Inhibition of LIPG phospholipase activity suppresses tumor formation of human basal-like triple-negative breast cancer

Bromocriptine protects perilesional spinal cord neurons from lipotoxicity after spinal cord injury

Recent studies have revealed that lipid droplets accumulate in neurons after brain injury and evoke lipotoxicity, damaging the neurons. However, how lipids are metabolized by spinal cord neurons after spinal cord injury remains unclear. Herein, we investigated lipid metabolism by spinal cord neurons after spinal cord injury and identified lipid-lowering compounds to treat spinal cord injury. We found that lipid droplets accumulated in perilesional spinal cord neurons after spinal cord injury in mice. Lipid droplet accumulation could be induced by myelin debris in HT22 cells. Myelin debris degradation by phospholipase led to massive free fatty acid production, which increased lipid droplet synthesis, β-oxidation, and oxidative phosphorylation. Excessive oxidative phosphorylation increased reactive oxygen species generation, which led to increased lipid peroxidation and HT22 cell apoptosis. Bromocriptine was identified as a lipid-lowering compound that inhibited phosphorylation of cytosolic phospholipase A2 by reducing the phosphorylation of extracellular signal-regulated kinases 1/2 in the mitogen-activated protein kinase pathway, thereby inhibiting myelin debris degradation by cytosolic phospholipase A2 and alleviating lipid droplet accumulation in myelin debris-treated HT22 cells. Motor function, lipid droplet accumulation in spinal cord neurons and neuronal survival were all improved in bromocriptine-treated mice after spinal cord injury. The results suggest that bromocriptine can protect neurons from lipotoxic damage after spinal cord injury via the extracellular signal-regulated kinases 1/2-cytosolic phospholipase A2 pathway.

Mechanistic analysis of endothelial lipase G promotion of the occurrence and development of cervical carcinoma by activating the phosphatidylinositol-4,5-bisphosphate 3-kinase/protein kinase B/mechanistic target of rapamycin kinase signalling pathway

Lipase G, endothelial type (LIPG) is expressed abundantly in tissues with a high metabolic rate and vascularisation. Research on LIPG has focussed on metabolic syndromes. However, the role of LIPG in providing lipid precursors suggests that it might function in the metabolism of carcinoma cells. Analysis in The Cancer Genome Atlas indicated that patients with cervical carcinoma with high LIPG expression had a lower survival prognosis compared with patients with low LIPG expression. The mechanism underlying the effects of LIPG in cervical carcinoma is unclear. The present study aimed to determine the role of LIPG in cervical carcinoma and its mechanism. The results showed that the LIPG expression level was higher in cervical cancer. Downregulation of LIPG expression inhibited cell migration, invasion, proliferation, and the formation of cell colonies, but increased the rate of apoptosis. The Human papillomavirus E6 protein might reduce the expression of miR-148a-3p, relieve the inhibitory effect of miR-148a-3p on LIPG expression, and promote the progression of cervical cancer through the phosphatidylinositol-4,5-bisphosphate 3-kinase/protein kinase B/mechanistic target of rapamycin kinase signalling pathway.IMPACT STATEMENTWhat is already known on this subject? LIPG provides lipid precursors, suggesting that it might function in the metabolism of carcinoma cellsWhat do the results of this study add? LIPG might be regulated by HPV16 E6/miR-148a-3p and promote cervical carcinoma progression via the PI3K/AKT/mTOR signalling pathway.What are the implications of these finding for clinical practice and/or further research? The results indicated that novel treatment and diagnosis strategies for cervical carcinoma could be developed related to LIPG. However, the detailed relationship between LIPG and cervical carcinoma remains to be fully determined.

Revealing Tissue Heterogeneity and Spatial Dark Genes from Spatially Resolved Transcriptomics by Multiview Graph Networks

Spatially resolved transcriptomics (SRT) is capable of comprehensively characterizing gene expression patterns and providing an unbiased image of spatial composition. To fully understand the organizational complexity and tumor immune escape mechanism, we propose stMGATF, a multiview graph attention fusion model that integrates gene expression, histological images, spatial location, and gene association. To better extract information, stMGATF exploits SimCLRv2 for visual feature exaction and employs edge feature enhanced graph attention networks for the learning potential embedding of each view. A global attention mechanism is used to adaptively integrate 3 views to obtain low-dimensional representation. Applied to diverse SRT datasets, stMGATF is robust and outperforms other methods in detecting spatial domains and denoising data even with different resolutions and platforms. In particular, stMGATF contributes to the elucidation of tissue heterogeneity and extraction of 3-dimensional expression domains. Importantly, considering the associations between genes in tumors, stMGATF can identify the spatial dark genes ignored by traditional methods, which can be used to predict tumor-driving transcription factors and reveal tumor immune escape mechanisms, providing theoretical evidence for the development of new immunotherapeutic strategies.

The breast cancer microenvironment and lipoprotein lipase: Another negative notch for a beneficial enzyme?

The energy demand of breast cancers is in part met through the β-oxidation of exogenous fatty acids. Fatty acids may also be used to aid in cell signaling and toward the construction of new membranes for rapidly proliferating tumor cells. A significant quantity of fatty acids comes from the hydrolysis of lipoprotein triacylglycerols and phospholipids by lipoprotein lipase (LPL). The lipid obtained via LPL in the breast tumor microenvironment may thus promote breast tumor growth and development. In this hypothesis article, we introduce LPL, provide a meta-analysis of RNAseq data showing that LPL is associated with poor prognosis, and explain how LPL might play a role in breast cancer prognosis over time.

Phase-Separated Liposomes Hijack Endogenous Lipoprotein Transport and Metabolism Pathways to Target Subsets of Endothelial Cells In Vivo

Plasma lipid transport and metabolism are essential to ensure correct cellular function throughout the body. Dynamically regulated in time and space, the well-characterized mechanisms underpinning plasma lipid transport and metabolism offers an enticing, but as yet underexplored, rationale to design synthetic lipid nanoparticles with inherent cell/tissue selectivity. Herein, a systemically administered liposome formulation, composed of just two lipids, that is capable of hijacking a triglyceride lipase-mediated lipid transport pathway resulting in liposome recognition and uptake within specific endothelial cell subsets is described. In the absence of targeting ligands, liposome-lipase interactions are mediated by a unique, phase-separated ("parachute") liposome morphology. Within the embryonic zebrafish, selective liposome accumulation is observed at the developing blood-brain barrier. In mice, extensive liposome accumulation within the liver and spleen - which is reduced, but not eliminated, following small molecule lipase inhibition - supports a role for endothelial lipase but highlights these liposomes are also subject to significant "off-target" by reticuloendothelial system organs. Overall, these compositionally simplistic liposomes offer new insights into the discovery and design of lipid-based nanoparticles that can exploit endogenous lipid transport and metabolism pathways to achieve cell selective targeting in vivo.

Cholangiocarcinoma progression depends on the uptake and metabolization of extracellular lipids

BACKGROUND AND AIMS

Cholangiocarcinoma (CCA) includes a heterogeneous group of biliary cancers with a dismal prognosis. We investigated if lipid metabolism is disrupted in CCA and its role in tumor proliferation.

APPROACH AND RESULTS

The in vitro and in vivo tumorigenic capacity of five human CCA cell lines was analyzed. Proteome, lipid content, and metabolic fluxes were evaluated in CCA cells and compared with normal human cholangiocytes (NHC). The Akt1/NOTCH1 intracellular cytoplasmic domain (Nicd1)-driven CCA mouse model was also evaluated. The proteome of CCA cells was enriched in pathways involved in lipid and lipoprotein metabolism. The EGI1 CCA cell line presented the highest tumorigenic capacity. Metabolic studies in high (EGI1) versus low (HUCCT1) proliferative CCA cells in vitro showed that both EGI1 and HUCCT1 incorporated more fatty acids (FA) than NHC, leading to increased triglyceride storage, also observed in Akt1/Nicd1-driven CCA mouse model. The highly proliferative EGI1 CCA cells showed greater uptake of very-low-density and HDLs than NHC and HUCCT1 CCA cells and increased cholesteryl ester content. The FA oxidation (FAO) and related proteome enrichment were specifically up-regulated in EGI1, and consequently, pharmacological blockade of FAO induced more pronounced inhibition of their tumorigenic capacity compared with HUCCT1. The expression of acyl-CoA dehydrogenase ACADM, the first enzyme involved in FAO, was increased in human CCA tissues and correlated with the proliferation marker PCNA.

CONCLUSIONS

Highly proliferative human CCA cells rely on lipid and lipoprotein uptake to fuel FA catabolism, suggesting that inhibition of FAO and/or lipid uptake could represent a therapeutic strategy for this CCA subclass.

A Proof-of-Concept Inhibitor of Endothelial Lipase Suppresses Triple-Negative Breast Cancer Cells by Hijacking the Mitochondrial Function

Simple Summary

Endothelial lipase (EL/LIPG) is a key regulator of tumor cell metabolism. In triple-negative breast cancer (TNBC) cells, we find that the expression of LIPG is associated with long non-coding RNA DANCR and positively correlates with gene signatures of mitochondrial metabolism-oxidative phosphorylation (OXPHOS). DANCR binds to LIPG, which enables tumor cells to maintain the expression. Importantly, LIPG knockdown inhibits OXPHOS and TNBC tumor formation. Finally, our study identifies a natural compound, the LIPG inhibitor cynaroside, which provides a new therapeutic strategy against TNBC.

Abstract

Triple-negative breast cancer (TNBC) cells reprogram their metabolism to provide metabolic flexibility for tumor cell growth and survival in the tumor microenvironment. While our previous findings indicated that endothelial lipase (EL/LIPG) is a hallmark of TNBC, the precise mechanism through which LIPG instigates TNBC metabolism remains undefined. Here, we report that the expression of LIPG is associated with long non-coding RNA DANCR and positively correlates with gene signatures of mitochondrial metabolism-oxidative phosphorylation (OXPHOS). DANCR binds to LIPG, enabling tumor cells to maintain LIPG protein stability and OXPHOS. As one mechanism of LIPG in the regulation of tumor cell oxidative metabolism, LIPG mediates histone deacetylase 6 (HDAC6) and histone acetylation, which contribute to changes in IL-6 and fatty acid synthesis gene expression. Finally, aided by a relaxed docking approach, we discovered a new LIPG inhibitor, cynaroside, that effectively suppressed the enzyme activity and DANCR in TNBC cells. Treatment with cynaroside inhibited the OXPHOS phenotype of TNBC cells, which severely impaired tumor formation. Taken together, our study provides mechanistic insights into the LIPG modulation of mitochondrial metabolism in TNBC and a proof-of-concept that targeting LIPG is a promising new therapeutic strategy for the treatment of TNBC.

TROP2 modulates the progression in papillary thyroid carcinoma

Background: Tumor-associated calcium signal transducer 2 (TROP2) is over expressed in various kinds of human cancers and plays important roles in the proliferation, invasion and metastasis of tumor cells. However, the expression and molecular mechanism of TROP2 in thyroid papillary carcinoma (PTC) are unclear. Methods: The expressions of TROP2 in PTC and control tissue were detected by real-time reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry. The proliferation and invasion of PTC cell lines were examined by cell cloning and transwell assays. RNA sequencing analysis and public data analysis were assessed to investigate the potential mechanisms of TROP2 in PTC. Gene correlation analysis was conducted to explore the association between TROP2 and the related gene ISG15 in patients with PTC. Results: The expression of TROP2 was significantly higher in PTC than control. The high expression of TROP2 protein was associated with lymph node metastasis, tumor size and capsular infiltration (P<0.05). SiRNA-mediated TROP2 gene expression silencing can significantly inhibit proliferation and migration of PTC cells. ISG15 decreased in TROP2 siRNA PTC cells and increased in PTC patients significantly. There was a significant correlation between the expression of TROP2 and ISG15 in PTC patients. TROP2 interacted directly with ATP6V1A, CEBPA and SOX5 and then further interacted with the immune genes. TROP2 expression and tumor-infiltrating immune cells were also correlated in thyroid cancer microenvironment. Conclusions: TROP2 promotes the development of PTC. TROP2 expression was correlated with ISG15 and tumor-infiltrating immune cells in thyroid cancer.

Endothelial Lipase Is Involved in Cold-Induced High-Density Lipoprotein Turnover and Reverse Cholesterol Transport in Mice

The physiologic activation of thermogenic brown and white adipose tissues (BAT/WAT) by cold exposure triggers heat production by adaptive thermogenesis, a process known to ameliorate hyperlipidemia and protect from atherosclerosis. Mechanistically, it has been shown that thermogenic activation increases lipoprotein lipase (LPL)-dependent hydrolysis of triglyceride-rich lipoproteins (TRL) and accelerates the generation of cholesterol-enriched remnants and high-density lipoprotein (HDL), which promotes cholesterol flux from the periphery to the liver. HDL is also subjected to hydrolysis by endothelial lipase (EL) (encoded by LIPG). Genome-wide association studies have identified various variants of EL that are associated with altered HDL cholesterol levels. However, a potential role of EL in BAT-mediated HDL metabolism has not been investigated so far. In the present study, we show that in mice, cold-stimulated activation of thermogenic adipocytes induced expression of Lipg in BAT and inguinal WAT but that loss of Lipg did not affect gene expression of thermogenic markers. Furthermore, in both wild type (WT) and Lipg-deficient mice, activation of thermogenesis resulted in a decline of HDL cholesterol levels. However, cold-induced remodeling of the HDL lipid composition was different between WT and Lipg-deficient mice. Notably, radioactive tracer studies with double-labeled HDL indicated that cold-induced hepatic HDL cholesterol clearance was lower in Lipg-deficient mice. Moreover, this reduced clearance was associated with impaired macrophage-to-feces cholesterol transport. Overall, these data indicate that EL is a determinant of HDL lipid composition, cholesterol flux, and HDL turnover in conditions of high thermogenic activity.

TROP2 modulates the progression in papillary thyroid carcinoma

Background: Tumor-associated calcium signal transducer 2 (TROP2) is over expressed in various kinds of human cancers and plays important roles in the proliferation, invasion and metastasis of tumor cells. However, the expression and molecular mechanism of TROP2 in thyroid papillary carcinoma (PTC) are unclear. Methods: The expressions of TROP2 in PTC and control tissue were detected by real-time reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry. The proliferation and invasion of PTC cell lines were examined by cell cloning and transwell assays. RNA sequencing analysis and public data analysis were assessed to investigate the potential mechanisms of TROP2 in PTC. Gene correlation analysis was conducted to explore the association between TROP2 and the related gene ISG15 in patients with PTC. Results: The expression of TROP2 was significantly higher in PTC than control. The high expression of TROP2 protein was associated with lymph node metastasis, tumor size and capsular infiltration (P<0.05). SiRNA-mediated TROP2 gene expression silencing can significantly inhibit proliferation and migration of PTC cells. ISG15 decreased in TROP2 siRNA PTC cells and increased in PTC patients significantly. There was a significant correlation between the expression of TROP2 and ISG15 in PTC patients. TROP2 interacted directly with ATP6V1A, CEBPA and SOX5 and then further interacted with the immune genes. TROP2 expression and tumor-infiltrating immune cells were also correlated in thyroid cancer microenvironment. Conclusions: TROP2 promotes the development of PTC. TROP2 expression was correlated with ISG15 and tumor-infiltrating immune cells in thyroid cancer.