... We demonstrate that mild serum starvation conditions increase LD breakdown, while depletion of both serum and amino acid stimulates LD accumulation during acute starvation (Figure 1, Supplementary Figure S1). These results support findings that LDs are primarily broken down during mild starvation conditions such as serum deprivation, while starving cells in HBSS medium or complete nutrient deprivation promotes LD synthesis [9,25,27,28,47]. Treating cells with DGAT1 and DGAT2 inhibitors revealed that amino-acid-starvation-induced LD synthesis primarily depends on DGAT1 activity (Figure 1), which has also been reported by others [9]. ...
Simple Summary
In this study, the relationship between autophagy and lipid droplets in the response of cancer cells to starvation was investigated. Under conditions of amino acid deprivation, autophagy was triggered and led to lipid droplet accumulation through diacylglycerol acyltransferase (DGAT)-mediated neutral lipid synthesis. Combined inhibition of autophagy and lipid droplet biogenesis during acute amino acid starvation was lethal for HeLa cervical cancer cells, but not for MDA-MB-231 breast cancer cells.
Abstract
Lipid droplets (LDs) are dynamic organelles involved in the management of fatty acid trafficking and metabolism. Recent studies suggest that autophagy and LDs serve complementary roles in the protection against nutrient stress, but the autophagy–LD interplay in cancer cells is not well understood. Here, we examined the relationship between autophagy and LDs in starving HeLa cervical cancer- and MDA-MB-231 breast cancer cells. We found that acute amino acid depletion induces autophagy and promotes diacylglycerol acyltransferase 1 (DGAT1)-mediated LD accumulation in HeLa cells. Inhibition of autophagy via late-stage autophagy inhibitors, or by knocking down autophagy-related 5 (ATG5), reduced LD accumulation in amino acid-starved cancer cells, suggesting that autophagy contributes to LD biogenesis. On the contrary, knockdown of adipose triglyceride lipase (ATGL) increased LD accumulation, suggesting that LD breakdown is mediated by lipolysis under these conditions. Concurrent inhibition of autophagy by silencing ATG5 and of LD biogenesis using DGAT inhibitors was effective in killing starving HeLa cells, whereas cell survival was not compromised by suppression of ATGL-mediated lipolysis. Autophagy-dependent LD biogenesis was also observed in the aggressive triple-negative MDA-MB-231 breast cancer cells deprived of amino acids, but these cells were not sensitized to starvation by the combined inhibition of LD biogenesis and autophagy. These findings reveal that while targeting autophagy-driven and DGAT-mediated LD biogenesis reduces the resilience of HeLa cervical cancer cells to amino acid deprivation, this strategy may not be successful in other cancer cell types.
... Lipid products produced due to phospholipase activity involved in tumor development are lysophosphatidic acid (LPA), AA, leukotrienes, and prostaglandins (Park et al., 2012). It was observed that human group X secreted phospholipase A 2 (hGX sPLA 2 ) leads to the development of lipid droplets, which help breast tumor cells to proliferate and survive in serum deprivation condition (Pucer et al., 2013). High level of LPA in serum is an indication of tumor commencement and development in breast cancer. ...
... Lipid products produced due to phospholipase activity involved in tumor development are lysophosphatidic acid (LPA), AA, leukotrienes, and prostaglandins (Park et al., 2012). It was observed that human group X secreted phospholipase A 2 (hGX sPLA 2 ) leads to the development of lipid droplets, which help breast tumor cells to proliferate and survive in serum deprivation condition (Pucer et al., 2013). High level of LPA in serum is an indication of tumor commencement and development in breast cancer. ...
... However, triple-negative breast cancer cells may also exhibit LDs production associated with increased proliferation and motility. In this case, production appears to be induced by stimulation via saturated Fas, leading to the activation of the PLA2 enzyme or by peroxisome proliferator-activated receptor (PPARγ) ligands [83,84]. ...
... However, doubts persist about their involvement in the survival of cancer cells. Indeed, some studies suggest that their accumulation characterizes cells undergoing apoptosis, whereas others have found a protective effect in cancer cells subjected to nutrient stress [83,95]. Added to these contradictions is the fact that no study so far has been interested in the potential relationship between resistance to chemotherapy and the production of LDs. ...
Simple Summary
Cancer cells are characterized by an increased energy metabolism, to cope with a high rate of proliferation. Recently, alterations in lipid metabolism have been recognized to be involved in tumor progression. Lipid droplets represent dynamic entities implied in such a phenomenon. This review aims to point out the metabolic pathways that are presumed to be engaged in cancer cell survival and growth in order to define potential biomarkers of tumor progression and new therapeutic strategies in the treatment of cancer.
Abstract
Cancer shares common risk factors with cardiovascular diseases such as dyslipidemia, obesity and inflammation. In both cases, dysregulations of lipid metabolism occur, and lipid vesicles emerge as important factors that can influence carcinogenesis. In this review, the role of different lipids known to be involved in cancer and its response to treatments is detailed. In particular, lipid droplets (LDs), initially described for their role in lipid storage, exert multiple functions, from the physiological prevention of LD coalescence and regulation of endoplasmic reticulum homeostasis to pathological involvement in tumor progression and aggressiveness. Analysis of LDs highlights the importance of phosphatidylcholine metabolism and the diversity of lipid synthesis enzymes. In many cancers, the phosphatidylcholine pathways are disrupted, modifying the expression of genes coding for metabolic enzymes. Tumor microenvironment conditions, such as hypoxia, different types of stress or inflammatory conditions, are also important determinants of LD behavior in cancer cells. Therefore, LDs represent therapeutic targets in cancer, and many lipid mediators have emerged as potential biomarkers for cancer onset, progression, and/or resistance.
... The association between PLIN2 and cancer is extensively documented. PLIN2 has been associated with tumorigenesis and is often considered as a poor prognosis indicator in cancers of the colon [90,91], breast [92,93], prostate [94,95], lung [96,97], bladder [95], kidney [82,[98][99][100][101][102][103][104][105], thyroid [106], gastric [107], and melanoma [108]. ...
... In the context of cancer, the overexpression of PLIN2 and PLIN3 is often observed [90][91][92][93]95,96,99,101,[105][106][107][108][128][129][130][131][132][133][160][161][162][163][164]. Considering their individual roles, this suggests that cancer cells might possess an enhanced ability to generate new LDs, as PLIN3 typically associates with nascent lipid droplets, and a heightened capability for lipid storage, since overexpression of PLIN2 could make lipid droplets less accessible to lipolytic enzymes [35]. ...
... Some cancer types are known to express PLIN2 [90][91][92][93]95,96,99,101,[105][106][107][108][160][161][162][163][164]. Consequently, PPARγ activators might heighten the expression of these PLIN isoforms, shielding FAs in the LDs more efficiently, thereby challenging the cancer cell's ability to utilize FAs to meet its metabolic demands [157,188]. ...
Simple Summary
This review highlights the importance of perilipins in lipid metabolism and their potential as therapeutic targets for lipid-associated diseases like cancer and obesity. Perilipins are proteins found in lipid droplets that regulate lipase activity and play a crucial role in maintaining the balance between lipid synthesis and breakdown. Modulating perilipins could improve existing treatments or offer new therapeutic opportunities for addressing these diseases.
Abstract
Perilipins (PLINs) are the most abundant proteins in lipid droplets (LD). These LD-associated proteins are responsible for upgrading LD from inert lipid storage structures to fully functional organelles, fundamentally integrated in the lipid metabolism. There are five distinct perilipins (PLIN1–5), each with specific expression patterns and metabolic activation, but all capable of regulating the activity of lipases on LD. This plurality creates a complex orchestrated mechanism that is directly related to the healthy balance between lipogenesis and lipolysis. Given the essential role of PLINs in the modulation of the lipid metabolism, these proteins can become interesting targets for the treatment of lipid-associated diseases. Since reprogrammed lipid metabolism is a recognized cancer hallmark, and obesity is a known risk factor for cancer and other comorbidities, the modulation of PLINs could either improve existing treatments or create new opportunities for the treatment of these diseases. Even though PLINs have not been, so far, directly considered for pharmacological interventions, there are many established drugs that can modulate PLINs activity. Therefore, the aim of this study is to assess the involvement of PLINs in diseases related to lipid metabolism dysregulation and whether PLINs can be viewed as potential therapeutic targets for cancer and obesity.
... Accordingly, in cancer cells exposed to exogenous PUFAs, LDs are enriched with PUFA-TAGs and their hydrolysis by ATGL promotes oxidative stress-dependent cell death [20]. Under these conditions, the transfer of unsaturated FAs from membrane phospholipids into LDs mediated by the human group X (hGX) sPLA 2 balances phospholipid and TAG acyl-chain composition and prevents PUFA lipotoxicity [20,24]. Based on these findings, we hypothesize that LD turnover modulates membrane PUFA content and affects PLA 2 -mediated lipid mediator production. ...
... PUFAs [20], and induces LD accumulation in several breast cancer cell lines [20,24]. Recombinant hGX sPLA 2 also induced LD accumulation in other cancer and immortalised non-tumorigenic cell lines ( Figure 1A, B), suggesting that its effects on LD metabolism are not limited to specific cell types. ...
... Figure 1B). We then asked whether hGX sPLA 2 alters TAG acyl chain composition in LDs of MDA-MB-231 cells ( Figure 1D), an invasive and metastatic breast cancer cell line showing enhanced proliferation and resistance to starvation upon treatment with hGX sPLA 2 [24]. Cells pre-incubated with [ 14 C]-OA readily incorporated the radiolabelled FA into phospholipids and TAGs, while hGX sPLA 2 treatment specifically increased the abundance of TAGs containing [ 14 Figure 1E). ...
Objectives:
Polyunsaturated fatty acids (PUFAs) are structural components of membrane phospholipids and precursors of oxygenated lipid mediators with diverse functions, including the control of cell growth, inflammation and tumourigenesis. However, the molecular pathways that control the availability of PUFAs for lipid mediator production are not well understood. Here, we investigated the crosstalk of three pathways in the provision of PUFAs for lipid mediator production: (i) secreted group X phospholipase A2 (GX sPLA2) and (ii) cytosolic group IVA PLA2 (cPLA2α), both mobilizing PUFAs from membrane phospholipids, and (iii) adipose triglyceride lipase (ATGL), which mediates the degradation of triacylglycerols (TAGs) stored in cytosolic lipid droplets (LDs).
Methods:
We combined lipidomic and functional analyses in cancer cell line models to dissect the trafficking of PUFAs between membrane phospholipids and LDs and determine the role of these pathways in lipid mediator production, cancer cell proliferation and tumour growth in vivo.
Results:
We demonstrate that lipid mediator production strongly depends on TAG turnover. GX sPLA2 directs ω-3 and ω-6 PUFAs from membrane phospholipids into TAG stores, whereas ATGL is required for their entry into lipid mediator biosynthetic pathways. ATGL controls the release of PUFAs from LD stores and their conversion into cyclooxygenase- and lipoxygenase-derived lipid mediators under conditions of nutrient sufficiency and during serum starvation. In starving cells, ATGL also promotes the incorporation of LD-derived PUFAs into phospholipids, representing substrates for cPLA2α. Furthermore, we demonstrate that the built-up of TAG stores by acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) is required for the production of mitogenic lipid signals that promote cancer cell proliferation and tumour growth.
Conclusion:
This study shifts the paradigm of PLA2-driven lipid mediator signalling and identifies LDs as central lipid mediator production hubs. Targeting DGAT1-mediated LD biogenesis is a promising strategy to restrict lipid mediator production and tumour growth.
... LDs have been implicated in the regulation of FA metabolism and trafficking in various pathophysiological contexts (Bailey et al., 2015;Jarc et al., 2018;Olzmann and Carvalho, 2019;Jarc and Petan, 2020) The importance of LD turnover has been recognized in stressed cells Petan et al., 2018) and associated with the protection from the harmful effects of dysregulated lipid and oxidative metabolism. LDs accumulate in cells experiencing various nutrient, energy and redox imbalances caused by hypoxia (Bailey et al., 2015;Schlaepfer et al., 2015), oxidative stress Liu et al., 2017;Ioannou et al., 2019), nutrient deficiency (Cabodevilla et al., 2013;Pucer et al., 2013;Rambold et al., 2015;Hariri et al., 2018), exogenous (PU)FA overload (Listenberger et al., 2003;Jarc et al., 2018), acidity (Dierge et al., 2021), inflammation and infection (Brok et al., 2018;Libbing et al., 2019;Jarc and Petan, 2020;Bosch and Pol, 2022). These findings suggest that cells increase LD abundance as a general protective mechanism against stress. ...
... Another important aspect of LD-mediated control of lipid peroxidation is their integration in cellular metabolism. For example, LDs channel FAs to mitochondria and activate signaling pathways in order to sustain respiration and energy production, but also to promote the generation of redox equivalents [e.g., NAD(P)H], which are essential for both redox defense and biosynthetic pathways (Pucer et al., 2013;Rambold et al., 2015;Zechner et al., 2017). In accordance, mitochondrial βoxidation may also protect cells from ferroptosis (Nassar et al., 2020;Hoy et al., 2021). ...
Lipid droplets are fat storage organelles ubiquitously distributed across the eukaryotic kingdom. They have a central role in regulating lipid metabolism and undergo a dynamic turnover of biogenesis and breakdown to meet cellular requirements for fatty acids, including polyunsaturated fatty acids. Polyunsaturated fatty acids esterified in membrane phospholipids define membrane fluidity and can be released by the activity of phospholipases A2 to act as ligands for nuclear receptors or to be metabolized into a wide spectrum of lipid signaling mediators. Polyunsaturated fatty acids in membrane phospholipids are also highly susceptible to lipid peroxidation, which if left uncontrolled leads to ferroptotic cell death. On the one hand, lipid droplets act as antioxidant organelles that control polyunsaturated fatty acid storage in triglycerides in order to reduce membrane lipid peroxidation, preserve organelle function and prevent cell death, including ferroptosis. On the other hand, lipid droplet breakdown fine-tunes the delivery of polyunsaturated fatty acids into metabolic and signaling pathways, but unrestricted lipid droplet breakdown may also lead to the release of lethal levels of polyunsaturated fatty acids. Precise regulation of lipid droplet turnover is thus essential for polyunsaturated fatty acid distribution and cellular homeostasis. In this review, we focus on emerging aspects of lipid droplet-mediated regulation of polyunsaturated fatty acid trafficking, including the management of membrane lipid peroxidation, ferroptosis and lipid mediator signaling.
... This was true for both, LDs and PLIN2 expression in both osteosarcoma cell lines. Oleic acid induced lipid accumulation has also been observed in several other cancer cell lines, including those arising from cervical, breast, and hepatocellular carcinoma (Guštin et al. 2017;Pucer et al. 2013;Giulitti et al. 2021). In contrast to the stimulating capacity of OA, no effect was found for supplemented cholesterol. ...
Lipid droplets were identified as important players in biological processes of various tumor types. With emphasis on lipid droplet-coating proteins (perilipins, PLINs), this study intended to shed light on the presence and formation of lipid droplets in canine osteosarcoma. For this purpose, canine osteosarcoma tissue samples ( n = 11) were analyzed via immunohistochemistry and electron microscopy for lipid droplets and lipid droplet-coating proteins (PLINs). Additionally, we used the canine osteosarcoma cell lines D-17 and COS4288 in 2D monolayer and 3D spheroid (cultivated for 7, 14, and 21 days) in vitro models, and further analyzed the samples by means of histochemistry, immunofluorescence, molecular biological techniques (RT-qPCR, Western Blot) and electron microscopical imaging. Lipid droplets, PLIN2, and PLIN3 were detected in osteosarcoma tissue samples as well as in 2D and 3D cultivated D-17 and COS4288 cells. In spheroids, specific distribution patterns of lipid droplets and perilipins were identified, taking into consideration cell line specific zonal apportionment. Upon external lipid supplementation (oleic acid), a rise of lipid droplet amount accompanied with an increase of PLIN2 expression was observed. Detailed electron microscopical analyzes revealed that lipid droplet sizes in tumor tissue were comparable to that of 3D spheroid models. Moreover, the biggest lipid droplets were found in the central zone of the spheroids at all sampling time-points, reaching their maximum size at 21 days. Thus, the 3D spheroids can be considered as a relevant in vitro model for further studies focusing on lipid droplets biology and function in osteosarcoma.
