Explore the vast range of titles available.

Lipids have diverse structures, with multifarious regulatory functions in membrane homeostasis and bioenergetic metabolism, in mediating functional protein–lipid and protein–protein interactions, as in cell signalling and proliferation. An increasing body of evidence supports the notion that aberrant lipid metabolism involving remodelling of cellular membrane structure and changes in energy homeostasis and signalling within cancer-associated pathways play a pivotal role in the onset, progression, and maintenance of colorectal cancer (CRC) and their tumorigenic properties. Recent advances in analytical lipidome analysis technologies have enabled the comprehensive identification and structural characterization of lipids and, consequently, our understanding of the role they play in tumour progression. However, despite progress in our understanding of cancer cell metabolism and lipidomics, the key lipid-associated changes in CRC have yet not been explicitly associated with the well-established ‘hallmarks of cancer’ defined by Hanahan and Weinberg. In this review, we summarize recent findings that highlight the role of reprogrammed lipid metabolism in CRC and use this growing body of evidence to propose eight lipid metabolism-associated hallmarks of colorectal cancer, and to emphasize their importance and linkages to the established cancer hallmarks.

BAK and BAX are essential mediators of apoptosis that oligomerize in response to death cues, thereby causing permeabilization of the mitochondrial outer membrane. Their transition from quiescent monomers to pore-forming oligomers involves a well-characterized symmetric dimer intermediate. However, no essential secondary interface that can be disrupted by mutagenesis has been identified. Here we describe crystal structures of human BAK core domain (α2–α5) dimers that reveal preferred binding sites for membrane lipids and detergents. The phospholipid headgroup and one acyl chain (sn2) associate with one core dimer while the other acyl chain (sn1) associates with a neighboring core dimer, suggesting a mechanism by which lipids contribute to the oligomerization of BAK. Our data support a model in which, unlike for other pore-forming proteins whose monomers assemble into oligomers primarily through protein–protein interfaces, the membrane itself plays a role in BAK and BAX oligomerization.Crystal structures of BAK core domain dimers suggest a mechanism by which lipids contribute to the oligomerization of BAK, which is essential for BAK-mediated permeabilization of the mitochondrial outer membrane.

Lipid dyshomeostasis is associated with the most common form of dementia, Alzheimer's disease (AD). Substantial progress has been made in identifying positron emission tomography (PET) and cerebrospinal fluid (CSF) biomarkers for AD, but they have limited use as front-line, non-invasive diagnostic tools. Small extracellular vesicles (EVs) are released by all cell types and contain an enriched subset of their parental cell molecular composition, including lipids. EVs are released from the brain into the periphery, providing a potential source of tissue and disease specific lipid biomarkers. However, the EV lipidome of the central nervous system (CNS) is currently unknown and the potential of brain-derived EVs (BDEVs) to inform on lipid dyshomeostasis in AD remains unclear. The aim of this study was to reveal the lipid composition of BDEVs in human frontal cortex tissue, and to determine whether BDEVs in AD have altered lipid profiles compared to age-matched neurological controls (NC). Using semi-quantitative mass spectrometry, we describe the BDEV lipidome, covering 4 lipid categories, 17 lipid classes and 692 lipid molecules. Frontal cortex-derived BDEVs were enriched in glycerophosphoserine (PS) lipids, a characteristic of small EVs. Here we further report that BDEVs are enriched in ether-containing PS lipids, a finding that further establishes ether lipids as a feature of EVs. While no significant changes were detected in the frontal cortex in AD relative to neurological control subjects, the lipid profile of the BDEVs from AD tissue exhibited disease related differences. AD BDEVs had significantly altered glycerophospholipid (GP) and sphingolipid (SP) levels, specifically increased plasmalogen glycerophosphoethanolamine (PE-P) and decreased polyunsaturated fatty acyl containing lipids (PUFAs), and altered amide-linked acyl chain content in sphingomyelin (SM) and ceramide (Cer) lipids relative to vesicles from neurological control subjects. The most prominent alteration was a two-fold decrease in lipid species containing the anti-inflammatory/pro-resolving docosahexaenoic acid (DHA). The in-depth lipidome analysis provided in this study highlights the advantage of EVs over more complex tissues for improved detection of dysregulated lipids that may serve as potential biomarkers in the periphery. Competing Interest Statement The authors have declared no competing interest.

Glucosylceramide (GlcCer) is a major membrane lipid and the precursor of gangliosides. It is continuously formed and degraded in glycosphingolipid metabolism. GlcCer is mainly degraded by two enzymes, lysosomal acid β-glucosidase (GBA) and nonlysosomal β-glucosidase (GBA2). Deficiencies of GBA and GBA2 affect glycosphingolipid metabolism, resulting in neurological diseases, such as Gaucher Disease and Hereditary Spastic Paraplegia. To understand which GBA2 isoforms are active and how they affect glycosphingolipid levels in cells, we expressed nine human GBA2 isoforms in COS-7 cells, confirmed their expression by qRT-PCR and western blotting, and assayed their activity to hydrolyze 4-methylumbelliferyl-β-D-glucopyranoside (4MUG) in cell extracts. Human GBA2 isoform 1 showed high activity, while the other isoforms had activity similar to the background. Comparison of sphingolipid levels by ultra-high resolution/accurate mass spectrometry (UHRAMS) analysis showed that isoform 1 overexpression increased ceramide and decreased hexosylceramide levels compared to control and other isoforms. Comparison of ratios of glucosylceramides to the corresponding ceramides in the extracts indicated that GBA2 isoform 1 has broad specificity for the lipid component of glucosylceramide. These studies suggest that only one GBA2 isoform 1 is active and affects sphingolipid levels in the cell, acting on glucosylceramides with a wide range of lipid components. Our study provides new insights into how increased breakdown of GlcCer affects cellular lipid metabolic networks.

The number, position, and configuration of double bonds in lipid acyl chains affects membrane packing, fluidity, and recruitment of signalling proteins. Studies on mammalian sphingolipids have focused on those with a saturated sphinganine or mono-unsaturated sphingosine long chain base. Sphingolipids with a di-unsaturated sphingadiene base have been reported but are poorly characterised. Employing high-resolution untargeted mass spectrometry, we observed marked accumulation of lipids containing a sphingadiene base, but not those with a more common sphingosine backbone, in the hippocampus of mice lacking the metabolic enzyme sphingosine kinase 2 (SphK2). Applying ultraviolet photodissociation tandem mass spectrometry (UVPD-MS/MS) the double bonds were confidently assigned to the C4-C5 and C14-C15 positions of the sphingoid base. Sphingosine kinases are involved in lysosomal catabolism of all sphingolipids, producing sphingoid base phosphates that are irreversibly degraded by sphingosine 1-phosphate lyase. Both SphK1 and SphK2 phosphorylated sphinga-4,14-diene as efficiently as sphingosine, however deuterated tracer experiments demonstrated that ceramides with a sphingosine base are more rapidly metabolised in cultured cells than those with a sphingadiene base. SphK2 silencing significantly impeded the catabolism of both sphingosine- and sphingadiene-based sphingolipids. Since SphK2 is the dominant sphingosine kinase in brain, we propose that accumulation of sphingadiene lipids in SphK2-deficient brains results from the intrinsically slower catabolism of sphingadiene lipids, combined with a bottleneck in the catabolic pathway created by the absence of SphK2. We speculate that accumulation of these lipids in the absence of SphK2 function may affect the fluidity and signalling properties of cell membranes.