DAG tales: the multiple faces of diacylglycerol--stereochemistry, metabolism, and signaling

Molecular docking simulation reveals the lipase-substrate binding mechanism in the enzymatic synthesis of diacylglycerol-enriched vegetable oils

Diacylglycerol (DAG) is a functional lipid that is naturally present in vegetable oils in limited concentrations (1 %-5 %). This study proposed an enzymatic method to afford high-content-DAG vegetable oils via a reaction catalyzed by an immobilized lipase, PS@OMS-C8, using high-speed homogenization and molecular distillation. Results indicated that 48.6 % DAG was initially obtained through the enzymatic glycerolysis of rapeseed oil with glycerol, of which 90.2 % was sn-1,3-DAG. PS@OMS-C8 maintained 35.5 % DAG content after 10 reuse cycles, confirming its catalytic stability; this was attributed to lipase immobilization on the ordered mesoporous silica that significantly improve the secondary protein structures, including α-helix and β-sheet, thereby strengthening the rigidity of PS@OMS-C8. In addition to producing DAG-enriched rapeseed oil, other edible oils with 39.4 %-50.2 % DAG content were obtained, as revealed via molecular docking simulation. This study offers new strategies for the sustainable synthesis of vegetable oils with a high content of functional lipids high-content functional lipids.

Nerve growth factor signaling tunes axon maintenance protein abundance and kinetics of Wallerian degeneration

Neurotrophic factors are critical for establishing functional connectivity in the nervous system and sustaining neuronal survival through adulthood. As the first neurotrophic factor purified, nerve growth factor (NGF) is extensively studied for its prolific role in axon outgrowth, pruning, and survival. Applying NGF to diseased neuronal tissue is an exciting therapeutic option and understanding how NGF regulates local axon susceptibility to pathological degeneration is critical for exploiting its full potential. Our study identifies surprising connections between NGF signaling and proteostasis of axon maintenance factors. NGF deprivation increases Nmnat2 and Stmn2 protein levels in axon segments with a corresponding delay in Wallerian degeneration. Conversely, acute NGF stimulation reduces local abundance of these axon maintenance factors and accelerates Wallerian degeneration. Pharmacological studies implicate phospholipase C as the key effector in tropomyosin-related kinase A (TrkA) activation, which drives degradation of palmitoylated Stmn2. While seemingly opposed to neuroprotective activities well-documented for NGF, downregulating Nmnat2 and Stmn2 favors axonal outgrowth over transient hypersusceptibility to Sarm1-dependent degeneration. This new facet of NGF biology has important implications for axonal remodeling during development and sustained integrity through adulthood.

Lipid metabolism, remodelling and intercellular transfer in the CNS

Lipid metabolism encompasses the catabolism and anabolism of lipids, and is fundamental for the maintenance of cellular homeostasis, particularly within the lipid-rich CNS. Increasing evidence further underscores the importance of lipid remodelling and transfer within and between glial cells and neurons as key orchestrators of CNS lipid homeostasis. In this Review, we summarize and discuss the complex landscape of processes involved in lipid metabolism, remodelling and intercellular transfer in the CNS. Highlighted are key pathways, including those mediating lipid (and lipid droplet) biogenesis and breakdown, lipid oxidation and phospholipid metabolism, as well as cell-cell lipid transfer mediated via lipoproteins, extracellular vesicles and tunnelling nanotubes. We further explore how the dysregulation of these pathways contributes to the onset and progression of neurodegenerative diseases, and examine the homeostatic and pathogenic impacts of environment, diet and lifestyle on CNS lipid metabolism.

Chiral supercritical fluid chromatography of monoacylglycerol and diacylglycerol enantiomers in biological samples: Adjusting selectivity via column coupling

The distinction of lipid isomers is gaining more attention in lipidomics due to their different biochemical properties in the organism. Herein, we aimed to develop a method for the analysis of monoacylglycerol (MG) and diacylglycerol (DG) enantiomers in biological samples using chiral supercritical fluid chromatography and mass spectrometry (SFC-MS). Amylose-based chiral columns showed a certain degree of separation of MG and DG isomers, but low selectivity for the acylglycerol classes in total lipid extracts, which could not be improved by modifier composition or other chromatographic conditions. The coelution of MG and DG enantiomers with highly concentrated triacylglycerols (TGs) negatively affected their MS determination based on the peak area ratio, therefore the interclass selectivity of chiral SFC was adjusted by coupling with an achiral column. The connection of the amylose tris-(3,5-dimethylphenylcarbamate) chiral column with octadecyl achiral column using a methanol as a modifier provided an excellent interclass separation of acylglycerols with the resolution of 5.53 and 15.17 for oleic acid-based MG/DG and DG/TG classes, respectively. The developed method enabled the determination of MG and DG enantiomers in complex total lipid extracts of biological samples in a 15 min gradient without time-consuming sample prefractionation. Chiral SFC-MS analysis of egg yolk, human plasma, and porcine brain samples showed different ratios of enantiomers, suggesting their unique roles within each sample type.

Spatial lipidomic profiles of atherosclerotic plaques: A mass spectrometry imaging study

Lipids contribute to atherosclerotic cardiovascular disease but their roles are not fully understood. Spatial lipid composition of atherosclerotic plaques was compared between species focusing on aortic plaques from New Zealand White rabbits and carotid plaques from humans (n = 3), using matrix-assisted laser desorption/ionization mass spectrometry imaging. Histologically discriminant lipids within plaque features (neointima and media in rabbits, and lipid-necrotic core and fibrous cap/tissue in humans) included sphingomyelins, phosphatidylcholines, and cholesteryl esters. There were 67 differential lipids between rabbit plaque features and 199 differential lipids in human, each with variable importance in projection score ≥1.0 and p < 0.05. The lipid profile of plaques in the rabbit model closely mimicked that of human plaques and two key pathways (impact value ≥ 0.1), sphingolipid and glycerophospholipid metabolism, were disrupted by atherosclerosis in both species. Thus, mass spectrometry imaging of spatial biomarkers offers valuable insights into atherosclerosis.

Blockage of ATGL-mediated breakdown of lipid droplets in microglia alleviates neuroinflammatory and behavioural responses to lipopolysaccharides

Lipid droplets (LD) are triglyceride storing organelles that have emerged as an important component of cellular inflammatory responses. LD lipolysis via adipose triglyceride lipase (ATGL), the enzyme that catalyses the rate-limiting step of triglyceride lipolysis, regulates inflammation in peripheral immune and non-immune cells. ATGL elicits both pro- and anti-inflammatory responses in the periphery in a cell-type dependent manner. The present study determined the impact of ATGL inhibition and microglia-specific ATGL genetic loss-of-function on acute inflammatory and behavioural responses to pro-inflammatory insult. First, we evaluated the impact of lipolysis inhibition on lipopolysaccharide (LPS)-induced expression and secretion of cytokines and phagocytosis in mouse primary microglia cultures. Lipase inhibitors (ORlistat and ATGListatin) and LPS led to LD accumulation in microglia. Pan-lipase inhibition with ORlistat alleviated LPS-induced expression of IL-1β and IL-6. Specific inhibition of ATGL had a similar action on CCL2, IL-1β and IL-6 expression in both neonatal and adult microglia cultures. CCL2 and IL-6 secretion were also reduced by ATGListatin or knockdown of ATGL. ATGListatin increased phagocytosis in neonatal cultures independently from LPS treatment. Second, targeted and untargeted lipid profiling revealed that ATGListatin reduced LPS-induced generation of pro-inflammatory prostanoids and modulated ceramide species in neonatal microglia. Finally, the role of microglial ATGL in neuroinflammation was assessed using a novel microglia-specific and inducible ATGL knockout mouse model. Loss of microglial ATGL in adult male mice dampened LPS-induced expression of IL-6 and IL-1β and microglial density. LPS-induced sickness- and anxiety-like behaviours were also reduced in male mice with loss of ATGL in microglia. Together, our results demonstrate potent anti-inflammatory effects produced by pharmacological or genetic inhibition of ATGL-mediated triglyceride lipolysis and thereby propose that supressing microglial LD lipolysis has beneficial actions in acute neuroinflammatory conditions.

Activation of Proteolysis During Oocyte In Vitro Maturation

In vitro maturation (IVM) is a form of assisted reproductive technology (ART) applied to obtain mature oocytes in culture. Decline in IVM success rates by age has led consideration of novel approaches based on cellular dynamics. Our aim was to achieve proteostasis in old bovine oocytes from 13 to 16-year-old bovine with a lower potential for fertilization. Lysosomal activation was achieved through increasing concentrations of proton pump activators PIP2 (0.1, 0.5, 1, and 5 μM), PMA (0.1, 1, 10, and 50 μM), and DOG (0.1, 1, 10, and 50 μM) at 6, 12, 18, and 24 h of IVM in old bovine oocytes. Morphological analysis was performed and IVM rates were determined. DQ-Red BSA was applied to live oocytes to determine proteolytic activation while lysosome density was determined by Lysotracker probe. Protein carbonylation was detected through oxyblot analysis. Polar body extrusion (PBE), through which a haploid nonfunctional polar body is released in the perivitelline space after completion of the first meiotic division, was observed in PIP2-0.1 μM, -0.5μM-6h; PIP2-5μM-12h; PMA-0.1μM-18h; PIP2-0.1μM, -0.5μM-24h groups. Oocyte diameter was the highest in DOG-1μM-6h, PMA-0.1μM-12h, PIP2-1μM-18h, and PIP2-0.5μM-24h groups. Morphological scores of oocytes were higher in young and old control groups. PIP2, PMA, and DOG affected oocyte quality positively after 6 h of IVM yielding in oocyte scores similar to the control group oocytes. However, they had a negative impact on the oocyte scores in longer periods of IVM, except for lower doses PMA (0.1 and 1 μM) at 12 h and PIP2 (0.5 μM) and PMA (0.1 μM) at 18 h, which were able to maintain the scores relatively closer to the control oocytes. Proteolytic activation was achieved in all groups at 6 h of culture. At all other time points PIP2 and PMA groups showed a better response to proteolytic activation. Lysosome density was increased in PIP2-5μM-6h; PIP2-0.1μM, -1μM-12h; PIP2-1μM, -5μM-18h as well as PMA-0.1μM-6h; PMA-1μM, -10μM-12h; PMA-1μM-18h; DOG-50μM-6h and DOG-0.1μM-12h. Protein carbonylation was the lowest in PIP2-0.1 μM groups at 12, 18, and 24 h. This study suggests that proton pump activators PIP2 and PMA was found to have a positive impact on IVM in terms of both morphological scores and proteolytic activation in a time and dose dependant manner.

Nerve Growth Factor Signaling Tunes Axon Maintenance Protein Abundance and Kinetics of Wallerian Degeneration

Neurotrophic factors are critical for establishing functional connectivity in the nervous system and sustaining neuronal survival through adulthood. As the first neurotrophic factor purified, nerve growth factor (NGF) is extensively studied for its prolific role in axon outgrowth, pruning, and survival. Applying NGF to diseased neuronal tissue is an exciting therapeutic option and understanding how NGF regulates local axon susceptibility to pathological degeneration is critical for exploiting its full potential. Our study identifies surprising connections between NGF signaling and proteostasis of axon maintenance factors. NGF deprivation increases Nmnat2 and Stmn2 protein levels in axon segments with a corresponding delay in Wallerian degeneration. Conversely, acute NGF stimulation reduces local abundance of these axon maintenance factors and accelerates Wallerian degeneration. Pharmacological studies implicate phospholipase C as the key effector in TrkA activation, which drives degradation of palmitoylated Stmn2. While seemingly opposed to neuroprotective activities well-documented for NGF, downregulating Nmnat2 and Stmn2 favors axonal outgrowth over transient hyper-susceptibility to Sarm1-dependent degeneration. This new facet of NGF biology has important implications for axonal remodeling during development and sustained integrity through adulthood.

Altered levels of phospholipases C, diacylglycerols, endocannabinoids, and N-acylethanolamines in patients with hereditary angioedema due to FXII mutation

BACKGROUND

Hereditary angioedema (HAE) is a rare genetic disorder characterized by local, self-limiting edema due to temporary increase in vascular permeability. HAE with normal C1 esterase inhibitor (C1INH) activity includes the form with mutations in the F12 gene encoding for coagulation factor XII (FXII-HAE) causing an overproduction of bradykinin (BK) leading to angioedema attack. BK binding to B2 receptors (BK2R) leads to an activation of phospholipase C (PLC) and subsequent generation of second messengers: diacylglycerols (DAGs) and possibly the endocannabinoids (eCBs), 2-arachidonoylglycerol (2-AG) and anandamide (AEA), and eCB-related N-acylethanolamines [palmitoylethanolamide (PEA) and oleoylethanolamide (OEA)]. To date, there are no data on the role of these lipid mediators in FXII-HAE.

METHODS

Here, we analyzed plasma levels of PLC, DAGs, and eCBs in 40 patients with FXII-HAE and 40 sex- and age-matched healthy individuals.

RESULTS

Plasma PLC activity was increased in FXII-HAE patients compared to controls. Concentrations of DAG 18:1-20:4, a lipid second messenger produced by PLC, were higher in FXII-HAE compared to controls, and positively correlated with PLC activity and cleaved high molecular kininogen (cHK). Also the concentrations of the DAG metabolite, 2-AG were altered in FXII-HAE. AEA and OEA were decreased in FXII-HAE patients compared to controls; by contrast, PEA, was increased. The levels of all tested mediators did not differ between symptomatic and asymptomatic patients. Moreover, C1INH-HAE patients had elevated plasma levels of PLC, which correlated with cHK, but the levels of DAGs and eCBs were the same as controls.

CONCLUSIONS

BK overproduction and BKR2 activation are linked to alteration of PLCs and their metabolites in patients with FXII-HAE. Our results may pave way to investigations on the functions of these mediators in the pathophysiology of FXII-HAE, and provide new potential biomarkers and therapeutic targets.

Diacylglycerol Kinases and Its Role in Lipid Metabolism and Related Diseases

Lipids are essential components of eukaryotic membranes, playing crucial roles in membrane structure, energy storage, and signaling. They are predominantly synthesized in the endoplasmic reticulum (ER) and subsequently transported to other organelles. Diacylglycerol kinases (DGKs) are a conserved enzyme family that phosphorylate diacylglycerol (DAG) to produce phosphatidic acid (PA), both of which are key intermediates in lipid metabolism and second messengers involved in numerous cellular processes. Dysregulation of DGK activity is associated with several diseases, including cancer and metabolic disorders. In this review, we provide a comprehensive overview of DGK types, functions, cellular localization, and their potential as therapeutic targets. We also discuss DGKs' roles in lipid metabolism and their physiological functions and related diseases.

Lipidomics and spatial metabolomics reveal the heterogeneity in lipid distribution within pecan kernels

Pecan (Carya illinoinensis) is a globally important nut crop, yet the processes of lipid biosynthesis and spatial lipid distribution within its embryo remain poorly understood. This study employed UHPLC-MS/MS and MALDI-MSI to profile lipids in developing pecan embryos, identifying 401 lipid molecules, including a high abundance of glycerolipids (148) and glycerophospholipids (144). Differential diacylglycerols showed gradual uptrends, highlighting their role in synthesizing glycerolipids and glycerophospholipids. Unsaturated fatty acids, especially oleic, linoleic, and linolenic acids, were enriched in triacylglycerols, diacylglycerols, phosphatidylethanolamines, and phosphatidylcholines. MALDI-MSI revealed the spatial distribution of phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI), suggesting heterogeneous lipid distribution within embryos. The proportion of linoleic and linolenic acids is higher in the kernel coat, whereas the proportion of oleic acid is relatively higher in the cotyledons. Differences in lipid content were also observed between the inner and outer cotyledons. This study provides the first comprehensive map of lipid distribution in pecan embryos, offering new insights into lipid metabolism regulation.

Human metabolic chambers reveal a coordinated metabolic-physiologic response to nutrition

Human studies linking metabolism with organism-wide physiologic function have been challenged by confounding, adherence, and precisionHere, we united physiologic and molecular phenotypes of metabolism during controlled dietary intervention to understand integrated metabolic-physiologic responses to nutrition. In an inpatient study of individuals who underwent serial 24-hour metabolic chamber experiments (indirect calorimetry) and metabolite profiling, we mapped a human metabolome onto substrate oxidation rates and energy expenditure across up to 7 dietary conditions (energy balance, fasting, multiple 200% caloric excess overfeeding of varying fat, protein, and carbohydrate composition). Diets exhibiting greater fat oxidation (e.g., fasting, high-fat) were associated with changes in metabolites within pathways of mitochondrial β-oxidation, ketogenesis, adipose tissue fatty acid liberation, and/or multiple anapleurotic substrates for tricarboxylic acid cycle flux, with inverse associations for diets with greater carbohydrate availability. Changes in each of these metabolite classes were strongly related to 24-hour respiratory quotient (RQ) and substrate oxidation rates (e.g., acylcarnitines related to lower 24-hour RQ and higher 24-hour lipid oxidation), underscoring links between substrate availability, physiology, and metabolism in humans. Physiologic responses to diet determined by gold-standard human metabolic chambers are strongly coordinated with biologically consistent, interconnected metabolic pathways encoded in the metabolome.

Multiple activities of sphingomyelin synthase 2 generate saturated fatty acid- and/or monounsaturated fatty acid-containing diacylglycerol

Phosphatidylcholine (PC)-specific phospholipase C (PC-PLC) (EC 3.1.4.3) and phosphatidylethanolamine (PE)-specific PLC (PE-PLC) (EC 3.1.4.62), which generate diacylglycerol (DG) and are tricyclodecan-9-yl-xanthogenate (D609)-sensitive, were detected in detergent-insoluble fractions of mammalian tissues approximately 70 and 35 years ago, respectively. However, the genes and proteins involved in PC-PLC and PE-PLC activities remain unknown. In a recent study, we observed that mammalian sphingomyelin synthase (SMS) 1 and SMS-related protein display PC-PLC and PE-PLC activities in vitro. In the present study, we showed that human SMS2, which is located in detergent-insoluble fractions of the plasma membrane, also possesses PC-PLC activity (approximately 41% of SMS activity), PE-PLC activity (approximately 4%), ceramide phosphoethanolamine synthase (CPES) activity (approximately 46%), and SMS activity in the presence of phospholipid-detergent mixed micelles. Moreover, purified SMS2 reconstituted in detergent-free proteoliposomes (near-native environments) showed PC-PLC, PE-PLC, and CPES activities. Notably, in the presence of approximately 2 mol% ceramide and 4 mol% PC (1:2 ratio), PC-PLC activity was almost equal to SMS activity. SMS2 as PC/PE-PLC showed substrate selectivity for saturated fatty acid- and/or monounsaturated fatty acid-containing PC and PE species. The PC-PLC/SMS inhibitor D609 inhibited all enzyme activities (SMS, PC-PLC, PE-PLC, and CPES) of SMS2. Moreover, Zn2+ strongly inhibited all the enzymatic activities of SMS2. Interestingly, diacylglycerol inhibited the SMS activity of SMS2 (feedback control). These results indicate that mammalian SMS2 has unique enzymatic properties and is a candidate for a long-sought mammalian PC/PE-PLC.

Metabolic phenotypes and vitamin D response in the critically ill: A metabolomic cohort study

BACKGROUND & AIMS

Although vitamin D deficiency is common in critically ill patients, randomized controlled trials fail to demonstrate benefits of supplementation. We aimed to identify distinct vitamin D3 responsive metabolic phenotypes prior to trial intervention of high-dose vitamin D3 by applying machine learning clustering method to metabolomics data from the Correction of Vitamin D Deficiency in Critically Ill Patients (VITdAL-ICU) trial.

METHODS

In the randomized, placebo-controlled VITdAL-ICU trial, critically ill adults received placebo or high-dose vitamin D3. To distinguish vitamin D3 responsive metabolic phenotypes prior to intervention, we implemented consensus clustering with partitioning around medoids algorithm to the plasma metabolome data before randomization. Individual metabolite differences were determined utilizing linear mixed-effects regression models stratified for metabolomic phenotypes with false discovery rate adjustment. The association between vitamin D3 supplementation and 180-day mortality was evaluated in each metabolic phenotype, applying multivariable logistic regression analysis.

RESULTS

In 453 critically ill adults, the study identified 4 distinct metabolic phenotypes (clusters A. N = 134; B. N = 123; C. N = 92; D. N = 104). We found differential metabolic pathway patterns in the four clusters. Specifically, branched chain amino acid catabolic metabolites, long-chain acylcarnitines and diacylglycerol species are significantly increased in a specific metabolic phenotype (cluster D) following high-dose vitamin D3. Further, in cluster D high-dose vitamin D3 supplementation had a significantly lower adjusted odds of 180-day mortality after controlling age, sex, Simplified Acute Physiology Score II, admission diagnosis, and baseline 25-hydroxyvitamin D (OR 0.28 (95%CI, 0.09-0.89); P = 0.03). In metabotype A, B, and C, high-dose vitamin D3 supplementation was not significantly associated with lower 180-day mortality following multivariable adjustment.

CONCLUSION

In this post-hoc cohort study of the VITdAL-ICU trial, the clustering analysis of plasma metabolome data identified biologically distinct metabolic phenotypes. Among clusters, we found the different associations between high-dose vitamin D3 supplementation and specific metabolite pathways as well as 180-day mortality. Our findings facilitate further research to validate metabolic phenotype-targeted strategies for critical illness treatments.

Spatially heterogeneous lipid dysregulation in tuberculous meningitis

Tuberculous (TB) meningitis is the deadliest form of extrapulmonary TB which disproportionately affects children and immunocompromised individuals. Studies in pulmonary TB have shown that Mycobacterium tuberculosis can alter host lipid metabolism to evade the immune system. Cholesterol lowering drugs (i.e., statins) reduce the risk of infection, making them a promising host-directed therapy in pulmonary TB. However, the effect of M. tuberculosis infection on the young or adult brain lipidome has not been studied. The brain is the second-most lipid-rich organ, after adipose tissue, with a temporally and spatially heterogeneous lipidome that changes from infancy to adulthood. The young, developing brain in children may be uniquely vulnerable to alterations in lipid composition and homeostasis, as perturbations in cholesterol metabolism can cause developmental disorders leading to intellectual disabilities. To begin to understand the alterations to the brain lipidome in pediatric TB meningitis, we utilized our previously published young rabbit model of TB meningitis and applied mass spectrometry (MS) techniques to elucidate spatial differences. We used matrix assisted laser desorption/ionization-MS imaging (MALDI-MSI) and complemented it with region-specific liquid chromatography (LC)-MS/MS developed to identify and quantify sterols and oxysterols difficult to identify by MALDI-MSI. MALDI-MSI revealed several sphingolipids, glycerolipids and glycerophospholipids that were downregulated in brain lesions. LC-MS/MS revealed the downregulation of cholesterol, several sterol intermediates along the cholesterol biosynthesis pathway and enzymatically produced oxysterols as a direct result of M. tuberculosis infection. However, oxysterols produced by oxidative stress were increased in brain lesions. Together, these results demonstrate significant spatially regulated brain lipidome dysregulation in pediatric TB meningitis.

Role of fatty acids in the pathogenesis of ß-cell failure and Type-2 diabetes

Pancreatic ß-cells are glucose sensors in charge of regulated insulin delivery to the organism, achieving glucose homeostasis and overall energy storage. The latter function promotes obesity when nutrient intake chronically exceeds daily expenditure. In case of ß-cell failure, such weight gain may pave the way for the development of Type-2 diabetes. However, the causal link between excessive body fat mass and potential degradation of ß-cells remains largely unknown and debated. Over the last decades, intensive research has been conducted on the role of lipids in the pathogenesis of ß-cells, also referred to as lipotoxicity. Among various lipid species, the usual suspects are essentially the non-esterified fatty acids (NEFA), in particular the saturated ones such as palmitate. This review describes the fundamentals and the latest advances of research on the role of fatty acids in ß-cells. This includes intracellular pathways and receptor-mediated signaling, both participating in regulated glucose-stimulated insulin secretion as well as being implicated in ß-cell dysfunction. The discussion extends to the contribution of high glucose exposure, or glucotoxicity, to ß-cell defects. Combining glucotoxicity and lipotoxicity results in the synergistic and more deleterious glucolipotoxicity effect. In recent years, alternative roles for intracellular lipids have been uncovered, pointing to a protective function in case of nutrient overload. This requires dynamic storage of NEFA as neutral lipid droplets within the ß-cell, along with active glycerolipid/NEFA cycle allowing subsequent recruitment of lipid species supporting glucose-stimulated insulin secretion. Overall, the latest studies have revealed the two faces of the same coin.

Overexpression of diglucosyldiacylglycerol synthase leads to daptomycin resistance in Bacillus subtilis

The lipopeptide antibiotic daptomycin exhibits bactericidal activity against Gram-positive bacteria by forming a complex with phosphatidylglycerol (PG) and lipid II in the cell membrane, causing membrane perforation. With the emergence of daptomycin-resistant bacteria, understanding the mechanisms of bacterial resistance to daptomycin has gained great importance. In this study, we aimed to identify the genetic factors contributing to daptomycin resistance in Bacillus subtilis, a model Gram-positive bacterium. Our findings demonstrated that overexpression of ugtP, which encodes diglucosyldiacylglycerol synthase, induces daptomycin resistance in B. subtilis. Specifically, overexpression of ugtP resulted in increased levels of diglucosyldiacylglycerol (Glc2DAG) and decreased levels of acidic phospholipids cardiolipin and PG, as well as the basic phospholipid lysylphosphatidylglycerol. However, ugtP overexpression did not alter the cell surface charge and the susceptibility to the cationic antimicrobial peptide nisin or the cationic surfactant hexadecyltrimethylammonium bromide. Furthermore, by serial passaging in the presence of daptomycin, we obtained daptomycin-resistant mutants carrying ugtP mutations. These mutants showed increased levels of Glc2DAG and a >4-fold increase in the minimum inhibitory concentration of daptomycin. These results suggest that increased Glc2DAG levels, driven by ugtP overexpression, modify the phospholipid composition and confer daptomycin resistance in B. subtilis without altering the cell surface charge of the bacteria.IMPORTANCEDaptomycin is one of the last-resort drugs for the treatment of methicillin-resistant Staphylococcus aureus infections, and the emergence of daptomycin-resistant bacteria has become a major concern. Understanding the mechanism of daptomycin resistance is important for establishing clinical countermeasures against daptomycin-resistant bacteria. In the present study, we found that overexpression of ugtP, which encodes diglucosyldiacylglycerol synthase, induces daptomycin resistance in B. subtilis, a model Gram-positive bacteria. The overexpression of UgtP increased diglucosyldiacylglycerol levels, resulting in altered phospholipid composition and daptomycin resistance. These findings are important for establishing clinical strategies against daptomycin-resistant bacteria, including their detection and management.

Diacylglycerol kinase γ facilitates the proliferation and migration of neural stem cells in the developing neural tube

In this study, we aim to investigate diacylglycerol kinase (DGK) γ expression in developing neural tubes (NTs) and its effects on neural stem cell (NSC) proliferation and migration. Whole-mount in situ hybridization (WMISH) and immunohistochemistry are performed to explore DGKγ localization in developing NTs in vivo. NSCs are treated with sh-DGKγ, R59949, or PMA in vitro. Cell counting kit-8 (CCK-8) assay, 5-ethynyl-2'-deoxyuridine (EdU) assay and neurosphere formation assay are utilized to evaluate NSC proliferation. Neurosphere migration assay and a transwell chamber assay are used to assess NSC migration. The diacylglycerol (DAG) content is detected via enzyme-linked immunosorbent assay (ELISA). The mRNA expression of DGKγ is detected via quantitative real-time polymerase chain reaction (qRT-PCR). The protein expression levels of DGKγ, protein kinase C (PKC) and phosphorylated PKC (p-PKC) are detected via western blot analysis. The results show that DGKγ mRNA is expressed predominantly in developing NTs. The neuroepithelium in developing NTs is positive for NSC markers, including Nestin, glial fibrillary acidic protein (GFAP), and DGKγ. DGKγ is expressed in the cytoplasm and nucleus of the neuroepithelium and is coexpressed with p-PKCγ and p-PKCδ. The proliferation of NSCs, the number of EdU-positive NSCs, and the number of neurospheres are decreased by sh-DGKγ and R59949 but increased by PMA. There is a shorter migration distance of NSCs and fewer migrated NSCs in the sh-DGKγ, R59949 and PMA groups. DAG content and the p-PKCδ/PKCδ ratio are increased by sh-DGKγ, R59949 and PMA, whereas the p-PKCγ/PKCγ ratio is decreased by PMA. Taken together, our findings indicate that DGKγ facilitates NSC proliferation and migration, which is responsible for the participation of DGK in NT development. DGKγ facilitates NSC migration via the DAG/PKCδ pathway.

MOGAT3-mediated DAG accumulation drives acquired resistance to anti-BRAF/anti-EGFR therapy in BRAFV600E-mutant metastatic colorectal cancer

BRAFV600E-mutant metastatic colorectal cancer (mCRC) is associated with poor prognosis. The combination of anti-BRAF/anti-EGFR (encorafenib/cetuximab) treatment for patients with BRAFV600E-mutant mCRC improves clinical benefits; unfortunately, inevitable acquired resistance limits the treatment outcome, and the mechanism has not been validated. Here, we discovered that monoacylglycerol O-acyltransferase 3-mediated (MOGAT3-mediated) diacylglycerol (DAG) accumulation contributed to acquired resistance to encorafenib/cetuximab by dissecting a BRAFV600E-mutant mCRC patient-derived xenograft (PDX) model exposed to encorafenib/cetuximab administration. Mechanistically, the upregulated MOGAT3 promoted DAG synthesis and reduced fatty acid oxidation-promoting DAG accumulation and activated PKCα/CRAF/MEK/ERK signaling, driving acquired resistance. Resistance-induced hypoxia promoted MOGAT3 transcriptional elevation; simultaneously, MOGAT3-mediated DAG accumulation increased HIF1A expression at the translation level through PKCα/CRAF/eIF4E activation, strengthening the resistance status. Intriguingly, reducing intratumoral DAG with fenofibrate or PF-06471553 restored the antitumor efficacy of encorafenib/cetuximab in resistant BRAFV600E-mutant mCRC, which interrupted PKCα/CRAF/MEK/ERK signaling. These findings reveal the critical role of the metabolite DAG as a modulator of encorafenib/cetuximab efficacy in BRAFV600E-mutant mCRC, suggesting that fenofibrate might prove beneficial for resistant BRAFV600E-mutant mCRC patients.

Downregulation of the GhROD1 Gene Improves Cotton Fiber Fineness by Decreasing Acyl Pool Saturation, Stimulating Small Heat Shock Proteins (sHSPs), and Reducing H2O2 Production

Cotton fiber is one of the most important natural fiber sources in the world, and lipid metabolism plays a critical role in its development. However, the specific role of lipid molecules in fiber development and the impact of fatty acid alterations on fiber quality remain largely unknown. In this study, we demonstrate that the downregulation of GhROD1, a gene encoding phosphatidylcholine diacylglycerol cholinephosphotransferase (PDCT), results in an improvement of fiber fineness. We found that GhROD1 downregulation significantly increases the proportion of linoleic acid (18:2) in cotton fibers, which subsequently upregulates genes encoding small heat shock proteins (sHSPs). This, in turn, reduces H2O2 production, thus delaying secondary wall deposition and leading to finer fibers. Our findings reveal how alterations in linoleic acid influence cellulose synthesis and suggest a potential strategy to improve cotton fiber quality by regulating lipid metabolism pathways.

Cannabinoids-Multifunctional Compounds, Applications and Challenges-Mini Review

Cannabinoids represent a highly researched group of plant-derived ingredients. The substantial investment of funds from state and commercial sources has facilitated a significant increase in knowledge about these ingredients. Cannabinoids can be classified into three principal categories: plant-derived phytocannabinoids, synthetic cannabinoids and endogenous cannabinoids, along with the enzymes responsible for their synthesis and degradation. All of these compounds interact biologically with type 1 (CB1) and/or type 2 (CB2) cannabinoid receptors. A substantial body of evidence from in vitro and in vivo studies has demonstrated that cannabinoids and inhibitors of endocannabinoid degradation possess anti-inflammatory, antioxidant, antitumour and antifibrotic properties with beneficial effects. This review, which spans the period from 1940 to 2024, offers an overview of the potential therapeutic applications of natural and synthetic cannabinoids. The development of these substances is essential for the global market of do-it-yourself drugs to fully exploit the promising therapeutic properties of cannabinoids.

The role of protein kinase D (PKD) in obesity: Lessons from the heart and other tissues

Obesity causes a range of tissue dysfunctions that increases the risk for morbidity and mortality. Protein kinase D (PKD) represents a family of stress-activated intracellular signalling proteins that regulate essential processes such as cell proliferation and differentiation, cell survival, and exocytosis. Evidence suggests that PKD regulates the cellular adaptations to the obese environment in metabolically important tissues and drives the development of a variety of diseases. This review explores the role that PKD plays in tissue dysfunction in obesity, with special consideration of the development of obesity-mediated cardiomyopathy, a distinct cardiovascular disease that occurs in the absence of common comorbidities and leads to eventual heart failure and death. The downstream mechanisms mediated by PKD that could contribute to dysfunctions observed in the heart and other metabolically important tissues in obesity, and the predicted cell types involved are discussed to suggest potential targets for the development of therapeutics against obesity-related disease.

Maternal Docosahexaenoic Acid Supplementation Alters Maternal and Fetal Docosahexaenoic Acid Status and Placenta Phospholipids in Pregnancies Complicated by High Body Mass Index

INTRODUCTION

An optimal fetal supply of docosahexaenoic acid (DHA) is critical for normal brain development. The relationship between maternal DHA intake and DHA delivery to the fetus is complex and is dependent on placental handling of DHA. Little data exist on placental DHA levels in pregnancies supplemented with the recommended dose of 200 mg/d. Our objective was to determine how prenatal DHA at the recommended 200 mg/d impacts maternal, placental, and fetal DHA status in both normal-weight and high-BMI women compared to women taking no supplements.

METHODS

Maternal blood, placenta, and cord blood were collected from 30 healthy pregnant women (BMI 18.9-43.26 kg/m2) giving birth at term. Red blood cells (RBCs) and villous tissue were isolated, and lipids were extracted to determine DHA content by LC-MS/MS. Data were analyzed by supplement group (0 vs. 200 mg/d) and maternal BMI (normal weight or high BMI) using two-way ANOVA. We measured maternal choline levels in maternal and cord plasma samples.

RESULTS

Supplementation with 200 mg/d DHA significantly increased (p < 0.05) maternal and cord RBC DHA content only in pregnancies complicated by high BMI. We did not find any impact of choline levels on maternal or cord RBC phospholipids. There were no significant differences in total placental DHA content by supplementation or maternal BMI (p > 0.05). Placental levels of phosphatidylinositol (PI) and phosphatidic acid containing DHA species were higher (p < 0.05) in high-BMI women without DHA supplementation compared to both normal-BMI and high-BMI women taking DHA supplements.

CONCLUSION

Maternal DHA supplementation at recommended doses cord increased RBC DHA content only in pregnancies complicated by higher BMI. Surprisingly, we found that obesity was related to an increase in placental PI and phosphatidic acid species, which was ameliorated by DHA supplementation. Phosphatidic acid activates placental mTOR, which regulates amino acid transport and may explain previous findings of the impact of DHA on placental function. Current recommendations for DHA supplementation may not be achieving the goal of improving fetal DHA levels in normal-weight women.

The triglyceride-synthesizing enzyme diacylglycerol acyltransferase 2 modulates the formation of the hepatitis C virus replication organelle

The replication organelle of hepatitis C virus (HCV), called membranous web, is derived from the endoplasmic reticulum (ER) and mainly comprises double membrane vesicles (DMVs) that concentrate the viral replication complexes. It also tightly associates with lipid droplets (LDs), which are essential for virion morphogenesis. In particular acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), a rate-limiting enzyme in triglyceride synthesis, promotes early steps of virus assembly. The close proximity between ER membranes, DMVs and LDs therefore permits the efficient coordination of the HCV replication cycle. Here, we demonstrate that exaggerated LD accumulation due to the excessive expression of the DGAT1 isozyme, DGAT2, dramatically impairs the formation of the HCV membranous web. This effect depended on the enzymatic activity and ER association of DGAT2, whereas the mere LD accumulation was not sufficient to hamper HCV RNA replication. Our lipidomics data indicate that both HCV infection and DGAT2 overexpression induced membrane lipid biogenesis and markedly increased phospholipids with long chain polyunsaturated fatty acids, suggesting a dual use of these lipids and their possible competition for LD and DMV biogenesis. On the other hand, overexpression of DGAT2 depleted specific phospholipids, particularly oleyl fatty acyl chain-containing phosphatidylcholines, which, in contrast, are increased in HCV-infected cells and likely essential for viral infection. In conclusion, our results indicate that lipid exchanges occurring during LD biogenesis regulate the composition of intracellular membranes and thereby affect the formation of the HCV replication organelle. The potent antiviral effect observed in our DGAT2 overexpression system unveils lipid flux that may be relevant in the context of steatohepatitis, a hallmark of HCV infection, but also in physiological conditions, locally in specific subdomains of the ER membrane. Thus, LD formation mediated by DGAT1 and DGAT2 might participate in the spatial compartmentalization of HCV replication and assembly factories within the membranous web.

Diacylglycerol kinase delta overexpression improves glucose clearance and protects against the development of obesity

BACKGROUND AND AIM

Diacylglycerol kinase (DGK) isoforms catalyze an enzymatic reaction that removes diacylglycerol (DAG) and thereby terminates protein kinase C signaling by converting DAG to phosphatidic acid. DGKδ (type II isozyme) downregulation causes insulin resistance, metabolic inflexibility, and obesity. Here we determined whether DGKδ overexpression prevents these metabolic impairments.

METHODS

We generated a transgenic mouse model overexpressing human DGKδ2 under the myosin light chain promoter (DGKδ TG). We performed deep metabolic phenotyping of DGKδ TG mice and wild-type littermates fed chow or high-fat diet (HFD). Mice were also provided free access to running wheels to examine the effects of DGKδ overexpression on exercise-induced metabolic outcomes.

RESULTS

DGKδ TG mice were leaner than wild-type littermates, with improved glucose tolerance and increased skeletal muscle glycogen content. DGKδ TG mice were protected against HFD-induced glucose intolerance and obesity. DGKδ TG mice had reduced epididymal fat and enhanced lipolysis. Strikingly, DGKδ overexpression recapitulated the beneficial effects of exercise on metabolic outcomes. DGKδ overexpression and exercise had a synergistic effect on body weight reduction. Microarray analysis of skeletal muscle revealed common gene ontology signatures of exercise and DGKδ overexpression that were related to lipid storage, extracellular matrix, and glycerophospholipids biosynthesis pathways.

CONCLUSION

Overexpression of DGKδ induces adaptive changes in both skeletal muscle and adipose tissue, resulting in protection against HFD-induced obesity. DGKδ overexpression recapitulates exercise-induced adaptations on energy homeostasis and skeletal muscle gene expression profiles.

P2X7 receptor-dependent increase in endocannabinoid 2-arachidonoyl glycerol production by neuronal cells in culture: Dynamics and mechanism

BACKGROUND AND PURPOSE

Neurotransmission and neuroinflammation are controlled by local increases in both extracellular ATP and the endocannabinoid 2-arachidonoyl glycerol (2-AG). While it is known that extracellular ATP stimulates 2-AG production in cells in culture, the dynamics and molecular mechanisms that underlie this response remain poorly understood. Detection of real-time changes in eCB levels with the genetically encoded sensor, GRABeCB2.0, can address this shortfall.

EXPERIMENTAL APPROACH

2-AG and arachidonoylethanolamide (AEA) levels in Neuro2a (N2a) cells were measured by LC-MS, and GRABeCB2.0 fluorescence changes were detected using live-cell confocal microscopy and a 96-well fluorescence plate reader.

KEY RESULTS

2-AG and AEA increased GRABeCB2.0 fluorescence in N2a cells with EC50 values of 81 and 58 nM, respectively; both responses were reduced by the cannabinoid receptor type 1 (CB1R) antagonist SR141617 and absent in cells expressing the mutant-GRABeCB2.0. ATP increased only 2-AG levels in N2a cells, as measured by LC-MS, and induced a transient increase in the GRABeCB2.0 signal within minutes primarily via activation of P2X7 receptors (P2X7R). This response was dependent on diacylglycerol lipase β activity, partially dependent on extracellular calcium and phospholipase C activity, but not controlled by the 2-AG hydrolysing enzyme, α/β-hydrolase domain containing 6 (ABHD6).

CONCLUSIONS AND IMPLICATIONS

Considering that P2X7R activation increases 2-AG levels within minutes, our results show how these molecular components are mechanistically linked. The specific molecular components in these signalling systems represent potential therapeutic targets for the treatment of neurological diseases, such as chronic pain, that involve dysregulated neurotransmission and neuroinflammation.

Diacylglycerol kinase is a keystone regulator of signaling relevant to the pathophysiology of asthma

Signal transduction by G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs) and immunoreceptors converge at the activation of phospholipase C (PLC) for the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). This is a point for second-messenger bifurcation where DAG via protein kinase C (PKC) and IP3 via calcium activate distinct protein targets and regulate cellular functions. IP3 signaling is regulated by multiple calcium influx and efflux proteins involved in calcium homeostasis. A family of lipid kinases belonging to DAG kinases (DGKs) converts DAG to phosphatidic acid (PA), negatively regulating DAG signaling and pathophysiological functions. PA, through a series of biochemical reactions, is recycled to produce new molecules of PIP2. Therefore, DGKs act as a central switch in terminating DAG signaling and resynthesis of membrane phospholipids precursor. Interestingly, calcium and PKC regulate the activation of α and ζ isoforms of DGK that are predominantly expressed in airway and immune cells. Thus, DGK forms a feedback and feedforward control point and plays a crucial role in fine-tuning phospholipid stoichiometry, signaling, and functions. In this review, we discuss the previously underappreciated complex and intriguing DAG/DGK-driven mechanisms in regulating cellular functions associated with asthma, such as contraction and proliferation of airway smooth muscle (ASM) cells and inflammatory activation of immune cells. We highlight the benefits of manipulating DGK activity in mitigating salient features of asthma pathophysiology and shed light on DGK as a molecule of interest for heterogeneous diseases such as asthma.

Myofiber-specific lipidomics unveil differential contributions to insulin sensitivity in individuals of African and European ancestry

Aims

Individuals of African ancestry (AA) present with lower insulin sensitivity compared to their European counterparts (EA). Studies show ethnic differences in skeletal muscle fiber type (lower type I fibers in AA), muscle fat oxidation capacity (lower in AA), whilst no differences in total skeletal muscle lipids. However, skeletal muscle lipid subtypes have not been examined in this context. We hypothesize that lower insulin sensitivity in AA is due to a greater proportion of type II (non-oxidative) muscle fibers, and that this would result in an ancestry-specific association between muscle lipid subtypes and peripheral insulin sensitivity. To test this hypothesis, we examined the association between insulin sensitivity and muscle lipids in AA and EA adults, and in an animal model of insulin resistance with muscle-specific fiber types.

Methods

In this cross-sectional study, muscle biopsies were obtained from individuals with a BMI ranging from normal to overweight with AA (N = 24) and EA (N = 19). Ancestry was assigned via genetic admixture analysis; peripheral insulin sensitivity via hyperinsulinaemic-euglycemic clamp; and myofiber content via myosin heavy chain immunohistochemistry. Further, muscle types with high (soleus) and low (vastus lateralis) type I fiber content were obtained from high-fat diet-induced insulin resistant F1 mice and littermate controls. Insulin sensitivity in mice was assessed via intraperitoneal glucose tolerance test. Mass spectrometry (MS)-based lipidomics was used to measure skeletal muscle lipid.

Results

Compared to EA, AA had lower peripheral insulin sensitivity and lower oxidative type 1 myofiber content, with no differences in total skeletal muscle lipid content. Muscles with lower type I fiber content (AA and vastus from mice) showed lower levels of lipids associated with fat oxidation capacity, i.e., cardiolipins, triacylglycerols with low saturation degree and phospholipids, compared to muscles with a higher type 1 fiber content (EA and soleus from mice). Further, we found that muscle diacylglycerol content was inversely associated with insulin sensitivity in EA, who have more type I fiber, whereas no association was found in AA. Similarly, we found that insulin sensitivity in mice was associated with diacylglycerol content in the soleus (high in type I fiber), not in vastus (low in type I fiber).Conclusions; Our data suggest that the lipid contribution to altered insulin sensitivity differs by ethnicity due to myofiber composition, and that this needs to be considered to increase our understanding of underlying mechanisms of altered insulin sensitivity in different ethnic populations.

Sex differences in lipidomic and bile acid plasma profiles in patients with and without coronary artery disease

BACKGROUND

Lipids, including phospholipids and bile acids, exert various signaling effects and are thought to contribute to the development of coronary artery disease (CAD). Here, we aimed to compare lipidomic and bile acid profiles in the blood of patients with and without CAD stratified by sex.

METHODS

From 2015 to 2022, 3,012 patients who underwent coronary angiography were recruited in the INTERCATH cohort. From the overall cohort, subgroups were defined using patient characteristics such as CAD vs. no CAD, 1st vs. 3rd tertile of LDL-c, and female vs. male sex. Hereafter, a matching algorithm based on age, BMI, hypertension status, diabetes mellitus status, smoking status, the Mediterranean diet score, and the intake of statins, triglycerides, HDL-c and hs-CRP in a 1:1 ratio was implemented. Lipidomic analyses of stored blood samples using the Lipidyzer platform (SCIEX) and bile acid analysis using liquid chromatography with tandem mass spectrometry (LC‒MS/MS) were carried out.

RESULTS

A total of 177 matched individuals were analyzed; the median ages were 73.5 years (25th and 75th percentile: 64.1, 78.2) and 71.9 years (65.7, 77.2) for females and males with CAD, respectively, and 67.6 years (58.3, 75.3) and 69.2 years (59.8, 76.8) for females and males without CAD, respectively. Further baseline characteristics, including cardiovascular risk factors, were balanced between the groups. Women with CAD had decreased levels of phosphatidylcholine and diacylglycerol, while no differences in bile acid profiles were detected in comparison to those of female patients without CAD. In contrast, in male patients with CAD, decreased concentrations of the secondary bile acid species glycolithocholic and lithocholic acid, as well as altered levels of specific lipids, were detected compared to those in males without CAD. Notably, male patients with low LDL-c and CAD had significantly greater concentrations of various phospholipid species, particularly plasmalogens, compared to those in high LDL-c subgroup.

CONCLUSIONS

We present hypothesis-generating data on sex-specific lipidomic patterns and bile acid profiles in CAD patients. The data suggest that altered lipid and bile acid composition might contribute to CAD development and/or progression, helping to understand the different disease trajectories of CAD in women and men.

REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT04936438 , Unique identifier: NCT04936438.

THP-1 Monocytic Cells Are Polarized to More Antitumorigenic Macrophages by Serial Treatment with Phorbol-12-Myristate-13-Acetate and PD98059

Background and Objectives: As modulators of the tumor microenvironment, macrophages have been extensively studied for their potential in developing anticancer strategies, particularly in regulating macrophage polarization towards an antitumorigenic (M1) phenotype rather than a protumorigenic (M2) one in various experimental models. Here, we evaluated the effect of PD98059, a mitogen-activated protein kinase kinase MAPKK MEK1-linked pathway inhibitor, on the differentiation and polarization of THP-1 monocytes in response to phorbol-12-myristate-13-acetate (PMA) under various culture conditions for tumor microenvironmental application. Materials and Methods: Differentiation and polarization of THP-1 were analyzed by flow cytometry and RT-PCR. Polarized THP-1 subsets with different treatment were compared by motility, phagocytosis, and so on. Results: Clearly, PMA induced THP-1 differentiation occurs in adherent culture conditions more than nonadherent culture conditions by increasing CD11b expression up to 90%, which was not affected by PD98059 when cells were exposed to PMA first (post-PD) but inhibited when PD98059 was treated prior to PMA treatment (pre-PD). CD11bhigh THP-1 cells treated with PMA and PMA-post-PD were categorized into M0 (HLA-DRlow and CD206low), M1 (HLA-DRhigh and CD206low), and M2 (HLA-DRlow and CD206high), resulting in an increased population of M1 macrophages. The transcription levels of markers of macrophage differentiation and polarization confirmed the increased M1 polarization of THP-1 cells with post-PD treatment rather than with PMA-only treatment. The motility and cytotoxicity of THP-1 cells with post-PD treatment were higher than THP-1 cells with PMA, suggesting that post-PD treatment enhanced the anti-tumorigenicity of THP-1 cells. Confocal microscopy and flow cytometry showed the effect of post-PD treatment on phagocytosis by THP-1 cells. Conclusions: We have developed an experimental model of macrophage polarization with THP-1 cells which will be useful for further studies related to the tumor microenvironment.

Role of carboxylesterase and arylacetamide deacetylase in drug metabolism, physiology, and pathology

Carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC), which are expressed primarily in the liver and/or gastrointestinal tract, hydrolyze drugs containing ester and amide bonds in their chemical structure. These enzymes often catalyze the conversion of prodrugs, including the COVID-19 drugs remdesivir and molnupiravir, to their pharmacologically active forms. Information on the substrate specificity and inhibitory properties of these enzymes, which would be useful for drug development and toxicity avoidance, has accumulated. Recently,in vitroandin vivostudies have shown that these enzymes are involved not only in drug hydrolysis but also in lipid metabolism. CES1 and CES2 are capable of hydrolyzing triacylglycerol, and the deletion of their orthologous genes in mice has been associated with impaired lipid metabolism and hepatic steatosis. Adeno-associated virus-mediated human CES overexpression decreases hepatic triacylglycerol levels and increases fatty acid oxidation in mice. It has also been shown that overexpression of CES enzymes or AADAC in cultured cells suppresses the intracellular accumulation of triacylglycerol. Recent reports indicate that AADAC can be up- or downregulated in tumors of various organs, and its varied expression is associated with poor prognosis in patients with cancer. Thus, CES and AADAC not only determine drug efficacy and toxicity but are also involved in pathophysiology. This review summarizes recent findings on the roles of CES and AADAC in drug metabolism, physiology, and pathology.

Molecular dynamics simulations of intracellular lipid droplets: a new tool in the toolbox

Lipid droplets (LDs) are ubiquitous intracellular organelles with a central role in multiple lipid metabolic pathways. However, identifying correlations between their structural properties and their biological activity has proved challenging, owing to their unique physicochemical properties as compared with other cellular membranes. In recent years, molecular dynamics (MD) simulations, a computational methodology allowing the accurate description of molecular assemblies down to their individual components, have been demonstrated to be a useful and powerful approach for studying LD structural and dynamical properties. In this short review, we attempt to highlight, as comprehensively as possible, how MD simulations have contributed to our current understanding of multiple molecular mechanisms involved in LD biology.

Glia-derived secretory fatty acid binding protein Obp44a regulates lipid storage and efflux in the developing Drosophila brain

Glia derived secretory factors play diverse roles in supporting the development, physiology, and stress responses of the central nervous system (CNS). Through transcriptomics and imaging analyses, we have identified Obp44a as one of the most abundantly produced secretory proteins from Drosophila CNS glia. Protein structure homology modeling and Nuclear Magnetic Resonance (NMR) experiments reveal Obp44a as a fatty acid binding protein (FABP) with a high affinity towards long-chain fatty acids in both native and oxidized forms. Further analyses demonstrate that Obp44a effectively infiltrates the neuropil, traffics between neuron and glia, and is secreted into hemolymph, acting as a lipid chaperone and scavenger to regulate lipid and redox homeostasis in the developing brain. In agreement with this essential role, deficiency of Obp44a leads to anatomical and behavioral deficits in adult animals and elevated oxidized lipid levels. Collectively, our findings unveil the crucial involvement of a noncanonical lipid chaperone to shuttle fatty acids within and outside the brain, as needed to maintain a healthy brain lipid environment. These findings could inspire the design of novel approaches to restore lipid homeostasis that is dysregulated in CNS diseases.

Human metabolic chambers reveal a coordinated metabolic-physiologic response to nutrition

The emerging field of precision nutrition is based on the notion that inter-individual responses across diets of different calorie-macronutrient content may contribute to inter-individual differences in metabolism, adiposity, and weight gain. Free-living diet studies have been traditionally challenged by difficulties in controlling adherence to prescribed calories and macronutrient content and rarely allow a period of metabolic stability prior to metabolic measures (to minimize influences of weight changes). In this context, key physiologic measures central to precision nutrition responses may be most precisely quantified via whole room indirect calorimetry over 24-h, in which precise control of activity and nutrition can be achieved. In addition, these studies represent unique "N of 1" human crossover metabolic-physiologic experiments during which specific molecular pathways central to nutrient metabolism may be discerned. Here, we quantified 263 circulating metabolites during a ≈40-day inpatient admission in which up to 94 participants underwent seven monitored 24-h nutritional interventions of differing macronutrient composition in a whole-room indirect calorimeter to capture precision metabolic responses. Broadly, we observed heterogenous responses in metabolites across dietary chambers, with the exception of carnitines which tracked with 24-h respiratory quotient. We identified excursions in shared metabolic species (e.g., carnitines, glycerophospholipids, amino acids) that mapped onto gold-standard calorimetric measures of substrate oxidation preference and lipid availability. These findings support a coordinated metabolic-physiologic response to nutrition, highlighting the relevance of these controlled settings to uncover biological pathways of energy utilization during precision nutrition studies.

Investigating mouse hepatic lipidome dysregulation following exposure to emerging per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) are environmental pollutants that have been associated with adverse health effects including liver damage, decreased vaccine responses, cancer, developmental toxicity, thyroid dysfunction, and elevated cholesterol. The specific molecular mechanisms impacted by PFAS exposure to cause these health effects remain poorly understood, however there is some evidence of lipid dysregulation. Thus, lipidomic studies that go beyond clinical triglyceride and cholesterol tests are greatly needed to investigate these perturbations. Here, we have utilized a platform coupling liquid chromatography, ion mobility spectrometry, and mass spectrometry (LC-IMS-MS) separations to simultaneously evaluate PFAS bioaccumulation and lipid metabolism disruptions. For the study, liver samples collected from C57BL/6 mice exposed to either of the emerging PFAS hexafluoropropylene oxide dimer acid (HFPO-DA or "GenX") or Nafion byproduct 2 (NBP2) were assessed. Sex-specific differences in PFAS accumulation and liver size were observed for both PFAS, in addition to disturbed hepatic liver lipidomic profiles. Interestingly, GenX resulted in less hepatic bioaccumulation than NBP2 yet gave a higher number of significantly altered lipids when compared to the control group, implying that the accumulation of substances in the liver may not be a reliable measure of the substance's capacity to disrupt the liver's natural metabolic processes. Specifically, phosphatidylglycerols, phosphatidylinositols, and various specific fatty acyls were greatly impacted, indicating alteration of inflammation, oxidative stress, and cellular signaling processes due to emerging PFAS exposure. Overall, these results provide valuable insight into the liver bioaccumulation and molecular mechanisms of GenX- and NBP2-induced hepatotoxicity.

The Role of Neutral Sphingomyelinase-2 (NSM2) in the Control of Neutral Lipid Storage in T Cells

The accumulation of lipid droplets (LDs) and ceramides (Cer) is linked to non-alcoholic fatty liver disease (NAFLD), regularly co-existing with type 2 diabetes and decreased immune function. Chronic inflammation and increased disease severity in viral infections are the hallmarks of the obesity-related immunopathology. The upregulation of neutral sphingomyelinase-2 (NSM2) has shown to be associated with the pathology of obesity in tissues. Nevertheless, the role of sphingolipids and specifically of NSM2 in the regulation of immune cell response to a fatty acid (FA) rich environment is poorly studied. Here, we identified the presence of the LD marker protein perilipin 3 (PLIN3) in the intracellular nano-environment of NSM2 using the ascorbate peroxidase APEX2-catalyzed proximity-dependent biotin labeling method. In line with this, super-resolution structured illumination microscopy (SIM) shows NSM2 and PLIN3 co-localization in LD organelles in the presence of increased extracellular concentrations of oleic acid (OA). Furthermore, the association of enzymatically active NSM2 with isolated LDs correlates with increased Cer levels in these lipid storage organelles. NSM2 enzymatic activity is not required for NSM2 association with LDs, but negatively affects the LD numbers and cellular accumulation of long-chain unsaturated triacylglycerol (TAG) species. Concurrently, NSM2 expression promotes mitochondrial respiration and fatty acid oxidation (FAO) in response to increased OA levels, thereby shifting cells to a high energetic state. Importantly, endogenous NSM2 activity is crucial for primary human CD4+ T cell survival and proliferation in a FA rich environment. To conclude, our study shows a novel NSM2 intracellular localization to LDs and the role of enzymatically active NSM2 in metabolic response to enhanced FA concentrations in T cells.

Diacylglycerols and Lysophosphatidic Acid, Enriched on Lipoprotein(a), Contribute to Monocyte Inflammation

BACKGROUND

Oxidized phospholipids play a key role in the atherogenic potential of lipoprotein(a) (Lp[a]); however, Lp(a) is a complex particle that warrants research into additional proinflammatory mediators. We hypothesized that additional Lp(a)-associated lipids contribute to the atherogenicity of Lp(a).

METHODS

Untargeted lipidomics was performed on plasma and isolated lipoprotein fractions. The atherogenicity of the observed Lp(a)-associated lipids was tested ex vivo in primary human monocytes by RNA sequencing, ELISA, Western blot, and transendothelial migratory assays. Using immunofluorescence staining and single-cell RNA sequencing, the phenotype of macrophages was investigated in human atherosclerotic lesions.

RESULTS

Compared with healthy individuals with low/normal Lp(a) levels (median, 7 mg/dL [18 nmol/L]; n=13), individuals with elevated Lp(a) levels (median, 87 mg/dL [218 nmol/L]; n=12) demonstrated an increase in lipid species, particularly diacylglycerols (DGs) and lysophosphatidic acid (LPA). DG and the LPA precursor lysophosphatidylcholine were enriched in the Lp(a) fraction. Ex vivo stimulation with DG(40:6) demonstrated a significant upregulation in proinflammatory pathways related to leukocyte migration, chemotaxis, NF-κB (nuclear factor kappa B) signaling, and cytokine production. Functional assessment showed a dose-dependent increase in the secretion of IL (interleukin)-6, IL-8, and IL-1β after DG(40:6) and DG(38:4) stimulation, which was, in part, mediated via the NLRP3 (NOD [nucleotide-binding oligomerization domain]-like receptor family pyrin domain containing 3) inflammasome. Conversely, LPA-stimulated monocytes did not exhibit an inflammatory phenotype. Furthermore, activation of monocytes by DGs and LPA increased their transendothelial migratory capacity. Human atherosclerotic plaques from patients with high Lp(a) levels demonstrated colocalization of Lp(a) with M1 macrophages, and an enrichment of CD68+IL-18+TLR4+ (toll-like receptor) TREM2+ (triggering receptor expressed on myeloid cells) resident macrophages and CD68+CASP1+ (caspase) IL-1B+SELL+ (selectin L) inflammatory macrophages compared with patients with low Lp(a). Finally, potent Lp(a)-lowering treatment (pelacarsen) resulted in a reduction in specific circulating DG lipid subspecies in patients with cardiovascular disease with elevated Lp(a) levels (median, 82 mg/dL [205 nmol/L]).

CONCLUSIONS

Lp(a)-associated DGs and LPA have a potential role in Lp(a)-induced monocyte inflammation by increasing cytokine secretion and monocyte transendothelial migration. This DG-induced inflammation is, in part, NLRP3 inflammasome dependent.

Peroxisome deficiency underlies failures in hepatic immune cell development and antigen presentation in a severe Zellweger disease model

Peroxisome biogenesis disorders (PBDs) represent a group of metabolic conditions that cause severe developmental defects. Peroxisomes are essential metabolic organelles, present in virtually every eukaryotic cell and mediating key processes in immunometabolism. To date, the full spectrum of PBDs remains to be identified, and the impact PBDs have on immune function is unexplored. This study presents a characterization of the hepatic immune compartment of a neonatal PBD mouse model at single-cell resolution to establish the importance and function of peroxisomes in developmental hematopoiesis. We report that hematopoietic defects are a feature in a severe PBD murine model. Finally, we identify a role for peroxisomes in the regulation of the major histocompatibility class II expression and antigen presentation to CD4+ T cells in dendritic cells. This study adds to our understanding of the mechanisms of PBDs and expands our knowledge of the role of peroxisomes in immunometabolism.

Processing of LtaS restricts LTA assembly and YSIRK preprotein trafficking into Staphylococcus aureus cross-walls

Septal membranes of Staphylococcus aureus serve as the site of secretion for precursors endowed with the YSIRK motif. Depletion of ltaS, a gene required for lipoteichoic acid (LTA) synthesis, results in the loss of restricted trafficking of YSIRK precursors to septal membranes. Here, we seek to understand the mechanism that ties LTA assembly and trafficking of YSIRK precursors. We confirm that catalytically inactive lipoteichoic acid synthase (LtaS)T300A does not support YSIRK precursor trafficking to septa. We hypothesize that the enzyme's reactants [gentiobiosyldiacylglycerol (Glc2-DAG) and phosphatidylglycerol (PG)] or products [LTA and diacylglycerol (DAG)], not LtaS, must drive this process. Indeed, we observe that septal secretion of the staphylococcal protein A YSIRK precursor is lost in ypfP and ltaA mutants that produce glycerophosphate polymers [poly(Gro-P)] without the Glc2-DAG lipid anchor. These mutants display longer poly(Gro-P) chains, implying enhanced PG consumption and DAG production. Our experiments also reveal that in the absence of Glc2-DAG, the processing of LtaS to the extracellular catalytic domain, eLtaS, is impaired. Conversely, LTA polymerization is delayed in a strain producing LtaSS218P, a variant processed more slowly than LtaS. We conclude that Glc2-DAG binding to the enzyme couples catalysis by LtaS and the physical release of eLtaS. We propose a model for the temporal and localized assembly of LTA into cross-walls. When LtaS is not processed in a timely manner, eLtaS no longer diffuses upon daughter cell splitting, LTA assembly continues, and the unique septal-lipid pool, PG over DAG ratio, is not established. This results in profound physiological changes in S. aureus cells, including the inability to restrict the secretion of YSIRK precursors at septal membranes.IMPORTANCEIn Staphylococcus aureus, peptidoglycan is assembled at the septum. Dedicated cell division proteins coordinate septal formation and the fission of daughter cells. Lipoteichoic acid (LTA) assembly and trafficking of preproteins with a YSIRK motif also occur at the septum. This begs the question as to whether cell division components also recruit these two pathways. This study shows that the processing of lipoteichoic acid synthase (LtaS) to extracellular LtaS by signal peptidase is regulated by gentiobiosyldiacylglycerol (Glc2-DAG), the priming substrate for LTA assembly. A model is proposed whereby a key substrate controls the temporal and spatial activity of an enzyme. In turn, this mechanism enables the establishment of a unique and transient lipid pool that defines septal membranes as a targeting site for the secretion of YSIRK preproteins.

Protein kinase D (PKD) on the crossroad of lipid absorption, synthesis and utilization

Inappropriate lipid levels in the blood, as well as its content and composition in different organs, underlie multiple metabolic disorders including obesity, non-alcoholic fatty liver disease, type 2 diabetes, and atherosclerosis. Multiple processes contribute to the complex metabolism of triglycerides (TGs), fatty acids (FAs), and other lipid species. These consist of digestion and absorption of dietary lipids, de novo FAs synthesis (lipogenesis), uptake of TGs and FAs by peripheral tissues, TGs storage in the intracellular depots as well as lipid utilization for β-oxidation and their conversion to lipid-derivatives. A majority of the enzymatic reactions linked to lipogenesis, TGs synthesis, lipid absorption, and transport are happening at the endoplasmic reticulum, while β-oxidation takes place in mitochondria and peroxisomes. The Golgi apparatus is a central sorting, protein- and lipid-modifying organelle and hence is involved in lipid metabolism as well. However, the impact of the processes taking part in the Golgi apparatus are often overseen. The protein kinase D (PKD) family (composed of three members, PKD1, 2, and 3) is the master regulator of Golgi dynamics. PKDs are also a sensor of different lipid species in distinct cellular compartments. In this review, we discuss the roles of PKD family members in the regulation of lipid metabolism including the processes executed by PKDs at the Golgi apparatus. We also discuss the role of PKDs-dependent signaling in different cellular compartments and organs in the context of the development of metabolic disorders.

APOE genotype dictates lipidomic signatures in primary human hepatocytes

Apolipoprotein E (APOE) genetic variants are most notably known for their divergent impact on the risk of developing Alzheimer's disease. While APOE genotype has been consistently shown to modulate lipid metabolism in a variety of cellular contexts, the effect of APOE alleles on the lipidome in hepatocytes is unknown. In this study, we investigated the contribution of APOE alleles to lipidomic profiles of donor-derived primary human hepatocytes from 77 subjects. Lipidomic data obtained by liquid chromatography-mass spectrometry were analyzed across ε2/ε3, ε3/ε3, and ε3/ε4 genotypes to reveal how APOE modulates lipid relative levels over age and between groups. Hepatic APOE concentration, measured by ELISA, was assessed for correlation with lipid abundance in subjects grouped as per APOE genotype and sex. APOE genotype-specific differential lipidomic signatures associated with age for multiple lipid classes but did not differ between sexes. Compared to ε2/ε3, ε3/ε4 hepatocytes had higher abundance of acylcarnitines (AC) and acylphosphatidylglycerol (AcylPG) as a class, as well as higher medium and long-chain ACs, AcylPG, phosphatidylglycerol (PG), bis(monoacylglycerol)phosphate (BMP), monoacylglycerol (MG) and diacylglycerol (DG) species. The ε3/ε4 hepatocytes also exhibited a higher abundance of medium and long-chain ACs compared to the ε3/ε3 hepatocytes. Only in the ε3/ε4 hepatocytes, APOE concentration was lower and showed a negative correlation with BMP levels, specifically in females. APOE genotype dictates a differential lipidome in primary human hepatocytes. The lipids involved suggest mitochondrial dysfunction with accompanying alterations in neutral lipid storage, reflective of a general disturbance of free fatty acid metabolism in human hepatocytes with the ε4 allele.

Untargeted serum metabolomic profiles and breast density in young women

PURPOSE OF THE STUDY

Breast density is an established risk factor for breast cancer. However, little is known about metabolic influences on breast density phenotypes. We conducted untargeted serum metabolomics analyses to identify metabolic signatures associated with breast density phenotypes among young women.

METHODS

In a cross-sectional study of 173 young women aged 25-29 who participated in the Dietary Intervention Study in Children 2006 Follow-up Study, 449 metabolites were measured in fasting serum samples using ultra-high-performance liquid chromatography-tandem mass spectrometry. Multivariable-adjusted mixed-effects linear regression identified metabolites associated with magnetic resonance imaging measured breast density phenotypes: percent dense breast volume (%DBV), absolute dense breast volume (ADBV), and absolute non-dense breast volume (ANDBV). Metabolite results were corrected for multiple comparisons using a false discovery rate adjusted p-value (q).

RESULTS

The amino acids valine and leucine were significantly inversely associated with %DBV. For each 1 SD increase in valine and leucine, %DBV decreased by 20.9% (q = 0.02) and 18.4% (q = 0.04), respectively. ANDBV was significantly positively associated with 16 lipid and one amino acid metabolites, whereas no metabolites were associated with ADBV. Metabolite set enrichment analysis also revealed associations of distinct metabolic signatures with %DBV, ADBV, and ANDBV; branched chain amino acids had the strongest inverse association with %DBV (p = 0.002); whereas, diacylglycerols and phospholipids were positively associated with ANDBV (p ≤ 0.002), no significant associations were observed for ADBV.

CONCLUSION

Our results suggest an inverse association of branched chain amino acids with %DBV. Larger studies in diverse populations are needed.

Rumen-protected methionine supplementation alters lipid profile of preimplantation embryo and endometrial tissue of Holstein cows

Our objective is to evaluate the effects of feeding rumen-protected Met (RPM) throughout the transition period and early lactation on the lipid profile of the preimplantation embryos and the endometrial tissue of Holstein cows. Treatments consisted of feeding a total mixed ration with top-dressed RPM (Smartamine® M, Adisseo, Alpharetta, GA, United States; MET; n = 11; RPM at a rate of 0.08% of DM: Lys:Met = 2.8:1) or not (CON; n = 9, Lys:Met = 3.5:1). Endometrial biopsies were performed at 15, 30, and 73 days in milk (DIM). Prior to the endometrial biopsy at 73 DIM, preimplantation embryos were harvested via flushing. Endometrial lipid profiles were analyzed using multiple reaction monitoring-profiling and lipid profiles of embryos were acquired using matrix assisted laser desorption/ionization mass spectrometry. Relative intensities levels were used for principal component analysis. Embryos from cows in MET had greater concentration of polyunsaturated lipids than embryos from cows in CON. The endometrial tissue samples from cows in MET had lesser concentrations of unsaturated and monounsaturated lipids at 15 DIM, and greater concentration of saturated, unsaturated (specifically diacylglycerol), and monounsaturated (primarily ceramides) lipids at 30 DIM than the endometrial tissue samples from cows in CON. In conclusion, feeding RPM during the transition period and early lactation altered specific lipid classes and lipid unsaturation level of preimplantation embryos and endometrial tissue.

Maturation and culture affect the metabolomic profile of oocytes and follicular cells in young and old mares

Introduction: Oocytes and follicular somatic cells within the ovarian follicle are altered during maturation and after exposure to culture in vitro. In the present study, we used a nontargeted metabolomics approach to assess changes in oocytes, cumulus cells, and granulosa cells from dominant, follicular-phase follicles in young and old mares. Methods: Samples were collected at three stages associated with oocyte maturation: (1) GV, germinal vesicle stage, prior to the induction of follicle/oocyte maturation in vivo; (2) MI, metaphase I, maturing, collected 24 h after induction of maturation in vivo; and (3) MIIC, metaphase II, mature with collection 24 h after induction of maturation in vivo plus 18 h of culture in vitro. Samples were analyzed using gas and liquid chromatography coupled to mass spectrometry only when all three stages of a specific cell type were obtained from the same mare. Results and Discussion: Significant differences in metabolite abundance were most often associated with MIIC, with some of the differences appearing to be linked to the final stage of maturation and others to exposure to culture medium. While differences occurred for many metabolite groups, some of the most notable were detected for energy and lipid metabolism and amino acid abundance. The study demonstrated that metabolomics has potential to aid in optimizing culture methods and evaluating cell culture additives to support differences in COCs associated with maternal factors.

Diacylglycerol metabolism and homeostasis in fungal physiology

Diacylglycerol (DAG) is a relatively simple and primitive form of lipid, which does not possess a phospholipid headgroup. Being a central metabolite of the lipid metabolism network, DAGs are omnipresent in all life forms. While the role of DAG has been established in membrane and storage lipid biogenesis, it can impart crucial physiological functions including membrane shapeshifting, regulation of membrane protein activity, and transduction of cellular signalling as a lipid-based secondary messenger. Besides, the chemical diversity of DAGs, due to fatty acyl chain composition, has been proposed to be the basis of its functional diversity. Therefore, cells must regulate DAG level at a spatio-temporal scale for homeostasis and adaptation. The vast network of eukaryotic lipid metabolism has been unravelled majorly by studying yeast models. Here, we review the current understanding and the emerging concepts in metabolic and functional aspects of DAG regulation in yeast. The implications can be extended to understand pathogenic fungi and mammalian counterparts as well as disease aetiology.

Exercise training adaptations in liver glycogen and glycerolipids require hepatic AMP-activated protein kinase in mice

Regular exercise elicits adaptations in glucose and lipid metabolism that allow the body to meet energy demands of subsequent exercise bouts more effectively and mitigate metabolic diseases including fatty liver. Energy discharged during the acute exercise bouts that comprise exercise training may be a catalyst for liver adaptations. During acute exercise, liver glycogenolysis and gluconeogenesis are accelerated to supply glucose to working muscle. Lower liver energy state imposed by gluconeogenesis and related pathways activates AMP-activated protein kinase (AMPK), which conserves ATP partly by promoting lipid oxidation. This study tested the hypothesis that AMPK is necessary for liver glucose and lipid adaptations to training. Liver-specific AMPKα1α2 knockout (AMPKα1α2fl/fl+AlbCre) mice and littermate controls (AMPKα1α2fl/fl) completed sedentary and exercise training protocols. Liver nutrient fluxes were quantified at rest or during acute exercise following training. Liver metabolites and molecular regulators of metabolism were assessed. Training increased liver glycogen in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. The inability to increase glycogen led to lower glycogenolysis, glucose production, and circulating glucose during acute exercise in trained AMPKα1α2fl/fl+AlbCre mice. Deletion of AMPKα1α2 attenuated training-induced declines in liver diacylglycerides. In particular, training lowered the concentration of unsaturated and elongated fatty acids comprising diacylglycerides in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. Training increased liver triacylglycerides and the desaturation and elongation of fatty acids in triacylglycerides of AMPKα1α2fl/fl+AlbCre mice. These lipid responses were independent of differences in tricarboxylic acid cycle fluxes. In conclusion, AMPK is required for liver training adaptations that are critical to glucose and lipid metabolism.NEW & NOTEWORTHY This study shows that the energy sensor and transducer, AMP-activated protein kinase (AMPK), is necessary for an exercise training-induced: 1) increase in liver glycogen that is necessary for accelerated glycogenolysis during exercise, 2) decrease in liver glycerolipids independent of tricarboxylic acid (TCA) cycle flux, and 3) decline in the desaturation and elongation of fatty acids comprising liver diacylglycerides. The mechanisms defined in these studies have implications for use of regular exercise or AMPK-activators in patients with fatty liver.

The heterogeneity and complexity of skin surface lipids in human skin health and disease

The outermost epidermal layer of the skin, the stratum corneum, is not simply a barrier that safeguards skin integrity from external insults and invaders, it is also a delicately integrated interface composed of firm, essentially dead corneocytes and a distinctive lipid matrix. Together, the stratum corneum lipid matrix and sebum lipids derived from sebaceous glands give rise to a remarkably complex but quite unique blend of skin surface lipids that demonstrates tremendous heterogeneity and provides the skin with its indispensable protective coating. The stratum corneum lipid matrix is composed primarily of three major lipid classes: ceramides, non-esterified fatty acids and cholesterol, whereas sebum is a waxy mixture predominantly composed of acylglycerols, wax esters, non-esterified fatty acids, squalene, cholesterol and cholesterol esters. The balance of these skin surface lipids in terms of their relative abundance, composition, molecular organisation and dynamics, and their intricate interactions play a crucial role in the maintenance of healthy skin. For that reason, even minuscule alterations in skin surface lipid properties or overall lipid profile have been implicated in the aetiology of many common skin diseases including atopic dermatitis, psoriasis, xerosis, ichthyosis and acne. Novel lipid-based interventions aimed at correcting the skin surface lipid abnormalities have the potential to repair skin barrier integrity and the symptoms associated with such skin diseases, even though the exact mechanisms of lipid restoration remain elusive.

Phosphatidic acid signaling and function in nuclei

Membrane lipidomes are dynamic and their changes generate lipid mediators affecting various biological processes. Phosphatidic acid (PA) has emerged as an important class of lipid mediators involved in a wide range of cellular and physiological responses in plants, animals, and microbes. The regulatory functions of PA have been studied primarily outside the nuclei, but an increasing number of recent studies indicates that some of the PA effects result from its action in nuclei. PA levels in nuclei are dynamic in response to stimuli. Changes in nuclear PA levels can result from activities of enzymes associated with nuclei and/or from movements of PA generated extranuclearly. PA has also been found to interact with proteins involved in nuclear functions, such as transcription factors and proteins undergoing nuclear translocation in response to stimuli. The nuclear action of PA affects various aspects of plant growth, development, and response to stress and environmental changes.

Metabolic and Molecular Amplification of Insulin Secretion

The pancreatic β cells are at the hub of myriad signals to regulate the secretion of an adequate amount of insulin needed to re-establish postprandial euglycemia. The β cell possesses sophisticated metabolic enzymes and a variety of extracellular receptors and channels that amplify insulin secretion in response to autocrine, paracrine, and neurohormonal signals. Considerable research has been undertaken to decipher the mechanisms regulating insulin secretion. While the triggering pathway induced by glucose is needed to initiate the exocytosis process, multiple other stimuli modulate the insulin secretion response. This chapter will discuss the recent advances in understanding the role of the diverse glucose- and fatty acid-metabolic coupling factors in amplifying insulin secretion. It will also highlight the intracellular events linking the extracellular receptors and channels to insulin secretion amplification. Understanding these mechanisms provides new insights into learning more about the etiology of β-cell failure and paves the way for developing new therapeutic strategies for type 2 diabetes.

Binding of perilipin 3 to membranes containing diacylglycerol is mediated by conserved residues within its PAT domain

Perilipins (PLINs) constitute an evolutionarily conserved family of proteins that specifically associate with the surface of lipid droplets (LDs). These proteins function in LD biogenesis and lipolysis and help to stabilize the surface of LDs. PLINs are typically composed of three different protein domains. They share an N-terminal PAT domain of unknown structure and function, a central region containing 11-mer repeats that form amphipathic helices, and a C-terminal domain that adopts a 4-helix bundle structure. How exactly these three distinct domains contribute to PLIN function remains to be determined. Here, we show that the N-terminal PAT domain of PLIN3 binds diacylglycerol (DAG), the precursor to triacylglycerol, a major storage lipid of LDs. PLIN3 and its PAT domain alone bind liposomes with micromolar affinity and PLIN3 binds artificial LDs containing low concentrations of DAG with nanomolar affinity. The PAT domain of PLIN3 is predicted to adopt an amphipathic triangular shaped structure. In silico ligand docking indicates that DAG binds to one of the highly curved regions within this domain. A conserved aspartic acid residue in the PAT domain, E86, is predicted to interact with DAG, and we found that its substitution abrogates high affinity binding of DAG as well as DAG-stimulated association with liposome and artificial LDs. These results indicate that the PAT domain of PLINs harbor specific lipid-binding properties that are important for targeting these proteins to the surface of LDs and to ER membrane domains enriched in DAG to promote LD formation.