Aberrant accumulation of ceramides in mitochondria triggers cell death by inducing autophagy in Arabidopsis.

Sphingolipids are membrane lipids and play critical roles in signal transduction. Ceramides are central components of sphingolipid metabolism that are involved in cell death. However, the mechanism of ceramides regulating cell death in plants remains unclear. Here, we found that ceramides accumulated in mitochondria of accelerated cell death 5 mutant (acd5), and expression of mitochondrion-localized ceramide kinase (ACD5) suppressed mitochondrial ceramide accumulation and the acd5 cell death phenotype. Using immuno-electron microscopy, we observed hyperaccumulation of ceramides in acer acd5 double mutants, which are characterized by mutations in both ACER (alkaline ceramidase) and ACD5 genes. The results confirmed that plants with specific ceramide accumulation exhibited localization of ceramides to mitochondria, resulting in an increase in mitochondrial reactive oxygen species production. Interestingly, when compared with the wild type, autophagy-deficient mutants showed stronger resistance to ceramide-induced cell death. Lipid profiling analysis demonstrated that plants with ceramide accumulation exhibited a significant increase in phosphatidylethanolamine levels. Furthermore, exogenous ceramide treatment or endogenous ceramide accumulation induces autophagy. When exposed to exogenous ceramides, an increase in the level of the autophagy-specific ubiquitin-like protein, ATG8e, associated with mitochondria, where it directly bound to ceramides. Taken together, we propose that the accumulation of ceramides in mitochondria can induce cell death by regulating autophagy.

Ceramides regulate defense response by binding to RbohD in Arabidopsis.

Sphingolipids, a class of bioactive lipids, play a critical role in signal transduction. Ceramides, which are central components of sphingolipid metabolism, are involved in plant development and defense. However, the mechanistic link between ceramides and downstream signaling remains unclear. Here, the mutation of alkaline ceramidase in a ceramide kinase mutant acd5 resulted in spontaneous programmed cell death early in development and was accompanied by ceramide accumulation, while other types of sphingolipids, such as long chain base, glucosylceramide, and glycosyl inositol phosphorylceramide, remained at the same level as the wild-type plants. Analysis of the transcriptome indicated that genes related to the salicylic acid (SA) pathway and oxidative stress pathway were induced dramatically in acer acd5 plants. Comparison of the level of reactive oxygen species (ROS), SA, and ceramides in the wild-type and acer acd5 plants at different developmental stages indicated that the acer acd5 mutant exhibited constitutive activation of SA and ROS signaling, which occurred simultaneously with the alteration of ceramides. Overexpressing NahG in the acer acd5 mutant could completely suppress its cell death and ceramide accumulation, while benzo-(1,2,3)-thiadiazole-7-carbothioc acid S-methyl ester treatment restored its phenotype again. Moreover, we found that the plasma membrane of acer acd5 mutant was the main site of ROS production. Ceramides accumulated in the plasma membrane of acer acd5, directly binding and activating the NADPH oxidase RbohD and promoting hydrogen peroxide generation and SA- or defense-related gene activation. Our data illustrated that ceramides play an essential role in plant defense.

Orosomucoid Proteins Interact with the Small Subunit of Serine Palmitoyltransferase and Contribute to Sphingolipid Homeostasis and Stress Responses in Arabidopsis.

Serine palmitoyltransferase (SPT), a pyridoxyl-5'-phosphate-dependent enzyme, catalyzes the first and rate-limiting step in sphingolipid biosynthesis. In humans and yeast, orosomucoid proteins (ORMs) negatively regulate SPT and thus play an important role in maintaining sphingolipid levels. Despite the importance of sphingoid intermediates as bioactive molecules, the regulation of sphingolipid biosynthesis through SPT is not well understood in plants. Here, we identified and characterized the Arabidopsis thaliana ORMs, ORM1 and ORM2. Loss of function of both ORM1 and ORM2 (orm1 amiR-ORM2) stimulated de novo sphingolipid biosynthesis, leading to strong sphingolipid accumulation, especially of long-chain bases and ceramides. Yeast two-hybrid, bimolecular fluorescence complementation, and coimmunoprecipitation assays confirmed that ORM1 and ORM2 physically interact with the small subunit of SPT (ssSPT), indicating that ORMs inhibit ssSPT function. We found that orm1 amiR-ORM2 plants exhibited an early-senescence phenotype accompanied by H2O2 production at the cell wall and in mitochondria, active vesicular trafficking, and formation of cell wall appositions. Strikingly, the orm1 amiR-ORM2 plants showed increased expression of genes related to endoplasmic reticulum stress and defenses and also had enhanced resistance to oxidative stress and pathogen infection. Taken together, our findings indicate that ORMs interact with SPT to regulate sphingolipid homeostasis and play a pivotal role in environmental stress tolerance in plants.

Loss of alkaline ceramidase inhibits autophagy in Arabidopsis and plays an important role during environmental stress response.

Sphingolipids, a class of bioactive lipids found in cell membranes, can modulate the biophysical properties of the membranes and play a critical role in signal transduction. Sphingolipids are involved in autophagy in humans and yeast, but their role in autophagy in plants is not well understood. In this study, we reported that the AtACER, an alkaline ceramidase that hydrolyses ceramide to long-chain base (LCB), functions in autophagy process in Arabidopsis. Our empirical data showed that the loss of AtACER inhibited autophagy, and its overexpression promoted autophagy under nutrient, salinity, and oxidative stresses. Interestingly, nitrogen deprivation significantly affected the sphingolipid's profile in Arabidopsis thaliana, especially the LCBs. Furthermore, the exogenous application of LCBs also induced autophagy. Our findings revealed a novel function of AtACER, where it was found to involve in the autophagy process, thus, playing a crucial role in the maintenance of a dynamic loop between sphingolipids and autophagy for cellular homeostasis under various environmental stresses.

Unsaturation of very-long-chain ceramides protects plant from hypoxia-induced damages by modulating ethylene signaling in Arabidopsis.

Lipid remodeling is crucial for hypoxic tolerance in animals, whilst little is known about the hypoxia-induced lipid dynamics in plants. Here we performed a mass spectrometry-based analysis to survey the lipid profiles of Arabidopsis rosettes under various hypoxic conditions. We observed that hypoxia caused a significant increase in total amounts of phosphatidylserine, phosphatidic acid and oxidized lipids, but a decrease in phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Particularly, significant gains in the polyunsaturated species of PC, PE and phosphatidylinositol, and losses in their saturated and mono-unsaturated species were evident during hypoxia. Moreover, hypoxia led to a remarkable elevation of ceramides and hydroxyceramides. Disruption of ceramide synthases LOH1, LOH2 and LOH3 enhanced plant sensitivity to dark submergence, but displayed more resistance to submergence under light than wild type. Consistently, levels of unsaturated very-long-chain (VLC) ceramide species (22:1, 24:1 and 26:1) predominantly declined in the loh1, loh2 and loh3 mutants under dark submergence. In contrast, significant reduction of VLC ceramides in the loh1-1 loh3-1 knockdown double mutant and lacking of VLC unsaturated ceramides in the ads2 mutants impaired plant tolerance to both dark and light submergences. Evidence that C24:1-ceramide interacted with recombinant CTR1 protein and inhibited its kinase activity in vitro, enhanced ER-to-nucleus translocation of EIN2-GFP and stabilization of EIN3-GFP in vivo, suggests a role of ceramides in modulating CTR1-mediated ethylene signaling. The dark submergence-sensitive phenotypes of loh mutants were rescued by a ctr1-1 mutation. Thus, our findings demonstrate that unsaturation of VLC ceramides is a protective strategy for hypoxic tolerance in Arabidopsis.

Loss of ceramide kinase in Arabidopsis impairs defenses and promotes ceramide accumulation and mitochondrial H2O2 bursts.

Arabidopsis thaliana plants that lack ceramide kinase, encoded by ACCELERATED CELL DEATH5 (ACD5), display spontaneous programmed cell death late in development and accumulate substrates of ACD5. Here, we compared ceramide accumulation kinetics, defense responses, ultrastructural features, and sites of reactive oxygen species (ROS) production in wild-type and acd5 plants during development and/or Botrytis cinerea infection. Quantitative sphingolipid profiling indicated that ceramide accumulation in acd5 paralleled the appearance of spontaneous cell death, and it was accompanied by autophagy and mitochondrial ROS accumulation. Plants lacking ACD5 differed significantly from the wild type in their responses to B. cinerea, showing earlier and higher increases in ceramides, greater disease, smaller cell wall appositions (papillae), reduced callose deposition and apoplastic ROS, and increased mitochondrial ROS. Together, these data show that ceramide kinase greatly affects sphingolipid metabolism and the site of ROS accumulation during development and infection, which likely explains the developmental and infection-related cell death phenotypes. The acd5 plants also showed an early defect in restricting B. cinerea germination and growth, which occurred prior to the onset of cell death. This early defect in B. cinerea restriction in acd5 points to a role for ceramide phosphate and/or the balance of ceramides in mediating early antifungal responses that are independent of cell death.

The Arabidopsis ceramidase AtACER functions in disease resistance and salt tolerance.

Ceramidases hydrolyze ceramide into sphingosine and fatty acids. In mammals, ceramidases function as key regulators of sphingolipid homeostasis, but little is known about their roles in plants. Here we characterize the Arabidopsis ceramidase AtACER, a homolog of human alkaline ceramidases. The acer-1 T-DNA insertion mutant has pleiotropic phenotypes, including reduction of leaf size, dwarfing and an irregular wax layer, compared with wild-type plants. Quantitative sphingolipid profiling showed that acer-1 mutants and the artificial microRNA-mediated silenced line amiR-ACER-1 have high ceramide levels and decreased long chain bases. AtACER localizes predominantly to the endoplasmic reticulum, and partially to the Golgi complex. Furthermore, we found that acer-1 mutants and AtACER RNAi lines showed increased sensitivity to salt stress, and lines overexpressing AtACER showed increased tolerance to salt stress. Reduction of AtACER also increased plant susceptibility to Pseudomonas syringae. Our data highlight the key biological functions of ceramidases in biotic and abiotic stresses in plants.

Arabidopsis acyl-CoA-binding protein ACBP3 participates in plant response to hypoxia by modulating very-long-chain fatty acid metabolism.

In Arabidopsis thaliana, acyl-CoA-binding proteins (ACBPs) are encoded by a family of six genes (ACBP1 to ACBP6), and are essential for diverse cellular activities. Recent investigations suggest that the membrane-anchored ACBPs are involved in oxygen sensing by sequestration of group VII ethylene-responsive factors under normoxia. Here, we demonstrate the involvement of Arabidopsis ACBP3 in hypoxic tolerance. ACBP3 transcription was remarkably induced following submergence under both dark (DS) and light (LS) conditions. ACBP3-overexpressors (ACBP3-OEs) showed hypersensitivity to DS, LS and ethanolic stresses, with reduced transcription of hypoxia-responsive genes as well as accumulation of hydrogen peroxide in the rosettes. In contrast, suppression of ACBP3 in ACBP3-KOs enhanced plant tolerance to DS, LS and ethanol treatments. By analyses of double combinations of OE-1 with npr1-5, coi1-2, ein3-1 as well as ctr1-1 mutants, we observed that the attenuated hypoxic tolerance in ACBP3-OEs was dependent on NPR1- and CTR1-mediated signaling pathways. Lipid profiling revealed that both the total amounts and very-long-chain species of phosphatidylserine (C42:2- and C42:3-PS) and glucosylinositolphosphorylceramides (C22:0-, C22:1-, C24:0-, C24:1-, and C26:1-GIPC) were significantly lower in ACBP3-OEs but increased in ACBP3-KOs upon LS exposure. By microscale thermophoresis analysis, the recombinant ACBP3 protein bound VLC acyl-CoA esters with high affinities in vitro. Further, a knockout mutant of MYB30, a master regulator of very-long-chain fatty acid (VLCFA) biosynthesis, exhibited enhanced sensitivities to LS and ethanolic stresses, phenotypes that were ameliorated by ACBP3-RNAi. Taken together, these findings suggest that Arabidopsis ACBP3 participates in plant response to hypoxia by modulating VLCFA metabolism.

[Role of serum 25-hydroxyvitamin D in the diagnosis of vitamin D deficiency rickets].

OBJECTIVE: To study the role of serum 25-hydroxyvitamin D in the early diagnosis of vitamin D deficiency rickets. METHODS: Concentrations of serum 25(OH)D, calcium, phosphorus and alkaline phosphatase were measured in normal control (n=73), suspected rickets (n=45) and confirmed rickets groups (n=65). Receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of serum 25(OH)D for rickets. RESULTS: Serum 25(OH)D levels in the suspected and confirmed rickets groups were 83±30 and 72±31 nmol/L respectively, which was lower than in the normal control group (112±37 nmol/L) (P<0.01). There was no significant difference between the suspected and confirmed rickets groups (P>0.05). Vitamin D deficiency rates in the suspected and confirmed rickets groups were higher than in the control group (P<0.01). The ROC curve area of serum 25(OH)D for the diagnosis of rickets was 0.760 (95%CI 0.692-0.820, P<0.01), and the optimal operating point was 90.70 nmol/L (sensitivity 68.49%, specificity 72.73%). There was no significant difference in levels of calcium, phosphorus and alkaline phosphatase between the three groups (P>0.05). CONCLUSIONS: Serum 25(OH)D levels in infants with suspected and confirmed rickets are significantly reduced and this may reflect vitamin D deficiency . Therefore, it may be useful to check serum 25(OH)D levels in screening for rickets.

Unusual patterns of neural tube defects in a high risk region of northern China.

OBJECTIVE: To study the prevalence of different types of neural tube defects (NTDs) in Luliang Prefecture, Shanxi province, where the prevalence of NTDs is unusually high and the correlation between NTDs prevalence and patterns. METHODS: A surveillance population-based birth defects was performed in Luliang Prefecture, Shanxi province. RESULTS: The results of our study showed that the prevalence of NTDs was 2-fold higher in Luliang Prefecture than in other areas of Shanxi province. Unusual patterns of NTDs were found, however, multiple NTDs were relatively common in Luliang Prefecture, accounting for over 13% of all NTDs cases in China. CONCLUSION: The prevalence of NTDs is associated with its patterns.

[DNA methyltransferases: classification, functions and research progress].

DNA methylation is a postreplicative modification occurred in most prokaryotic and eukaryotic genomes, which has a variety of important biological functions including regulation of gene expression, gene imprinting, preservation of chromosomal integrity, and X-chromosome inactivation. According to their structure and functions, DNA methyltransferases (Dnmts) are divided into two major families in mammalian cells: maintenance methyltransferase (Dnmt1) and de novo methyltransferases (Dnmt3a, Dnmt3b, and Dnmt3L). In addition, Dnmt2 also displays weak DNA methyltransferase catalytic activity, but newly founded function is to methylate cytosine 38 in the anti-codon loop of tRNAAsp. These Dnmts are crucial for mammalian growth and development. Dnmts deficiency will lead to embryonic development defects, cancer, and other diseases. Therefore, Dnmts could be important therapeutical targets. This article summarizes the classification, function, and recent research progress in DNA methyltransferases.

Simultaneous quantification of 11 pivotal metabolites in neural tube defects by HPLC-electrospray tandem mass spectrometry.

One-carbon metabolism that involves folate metabolism and homocysteine metabolism plays a powerful role in embryonic development. Any impairment to this metabolism during the neurulation process would trigger the occurrence of neural tube defects (NTDs). The great importance of one-carbon metabolism necessitates the establishment of methodology to determine the relative compounds involved in the metabolic cycles. We have developed a sensitive method for measurement of 11 pivotal compounds by using high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS/MS) in sera of pregnant women. Use of an aqueous chromatography column increased retention time and separation of the polar compounds in the system, resulting in fewer co-elution and interference from the other compounds that can lead to ion suppression. Calibration curves suitable for the analysis of maternal serum were linear (r(2)>0.997) with limits of detection from 0.05 to 1ng/mL. Intra-day coefficients of variation (CVs) and inter-day CVs were both lower than 11%. With the developed method, 96 serum samples including 46 cases and 50 controls were analyzed. The established method provided a reliable method for quantifying most of the compounds involved in the one-carbon metabolism simultaneously, thus made it possible to elucidate NTDs with multiple factors instead of one single and provided a solid foundation for the diagnosis and prevention of NTDs as well as some other one-carbon metabolism related diseases.

Detection of metastatic cancer cells in mesentery of colorectal cancer patients.

AIM: To detect the existence of isolated cancer cells in the mesentery of colorectum (named as Metastasis V), and investigate its clinical significance in colorectal cancer (CRC) patients. METHODS: Sixty-three CRC patients who received radical excision between January 2012 and September 2015 were included. All the patients underwent laparoscopy-assisted radical colorectomy or proctectomy [with complete mesocolic excision (CME) or total mesorectal excision (TME)] with R0 dissections at the Department of Gastrointestinal Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology. The location and size of the primary lesions were recorded immediately after the tumor was removed, with the surrounding mesenterium completely separated along the intestinal wall. Each dissected mesentery sample was analyzed for hematoxylin-eosin staining and immunohistochemistry using cytokeratin 19 antibody. Image Pro Plus Software 6.0 (Media Cybernetics, CA, United States) was used to semi-quantitatively measure the concentration of the cytokeratin 19 immunohistochemistry. The correlation between metastasis found in mesentery and clinicopathological characteristics was examined. The prognosis of patients was also evaluated by preoperative serum CEA level. RESULTS: Metastasis V was detected in 14 of 63 (22.2%) CRC patients who underwent laparoscopy-assisted radical colorectomy or proctectomy (with CME or TME) with R0 dissection in our hospital between January 2012 and September 2015. There was no significant difference in age, gender, tumor size, and tumor location in patients with Metastasis V (P > 0.05). Metastasis V was more likely to occur in poorly differentiated tumor (5/11; 45.5%) than moderately (8/46; 17.4%) and well- differentiated one (1/6; 16.7%). The Metastasis V in N2 stage (9/14; 64.3%) was more frequent that in the N0 stage (3/35; 8.6%) or N1 stages (2/14; 14.3%). In addition, Metastasis V was positively related to the tumor invasive depth (T1:0/1, 0%; T2:1/12, 8.3%; T3:7/39, 17.9%; T4:6/11, 54.5%). Furthermore, preoperative serum CEA level in Metastasis V-positive patients was significantly higher than in Metastasis V-negative patients (4.27 ng/mL vs 3.00 ng/mL). CONCLUSION: Metastasis V might be associated with a poor prognosis of CRC patients.

[DNA methylation: an epigenetic mechanism for tumorigenesis].

DNA methylation is a kind of epigenetic modification in human genome. Both hypermethylation of tumor suppressor gene or DNA repair gene and hypomethylation of repetitious DNA are closely related to different kinds of tumors. Loss of imprinting can also cause tumorigenesis. The recent study confirmed that the level of DNA methylation in genome was not only affected by DNA methyltransferase(DNMT), but also by other factors such as histone modification, diet and environment and RNA interference, etc. DNA methylation has an important role in transcriptional regulation, together with histone modification and chromatin remodeling.

Tetrandrine inhibits activation of rat hepatic stellate cells in vitro via transforming growth factor-beta signaling.

AIM: To investigate the effect of various concentrations of tetrandrine on activation of quiescent rat hepatic stellate cells (HSCs) and transforming growth factor-beta (TGF-beta) signaling in vitro. METHODS: HSCs were isolated from rats by in situ perfusion of liver and 18% Nycodenz gradient centrifugation, and primarily cultured on uncoated plastic plates for 24 h with DMEM containing 20% fetal bovine serum (FBS/DMEM) before the culture medium was substituted with 2% FBS/DMEM for another 24 h. Then, the HSCs were cultured in 2% FBS/DMEM with tetrandrine (0.25, 0.5, 1, 2 mg/L, respectively). Cell morphological features were observed under an inverted microscope, smooth muscle-alpha-actin (alpha-SMA) was detected by immunocytochemistry and image analysis system, laminin (LN) and type III procollagen (PCIII) in supernatants were determined by radioimmunoassay. TGF-beta1 mRNA, Smad 7 mRNA and Smad 7 protein were analyzed with RT-PCR and Western blotting, respectively. RESULTS: Tetrandrine at the concentrations of 0.25-2 mg/L prevented morphological transformation of HSC from the quiescent state to the activated one, while alpha-SMA, LN and PCIII expressions were inhibited. As estimated by gray values, the expression of alpha-SMA in tetrandrine groups (0.25, 0.5, 1, 2 mg/L) was reduced from 21.3% to 42.2% (control: 0.67, tetrandrine groups: 0.82, 0.85, 0.96, or 0.96, respectively, which were statistically different from the control, P<0.01), and the difference was more significant in tetrandrine at 1 and 2 mg/L. The content of LN in supernatants was significantly decreased in tetrandrine groups to 58.5%, 69.1%, 65.8% or 60.0% that of the control respectively, and that of PCIII to 84.6%, 81.5%, 75.7% or 80.7% respectively (P<0.05 vs control), with no significant difference among tetrandrine groups. RT-PCR showed that TGF-beta1 mRNA expression was reduced by tetrandrine treatments from 56.56% to 87.90% in comparison with the control, while Smad 7 mRNA was increased 1.4-4.8 times. The TGF-beta1 mRNA and Smad 7 mRNA expression was in a significant negative correlation (r=-0.755, P<0.01), and both were significantly correlated with alpha-SMA protein expression (r=-0.938, P<0.01; r=0.938, P<0.01, respectively). The up-regulation of Smad 7 protein by tetrandrine (1 mg/L) was confirmed by Western blotting as well. CONCLUSION: Tetrandrine has a direct inhibiting effect on the activation of rat HSCs in culture. It up-regulates the expression of Smad 7 which in turn blocks TGF-beta1 expression and signaling.

Tetrandrine inhibits activation of rat hepatic stellate cells stimulated by transforming growth factor-beta in vitro via up-regulation of Smad 7.

Tetrandrine is a bisbenzylisoquinoline alkaloid derived from the root of a Chinese herbal medicine Stephania tetrandra S. Moore, which has been used traditionally for the treatment of hepatofibrogenic disease in China for several decades. In the present study, the inhibitory effects of tetrandrine lower concentrations (0.25, 0.5, 1, 2 mg/L) on culture-activation and transforming growth factor-beta(1) (TGF-beta(1))-stimulated activation of quiescent rat hepatic stellate cells (HSCs) in vitro were assessed, and the possible relations between the underlying mechanism of these effects and TGF-beta signaling via its receptors were investigated. As shown by the examination of alpha-SMA using immunocytochemical staining or Western blot, tetrandrine inhibited both culture-activation and TGF-beta(1)-stimulated activation of HSCs. Further investigations revealed that, in this process, TGF-beta(1) mRNA expression was suppressed significantly in contrast to an up-regulation of Smad 7, while the expressions of type I and type II TGF-beta(1) receptors and Smad 3 mRNA were insignificantly changed by tetrandrine. These results suggest that tetrandrine at lower concentrations has a significant inhibiting effect on culture-activation and TGF-beta(1)-stimulated activation of rat HSCs, and that it may be due to an up-regulation of Smad 7 which in turn blocks TGF-beta(1) expression and its downstream signaling.

Ethylene Modulates Sphingolipid Synthesis in Arabidopsis.

Sphingolipids have essential structural and bioactive functions in membranes and in signaling. However, how plants regulate sphingolipid biosynthesis in the response to stress remains unclear. Here, we reveal that the plant hormone ethylene can modulate sphingolipid synthesis. The fungal toxin Fumonisin B1 (FB1) inhibits the activity of ceramide synthases, perturbing sphingolipid homeostasis, and thus inducing cell death. We used FB1 to test the role of ethylene signaling in sphingolipid synthesis in Arabidopsis thaliana. The etr1-1 and ein2 mutants, which have disrupted ethylene signaling, exhibited hypersensitivity to FB1; by contrast, the eto1-1 and ctr1-1 mutants, which have enhanced ethylene signaling, exhibited increased tolerance to FB1. Gene expression analysis showed that during FB1 treatment, transcripts of genes involved in de novo sphingolipid biosynthesis were down-regulated in ctr1-1 mutants but up-regulated in ein2 mutants. Strikingly, under normal conditions, ctr1-1 mutants contained less ceramides and hydroxyceramides, compared with wild type. After FB1 treatment, ctr1-1 and ein2 mutants showed a significant improvement in sphingolipid contents, except the ctr1-1 mutants showed little change in hydroxyceramide levels. Treatment of wild-type seedlings with the ethylene precursor 1-aminocyclopropane carboxylic acid down-regulated genes involved in the sphingolipid de novo biosynthesis pathway, thus reducing sphingolipid contents and partially rescuing FB1-induced cell death. Taking these results together, we propose that ethylene modulates sphingolipids by regulating the expression of genes related to the de novo biosynthesis of sphingolipids.

A systematic simulation of the effect of salicylic acid on sphingolipid metabolism.

The phytohormone salicylic acid (SA) affects plant development and defense responses. Recent studies revealed that SA also participates in the regulation of sphingolipid metabolism, but the details of this regulation remain to beexplored. Here, we use in silico Flux Balance Analysis (FBA) with published microarray data to construct a whole-cell simulation model, including 23 pathways, 259 reactions, and 172 metabolites, to predict the alterations in flux of major sphingolipid species after treatment with exogenous SA. This model predicts significant changes in fluxes of certain sphingolipid species after SA treatment, changes that likely trigger downstream physiological and phenotypic effects. To validate the simulation, we used (15)N-labeled metabolic turnover analysis to measure sphingolipid contents and turnover rate in Arabidopsis thaliana seedlings treated with SA or the SA analog benzothiadiazole (BTH). The results show that both SA and BTH affect sphingolipid metabolism, altering the concentrations of certain species and also changing the optimal flux distribution and turnover rate of sphingolipids. Our strategy allows us to estimate sphingolipid fluxes on a short time scale and gives us a systemic view of the effect of SA on sphingolipid homeostasis.

Association between Long Interspersed Nuclear Element-1 Methylation and Relative Telomere Length in Wilms Tumor.

BACKGROUND: DNA hypomethylation of long interspersed nuclear elements-1 (LINEs-1) occurs during carcinogenesis, whereas information addressing LINE-1 methylation in Wilms tumor (WT) is limited. The main purpose of our study was to quantify LINE-1 methylation levels and evaluate their relationship with relative telomere length (TL) in WT. METHODS: We investigated LINE-1 methylation and relative TL using bisulfite-polymerase chain reaction (PCR) pyrosequencing and quantitative PCR, respectively, in 20 WT tissues, 10 normal kidney tissues and a WT cell line. Significant changes were analyzed by t-tests. RESULTS: LINE-1 methylation levels were significantly lower (P < 0.05) and relative TLs were significantly shorter (P < 0.05) in WT compared with normal kidney. There was a significant positive relationship between LINE-1 methylation and relative TL in WT (r = 0.671, P = 0.001). LINE-1 Methylation levels were significantly associated with global DNA methylation (r = 0.332, P < 0.01). In addition, relative TL was shortened and LINE-1 methylation was decreased in a WT cell line treated with the hypomethylating agent 5-aza-2'-deoxycytidine compared with untreated WT cell line. CONCLUSION: These results suggest that LINE-1 hypomethylation is common and may be linked to telomere shortening in WT.

An Arabidopsis neutral ceramidase mutant ncer1 accumulates hydroxyceramides and is sensitive to oxidative stress.

Ceramidases hydrolyze ceramide into sphingosine and fatty acids and, although ceramidases function as key regulators of sphingolipid homeostasis in mammals, their roles in plants remain largely unknown. Here, we characterized the Arabidopsis thaliana ceramidase AtNCER1, a homolog of human neutral ceramidase. AtNCER1 localizes predominantly on the endoplasmic reticulum. The ncer1 T-DNA insertion mutants had no visible phenotype, but accumulated hydroxyceramides, and showed increased sensitivity to oxidative stress induced by methyl viologen. Plants over-expressing AtNCER1 showed increased tolerance to oxidative stress. These data indicate that the Arabidopsis neutral ceramidase affects sphingolipid homeostasis and oxidative stress responses.