Inhibiting adipose tissue lipogenesis reprograms thermogenesis and PPARγ activation to decrease diet-induced obesity

The role of mesenchymal stem cells in early programming of adipose tissue in the offspring of women with obesity

Maternal obesity is a well-known risk factor for developing premature obesity, metabolic syndrome, cardiovascular disease and type 2 diabetes in the progeny. The development of white adipose tissue is a dynamic process that starts during prenatal life: fat depots laid down in utero are associated with the proportion of fat in children later on. How early this programming takes place is still unknown. However, recent evidence shows that mesenchymal stem cells (MSC), the embryonic adipocyte precursor cells, show signatures of the early setting of an adipogenic committed phenotype when exposed to maternal obesity. This review aims to present current findings on the cellular adaptations of MSCs from the offspring of women with obesity and how the metabolic environment of MSCs could affect the early commitment towards adipocytes. In conclusion, maternal obesity can induce early programming of fetal adipose tissue by conditioning MSCs. These cells have higher expression of adipogenic markers, altered insulin signalling and mitochondrial performance, compared to MSCs of neonates from lean pregnancies. Fetal MSCs imprinting by maternal obesity could help explain the increased risk of childhood obesity and development of further noncommunicable diseases.

Adipose tissue peroxisomal lipid synthesis orchestrates obesity and insulin resistance through LXR-dependent lipogenesis

OBJECTIVE

Adipose tissue mass is maintained by a balance between lipolysis and lipid storage. The contribution of adipose tissue lipogenesis to fat mass, especially in the setting of high-fat feeding, is considered minor. Here we investigated the effect of adipose-specific inactivation of the peroxisomal lipid synthetic protein PexRAP on fatty acid synthase (FASN)-mediated lipogenesis and its impact on adiposity and metabolic homeostasis.

METHODS

To explore the role of PexRAP in adipose tissue, we metabolically phenotyped mice with adipose-specific knockout of PexRAP. Bulk RNA sequencing was used to determine transcriptomic responses to PexRAP deletion and 14C-malonyl CoA allowed us to measure de novo lipogenic activity in adipose tissue of these mice. In vitro cell culture models were used to elucidate the mechanism of cellular responses to PexRAP deletion.

RESULTS

Adipose-specific PexRAP deletion promoted diet-induced obesity and insulin resistance through activation of de novo lipogenesis. Mechanistically, PexRAP inactivation inhibited the flux of carbons to ethanolamine plasmalogens. This increased the nuclear PC/PE ratio and promoted cholesterol mislocalization, resulting in activation of liver X receptor (LXR), a nuclear receptor known to be activated by increased intracellular cholesterol. LXR activation led to increased expression of the phospholipid remodeling enzyme LPCAT3 and induced FASN-mediated lipogenesis, which promoted diet-induced obesity and insulin resistance.

CONCLUSIONS

These studies reveal an unexpected role for peroxisome-derived lipids in regulating LXR-dependent lipogenesis and suggest that activation of lipogenesis, combined with dietary lipid overload, exacerbates obesity and metabolic dysregulation.

Exosomes derived from impaired liver aggravate alveolar bone loss via shuttle of Fasn in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) exacerbates irreversible bone loss in periodontitis, but the mechanism of impaired bone regeneration caused by the abnormal metabolic process of T2DM remains unclear. Exosomes are regarded as the critical mediator in diabetic impairment of regeneration via organ or tissue communication. Here, we find that abnormally elevated exosomes derived from metabolically impaired liver in T2DM are significantly enriched in the periodontal region and induced pyroptosis of periodontal ligament cells (PDLCs). Mechanistically, fatty acid synthase (Fasn), the main differentially expressed molecule in diabetic exosomes results in ectopic fatty acid synthesis in PDLCs and activates the cleavage of gasdermin D. Depletion of liver Fasn effectively mitigates pyroptosis of PDLCs and alleviates bone loss. Our findings elucidate the mechanism of exacerbated bone loss in diabetic periodontitis and reveal the exosome-mediated organ communication in the "liver-bone" axis, which shed light on the prevention and treatment of diabetic bone disorders in the future.

Ether-lipids and cellular signaling: A differential role of alkyl- and alkenyl-ether-lipids?

Ether-lipids (EL) are specific lipids bearing a characteristic sn-1 ether bond. Depending on the ether or vinyl-ether nature of this bond, they are present as alkyl- or alkenyl-EL, respectively. Among EL, alkenyl-EL, also referred as plasmalogens in the literature, attract most of the scientific interest as they are the predominant EL species in eukaryotic cells, thus less is known about alkyl-EL. EL have been implicated in various signaling pathways and alterations in their quantity are frequently observed in pathologies such as neurodegenerative and cardiovascular diseases or cancer. However, it remains unknown whether both alkyl- and alkenyl-EL play the same roles in these processes. This review summarizes the roles and mechanisms of action of EL in cellular signaling and tries to discriminate between alkyl- and alkenyl-EL. We also focus on the involvement of EL-mediated alterations of cellular signaling in diseases and discuss the potential interest for EL in therapy.

Dietary Supplementation with Lauric Acid Improves Aerobic Endurance in Sedentary Mice via Enhancing Fat Mobilization and Glyconeogenesis

BACKGROUND

Lauric acid (LA), a major, natural, medium-chain fatty acid, is considered an efficient energy substrate for intense exercise and in patients with long-chain fatty acid β-oxidation disorders. However, few studies have focused on the role of LA in exercise performance and related glucolipid metabolism in vivo.

OBJECTIVES

We aimed to investigate the effect of dietary supplementation with LA on exercise performance and related metabolic mechanisms.

METHODS

Male C57BL/6N mice (14 wk old) were fed a basal diet or a diet containing 1% LA, and a series of exercise tests, including a high-speed treadmill test, aerobic endurance exercises, a 4-limb hanging test, and acute aerobic exercises, were performed.

RESULTS

Dietary supplementation with 1.0% LA accelerated the recovery from fatigue after explosive exercise (P < 0.05) and improved aerobic endurance and muscle strength in sedentary mice (P = 0.039). Lauric acid intake not only changed muscle fatty acid profiles, including increases in C12:0 and n-6/n-3 PUFAs (P < 0.001) and reductions in C18:0, C20:4n-6, C22:6n-3, and n-3 PUFAs (P < 0.05) but also enhanced fat mobilization from adipose tissue and fatty acid oxidation in the liver, at least partly via the AMP-activated protein kinase-acetyl CoA carboxylase pathway (P < 0.05). Likewise, LA supplementation promoted liver glyconeogenesis and conserved muscular glycogen during acute aerobic exercise (P < 0.05), which was accompanied by an increase in the mitochondrial DNA copy number and Krebs cycle activity in skeletal muscle (P < 0.05).

CONCLUSIONS

Dietary supplemental LA serves as an efficient energy substrate for sedentary mice to improve aerobic exercise endurance and muscle strength through regulation of glucolipid metabolism. These findings imply that LA supplementation might be a promising nutritional strategy to improve aerobic exercise performance in sedentary people.

Targeting Kindlin-2 in adipocytes increases bone mass through inhibiting FAS/PPARγ/FABP4 signaling in mice

Osteoporosis (OP) is a systemic skeletal disease that primarily affects the elderly population, which greatly increases the risk of fractures. Here we report that Kindlin-2 expression in adipose tissue increases during aging and high-fat diet fed and is accompanied by decreased bone mass. Kindlin-2 specific deletion (K2KO) controlled by Adipoq-Cre mice or adipose tissue-targeting AAV (AAV-Rec2-CasRx-sgK2) significantly increases bone mass. Mechanistically, Kindlin-2 promotes peroxisome proliferator-activated receptor gamma (PPARγ) activation and downstream fatty acid binding protein 4 (FABP4) expression through stabilizing fatty acid synthase (FAS), and increased FABP4 inhibits insulin expression and decreases bone mass. Kindlin-2 inhibition results in accelerated FAS degradation, decreased PPARγ activation and FABP4 expression, and therefore increased insulin expression and bone mass. Interestingly, we find that FABP4 is increased while insulin is decreased in serum of OP patients. Increased FABP4 expression through PPARγ activation by rosiglitazone reverses the high bone mass phenotype of K2KO mice. Inhibition of FAS by C75 phenocopies the high bone mass phenotype of K2KO mice. Collectively, our study establishes a novel Kindlin-2/FAS/PPARγ/FABP4/insulin axis in adipose tissue modulating bone mass and strongly indicates that FAS and Kindlin-2 are new potential targets and C75 or AAV-Rec2-CasRx-sgK2 treatment are potential strategies for OP treatment.

A subpopulation of lipogenic brown adipocytes drives thermogenic memory

Sustained responses to transient environmental stimuli are important for survival. The mechanisms underlying long-term adaptations to temporary shifts in abiotic factors remain incompletely understood. Here, we find that transient cold exposure leads to sustained transcriptional and metabolic adaptations in brown adipose tissue, which improve thermogenic responses to secondary cold encounter. Primary thermogenic challenge triggers the delayed induction of a lipid biosynthesis programme even after cessation of the original stimulus, which protects from subsequent exposures. Single-nucleus RNA sequencing and spatial transcriptomics reveal that this response is driven by a lipogenic subpopulation of brown adipocytes localized along the perimeter of Ucp1hi adipocytes. This lipogenic programme is associated with the production of acylcarnitines, and supplementation of acylcarnitines is sufficient to recapitulate improved secondary cold responses. Overall, our data highlight the importance of heterogenous brown adipocyte populations for 'thermogenic memory', which may have therapeutic implications for leveraging short-term thermogenesis to counteract obesity.

TMEM135 links peroxisomes to the regulation of brown fat mitochondrial fission and energy homeostasis

Mitochondrial morphology, which is controlled by mitochondrial fission and fusion, is an important regulator of the thermogenic capacity of brown adipocytes. Adipose-specific peroxisome deficiency impairs thermogenesis by inhibiting cold-induced mitochondrial fission due to decreased mitochondrial membrane content of the peroxisome-derived lipids called plasmalogens. Here, we identify TMEM135 as a critical mediator of the peroxisomal regulation of mitochondrial fission and thermogenesis. Adipose-specific TMEM135 knockout in mice blocks mitochondrial fission, impairs thermogenesis, and increases diet-induced obesity and insulin resistance. Conversely, TMEM135 overexpression promotes mitochondrial division, counteracts obesity and insulin resistance, and rescues thermogenesis in peroxisome-deficient mice. Mechanistically, thermogenic stimuli promote association between peroxisomes and mitochondria and plasmalogen-dependent localization of TMEM135 in mitochondria, where it mediates PKA-dependent phosphorylation and mitochondrial retention of the fission factor Drp1. Together, these results reveal a previously unrecognized inter-organelle communication regulating mitochondrial fission and energy homeostasis and identify TMEM135 as a potential target for therapeutic activation of BAT.

Dietary Eicosapentaenoic Acid Containing Phosphoethanolamine Plasmalogens Remodels the Lipidome of White Adipose Tissue and Suppresses High-Fat Diet Induced Obesity in Mice

SCOPE

Dietary supplementation of docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) can alter the lipidome profiles of adipocytes, thereby counteract obesity. DHA/EPA in the form of phospholipids demonstrates higher bioavailability than triglyceride or ethyl ester (EE), but their effects on the lipidome and metabolic changes during obesity are still unknown.

METHODS AND RESULTS

High-fat diet-induced obese mice are treated with different molecular forms of EPA, and EPA supplemented as phosphoethanolamine plasmalogens (PlsEtn) has a superior effect on reducing fat mass accumulation than phosphatidylcholine (PC) or EE. The lipidomics analysis indicates that EPA in form of PlsEtn but not PC or EE significantly decreases total PC and sphingomyelin content in white adipose tissue (WAT). Some specific polyunsaturated fatty acid -containing PCs and ether phospholipids are increased in EPA-PlsEtn-fed mice, which may attribute to the upregulation of unsaturated fatty acid biosynthesis and fatty acid elongation reactions in WAT. In addition, the expression of genes related to fatty acid catabolism is also promoted by EPA-PlsEtn supplementation, which may cause the decreased content of saturated and monounsaturated fatty acid-containing PCs.

CONCLUSIONS

EPA-PlsEtn supplementation is demonstrated to remodel lipidome and regulate the fatty acid metabolic process in WAT, indicating it may serve as a new strategy for obesity treatment in the future.

Renal ischemia alters the transcriptomic and epigenetic profile of inflammatory genes in swine scattered tubular-like cells

BACKGROUND

Scattered tubular-like cells (STCs) are differentiated renal tubular cells that during recovery from ischemic injury dedifferentiate to repair other injured renal cells. Renal artery stenosis (RAS), often associated with chronic inflammatory injury, compromises the integrity and function of STCs, but the underlying mechanisms remain unknown. We hypothesized that RAS alters the transcriptomic and epigenetic profile of inflammatory genes in swine STCs.

METHODS

STCs were harvested from pig kidneys after 10 weeks of RAS or sham (n=6 each). STC mRNA profiles of inflammatory genes were analyzed using high-throughput mRNA-sequencing (seq) and their DNA methylation (5mC) and hydroxymethylation (5hmC) profiles by DNA immunoprecipitation and next-generation sequencing (MeDIP-seq) (n=3 each), followed by an integrated (mRNA-seq/MeDIP-seq) analysis. STC protein expression of candidate differentially expressed (DE) genes and common proinflammatory proteins were subsequently assessed in vitro before and after epigenetic (Bobcat339) modulation.

RESULTS

mRNA-seq identified 57 inflammatory genes up-regulated in RAS-STCs versus Normal-STCs (>1.4 or <0.7-fold, P<0.05), of which 14% exhibited lower 5mC and 5% higher 5hmC levels in RAS-STCs versus Normal-STCs, respectively. Inflammatory gene and protein expression was higher in RAS-STCs compared with Normal-STCs but normalized after epigenetic modulation.

CONCLUSIONS

These observations highlight a novel modulatory mechanism of this renal endogenous repair system and support development of epigenetic or anti-inflammatory therapies to preserve the reparative capacity of STCs in individuals with RAS.

Alveolar type II epithelial cell FASN maintains lipid homeostasis in experimental COPD

Alveolar epithelial type II (AEC2) cells strictly regulate lipid metabolism to maintain surfactant synthesis. Loss of AEC2 cell function and surfactant production are implicated in the pathogenesis of the smoking-related lung disease chronic obstructive pulmonary disease (COPD). Whether smoking alters lipid synthesis in AEC2 cells and whether altering lipid metabolism in AEC2 cells contributes to COPD development are unclear. In this study, high-throughput lipidomic analysis revealed increased lipid biosynthesis in AEC2 cells isolated from mice chronically exposed to cigarette smoke (CS). Mice with a targeted deletion of the de novo lipogenesis enzyme, fatty acid synthase (FASN), in AEC2 cells (FasniΔAEC2) exposed to CS exhibited higher bronchoalveolar lavage fluid (BALF) neutrophils, higher BALF protein, and more severe airspace enlargement. FasniΔAEC2 mice exposed to CS had lower levels of key surfactant phospholipids but higher levels of BALF ether phospholipids, sphingomyelins, and polyunsaturated fatty acid-containing phospholipids, as well as increased BALF surface tension. FasniΔAEC2 mice exposed to CS also had higher levels of protective ferroptosis markers in the lung. These data suggest that AEC2 cell FASN modulates the response of the lung to smoke by regulating the composition of the surfactant phospholipidome.

Adipose tissue-derived lipokines in metabolism

Adipose tissue is a crucial regulator of metabolism with functions that include energy storage and dissipation as well as the secretion of bioactive molecules. As the largest endocrine organ in the body, the adipose tissue produces diverse bioactive molecules, including peptides, metabolites, and extracellular vesicles, which communicate with and modulate the function of other organs. In recent years, lipid metabolites, also known as lipokines, have emerged as key signaling molecules that actively participate in multiple metabolic processes. This review highlights the latest advances in adipose tissue-derived lipokines and their underlying cellular and molecular functions. Furthermore, we offer our perspective on the future directions for adipose-derived bioactive lipids and potential therapeutic implications for obesity and its associated complications.

Systematic crosstalk in plasmalogen and diacyl lipid biosynthesis for their differential yet concerted molecular functions in the cell

Plasmalogen is a major phospholipid of mammalian cell membranes. Recently it is becoming evident that the sn-1 vinyl-ether linkage in plasmalogen, contrasting to the ester linkage in the counterpart diacyl glycerophospholipid, yields differential molecular characteristics for these lipids especially related to hydrocarbon-chain order, so as to concertedly regulate biological membrane processes. A role played by NMR in gaining information in this respect, ranging from molecular to tissue levels, draws particular attention. We note here that a broad range of enzymes in de novo synthesis pathway of plasmalogen commonly constitute that of diacyl glycerophospholipid. This fact forms the basis for systematic crosstalk that not only controls a quantitative balance between these lipids, but also senses a defect causing loss of lipid in either pathway for compensation by increase of the counterpart lipid. However, this inherent counterbalancing mechanism paradoxically amplifies imbalance in differential effects of these lipids in a diseased state on membrane processes. While sharing of enzymes has been recognized, it is now possible to overview the crosstalk with growing information for specific enzymes involved. The overview provides a fundamental clue to consider cell and tissue type-dependent schemes in regulating membrane processes by plasmalogen and diacyl glycerophospholipid in health and disease.

Acetyl-CoA carboxylase 1 is a suppressor of the adipocyte thermogenic program

Disruption of adipocyte de novo lipogenesis (DNL) by deletion of fatty acid synthase (FASN) in mice induces browning in inguinal white adipose tissue (iWAT). However, adipocyte FASN knockout (KO) increases acetyl-coenzyme A (CoA) and malonyl-CoA in addition to depletion of palmitate. We explore which of these metabolite changes triggers adipose browning by generating eight adipose-selective KO mouse models with loss of ATP-citrate lyase (ACLY), acetyl-CoA carboxylase 1 (ACC1), ACC2, malonyl-CoA decarboxylase (MCD) or FASN, or dual KOs ACLY/FASN, ACC1/FASN, and ACC2/FASN. Preventing elevation of acetyl-CoA and malonyl-CoA by depletion of adipocyte ACLY or ACC1 in combination with FASN KO does not block the browning of iWAT. Conversely, elevating malonyl-CoA levels in MCD KO mice does not induce browning. Strikingly, adipose ACC1 KO induces a strong iWAT thermogenic response similar to FASN KO while also blocking malonyl-CoA and palmitate synthesis. Thus, ACC1 and FASN are strong suppressors of adipocyte thermogenesis through promoting lipid synthesis rather than modulating the DNL intermediates acetyl-CoA or malonyl-CoA.

Ether lipids and a peroxisomal riddle in sperm

Sperm are terminally differentiated cells that lack most of the membranous organelles, resulting in a high abundance of ether glycerolipids found across different species. Ether lipids include plasmalogens, platelet activating factor, GPI-anchors and seminolipid. These lipids play important roles in sperm function and performance, and thus are of special interest as potential fertility markers and therapeutic targets. In the present article, we first review the existing knowledge on the relevance of the different types of ether lipids for sperm production, maturation and function. To further understand ether-lipid metabolism in sperm, we then query available proteomic data from highly purified sperm, and produce a map of metabolic steps retained in these cells. Our analysis pinpoints the presence of a truncated ether lipid biosynthetic pathway that would be competent for the production of precursors through the initial peroxisomal core steps, but devoid of subsequent microsomal enzymes responsible for the final synthesis of all complex ether-lipids. Despite the widely accepted notion that sperm lack peroxisomes, the thorough analysis of published data conducted herein identifies nearly 70% of all known peroxisomal resident proteins as part of the sperm proteome. In view of this, we highlight open questions related to lipid metabolism and possible peroxisomal functions in sperm. We propose a repurposed role for the truncated peroxisomal ether-lipid pathway in detoxification of products from oxidative stress, which is known to critically influence sperm function. The likely presence of a peroxisomal-derived remnant compartment that could act as a sink for toxic fatty alcohols and fatty aldehydes generated by mitochondrial activity is discussed. With this perspective, our review provides a comprehensive metabolic map associated with ether-lipids and peroxisomal-related functions in sperm and offers new insights into potentially relevant antioxidant mechanisms that warrant further research.

Quantitative Determination of De Novo Fatty Acid Synthesis in Brown Adipose Tissue Using Deuterium Oxide

Fatty acid synthesis is a complex and highly energy demanding metabolic pathway with important functional roles in the control of whole-body metabolic homeostasis and other physiological and pathological processes. Contrary to other key metabolic pathways, such as glucose disposal, fatty acid synthesis is not routinely functionally assessed, leading to incomplete interpretations of metabolic status. In addition, there is a lack of publicly available detailed protocols suitable for newcomers in the field. Here, we describe an inexpensive quantitative method utilizing deuterium oxide and gas chromatography mass spectrometry (GCMS) for the analysis of total fatty acid de novo synthesis in brown adipose tissue in vivo. This method measures the synthesis of the products of fatty acid synthase independently of a carbon source, and it is potentially useful for virtually any tissue, in any mouse model, and under any external perturbation. Details on the sample preparation for GCMS and downstream calculations are provided. We focus on the analysis of brown fat due to its high levels of de novo fatty acid synthesis and critical roles in maintaining metabolic homeostasis.

Uncoupling Lipid Synthesis from Adipocyte Development

Obesity results from the expansion of adipose tissue, a versatile tissue regulating energy homeostasis, adipokine secretion, thermogenesis, and inflammation. The primary function of adipocytes is thought to be lipid storage through lipid synthesis, which is presumably intertwined with adipogenesis. However, during prolonged fasting, adipocytes are depleted of lipid droplets yet retain endocrine function and an instant response to nutrients. This observation led us to question whether lipid synthesis and storage can be uncoupled from adipogenesis and adipocyte function. By inhibiting key enzymes in the lipid synthesis pathway during adipocyte development, we demonstrated that a basal level of lipid synthesis is essential for adipogenesis initiation but not for maturation and maintenance of adipocyte identity. Furthermore, inducing dedifferentiation of mature adipocytes abrogated adipocyte identity but not lipid storage. These findings suggest that lipid synthesis and storage are not the defining features of adipocytes and raise the possibility of uncoupling lipid synthesis from adipocyte development to achieve smaller and healthier adipocytes for the treatment of obesity and related disorders.

High-Fat-Diet Suppressed Ketone Body Utilization for Lipogenic Pathway in Brown Adipose Tissues

Brown adipose tissue (BAT) consumes excess lipids and produces lipid metabolites as ketone bodies. These ketone bodies are then recycled for lipogenesis by the enzyme acetoacetyl-CoA synthetase (AACS). Previously, we found that a high-fat diet (HFD) upregulated AACS expression in white adipose tissue. In this study, we investigated the effects of diet-induced obesity on AACS in BAT. When 4-week-old ddY mice were fed a HFD or high-sucrose diet (HSD) for 12 weeks, a significant decrease in Aacs, acetyl-CoA carboxylase-1 (Acc-1), and fatty acid synthase (Fas) expression was observed in the BAT of the HFD group, whereas expression was not affected in the HSD group. In vitro analysis showed decreased Aacs and Fas expression in rat primary-cultured brown adipocytes following isoproterenol treatment for 24 h. In addition, the suppression of Aacs by siRNA markedly decreased the expression of Fas and Acc-1 but did not affect the expression of uncoupling protein-1 (UCP-1) or other factors. These results suggested that HFD may suppress ketone body utilization for lipogenesis in BAT and that AACS gene expression may be important for regulating lipogenesis in BAT. Therefore, the AACS-mediated ketone body utilization pathway may regulate lipogenesis under conditions of excess dietary fat.

The adipocyte supersystem of insulin and cAMP signaling

Adipose tissue signals to brain, liver, and muscles to control whole body metabolism through secreted lipid and protein factors as well as neurotransmission, but the mechanisms involved are incompletely understood. Adipocytes sequester triglyceride (TG) in fed conditions stimulated by insulin, while in fasting catecholamines trigger TG hydrolysis, releasing glycerol and fatty acids (FAs). These antagonistic hormone actions result in part from insulin's ability to inhibit cAMP levels generated through such G-protein-coupled receptors as catecholamine-activated β-adrenergic receptors. Consistent with these antagonistic signaling modes, acute actions of catecholamines cause insulin resistance. Yet, paradoxically, chronically activating adipocytes by catecholamines cause increased glucose tolerance, as does insulin. Recent results have helped to unravel this conundrum by revealing enhanced complexities of these hormones' signaling networks, including identification of unexpected common signaling nodes between these canonically antagonistic hormones.

De novo lipogenesis fuels adipocyte autophagosome and lysosome membrane dynamics

Adipocytes robustly synthesize fatty acids (FA) from carbohydrate through the de novo lipogenesis (DNL) pathway, yet surprisingly DNL contributes little to their abundant triglyceride stored in lipid droplets. This conundrum raises the hypothesis that adipocyte DNL instead enables membrane expansions to occur in processes like autophagy, which requires an abundant supply of phospholipids. We report here that adipocyte Fasn deficiency in vitro and in vivo markedly impairs autophagy, evident by autophagosome accumulation and severely compromised degradation of the autophagic substrate p62. Our data indicate the impairment occurs at the level of autophagosome-lysosome fusion, and indeed, loss of Fasn decreases certain membrane phosphoinositides necessary for autophagosome and lysosome maturation and fusion. Autophagy dependence on FA produced by Fasn is not fully alleviated by exogenous FA in cultured adipocytes, and interestingly, imaging studies reveal that Fasn colocalizes with nascent autophagosomes. Together, our studies identify DNL as a critical source of FAs to fuel autophagosome and lysosome maturation and fusion in adipocytes.

Blockage of PPARγ T166 phosphorylation enhances the inducibility of beige adipocytes and improves metabolic dysfunctions

Beige adipocytes in mammalian white adipose tissue (WAT) can reinforce fat catabolism and energy expenditure. Promoting beige adipocyte biogenesis is a tantalizing tactic for combating obesity and its associated metabolic disorders. Here, we report that a previously unidentified phosphorylation pattern (Thr166) in the DNA-binding domain of PPARγ regulates the inducibility of beige adipocytes. This unique posttranslational modification (PTM) pattern influences allosteric communication between PPARγ and DNA or coactivators, which impedes the PPARγ-mediated transactivation of beige cell-related gene expression in WAT. The genetic mutation mimicking T166 phosphorylation (p-T166) hinders the inducibility of beige adipocytes. In contrast, genetic or chemical intervention in this PTM pattern favors beige cell formation. Moreover, inhibition of p-T166 attenuates metabolic dysfunction in obese mice. Our results uncover a mechanism involved in beige cell fate determination. Moreover, our discoveries provide a promising strategy for guiding the development of novel PPARγ agonists for the treatment of obesity and related metabolic disorders.

N-end Rule-Mediated Proteasomal Degradation of ATGL Promotes Lipid Storage

Cellular lipid storage is regulated by the balance of lipogenesis and lipolysis. The rate-limiting triglyceride hydrolase ATGL (desnutrin/PNPLA2) is critical for lipolysis. The control of ATGL transcription, localization, and activation has been intensively studied, while regulation of the protein stability of ATGL is much less explored. In this study, we showed that the protein stability of ATGL is regulated by the N-end rule in cultured cells and in mice. The N-end rule E3 ligases UBR1 and UBR2 reduce the level of ATGL and affect lipid storage. The N-end rule-resistant ATGL(F2A) mutant, in which the N-terminal phenylalanine (F) of ATGL is substituted by alanine (A), has increased protein stability and enhanced lipolysis activity. ATGLF2A/F2A knock-in mice are protected against high-fat diet (HFD)-induced obesity, hepatic steatosis, and insulin resistance. Hepatic knockdown of Ubr1 attenuates HFD-induced hepatic steatosis by enhancing the ATGL level. Finally, the protein levels of UBR1 and ATGL are negatively correlated in the adipose tissue of obese mice. Our study reveals N-end rule-mediated proteasomal regulation of ATGL, a finding that may potentially be beneficial for treatment of obesity.

Phosphatidylethanolamine homeostasis under conditions of impaired CDP-ethanolamine pathway or phosphatidylserine decarboxylation

Phosphatidylethanolamine is the major inner-membrane lipid in the plasma and mitochondrial membranes. It is synthesized in the endoplasmic reticulum from ethanolamine and diacylglycerol (DAG) by the CDP-ethanolamine pathway and from phosphatidylserine by decarboxylation in the mitochondria. Recently, multiple genetic disorders that impact these pathways have been identified, including hereditary spastic paraplegia 81 and 82, Liberfarb syndrome, and a new type of childhood-onset neurodegeneration-CONATOC. Individuals with these diseases suffer from multisystem disorders mainly affecting neuronal function. This indicates the importance of maintaining proper phospholipid homeostasis when major biosynthetic pathways are impaired. This study summarizes the current knowledge of phosphatidylethanolamine metabolism in order to identify areas of future research that might lead to the development of treatment options.

The physiological functions of human peroxisomes

Peroxisomes are subcellular organelles that play a central role in human physiology by catalyzing a range of unique metabolic functions. The importance of peroxisomes for human health is exemplified by the existence of a group of usually severe diseases caused by an impairment in one or more peroxisomal functions. Among others these include the Zellweger spectrum disorders, X-linked adrenoleukodystrophy, and Refsum disease. To fulfill their role in metabolism, peroxisomes require continued interaction with other subcellular organelles including lipid droplets, lysosomes, the endoplasmic reticulum, and mitochondria. In recent years it has become clear that the metabolic alliance between peroxisomes and other organelles requires the active participation of tethering proteins to bring the organelles physically closer together, thereby achieving efficient transfer of metabolites. This review intends to describe the current state of knowledge about the metabolic role of peroxisomes in humans, with particular emphasis on the metabolic partnership between peroxisomes and other organelles and the consequences of genetic defects in these processes. We also describe the biogenesis of peroxisomes and the consequences of the multiple genetic defects therein. In addition, we discuss the functional role of peroxisomes in different organs and tissues and include relevant information derived from model systems, notably peroxisomal mouse models. Finally, we pay particular attention to a hitherto underrated role of peroxisomes in viral infections.

Dietary Sinapic Acid Alleviates Adiposity and Inflammation in Diet-Induced Obese Mice

Sinapic acid (SA), a hydroxycinnamic acid, is known to confer protection against oxidative stress, inflammation, diabetes, and liver disease. However, the effectiveness of SA in improving obesity remains obscure. Therefore, this study evaluated anti-obesity efficacy of SA and to elucidate its mechanism of action. Male mice were maintained for 16 weeks on high-fat diet (HFD) alone or with SA (0.004%, w/w) and bodyweight, fat mass, adipocyte size, food intake, and biochemical and molecular markers were evaluated. SA-supplemented mice demonstrated markedly decreased fat mass and adipocyte size compared to unsupplemented group, without any changes in bodyweight and food intake between the two groups. Plasma adipocytokines levels including leptin, resistin, monocyte chemoattractant protein (MCP)-1 and interleukin-6 were also markedly reduced by SA supplementation. SA tended to lower plasma insulin level and improved homeostatic index of insulin resistance and intraperitoneal glucose tolerance test in HFD-induced obese mice. The anti-adiposity effect of SA was maybe owing to down-regulation of the mRNA expression of lipogenic genes, including acetyl coenzyme A (CoA) carboxylase, fatty acid synthesis, stearoyl-CoA desaturase 1, and phosphatidate phosphatase, and peroxisome proliferator-activated receptor γ, a transcription factor responsible for governing lipid metabolism, in adipose tissues. SA significantly down-regulated pro-inflammatory nuclear factor kappa B, MCP-1, tumor necrosis factor-α, and Toll-like receptor 4 mRNA expression in adipose tissue. Thus, SA could be beneficial for the development of functional foods or herbal medications to combat obesity.

Architecture of the outbred brown fat proteome defines regulators of metabolic physiology

Brown adipose tissue (BAT) regulates metabolic physiology. However, nearly all mechanistic studies of BAT protein function occur in a single inbred mouse strain, which has limited the understanding of generalizable mechanisms of BAT regulation over physiology. Here, we perform deep quantitative proteomics of BAT across a cohort of 163 genetically defined diversity outbred mice, a model that parallels the genetic and phenotypic variation found in humans. We leverage this diversity to define the functional architecture of the outbred BAT proteome, comprising 10,479 proteins. We assign co-operative functions to 2,578 proteins, enabling systematic discovery of regulators of BAT. We also identify 638 proteins that correlate with protection from, or sensitivity to, at least one parameter of metabolic disease. We use these findings to uncover SFXN5, LETMD1, and ATP1A2 as modulators of BAT thermogenesis or adiposity, and provide OPABAT as a resource for understanding the conserved mechanisms of BAT regulation over metabolic physiology.

Discovery of an insulin-induced gene binding compound that ameliorates nonalcoholic steatohepatitis by inhibiting sterol regulatory element-binding protein-mediated lipogenesis

BACKGROUND AND AIMS

NASH is associated with high levels of cholesterol and triglyceride (TG) in the liver; however, there is still no approved pharmacological therapy. Synthesis of cholesterol and TG is controlled by sterol regulatory element-binding protein (SREBP), which is found to be abnormally activated in NASH patients. We aim to discover small molecules for treating NASH by inhibiting the SREBP pathway.

APPROACH AND RESULTS

Here, we identify a potent SREBP inhibitor, 25-hydroxylanosterol (25-HL). 25-HL binds to insulin-induced gene (INSIG) proteins, stimulates the interaction between INSIG and SCAP, and retains them in the endoplasmic reticulum, thereby suppressing SREBP activation and inhibiting lipogenesis. In NASH mouse models, 25-HL lowers levels of cholesterol and TG in serum and the liver, enhances energy expenditure to prevent obesity, and improves insulin sensitivity. 25-HL dramatically ameliorates hepatic steatosis, inflammation, ballooning, and fibrosis through down-regulating the expression of lipogenic genes. Furthermore, 25-HL exhibits both prophylactic and therapeutic efficacies of alleviating NASH and atherosclerosis in amylin liver NASH model diet-treated Ldlr^-/- mice, and reduces the formation of cholesterol crystals and associated crown-like structures of Kupffer cells. Notably, 25-HL lowers lipid contents in serum and the liver to a greater extent than lovastatin or obeticholic acid. 25-HL shows a good safety and pharmacokinetics profile.

CONCLUSIONS

This study provides the proof of concept that inhibiting SREBP activation by targeting INSIG to lower lipids could be a promising strategy for treating NASH. It suggests the translational potential of 25-HL in human NASH and demonstrates the critical role of SREBP-controlled lipogenesis in the progression of NASH by pharmacological inhibition.

Regulation of plasmalogen metabolism and traffic in mammals: The fog begins to lift

Due to their unique chemical structure, plasmalogens do not only exhibit distinct biophysical and biochemical features, but require specialized pathways of biosynthesis and metabolization. Recently, major advances have been made in our understanding of these processes, for example by the attribution of the gene encoding the enzyme, which catalyzes the final desaturation step in plasmalogen biosynthesis, or by the identification of cytochrome C as plasmalogenase, which allows for the degradation of plasmalogens. Also, models have been presented that plausibly explain the maintenance of adequate cellular levels of plasmalogens. However, despite the progress, many aspects around the questions of how plasmalogen metabolism is regulated and how plasmalogens are distributed among organs and tissues in more complex organisms like mammals, remain unresolved. Here, we summarize and interpret current evidence on the regulation of the enzymes involved in plasmalogen biosynthesis and degradation as well as the turnover of plasmalogens. Finally, we focus on plasmalogen traffic across the mammalian body - a topic of major importance, when considering plasmalogen replacement therapies in human disorders, where deficiencies in these lipids have been reported. These involve not only inborn errors in plasmalogen metabolism, but also more common diseases including Alzheimer's disease and neurodevelopmental disorders.

Peroxisomal regulation of energy homeostasis: Effect on obesity and related metabolic disorders

BACKGROUND

Peroxisomes are single membrane-bound organelles named for their role in hydrogen peroxide production and catabolism. However, their cellular functions extend well beyond reactive oxygen species (ROS) metabolism and include fatty acid oxidation of unique substrates that cannot be catabolized in mitochondria, and synthesis of ether lipids and bile acids. Metabolic functions of peroxisomes involve crosstalk with other organelles, including mitochondria, endoplasmic reticulum, lipid droplets and lysosomes. Emerging studies suggest that peroxisomes are important regulators of energy homeostasis and that disruption of peroxisomal functions influences the risk for obesity and the associated metabolic disorders, including type 2 diabetes and hepatic steatosis.

SCOPE OF REVIEW

Here, we focus on the role of peroxisomes in ether lipid synthesis, β-oxidation and ROS metabolism, given that these functions have been most widely studied and have physiologically relevant implications in systemic metabolism and obesity. Efforts are made to mechanistically link these cellular and systemic processes.

MAJOR CONCLUSIONS

Circulating plasmalogens, a form of ether lipids, have been identified as inversely correlated biomarkers of obesity. Ether lipids influence metabolic homeostasis through multiple mechanisms, including regulation of mitochondrial morphology and respiration affecting brown fat-mediated thermogenesis, and through regulation of adipose tissue development. Peroxisomal β-oxidation also affects metabolic homeostasis through generation of signaling molecules, such as acetyl-CoA and ROS that inhibit hydrolysis of stored lipids, contributing to development of hepatic steatosis. Oxidative stress resulting from increased peroxisomal β-oxidation-generated ROS in the context of obesity mediates β-cell lipotoxicity. A better understanding of the roles peroxisomes play in regulating and responding to obesity and its complications will provide new opportunities for their treatment.

Reducing ether lipids improves Drosophila overnutrition-associated pathophysiology phenotypes via a switch from lipid storage to beta-oxidation

High-calorie diets increase the risk of developing obesity, cardiovascular disease, type-two diabetes (T2D), and other comorbidities. These "overnutrition" diets also promote the accumulation of a variety of harmful lipids in the heart and other peripheral organs, known as lipotoxicity. However, the mechanisms underlying lipotoxicity and its influence on pathophysiology remain unknown. Our study uses genetics to identify the role of ether lipids, a class of potential lipotoxins, in a Drosophila model of overnutrition. A high-sugar diet (HSD) increases ether lipids and produces T2D-like pathophysiology phenotypes, including obesity, insulin resistance, and cardiac failure. Therefore, we targeted ether lipid biosynthesis through the enzyme dihydroxyacetonephosphate acyltransferase (encoded by the gene DHAPAT). We found that reducing DHAPAT in the fat body improved TAG and glucose homeostasis, cardiac function, respiration, and insulin signaling in flies fed a HSD. The reduction of DHAPAT may cause a switch in molecular signaling from lipogenesis to fatty acid oxidation via activation of a PPARα-like receptor, as bezafibrate produced similar improvements in HS-fed flies. Taken together, our findings suggest that ether lipids may be lipotoxins that reduce fitness during overnutrition.

Plasmalogens and Photooxidative Stress Signaling in Myxobacteria, and How it Unmasked CarF/TMEM189 as the Δ1'-Desaturase PEDS1 for Human Plasmalogen Biosynthesis

Plasmalogens are glycerophospholipids with a hallmark sn-1 vinyl ether bond that endows them with unique physical-chemical properties. They have proposed biological roles in membrane organization, fluidity, signaling, and antioxidative functions, and abnormal plasmalogen levels correlate with various human pathologies, including cancer and Alzheimer’s disease. The presence of plasmalogens in animals and in anaerobic bacteria, but not in plants and fungi, is well-documented. However, their occurrence in the obligately aerobic myxobacteria, exceptional among aerobic bacteria, is often overlooked. Tellingly, discovery of the key desaturase indispensable for vinyl ether bond formation, and therefore fundamental in plasmalogen biogenesis, emerged from delving into how the soil myxobacterium Myxococcus xanthus responds to light. A recent pioneering study unmasked myxobacterial CarF and its human ortholog TMEM189 as the long-sought plasmanylethanolamine desaturase (PEDS1), thus opening a crucial door to study plasmalogen biogenesis, functions, and roles in disease. The findings demonstrated the broad evolutionary sweep of the enzyme and also firmly established a specific signaling role for plasmalogens in a photooxidative stress response. Here, we will recount our take on this fascinating story and its implications, and review the current state of knowledge on plasmalogens, their biosynthesis and functions in the aerobic myxobacteria.

IL-1R-IRAKM-Slc25a1 signaling axis reprograms lipogenesis in adipocytes to promote diet-induced obesity in mice

Toll-like receptors/Interleukin-1 receptor signaling plays an important role in high-fat diet-induced adipose tissue dysfunction contributing to obesity-associated metabolic syndromes. Here, we show an unconventional IL-1R-IRAKM-Slc25a1 signaling axis in adipocytes that reprograms lipogenesis to promote diet-induced obesity. Adipocyte-specific deficiency of IRAKM reduces high-fat diet-induced body weight gain, increases whole body energy expenditure and improves insulin resistance, associated with decreased lipid accumulation and adipocyte cell sizes. IL-1β stimulation induces the translocation of IRAKM Myddosome to mitochondria to promote de novo lipogenesis in adipocytes. Mechanistically, IRAKM interacts with and phosphorylates mitochondrial citrate carrier Slc25a1 to promote IL-1β-induced mitochondrial citrate transport to cytosol and de novo lipogenesis. Moreover, IRAKM-Slc25a1 axis mediates IL-1β induced Pgc1a acetylation to regulate thermogenic gene expression in adipocytes. IRAKM kinase-inactivation also attenuates high-fat diet-induced obesity. Taken together, our study suggests that the IL-1R-IRAKM-Slc25a1 signaling axis tightly links inflammation and adipocyte metabolism, indicating a potential therapeutic target for obesity.

Tricky Isomers—The Evolution of Analytical Strategies to Characterize Plasmalogens and Plasmanyl Ether Lipids

Typically, glycerophospholipids are represented with two esterified fatty acids. However, by up to 20%, a significant proportion of this lipid class carries an ether-linked fatty alcohol side chain at the sn-1 position, generally referred to as ether lipids, which shape their specific physicochemical properties. Among those, plasmalogens represent a distinct subgroup characterized by an sn-1 vinyl-ether double bond. The total loss of ether lipids in severe peroxisomal defects such as rhizomelic chondrodysplasia punctata indicates their crucial contribution to diverse cellular functions. An aberrant ether lipid metabolism has also been reported in multifactorial conditions including Alzheimer’s disease. Understanding the underlying pathological implications is hampered by the still unclear exact functional spectrum of ether lipids, especially in regard to the differentiation between the individual contributions of plasmalogens (plasmenyl lipids) and their non-vinyl-ether lipid (plasmanyl) counterparts. A primary reason for this is that exact identification and quantification of plasmalogens and other ether lipids poses a challenging and usually labor-intensive task. Diverse analytical methods for the detection of plasmalogens have been developed. Liquid chromatography–tandem mass spectrometry is increasingly used to resolve complex lipid mixtures, and with optimized parameters and specialized fragmentation strategies, discrimination between ethers and plasmalogens is feasible. In this review, we recapitulate historic and current methodologies for the recognition and quantification of these important lipids and will discuss developments in this field that can contribute to the characterization of plasmalogens in high structural detail.

Browning Epicardial Adipose Tissue: Friend or Foe?

The epicardial adipose tissue (EAT) is the visceral fat depot of the heart which is highly plastic and in direct contact with myocardium and coronary arteries. Because of its singular proximity with the myocardium, the adipokines and pro-inflammatory molecules secreted by this tissue may directly affect the metabolism of the heart and coronary arteries. Its accumulation, measured by recent new non-invasive imaging modalities, has been prospectively associated with the onset and progression of coronary artery disease (CAD) and atrial fibrillation in humans. Recent studies have shown that EAT exhibits beige fat-like features, and express uncoupling protein 1 (UCP-1) at both mRNA and protein levels. However, this thermogenic potential could be lost with age, obesity and CAD. Here we provide an overview of the physiological and pathophysiological relevance of EAT and further discuss whether its thermogenic properties may serve as a target for obesity therapeutic management with a specific focus on the role of immune cells in this beiging phenomenon.

3-Hydroxyacyl-CoA dehydratase 2 deficiency confers resistance to diet-induced obesity and glucose intolerance

Obesity and associated complications are becoming a pandemic. Inhibiting fatty acid synthesis and elongation is an important intervention for the treatment of obesity. Despite intensive investigations, many potential therapeutic targets have yet to be discovered. In this study, decreased expression of Hacd2 (a newly found enzyme in fatty acid elongation) was found in HFD induced mice and loss of Hacd2 expression in the liver protected mice against HFD induced obesity as well as associated fatty liver disease and diabetes. Additionally, further study indicated that hepatic HACD2 deficiency increased energy expenditure by upregulating the transcription of thermogenic programming genes. Our results suggest that HACD2 may be a promising therapeutic target for the management of obesity and associated metabolic diseases.

Lipogenesis inhibitors: therapeutic opportunities and challenges

Fatty acids are essential for survival, acting as bioenergetic substrates, structural components and signalling molecules. Given their vital role, cells have evolved mechanisms to generate fatty acids from alternative carbon sources, through a process known as de novo lipogenesis (DNL). Despite the importance of DNL, aberrant upregulation is associated with a wide variety of pathologies. Inhibiting core enzymes of DNL, including citrate/isocitrate carrier (CIC), ATP-citrate lyase (ACLY), acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), represents an attractive therapeutic strategy. Despite challenges related to efficacy, selectivity and safety, several new classes of synthetic DNL inhibitors have entered clinical-stage development and may become the foundation for a new class of therapeutics.

De novo lipogenesis (DNL) is vital for the maintenance of whole-body and cellular homeostasis, but aberrant upregulation of the pathway is associated with a broad range of conditions, including cardiovascular disease, metabolic disorders and cancers. Here, Steinberg and colleagues provide an overview of the physiological and pathological roles of the core DNL enzymes and assess strategies and agents currently in development to therapeutically target them.

Lactobacillus acidophilus ameliorates obesity in mice through modulation of gut microbiota dysbiosis and intestinal permeability

Obesity associated with low-grade chronic inflammation and intestinal dysbiosis is considered as a worldwide public health crisis. In the meanwhile, different probiotics have demonstrated beneficial effects on this condition, thus increasing the interest in the development of probiotic treatments. In this context, the aim of this study is to investigate the anti-obesity effects of potential probiotic Lactobacillus acidophilus isolated from the porcine gut. Then, it is found that L. acidophilus reduces body weight, fat mass, inflammation and insulin resistance in mice fed with a high-fat diet (HFD), accompanied by activation in brown adipose tissue (BAT) as well as improvements of energy, glucose and lipid metabolism. Besides, our data indicate that L. acidophilus not only reverses HFD-induced gut dysbiosis, as indicated by the decreased Firmicutes-to-Bacteroidetes ratios and endotoxin bearing Gram-negative bacteria levels, but also maintains intestinal barrier integrity, reduces metabolic endotoxemia, and inhibits the TLR4 / NF- κB signaling pathway. In addition, the results of microbiome phenotype prediction by BugBase and bacterial functional potential prediction using PICRUSt show that L. acidophilus treatment improves the gut microbiota functions involving metabolism, immune response, and pathopoiesia. Furthermore, the anti-obesity effect is transmissible via horizontal faeces transfer from L. acidophilus-treated mice to HFD-fed mice. According to our data, it is seen that L. acidophilus could be a good candidate for probiotic of ameliorating obesity and associated diseases such as hyperlipidemia, nonalcoholic fatty liver diseases, and insulin resistance through its anti-inflammatory properties and alleviation of endothelial dysfunction and gut dysbiosis.

Developmentally regulated GTP-binding protein-2 regulates adipocyte differentiation

Developmentally regulated GTP-binding protein 2 (DRG2) participates in the regulation of proliferation and differentiation of multiple cells. However, whether DRG2 regulates adipocyte differentiation and related metabolic control remains elusive. This study revealed increases in body weight and adiposity in DRG2 transgenic (Tg) mice overexpressing DRG2. Consistent with these results, DRG2 Tg mice showed increased expression of genes involved in adipogenesis and lipid metabolism in the white adipose tissue. DRG2 was also identified to control adipogenesis by cooperating with peroxisome proliferator activated receptor-γ (PPAR-γ) in cultured adipocytes. Overall, the findings of the current study suggest that DRG2 plays an active role in regulating adipocyte differentiation, and thus participates in the development of obesity during exposure to a fat-rich diet.

Transcriptional Landscaping Identifies a Beige Adipocyte Depot in the Newborn Mouse

The present study sought to identify gene networks that are hallmarks of the developing inguinal subcutaneous adipose tissue (iWAT) and the interscapular brown adipose tissue (BAT) in the mouse. RNA profiling revealed that the iWAT of postnatal (P) day 6 mice expressed thermogenic and lipid catabolism transcripts, along with the abundance of transcripts associated with the beige adipogenesis program. This was an unexpected finding, as thermogenic BAT was believed to be the only site of nonshivering thermogenesis in the young mouse. However, the transcriptional landscape of BAT in P6 mice suggests that it is still undergoing differentiation and maturation, and that the iWAT temporally adopts thermogenic and lipolytic potential. Moreover, P6 iWAT and adult (P56) BAT were similar in their expression of immune gene networks, but P6 iWAT was unique in the abundant expression of antimicrobial proteins and virus entry factors, including a possible receptor for SARS-CoV-2. In summary, postnatal iWAT development is associated with a metabolic shift from thermogenesis and lipolysis towards fat storage. However, transcripts of beige-inducing signal pathways including β-adrenergic receptors and interleukin-4 signaling were underrepresented in young iWAT, suggesting that the signals for thermogenic fat differentiation may be different in early postnatal life and in adulthood.

Protective effects of p-coumaric acid against high-fat diet-induced metabolic dysregulation in mice

p-Coumaric acid (PC), a naturally occurring phytochemical, possesses antioxidant and anti-inflammatory properties; however, the mechanisms underlying its protective effects against obesity-related metabolic dysfunction are largely unknown. Here, we treated C57BL/6J mice to a high-fat diet (HFD) with or without PC (10 mg/kg body weight/day) for 16 weeks to determine whether PC ameliorates HFD-induced obesity, insulin resistance, inflammation, and non-alcoholic fatty liver disease (NAFLD). We found no significant differences in food intake and body weight between the groups. However, PC-treated mice showed significantly lower white adipose tissue (WAT) weight, adipocyte size, and plasma leptin level, which were associated with decreased lipogenic enzyme activity and mRNA expression of their genes in the epididymal WAT. Moreover, hepatic lipogenic enzymes activities and expression of their genes and proteins were decreased with concomitant increases in hepatic fatty acid oxidation and mRNA expression of its gene; fecal lipid excretion was significantly increased, resulting in decreased liver weight, hepatic lipid levels, lipid droplet accumulation, and plasma aspartate aminotransferase and lipid levels. Additionally, PC-treated mice showed lower fasting blood glucose, plasma resistin, and MCP-1 levels, HOMA-IR, and mRNA expression of inflammatory genes in the epididymal WAT and liver. Our findings reveal potential mechanisms underlying the action of PC against HFD-induced adiposity, NAFLD, and other metabolic disturbances.

Peroxisomes as cellular adaptors to metabolic and environmental stress

Peroxisomes are involved in multiple metabolic processes, including fatty acid oxidation, ether lipid synthesis, and reactive oxygen species (ROS) metabolism. Recent studies suggest that peroxisomes are critical mediators of cellular responses to various forms of stress, including oxidative stress, hypoxia, starvation, cold exposure, and noise. As dynamic organelles, peroxisomes can modulate their proliferation, morphology, and movement within cells, and engage in crosstalk with other organelles in response to external cues. Although peroxisome-derived hydrogen peroxide has a key role in cellular signaling related to stress, emerging studies suggest that other products of peroxisomal metabolism, such as acetyl-CoA and ether lipids, are also important for metabolic adaptation to stress. Here, we review molecular mechanisms through which peroxisomes regulate metabolic and environmental stress.

Anti-Obesity and Hypocholesterolemic Actions of Protamine-Derived Peptide RPR (Arg-Pro-Arg) and Protamine in High-Fat Diet-Induced C57BL/6J Mice

Dietary protamine can ameliorate hyperlipidemia; however, the protamine-derived active peptide and its hypolipidemic mechanism of action are unclear. Here, we report the discovery of a novel anti-obesity and hypocholesterolemic peptide, RPR (Arg-Pro-Arg), derived from protamine in mice fed a high-fat diet for 50 days. Serum cholesterol levels were significantly lower in the protamine and RPR groups than in the control group. White adipose tissue weight was significantly decreased in the protamine and RPR groups. The fecal excretion of cholesterol and bile acid was significantly higher in the protamine and RPR groups than in the control group. We also observed a significant decrease in the expression of hepatic SCD1, SREBP1, and adipocyte FAS mRNA, and significantly increased expression of hepatic PPARα and adipocyte PPARγ1 mRNA in the protamine group. These findings demonstrate that the anti-obesity effects of protamine are linked to the upregulation of adipocyte PPARγ1 and hepatic PPARα and the downregulation of hepatic SCD1 via SREBP1 and adipocyte FAS. RPR derived from protamine has a crucial role in the anti-obesity action of protamine by evaluating the effective dose of adipose tissue weight loss.

Defective insulin-stimulated GLUT4 translocation in brown adipocytes induces systemic glucose homeostasis dysregulation independent of thermogenesis in female mice

OBJECTIVE

Recent studies indicate that brown adipose tissue, in addition to its role in thermogenesis, has a role in the regulation of whole-body metabolism. Here we characterize the metabolic effects of deleting Rab10, a protein key for insulin stimulation of glucose uptake into white adipocytes, solely from brown adipocytes.

METHODS

We used a murine brown adipocyte cell line and stromal vascular fraction-derived in vitro differentiated brown adipocytes to study the role of Rab10 in insulin-stimulated GLUT4 translocation to the plasma membrane and insulin-stimulated glucose uptake. We generated a brown adipocyte-specific Rab10 knockout for in vivo studies of metabolism and thermoregulation.

RESULTS

We demonstrate that deletion of Rab10 from brown adipocytes results in a two-fold reduction of insulin-stimulated glucose transport by reducing translocation of the GLUT4 glucose transporter to the plasma membrane, an effect linked to whole-body glucose intolerance and insulin resistance in female mice. This effect on metabolism is independent of the thermogenic function of brown adipocytes, thereby revealing a metabolism-specific role for brown adipocytes in female mice. The reduced glucose uptake induced by Rab10 deletion disrupts ChREBP regulation of de novo lipogenesis (DNL) genes, providing a potential link between DNL in brown adipocytes and whole-body metabolic regulation in female mice. However, deletion of Rab10 from male mice does not induce systemic insulin resistance, although ChREBP regulation is disrupted.

CONCLUSIONS

Our studies of Rab10 reveal the role of insulin-regulated glucose transport into brown adipocytes in whole-body metabolic homeostasis of female mice. Importantly, the contribution of brown adipocytes to whole-body metabolic regulation is independent of its role in thermogenesis. It is unclear whether the whole-body metabolic sexual dimorphism is because female mice are permissive to the effects of Rab10 deletion from brown adipocytes or because male mice are resistant to the effect.

Single-Cell RNA Profiling Reveals Adipocyte to Macrophage Signaling Sufficient to Enhance Thermogenesis

Adipocytes deficient in fatty acid synthase (iAdFASNKO) emit signals that mimic cold exposure to enhance the appearance of thermogenic beige adipocytes in mouse inguinal white adipose tissues (iWATs). Both cold exposure and iAdFASNKO upregulate the sympathetic nerve fiber (SNF) modulator Neuregulin 4 (Nrg4), activate SNFs, and require adipocyte cyclic AMP/protein kinase A (cAMP/PKA) signaling for beige adipocyte appearance, as it is blocked by adipocyte Gsα deficiency. Surprisingly, however, in contrast to cold-exposed mice, neither iWAT denervation nor Nrg4 loss attenuated adipocyte browning in iAdFASNKO mice. Single-cell transcriptomic analysis of iWAT stromal cells revealed increased macrophages displaying gene expression signatures of the alternately activated type in iAdFASNKO mice, and their depletion abrogated iWAT beiging. Altogether, these findings reveal that divergent cellular pathways are sufficient to cause adipocyte browning. Importantly, adipocyte signaling to enhance alternatively activated macrophages in iAdFASNKO mice is associated with enhanced adipose thermogenesis independent of the sympathetic neuron involvement this process requires in the cold.

Henriques et al. show an alternative pathway to enhance thermogenesis through an adipocyte cAMP/PKA axis in denervated iWAT. Signals emanating from this pathway generate M2-type macrophages associated with iWAT browning.

Acetyl-CoA and Metabolite Fluxes Regulate White Adipose Tissue Expansion

White adipose tissue (WAT) depends on coordinated regulation of transcriptional and metabolic pathways to respond to whole-body energy demands. We highlight metabolites that contribute to biosynthetic reactions for WAT expansion. Recent studies have precisely defined how byproducts of carbohydrate and lipid metabolism affect physiological and endocrine functions in adipocytes. We emphasize the critical emerging roles of short-chain fatty acids (SCFAs) and tricarboxylic acid (TCA) cycle metabolites that connect lipogenesis to WAT energy balance and endocrine functions. These insights address how adipocytes use small molecules generated from central carbon metabolism to measure responses to nutritional stress.

Endothelial ether lipids link the vasculature to blood pressure, behavior, and neurodegeneration

Vascular disease contributes to neurodegeneration, which is associated with decreased blood pressure in older humans. Plasmalogens, ether phospholipids produced by peroxisomes, are decreased in Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. However, the mechanistic links between ether phospholipids, blood pressure, and neurodegeneration are not fully understood. Here, we show that endothelium-derived ether phospholipids affect blood pressure, behavior, and neurodegeneration in mice. In young adult mice, inducible endothelial-specific disruption of PexRAP, a peroxisomal enzyme required for ether lipid synthesis, unexpectedly decreased circulating plasmalogens. PexRAP endothelial knockout (PEKO) mice responded normally to hindlimb ischemia but had lower blood pressure and increased plasma renin activity. In PEKO as compared with control mice, tyrosine hydroxylase was decreased in the locus coeruleus, which maintains blood pressure and arousal. PEKO mice moved less, slept more, and had impaired attention to and recall of environmental events as well as mild spatial memory deficits. In PEKO hippocampus, gliosis was increased, and a plasmalogen associated with memory was decreased. Despite lower blood pressure, PEKO mice had generally normal homotopic functional connectivity by optical neuroimaging of the cerebral cortex. Decreased glycogen synthase kinase-3 phosphorylation, a marker of neurodegeneration, was detected in PEKO cerebral cortex. In a co-culture system, PexRAP knockdown in brain endothelial cells decreased glycogen synthase kinase-3 phosphorylation in co-cultured astrocytes that was rescued by incubation with the ether lipid alkylglycerol. Taken together, our findings suggest that endothelium-derived ether lipids mediate several biological processes and may also confer neuroprotection in mice.

Anti-hyperlipidemic potential of natural product based labdane-pyrroles via inhibition of cholesterol and triglycerides synthesis

Hyperlipidemia is the clinical condition where blood has an increased level of lipids, such as cholesterol and triglycerides. Therefore controlling hyperlipidemia is considered to be a protective strategy to treat many associated diseases. Thus, a novel natural product derived pyrrole, and pyrazole-(E)-Labda-8(17),12-diene-15,16-dial conjugates with cholesterol and triglycerides synthesis inhibition potential was designed through scaffold hopping approach and synthesized via one-pot selective cycloaddition. Amongst the tested hybrids, 3i exhibited excellent activity against triglyceride and cholesterol synthesis with the percentage inhibition of 71.73 ± 0.78 and 68.61 ± 1.19, which is comparable to the positive controls fenofibrate and atorvastatin, respectively. Compounds 3j and 3k also exhibited the considerable potential of promising leads. The HMG CoA reductase inhibitory activity of the compounds was consistent with that of inhibitory activity of cholesterol synthesis. Compound 3i showed the highest inhibitory potential (78.61 ± 2.80) percentage of suppression, which was comparable to that of the positive control pravastatin (78.05 ± 5.4). Favourably, none of the compounds showed cytotoxicity (HepG2) in the concentration ranging from 0.5 to 100 μM.

Ascending dorsal column sensory neurons respond to spinal cord injury and downregulate genes related to lipid metabolism

Regeneration failure after spinal cord injury (SCI) results in part from the lack of a pro-regenerative response in injured neurons, but the response to SCI has not been examined specifically in injured sensory neurons. Using RNA sequencing of dorsal root ganglion, we determined that thoracic SCI elicits a transcriptional response distinct from sciatic nerve injury (SNI). Both SNI and SCI induced upregulation of ATF3 and Jun, yet this response failed to promote growth in sensory neurons after SCI. RNA sequencing of purified sensory neurons one and three days after injury revealed that unlike SNI, the SCI response is not sustained. Both SCI and SNI elicited the expression of ATF3 target genes, with very little overlap between conditions. Pathway analysis of differentially expressed ATF3 target genes revealed that fatty acid biosynthesis and terpenoid backbone synthesis were downregulated after SCI but not SNI. Pharmacologic inhibition of fatty acid synthase, the enzyme generating palmitic acid, decreased axon growth and regeneration in vitro. These results support the notion that decreased expression of lipid metabolism-related genes after SCI, including fatty acid synthase, may restrict axon regenerative capacity after SCI.

Bioactive Ether Lipids: Primordial Modulators of Cellular Signaling

The primacy of lipids as essential components of cellular membranes is conserved across taxonomic domains. In addition to this crucial role as a semi-permeable barrier, lipids are also increasingly recognized as important signaling molecules with diverse functional mechanisms ranging from cell surface receptor binding to the intracellular regulation of enzymatic cascades. In this review, we focus on ether lipids, an ancient family of lipids having ether-linked structures that chemically differ from their more prevalent acyl relatives. In particular, we examine ether lipid biosynthesis in the peroxisome of mammalian cells, the roles of selected glycerolipids and glycerophospholipids in signal transduction in both prokaryotes and eukaryotes, and finally, the potential therapeutic contributions of synthetic ether lipids to the treatment of cancer.

Anti-Obesity Effects of a Prunus persica and Nelumbo nucifera Mixture in Mice Fed a High-Fat Diet

Prunus persica and Nelumbo nucifera are major crops cultivated worldwide. In East Asia, both P. persica flowers and N. nucifera leaves are traditionally used for therapeutic purposes and consumed as teas for weight loss. Herein, we investigated the anti-obesity effects of an herbal extract mixture of P. persica and N. nucifera (HT077) and the underlying mechanism using a high-fat diet (HFD)-induced obesity model. Male C57BL/6 mice were fed a normal diet, HFD, HFD containing 0.02% orlistat (positive control), or HFD containing 0.1, 0.2, or 0.4% HT077 for 12 weeks. HT077 significantly reduced final body weights, weight gain, abdominal fat weights, liver weights, and hepatic levels of triglycerides and total cholesterol. HT077 also lowered glucose, cholesterol, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and leptin levels and increased AST/ALT and adiponectin/leptin ratios and adiponectin levels. Real-time polymerase chain reaction analysis showed that HT077 decreased the expression of lipogenic genes and increased the expression of fatty acid oxidation-related genes in adipose tissue. Our results indicate that HT077 exerts anti-obesity effects and prevents the development of obesity-related metabolic disorders. These beneficial effects might be partially attributed to ameliorating adipokine imbalances and regulating lipid synthesis and fatty acid oxidation in adipose tissue.