Mice lacking lipid droplet-associated hydrolase, a gene linked to human prostate cancer, have normal cholesterol ester metabolism

Targeting lipid droplets and lipid droplet-associated proteins: a new perspective on natural compounds against metabolic diseases

BACKGROUND

Lipid droplet (LD) is a metabolically active organelle, which changes dynamically with the metabolic state and energy requirements of cells. Proteins that either insert into the LD phospholipid monolayer or are present in the cytoplasm, playing a crucial role in lipid homeostasis and signaling regulation, are known as LD-associated proteins.

METHODS

The keywords "lipid droplets" and "metabolic diseases" were used to obtain literature on LD metabolism and pathological mechanism. After searching databases including Scopus, OVID, Web of Science, and PubMed from 2013 to 2024 using terms like "lipid droplets", "lipid droplet-associated proteins", "fatty liver disease", "diabetes", "diabetic kidney disease", "obesity", "atherosclerosis", "hyperlipidemia", "natural drug monomers" and "natural compounds", the most common natural compounds were identified in about 954 articles. Eventually, a total of 91 studies of 10 natural compounds reporting in vitro or in vivo studies were refined and summarized.

RESULTS

The most frequently used natural compounds include Berberine, Mangostin, Capsaicin, Caffeine, Genistein, Epigallocatechin-3-gallate, Chlorogenic acid, Betaine, Ginsenoside, Resveratrol. These natural compounds interact with LD-associated proteins and help ameliorate abnormal LDs in various metabolic diseases.

CONCLUSION

Natural compounds involved in the regulation of LDs and LD-associated proteins hold promise for treating metabolic diseases. Further research into these interactions may lead to new therapeutic applications.

Lipid droplet-associated hydrolase mobilizes stores of liver X receptor sterol ligands and protects against atherosclerosis

Foam cells in atheroma are engorged with lipid droplets (LDs) that contain esters of regulatory lipids whose metabolism remains poorly understood. LD-associated hydrolase (LDAH) has a lipase structure and high affinity for LDs of foam cells. Using knockout and transgenic mice of both sexes, here we show that LDAH inhibits atherosclerosis development and promotes stable lesion architectures. Broad and targeted lipidomic analyzes of primary macrophages and comparative lipid profiling of atheroma identified a broad impact of LDAH on esterified sterols, including natural liver X receptor (LXR) sterol ligands. Transcriptomic analyzes coupled with rescue experiments show that LDAH modulates the expression of prototypical LXR targets and leads macrophages to a less inflammatory phenotype with a profibrotic gene signature. These studies underscore the role of LDs as reservoirs and metabolic hubs of bioactive lipids, and suggest that LDAH favorably modulates macrophage activation and protects against atherosclerosis via lipolytic mobilization of regulatory sterols.

Host genetics and gut microbiota jointly regulate blood biochemical indicators in chickens

Blood biochemical indicators play a crucial role in assessing an individual's overall health status and metabolic function. In this study, we measured five blood biochemical indicators, including total cholesterol (CHOL), low-density lipoprotein cholesterol (LDL-CH), triglycerides (TG), high-density lipoprotein cholesterol (HDL-CH), and blood glucose (BG), as well as 19 growth traits of 206 male chickens. By integrating host whole-genome information and 16S rRNA sequencing of the duodenum, jejunum, ileum, cecum, and feces microbiota, we assessed the contributions of host genetics and gut microbiota to blood biochemical indicators and their interrelationships. Our results demonstrated significant negative phenotypic and genetic correlations (r =  - 0.20 ~  - 0.67) between CHOL and LDL-CH with growth traits such as body weight, abdominal fat content, muscle content, and shin circumference. The results of heritability and microbiability indicated that blood biochemical indicators were jointly regulated by host genetics and gut microbiota. Notably, the heritability of HDL-CH was estimated to be 0.24, while the jejunal microbiability for BG and TG reached 0.45 and 0.23. Furthermore, by conducting genome-wide association study (GWAS) with the single-nucleotide polymorphism (SNPs), insertion/deletion (indels), and structural variation (SV), we identified RAP2C, member of the RAS oncogene family (RAP2C), dedicator of cytokinesis 11 (DOCK11), neurotensin (NTS) and BOP1 ribosomal biogenesis factor (BOP1) as regulators of HDL-CH, and glycerophosphodiester phosphodiesterase domain containing 5 (GDPD5), dihydrodiol dehydrogenase (DHDH), and potassium voltage-gated channel interacting protein 1 (KCNIP1) as candidate genes of BG. Moreover, our findings suggest that cecal RF39 and Clostridia_UCG_014 may be linked to the regulation of CHOL, and jejunal Streptococcaceae may be involved in the regulation of TG. Additionally, microbial GWAS results indicated that the presence of gut microbiota was under host genetic regulation. Our findings provide valuable insights into the complex interaction between host genetics and microbiota in shaping the blood biochemical profile of chickens. KEY POINTS: • Multiple candidate genes were identified for the regulation of CHOL, HDL-CH, and BG. • RF39, Clostridia_UCG_014, and Streptococcaceae were implicated in CHOL and TG modulation. • The composition of gut microbiota is influenced by host genetics.

A transcriptome-wide association study identifies novel candidate susceptibility genes for prostate cancer risk

A large proportion of heritability for prostate cancer risk remains unknown. Transcriptome-wide association study combined with validation comparing overall levels will help to identify candidate genes potentially playing a role in prostate cancer development. Using data from the Genotype-Tissue Expression Project, we built genetic models to predict normal prostate tissue gene expression using the statistical framework PrediXcan, a modified version of the unified test for molecular signatures and Joint-Tissue Imputation. We applied these prediction models to the genetic data of 79 194 prostate cancer cases and 61 112 controls to investigate the associations of genetically determined gene expression with prostate cancer risk. Focusing on associated genes, we compared their expression in prostate tumor vs normal prostate tissue, compared methylation of CpG sites located at these loci in prostate tumor vs normal tissue, and assessed the correlations between the differentiated genes' expression and the methylation of corresponding CpG sites, by analyzing The Cancer Genome Atlas (TCGA) data. We identified 573 genes showing an association with prostate cancer risk at a false discovery rate (FDR) ≤ 0.05, including 451 novel genes and 122 previously reported genes. Of the 573 genes, 152 showed differential expression in prostate tumor vs normal tissue samples. At loci of 57 genes, 151 CpG sites showed differential methylation in prostate tumor vs normal tissue samples. Of these, 20 CpG sites were correlated with expression of 11 corresponding genes. In this TWAS, we identified novel candidate susceptibility genes for prostate cancer risk, providing new insights into prostate cancer genetics and biology.

The CYTOLD and ERTOLD pathways for lipid droplet-protein targeting

Lipid droplets (LDs) are the main organelles for lipid storage, and their surfaces contain unique proteins with diverse functions, including those that facilitate the deposition and mobilization of LD lipids. Among organelles, LDs have an unusual structure with an organic, hydrophobic oil phase covered by a phospholipid monolayer. The unique properties of LD monolayer surfaces require proteins to localize to LDs by distinct mechanisms. Here we review the two pathways known to mediate direct LD protein localization: the CYTOLD pathway mediates protein targeting from the cytosol toLDs, and the ERTOLD pathway functions in protein targeting from the endoplasmic reticulum toLDs. We describe the emerging principles for each targeting pathway in animal cells and highlight open questions in the field.

Lipolysis: cellular mechanisms for lipid mobilization from fat stores

The perception that intracellular lipolysis is a straightforward process that releases fatty acids from fat stores in adipose tissue to generate energy has experienced major revisions over the last two decades. The discovery of new lipolytic enzymes and coregulators, the demonstration that lipophagy and lysosomal lipolysis contribute to the degradation of cellular lipid stores and the characterization of numerous factors and signalling pathways that regulate lipid hydrolysis on transcriptional and post-transcriptional levels have revolutionized our understanding of lipolysis. In this review, we focus on the mechanisms that facilitate intracellular fatty-acid mobilization, drawing on canonical and noncanonical enzymatic pathways. We summarize how intracellular lipolysis affects lipid-mediated signalling, metabolic regulation and energy homeostasis in multiple organs. Finally, we examine how these processes affect pathogenesis and how lipolysis may be targeted to potentially prevent or treat various diseases.

Determinants of Endoplasmic Reticulum-to-Lipid Droplet Protein Targeting

Lipid droplet (LD) formation from the endoplasmic reticulum (ER) is accompanied by the targeting and accumulation of specific hydrophobic, membrane-embedded proteins on LDs. The determinants of this process are unknown. Here, we study the hydrophobic membrane motifs of two Drosophila melanogaster proteins, GPAT4 and ALG14, that utilize this pathway, and we identify crucial sequence features that mediate LD accumulation. Molecular dynamics simulations and studies in cells reveal that LD targeting of these motifs requires deeply inserted tryptophans that have lower free energy in the LD oil phase and positively charged residues near predicted hairpin hinges that become less constrained in the LD environment. Analyzing hydrophobic motifs from similar LD-targeting proteins, it appears that the distribution of tryptophan and positively charged residues distinguishes them from non-LD-targeting membrane motifs. Our studies identify specific sequence features and principles of hydrophobic membrane motifs that mediate their accumulation on LDs.

Lipid droplets can promote drug accumulation and activation

Genetic screens in cultured human cells represent a powerful unbiased strategy to identify cellular pathways that determine drug efficacy, providing critical information for clinical development. We used insertional mutagenesis-based screens in haploid cells to identify genes required for the sensitivity to lasonolide A (LasA), a macrolide derived from a marine sponge that kills certain types of cancer cells at low nanomolar concentrations. Our screens converged on a single gene, LDAH, encoding a member of the metabolite serine hydrolase family that is localized on the surface of lipid droplets. Mechanistic studies revealed that LasA accumulates in lipid droplets, where it is cleaved into a toxic metabolite by LDAH. We suggest that selective partitioning of hydrophobic drugs into the oil phase of lipid droplets can influence their activation and eventual toxicity to cells.

Cholesterol depletion sensitizes gallbladder cancer to cisplatin by impairing DNA damage response

Gallbladder cancer (GBC) is the common malignancy of the bile tract system with extremely poor clinical outcomes, owing to its metastatic property and intrinsic resistance to the first-line drugs. Although it is well-established that cholesterol abnormity contributes to gallstone formation, a leading risk factor for GBC, the link of cholesterol homeostasis with GBC has not been investigated. The present study systematically examined the genes implicated in cholesterol homeostasis, and revealed altered gene expressions of de novo cholesterol biosynthesis and sterol sulfonation (SULT2B1), reduced bile acid synthesis (CYP7B1 and CYP39A1) and impaired sterol efflux (ABCA1, ABCG5, LCAT, and CETP) in GBC tissues. Suppression of cholesterol biosynthesis by lovastatin inhibited GBC cell proliferation possibly through attenuating the DNA repair process. Further investigation revealed lovastatin sensitized GBC cells to cisplatin-induced apoptosis and suppressed the activation of CHK1, CHK2, and H2AX during DNA damage response. By using chemically distinct statins, HMGCR depletion or supplementing mevalonate, the product of HMGCR, we showed the inhibitory effects on DNA repair process of lovastatin were due to the blockage of the mevalonate pathway. Subcutaneous xenograft mice model suggested lovastatin promoted the therapeutic efficacy of cisplatin, and significantly prolonged the survival times of tumor-bearing mice. Moreover, HMGCR ablation repressed tumor growth in vivo, which can be rescued partially by restored expression of HMGCR, suggesting the on-target effects of lovastatin. Therefore, our study provides the clinical relevance of cholesterol homeostasis with GBC progression, and highlights a novel intervention of combined use of lovastatin and cisplatin for GBC.

Loss of LDAH associated with prostate cancer and hearing loss

Great strides in gene discovery have been made using a multitude of methods to associate phenotypes with genetic variants, but there still remains a substantial gap between observed symptoms and identified genetic defects. Herein, we use the convergence of various genetic and genomic techniques to investigate the underpinnings of a constellation of phenotypes that include prostate cancer (PCa) and sensorineural hearing loss (SNHL) in a human subject. Through interrogation of the subject's de novo, germline, balanced chromosomal translocation, we first identify a correlation between his disorders and a poorly annotated gene known as lipid droplet associated hydrolase (LDAH). Using data repositories of both germline and somatic variants, we identify convergent genomic evidence that substantiates a correlation between loss of LDAH and PCa. This correlation is validated through both in vitro and in vivo models that show loss of LDAH results in increased risk of PCa and, to a lesser extent, SNHL. By leveraging convergent evidence in emerging genomic data, we hypothesize that loss of LDAH is involved in PCa and other phenotypes observed in support of a genotype-phenotype association in an n-of-one human subject.

SOD1 activity threshold and TOR signalling modulate VAP(P58S) aggregation via reactive oxygen species-induced proteasomal degradation in a Drosophila model of amyotrophic lateral sclerosis

Familial amyotrophic lateral sclerosis (ALS) is an incurable, late-onset motor neuron disease, linked strongly to various causative genetic loci. ALS8 codes for a missense mutation, P56S, in VAMP-associated protein B (VAPB) that causes the protein to misfold and form cellular aggregates. Uncovering genes and mechanisms that affect aggregation dynamics would greatly help increase our understanding of the disease and lead to potential therapeutics. We developed a quantitative high-throughput Drosophila S2R+ cell-based kinetic assay coupled with fluorescent microscopy to score for genes involved in the modulation of aggregates of the fly orthologue, VAP(P58S), fused with GFP. A targeted RNA interference screen against 900 genes identified 150 hits that modify aggregation, including the ALS loci Sod1 and TDP43 (also known as TBPH), as well as genes belonging to the mTOR pathway. Further, a system to measure the extent of VAP(P58S) aggregation in the Drosophila larval brain was developed in order to validate the hits from the cell-based screen. In the larval brain, we find that reduction of SOD1 levels or decreased mTOR signalling reduces aggregation, presumably by increasing the levels of cellular reactive oxygen species (ROS). The mechanism of aggregate clearance is, primarily, proteasomal degradation, which appears to be triggered by an increase in ROS. We have thus uncovered an interesting interplay between SOD1, ROS and mTOR signalling that regulates the dynamics of VAP aggregation. Mechanistic processes underlying such cellular regulatory networks will lead to better understanding of the initiation and progression of ALS.This article has an associated First Person interview with the first author of the paper.

Lipidomics Suggests a New Role for Ceramide Synthase in Phagocytosis

Phagocytosis is an evolutionarily conserved biological process where pathogens or cellular debris are cleared by engulfing them in a membrane-enclosed cellular compartment called the phagosome. The formation, maturation, and subsequent degradation of a phagosome is an important immune response essential for protection against many pathogens. Yet, the global lipid profile of phagosomes remains unknown, especially as a function of their maturation in immune cells. Here, we show using mass spectrometry based quantitative lipidomics that the ceramide class of lipids, especially very long chain ceramides, are enriched on maturing phagosomes with a concomitant decrease in the biosynthetic precursors of ceramides. We thus posit a new function for the enzyme ceramide synthase during phagocytosis in mammalian macrophages. Biochemical assays, cellular lipid feeding experiments, and pharmacological blockade of ceramide synthase together show that this enzyme indeed controls the flux of ceramides on maturing phagosomes. We also find similar results in the primitive eukaryote Dictyostelium discoideum, suggesting that ceramide enrichment may be evolutionarily conserved and likely an indispensible step in phagosome maturation.

Lipid Droplet-Associated Hydrolase Promotes Lipid Droplet Fusion and Enhances ATGL Degradation and Triglyceride Accumulation

Lipid droplet (LD)-associated hydrolase (LDAH) is a newly identified LD protein abundantly expressed in tissues that predominantly store triacylglycerol (TAG). However, how LDAH regulates TAG metabolism remains unknown. We found that upon oleic acid loading LDAH translocalizes from the ER to newly formed LDs, and induces LD coalescence in a tubulin-dependent manner. LDAH overexpression and downregulation in HEK293 cells increase and decrease, respectively, TAG levels. Pulse and chase experiments show that LDAH enhances TAG biogenesis, but also decreases TAG turnover and fatty acid release from cells. Mutations in predicted catalytic and acyltransferase motifs do not influence TAG levels, suggesting that the effect is independent of LDAH’s enzymatic activity. However, a LDAH alternative-splicing variant missing 90 amino acids at C-terminus does not promote LD fusion or TAG accumulation, while it still localizes to LDs. Interestingly, LDAH enhances polyubiquitination and proteasomal degradation of adipose triglyceride lipase (ATGL), a rate limiting enzyme of TAG hydrolysis. Co-expression of ATGL reverses the changes in LD phenotype induced by LDAH, and both proteins counterbalance their effects on TAG stores. Together, these studies support that under conditions of TAG storage in LDs LDAH plays a primarily lipogenic role, inducing LD growth and enhancing degradation of ATGL.