CHP1 Regulates Compartmentalized Glycerolipid Synthesis by Activating GPAT4.

Cells require a constant supply of fatty acids to survive and proliferate. Fatty acids incorporate into membrane and storage glycerolipids through a series of endoplasmic reticulum (ER) enzymes, but how these enzymes are regulated is not well understood. Here, using a combination of CRISPR-based genetic screens and unbiased lipidomics, we identified calcineurin B homologous protein 1 (CHP1) as a major regulator of ER glycerolipid synthesis. Loss of CHP1 severely reduces fatty acid incorporation and storage in mammalian cells and invertebrates. Mechanistically, CHP1 binds and activates GPAT4, which catalyzes the initial rate-limiting step in glycerolipid synthesis. GPAT4 activity requires CHP1 to be N-myristoylated, forming a key molecular interface between the two proteins. Interestingly, upon CHP1 loss, the peroxisomal enzyme, GNPAT, partially compensates for the loss of ER lipid synthesis, enabling cell proliferation. Thus, our work identifies a conserved regulator of glycerolipid metabolism and reveals plasticity in lipid synthesis of proliferating cells.

The GPAT4/6/8 clade functions in Arabidopsis root suberization nonredundantly with the GPAT5/7 clade required for suberin lamellae.

Lipid polymers such as cutin and suberin strengthen the diffusion barrier properties of the cell wall in specific cell types and are essential for water relations, mineral nutrition, and stress protection in plants. Land plant-specific glycerol-3-phosphate acyltransferases (GPATs) of different clades are central players in cutin and suberin monomer biosynthesis. Here, we show that the GPAT4/6/8 clade in Arabidopsis thaliana, which is known to mediate cutin formation, is also required for developmentally regulated root suberization, in addition to the established roles of GPAT5/7 in suberization. The GPAT5/7 clade is mainly required for abscisic acid-regulated suberization. In addition, the GPAT5/7 clade is crucial for the formation of the typical lamellated suberin ultrastructure observed by transmission electron microscopy, as distinct amorphous globular polyester structures were deposited in the apoplast of the gpat5 gpat7 double mutant, in contrast to the thinner but still lamellated suberin deposition in the gpat4 gpat6 gpat8 triple mutant. Site-directed mutagenesis revealed that the intrinsic phosphatase activity of GPAT4, GPAT6, and GPAT8, which leads to monoacylglycerol biosynthesis, contributes to suberin formation. GPAT5/7 lack an active phosphatase domain and the amorphous globular polyester structure observed in the gpat5 gpat7 double mutant was partially reverted by treatment with a phosphatase inhibitor or the expression of phosphatase-dead variants of GPAT4/6/8. Thus, GPATs that lack an active phosphatase domain synthetize lysophosphatidic acids that might play a role in the formation of the lamellated structure of suberin. GPATs with active and nonactive phosphatase domains appear to have nonredundant functions and must cooperate to achieve the efficient biosynthesis of correctly structured suberin.

Identification of a 1-acyl-glycerol-3-phosphate acyltransferase from Mycobacterium tuberculosis, a key enzyme involved in triacylglycerol biosynthesis.

Latent tuberculosis, caused by dormant Mycobacterium tuberculosis (Mtb), poses a threat to global health through the incubation of undiagnosed infections within the community. Dormant Mtb, which is phenotypically tolerant to antibiotics, accumulates triacylglycerol (TAG) utilizing fatty acids obtained from macrophage lipid droplets. TAG is vital to mycobacteria, serving as a cell envelope component and energy reservoir during latency. TAG synthesis occurs by sequential acylation of glycerol-3-phosphate, wherein the second acylation step is catalyzed by acylglycerol-3-phosphate acyltransferase (AGPAT), resulting in the production of phosphatidic acid (PA), a precursor for the synthesis of TAG and various phospholipids. Here, we have characterized a putative acyltransferase of Mtb encoded by Rv3816c. We found that Rv3816c has all four characteristic motifs of AGPAT, exists as a membrane-bound enzyme, and functions as 1-acylglycerol-3-phosphate acyltransferase. The enzyme could transfer the acyl group to acylglycerol-3-phosphate (LPA) from monounsaturated fatty acyl-coenzyme A of chain length 16 or 18 to produce PA. Complementation of Escherichia coli PlsC mutant in vivo by Rv3816c confirmed that it functions as AGPAT. Its active site mutants, H43A and D48A, were incapable of transferring the acyl group to LPA in vitro and were not able to rescue the growth defect of E. coli PlsC mutant in vivo. Identifying Rv3816c as AGPAT and comparing its properties with other AGPAT homologs is not only a step toward understanding the TAG biosynthesis in mycobacteria but has the potential to explore it as a drug target.

The functional divergence of homologous GPAT9 genes contributes to the erucic acid content of Brassica napus seeds.

BACKGROUND: The early allopolyploid Brassica napus was a hybrid of two Brassica species, that had undergone a whole genome duplication event followed by genome restructuring, including deletions and small scale duplications. A large number of homologous genes appeared functional divergence during species domestication. Due to the high conservation of de novo glycerolipid biosynthesis, multiple homologues of glycerol-3-phosphate acyltransferases (GPATs) have been found in B. napus. Moreover, the functional variances among these homologous GPAT-encoding genes are unclear. RESULTS: In this study, four B. napus homologous genes encoding glycerol-3-phosphate acyltransferase 9 (BnaGPAT9) were characterized. Although a bioinformatics analysis indicated high protein sequence similarity, the homologues demonstrated tissue-specific expression patterns and functional divergence. Yeast genetic complementation assays revealed that BnaGPAT9-A1/C1 homologues but not BnaGPAT9-A10/C9 homologues encoded functional GPAT enzymes. Furthermore, a single nucleotide polymorphism of BnaGPAT9-C1 that occurred during the domestication process was associated with enzyme activity and contributed to the fatty acid composition. The seed-specific expression of BnGPAT9-C11124A increased the erucic acid content in the transformant seeds. CONCLUSIONS: This study revealed that BnaGPAT9 gene homologues evolved into functionally divergent forms with important roles in erucic acid biosynthesis.

Microalgal glycerol-3-phosphate acyltransferase role in galactolipids and high-value storage lipid biosynthesis.

Glycerolipids are the most abundant lipids in microalgae, and glycerol-3-phosphate:acyl-CoA acyltransferase (GPAT) plays an important role in their biosynthesis. However, the biochemical and biological functions of algal GPAT remain poorly characterized. Here, we characterized the endoplasmic reticulum (ER)-associated GPAT of the model unicellular green alga Chlamydomonas reinhardtii (CrGPATer). Enzymatic assays indicated that CrGPATer is an sn-1 acyltransferase using a variety of acyl-CoAs as the acyl donor. Subcellular localization revealed that CrGPATer was associated with ER membranes and lipid droplets. We constructed overexpression (OE) and knockdown (KD) transgenic C. reinhardtii lines to investigate the in vivo function of CrGPATer. Lipidomic analysis indicated that CrGPATer OE enhanced the cellular content of galactolipids, especially monogalactosyldiacylglycerol, under nitrogen deficiency stress. Correspondingly, CrGPATer KD lines contained lower contents of galactolipids than the control. Feeding experiments with labeled phosphatidic acid revealed that the intermediate of the eukaryotic Kennedy pathway could be used for galactolipid biosynthesis in the chloroplasts. These results provided multiple lines of evidence that the eukaryotic Kennedy pathway mediated by CrGPATer may be involved in galactolipid biosynthesis in C. reinhardtii. OE of CrGPATer significantly increased the content of triacylglycerol and the yield of biomass. Moreover, the content and yield of 1, 3-olein-2-palmitin, a high-value lipid that can be used as an alternative for human milk fat in infant formula, were significantly enhanced in the OE transgenic lines. Taken together, this study provided insights into the biochemical and biological functions of CrGPATer and its potential as a genetic engineering target in functional lipid manufacturing.

GPAT1 Activity and Abundant Palmitic Acid Impair Insulin Suppression of Hepatic Glucose Production in Primary Mouse Hepatocytes.

BACKGROUND: Glycerol-3-phosphate acyltransferase (GPAT) activity is correlated with obesity and insulin resistance in mice and humans. However, insulin resistance exists in people with normal body weight, and individuals with obesity may be metabolically healthy, implying the presence of complex pathophysiologic mechanisms underpinning insulin resistance. OBJECTIVE: We asked what conditions related to GPAT1 must be met concurrently for hepatic insulin resistance to occur. METHODS: Mouse hepatocytes were overexpressed with GPATs via adenoviral infection or exposed to high or low concentrations of glucose. Glucose production by the cells and phosphatidic acid (PA) content in the cells were assayed, GPAT activity was measured, relative messenger RNA expressions of sterol-regulatory element-binding protein 1c (SREBP1c), carbohydrate response element-binding protein (ChREBP), and GPAT1 were analyzed, and insulin signaling transduction was examined. RESULTS: Overexpressing GPAT1 in mouse hepatocytes impaired insulin's suppression of glucose production, together with an increase in both N-ethylmaleimide-resistant GPAT activity and the content of di-16:0 PA. Akt-mediated insulin signaling was inhibited in hepatocytes that overexpressed GPAT1. When the cells were exposed to high-glucose concentrations, insulin suppression of glucose production was impaired, and adding palmitic acid exacerbated this impairment. High-glucose exposure increased the expression of SREBP1c, ChREBP, and GPAT1 by ∼2-, 5-, and 5.7-fold, respectively. The addition of 200 mM palmitic acid or linoleic acid to the culture media did not change the upregulation of expression of these genes by high glucose. High-glucose exposure increased di-16:0 PA content in the cells, and adding palmitic acid further increased di-16:0 PA content. The effect was specific to palmitic acid because linoleic acid did not show these effects. CONCLUSION: These data demonstrate that high-GPAT1 activity, whether induced by glucose exposure or acquired by transfection, and abundant palmitic acid can impair insulin's ability to suppress hepatic glucose production in primary mouse hepatocytes.

LncRNA ENSGALG00000021686 regulates fat metabolism in chicken hepatocytes via miR-146b/AGPAT2 pathway.

The liver contributes to lipid metabolism as the hub of fat synthesis. Long non-coding RNAs (lncRNAs) are considered the regulators of cellular processes. Since LncRNA ENSGALG00000021686 (lncRNA 21 686) has been described as a regulator of lipid metabolism, the present study aimed to clarify the role of lncRNA 21 686 in chicken hepatocytes' lipid metabolism. Thirty-two chickens were divided into four groups and were treated with diets containing different amounts of fat, and the hepatic expression of lncRNA 21 686 and miR-146b along with the levels of proteins involved in the regulation of fat metabolism, lipid indices and oxidative stress were measured. Moreover, primary chicken hepatocytes were transfected with lncRNA 21 686 small interfering RNA or microRNA (miRNA, miR)-146b mimics to measure the consequences of suppressing lncRNA or inducing miRNA expression on the levels of proteins involved in fat metabolism and stress markers. The results showed that the high-fat diet modulated the expression of lncRNA 21 686 and miR-146b (p-value < 0.001). Moreover, there was a significant increase in 1-acyl-sn-glycerol-3-phosphate acyltransferase 2 (AGPAT2) gene expression and protein levels and modulated fat-related markers. Furthermore, the results showed that lncRNA 21 686 suppression reduced the expression of AGPAT2 and its downstream proteins (p-value < 0.05). Overexpression of miR-146b regulated fat metabolism indicator expression. Transfection experiments revealed that lncRNA 21 686 suppression increased miR-146b expression. The findings suggested a novel mechanism containing lncRNA 21 686/miR-146b/AGPAT2 in the regulation of fat metabolism in chicken hepatocytes.

Identifying Residues for Substrate Recognition in Human GPAT4 by Molecular Dynamics Simulations.

Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the first step in triacylglycerol synthesis. Understanding its substrate recognition mechanism may help to design drugs to regulate the production of glycerol lipids in cells. In this work, we investigate how the native substrate, glycerol-3-phosphate (G3P), and palmitoyl-coenzyme A (CoA) bind to the human GPAT isoform GPAT4 via molecular dynamics simulations (MD). As no experimentally resolved GPAT4 structure is available, the AlphaFold model is employed to construct the GPAT4-substrate complex model. Using another isoform, GPAT1, we demonstrate that once the ligand binding is properly addressed, the AlphaFold complex model can deliver similar results to the experimentally resolved structure in MD simulations. Following the validated protocol of complex construction, we perform MD simulations using the GPAT4-substrate complex. Our simulations reveal that R427 is an important residue in recognizing G3P via a stable salt bridge, but its motion can bring the ligand to different binding hotspots on GPAT4. Such high flexibility can be attributed to the flexible region that exists only on GPAT4 and not on GPAT1. Our study reveals the substrate recognition mechanism of GPAT4 and hence paves the way towards designing GPAT4 inhibitors.

Genome-Wide Identification, Characterization, Evolutionary Analysis, and Expression Pattern of the GPAT Gene Family in Barley and Functional Analysis of HvGPAT18 under Abiotic Stress.

Glycerol-3-phosphoacyltransferase (GPAT) is an important rate-limiting enzyme in the biosynthesis of triacylglycerol (TAG), which is of great significance for plant growth, development, and response to abiotic stress. Although the characteristics of GPAT have been studied in many model plants, little is known about its expression profile and function in barley, especially under abiotic stress. In this study, 22 GPAT genes were identified in the barley genome and divided into three groups (I, II, III), with the latter Group III subdivided further into three subgroups based on the phylogenetic analysis. The analyses of conserved motifs, gene structures, and the three-dimensional structure of HvGPAT proteins also support this classification. Through evolutionary analysis, we determined that HvGPATs in Group I were the earliest to diverge during 268.65 MYA, and the differentiation of other HvGPATs emerged during 86.83-169.84 MYA. The tissue expression profile showed that 22 HvGPAT genes were almost not expressed in INF1 (inflorescence 1). Many functional elements related to stress responses and hormones in cis-element analysis, as well as qRT-PCR results, confirm that these HvGPAT genes were involved in abiotic stress responses. The expression level of HvGPAT18 was significantly increased under abiotic stress and its subcellular localization indicated its function in the endoplasmic reticulum. Various physiological traits under abiotic stress were evaluated using transgenic Arabidopsis to gain further insight into the role of HvGPAT18, and it was found that transgenic seedlings have stronger resistance under abiotic stress than to the wild-type (WT) plants. Overall, our results provide new insights into the evolution and function of the barley GPAT gene family and enable us to explore the molecular mechanism of functional diversity behind the evolutionary history of these genes.

Expression of glycerol-3-phosphate acyltransferase increases non-polar lipid accumulation in Nannochloropsis oceanica.

Microalgae are considered a suitable production platform for high-value lipids and oleochemicals. Several species including Nannochloropsis oceanica produce large amounts of essential [Formula: see text]-3 polyunsaturated fatty acids (PUFAs) which are integral components of food and feed and have been associated with health-promoting effects. N. oceanica can further accumulate high contents of non-polar lipids with chemical properties that render them a potential replacement for plant oils such as palm oil. However, biomass and lipid productivities obtained with microalgae need to be improved to reach commercial feasibility. Genetic engineering can improve biomass and lipid productivities, for instance by increasing carbon flux to lipids. Here, we report the overexpression of glycerol-3-phosphate acyltransferase (GPAT) in N. oceanica during favorable growth conditions as a strategy to increase non-polar lipid content. Transformants overproducing either an endogenous (NoGPAT) or a heterologous (Acutodesmus obliquus GPAT) GPAT enzyme targeted to the endoplasmic reticulum had up to 42% and 51% increased non-polar lipid contents, respectively, compared to the wild type. Biomass productivities of transformant strains were not substantially impaired, resulting in lipid productivities that were increased by up to 37% and 42% for NoGPAT and AoGPAT transformants, respectively. When exposed to nutrient stress, transformants and wild type had similar lipid contents, suggesting that GPAT enzyme exerts strong flux control on lipid synthesis in N. oceanica under favorable growth conditions. NoGPAT transformants further accumulated PUFAs in non-polar lipids, reaching a total of 6.8% PUFAs per biomass, an increase of 24% relative to the wild type. Overall, our results indicate that GPAT is an interesting target for engineering of lipid metabolism in microalgae, in order to improve non-polar lipid and PUFAs accumulation in microalgae.

Oleic Acid Promotes the Biosynthesis of 10-Hydroxy-2-decenoic Acid via Species-Selective Remodeling of TAGs in Apis mellifera ligustica.

This study aimed to assess the impact of oleic acid (OA) supplementation on the biosynthesis of 10-hydroxy-2-decenoic acid (10-HDA) in Apis mellifera ligustica. In experiment 1, varying concentrations of OA (2%, 4%, 6% and 8%) were added to an artificial diet for newly emerged bees reared in cages. Analysis of 10-HDA content and gene expression in the mandibular gland (MG) revealed that the 8% OA treatment had the greatest impact on promoting the synthesis of 10-HDA. Subsequent investigations utilized RNA-seq and lipidomics to characterize the molecular signature in the MG after feeding the 8% OA diet. Phosphatidylcholine (PC) and triacylglycerol (TAG) were found to be the predominant lipids in the MG of worker bees. A total of 154 TAGs were identified, with TAG (18:1-18:1-18:1) exhibiting the highest abundance, which increased by 1.5 times. The major TAG species contained palmitic acid (16:0) and oleic acid (18:1) in their structure, which was associated with fatty acid composition of diet. The increase in abundance of main TAGs may be attributed to the upregulation of glycerol-3-phosphate acyltransferase (Gpat) and glycerol kinase (GK) gene expression at the transcriptional level. The upregulation of differentially expressed genes (DEGs) related to carbohydrate metabolism may contribute to meeting the heightened metabolic demands of the MGs in worker bees. Royal jelly (RJ) samples from bee colonies fed with the 8% OA diet exhibited higher 10-HDA level than RJ collected from bee colonies fed with the artificial diet. These results indicate that 8% OA addition in the diet enhanced biosynthesis of 10-HDA in the mandibular gland, which was accompanied by significant and highly species-selective remodeling of TAGs.

Genome-Wide Analysis of Glycerol-3-Phosphate Acyltransferase (GPAT) Family in Perilla frutescens and Functional Characterization of PfGPAT9 Crucial for Biosynthesis of Storage Oils Rich in High-Value Lipids.

Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the first step in triacylglycerol (TAG) biosynthesis. However, GPAT members and their functions remain poorly understood in Perilla frutescens, a special edible-medicinal plant with its seed oil rich in polyunsaturated fatty acids (mostly α-linolenic acid, ALA). Here, 14 PfGPATs were identified from the P. frutescens genome and classified into three distinct groups according to their phylogenetic relationships. These 14 PfGPAT genes were distributed unevenly across 11 chromosomes. PfGPAT members within the same subfamily had highly conserved gene structures and four signature functional domains, despite considerable variations detected in these conserved motifs between groups. RNA-seq and RT-qPCR combined with dynamic analysis of oil and FA profiles during seed development indicated that PfGPAT9 may play a crucial role in the biosynthesis and accumulation of seed oil and PUFAs. Ex vivo enzymatic assay using the yeast expression system evidenced that PfGPAT9 had a strong GPAT enzyme activity crucial for TAG assembly and also a high substrate preference for oleic acid (OA, C18:1) and ALA (C18:3). Heterogeneous expression of PfGPAT9 significantly increased total oil and UFA (mostly C18:1 and C18:3) levels in both the seeds and leaves of the transgenic tobacco plants. Moreover, these transgenic tobacco lines exhibited no significant negative effect on other agronomic traits, including plant growth and seed germination rate, as well as other morphological and developmental properties. Collectively, our findings provide important insights into understanding PfGPAT functions, demonstrating that PfGPAT9 is the desirable target in metabolic engineering for increasing storage oil enriched with valuable FA profiles in oilseed crops.

Glycerol-3-Phosphate Acyltransferase GPAT9 Enhanced Seed Oil Accumulation and Eukaryotic Galactolipid Synthesis in Brassica napus.

Glycerol-3-phosphate acyltransferase GPAT9 catalyzes the first acylation of glycerol-3-phosphate (G3P), a committed step of glycerolipid synthesis in Arabidopsis. The role of GPAT9 in Brassica napus remains to be elucidated. Here, we identified four orthologs of GPAT9 and found that BnaGPAT9 encoded by BnaC01T0014600WE is a predominant isoform and promotes seed oil accumulation and eukaryotic galactolipid synthesis in Brassica napus. BnaGPAT9 is highly expressed in developing seeds and is localized in the endoplasmic reticulum (ER). Ectopic expression of BnaGPAT9 in E. coli and siliques of Brassica napus enhanced phosphatidic acid (PA) production. Overexpression of BnaGPAT9 enhanced seed oil accumulation resulting from increased 18:2-fatty acid. Lipid profiling in developing seeds showed that overexpression of BnaGPAT9 led to decreased phosphatidylcholine (PC) and a corresponding increase in phosphatidylethanolamine (PE), implying that BnaGPAT9 promotes PC flux to storage triacylglycerol (TAG). Furthermore, overexpression of BnaGPAT9 also enhanced eukaryotic galactolipids including monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), with increased 36:6-MGDG and 36:6-DGDG, and decreased 34:6-MGDG in developing seeds. Collectively, these results suggest that ER-localized BnaGPAT9 promotes PA production, thereby enhancing seed oil accumulation and eukaryotic galactolipid biosynthesis in Brassica napus.

Glycerol-3-phosphate acyltransferases and metabolic syndrome: recent advances and future perspectives.

Triglycerol-3-phosphate acyltransferases (GPATs) are the key enzymes in the first step of the synthesis of triacylglycerol (TAG). In mammals, there are four isoforms of GPATs. GPAT1 and GPAT2 are localised in the outer mitochondrial membrane, while GPAT3 and GPAT4 are localised in the endoplasmic reticulum. Previous research has emphasised that GPAT plays a critical effect on the development of metabolic syndromes, such as liver steatosis, obesity, and insulin resistance. In this review, we will critically evaluate the regulatory effects of GPATs isoforms in metabolic syndrome. In addition, we also discuss perspectives on clinical intervention strategies for the neurometabolic disease.

Metabolically Distinct Pools of Phosphatidylcholine Are Involved in Trafficking of Fatty Acids out of and into the Chloroplast for Membrane Production.

The eukaryotic pathway of galactolipid synthesis involves fatty acid synthesis in the chloroplast, followed by assembly of phosphatidylcholine (PC) in the endoplasmic reticulum (ER), and then turnover of PC to provide a substrate for chloroplast galactolipid synthesis. However, the mechanisms and classes of lipids transported between the chloroplast and the ER are unclear. PC, PC-derived diacylglycerol, phosphatidic acid, and lyso-phosphatidylcholine (LPC) have all been implicated in ER-to-chloroplast lipid transfer. LPC transport requires lysophosphatidylcholine acyltransferase (LPCAT) activity at the chloroplast to form PC before conversion to galactolipids. However, LPCAT has also been implicated in the opposite chloroplast-to-ER trafficking of newly synthesized fatty acids through PC acyl editing. To understand the role of LPC and LPCAT in acyl trafficking we produced and analyzed the Arabidopsis (Arabidopsis thaliana) act1 lpcat1 lpcat2 triple mutant. LPCAT1 and LPCAT2 encode the major lysophospholipid acyltransferase activity of the chloroplast, and it is predominantly for incorporation of nascent fatty acids exported form the chloroplast into PC by acyl editing. In vivo acyl flux analysis revealed eukaryotic galactolipid synthesis is not impaired in act1 lpcat1 lpcat2 and uses a PC pool distinct from that of PC acyl editing. We present a model for the eukaryotic pathway with metabolically distinct pools of PC, suggesting an underlying spatial organization of PC metabolism as part of the ER-chloroplast metabolic interactions.

Identification of a promoter polymorphism affecting GPAT3 gene expression that is likely related to intramuscular fat content in pigs.

The intramuscular fat content (IMF) is an economically important trait in pigs and the Laiwu pig is famous for its excessively extremely high level of IMF. Our previous transcriptome study revealed that the dynamic expression of glycerol-phosphate acyltransferase 3 (GPAT3) is consistent with changes in the IMF of Laiwu pigs. In this study, we further analyzed the expression and polymorphism of GPAT3 in its promoter region. The results indicated that the expression of GPAT3 increased dramatically from 120 to 240 days and is consistent with changes in IMF deposition, and at both mRNA and protein levels, GPAT3 expression was markedly higher in the LD muscle of Laiwu pigs than that of Duroc × Landrace × Yorkshire pigs. Deletion from -1695 to -1187 of porcine GPAT3 greatly increased its transcription. Of the two SNPs identified, the transition from C to T at -1526 site increased the transcription of porcine GPAT3 and allele T mainly distributed in Laiwu pig population. These results collectively suggest that the SNP at -1526 site of GPAT3 may contribute to IMF deposition by affecting its expression in pigs.

[Identification of GPAT1-dependent mitochondrial metabolism as a novel therapeutic target for AML].

Recent studies have demonstrated that cancer-specific metabolism plays a crucial role in a variety of malignancies, including acute myeloid leukemia (AML). To identify a novel therapeutic target for AML, we conducted a metabolite screen on AML cells and normal hematopoietic stem/progenitor cells (HSPCs) and detected that the metabolism of glycerol-3-phosphate (G3P) is reprogrammed in AML. Glycerol-3-phosphate acyltransferases (GPATs), the first and rate-limiting enzymes in the lipid biosynthesis pathway, convert G3P into lysophosphatidic acid (LPA). Among various GPAT isozymes, GPAT1 was highly expressed in AML cells and silencing it inhibited the cell growth of AML. GPAT1 is located on the outer membrane of the mitochondria and regulates mitochondrial fusion and oxidative phosphorylation (OXPHOS). Silencing GPAT1 promoted mitochondrial fission and reduced OXPHOS. In AML, the GPAT1 inhibitor also suppressed cell proliferation and mitochondrial metabolism. However, this inhibitor had no effect on normal hematopoiesis in vivo. In conclusion, these findings indicate that targeting GPAT1 may be a promising therapeutic strategy for AML, since it suppresses leukemia-specific metabolism without impairing normal HSPCs.

LncRNA MSC-AS1 facilitates lung adenocarcinoma through sponging miR-33b-5p to up-regulate GPAM.

Many reports have indicated that long non-coding RNAs (lncRNAs) are closely associated with the occurrence and development of various cancers. Musculin antisense RNA 1 (MSC-AS1) is a an lncRNA known to act as an oncogene in several types of human cancers; however, its specific function in lung adenocarcinoma (LUAD) is still unclear. For this study, we designed and conducted experiments to clarify the function of the lncRNA MSC-AS1 in LUAD and its underlying mechanisms. We found that the expression of MSC-AS1 was significantly higher in LUAD tissues and cells than that in normal ones. Through loss-of function assays, we confirmed that the proliferation of LUAD cells was significantly restrained by down-regulation of MSC-AS1 and the rate of cell apoptosis was accelerated. The results from our mechanistic experiments showed that MSC-AS1 interacts with microRNA-33b-5p (miR-33b-5p). Moreover, glycerol-3-phosphate acyltransferase, mitochondrial (GPAM) was found to be a direct target gene of miR-33b-5p, and it has similar functions to MSC-AS1. Further, inhibition of miR-33b-5p or overexpression GPAM reversed the inhibitory effects of MSC-AS1 silencing on LUAD cell growth. In short, MSC-AS1 facilitates LUAD progression through sponging miR-33b-5p to up-regulate GPAM.

The role of increased FGF21 in VLDL-TAG secretion and thermogenic gene expression in mice under protein malnutrition.

Protein malnutrition promotes hepatic lipid accumulation in growing animals. In these animals, fibroblast growth factor 21 (FGF21) rapidly increases in the liver and circulation and plays a protective role in hepatic lipid accumulation. To investigate the mechanism by which FGF21 protects against liver lipid accumulation under protein malnutrition, we determined whether upregulated FGF21 promotes the thermogenesis or secretion of very-low-density lipoprotein (VLDL)-triacylglycerol (TAG). The results showed that protein malnutrition decreased VLDL-TAG secretion, but the upregulation of FGF21 did not oppose this effect. In addition, protein malnutrition increased expression of the thermogenic gene uncoupling protein 1 in inguinal white adipose and brown adipose tissue in an FGF21-dependent manner. However, surgically removing inguinal white adipose tissue did not affect liver triglyceride levels in protein-malnourished mice. These data suggest that FGF21 stimulates thermogenesis under protein malnutrition, but this is not the causative factor underlying the protective role of FGF21 against liver lipid accumulation.

A GPAT1 Mutation in Arabidopsis Enhances Plant Height but Impairs Seed Oil Biosynthesis.

Glycerol-3-phosphate acyltransferases (GPATs) play an important role in glycerolipid biosynthesis, and are mainly involved in oil production, flower development, and stress response. However, their roles in regulating plant height remain unreported. Here, we report that Arabidopsis GPAT1 is involved in the regulation of plant height. GUS assay and qRT-PCR analysis in Arabidopsis showed that GPAT1 is highly expressed in flowers, siliques, and seeds. A loss of function mutation in GPAT1 was shown to decrease seed yield but increase plant height through enhanced cell length. Transcriptomic and qRT-PCR data revealed that the expression levels of genes related to gibberellin (GA) biosynthesis and signaling, as well as those of cell wall organization and biogenesis, were significantly upregulated. These led to cell length elongation, and thus, an increase in plant height. Together, our data suggest that knockout of GPAT1 impairs glycerolipid metabolism in Arabidopsis, leading to reduced seed yield, but promotes the biosynthesis of GA, which ultimately enhances plant height. This study provides new evidence on the interplay between lipid and hormone metabolism in the regulation of plant height.