Mechanism Of Lipid Accumulation Research Articles

Bioenergy feedstock production in Chlamydomonas reinhardtii (microalgae) cultivated under mixotrophic growth with cellulose hydrolysate from agricultural waste.

In the present study, cellulose purified from finger millet agricultural waste is subjected to enzymatic hydrolysis, and the hydrolysate (predominantly glucose) is used as a carbon source supplement in the media for the mixotrophic growth of Chlamydomonas reinhardtii. Interestingly, a switch between excess starch production and excess lipid (triacylglycerols, TAG) production occurs by a small change in hydrolysate concentration in the media. Starch production increased 4.5-fold with respect to the photoautotrophic control, with a glucose concentration of 3mg/mL in the media after hydrolysate addition. This culture had TAG production enhancement by 1.5-fold. However, mixotrophic cultivation with 4mg/mL glucose concentration in the media with hydrolysate addition resulted in TAG productivity enhancement by 4.2-fold compared to control and starch amount increase of 1.3-fold. The organic carbon source (glucose) and the inorganic carbon source (citrate ions) in the hydrolysate together played a role in this delicate switching between starch and lipid pathways. Proteins, starch, and TAG molecules are analyzed in the microalgal cells grown under different conditions with FTIR spectroscopy, a rapid, high-throughput method of biomolecular estimation. High-resolution single-cell AFM studies of the cell wall structure reveal enhanced corrugations in surface morphology during mixotrophic growth with cellulose hydrolysate, illustrating an adaptive mechanism with improved mechanical stress management. Lipid droplet morphology at the single-cell level points to two distinct mechanisms of lipid accumulation: one in which the lipids are segregated as droplets, and the other in which lipid molecules are uniformly dispersed in the cytosol as unresolved, ultra-small droplets. The present study therefore analyzes both the bulk and the single-cell level changes when cellulose hydrolysate is used as a carbon source for Chlamydomonas reinhardtii mixotrophic cultivation, which serves a four-fold purpose: value from waste, fixation of atmospheric CO2, production of lipids for biodiesel, and starch for bioethanol.

Molecular mechanism of renal lipid accumulation in diabetic kidney disease.

Diabetic kidney disease (DKD) is a leading cause of end stage renal disease with unmet clinical demands for treatment. Lipids are essential for cell survival; however, renal cells have limited capability to metabolize overloaded lipids. Dyslipidaemia is common in DKD patients and renal ectopic lipid accumulation is associated with disease progression. Unveiling the molecular mechanism involved in renal lipid regulation is crucial for exploring potential therapeutic targets. In this review, we focused on the mechanism underlying cholesterol, oxysterol and fatty acid metabolism disorder in the context of DKD. Specific regulators of lipid accumulation in different kidney compartment and TREM2 macrophages, a lipid-related macrophages in DKD, were discussed. The role of sodium-glucose transporter 2 inhibitors in improving renal lipid accumulation was summarized.

Nitrogen starvation causes lipid remodeling in Rhodotorula toruloides

BackgroundThe oleaginous yeast Rhodotorula toruloides is a promising chassis organism for the biomanufacturing of value-added bioproducts. It can accumulate lipids at a high fraction of biomass. However, metabolic engineering efforts in this organism have progressed at a slower pace than those in more extensively studied yeasts. Few studies have investigated the lipid accumulation phenotype exhibited by R. toruloides under nitrogen limitation conditions. Consequently, there have been only a few studies exploiting the lipid metabolism for higher product titers.ResultsWe performed a multi-omic investigation of the lipid accumulation phenotype under nitrogen limitation. Specifically, we performed comparative transcriptomic and lipidomic analysis of the oleaginous yeast under nitrogen-sufficient and nitrogen deficient conditions. Clustering analysis of transcriptomic data was used to identify the growth phase where nitrogen-deficient cultures diverged from the baseline conditions. Independently, lipidomic data was used to identify that lipid fractions shifted from mostly phospholipids to mostly storage lipids under the nitrogen-deficient phenotype. Through an integrative lens of transcriptomic and lipidomic analysis, we discovered that R. toruloides undergoes lipid remodeling during nitrogen limitation, wherein the pool of phospholipids gets remodeled to mostly storage lipids. We identify specific mRNAs and pathways that are strongly correlated with an increase in lipid levels, thus identifying putative targets for engineering greater lipid accumulation in R. toruloides. One surprising pathway identified was related to inositol phosphate metabolism, suggesting further inquiry into its role in lipid accumulation.ConclusionsIntegrative analysis identified the specific biosynthetic pathways that are differentially regulated during lipid remodeling. This insight into the mechanisms of lipid accumulation can lead to the success of future metabolic engineering strategies for overproduction of oleochemicals.

Pre-eclamptic foetal programming predisposes offspring to hepatic steatosis via DNA methylation

ObjectivesGamete and embryo–foetal origins of adult diseases hypothesis proposes that adulthood chronic disorders are associated with adverse foetal and early life traits. Our study aimed to characterise developmental changes and underlying mechanisms of metabolic disorders in offspring of pre-eclampsia (PE) programmed pregnancy. MethodsNω-Nitro-l-arginine methyl ester hydrochloride (L-NAME) induced pre-eclampsia-like C57BL/6J mouse model was used. Lipid profiling, histological morphology, indirect calorimetry, mRNA sequencing, and pyrosequencing were performed on PE offspring of both young and elderly ages. ResultsPE offspring exhibited increased postnatal weight gain, hepatic lipid accumulation, enlarged adipocytes, and impaired energy balance that continued to adulthood. Integrated RNA sequencing of foetal and 52-week-old livers revealed that the differentially expressed genes were mainly enriched in lipid metabolism, including glycerol-3-phosphate acyl-transferase 3 (Gpat3), a key enzyme for de novo synthesis of triglycerides (TG), and carnitine palmitoyltransferase-1a (Cpt1a), a key transmembrane enzyme that mediates fatty acid degradation. Pyrosequencing of livers from PE offspring identified hypomethylated and hypermethylated regions in Gpat3 and Cpt1a promoters, which were associated with upregulated and downregulated expressions of Gpat3 and Cpt1a, respectively. These epigenetic alterations are persistent and consistent from the foetal stage to adulthood in PE offspring. ConclusionThese findings suggest a methylation-mediated epigenetic mechanism for PE-induced intergenerational lipid accumulation, impaired energy balance and obesity in offspring, and indicate the potential benefits of early interventions in offspring exposed to maternal PE to reduce their susceptibility to metabolic disorder in their later life.

Variations in lipid composition of ovaries and hepatopancreas during vitellogenesis in the mud crab Scylla paramamosain: Implications of lipid transfer from hepatopancreas to ovaries

Lipid accumulation in ovaries is essential for reproductive success in decapods. Understanding of the mechanism of ovarian lipid accumulation is still in its infancy. In this study, we investigated lipid compositions of ovaries and hepatopancreas throughout vitellogenesis and hemolymph in the late-vitellogenic stage in the mud crab Scylla paramamosain. Total lipid content in ovaries consecutively increased from the early to late stage, and the main accumulated lipids were phosphatidylcholine (PC), alkenylglycerophosphoethanolamine (alkenyl-PE), triacylglycerol (TG), cholesteryl ester, and cholesterol. The lipid composition of hemolymph indicated that PC, alkenyl-PE, diacylglycerol (DG), ether DG, monoacylglycerol, and cholesterol were the main lipids transferred to ovaries from hepatopancreas. In hepatopancreas, the total lipid content appeared to increase during vitellogenesis and the late stage was significantly different from early and mid-stages. TG was the predominant lipid class that slightly decreased from the early to mid-stage, but dramatically increased in the late stage. In contrast, PC and alkenyl-PE significantly increased from the early to mid-stage and remained constantly in relatively low proportion until the late stage. These findings suggested PC and alkenyl-PE in the hepatopancreas likely play critical roles in regulating lipid transfer. Esterified fatty acids in ovaries and hepatopancreas were mainly C16:0, C18:0, 16:1, C18:1, C18:2, C20:4, C20:5, and C22:6, of which highly unsaturated fatty acids (HUFA) primarily occurred in alkenyl-PE and phosphatidylserine (PS) but not PC. In hemolymph, PC was abundant in HUFA besides of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA), while PS was predominantly composed of SFA and MUFA, implying a transformation of HUFA between phospholipids prior to transfer. These findings highlight the importance of phospholipid metabolism in the hepatopancreas to ovarian lipid accumulation. Our study provides novel insights into the mechanism of ovarian lipid accumulation in decapods.

New insights into rare earth element-induced microalgae lipid accumulation: Implication for biodiesel production and adsorption mechanism

A coupling technology for lipid production and adsorption of rare earth elements (REEs) using microalgae was studied in this work. The microalgae cell growth, lipid production, biochemical parameters and lipid profiles were investigated under different REEs (Ce3+, Gd3+and La3+). The results showed that the maximum lipid production was achieved at different concentrations of REEs, with lipid productivities of 300.44, 386.84 and 292.19 mg L−1 d−1 under treatment conditions of 100 μg L−1 Ce3+, 250 μg L−1 Gd3+ and 1 mg L−1 La3+, respectively. Moreover, the adsorption efficiency of Ce3+, Gd3+ and La3+exceeded 96.58 %, 93.06 % and 91.3 % at concentrations of 25–1000 μg L−1, 100–500 μg L−1 and 0.25–1 mg L−1, respectively. In addition, algal cells were able to adsorb 66.2 % of 100 μg L−1 Ce3+, 48.4 % of 250 μg L−1 Gd3+ and 59.9 % of 1 mg L−1 La3+. The combination of extracellular polysaccharide and algal cell wall could adsorb 25.2 % of 100 μg L−1 Ce3+, 44.5 % of 250 μg L−1 Gd3+ and 30.5 % of 1 mg L−1 La3+, respectively. These findings indicated that microalgae predominantly adsorbed REEs through the intracellular pathway. This study elucidates the mechanism of effective lipid accumulation and adsorption of REEs by microalgae under REEs stress conditions. It establishes a theoretical foundation for the efficient microalgae lipid production and REEs recovery from wastewater or waste residues containing REEs.

Lipid accumulation mechanism of Amphora coffeaeformis under nitrogen deprivation and its application as a feed additive in Carassius auratus aquaculture

BackgroundAmphora coffeaeformis, a unicellular diatom, can significantly accumulate lipids under nitrogen (N) limitation. However, the molecular mechanism underlying lipid accumulation in A. coffeaeformis remains unknown and its application development is lagging.ResultsThis work analyzed the lipid composition of A. coffeaeformis under N deprivation and investigated its mechanism underlying lipid accumulation using RNA-seq. The results showed that the total lipid content of A. coffeaeformis increased from 28.22 to 44.05% after 5 days of N deprivation, while the neutral lipid triacylglycerol (TAG) content increased from 10.41 to 25.21%. The transcriptional profile showed that N deprivation induced wide-ranging reprogramming of regulation and that most physiological activities were repressed, while the upregulation of glycerol-3-phosphate acyltransferase directly determined TAG accumulation. Moreover, we explored the effect of A. coffeaeformis as a food additive on the lipid composition of crucian carp. The results showed that the contents of unsaturated fatty acids in the meat of fish supplemented with A. coffeaeformis were significantly increased, indicating its potential application in animal nutrition for improving meat quality indicators.ConclusionThe findings shed light on the molecular mechanisms of neutral lipid accumulation and revealed the key genes involved in lipid metabolism in A. coffeaeformis. Moreover, we also confirmed that A. coffeaeformis can be used as feed additive for improving the lipid composition of crucian carp meat, which provided evidence for the biotechnology application of this high-oil microalgae.

Comprehensive Exploration of the Growth and Lipid Synthesis Phases of T. oleaginosus Cultures Implementing Design of Experiments and Response Surface Methodology.

Trichosporon oleaginosus is an unconventional oleaginous yeast distinguished by its remarkable capacity to accumulate lipids in excess of 70% of its dry weight, particularly when cultivated in nitrogen-restricted conditions with ample carbon sources. A pivotal question that arises pertains to the nutrient dynamics in the culture medium, which give rise to both the excessive lipid content and corresponding lipid concentration. While previous research has predominantly focused on evaluating the impact of the initial carbon-to-nitrogen (C/N) ratio on lipid production, the precise critical thresholds of glucose and ammonium sulfate ((NH4)2SO4) at which growth and intracellular lipid production are either stimulated or impeded remain inadequately defined. This study employs an experimental design and response surface methodology to investigate the complex mechanism of lipid accumulation and its interaction with cellular growth. Application of the aforementioned methodologies resulted in the production of 10.6 g/L of microbial oil in batch cultures under conditions that correspond to a C/N ratio of 76. However, the primary objective is to generate knowledge to facilitate the development of efficient fed-batch cultivation strategies that optimize lipid production exclusively employing inorganic nitrogen sources by finely adjusting carbon and nitrogen levels. The intricate interaction between these levels is comprehensively addressed in the present study, while it is additionally revealed that as glucose levels rise within a non-inhibitory range, lipid-free biomass production decreases while lipid accumulation simultaneously increases. These findings set the stage for further exploration and the potential development of two-stage cultivation approaches, aiming to fully decouple growth and lipid production. This advancement holds the promise of bringing microbial oil production closer to commercial viability.

Metabolic interpretation of NaCl stress-induced lipid accumulation in microalgae for promising biodiesel production with saline wastewater

The rising use of saline wastewater for biodiesel production through oleaginous microalgae demands fundamental studies on the metabolic response of microalgal cells to salt stress. Thus, we investigated how salt stress promotes lipid accumulation inside Botryococcus sp. NJD-1 by tracking critical metabolites and proteases as well as analyzing the cellular redox balance. The results showed that the lipid content of microalgal cells followed a negative binomial correlation with intracellular reactive oxygen species (ROS), while the neutral lipid content increased linearly with salinity in range of 0–20 g/L NaCl. The optimal lipid production was achieved as 54.5 % and 110.5 mg/L d-1 at 10 g/L NaCl. Further comparing the metabolomics and proteomics data at 0 and 10 g/L NaCl, the adenosine triphosphate (ATP) and nicotinamide adenine nucleotide phosphate (NADPH) were found significantly increased to quench the Na+-induced ROS. The created NADPH and ATP accord the enhanced activity of the upper Pyruvate-Malate cycle and tricarboxylic acid cycle (TCA) cycle. Therefore, ROS detoxification is proposed to be the essential mechanism for microalgal lipid accumulation under salt stress. The cellular triacylglycerol (TAG) synthesis triggered by salinity is mainly mediated by an acetyl-CoA-dependent Kennedy pathway. These findings will deepen our understanding of the nexus of ambient salt, intracellular ROS and lipid metabolism for microalgae and advance the exploit of saline wastewater for microalgal lipid production.

Molecular characterization and expression profiling of two flavohemoglobin genes play essential roles in dissolved oxygen and NO stress in Saitozyma podzolica zwy2–3

Flavohemoglobins (Fhbs) are key enzymes involved in microbial nitrosative stress resistance and nitric oxide degradation. However, the roles of Fhbs in fungi remain largely unknown. In this study, SpFhb1 and SpFhb2, two flavohemoglobin-encoding genes in Saitozyma podzolica zwy2–3 were characterized. Protein structure analysis and molecular docking showed that SpFhbs were conserved in bacteria and fungi. Phylogenetic analysis revealed that SpFhb2 may be acquired through the transfer event of independent horizontal genes from bacteria. The expression levels of SpFhb1 and SpFhb2 showed opposite trend under high/low dissolved oxygen, implying that they may exhibited different functions. Through deletion and overexpression of SpFhbs, we confirmed that SpFhbs were conducive to lipid accumulation under high stress. The sensitivities of ΔFhb mutants to NO stress were significantly increased compared with that in the WT, indicating that they were required for NO detoxification and nitrosative stress resistance in S. podzolica zwy2–3. Furthermore, SpAsg1 was identified that simultaneously regulates SpFhbs, which functions in the lipid accumulation under high/low dissolved oxygen and NO stress in S. podzolica zwy2–3. Overall, two different SpFhbs were identified in this study, providing new insights into the mechanism of lipid accumulation in fungi under high/low dissolved oxygen and NO stress.

Four-and-a-Half LIM-Domain Protein 2 (FHL2) Induces Neuropeptide Y (NPY) in Macrophages in Visceral Adipose Tissue and Promotes Diet-Induced Obesity.

Obesity is characterized by the expansion of the adipose tissue, usually accompanied by inflammation, with a prominent role of macrophages infiltrating the visceral adipose tissue (VAT). This chronic inflammation is a major driver of obesity-associated comorbidities. Four-and-a-half LIM-domain protein 2 (FHL2) is a multifunctional adaptor protein that is involved in the regulation of various biological functions and the maintenance of the homeostasis of different tissues. In this study, we aimed to gain new insights into the expression and functional role of FHL2 in VAT in diet-induced obesity. We found enhanced FHL2 expression in the VAT of mice with Western-type diet (WTD)-induced obesity and obese humans and identified macrophages as the cellular source of enhanced FHL2 expression in VAT. In mice with FHL2 deficiency (FHL2KO), WTD feeding resulted in reduced body weight gain paralleled by enhanced energy expenditure and uncoupling protein 1 (UCP1) expression, indicative of activated thermogenesis. In human VAT, FHL2 was inversely correlated with UCP1 expression. Furthermore, macrophage infiltration and the expression of the chemokine MCP-1, a known promotor of macrophage accumulation, was significantly reduced in WTD-fed FHL2KO mice compared with wild-type (wt) littermates. While FHL2 depletion did not affect the differentiation or lipid metabolism of adipocytes in vitro, FHL2 depletion in macrophages resulted in reduced expressions of MCP-1 and the neuropeptide Y (NPY). Furthermore, WTD-fed FHL2KO mice showed reduced NPY expression in VAT compared with wt littermates, and NPY expression was enhanced in VAT resident macrophages of obese individuals. Stimulation with recombinant NPY induced not only UCP1 expression and lipid accumulation but also MCP-1 expression in adipocytes. Collectively, these findings indicate that FHL2 is a positive regulator of NPY and MCP-1 expression in macrophages and herewith closely linked to the mechanism of obesity-associated lipid accumulation and inflammation in VAT. Thus, FHL2 appears as a potential novel target to interfere with the macrophage-adipocyte crosstalk in VAT for treating obesity and related metabolic disorders.

The Different Mechanisms of Lipid Accumulation in Hepatocytes Induced by Oleic Acid/Palmitic Acid and High-Fat Diet.

Non-alcoholic fatty liver disease (NAFLD) is the primary chronic liver disease worldwide, mainly manifested by hepatic steatosis. Hepatic lipids may be derived from dietary intake, plasma free fatty acid (FFA) uptake, or hepatic de novo lipogenesis (DNL). Currently, cellular and animal models of hepatocellular steatosis are widely used to study the pathogenesis of NAFLD and to investigate therapeutic agents. However, whether there are differences between the in vivo and in vitro models of the mechanisms that cause lipid accumulation has not been reported. We used OA/PA-induced NCTC 1469 cells and high-fat-diet-fed C57BL/6J mice to simulate a hepatocyte steatosis model of NAFLD and to detect indicators related to FFA uptake and DNL. In addition, when serological indicators were analysed in the mouse model, it was found that serum FASN levels decreased. The results revealed that, in the cellular model, indicators related to DNL were decreased, FASN enzyme activity was unchanged, and indicators related to FFA uptake were increased, including the high expression of CD36; while, in the animal model, indicators related to both FFA uptake and de novo synthesis were increased, including the high expression of CD36 and the increased protein levels of FASN with enhanced enzyme activity. In addition, after an analysis of the serological indicators in the mouse model, it was found that the serum levels of FASN were reduced. In conclusion, the OA/PA-induced cellular model can be used to study the mechanism of FFA uptake, whereas the high-fat-diet-induced mouse model can be used to study the mechanism of FFA uptake and DNL. Combined treatment with CD36 and FASN may be more effective against NAFLD. FASN in the serum can be used as one of the indicators for the clinical diagnosis of NAFLD.

Integrated lipidomic and transcriptomic analyses reveal the mechanism of lipid biosynthesis and accumulation during seed development in sesame.

Sesame is one of the most important oilseed crops and attracts significant attention because of its huge nutritional capacity. However, the molecular mechanisms underlying oil accumulation in sesame remains poorly understood. In this study, lipidomic and transcriptomic analyses in different stages of sesame seed (Luzhi No.1, seed oil content 56%) development were performed to gain insight into the regulatory mechanisms that govern differences in lipid composition, content, biosynthesis, and transport. In total, 481 lipids, including fatty acids (FAs, 38 species), triacylglycerol (TAG, 127 species), ceramide (33 species), phosphatidic acid (20 species), and diacylglycerol (17 species), were detected in developing sesame seed using gas and liquid chromatography-mass spectrometry. Most FAs and other lipids accumulated 21-33 days after flowering. RNA-sequence profiling in developing seed highlighted the enhanced expression of genes involved in the biosynthesis and transport of FAs, TAGs, and membrane lipids, which was similar to that seen during lipid accumulation. Through the differential expression analysis of genes involved in lipid biosynthesis and metabolism during seed development, several candidate genes were found to affect the oil content and FA composition of sesame seed, including ACCase, FAD2, DGAT, G3PDH, PEPCase, WRI1 and WRI1-like genes. Our study reveals the patterns of lipid accumulation and biosynthesis-related gene expression and lays an important foundation for the further exploration of sesame seed lipid biosynthesis and accumulation.

Discovery, characterization, and adipocyte differentiation regulation in perirenal adipose tissue of large yellow croaker (Larimichthys crocea).

Adipose tissue is an essential tissue for lipid deposition in fish and is associated with excess lipid accumulation in aquaculture. However, the knowledge of the distribution and characterization of adipose tissue in fish still needs further investigation. This study for the first time discovered perirenal adipose tissue (PAT) in large yellow croaker by MRI and CT technologies. Then, the morphological and cytological characteristics of PAT were observed, showing a typical characteristic of white adipose tissue. Meanwhile, the mRNA expression of marker genes of white adipose tissue was highly expressed in PAT compared with the liver and muscle in large yellow croaker. Moreover, based on the discovery of PAT, preadipocytes from PAT were isolated, and the differentiation system of preadipocytes was established. The lipid droplet and TG content of cell were gradually increased during adipocyte differentiation. In addition, mRNA expressions of lipoprotein lipase, adipose triglyceride lipase, and transcription factors related to adipogenesis (cebpα, srebp1, pparα, and pparγ) were quantified to explain the regulation mechanism during the differentiation process. In summary, the present study first discovered perirenal adipose tissue in fish, then explored the characterization of PAT, and revealed the regulation of adipocyte differentiation. These results could advance the understanding of adipose tissue in fish and provide a novel idea for the study of the mechanism of lipid accumulation.

1688-P: Glucokinase Activator Triggers PERK-UPR Pathway in Diet-Induced Obese Mice via Inducing Hepatic Lipid Accumulation

Background: To investigate the effect of glucokinase activation on glucose and lipid metabolism in diet-induced obese mice. Methods: Mice fed with High-fat-diet (HFD) or control diet for 16 weeks were subjected to glucokinase activator (GKA) or vehicle treatment by gavage for 4 weeks. Glucose tolerance tests were performed to evaluate the glucose-lowering effect of GKA. Hepatic lipid accumulation was assessed by H&E, Oil-red’O staining, and transmission electronic microscopy. The underlying mechanism and subsequent effects of glucokinase activation-induced lipid accumulation was analyzed in liver. Protein levels of related genes were analyzed in mouse livers or AML12 cells. Results: Glucokinase activation improved glucose tolerance and insulin sensitivity in obese mice. Moreover, increased liver weight and TG Content were found in GKA-treated obese mice. Significant hepatic lipid accumulation was observed by multiple assays. RNA sequencing analysis indicated the increased expression of lipogenesis genes and activated PERK-UPR pathway in the liver. Inhibition of the lipogenesis-related gene Acc reduced the lipid levels caused by GKA treatment and alleviated PERK-UPR pathway in AML12 cell line. Conclusions: Glucokinase activation improved glucose tolerance while induced hepatic lipid accumulation through increased lipogenesis, which subsequently triggered PERK-UPR signaling pathway. Disclosure N.Cai: None. L.Zeng: None. X.Chen: None. J.Liu: None. Z.Wen: None. S.Wen: None. W.Zeng: None. S.Lin: None. Y.Chen: None. G.Shi: None. Funding National Natural Science Foundation of China (81770826, 82070811); National Key R&D Program of China (2017YFA0105803); Key Area R&D Program of Guangdong Province (2019B020227003); Sci-Tech Research Development Program of Guangzhou City (202201020497); Natural Science Foundation of Guangdong Province (2018B030311012)

Homologous Overexpression of Acyl-CoA Thioesterase 8 Enhanced Free Fatty Acid Accumulation in Oleaginous Fungus Mucor circinelloides WJ11

Thioesterases play an essential role in the metabolism of fatty acids since they are considered one of the key enzymes to change the total amount and composition of fatty acid in an organism’s cells. Acyl-coenzyme A thioesterase 8 (ACOT8) exhibits substrate specificity mainly for short- to long-chain acyl-CoA. To identify and characterize the ACOT8 enzyme’s superfamily in Mucor circinelloides, three genes were characterized and homologously expressed in M. circinelloides WJ11 which has been used as a model organism to investigate the mechanism of lipid accumulation. Multiple sequence alignment showed that McACOT8s had significant conserved motifs in the ACOT8 family. Experimental data indicated that the biomass of the three recombinant strains (McACOT8a, McACOT8b and McACOT8c) was slightly lower than that of the control strain Mc2075, but the total fatty acid (TFA) content was significantly increased by 30.3, 21.5 and 23.9%, respectively, and the free fatty acid production increased from 12.9% (control strain) to 19.2, 25.2 and 26.2% (recombinant types), respectively, with a maximum increase of 103.1% in McACOT8c. The three strains did not show any significant improvement in fatty acid composition compared to the control strain. However, in terms of fatty acid composition of free fatty acid, McACOT8b and McACOT8c contained γ-linolenic acid (C18:3), which was not detected in the control strain or in McACOT8a, indicating that ACOT8b and ACOT8c had substrate specificity for C18:3. These results displayed that ACOT8 can increase TFA accumulation and that it may be an important target of genetic manipulation for microbial oil production.

Benzo[a]pyrene and a high-fat diet induce aortic injury and promote low-density lipoprotein accumulation in the endothelium

Benzo[a]pyrene (BaP) is a ubiquitous environmental pollutant which mainly exposed though diet. High-fat diet (HFD) can induce atherosclerosis, as can BaP. Unhealthy dietary habits lead to high intake of both BaP and lipids. However, the combined effect of BaP and HFD on atherosclerosis and lipid accumulation in the arterial wall, the initial stage of atherosclerosis, is unclear. In this study, C57BL/6 J mice were subchronically exposed to BaP and a HFD, and the mechanism of lipid accumulation was investigated in EA.hy926 and HEK293 cells. Results showed that BaP and HFD increased blood lipids and damaged aortic wall synergistically. Meanwhile, LDL enhanced the toxicity of BaP, and BaP promoted the production of reactive oxygen species and malonaldehyde in EA.hy926 cells, which aggravated LDL-induced cell injury. Moreover, BaP and HFD/LDL induced LDL accumulation in the aortic wall of C57BL/6 J mice/EA.hy926, and the mechanism was by activating AHR/ARNT heterodimer to combine with the scavenger receptor BⅠ (SR-BⅠ) and activin receptor-like kinase 1 (ALK1) promoter regions to transcriptional upregulate its expression, which enhanced the uptake of LDL, and promoting the production of AGEs to inhibit reverse cholesterol transport by SR-BI. BaP and lipid synergistically promoted aortic and endothelial damage, and the health risk of their combined intake should be paid attention to.

Stramenopile-type Lipid Droplet Protein Functions as a Lipid Droplet Scaffold Protein in the Marine Diatom Phaeodactylum tricornutum.

Oleaginous microalgae gain great attention as feedstock for biofuels because of their substantial accumulation capacity of neutral lipids in the cytosolic compartment called lipid droplet (LD). Understanding the regulation mechanism of neutral lipid accumulation and degradation, which is mediated by LD-associated proteins, is an important issue in improving lipid productivity. However, LD-associated proteins vary among species and wait to be characterized in many microalgae. Stramenopile-type lipid droplet protein (StLDP) was previously identified as a primary LD protein in the marine diatom Phaeodactylum tricornutum. We produced a knockout mutant of StLDP by CRISPR/Cas9 genome editing. Also, we tried to complement this mutant by expressing recognition site-modified StLDP (RSM-StLDP) which is designed to avoid an attack by Cas9 nuclease expressing in the mutant. The RSM-StLDP:EGFP was localized to both LDs and the outer chloroplast-endoplasmic reticulum. Decrease of LD number per cell, increase of LD size, and no alteration of neutral lipid content in the mutant under nitrogen deficiency clearly indicate that StLDP acts as an LD scaffold protein. The number of LD per cell increased in the complemented strain compared to wild-type cells. The LD morphology in the mutant is probably over-rescued in the complemented strain by the strong function of the nitrate reductase promoter, which is also supported by high neutral lipid content in the complemented strain. The growth of stldp mutant showed a long lag phase relative to wild-type cells, suggesting that the low surface-to-volume ratio of fused LD decreased the efficiency of LD hydrolysis during the initial growth phase.

Comparative Transcriptome Analysis Identifies MAPK Signaling Pathway Associated with Regulating Ovarian Lipid Metabolism during Vitellogenesis in the Mud Crab, Scylla paramamosain

The mud crab, Scylla paramamosain, has abundant nutrients in the ovary, where numerous lipids accumulate during ovarian maturation. However, the mechanism behind the accumulation of lipids in the ovary of mud crab during ovarian maturation is largely unknown. This study conducted a comparative transcriptome analysis of the ovaries of mud crabs at various stages of ovarian maturation. A total of 63.69 Gb of clean data was obtained, with a Q30 of 93.34%, and 81,893 unigenes were identified, including 10,996 differentially expressed genes (DEGs). After KEGG enrichment of these DEGs, MAPK signaling pathway was significantly enriched during vitellogenesis. Moreover, the expression levels of genes involved in carbohydrate, amino acid, and lipid metabolism were found to be higher during vitellogenesis. The two genes (Sp-Eip75B and Sp-Eip78C) that are homologous to the vertebrate gene PPARγ in the PPAR signaling pathway, were identified. Additionally, genes in MAPK signaling pathway might regulate lipid metabolism through PPAR signaling pathway based on Protein-Protein Interaction (PPI) network. These findings suggest that MAPK signaling pathway plays a critical role in lipid metabolism in the ovary during vitellogenesis, which provides new insights into the mechanism of lipid accumulation during ovarian maturation in mud crabs.

Heat-Killed Enterococcus faecalis Inhibit FL83B Hepatic Lipid Accumulation and High Fat Diet-Induced Fatty Liver Damage in Rats by Activating Lipolysis through the Regulation the AMPK Signaling Pathway

Continuous consumption of high-calorie meals causes lipid accumulation in the liver and liver damage, leading to non-alcoholic fatty liver disease (NAFLD). A case study of the hepatic lipid accumulation model is needed to identify the mechanisms underlying lipid metabolism in the liver. In this study, the prevention mechanism of lipid accumulation in the liver of Enterococcus faecalis 2001 (EF-2001) was extended using FL83B cells (FL83Bs) and high-fat diet (HFD)-induced hepatic steatosis. EF-2001 treatment inhibited the oleic acid (OA) lipid accumulation in FL83B liver cells. Furthermore, we performed lipid reduction analysis to confirm the underlying mechanism of lipolysis. The results showed that EF-2001 downregulated proteins and upregulated AMP-activated protein kinase (AMPK) phosphorylation in the sterol regulatory element-binding protein 1c (SREBP-1c) and AMPK signaling pathways, respectively. The effect of EF-2001 on OA-induced hepatic lipid accumulation in FL83Bs enhanced the phosphorylation of acetyl-CoA carboxylase and reduced the levels of lipid accumulation proteins SREBP-1c and fatty acid synthase. EF-2001 treatment increased the levels of adipose triglyceride lipase and monoacylglycerol during lipase enzyme activation, which, when increased, contributed to increased liver lipolysis. In conclusion, EF-2001 inhibits OA-induced FL83B hepatic lipid accumulation and HFD-induced hepatic steatosis in rats through the AMPK signaling pathway.