Erratum to: Activities of genes controlling sphingolipid metabolism in human fibroblasts treated with flavonoids

Metabolic Brain Disease -     

Effects of Chamomilla recutita flavonoids on age-related liver sphingolipid turnover in rats

The increased sphingolipid turnover in the liver is associated with elevation of free radical production and state of chronic inflammation at old age. Plant polyphenols are reported to exhibit antioxidant and anti-inflammatory effects. In the present paper, the lipids contents and ceramide production in the liver and hepatocytes as well as the correction of sphingolipid metabolism at old age using the mixture of Chamomilla recutita flavonoids (chamiloflan) or apigenin-7-glucoside or luteolin-7-glucoside alone have been investigated. To study the sphingolipids turnover, the [14C]serine-pre-labeled hepatocytes and [14C-methyl]- or [14C]palmitate-pre-labeled sphingomyelin (SM) and ceramide were used. The ceramide content was higher in the liver and hepatocytes of 24- and 27-28-month-old animals as compared to adult 3-month-old Wistar rats. An addition of flavonoids to the culture medium did not influence significantly on the lipids contents and metabolism in the isolated hepatocytes. The administration of flavonoids to old rats decreased the elevated neutral and acid SMases activities and ceramide mass and did not affect both the lipid content in the liver of adult animals and ceramide conversion to the sphingosine or SM. These results suggest that the SMases play a key role in the flavonoid-induced decrease of ceramide levels in the liver of old rats.     

Growth-regulated expression of D-type cyclin genes in human diploid fibroblasts.

The human CCND1 cyclin D1/PRAD1 gene was previously identified by a genetic screen for G1 cyclin function in Saccharomyces cerevisiae and also was identified as the putative BCL1 oncogene. However, its role in human cell proliferation is not known. To determine if expression of human D-type cyclin genes correlates with the state of cell growth, we examined the level of mRNAs for CCND1 and a related gene, CCND3, in normal human diploid fibroblasts (HDF). The levels of both mRNAs decrease upon serum depletion or at high cell densities. Following stimulation of quiescent fibroblasts with serum, the mRNA levels increase gradually to a peak at about 12 hr, prior to the onset of S phase. Induction of cyclin gene expression by serum is reduced concomitantly with the decline in FOS induction in aging HDFs, suggesting a possible relationship to the decrease in the proliferative response to mitogens during cellular senescence. Cycloheximide partially blocks the induction of CCND1 and CCND3 gene expression by serum, suggesting that both de novo protein synthesis-dependent and -independent pathways contribute to induction. Treatment of HDFs with defined growth factors suggests a correlation between CCND mRNA induction and DNA synthesis. However, induction of these genes is not sufficient for the transition from quiescence through G1 into S phase.     

Direct chemical evidence for sphingolipid domains in the plasma membranes of fibroblasts

Sphingolipids play important roles in plasma membrane structure and cell signaling. However, their lateral distribution in the plasma membrane is poorly understood. Here we quantitatively analyzed the sphingolipid organization on the entire dorsal surface of intact cells by mapping the distribution of ¹⁵N-enriched ions from metabolically labeled ¹⁵N-sphingolipids in the plasma membrane, using high-resolution imaging mass spectrometry. Many types of control experiments (internal, positive, negative, and fixation temperature), along with parallel experiments involving the imaging of fluorescent sphingolipids—both in living cells and during fixation of living cells—exclude potential artifacts. Micrometer-scale sphingolipid patches consisting of numerous ¹⁵N-sphingolipid microdomains with mean diameters of ∼200 nm are always present in the plasma membrane. Depletion of 30% of the cellular cholesterol did not eliminate the sphingolipid domains, but did reduce their abundance and long-range organization in the plasma membrane. In contrast, disruption of the cytoskeleton eliminated the sphingolipid domains. These results indicate that these sphingolipid assemblages are not lipid rafts and are instead a distinctly different type of sphingolipid-enriched plasma membrane domain that depends upon cortical actin.     

Genetic complementation in heterokaryons of human fibroblasts defective in cobalamin metabolism.

Inherited methylmalonicacidemia due to deficiency of methylmalonyl-CoA mutase (methylmalonyl-CoA CoA-carbonylmutase; EC 5.4.99.2) activity results from at least three classes of biochemically distinct defects affecting cobalamin (Cbl: vitamin B12) metabolism (cbl A, cbl B, and cbl C mutants) and a fourth class producing a defective mutase apoenzyme. We have obtained genetic evidence in support of this biochemical heterogeneity, using heterokaryons prepared by Sendai-virus-mediated cell fusion. Nine fibroblast lines from patients with defective Cbl metabolism (4 cbl A, 3 cbl B, and 2 cbl C), two from patients with defective mutase apoenzyme, and two from controls were fused in pairwise combinations and tested for functional mutase holoenzyme using a radioautographic procedure which detects [14C]propionate incorporation into trichloroacetic-acid-precipitable material in fibroblast monolayers in situ. Each of the mutants incorporates negligible radioactivity compared to control cells. Activity is also negligible when different mutants are mixed without virus or when homokaryons are produced by self-fusion. Heterokaryons produced by fusing members of each of the four mutant classes with representatives of any other class recover the ability to incorporate [14C]propionate to levels comparable to those of control cells. However, heterokaryons produced between members of the same class fail to complement in all cases. We conclude that the mutants with defective Cbl metabolism (cbl A, cbl B, cbl C) comprise three complementation groups, that a fourth group corresponds to mutase apoenzyme deficiency, and that all four classes of mutations are recessively inherited.     

Alteration in the retinoblastoma gene associated with immortalization of human fibroblasts treated with60Co gamma rays

Genetic analysis was carried out in human fibroblasts (KMST-6) immortalized by treatment with⁶⁰Co gamma rays in order to determine if any genetic change was involved in the immortal transformation of human cells. Analysis by restriction fragment length polymorphism revealed an alteration in chromosome 13q12–14, in which the retinoblastoma (RB) gene locus (13q14) is located. Then the RB gene itself was examined. Structural abnormalities in the RB gene were detected by Southern blot analysis. Furthermore, abnormal RB protein (pRB) was expressed in immortalized KMST-6 cells, as shown by in vitro phosphorylation, whereas normal KMS-6 cells expressed the intact pRB. These findings indicated that inactivation of the RB gene is one of the key events of the immortalization of human cells.Abbreviations RB retinoblastoma - pRB retinoblastoma gene product (protein) - T simian virus 40 large T antigen - E1A adenovirus E1A protein     

Low-density lipoprotein metabolism by cultured human fibroblasts: relationship with aging and atherosclerosis

22 male subjects aged 21-55 years with normal plasma lipid concentrations were divided into two groups on the basis of the presence or absence of proven coronary artery disease and/or peripheral vascular disease. The rates of uptake and degradation of low-density lipoprotein (LDL) by fibroblast cultures obtained from each subject were assessed using 125I-labelled LDL, and an attempt was made to relate them to the presence or absence of atherosclerosis and to the age of the subject. Atherosclerosis was found to be significantly correlated with elevated rates of LDL uptake and degradation. On the other hand, aging was shown to be associated with a significant reduction in cellular LDL metabolism.     

The antidiabetic drug metformin decreases cholesterol metabolism in cultured human fibroblasts

The effect of the hypoglycemic biguanide drug Metformin was investigated after a 72 h pretreatment of human cultured fibroblasts. Metformin induced a moderate increase in low density lipoprotein binding, uptake and internalization (25% increase after treatment with 5 X 10(-4) M of drug). A decrease in sterol, fatty acid and triacyglycerol synthesis from sodium acetate was observed after pretreatment with the drug, with a dose-dependent effect in the range of 5 X 10(-5) to 5 X 10(-4) M (50% reduction of sterol synthesis after treatment with Metformin 5 X 10(-4) M). This effect was also observed in fibroblasts from a patient with homozygous familial hypercholesterolemia. Cholesterol esterification studied by incorporation of radiolabeled oleic acid was reduced by Metformin (40% of control after treatment with Metformin 5 X 10(-4) M) whereas incorporation into triacylglycerols was less impaired. These effects of Metformin on cholesterol metabolism were observed either in the presence or in the absence of low density lipoproteins. Moreover, Metformin also reduced cholesterol esterification in J774 monocyte-macrophage cells. Metformin also induced a decrease of hydroxymethylglutaryl coenzyme A reductase activity in cultured fibroblasts and a reduction of acyl-coenzyme A: cholesterol-O-acyltransferase activity in cultured fibroblasts and J774 cells.     

Ceramide accumulation is associated with increased apoptotic cell death in cultured fibroblasts of sphingolipid activator protein-deficient mouse but not in fibroblasts of patients with Farber disease

Ceramide is recognized as an intracellular mediator of cell growth, differentiation and apoptosis. Tumour necrosis factor, anti-fas antibody, radiation and anticancer drugs such as actinomycin D are known to induce apoptosis in several cell types through generation of ceramide by activation of the sphingomyelinase pathway or ceramide synthetase. In this study, we examined the occurrence of apoptosis in fibroblasts from patients with Farber disease and from sphingolipid activator protein-deficient (sap–/–) mouse. These cells accumulate ceramide as the result of genetic deficiency of acid ceramidase and the ceramidase activator (sap-D), respectively. Amounts of ceramide in fibroblasts from Farber patients and in fibroblasts from sap–/– mouse were increased 2.9-fold and 2.8-fold, respectively, over the level of controls. Despite the similar degree of ceramide accumulation, cells exhibiting apoptotic features were increased only in fibroblasts from the sap–/– mouse but not those from the Farber patients. Thymidine uptake of Farber fibroblasts was normal while that of sap–/– mouse fibroblasts was twice normal, consistent with the apparently normal growth and the different rates of apoptotic cell death in these two cell lines. These data suggest that intralysosomal accumulation of ceramide due to defective acid ceramidase or its activator may not play an important role as a mediator of apoptosis. The increased apoptosis in the cultured fibroblasts from the sap–/– mouse may be caused by mechanisms other than the ceramide accumulation. Although more frequent than normal, significant apoptotic cell death was not observed in sap–/– mouse brain in vivo.     

Rapamycin increases oxidative metabolism and enhances metabolic flexibility in human cardiac fibroblasts

Inhibition of mTOR signaling using rapamycin has been shown to increase lifespan and healthspan in multiple model organisms; however, the precise mechanisms for the beneficial effects of rapamycin remain uncertain. We have previously reported that rapamycin delays senescence in human cells and that enhanced mitochondrial biogenesis and protection from mitochondrial stress is one component of the benefit provided by rapamycin treatment. Here, using two models of senescence, replicative senescence and senescence induced by the presence of the Hutchinson-Gilford progeria lamin A mutation, we report that senescence is accompanied by elevated glycolysis and increased oxidative phosphorylation, which are both reduced by rapamycin. Measurements of mitochondrial function indicate that direct mitochondria targets of rapamycin are succinate dehydrogenase and matrix alanine aminotransferase. Elevated activity of these enzymes could be part of complex mechanisms that enable mitochondria to resume their optimal oxidative phosphorylation and resist senescence. This interpretation is supported by the fact that rapamycin-treated cultures do not undergo a premature senescence in response to the replacement of glucose with galactose in the culture medium, which forces a greater reliance on oxidative phosphorylation. Additionally, long-term treatment with rapamycin increases expression of the mitochondrial carrier protein UCP2, which facilitates the movement of metabolic intermediates across the mitochondrial membrane. The results suggest that rapamycin impacts mitochondrial function both through direct interaction with the mitochondria and through altered gene expression of mitochondrial carrier proteins.     

Exploration of replicative senescence-associated genes in human dermal fibroblasts by cDNA microarray technology

The aging process is known to be regulated by specific genes in various organisms, including yeast, the nematode C. elegans, fruitflies and mice. To explore the novel genes involved in aging process, we applied cDNA microarray technology to a replicative senescence model of human dermal fibroblasts (HDF). Eighty-four genes, including inflammatory genes, cell cycle regulatory genes, cytoskeletal genes, and metabolic genes were found to show more than two fold expressional differences in young and old fibroblasts. Furthermore, 31 genes were confirmed to be up- or down-regulated during replicative senescence by semi-quantitative RT-PCR. The overexpressions of several genes including CD36, putative lymphocyte G0/G1 switch gene (G0S2), tumor protein D52-like 1 (TPD52L1), chemokine (C-X-C motif) ligand 6, myxovirus resistant gene 1 (MX1), and the down-regulation of the immunoglobulin superfamily containing leucine-rich repeat (ISLR), neurotrimin, insulin-like growth factor 2 associated protein (IGF2A), and apoptosis-related RNA binding protein (NAPOR3) were newly identified. These results suggest that fibroblasts show the deregulation of various cellular processes, such as inflammatory response, mitosis, cell adhesion, transport, signal transduction, and metabolism during replicative senescence.     

Screening of sphingolipid metabolism-related genes associated with immune cells in myocardial infarction: a bioinformatics analysis

BackgroundInflammation and immune cell infiltration in infarcted myocardial tissue are critical to myocardial infarction (MI) prognosis, and alterations in sphingolipid metabolism (SM) have been shown to potentially influence the inflammatory response and induce cardioprotection, but the underlying mechanisms are unclear. We therefore performed bioinformatics analysis to screen for key genes of SM in MI immune cells.MethodsThree matrix files including {"type":"entrez-geo","attrs":{"text":"GSE61145","term_id":"61145"}}GSE61145, {"type":"entrez-geo","attrs":{"text":"GSE23294","term_id":"23294"}}GSE23294, and {"type":"entrez-geo","attrs":{"text":"GSE71906","term_id":"71906"}}GSE71906 were downloaded from the Gene Expression Omnibus (GEO) database. {"type":"entrez-geo","attrs":{"text":"GSE61145","term_id":"61145"}}GSE61145 was a human peripheral blood database, and {"type":"entrez-geo","attrs":{"text":"GSE23294","term_id":"23294"}}GSE23294 and {"type":"entrez-geo","attrs":{"text":"GSE71906","term_id":"71906"}}GSE71906 were 2 mouse myocardial tissue databases. R and annotation packages were used to screen for differentially-expressed genes (DEGs). Datasets of human and mouse cardiac tissues were downloaded from the GEO database for subsequent validation. The downloaded platform and matrix files were processed using R language and annotation packages. Key targets and enrichment pathways were identified using Gene Ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. The Wilcoxon test was performed on the genes involved in SM pathways in neutrophils.ResultsA total of 261 DEGs were obtained from human peripheral blood datasets, among which 101 were immune-related. GO analysis revealed that neutrophil activation, T cell activation, and T cell differentiation were significantly enriched in the immune-related DEGs. Three types of immune cells were identified in infarcted myocardial tissues. In addition, 194 DEGs were obtained from mouse myocardial tissue data, among which 6 SM-related genes (Asah1, Degs1, Neu1, Sptlc2, Sphk1, and Gba2) were significantly associated with MI. Evaluation of the relationships between these DEGs and neutrophils showed that the expression of the Sptlc2 gene was significantly upregulated in neutrophils of the MI group, while the expression levels of the Asah1 and Degs1 genes were downregulated.ConclusionsWe identified 3 SM-related genes that were highly associated with neutrophils in MI, which may advance our understanding of SM in immune cells after MI.     

Human embryonic lung fibroblasts treated with artesunate exhibit reduced rates of proliferation and human cytomegalovirus infection in vitro

Background

Cytomegalovirus (CMV) pneumonia is a major cause of death in immunosuppressed patients. Despite the effective treatment with ganciclovir (GCV) and other antiviral agents, the mortality rate remains between 30% to 50%. Recently, the anti-malarial drug artesunate (ART) wasfound to exhibit significant anti-viral activity. Here, we examined the effects of ART on human cytomegalovirus (HCMV) infection and human embryonic lung fibroblast (HELF) proliferation in vitro.

Methods

HELFs infected with the GFP-expressing Towne-BAC strain of HCMV were divided into three treatment groups: Group I, cells treated with ART for 1.5 h before HCMV inoculation; Group II, cells infected with HCMV that was pre-treated with ART for 1.5 h before HCMV inoculation; Group III, cells that were treated with ART at 1.5 h post-HCMV inoculation. GFP expression was observed daily by fluorescence microscopy, and the number of GFP-positive cells in each experimental group was recorded at 4-5 days post-infection. At 10 days post-infection, the viability of cells in each group was recorded. GCV treatment was used as a control.

Results

While no significant effects on cytotoxicity, cell viability, viral infection rates, or antiviral activity were observed upon treatment of Group I or II cells with GCV or low levels of ART, the ART-treated Group III population exhibited significantly reduced rates of infection at drug concentrations higher than 12.5 µM. Similarly, we observed a GCV concentration-dependent reduction in the viral infection rate in Group III cells. Notably, ART-treated, but not GCV-treated, cells also exhibited decreased proliferation. The 50% cytostatic concentrations (CC50) and the half maximal inhibitory concentrations (IC50) of ART and GCV were 54.382 µM and 12.679 µM, and 3.76 M and 14.479 µM, respectively.

Conclusions

In addition to its robust antiviral activity, ART inhibits proliferation of HCMV-infected lung fibroblasts, making it a potential next-generation drug for CMV pneumonia treatment and for reducing fibroproliferation and fibrosis in these patients.     

Glucose metabolism in fibroblasts from patients with erythrocyte hexokinase deficiency

Four different hexokinase (HK) isoenzymes are distributed in different proportions in human tissues. Fibroblasts contain HK type I as the predominant glucose phosphorylating activity, the same isoenzyme that predominates in red blood cells (RBC). We have established cell lines from two patients homozygous for RBC HK deficiency but carrying different mutations. In one case (HK-Melzo) the residual RBC enzyme shows a marked heat instability but possesses normal kinetic and regulatory properties; in the other (HK-Napoli), the enzyme is characterized by an increased Ki for glucose-1,6-diphosphate. These properties are also retained by the fibroblasts' hexokinase. Glucose utilization by cultured fibroblasts from these patients was markedly reduced in the cell lines where HK deficiency was more pronounced. However, cells with only 30% HK activity retained their full ability to utilize glucose in the hexose monophosphate pathway. This was shown to be true not only under basal conditions but also in the presence of oxidative agents such as methylene blue. Significant reduction of the ATP level was also found in HK-Melzo fibroblasts. Thus, HK deficiency is associated with reduced glucose utilization and normal hexose monophosphate shunt rates. Results previously obtained on RBC support similar conclusions.     

Anemia in beta-thalassemia patients targets hepatic hepcidin transcript levels independently of iron metabolism genes controlling hepcidin expression

Thalassemia associates anemia and iron overload, two opposite stimuli regulating hepcidin gene expression. We characterized hepatic hepcidin expression in 10 thalassemia major and 13 thalassemia intermedia patients. Hepcidin mRNA levels were decreased in the thalassemia intermedia group which presented both lower hemoglobin and higher plasma soluble transferrin receptor levels. There was no relationship between hepcidin mRNA levels and those of genes controlling iron metabolism, including HFE, hemojuvelin, transferrin receptor-2 and ferroportin. These results underline the role of erythropoietic activity on hepcidin decrease in thalassemic patients and suggest that mRNA modulations of other studied genes do not have a significant impact.     

Abnormal glucose metabolism in patients treated with antipsychotics

Second-generation (atypical) antipsychotic medications are of great benefit to a wide variety of people with psychiatric disorders, especially patients with schizophrenia. However, one constellation of adverse effects is an increased risk of obesity, diabetes, and metabolic syndrome. Increasing numbers of reports concerning impaired glucose tolerance, diabetes, and ketoacidosis have raised concerns about a possible association between abnormal glucose metabolism and treatment with atypical antipsychotics, although the question is still debated because of the presence of many confounding factors. A close relationship between drug-induced weight gain and risk of diabetes has been reported, emphasizing the role of insulin resistance. However, some cases of diabetes developed independently of weight gain, rather rapidly and possibly progressing to ketoacidosis, thus arguing for a severe impairment of insulin secretion. Another debated question is whether diabetes risk is a class action or a differential action. Although not fully scientifically proven yet, available evidence suggests that clozapine and olanzapine have a higher propensity to induce diabetes and metabolic syndrome compared with other atypical antipsychotic drugs, risperidone and quetiapine. Despite more limited available data, amisulpride, aripiprazole and ziprazidone showed less likelihood of precipitating diabetes. Interestingly, reversibility of drug-related diabetes has been reported with aripiprazole. The choice of atypical antipsychotic medication for a specific patient depends on many factors, but the likelihood of developing diabetes should become an important consideration. When prescribing an atypical antipsychotic, a commitment to careful baseline screening and follow-up monitoring is essential in order to mitigate the risk of developing diabetes and associated complications.