Genetic Screen for Cell Fitness in High or Low Oxygen Highlights Mitochondrial and Lipid Metabolism.

Human cells are able to sense and adapt to variations in oxygen levels. Historically, much research in this field has focused on hypoxia-inducible factor (HIF) signaling and reactive oxygen species (ROS). Here, we perform genome-wide CRISPR growth screens at 21%, 5%, and 1% oxygen to systematically identify gene knockouts with relative fitness defects in high oxygen (213 genes) or low oxygen (109 genes), most without known connection to HIF or ROS. Knockouts of many mitochondrial pathways thought to be essential, including complex I and enzymes in Fe-S biosynthesis, grow relatively well at low oxygen and thus are buffered by hypoxia. In contrast, in certain cell types, knockout of lipid biosynthetic and peroxisomal genes causes fitness defects only in low oxygen. Our resource nominates genetic diseases whose severity may be modulated by oxygen and links hundreds of genes to oxygen homeostasis.

Mining Fatty Acid Biosynthesis for New Antimicrobials.

Antibiotic resistance is a serious public health concern, and new drugs are needed to ensure effective treatment of many bacterial infections. Bacterial type II fatty acid synthesis (FASII) is a vital aspect of bacterial physiology, not only for the formation of membranes but also to produce intermediates used in vitamin production. Nature has evolved a repertoire of antibiotics inhibiting different aspects of FASII, validating these enzymes as potential targets for new antibiotic discovery and development. However, significant obstacles have been encountered in the development of FASII antibiotics, and few FASII drugs have advanced beyond the discovery stage. Most bacteria are capable of assimilating exogenous fatty acids. In some cases they can dispense with FASII if fatty acids are present in the environment, making the prospects for identifying broad-spectrum drugs against FASII targets unlikely. Single-target, pathogen-specific FASII drugs appear the best option, but a major drawback to this approach is the rapid acquisition of resistance via target missense mutations. This complication can be mitigated during drug development by optimizing the compound design to reduce the potential impact of on-target missense mutations at an early stage in antibiotic discovery. The lessons learned from the difficulties in FASII drug discovery that have come to light over the last decade suggest that a refocused approach to designing FASII inhibitors has the potential to add to our arsenal of weapons to combat resistance to existing antibiotics.

A pyruvate transporter in the apicoplast of apicomplexan parasites.

Pyruvate lies at a pivotal node of carbon metabolism in eukaryotes. It is involved in diverse metabolic pathways in multiple organelles, and its interorganelle shuttling is crucial for cell fitness. Many apicomplexan parasites harbor a unique organelle called the apicoplast that houses metabolic pathways like fatty acid and isoprenoid precursor biosyntheses, requiring pyruvate as a substrate. However, how pyruvate is supplied in the apicoplast remains enigmatic. Here, deploying the zoonotic parasite Toxoplasma gondii as a model apicomplexan, we identified two proteins residing in the apicoplast membranes that together constitute a functional apicoplast pyruvate carrier (APC) to mediate the import of cytosolic pyruvate. Depletion of APC results in reduced activities of metabolic pathways in the apicoplast and impaired integrity of this organelle, leading to parasite growth arrest. APC is a pyruvate transporter in diverse apicomplexan parasites, suggesting a common strategy for pyruvate acquisition by the apicoplast in these clinically relevant intracellular pathogens.

Phosphorylation of Insig-2 mediates inhibition of fatty acid synthesis by polyunsaturated fatty acids.

Insig-1 and Insig-2 are endoplasmic reticulum (ER) proteins that inhibit lipid synthesis by blocking transport of sterol regulatory element-binding proteins (SREBP-1 and SREBP-2) from ER to Golgi. In the Golgi, SREBPs are processed proteolytically to release their transcription-activating domains, which enhance the synthesis of fatty acids, triglycerides, and cholesterol. Heretofore, the two Insigs have redundant functions, and there is no rationale for two isoforms. The current data identify a specific function for Insig-2. We show that eicosapentaenoic acid (EPA), a polyunsaturated fatty acid, inhibits fatty acid synthesis in human fibroblasts and rat hepatocytes by activating adenylate cyclase, which induces protein kinase A (PKA) to phosphorylate serine-106 in Insig-2. Phosphorylated Insig-2 inhibits the proteolytic processing of SREBP-1, thereby blocking fatty acid synthesis. Phosphorylated Insig-2 does not block the processing of SREBP-2, which activates cholesterol synthesis. Insig-1 lacks serine-106 and is not phosphorylated at this site. EPA inhibition of SREBP-1 processing was reduced by the replacement of serine-106 in Insig-2 with alanine or by treatment with KT5720, a PKA inhibitor. Inhibition did not occur in mutant human fibroblasts that possess Insig-1 but lack Insig-2. These data provide an Insig-2-specific mechanism for the long-known inhibition of fatty acid synthesis by polyunsaturated fatty acids.

ACP Acylation Is an Acetyl-CoA-Dependent Modification Required for Electron Transport Chain Assembly.

The electron transport chain (ETC) is an important participant in cellular energy conversion, but its biogenesis presents the cell with numerous challenges. To address these complexities, the cell utilizes ETC assembly factors, which include the LYR protein family. Each member of this family interacts with the mitochondrial acyl carrier protein (ACP), the scaffold protein upon which the mitochondrial fatty acid synthesis (mtFAS) pathway builds fatty acyl chains from acetyl-CoA. We demonstrate that the acylated form of ACP is an acetyl-CoA-dependent allosteric activator of the LYR protein family used to stimulate ETC biogenesis. By tuning ETC assembly to the abundance of acetyl-CoA, which is the major fuel of the TCA cycle and ETC, this system could provide an elegant mechanism for coordinating the assembly of ETC complexes with one another and with substrate availability.

Diversity in fatty acid elongation enzymes: The FabB long-chain ß-ketoacyl-ACP synthase I initiates fatty acid synthesis in Pseudomonas putida F1.

The condensation of acetyl-CoA with malonyl-acyl carrier protein (ACP) by ß-ketoacyl-ACP synthase III (KAS III, FabH) and decarboxylation of malonyl-ACP by malonyl-ACP decarboxylase are the two pathways that initiate bacterial fatty acid synthesis (FAS) in Escherichia coli. In addition to these two routes, we report that Pseudomonas putida F1 ß-ketoacyl-ACP synthase I (FabB), in addition to playing a key role in fatty acid elongation, also initiates FAS in vivo. We report that although two P. putida F1 fabH genes (PpfabH1 and PpfabH2) both encode functional KAS III enzymes, neither is essential for growth. PpFabH1 is a canonical KAS III similar to E. coli FabH whereas PpFabH2 catalyzes condensation of malonyl-ACP with short- and medium-chain length acyl-CoAs. Since these two KAS III enzymes are not essential for FAS in P. putida F1, we sought the P. putida initiation enzyme and unexpectedly found that it was FabB, the elongation enzyme of the oxygen-independent unsaturated fatty acid pathway. P. putida FabB decarboxylates malonyl-ACP and condenses the acetyl-ACP product with malonyl-ACP for initiation of FAS. These data show that P. putida FabB, unlike the paradigm E. coli FabB, can catalyze the initiation reaction in FAS.

Arabidopsis trigalactosyldiacylglycerol1 mutants reveal a critical role for phosphtidylcholine remodeling in lipid homeostasis.

Lipid remodeling plays a critical role in plant response to abiotic stress and metabolic perturbations. Key steps in this process involve modifications of phosphatidylcholine (PC) acyl chains mediated by lysophosphatidylcholine: acyl-CoA acyltransferases (LPCATs) and phosphatidylcholine: diacylglycerol cholinephosphotransferase (ROD1). To assess their importance in lipid homeostasis, we took advantage of the trigalactosyldiacylglycerol1 (tgd1) mutant that exhibits marked increases in fatty acid synthesis and fatty acid flux through PC due to a block in inter-organelle lipid trafficking. Here, we showed that the increased fatty acid synthesis in tgd1 is due to posttranslational activation of the plastidic acetyl-coenzyme A carboxylase. Genetic analysis showed that knockout of LPCAT1 and 2 resulted in a lethal phenotype in tgd1. In addition, plants homozygous for lpcat2 and heterozygous for lpcat1 in the tgd1 background showed reduced levels of PC and triacylglycerols (TAG) and alterations in their fatty acid profiles. We further showed that disruption of ROD1 in tgd1 resulted in changes in fatty acid composition of PC and TAG, decreased leaf TAG content and reduced seedling growth. Together, our results reveal a critical role of LPCATs and ROD1 in maintaining cellular lipid homeostasis under conditions, in which fatty acid production largely exceeds the cellular demand for membrane lipid synthesis.

Bergenin, the main active ingredient of Bergenia purpurascens, attenuates Th17 cell differentiation by downregulating fatty acid synthesis.

Bergenin is the main active ingredient of Bergenia purpurascens, a medicinal plant which has long been used to treat a variety of Th17 cell-related diseases in China, such as allergic airway inflammation and colitis. This study aimed to uncover the underlying mechanisms by which bergenin impedes Th17 cell response in view of cellular metabolism. In vitro, bergenin treatment reduced the frequency of Th17 cells generated from naïve CD4+ T cells of mice. Mechanistically, bergenin preferentially restrained fatty acid synthesis (FAS) but not other metabolic pathways in differentiating Th17 cells, and exogenous addition of either palmitic acid (PA) or oleic acid (OA) and combination with acetyl-CoA carboxylase 1 (ACC1) activator citric acid dampened the inhibition of bergenin on Th17 cell differentiation. Bergenin inhibited FAS through downregulating the expression of SREBP1 via restriction of histone H3K27 acetylation in the SREBP1 promoter, and SREBP1 overexpression weakened the inhibition of bergenin on Th17 differentiation. Furthermore, bergenin was shown to directly interact with SIRT1 and result in activation of SIRT1. Either combination with SIRT1 inhibitor EX527 or point mutation plasmid of SIRT1 diminished the inhibitory effect of bergenin on FAS and Th17 cell differentiation. Finally, the inhibitory effect of bergenin on Th17 cell response and SIRT1 dependence were verified in mice with dextran sulfate sodium-induced colitis. In short, bergenin repressed Th17 cell response by downregulating FAS via activation of SIRT1, which might find therapeutic use in Th17 cell-related diseases.

The Regulation of Fatty Acid Synthase by Exosomal miR-143-5p and miR-342-5p in Idiopathic Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive disease caused by an aberrant repair of injured alveolar epithelial cells. The maintenance of the alveolar epithelium and its regeneration after the damage is fueled by alveolar type II (ATII) cells. Injured cells release exosomes containing microRNAs (miRNAs), which can alter the recipient cells' function. Lung tissue, ATII cells, fibroblasts, plasma, and exosomes were obtained from naive patients with IPF, patients with IPF taking pirfenidone or nintedanib, and control organ donors. miRNA expression was analyzed to study their impact on exosome-mediated effects in IPF. High miR-143-5p and miR-342-5p levels were detected in ATII cells, lung tissue, plasma, and exosomes in naive patients with IPF. Decreased FASN (fatty acid synthase) and ACSL-4 (acyl-CoA-synthetase long-chain family member 4) expression was found in ATII cells. miR-143-5p and miR-342-5p overexpression or ATII cell treatment with IPF-derived exosomes containing these miRNAs lowered FASN and ACSL-4 levels. Also, this contributed to ATII cell injury and senescence. However, exosomes isolated from patients with IPF taking nintedanib or pirfenidone increased FASN expression in ATII cells compared with naive patients with IPF. Furthermore, fibroblast treatment with exosomes obtained from naive patients with IPF increased SMAD3, CTGF, COL3A1, and TGFß1 expression. Our results suggest that IPF-derived exosomes containing miR-143-5p and miR-342-5p inhibited the de novo fatty acid synthesis pathway in ATII cells. They also induced the profibrotic response in fibroblasts. Pirfenidone and nintedanib improved ATII cell function and inhibited fibrogenesis. This study highlights the importance of exosomes in IPF pathophysiology.

A short-chain acyl-CoA synthetase that supports branched-chain fatty acid synthesis in Staphylococcus aureus.

Staphylococcus aureus controls its membrane biophysical properties using branched-chain fatty acids (BCFAs). The branched-chain acyl-CoA precursors, utilized to initiate fatty acid synthesis, are derived from branched-chain ketoacid dehydrogenase (Bkd), a multiprotein complex that converts α-keto acids to their corresponding acyl-CoAs; however, Bkd KO strains still contain BCFAs. Here, we show that commonly used rich medias contain substantial concentrations of short-chain acids, like 2-methylbutyric and isobutyric acids, that are incorporated into membrane BCFAs. Bkd-deficient strains cannot grow in defined medium unless it is supplemented with either 2-methylbutyric or isobutyric acid. We performed a screen of candidate KO strains and identified the methylbutyryl-CoA synthetase (mbcS gene; SAUSA300_2542) as required for the incorporation of 2-methylbutyric and isobutyric acids into phosphatidylglycerol. Our mass tracing experiments show that isobutyric acid is converted to isobutyryl-CoA that flows into the even-chain acyl-acyl carrier protein intermediates in the type II fatty acid biosynthesis elongation cycle. Furthermore, purified MbcS is an ATP-dependent acyl-CoA synthetase that selectively catalyzes the activation of 2-methylbutyrate and isobutyrate. We found that butyrate and isovalerate are poor MbcS substrates and activity was not detected with acetate or short-chain dicarboxylic acids. Thus, MbcS functions to convert extracellular 2-methylbutyric and isobutyric acids to their respective acyl-CoAs that are used by 3-ketoacyl-ACP synthase III (FabH) to initiate BCFA biosynthesis.

Acetyl-CoA carboxylase 1 depletion suppresses de novo fatty acid synthesis and mitochondrial ß-oxidation in castration-resistant prostate cancer cells.

Cancer cells, including those of prostate cancer (PCa), often hijack intrinsic cell signaling to reprogram their metabolism. Part of this reprogramming includes the activation of de novo synthesis of fatty acids that not only serve as building blocks for membrane synthesis but also as energy sources for cell proliferation. However, how de novo fatty acid synthesis contributes to PCa progression is still poorly understood. Herein, by mining public datasets, we discovered that the expression of acetyl-CoA carboxylase alpha (ACACA), which encodes acetyl-CoA carboxylase 1 (ACC1), was highly expressed in human PCa. In addition, patients with high ACACA expression had a short disease-free survival time. We also reported that depletion of ACACA reduced de novo fatty acid synthesis and PI3K/AKT signaling in the human castration-resistant PCa (CRPC) cell lines DU145 and PC3. Furthermore, depletion of ACACA downregulates mitochondrial beta-oxidation, resulting in mitochondrial dysfunction, a reduction in ATP production, an imbalanced NADP+/NADPhydrogen(H) ratio, increased reactive oxygen species, and therefore apoptosis. Reduced exogenous fatty acids by depleting lipid or lowering serum supplementation exacerbated both shRNA depletion and pharmacological inhibition of ACACA-induced apoptosis in vitro. Collectively, our results suggest that inhibition of ectopic ACACA, together with suppression of exogenous fatty acid uptake, can be a novel strategy for treating currently incurable CRPC.

Dimethyloxalylglycine Suppresses SREBP1c and Lipogenic Gene Expressions in Hepatocytes Independently of HIF1A.

Dimethyloxalylglycine (DMOG) is a representative inhibitor of the prolyl hydroxylase domain (PHD), which mediates the degradation of hypoxia-inducible factor-1-alpha (HIF1A). DMOG exerts its pharmacological effects via the canonical pathway that involves PHD inhibition; however, it remains unclear whether DMOG affects lipogenic gene expression in hepatocytes. We aimed to elucidate the effects of DMOG on sterol regulatory element-binding protein-1c (SREBP1c), a master regulator of fatty acid synthesis in hepatocytes. DMOG treatment inhibited SREBP1c mRNA and protein expression in HepG2 and AML12 hepatocytes and reduced the transcript levels of SREBP1c-regulated lipogenic genes. A luciferase reporter assay revealed that DMOG inhibited the transcriptional activity of SREBP1c. Moreover, DMOG suppressed SREBP1c expression in mice liver. Mechanistically, treatment with DMOG enhanced the expression of HIF1A and insulin-induced gene 2 (INSIG2), which inhibits the activation of SREBP1c. However, HIF1A or INSIG2 knockdown failed to reverse the inhibitory effect of DMOG on SREBP1c expression, suggesting a redundant role of HIF1A and INSIG2 in terms of repressing SREBP1c. DMOG did not function through the canonical pathway involving inhibition of SREBP1c by PHD, highlighting the presence of non-canonical pathways that mediate its anti-lipogenic effect.

Increased fatty acid synthesis and disturbed lipid metabolism in Neuro2a cells after repeated cocaine exposure: A preliminary study.

Chronic use of cocaine prompts neurodegeneration and neuroinflammation. Lipids play pivotal roles in neuronal function and pathology. Although evidence correlates cocaine use with the alteration of lipid metabolism in blood and brain, the precise mechanism remains to be elucidated. In this study, we explore the effect of cocaine on neuronal fatty acid profiles in vitro. Neuro2a cells following seven days of repeated exposure to cocaine (0, 600, 800, 1000 µM) showed apoptosis-irrelevant cell death, dysregulated autophagy, activation of atypical endoplasmic reticulum stress response, increased saturated and unsaturated fatty acid synthesis, and disrupted lipid metabolism. These preliminary findings indicated the association between lipid metabolism and cocaine-induced neurotoxicity, which should be beneficial for understanding the neurotoxicity of cocaine.

Arachidonic acid regulates pluripotency by modulating cellular energetics via fatty acid synthesis and mitochondrial fission.

Arachidonic acid (AA) is an important omega-6 fatty acid that can be metabolised into an impressive spectrum of biologically active mediators participating in various cellular functions. Studies have shown that fatty acid synthesis is enhanced in embryonic stem cells (ESCs), and it is crucial for the cellular reprogramming of somatic cells into induced pluripotent stem cells (iPSCs). Fatty acid synthesis increases the cellular lipid contents and, in turn, promotes mitochondrial fission and cellular reprogramming. AA was found to induce acetyl-CoA carboxylase 1 (ACC1) expression, a major enzyme in fatty acid synthesis. In this study, we have investigated the regulation of pluripotency, fatty acid synthesis and mitochondrial activities of the human induced pluripotent stem cells (hiPSCs) and the human embryonal carcinoma (hEC) NTERA-2 cells upon treatment with varying concentrations of AA. Our results indicate that a lower concentration of AA can increase pluripotency, as evidenced by an increased expression of pluripotency markers, increased fatty acid synthesis as evidenced by lipid estimation and modulated mitochondrial fission, as evidenced by mitotracker staining for fissioned mitochondria. Moreover, higher concentrations of AA-induced the opposite effect, leading to pluripotent stem cell differentiation. Molecular docking simulations predicted the possible interactions between AA and its metabolites with fatty acid synthesis regulators ACC1 and CREB1 (Cyclic adenosine monophosphate Response Element Binding Protein 1) as a mechanism for AA regulating pluripotency.

Nitrogen starvation leads to TOR kinase-mediated downregulation of fatty acid synthesis in the algae Chlorella sorokiniana and Chlamydomonas reinhardtii.

BACKGROUND: When subject to stress conditions such as nutrient limitation microalgae accumulate triacylglycerol (TAG). Fatty acid, a substrate for TAG synthesis is derived from de novo synthesis or by membrane remodeling. The model industrial alga Chlorellasorokiniana accumulates TAG and other storage compounds under nitrogen (N)-limited growth. Molecular mechanisms underlying these processes are still to be elucidated. RESULT: Previously we used transcriptomics to explore the regulation of TAG synthesis in C. sorokiniana. Surprisingly, our analysis showed that the expression of several key genes encoding enzymes involved in plastidic fatty acid synthesis are significantly repressed. Metabolic labeling with radiolabeled acetate showed that de novo fatty acid synthesis is indeed downregulated under N-limitation. Likewise, inhibition of the Target of Rapamycin kinase (TOR), a key regulator of metabolism and growth, decreased fatty acid synthesis. We compared the changes in proteins and phosphoprotein abundance using a proteomics and phosphoproteomics approach in C. sorokiniana cells under N-limitation or TOR inhibition and found extensive overlap between the N-limited and TOR-inhibited conditions. We also identified changes in the phosphorylation status of TOR complex proteins, TOR-kinase, and RAPTOR, under N-limitation. This indicates that TOR signaling is altered in a nitrogen-dependent manner. We find that TOR-mediated metabolic remodeling of fatty acid synthesis under N-limitation is conserved in the chlorophyte algae Chlorella sorokiniana and Chlamydomonas reinhardtii. CONCLUSION: Our results indicate that under N-limitation there is significant metabolic remodeling, including fatty acid synthesis, mediated by TOR signaling. This process is conserved across chlorophyte algae. Using proteomic and phosphoproteomic analysis, we show that N-limitation affects TOR signaling and this in-turn affects the metabolic status of the cells. This study presents a link between N-limitation, TOR signaling and fatty acid synthesis in green-lineage.

Creating yellow seed Camelina sativa with enhanced oil accumulation by CRISPR-mediated disruption of Transparent Testa 8.

Camelina (Camelina sativa L.), a hexaploid member of the Brassicaceae family, is an emerging oilseed crop being developed to meet the increasing demand for plant oils as biofuel feedstocks. In other Brassicas, high oil content can be associated with a yellow seed phenotype, which is unknown for camelina. We sought to create yellow seed camelina using CRISPR/Cas9 technology to disrupt its Transparent Testa 8 (TT8) transcription factor genes and to evaluate the resulting seed phenotype. We identified three TT8 genes, one in each of the three camelina subgenomes, and obtained independent CsTT8 lines containing frameshift edits. Disruption of TT8 caused seed coat colour to change from brown to yellow reflecting their reduced flavonoid accumulation of up to 44%, and the loss of a well-organized seed coat mucilage layer. Transcriptomic analysis of CsTT8-edited seeds revealed significantly increased expression of the lipid-related transcription factors LEC1, LEC2, FUS3, and WRI1 and their downstream fatty acid synthesis-related targets. These changes caused metabolic remodelling with increased fatty acid synthesis rates and corresponding increases in total fatty acid (TFA) accumulation from 32.4% to as high as 38.0% of seed weight, and TAG yield by more than 21% without significant changes in starch or protein levels compared to parental line. These data highlight the effectiveness of CRISPR in creating novel enhanced-oil germplasm in camelina. The resulting lines may directly contribute to future net-zero carbon energy production or be combined with other traits to produce desired lipid-derived bioproducts at high yields.

Genomic and biochemical analysis of lipid biosynthesis in Cyanophora paradoxa: Limited role of chloroplast in fatty acid synthesis.

Archaeplastida, a group of photosynthetic organisms with primary plastids, consists of green algae (plus plants), red algae, and glaucophytes. In contrast to green and red algae, information on lipids and lipid biosynthesis still needs to be included in the glaucophytes. The chloroplast is the site of photosynthesis and fatty acid synthesis in all photosynthetic organisms known to date. However, the genomic data of the glaucophyte Cyanophora paradoxa suggested the lack of acetyl CoA carboxylase and most components of fatty acid synthase in the chloroplast. Instead, multifunctional fatty acid synthase and acetyl CoA carboxylase are likely to reside in the cytosol. To examine this hypothesis, we measured fatty acid synthesis in isolated chloroplasts and whole cells using stable isotope labeling. The chloroplasts had very low activity of fatty acid synthesis, if any. Most processes of fatty acid synthesis, including elongation and desaturation, must be performed within the cytosol, and the fatty acids imported into the chloroplasts are assembled into the chloroplast lipids by the enzymes common to other algae and plants. Cyanophora paradoxa is a rare organism in which fatty acid synthesis and photosynthesis are not tightly linked. This could question the common origin of these two biosynthetic processes in Archaeplastida.

Sirtuin 1 Inhibits Fatty Acid Synthesis through Forkhead Box Protein O1-Mediated Adipose Triglyceride Lipase Expression in Goat Mammary Epithelial Cells.

Sirtuin 1 (SIRT1) is a key upstream regulator of lipid metabolism; however, the molecular mechanisms by which SIRT1 regulates milk fat synthesis in dairy goats remain unclear. This study aimed to investigate the regulatory roles of SIRT1 in modulating lipid metabolism in goat mammary epithelial cells (GMECs) and its impact on the adipose triglyceride lipase (ATGL) promoter activity using RNA interference (RNAi) and gene overexpression techniques. The results showed that SIRT1 is significantly upregulated during lactation compared to the dry period. Additionally, SIRT1 knockdown notably increased the expressions of genes related to fatty acid synthesis (SREBP1, SCD1, FASN, ELOVL6), triacylglycerol (TAG) production (DGAT2, AGPAT6), and lipid droplet formation (PLIN2). Consistent with the transcriptional changes, SIRT1 knockdown significantly increased the intracellular contents of TAG and cholesterol and the lipid droplet abundance in the GMECs, while SIRT1 overexpression had the opposite effects. Furthermore, the co-overexpression of SIRT1 and Forkhead box protein O1 (FOXO1) led to a more pronounced increase in ATGL promoter activity, and the ability of SIRT1 to enhance ATGL promoter activity was nearly abolished when the FOXO1 binding sites (FKH1 and FKH2) were mutated, indicating that SIRT1 enhances the transcriptional activity of ATGL via the FKH element in the ATGL promoter. Collectively, our data reveal that SIRT1 enhances the transcriptional activity of ATGL through the FOXO1 binding sites located in the ATGL promoter, thereby regulating lipid metabolism. These findings provide novel insights into the role of SIRT1 in fatty acid metabolism in dairy goats.

Nucleoside Diphosphate Kinases Are ATP-Regulated Carriers of Short-Chain Acyl-CoAs.

Nucleoside diphosphate (NDP) kinases 1 and 2 (NME1/2) are well-characterized enzymes known for their NDP kinase activity. Recently, these enzymes have been shown by independent studies to bind coenzyme A (CoA) or acyl-CoA. These findings suggest a hitherto unknown role for NME1/2 in the regulation of CoA/acyl-CoA-dependent metabolic pathways, in tight correlation with the cellular NTP/NDP ratio. Accordingly, the regulation of NME1/2 functions by CoA/acyl-CoA binding has been described, and additionally, NME1/2 have been shown to control the cellular pathways consuming acetyl-CoA, such as histone acetylation and fatty acid synthesis. NME1/2-controlled histone acetylation in turn mediates an important transcriptional response to metabolic changes, such as those induced following a high-fat diet (HFD). This review discusses the CoA/acyl-CoA-dependent NME1/2 activities and proposes that these enzymes be considered as the first identified carriers of CoA/short-chain acyl-CoAs.

The Role of SCAP/SREBP as Central Regulators of Lipid Metabolism in Hepatic Steatosis.

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) is rapidly increasing worldwide at an alarming pace, due to an increase in obesity, sedentary and unhealthy lifestyles, and unbalanced dietary habits. MASLD is a unique, multi-factorial condition with several phases of progression including steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Sterol element binding protein 1c (SREBP1c) is the main transcription factor involved in regulating hepatic de novo lipogenesis. This transcription factor is synthesized as an inactive precursor, and its proteolytic maturation is initiated in the membrane of the endoplasmic reticulum upon stimulation by insulin. SREBP cleavage activating protein (SCAP) is required as a chaperon protein to escort SREBP from the endoplasmic reticulum and to facilitate the proteolytic release of the N-terminal domain of SREBP into the Golgi. SCAP inhibition prevents activation of SREBP and inhibits the expression of genes involved in triglyceride and fatty acid synthesis, resulting in the inhibition of de novo lipogenesis. In line, previous studies have shown that SCAP inhibition can resolve hepatic steatosis in animal models and intensive research is going on to understand the effects of SCAP in the pathogenesis of human disease. This review focuses on the versatile roles of SCAP/SREBP regulation in de novo lipogenesis and the structure and molecular features of SCAP/SREBP in the progression of hepatic steatosis. In addition, recent studies that attempt to target the SCAP/SREBP axis as a therapeutic option to interfere with MASLD are discussed.