Lipid droplet-associated PAT-proteins show frequent and differential expression in neoplastic steatogenesis

Lipid droplet - organelle crosstalk and its implication in cancer

Lipid droplets (LDs) store lipids in cells, provide phospholipids for membrane synthesis, and maintain the intracellular balance of energy and lipid metabolism. Undoubtedly, the crosstalk between LDs and other organelles is the foundation for performing functions. Many studies indicate that LDs promote tumor progression. LD accumulation has been observed in a variety of cancers, and high LD content is associated with malignant phenotype and poor prognosis of cancers. In this paper, we summarized the intimate crosstalk between LDs and intracellular organelles, including endoplasmic reticulum (ER), mitochondria, lysosomes and peroxisomes, and addressed the effects of LD-organelle crosstalk on cancer initiation and progression. We also integrated the changes of LD-organelle interactions in cancers to provide an insightful knowledge for cancer therapeutics.

The Warburg hypothesis and the emergence of the mitochondrial metabolic theory of cancer

Otto Warburg originally proposed that cancer arose from a two-step process. The first step involved a chronic insufficiency of mitochondrial oxidative phosphorylation (OxPhos), while the second step involved a protracted compensatory energy synthesis through lactic acid fermentation. His extensive findings showed that oxygen consumption was lower while lactate production was higher in cancerous tissues than in non-cancerous tissues. Warburg considered both oxygen consumption and extracellular lactate as accurate markers for ATP production through OxPhos and glycolysis, respectively. Warburg's hypothesis was challenged from findings showing that oxygen consumption remained high in some cancer cells despite the elevated production of lactate suggesting that OxPhos was largely unimpaired. New information indicates that neither oxygen consumption nor lactate production are accurate surrogates for quantification of ATP production in cancer cells. Warburg also did not know that a significant amount of ATP could come from glutamine-driven mitochondrial substrate level phosphorylation in the glutaminolysis pathway with succinate produced as end product, thus confounding the linkage of oxygen consumption to the origin of ATP production within mitochondria. Moreover, new information shows that cytoplasmic lipid droplets and elevated aerobic lactic acid fermentation are both biomarkers for OxPhos insufficiency. Warburg's original hypothesis can now be linked to a more complete understanding of how OxPhos insufficiency underlies dysregulated cancer cell growth. These findings can also address several questionable assumptions regarding the origin of cancer thus allowing the field to advance with more effective therapeutic strategies for a less toxic metabolic management and prevention of cancer.

Transcription Factor FOSL1 Promotes Cisplatin Resistance in Non-Small Cell Lung Cancer Cells by Modulating the Wnt3a/β-Catenin Signaling through Upregulation of PLIN3 Expression

BACKGROUND

Lung adenocarcinoma (LUAD) is the most prevalent histological subtype of lung cancer, accounting for 45.3% of all cases and serving as a major cause of cancer-related mortality. Although cisplatin (DDP) is a cornerstone in LUAD therapy, its efficacy is often compromised by resistance, leading to therapeutic failure and poor patient outcomes. Lipid metabolism and associated proteins, such as perilipin 3 (PLIN3), have been increasingly implicated in cancer progression and chemoresistance. However, the precise mechanisms through which PLIN3 contributes to cisplatin (DDP) resistance in LUAD remain poorly understood.

METHODS

To investigate the role of PLIN3 in DDP resistance, its expression in LUAD tissues and its correlation with patient prognosis were analyzed using bioinformatics databases and validated through clinical sample analysis. The effects of PLIN3 knockdown and overexpression on DDP resistance and Wnt3a/β-catenin signaling were assessed using quantitative real-time PCR (qPCR), western blotting, cytotoxicity assays, and colony formation assays. Bioinformatics screening identified FOS-like antigen 1 (FOSL1) as a transcription factor positively correlated with PLIN3, and its involvement in DDP resistance was further examined both in vitro and in vivo.

RESULTS

PLIN3 expression is significantly elevated in LUAD tissues and correlates with poor overall survival. In LUAD cells, PLIN3 overexpression enhanced DDP resistance by upregulating Wnt3a expression and promoting β-catenin nuclear translocation. Bioinformatics analysis identified FOSL1 as a key transcription factor regulating PLIN3 expression. Experimental validation confirmed that FOSL1 directly binds to the PLIN3 promoter, activating the Wnt3a/β-catenin pathway and promoting DDP resistance. Knockdown of PLIN3 or inhibition of Wnt3a signaling reversed the effects of FOSL1 overexpression on DDP resistance.

CONCLUSION

This study demonstrates that PLIN3 contributes to DDP resistance in LUAD by activating the Wnt3a/β-catenin signaling pathway, with FOSL1 acting as a critical upstream regulator. Targeting the FOSL1/PLIN3/Wnt/β-catenin axis may provide a promising therapeutic strategy for overcoming chemoresistance in LUAD.

The Role of PLIN3 in Prognosis and Tumor-Associated Macrophage Infiltration: A Pan-Cancer Analysis

Background

Nucleolar and spindle-associated protein 1 (PLIN3), a member of the perilipin family, plays a critical role in lipid droplet dynamics and is implicated in promoting tumor progression across several cancers. However, its influence on the tumor immune microenvironment and its potential as a prognostic indicator regarding immunotherapy responses have yet to be systematically evaluated. This study leverages data retrieved from multiple databases to address these questions.

Methods

PLIN3 mRNA and protein expressions were analyzed across a diverse range of normal and cancerous tissues, utilizing data retrieved from multiple databases. The potential of PLIN3 as a diagnostic and prognostic biomarker in cancers was assessed. Advanced computational algorithms were employed to examine the impact of PLIN3 on immune cell infiltration. The association between PLIN3 expression and the presence of M2 macrophages was validated through analyses incorporating bulk and single-cell transcriptomics, spatial transcriptomics, and multicolor fluorescence staining techniques. Furthermore, the effects of PLIN3 on tumor malignancy and growth were investigated in vitro in lung adenocarcinoma (LUAD) cells. Potential compounds targeting PLIN3 were identified using the Connectivity Map (cMap) web tool, and their efficacy was further assessed through molecular docking.

Results

PLIN3 was predominantly upregulated in various cancers, correlating with adverse prognostic outcomes. A strong positive association was observed between PLIN3 levels and M2 macrophage infiltration in several cancer types, establishing it as a potential pan-cancer marker for M2 macrophage presence. This was confirmed by integrative multi-omics analysis and multiple fluorescence staining. Additionally, PLIN3 knockdown in LUAD cells diminished their malignant traits, resulting in decreased proliferation and migration. In LUAD, clofibrate was identified as a potential inhibitor of PLIN3's pro-oncogenic functions.

Conclusion

PLIN3 may serve as a potential biomarker and oncogene, particularly in LUAD. It plays a key role in mediating M2 macrophage infiltration in various cancers and presents a promising immunotherapeutic target.

Obesity-Facilitated Colon Cancer Progression Is Mediated by Increased Diacylglycerol O-Acyltransferases 1 and 2 Levels

BACKGROUND & AIMS

The obesity epidemic is associated with increased colon cancer progression. As lipid droplets (LDs) fuel tumor growth, we aimed to determine the significance of diacyltransferases (diacylglycerol o-acyltransferases 1 and 2 [DGAT1/2]), responsible for LDs biogenesis, in obesity-mediated colonic tumorigenesis.

METHODS

Human colon cancer samples, colon cancer cells, colonospheres, and ApcMin/+ colon cancer mouse model on a high-fat diet were employed. For DGAT1/2 inhibition, enzymatic inhibitors and small interfering RNA were used. Expression, pathways, cell cycle, and growth were assessed. Bioinformatic analyses of CUT&RUN and RNA sequencing data were performed.

RESULTS

DGAT1/2 levels in human colon cancer tissue are significantly elevated with disease severity and obesity (vs normal). Their levels are increased in human colon cancer cells (vs nontransformed) and further enhanced by fatty acids prevalent in obesity; augmented DGAT2 expression is MYC-dependent. Inhibition of DGAT1/2 improves FOXO3 activity by attenuating PI3K, resulting in reduced MYC-dependent DGAT2 expression and accumulation of LDs, suggesting feedback. This inhibition attenuated growth in colon cancer cells and colonospheres via FOXO3/p27kip1 cell cycle arrest and reduced colonic tumors in ApcMin/+ mice on a high-fat diet. Transcriptomic analysis revealed that DGAT1/2 inhibition targeted metabolic and tumorigenic pathways in human colon cancer and colon cancer crypts, stratifying human colon cancer samples from normal. Further analysis revealed that this inhibition is predictive of advanced disease-free state and survival in patients with colon cancer.

CONCLUSIONS

This is a novel mechanism of DGAT1/2-dependent metabolic and tumorigenic remodeling in obesity-facilitated colon cancer, providing a platform for future development of effective treatments for patients with colon cancer.

PLIN5 contributes to lipophagy of hepatic stellate cells induced by inorganic arsenic

Arsenic exposure triggers the activation of hepatic stellate cells (HSCs), resulting in liver fibrosis (LF). A significant decrease in lipid droplets marks the activation of HSCs. However, the exact underlying molecular mechanism remains elusive. Lipophagy, a specialized form of selective autophagy, is crucial for the degradation of lipid droplets to maintain intracellular lipid metabolism homeostasis. In this study, arsenic treatment induced lipophagy, as evidenced by the co-localization of LC3 with lipid droplets. Remarkably, arsenic exposure increased the expression levels of Perilipin 5 (PLIN5), a lipid droplet-associated protein, both at the mRNA and protein levels. Moreover, silencing PLIN5 influenced arsenic-induced lipolysis. Consequently, the results of this study indicate that PLIN5 serves as a substrate protein involved in arsenic-induced lipophagy. This research offers a novel perspective on the mechanisms of arsenic-induced HSCs activation and liver lipid metabolism, potentially guiding new strategies for the prevention and treatment of arsenic-related liver diseases.

Neuroinvasive virus utilizes a lipid droplet surface protein, perilipin2, to restrict apoptosis by decreasing Bcl-2 ubiquitination

Lipid droplets (LDs) can interact with other organelles to regulate cell death, and it has also been reported to play an important role in virus replication. However, the interplay among LDs, cell death, and viral replication remains unclear. Neuroinvasive viruses, such as Japanese encephalitis virus (JEV), rabies virus (RABV), and encephalomyocarditis virus (EMCV) still threaten global public health and raise intensive concerns. Here, we reveal that neuroinvasive virus infection enhances cellular triglyceride biosynthesis by upregulating the expression of diacylglycerol O-acyltransferase 2 (DGAT2) to promote LD formation and increase the expression of Perilipin 2 (PLIN2), an LD surface protein, which consequently facilitates neuroinvasive virus replication. Furthermore, PLIN2 could reduce mitochondrial damage and suppress apoptosis by restoring mitochondrial potential and interacting with anti-apoptotic protein Bcl-2, specifically the 136-209 amino acid region, to interrupt the BAX-Cytc-caspase-3 apoptotic pathway by decreasing the K48-linked ubiquitination of Bcl-2 at the 17th lysine. Together, we elucidate that neuroinvasive virus utilizes an LD surface protein to restrict the apoptosis of infected cells, providing a fresh insight into the pathogenesis and antiviral therapeutics development of neuroinvasive viruses.

IMPORTANCE

The neuroinvasive virus is a kind of pathogen that is capable of infiltrating and infecting the central nervous system to potentially induce severe neurological damage and disorders, which pose a significant threat to public health. Here, we found that neuroinvasive viruses can utilize an LD surface protein PLIN2 to facilitate viral replication. Notably, PLIN2 could reduce mitochondrial damage and suppress apoptosis by restoring mitochondrial potential and interacting with anti-apoptotic protein Bcl-2, specifically the 136-209 amino acid region, to interrupt the BAX-Cytc-caspase-3 apoptotic pathway by decreasing the K48-linked ubiquitination of Bcl-2 at the 17th lysine. This study reveals a common strategy for neuroinvasive viruses to avoid apoptosis of infected cells by employing LDs, which extends the important role of LDs in viral pathogenesis and may inspire further research in this field.

Clinical pathological significance and biological function of PLIN1 in hepatocellular carcinoma: bioinformatics analysis and in vitro experiments

BACKGROUND & AIMS

Perilipin 1 (PLIN1) is an essential lipid droplet surface protein that participates in cell life activities by regulating energy balance and lipid metabolism. PLIN1 has been shown to be closely related to the development of numerous tumor types. The purpose of this work was to elucidate the clinicopathologic significance of PLIN1 in hepatocellular carcinoma (HCC), as well as its impact on the biological functions of HCC cells, and to investigate the underlying mechanisms involved.

METHODS

Public high-throughput RNA microarray and RNA sequencing data were collected to examine PLIN1 levels and clinical significance in patients with HCC. Immunohistochemistry (IHC) and real-time quantitative reverse transcription polymerase chain reaction (RT‒qPCR) were conducted to assess the expression levels and the clinicopathological relevance of PLIN1 in HCC. Then, SK and Huh7 cells were transfected with a lentivirus overexpressing PLIN1. CCK8 assay, wound healing assay, transwell assay, and flow cytometric analysis were conducted to explore the effects of PLIN1 overexpression on HCC cell proliferation, migration, invasion, and cell cycle distribution. Ultimately, Gene Ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to investigate the underlying mechanisms of PLIN1 in HCC progression based on HCC differentially expressed genes and PLIN1 co-expressed genes.

RESULTS

PLIN1 was markedly downregulated in HCC tissues, which correlated with a noticeably worse prognosis for HCC patients. Additionally, PLIN1 overexpression inhibited the proliferation, migration, and invasion of SK and Huh7 cells in vitro, as well as arresting the HCC cell cycle at the G0/G1 phase. More significantly, energy conversion-related biological processes, lipid metabolism, and cell cycle signalling pathways were the three most enriched molecular mechanisms.

CONCLUSION

The present study revealed that PLIN1 downregulation is associated with poor prognosis in HCC patients and accelerated HCC progression by promoting cellular proliferation, migration, and metastasis, as well as the mechanisms underlying the regulation of lipid metabolism-related pathways in HCC.

Review article: Hepatic steatosis and its associations with acute and chronic liver diseases

BACKGROUND

Hepatic steatosis is a common finding in liver histopathology and the hallmark of metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), whose global prevalence is rising.

AIMS

To review the histopathology of hepatic steatosis and its mechanisms of development and to identify common and rare disease associations.

METHODS

We reviewed literature on the basic science of lipid droplet (LD) biology and clinical research on acute and chronic liver diseases associated with hepatic steatosis using the PubMed database.

RESULTS

A variety of genetic and environmental factors contribute to the development of chronic hepatic steatosis or steatotic liver disease, which typically appears macrovesicular. Microvesicular steatosis is associated with acute mitochondrial dysfunction and liver failure. Fat metabolic processes in hepatocytes whose dysregulation leads to the development of steatosis include secretion of lipoprotein particles, uptake of remnant lipoprotein particles or free fatty acids from blood, de novo lipogenesis, oxidation of fatty acids, lipolysis and lipophagy. Hepatic insulin resistance is a key feature of MASLD. Seipin is a polyfunctional protein that facilitates LD biogenesis. Assembly of hepatitis C virus takes place on LD surfaces. LDs make important, functional contact with the endoplasmic reticulum and other organelles.

CONCLUSIONS

Diverse liver pathologies are associated with hepatic steatosis, with MASLD being the most important contributor. The biogenesis and dynamics of LDs in hepatocytes are complex and warrant further investigation. Organellar interfaces permit co-regulation of lipid metabolism to match generation of potentially toxic lipid species with their LD depot storage.

Cardiometabolic risk factors in MASLD patients with HCC: the other side of the coin

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) constitutes the commonest cause of chronic liver disorder worldwide, whereby affecting around one third of the global population. This clinical condition may evolve into Metabolic Dysfunction-Associated Steatohepatitis (MASH), fibrosis, cirrhosis and hepatocellular carcinoma (HCC), in a predisposed subgroup of patients. The complex pathogenesis of MASLD is severely entangled with obesity, dyslipidemia and type 2 diabetes (T2D), so far so nutritional and lifestyle recommendations may be crucial in influencing the risk of HCC and modifying its prognosis. However, the causative association between HCC onset and the presence of metabolic comorbidities is not completely clarified. Therefore, the present review aimed to summarize the main literature findings that correlate the presence of inherited or acquired hyperlipidemia and metabolic risk factors with the increased predisposition towards liver cancer in MASLD patients. Here, we gathered the evidence underlining the relationship between circulating/hepatic lipids, cardiovascular events, metabolic comorbidities and hepatocarcinogenesis. In addition, we reported previous studies supporting the impact of triglyceride and/or cholesterol accumulation in generating aberrancies in the intracellular membranes of organelles, oxidative stress, ATP depletion and hepatocyte degeneration, influencing the risk of HCC and its response to therapeutic approaches. Finally, our pursuit was to emphasize the link between HCC and the presence of cardiometabolic abnormalities in our large cohort of histologically-characterized patients affected by MASLD (n=1538), of whom 86 had MASLD-HCC by including unpublished data.

Lipid droplets provide metabolic flexibility for cancer progression

A hallmark of cancer cells is their remarkable ability to efficiently adapt to favorable and hostile environments. Due to a unique metabolic flexibility, tumor cells can grow even in the absence of extracellular nutrients or in stressful scenarios. To achieve this, cancer cells need large amounts of lipids to build membranes, synthesize lipid-derived molecules, and generate metabolic energy in the absence of other nutrients. Tumor cells potentiate strategies to obtain lipids from other cells, metabolic pathways to synthesize new lipids, and mechanisms for efficient storage, mobilization, and utilization of these lipids. Lipid droplets (LDs) are the organelles that collect and supply lipids in eukaryotes and it is increasingly recognized that the accumulation of LDs is a new hallmark of cancer cells. Furthermore, an active role of LD proteins in processes underlying tumorigenesis has been proposed. Here, by focusing on three major classes of LD-resident proteins (perilipins, lipases, and acyl-CoA synthetases), we provide an overview of the contribution of LDs to cancer progression and discuss the role of LD proteins during the proliferation, invasion, metastasis, apoptosis, and stemness of cancer cells.

Lipid droplets-related Perilipin-3: potential immune checkpoint and oncogene in oral squamous cell carcinoma

BACKGROUND

Lipid droplets (LDs) as major lipid storage organelles are recently reported to be innate immune hubs. Perilipin-3 (PLIN3) is indispensable for the formation and accumulation of LDs. Since cancer patients show dysregulated lipid metabolism, we aimed to elaborate the role of LDs-related PLIN3 in oral squamous cell carcinoma (OSCC).

METHODS

PLIN3 expression patterns (n = 87), its immune-related landscape (n = 74) and association with B7-H2 (n = 51) were assessed by immunohistochemistry and flow cytometry. Real-time PCR, Western blot, Oil Red O assay, immunofluorescence, migration assay, spheroid-forming assay and flow cytometry were performed for function analysis.

RESULTS

Spotted LDs-like PLIN3 staining was dominantly enriched in tumor cells than other cell types. PLIN3high tumor showed high proliferation index with metastasis potential, accompanied with less CD3+CD8+ T cells in peripheral blood and in situ tissue, conferring immunosuppressive microenvironment and shorter postoperative survival. Consistently, PLIN3 knockdown in tumor cells not only reduced LD deposits and tumor migration, but benefited for CD8+ T cells activation in co-culture system with decreased B7-H2. An OSCC subpopulation harbored PLIN3highB7-H2high tumor showed more T cells exhaustion, rendering higher risk of cancer-related death (95% CI 1.285-6.851).

CONCLUSIONS

LDs marker PLIN3 may be a novel immunotherapeutic target in OSCC.

FOXO3: at the crossroads of metabolic, inflammatory, and tumorigenic remodeling in the colon

The Forkhead box O3 (FOXO3) transcription factor regulates the expression of genes critical for diverse cellular functions in homeostasis. Diminished FOXO3 activity is associated with human diseases such as obesity, metabolic diseases, inflammatory diseases, and cancer. In the mouse colon, FOXO3 deficiency leads to an inflammatory immune landscape and dysregulated molecular pathways, which, under various insults, exacerbates inflammation and tumor burden, mimicking characteristics of human diseases. This deficiency also results in dysregulated lipid metabolism, and consequently, the accumulation of intracellular lipid droplets (LDs) in colonic epithelial cells and infiltrated immune cells. FOXO3 and LDs form a self-reinforcing negative regulatory loop in colonic epithelial cells, neutrophils, and macrophages, which is associated with inflammatory bowel disease and colon cancer, particularly in the context of obesity.

Silencing of Perilipin 3 Inhibits Lung Adenocarcinoma Cell Immune Resistance by Regulating the Transcription of PD-L1 Through c-Myc

BACKGROUND

Perilipin 3 (PLIN3), a lipid droplet-associated protein, is found to be highly expressed in human cancers. This study aimed to investigate the biological functions and underlying mechanism of PLIN3 in lung adenocarcinoma (LUAD).

METHODS

To analyse PLIN3 expression in normal and cancerous tissues, relevance between PLIN3 expression and survival prognosis, and to predict the pathways related to PLIN3, bioinformatic analysis was performed. In A549 and H1299 cells, qRT-PCR or western blotting was used to determine mRNA/protein expression of PLIN3, PD-L1, and c-Myc. In A549 and H1299 cells, CCK-8 assay, EdU, and flow cytometry were used to assess cell viability, proliferation, and apoptosis. Chip and luciferase reporter assays were performed to verify the binding of PD-L1 with c-Myc. The functions of PLIN3 were examined in vivo in a xenograft tumor model.

RESULTS

In LUAD tissues and cells, PLIN3 expression was downregulated. A shorter survival time was observed in patients with high PLIN3 expression than in patients with low PLIN3 expression. Silencing of PLIN3 inhibited cell proliferation, PD-L1 expression, and Myc pathway, as well as induced apoptosis in LUAD cells. c-Myc acts as a transcription factor of PD-L1. Moreover, the inhibitory actions of PLIN3 silencing on c-Myc and PD-L1 expression as well as cell proliferation and stimulatory action of PLIN3 silencing on cell apoptosis were reversed by c-Myc overexpression. In vivo, PLIN3 silencing inhibited the growth of xenograft tumour and reduced PLIN3, PD-L1, and c-Myc protein expression.

CONCLUSION

Silencing of PLIN3 inhibited tumour growth by regulating the Myc/PD-L1 pathway.

FABP5 regulates lipid metabolism to facilitate pancreatic neuroendocrine neoplasms progression via FASN mediated Wnt/β-catenin pathway

Pancreatic neuroendocrine neoplasms (pNENs) are among the most frequently occurring neuroendocrine neoplasms (NENs) and require targeted therapy. High levels of fatty acid binding protein 5 (FABP5) are involved in tumor progression, but its role in pNENs remains unclear. We investigated the mRNA and protein levels of FABP5 in pNEN tissues and cell lines and found them to be upregulated. We evaluated changes in cell proliferation using CCK-8, colony formation, and 5-ethynyl-2'-deoxyuridine assays and examined the effects on cell migration and invasion using transwell assays. We found that knockdown of FABP5 suppressed the proliferation, migration, and invasion of pNEN cell lines, while overexpression of FABP5 had the opposite effect. Co-immunoprecipitation experiments were performed to clarify the interaction between FABP5 and fatty acid synthase (FASN). We further showed that FABP5 regulates the expression of FASN via the ubiquitin proteasome pathway and both proteins facilitate the progression of pNENs. Our study demonstrated that FABP5 acts as an oncogene by promoting lipid droplet deposition and activating the WNT/β-catenin signaling pathway. Moreover, the carcinogenic effects of FABP5 can be reversed by orlistat, providing a novel therapeutic intervention option.

High-expressed PTPN1 promotes tumor proliferation signature in human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly prevalent malignant tumor that is associated with substantial morbidity and mortality rates. Despite the progress made in diagnostic technology, the survival rate of HCC patients remains unsatisfactory due to the complex nature and extensive metastasis of the disease. Consequently, the discovery of new molecular targets is of great practical significance for the diagnosis and treatment of HCC. Protein tyrosine phosphatases (PTPs) play a crucial role in cell signal transduction by catalyzing the dephosphorylation of tyrosine residues in proteins. The present study has revealed that the upregulation of protein tyrosine phosphatase non-receptor type 1 (PTPN1) is a characteristic feature of HCC and is associated with a poor prognosis. Additionally, our investigation into the functional roles of PTPN1-regulated genes in HCC has demonstrated that alterations in PTPN1 expression disrupt normal cell cycle progression metabolism. Additionally, the capacity for proliferation and migration of HCC cells was notably diminished subsequent to PTPN1 silencing, resulting in the prevention of cell entry into the S phase from the G1 phase. Our investigation indicates that PTPN1 may facilitate the onset and progression of HCC by disrupting the cell cycle, thereby presenting a promising molecular target for the diagnosis and treatment of liver cancer.

Challenges in Pharmacological Intervention in Perilipins (PLINs) to Modulate Lipid Droplet Dynamics in Obesity and Cancer

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.

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

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

RIPK3 dampens mitochondrial bioenergetics and lipid droplet dynamics in metabolic liver disease

BACKGROUND AND AIMS

Receptor-interacting protein kinase 3 (RIPK3) mediates NAFLD progression, but its metabolic function is unclear. Here, we aimed to investigate the role of RIPK3 in modulating mitochondria function, coupled with lipid droplet (LD) architecture in NAFLD.

APPROACH AND RESULTS

Functional studies evaluating mitochondria and LD biology were performed in wild-type (WT) and Ripk3-/- mice fed a choline-deficient, amino acid-defined (CDAA) diet for 32 and 66 weeks and in CRISPR-Cas9 Ripk3 -null fat-loaded immortalized hepatocytes. The association between hepatic perilipin (PLIN) 1 and 5, RIPK3, and disease severity was also addressed in a cohort of patients with NAFLD and in PLIN1 -associated familial partial lipodystrophy. Ripk3 deficiency rescued impairment in mitochondrial biogenesis, bioenergetics, and function in CDAA diet-fed mice and fat-loaded hepatocytes. Ripk3 deficiency was accompanied by a strong upregulation of antioxidant systems, leading to diminished oxidative stress upon fat loading both in vivo and in vitro. Strikingly, Ripk3-/- hepatocytes displayed smaller size LD in higher numbers than WT cells after incubation with free fatty acids. Ripk3 deficiency upregulated adipocyte and hepatic levels of LD-associated proteins PLIN1 and PLIN5. PLIN1 upregulation controlled LD structure and diminished mitochondrial stress upon free fatty acid overload in Ripk3-/- hepatocytes and was associated with diminished human NAFLD severity. Conversely, a pathogenic PLIN1 frameshift variant was associated with NAFLD and fibrosis, as well as with increased hepatic RIPK3 levels in familial partial lipodystrophy.

CONCLUSIONS

Ripk3 deficiency restores mitochondria bioenergetics and impacts LD dynamics. RIPK3 inhibition is promising in ameliorating NAFLD.

Integrative Analysis of the Predictive Value of Perilipin Family on Clinical Significance, Prognosis and Immunotherapy of Glioma

Gliomas are common tumors of the central nervous system. The PLINs family is widely involved in the regulation of lipid metabolism and has been associated with the development and invasive metastasis of various malignancies. However, the biological role of the PLINs family in gliomas is still unclear. TIMER and UALCAN were used to assess PLINs mRNA expression in gliomas. “Survminer” and “Survival” were used to evaluate the connection between PLINs expression and glioma patients’ survival. cBioPortal was applied to assess PLINs’ genetic alterations in glioblastoma multiforme (GBM) and low-grade glioma (LGG). The correlation of PLINs expression with tumor immune cells was analyzed by TIMER. The expressions of PLIN1, PLIN4, and PLIN5 were decreased in GBM compared to normal tissues. However, PLIN2 and PLIN3 were significantly increased in GBM. Prognostic analysis showed that LGG patients with high PLIN1 expression had better overall survival (OS), and high expression of PLIN2/3/4/5 was associated with unfavorable OS. We further determined that the expression of PLINs members in gliomas was strongly related to tumor immune cells and immune checkpoint-associated genes. PLINS may be potential biomarkers for regulating the tumor microenvironment and predicting the efficacy of immunotherapy. In addition, we determined that PLIN1 may affect glioma patients’ therapeutic sensitivity to temozolomide. Our results demonstrated the biological significance and clinical values of PLINs in gliomas and provide a basis for future in-depth exploration of the specific mechanisms of each member of PLINs in gliomas.

The Non-Invasive Assessment of Circulating D-Loop and mt-ccf Levels Opens an Intriguing Spyhole into Novel Approaches for the Tricky Diagnosis of NASH

Nonalcoholic fatty liver disease (NAFLD) is the commonest liver disease worldwide affecting both adults and children. Nowadays, no therapeutic strategies have been approved for NAFLD management, and hepatic biopsy remains the gold standard procedure for its diagnosis. NAFLD is a multifactorial disease whose pathogenesis is affected by environmental and genetic factors, and it covers a spectrum of conditions ranging from simple steatosis up to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Several studies underlined the urgent need to develop an NAFLD risk prediction model based on genetics, biochemical indicators, and metabolic disorders. The loss of mitochondrial dynamics represents a typical feature of progressive NAFLD. The imbalance of mitochondrial lifecycle together with the impairment of mitochondrial biomass and function trigger oxidative stress, which in turn damages mitochondrial DNA (mtDNA). We recently demonstrated that the main genetic predictors of NAFLD led to mitochondrial dysfunction. Moreover, emerging evidence shows that variations in the displacement loop (D-loop) region impair mtDNA replication, and they have been associated with advanced NAFLD. Finally, lower levels of mitophagy foster the overload of damaged mitochondria, resulting in the release of cell-free circulating mitochondrial DNA (mt-ccf) that exacerbates liver injury. Thus, in this review we summarized what is known about D-loop region alterations and mt-ccf content during NAFLD to propose them as novel non-invasive biomarkers.

PNPLA3(I148M) Inhibits Lipolysis by Perilipin-5-Dependent Competition with ATGL

The single nucleotide polymorphism I148M of the lipase patatin-like phospholipase domain containing 3 (PNPLA3) is associated with an unfavorable prognosis in alcoholic and non-alcoholic steatohepatitis (ASH, NASH), with progression to liver cirrhosis and development of hepatocellular carcinoma. In this study, we investigated the mechanistic interaction of PNPLA3 with lipid droplet (LD)-associated proteins of the perilipin family, which serve as gatekeepers for LD degradation. In a collective of 106 NASH, ASH and control liver samples, immunohistochemical analyses revealed increased ballooning, inflammation and fibrosis, as well as an accumulation of PNPLA3-perilipin 5 complexes on larger LDs in patients homo- and heterozygous for PNPLA3(I148M). Co-immunoprecipitation demonstrated an interaction of PNPLA3 with perilipin 5 and the key enzyme of lipolysis, adipose triglyceride lipase (ATGL). Localization studies in cell cultures and human liver showed colocalization of perilipin 5, ATGL and PNPLA3. Moreover, the lipolytic activity of ATGL was negatively regulated by PNPLA3 and perilipin 5, whereas perilipin 1 displaced PNPLA3 from the ATGL complex. Furthermore, ballooned hepatocytes, the hallmark of steatohepatitis, were positive for PNPLA3 and perilipins 2 and 5, but showed decreased perilipin 1 expression with respect to neighboured hepatocytes. In summary, PNPLA3- and ATGL-driven lipolysis is significantly regulated by perilipin 1 and 5 in steatohepatitis.

Lipid Droplet-Associated Proteins Perilipin 1 and 2: Molecular Markers of Steatosis and Microvesicular Steatotic Foci in Chronic Hepatitis C

Chronic infection with hepatitis C (HCV) is a major risk factor in the development of cirrhosis and hepatocellular carcinoma. Lipid metabolism plays a major role in the replication and deposition of HCV at lipid droplets (LDs). We have demonstrated the importance of LD-associated proteins of the perilipin family in steatotic liver diseases. Using a large collection of 231 human liver biopsies with HCV, perilipins 1 and 2 have been localized to LDs of hepatocytes that correlate with the degree of steatosis and specific HCV genotypes, but not significantly with the HCV viral load. Perilipin 1- and 2-positive microvesicular steatotic foci were observed in 36% of HCV liver biopsies, and also in chronic hepatitis B, autoimmune hepatitis and mildly steatotic or normal livers, but less or none were observed in normal livers of younger patients. Microvesicular steatotic foci did not frequently overlap with glycogenotic/clear cell foci as determined by PAS stain in serial sections. Steatotic foci were detected in all liver zones with slight architectural disarrays, as demonstrated by immunohistochemical glutamine synthetase staining of zone three, but without elevated Ki67-proliferation rates. In conclusion, microvesicular steatotic foci are frequently found in chronic viral hepatitis, but the clinical significance of these foci is so far not clear.

Mass Spectrometry-Based Proteomics of Human Milk to Identify Differentially Expressed Proteins in Women with Breast Cancer versus Controls

It is thought that accurate risk assessment and early diagnosis of breast cancer (BC) can help reduce cancer-related mortality. Proteomics analysis of breast milk may provide biomarkers of risk and occult disease. Our group works on the analysis of human milk samples from women with BC and controls to investigate alterations in protein patterns of milk that could be related to BC. In the current study, we used mass spectrometry (MS)-based proteomics analysis of 12 milk samples from donors with BC and matched controls. Specifically, we used one-dimensional (1D)-polyacrylamide gel electrophoresis (PAGE) coupled with nanoliquid chromatography tandem MS (nanoLC-MS/MS), followed by bioinformatics analysis. We confirmed the dysregulation of several proteins identified previously in a different set of milk samples. We also identified additional dysregulations in milk proteins shown to play a role in cancer development, such as Lactadherin isoform A, O-linked N-acetylglucosamine (GlcNAc) transferase, galactosyltransferase, recoverin, perilipin-3 isoform 1, histone-lysine methyltransferase, or clathrin heavy chain. Our results expand our current understanding of using milk as a biological fluid for identification of BC-related dysregulated proteins. Overall, our results also indicate that milk has the potential to be used for BC biomarker discovery, early detection and risk assessment in young, reproductively active women.

Statins Lower Lipid Synthesis But Promote Secretion of Cholesterol-Enriched Extracellular Vesicles and Particles

Lipid droplets are lipid-rich cytosolic organelles that play roles in cell signaling, membrane trafficking, and many other cellular activities. Recent studies revealed that lipid droplets in cancer cells have various biological functions, such as energy production, membrane synthesis, and chemoresistance, thereby fostering cancer progression. Accordingly, the administration of antilipemic agents could improve anti-cancer treatment efficacy given hydrophobic chemotherapeutic drugs could be encapsulated into lipid droplets and then expelled to extracellular space. In this study, we investigated whether statins could promote treatment efficacy of lipid droplet-rich ovarian SKOV-3 cells and the potential influences on generation and composition of cell-derived extracellular vesicles and particles (EVP). Our studies indicate that statins can significantly lower lipid biosynthesis. Moreover, statins can inhibit proliferation, migration, and invasion of SKOV-3 cells and enhance chemosensitivity in vitro and in vivo. Furthermore, statins can lower EVP secretion but enforce the release of cholesterol-enriched EVPs, which can further lower lipid contents in parental cells. It is the first time that the influence of statins on EVP generation and EVP-lipid composition is observed. Overall, we demonstrated that statins could inhibit lipid production, expel cholesterol to extracellular space via EVPs, and improve chemosensitivity.

Perilipins at a glance

Lipid droplets (LDs) are ubiquitous organelles that store and supply lipids for energy metabolism, membrane synthesis and production of lipid-derived signaling molecules. While compositional differences in the phospholipid monolayer or neutral lipid core of LDs impact their metabolism and function, the proteome of LDs has emerged as a major influencer in all aspects of LD biology. The perilipins (PLINs) are the most studied and abundant proteins residing on the LD surface. This Cell Science at a Glance and the accompanying poster summarize our current knowledge of the common and unique features of the mammalian PLIN family of proteins, the mechanisms through which they affect cell metabolism and signaling, and their links to disease.

Lipophagy-related protein perilipin-3 (PLIN3) and resistance of prostate cancer to radiotherapy

PURPOSE

Radiotherapy is a principal treatment modality for localized and locally advanced prostate cancer (PCa). Metabolic alterations, including lipid metabolism, may reduce treatment efficacy resulting in tumor relapse and poor therapeutic outcome. In the current study, we investigated the role of the lipophagy-related protein perilipin-3 (PLIN3) and the lysosomal acid lipase (LAL) in PCa response to radiotherapy.

METHODS AND MATERIALS

We explored the in vitro and xenograft (in NOD.SCID and R2G2 mice) response to radiation of either PLIN3-depleted or LAL-depleted hormone-refractory (DU145, PC3), and hormone-responsive 22Rv1 PCa cell lines. Moreover, we evaluated the clinical role of PLIN3 and LAL protein expression in a series of PCa tissue specimens from patients treated with radical radiotherapy.

RESULTS

In vitro and in vivo experiments showed reduced proliferation and strong radiosensitization of all studied PCa cell lines upon PLIN3 depletion. In vivo experiments demonstrated the significantly augmented radiotherapy efficacy upon PLIN3 depletion, resulting in extensive tissue necrosis. PLIN3 overexpression in tissue specimens was correlated with increased MIB1 proliferation index, increased autophagy flux, reduced response to radiotherapy and poor prognosis. The impact of LAL depletion on radiotherapy was of lesser importance.

CONCLUSIONS

Assessment of PLIN3 expression may identify subgroups of PCa patients less responsive to radiotherapy, and at high risk of relapse post irradiation. Whether radiotherapy efficacy may be enhanced by concurrent autophagy or PLIN3 inhibition in this sub-group of patients demands clinical evaluation.

TGFβ Drives Metabolic Perturbations during Epithelial Mesenchymal Transition in Pancreatic Cancer: TGFβ Induced EMT in PDAC

Simple Summary

Pancreatic cancer is an aggressive disease with most patients diagnosed at late stages resulting in poor outcomes. While it is known that pancreatic tumor cells undergo epithelial to mesenchymal transition, the metabolic alterations accompanying that transition are not characterized. This study leveraged a metabolomics approach to understand the small molecule and biochemical perturbations that can be targeted for designing strategies for improving outcomes in pancreatic cancer.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy wherein a majority of patients present metastatic disease at diagnosis. Although the role of epithelial to mesenchymal transition (EMT), mediated by transforming growth factor beta (TGFβ), in imparting an aggressive phenotype to PDAC is well documented, the underlying biochemical pathway perturbations driving this behaviour have not been elucidated. We used high-resolution mass spectrometry (HRMS) based molecular phenotyping approach in order to delineate metabolic changes concomitant to TGFβ-induced EMT in pancreatic cancer cells. Strikingly, we observed robust changes in amino acid and energy metabolism that may contribute to tumor invasion and metastasis. Somewhat unexpectedly, TGFβ treatment resulted in an increase in intracellular levels of retinoic acid (RA) that in turn resulted in increased levels of extracellular matrix (ECM) proteins including fibronectin (FN) and collagen (COL1). These findings were further validated in plasma samples obtained from patients with resectable pancreatic cancer. Taken together, these observations provide novel insights into small molecule dysregulation that triggers a molecular cascade resulting in increased EMT-like changes in pancreatic cancer cells, a paradigm that can be potentially targeted for better clinical outcomes.

The Bank Vole (Clethrionomys glareolus)—Small Animal Model for Hepacivirus Infection

Many people worldwide suffer from hepatitis C virus (HCV) infection, which is frequently persistent. The lack of efficient vaccines against HCV and the unavailability of or limited compliance with existing antiviral therapies is problematic for health care systems worldwide. Improved small animal models would support further hepacivirus research, including development of vaccines and novel antivirals. The recent discovery of several mammalian hepaciviruses may facilitate such research. In this study, we demonstrated that bank voles (Clethrionomys glareolus) were susceptible to bank vole-associated Hepacivirus F and Hepacivirus J strains, based on the detection of hepaciviral RNA in 52 of 55 experimentally inoculated voles. In contrast, interferon α/β receptor deficient C57/Bl6 mice were resistant to infection with both bank vole hepaciviruses (BvHVs). The highest viral genome loads in infected voles were detected in the liver, and viral RNA was visualized by in situ hybridization in hepatocytes, confirming a marked hepatotropism. Furthermore, liver lesions in infected voles resembled those of HCV infection in humans. In conclusion, infection with both BvHVs in their natural hosts shares striking similarities to HCV infection in humans and may represent promising small animal models for this important human disease.

Elevated ATGL in colon cancer cells and cancer stem cells promotes metabolic and tumorigenic reprogramming reinforced by obesity

Obesity is a worldwide epidemic associated with increased risk and progression of colon cancer. Here, we aimed to determine the role of adipose triglyceride lipase (ATGL), responsible for intracellular lipid droplet (LD) utilization, in obesity-driven colonic tumorigenesis. In local colon cancer patients, significantly increased ATGL levels in tumor tissue, compared to controls, were augmented in obese individuals. Elevated ATGL levels in human colon cancer cells (CCC) relative to non-transformed were augmented by an obesity mediator, oleic acid (OA). In CCC and colonospheres, enriched in colon cancer stem cells (CCSC), inhibition of ATGL prevented LDs utilization and inhibited OA-stimulated growth through retinoblastoma-mediated cell cycle arrest. Further, transcriptomic analysis of CCC, with inhibited ATGL, revealed targeted pathways driving tumorigenesis, and high-fat-diet obesity facilitated tumorigenic pathways. Inhibition of ATGL in colonospheres revealed targeted pathways in human colonic tumor crypt base cells (enriched in CCSC) derived from colon cancer patients. In CCC and colonospheres, we validated selected transcripts targeted by ATGL inhibition, some with emerging roles in colonic tumorigeneses (ATG2B, PCK2, PGAM1, SPTLC2, IGFBP1, and ABCC3) and others with established roles (MYC and MUC2). These findings demonstrate obesity-promoted, ATGL-mediated colonic tumorigenesis and establish the therapeutic significance of ATGL in obesity-reinforced colon cancer progression.

Steatotic and Steatohepatitic Hepatocellular Carcinomas: Features in a Series With Predominantly Viral Etiology

Hepatocellular carcinomas (HCCs) with steatohepatitis and steatosis are reported with varying definitions and clinicopathologic features. We aimed to search the attributes of steatohepatitic hepatocellular carcinoma (SH-HCC) and steatotic-HCC in our series. A retrospective clinicopathologic analyses of 150 HCCs and immunostaining for C-reactive protein (CRP) and serum amyloid A (SAA) were performed. Tumors were reclassified as all SH-HCC, limited SH-HCC, typical SH-HCC (steatohepatitic features in >5%, 5% to 50%, and ≥50% of the tumor, respectively), steatotic-HCC, and classic HCC (C-HCC). Group comparisons were made using Kruskal-Wallis and Kaplan-Meier tests. The background etiology in all SH-HCCs was pure viral in 51.4%, nonalcoholic steatohepatitis (NASH)/alcoholic liver disease (ALD) alone/mixed in 34.3%, and unidentified in normal liver in 14.3%. All SH-HCCS (n=35, 23.3%) and typical SH-HCCs (n=13, 8.6%) had higher NASH/ALD. Limited SH-HCCs (n=22, 14.6%) had higher ALD (all P<0.05). Typical SH-HCCs tended to have more NASH (P=0.054). Steatotic-HCCs (n=13, 9%) and C-HCCs (n=102, 68%) had higher pure viral etiology and serum CRP (all P<0.05). CRP and SAA were positive in 69% and 27% of the tumors, respectively. SAA positivity correlated with ALD (P=0.026). In the overall group disease-free survival rates at 1, 5, 10, and 20 years were 97.0%, 82.3%, 79.6%, and 77.2%, respectively. Demographics, tumor characteristics, CRP and SAA positivity, and survival were similar between the groups (P>0.05). SH-HCC is heterogenous in terms of underlying etiologies, and can be seen in NASH/ALD, pure viral and noncirrhotic/normal background. The ≥50% cutoff for the definition of SH-HCC can lead to overlook ALD-related SH-HCC. Steatotic-HCC seems more similar to C-HCC rather than SH-HCC, but none of them feature as a different prognostic group.

Lipid Droplet-Associated Factors, PNPLA3, TM6SF2, and HSD17B Proteins in Hepatopancreatobiliary Cancer

Simple Summary

Aberrant lipid synthesis and reprogrammed lipid metabolism are both associated with the development and progression of pancreatic and liver cancer. Most cells store fatty acids in the form of triacylglycerols in lipid droplets. Lipid droplets are intracellular organelles that not only store neutral lipids, but also play roles as molecular messengers and signaling factors. Some cancer cells accumulate massive amount of lipid droplets. Lipid droplets and lipid droplet-associated factors are further implicated to mediate proliferation, invasion, metastasis, as well as chemotherapy resistance in several types of cancer. This review dissected recent findings on the role of several lipid droplet-associated factors, patatin-like phospholipase domain-containing 3 (PNPLA3), Transmembrane 6 superfamily member 2 (TM6SF2), and 17β-hydroxysteroid dehydrogenase (HSD17B) 11 and 13 as well as their genetic variations in hepatopancreatobiliary diseases, especially cancer.

Abstract

Pancreatic and liver cancer are leading causes of cancer deaths, and by 2030, they are projected to become the second and the third deadliest cancer respectively. Cancer metabolism, especially lipid metabolism, plays an important role in progression and metastasis of many types of cancer, including pancreatic and liver cancer. Lipid droplets are intracellular organelles that store neutral lipids, but also act as molecular messengers, and signaling factors. It is becoming increasingly evident that alterations in the regulation of lipid droplets and their associated factors influence the risk of developing not only metabolic disease but also fibrosis and cancer. In the current review article, we summarized recent findings concerning the roles of lipid droplet-associated factors, patatin-like phospholipase domain-containing 3, Transmembrane 6 superfamily member 2, and 17β-hydroxysteroid dehydrogenase 11 and 13 as well as genetic variants in pancreatic and hepatic diseases. A better understanding of cancer type- and cell type-specific roles of lipid droplet-associated factors is important for establishing new therapeutic options in the future.

Suppressed PLIN3 frequently occurs in prostate cancer, promoting docetaxel resistance via intensified autophagy, an event reversed by chloroquine

Lipid metabolism reprogramming is one of the adaptive events that drive tumor development and survival, and may account for resistance to chemotherapeutic drugs. Perilipins are structural proteins associated with lipophagy and lipid droplet integrity, and their overexpression is associated with tumor aggressiveness. Here, we sought to explore the role of lipid droplet-related protein perilipin-3 (PLIN3) in prostate cancer (PCa) chemotherapy. We investigated the role of PLIN3 suppression in docetaxel cytotoxic activity in PCa cell lines. Additional effects of PLIN3 depletion on autophagy-related proteins and gene expression patterns, apoptotic potential, proliferation rate, and ATP levels were examined. Depletion of PLIN3 resulted in docetaxel resistance, accompanied by enhanced autophagic flux. We further assessed the synergistic effect of autophagy suppression with chloroquine on docetaxel cytotoxicity. Inhibition of autophagy with chloroquine reversed chemoresistance of stably transfected shPLIN3 PCa cell lines, with no effect on the parental ones. The shPLIN3 cell lines also exhibited reduced Caspase-9 related apoptosis initiation. Moreover, we assessed PLIN3 expression in a series of PCa tissue specimens, were complete or partial loss of PLIN3 expression was frequently noted in 70% of the evaluated specimens. Following PLIN3 silencing, PCa cells were characterized by impaired lipophagy and acquired an enhanced autophagic response upon docetaxel-induced cytotoxic stress. Such an adaptation leads to resistance to docetaxel, which could be reversed by the autophagy blocker chloroquine. Given the frequent loss of PLIN3 expression in PCa specimens, we suggest that combination of docetaxel with chloroquine may improve the efficacy of docetaxel treatment in PLIN3-deficient cancer patients.

Understanding the Role of Perilipin 5 in Non-Alcoholic Fatty Liver Disease and Its Role in Hepatocellular Carcinoma: A Review of Novel Insights

Consumption of high-calorie foods, such as diets rich in fats, is an important factor leading to the development of steatohepatitis. Several studies have suggested how lipid accumulation creates a lipotoxic microenvironment for cells, leading cells to deregulate their transcriptional and translational activity. This deregulation induces the development of liver diseases such as non-alcoholic fatty liver disease (NAFLD) and subsequently also the appearance of hepatocellular carcinoma (HCC) which is one of the deadliest types of cancers worldwide. Understanding its pathology and studying new biomarkers with better specificity in predicting disease prognosis can help in the personalized treatment of the disease. In this setting, understanding the link between NAFLD and HCC progression, the differentiation of each stage in between as well as the mechanisms underlying this process, are vital for development of new treatments and in exploring new therapeutic targets. Perilipins are a family of five closely related proteins expressed on the surface of lipid droplets (LD) in several tissues acting in several pathways involved in lipid metabolism. Recent studies have shown that Plin5 depletion acts protectively in the pathogenesis of liver injury underpinning the importance of pathways associated with PLIN5. PLIN5 expression is involved in pro-inflammatory cytokine regulation and mitochondrial damage, as well as endoplasmic reticulum (ER) stress, making it critical target of the NAFLD-HCC studies. The aim of this review is to dissect the recent findings and functions of PLIN5 in lipid metabolism, metabolic disorders, and NAFLD as well as the progression of NAFLD to HCC.

Remodeling of Mitochondrial Plasticity: The Key Switch from NAFLD/NASH to HCC

Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver and the third-leading cause of cancer-related mortality. Currently, the global burden of nonalcoholic fatty liver disease (NAFLD) has dramatically overcome both viral and alcohol hepatitis, thus becoming the main cause of HCC incidence. NAFLD pathogenesis is severely influenced by lifestyle and genetic predisposition. Mitochondria are highly dynamic organelles that may adapt in response to environment, genetics and epigenetics in the liver ("mitochondrial plasticity"). Mounting evidence highlights that mitochondrial dysfunction due to loss of mitochondrial flexibility may arise before overt NAFLD, and from the early stages of liver injury. Mitochondrial failure promotes not only hepatocellular damage, but also release signals (mito-DAMPs), which trigger inflammation and fibrosis, generating an adverse microenvironment in which several hepatocytes select anti-apoptotic programs and mutations that may allow survival and proliferation. Furthermore, one of the key events in malignant hepatocytes is represented by the remodeling of glucidic-lipidic metabolism combined with the reprogramming of mitochondrial functions, optimized to deal with energy demand. In sum, this review will discuss how mitochondrial defects may be translated into causative explanations of NAFLD-driven HCC, emphasizing future directions for research and for the development of potential preventive or curative strategies.

Lipid droplet biogenesis and COX-2 pathway activation are triggered by Barrett's esophagus and adenocarcinoma, but not esophageal squamous cell carcinoma risk factors

Esophageal cancer (EC) is an aggressive disease, presenting two main histological subtypes: adenocarcinoma (EAC) and squamous cell carcinoma (ESCC). The two EC subtypes widely differ concerning virtually all factors. ESCC development is mainly associated with tobacco and alcohol abuse, whereas obesity and chronic gastroesophageal reflux disease (GERD) are important risk factors not only for EAC, but also for for Barrett’s esophagus (BE), an intestinal metaplasia that precedes EAC. Obesity triggers ectopic lipid droplets (LD) accumulation in non-adipose tissues. LD are organelles involved in cell metabolism, signaling, proliferation and production of inflammatory mediators. Therefore, the aim of this work was to investigate LD occurrence and role in EC. This study shows progressive LD levels increase along EAC development, in esophageal samples from non-obese through obese individuals, as well as BE, and EAC patients, whereas no significant changes were observed in ESCC samples, when compared to non-tumor samples. Additionally, in order to mimic BE and EAC risk factors exposure, a non-tumor esophageal cell line was incubated with oleic acid (OA) and acidified medium and/or deoxycholic acid (DCA), revealing a significant increment in LD amount as well as in COX-2 and CXCL-8 expression, and in IL-8 secretion. Further, COX-2 expression and LD amount presented a significant positive correlation and were detected co-localized in EAC, but not in ESCC, suggesting that LD may be the site for eicosanoid production in EAC. In conclusion, this study shows that obesity, and BE- and EAC-associated inflammatory stimuli result in a gradual increase of LD, that may be responsible for orchestrating inflammatory mediators’ production and/or action, thus contributing to BE and EAC genesis and progression.

Hepatic lipid droplets: A balancing act between energy storage and metabolic dysfunction in NAFLD

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is defined by the abundance of lipid droplets (LDs) in hepatocytes. While historically considered simply depots for energy storage, LDs are increasingly recognized to impact a wide range of biological processes that influence cellular metabolism, signaling, and function. While progress has been made toward understanding the factors leading to LD accumulation (i.e. steatosis) and its progression to advanced stages of NAFLD and/or systemic metabolic dysfunction, much remains to be resolved.

SCOPE OF REVIEW

This review covers many facets of LD biology. We provide a brief overview of the major pathways of lipid accretion and degradation that contribute to steatosis and how they are altered in NAFLD. The major focus is on the relationship between LDs and cell function and the detailed mechanisms that couple or uncouple steatosis from the severity and progression of NAFLD and systemic comorbidities. The importance of specific lipids and proteins within or on LDs as key components that determine whether LD accumulation is linked to cellular and metabolic dysfunction is presented. We discuss emerging areas of LD biology and future research directions that are needed to advance our understanding of the role of LDs in NAFLD etiology.

MAJOR CONCLUSIONS

Impairments in LD breakdown appear to contribute to disease progression, but inefficient incorporation of fatty acids (FAs) into LD-containing triacylglycerol (TAG) and the consequential changes in FA partitioning also affect NAFLD etiology. Increased LD abundance in hepatocytes does not necessarily equate to cellular dysfunction. While LD accumulation is the prerequisite step for most NAFLD cases, the protein and lipid composition of LDs are critical factors in determining the progression from simple steatosis. Further defining the detailed molecular mechanisms linking LDs to metabolic dysfunction is important for designing effective therapeutic approaches targeting NAFLD and its comorbidities.

Fatty-acid-induced FABP5/HIF-1 reprograms lipid metabolism and enhances the proliferation of liver cancer cells

Hypoxia-inducible factor-1 alpha (HIF-1α) is a transcription factor essential for cancer cell survival. The reprogramming of lipid metabolism has emerged as a hallmark of cancer, yet the relevance of HIF-1α to this process remains elusive. In this study, we profile HIF-1α-interacting proteins using proteomics analysis and identify fatty acid-binding protein 5 (FABP5) as a critical HIF-1α-binding partner. In hepatocellular carcinoma (HCC) tissues, both FABP5 and HIF-1α are upregulated, and their expression levels are associated with poor prognosis. FABP5 enhances HIF-1α activity by promoting HIF-1α synthesis while disrupting FIH/HIF-1α interaction at the same time. Oleic-acid treatment activates the FABP5/HIF-1α axis, thereby promoting lipid accumulation and cell proliferation in HCC cells. Our results indicate that fatty-acid-induced FABP5 upregulation drives HCC progression through HIF-1-driven lipid metabolism reprogramming.

Seo et al. identify fatty acid-binding protein 5 (FABP5) as a booster of HIF-1α activity. They find that oleic-acid treatment activates the FABP5/HIF-1α axis, promoting lipid accumulation and cell proliferation in liver cancer cells. This study provides insights into how fatty acids drive the progression of cancer.

Adipophilin expression in cutaneous malignant melanoma is associated with high proliferation and poor clinical prognosis

Adipophilin (ADP) is a primary protein component of lipid droplets (LDs). For more than half a century, certain types of cancer cells have been known to contain LDs in their cytoplasm. However, the pathological significance of ADP or LDs in cancer remains unclear. In the present study, we investigated the association between ADP and other pathological characteristics in cutaneous malignant melanomas to clarify the role of ADP in melanoma cells. We immunostained whole paraffin sections of primary cutaneous melanomas obtained from 90 cases for ADP, after which we analyzed the correlation between ADP immunohistochemistry (IHC) and patient survival data. We also studied the relationship between the ADP IHC score and in situ hybridization (ISH) score of ADP mRNA, and the Ki67-labeling index (Ki67-LI) by using tissue microarrays consisting of 74 primary cutaneous malignant melanomas, 19 metastasizing melanomas, and 29 melanocytic nevi. Finally, we analyzed the relationship between ADP expression and cell proliferation in cutaneous melanoma cell lines. We found that high ADP expression was associated with poor metastasis-free survival, disease-specific survival, and overall survival rates of patients with cutaneous melanomas (P < 0.05). By linear regression analysis, ADP IHC was correlated with increasing ADP mRNA ISH H-scores and Ki67-LI scores in melanocytic lesions (P < 0.01). ADP IHC and ADP ISH H-scores and Ki67-LI scores were greater in pT3-4 melanomas than in pT1-2 melanomas. In cell-based assays, cells with increased ADP expression showed higher proliferation rates compared with those of low-ADP cells. Thus, ADP expression in malignant melanoma was significantly associated with high cell proliferation and poor clinical prognosis. Our results thus indicate a significant association between ADP and melanoma progression, and we propose that ADP may be a novel marker of aggressive cutaneous melanoma with a lipogenic phenotype.

The Utility of Perilipin in Liposarcomas: PLIN1 Differentiates Round Cell Liposarcoma From Other Round Cell Sarcomas

Liposarcoma is the most common soft tissue sarcoma in adults; however, accurate diagnosis often depends on the use of ancillary molecular testing which can be time consuming and expensive. Myxoid/round cell liposarcoma may be a diagnostic challenge due to the morphologic similarities with other nonadipocytic sarcomas with round cell morphology. Immunohistochemistry may be a helpful adjunct to appropriately triage cases for molecular testing. Perilipin 1 (PLIN1) and perilipin 2 (adipophilin) (PLIN2) are intracellular proteins involved in lipid droplet formation, which we hypothesized may be useful as immunohistochemical markers for liposarcoma. Using archival tumor tissue, we assessed pattern of PLIN1 and PLIN2 expression in 46 adipocytic tumors and 36 nonadipocytic sarcomas. PLIN1 was expressed in 88% of liposarcomas, including 100% of myxoid/round cell liposarcomas, and did not have any expression in nonadipocytic sarcomas. PLIN1 was not expressed in dedifferentiated liposarcoma. Although PLIN2 demonstrates increased sensitivity for liposarcoma, including expression in dedifferentiated liposarcoma, it is not specific for adipocytic differentiation and is expressed in other nonadipocytic sarcomas. Furthermore, PLIN2 is not expressed in lipoma-like well-differentiated liposarcoma, and as such has limited diagnostic utility.

Lipid droplets: platforms with multiple functions in cancer hallmarks

Lipid droplets (also known as lipid bodies) are lipid-rich, cytoplasmic organelles that play important roles in cell signaling, lipid metabolism, membrane trafficking, and the production of inflammatory mediators. Lipid droplet biogenesis is a regulated process, and accumulation of these organelles within leukocytes, epithelial cells, hepatocytes, and other nonadipocyte cells is a frequently observed phenotype in several physiologic or pathogenic situations and is thoroughly described during inflammatory conditions. Moreover, in recent years, several studies have described an increase in intracellular lipid accumulation in different neoplastic processes, although it is not clear whether lipid droplet accumulation is directly involved in the establishment of these different types of malignancies. This review discusses current evidence related to the biogenesis, composition and functions of lipid droplets related to the hallmarks of cancer: inflammation, cell metabolism, increased proliferation, escape from cell death, and hypoxia. Moreover, the potential of lipid droplets as markers of disease and targets for novel anti-inflammatory and antineoplastic therapies will be discussed.

Clinicopathological features of hepatocellular carcinoma with fatty change: Tumors with macrovesicular steatosis have better prognosis and aberrant expression patterns of perilipin and adipophilin

The clinicopathological characteristics of steatosis in hepatocellular carcinoma (HCC) remain unclear. Here, we elucidate the features of macrovesicular steatosis (MaS) and microvesicular steatosis (MiS) in HCC and their relationships with background liver steatosis. A total of 165 HCC lesions were classified as MaS-HCC, MiS-HCC, or conventional HCC (cHCC) according to the cutoff value of 30% MaS or MiS in tumor cells. We analyzed the clinicopathological differences among these groups. MaS-HCC had less portal vein invasion, a higher proportion of HCC with intratumoral fibrosis, and a lower cumulative risk of recurrence than MiS-HCC or cHCC. Moreover, both MaS-HCC and MiS-HCC had lower incidences of hepatitis virus infection and higher levels of HbA1c than cHCC. Background liver steatosis was also higher in MaS-HCC than in cHCC. Immunohistochemical expression of perilipin (Plin1) and adipophilin (ADRP), major proteins expressed on lipid droplet membranes, revealed that almost all lipid droplets in HCC were Plin1 negative, whereas those in background liver were positive. In contrast, ADRP was expressed on lipid droplets in both HCC and background liver. We concluded that MaS-HCC and MiS-HCC were associated with metabolic abnormalities but exhibited different biologic behaviors. Furthermore, lipid droplets in HCC were pathophysiologically different from those in background liver.

Non-alcoholic Fatty Liver Disease and Diabetes Mellitus

Nonalcoholic fatty liver disease (NAFLD) has emerged as the leading liver disease globally. NAFLD patients can have a progressive phenotype, non-alcoholic steatohepatitis (NASH) that could lead to cirrhosis, liver failure and cancer. There is a close bi-directional relationship between NAFLD and type 2 diabetes mellitus (T2DM); NAFLD increases the risk for T2DM and its complications whereas T2DM increases the severity of NAFLD and its complications. The large global impact of NAFLD and T2DM on healthcare systems requires a paradigm shift from specialty care to early identification and risk stratification of NAFLD in primary care and diabetes clinics. Approach to diagnosis, risk stratification and management of NAFLD is discussed. In addition to optimizing the control of coexisting cardiometabolic comorbidities, early referral of NAFLD patients at high risk of having NASH or significant fibrosis to hepatology specialist care may improve management and allow access for clinical trials. Lifestyle modifications, vitamin E, pioglitazone and metformin are currently available options that may benefit patients with T2DM and NAFLD. The burst of clinical trials investigating newer therapeutic agents for NAFLD and NASH offer hope for new, effective and safe therapies in the near future.

CGI-58: Versatile Regulator of Intracellular Lipid Droplet Homeostasis

Comparative gene identification-58 (CGI-58), also known as α/β-hydrolase domain-containing 5 (ABHD5), is a member of a large family of proteins containing an α/β-hydrolase-fold. CGI-58 is well-known as the co-activator of adipose triglyceride lipase (ATGL), which is a key enzyme initiating cytosolic lipid droplet lipolysis. Mutations in either the human CGI-58 or ATGL gene cause an autosomal recessive neutral lipid storage disease, characterized by the excessive accumulation of triglyceride (TAG)-rich lipid droplets in the cytoplasm of almost all cell types. CGI-58, however, has ATGL-independent functions. Distinct phenotypes associated with CGI-58 deficiency commonly include ichthyosis (scaly dry skin), nonalcoholic steatohepatitis, and hepatic fibrosis. Through regulated interactions with multiple protein families, CGI-58 controls many metabolic and signaling pathways, such as lipid and glucose metabolism, energy balance, insulin signaling, inflammatory responses, and thermogenesis. Recent studies have shown that CGI-58 regulates the pathogenesis of common metabolic diseases in a tissue-specific manner. Future studies are needed to molecularly define ATGL-independent functions of CGI-58, including the newly identified serine protease activity of CGI-58. Elucidation of these versatile functions of CGI-58 may uncover fundamental cellular processes governing lipid and energy homeostasis, which may help develop novel approaches that counter against obesity and its associated metabolic sequelae.

Three-dimensional label-free imaging throughout adipocyte differentiation by stimulated Raman microscopy

Lipid droplets are lipid-storage organelles with a key role in lipid accumulation pathologies such as diabetes, obesity and atherosclerosis. Despite their important functions many aspects of lipid droplets biology are still unknown. This is partially due to the current use of exogenous labels to monitor their formation and remodelling by invasive imaging methods. Here, we apply stimulated Raman scattering microscopy to acquire images with high spatial resolution along with resolving capabilities of lipids and proteins and three-dimensional sectioning. Our images and data analysis demonstrate an increase in the number of large (>15μm²) lipid droplets in human adipocyte cells during differentiation process. In addition, spatially-resolved maps of lipids and proteins inside cells and three dimensional reconstructions of lipids at the initial and final steps of adipocyte differentiation are reported, too.

Cell Cycle Progression Regulates Biogenesis and Cellular Localization of Lipid Droplets

Intracellular lipid accumulation has been associated with a poor prognosis in cancer. We have previously reported the involvement of lipid droplets in cell proliferation in colon cancer cells, suggesting a role for these organelles in cancer development.

Intracellular lipid accumulation has been associated with a poor prognosis in cancer. We have previously reported the involvement of lipid droplets in cell proliferation in colon cancer cells, suggesting a role for these organelles in cancer development. In this study, we evaluate the role of lipid droplets in cell cycle regulation and cellular transformation. Cell cycle synchronization of NIH 3T3 cells revealed increased numbers and dispersed distribution of lipid droplets specifically during S phase. Also, the transformed cell lineage NIH 3T3-H-rasV12 showed an accumulation of both lipid droplets and PLIN2 protein above the levels in NIH 3T3 cells. PLIN2 gene overexpression, however, was not able to induce NIH 3T3 cell transformation, disproving the hypothesis that PLIN2 is an oncogene. Furthermore, positive PLIN2 staining was strongly associated with highly proliferative Ki-67-positive areas in human colon adenocarcinoma tissue samples. Taken together, these results indicate that cell cycle progression is associated with tight regulation of lipid droplets, a process that is altered in transformed cells, suggesting the existence of a mechanism that connects cell cycle progression and cell proliferation with lipid accumulation.

Adipophilin expression is an indicator of poor prognosis in patients with pancreatic ductal adenocarcinoma: An immunohistochemical analysis

OBJECTIVE

Adipophilin is a lipid droplet-associated protein, and its expression has been correlated with aggressive clinical behavior in some types of carcinomas, though its role in pancreatic ductal adenocarcinoma (PDAC) has not been clarified. This study aimed to evaluate the role of adipophilin in PDAC.

METHODS

By immunohistochemical staining using tissue microarrays, we analyzed the expression profiles of adipophilin in 181 consecutive PDAC patients who underwent macroscopic margin-negative resection from January 2008 to December 2015. Overall survival (OS) and recurrence-free survival (RFS) were compared based on adipophilin expression, and the risk factors for OS, RFS, and early recurrence (within 6 months) were analyzed.

RESULTS

Of the 181 evaluated patients, 51 (28.2%) were positive for adipophilin expression. A histopathological grade of 3 (p = 0.0012), higher CA19-9 level (p = 0.0016), and R1 status (p = 0.028) were significantly associated with adipophilin-positive patients who had significantly poor OS and RFS compared to those associated with adipophilin-negative patients (p = 0.0007 and p = 0.0022, respectively). They also showed a significantly higher incidence of early recurrence (p = 0.030), based on multivariate analyses.

CONCLUSIONS

Adipophilin is a potential independent prognostic marker for PDAC.

Perilipin 5 and Lipocalin 2 Expression in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most prevalent and deadly cancers worldwide. Therefore, current global research focuses on molecular tools for early diagnosis of HCC, which can lead to effective treatment at an early stage. Perilipin 5 (PLIN5) has been studied as one of the main proteins of the perilipin family, whose role is to maintain lipid homeostasis by inhibiting lipolysis. In this study, we show for the first time that PLIN5 is strongly expressed in tumors of human patients with HCC as well as in mouse livers, in which HCC was genetically or experimentally induced by treatment with the genotoxic agent diethylnitrosamine. Moreover, the secreted acute phase glycoprotein Lipocalin 2 (LCN2) established as a biomarker of acute kidney injury, is also proven to indicate liver injury with upregulated expression in numerous cases of hepatic damage, including steatohepatitis. LCN2 has been studied in various cancers, and it has been assigned roles in multiple cellular processes such as the suppression of the invasion of HCC cells and their metastatic abilities. The presence of this protein in blood and urine, in combination with the presence of α-Fetoprotein (AFP), is hypothesized to serve as a biomarker of early stages of HCC. In the current study, we show in humans and mice that LCN2 is secreted into the serum from liver cancer tissue. We also show that AFP-positive hepatocytes represent the main source for the massive expression of LCN2 in tumoral tissue. Thus, the strong presence of PLIN5 and LCN2 in HCC and understanding their roles could establish them as markers for diagnosis or as treatment targets against HCC.

Combinatorial Electrophoresis and Mass Spectrometry-Based Proteomics in Breast Milk for Breast Cancer Biomarker Discovery

Innovations in approaches for early detection and individual risk assessment of different cancers, including breast cancer (BC), are needed to reduce cancer morbidity and associated mortality. The assessment of potential cancer biomarkers in accessible bodily fluids provides a novel approach to identify the risk and/or onset of cancer. Biomarkers are biomolecules, such as proteins, that are indicative of an abnormality or a disease. Human milk is vastly underutilized biospecimen that offers the opportunity to investigate potential protein BC-biomarkers in young, reproductively active women. As a first step, we have examined the entire protein pattern in human milk samples from breastfeeding mothers with cancer, who were diagnosed either before or after milk donation, and from women without cancer, using mass spectrometry (MS)-based proteomics.