Relationship between the pentose-phosphate pathway and the de novo synthesis of fatty acids and cholesterol in oligodendrocyte-enriched glial cultures

This study focuses on the activity of the pentose-phosphate pathway and its relationship to de novo synthesis of fatty acids and cholesterol in oligodendrocyte-enriched glial cell cultures derived from 1-week old rat brain. The proportion of glucose that was metabolized along the pentose-phosphate pathway was estimated by measuring ¹⁴CO₂ production from [1-¹⁴C]-, [2-¹⁴C]- and [6-¹⁴C]glucose, the utilization of glucose and the production of lactate. Incorporation of ¹⁴C from [¹⁴C]glucose and from [3-¹⁴C]acetoacetate into lipids was analysed. The pentose- phosphate pathway produced much more CO₂ from glucose than the Krebs cycle, although it accounted for only a small part of the consumption of glucose (< 3%). The higher ¹⁴CO₂ production from [2-¹⁴C]glucose than from [6-¹⁴C]glucose indicated that recycling of the products of the pentose-phosphate pathway takes place in these cells.Gradual inhibition of the pathway with increasing concentrations of 6-aminonicotinamide resulted in a parallel inhibition of the conversion of acetoacetate and of glucose into fatty acids and into cholesterol. Glycolysis was also strongly inhibited in the presence of 6-aminonicotinamide whereas the activity of the Krebs cycle was not affected.These results suggest that de novo synthesis of fatty acids and cholesterol by oligodendrocytes of neonatal rats is closely geared to the activity of the pentose-phosphate pathway in these cells.     

The effect of serum on lipid synthesis and on the expression of oligodendrocyte marker-enzymes in oligodendrocyte-enriched glial cells in culture

Glial cells were isolated from the cerebra of 7-day old rats and the effect of serum on the development of these cells in culture was studied. The activities of the oligodendrocyte marker-enzymes, 2′3′-cyclic nucleotide 3′-phosphodiesterase and glycerol 3-phosphate dehydrogenase and the synthesis of the myelin-associated sulpholipid, sulphatide, were used to monitor the differentiation of these cells in vitro. The results indicate that serum: (i) represses lipogenesis, cholesterogenesis and sulphatide synthesis, (ii) lowers the expression of 2′3′-cyclic nucleotide 3′ phosphodiesterase and glycerol 3-phosphate dehydrogenase but not of lactate dehydrogenase and (iii) thus impairs the differentiation of oligodendrocytes.     

Substrate utilization for energy production and lipid synthesis in oligodendrocyte-enriched cultures prepared from rat brain

The metabolism of oligodendrocytes has been studied using cultures of oligodendrocyte-enriched glial cells isolated from cerebra of 5–8-day old rats. Cultures containing 60–80% oligodendrocytes were incubated for 16h with [3-¹⁴C]acetoacetate, d-[3-¹⁴C]3-hydroxybutyrate, [U-¹⁴C]glucose, l-[U-¹⁴C]glutamine and [1-¹⁴C]pyruvate or [2-¹⁴C]pyruvate in the presence or absence of other oxidizable substrates. Labelled CO₂ was collected as an index of oxidative metabolism and the incorporation of label into total lipids, fatty acids and cholesterol was used as an index of the de novo synthesis of lipids. Glucose, acetoacetate, D-3-hydroxybutyrate, pyruvate and l-lactate were measured to determine substrate utilization and product formation under various conditions. Our results indicate that glucose is rapidly converted to lactate and is a relatively poor substrate for oxidative metabolism and lipid synthesis. Ketone bodies were used as an energy source and as precursors for the synthesis of fatty acids and cholesterol. Preferential incorporation of acetoacetate into cholesterol was not observed. Exogenous pyruvate was incorporated into both the glycerol skeleton of complex lipids and into cholesterol and fatty acids. l-Glutamine appeared to be an important substrate for the energy metabolism of these cells.     

Opioid-dependent growth of glial cultures: suppression of astrocyte DNA synthesis by met-enkephalin

The action of met-enkephalin on the growth of astrocytes in mixed-glial cultures was examined. Primary, mixed-glial cultures were isolated from 1 day-old mouse cerebral hemispheres and continuously treated with either basal growth media (controls), 1 microM met-enkephalin, 1 microM met-enkephalin plus the opioid antagonist naloxone (3 microM), or naloxone alone (3 microM). Absolute numbers of neural cells were counted in unstained preparations, while combined [3H]-thymidine autoradiography and glial fibrillary acid protein (GFAP) immunocytochemistry was performed to identify specific changes in astrocytes. When compared to control and naloxone treated cultures, met-enkephalin caused a significant decrease in both total cell numbers, and in [3H]-thymidine incorporation by GFAP-positive cells with flat morphology. These results indicate that met-enkephalin suppresses astrocyte growth in culture.     

Effects of culture conditions on the synthesis of human chorionic gonadotropin by placental organ cultures

Summary Culture conditions for maintaining first trimester human placenta in organ culture, which enhance the secretion of human chorionic gonadotropin (hCG), are described. Nutrient medium, oxygen tension and Gelfoam support matrix infuence the synthesis of hCG by these cultures. Placental tissue remained viable for the duration of experiments (12 days) as judged by the incorporation of tritiated thymidine into DNA and the lack of release of incorporated [¹²⁵Iiododeoxyuridine. Optimal conditions for hCG synthesis in placental organ culture included an atmosphere of 95% air and 5% CO₂ (approximately 20% O₂), CMRL 1066 medium containing fetal human or bovine serum, insulin, hydrocortisone and retinal acetate. Multiple pieces of placenta could be cultured in the same dish with an additive effect on hCG secretion. The functional responsiveness of these placental cultures was demonstrated by modulation of hCG synthesis with theophylline and 3′5′ dibutyryl cyclic AMP. Presented in part at the meeting of the American Association for Cancer Research, April 1978. This work is being submitted in partial fulfillment of the Ph.D. requirements in the Department of Biology, Catholic University of America.     

Effects of triiodothyronine (T3) on differentiation of rat cortical neurons in primary cultures

Some of the events which characterize neuronal terminal differentiation have been studied in rat cortical neurons cultured in a selective synthetic medium for a period which corresponds to terminal brain maturation in vivo. In particular, we have studied the effect of T3 on the synthesis of nuclear proteins and the expression of the mRNAs which encode different variants of T3 nuclear receptors (c erb A proteins). We have shown that: a) T3 stimulates the turnover of nuclear proteins, with a more evident effect on the non-histone component; b) for the whole lifespan of cultures the predominant form of c erb A mRNA is the 2 variant (which encodes a protein unable to bind T3); whatever the function of 2 protein this finding suggests that its predominance on 1 is settled very early during mammalian brain maturation.     

Short-term stimulation of lipogenesis by triiodothyronine in maintenance cultures of rat hepatocytes

Within 4 h following the addition of 3,3',5 triiodo-L-thyronine to monolayer cultures of hepatocytes isolated from hypothyroid rats, a very distinct stimulation of fatty acid and cholesterol synthesis, measured as incorporation of either [1-14C]acetate or [3H]H2O into these lipid fractions, is observed. A smaller but significant increase in the rate of lipogenesis occurs in hepatocytes derived from euthyroid animals. These stimulatory effects of triiodothyronine are also observed in the presence of cycloheximide, indicating that the described early and direct stimulation of lipogenesis by the thyroid hormone is, at least in part, independent of protein synthesis.     

Effects of 2,4-D removal on the synthesis of specific proteins by Catharanthus roseus cell cultures

Total and neosynthesized proteins of periwinkle cell suspensions (Catharanthus roseus) were first investigated in cells grown in a 2,4-D-containing medium. Analysis of total (silver-stained) proteins by two-dimensional gel electrophoresis revealed that the levels of seventeen polypeptides were altered during the growth cycle of the cells. Analysis of in vivo [³⁵S]-methionine labeled polypeptides revealed differences in the synthesis of at least 35 polypeptides. Three polypeptides with molecular masses of 30, 35 and 39 kDa appeared to be specific markers of the early stationary phase. In a second sequence of experiments, cells were grown in a 2,4-D-free medium. Alterations in protein synthesis were observed: several polypeptides were expressed earlier in the 2,4-D-starved cells than in control cells; the synthesis of at least two specific polypeptides was increased in cells grown in 2,4-D-free medium, whereas the synthesis of three other polypeptides (molecular masses 33, 34 and 52.5 kDa) was switched on in these cells. As previous studies showed that 2,4-D depletion increased the alkaloid production in C. roseus cells, the present results may suggest that these polypeptides are implicated in the regulation of the alkaloid pathway.     

Effects of culture conditions on the synthesis of human chorionic gonadotropin by placental organ cultures.

Culture conditions for maintaining first trimester human placenta in organ culture, which enhance the secretion of human chorionic gonadotropin (hCG), are described. Nutrient medium, oxygen tension and Gelfoam support matrix influence the synthesis of hCG by these cultures. Placental tissue remained viable for the duration of experiments (12 days) as judged by the incorporation of tritiated thymidine into DNA and the lack of release of incorporated [125I]iododeoxyuridine. Optimal conditions for hCG synthesis in placental organ culture included an atmosphere of 95% air and 5% Co2 (approximately 20% O2), CMRL 1066 medium containing fetal human or bovine serum, insulin, hydrocortisone and retinal acetate. Multiple pieces of placenta could be cultured in the same dish with an additive effect on hCG secretion. The functional responsiveness of these placental cultures was demonstrated by modulation of hCG synthesis with theophylline and 3'5' dibutyryl cyclic AMP.     

NAA对胡萝卜（Daucus carota）悬浮细胞茄红素合成的影响

通过对胡萝卜新透心红 DaucuscarotaCV.XinTouxinhong 细胞悬浮系单位鲜重细胞的茄红素含量、细胞总产量以及茄红素总产量的分析比较,研究了培养基中不同NAA浓度对胡萝卜细胞悬浮系茄红素代谢的影响.结果表明,NAA具有增强细胞茄红素代谢水平、提高单位鲜重细胞中茄红素的含量的作用,但对细胞的生长具有抑制作用.从茄红素单产和总产量综合评价,培养基中加入3.0mg·L-1NAA效果最佳.     

Regulation of synthesis of a brain-specific protein in monolayer cultures of clonal rat glial cells

C6 cells were grown in monolayer culture under conditions permitting continued exponential cell division after attainment of a density at which extensive intercellular contacts were formed. An increase in the relative synthesis of S100 protein coincided with the time of formation of extensive intercellular contacts and preceded the onset of the stationary phase of growth by three generations. These observations suggested that the induction of S100 protein synthesis was mediated by cell contact and not by an arrest of cellular growth. The mechanism of this induction was first studied in a homologous non-initiating cell-free protein-synthesizing system from C6 cells, using fixed amounts of free amino acids or fully charged rat liver aminoacyl-tRNA as a source of precursors for protein synthesis. Real synthesis of total soluble proteins decreased as the cells progressed from logarithmic to stationary growth while synthesis of S100 protein increased during this period. The capacity of poly(A)+ RNA from logarithmic and stationary cultures to direct the synthesis of S100 protein was estimated in a cell-free protein-synthesizing system derived from wheat embryos. Increased synthesis of S100 protein in stationary cultures was directly correlated with an increase in translatable S100 protein mRNA.     

Nuclear and mitochondrial DNA synthesis and energy metabolism in primary rat glial cell cultures

DNA synthesis in nuclei and mitochondria purified from serum-supplemented rat glial cell cultures at different days after plating was studied. Furthermore in mitochondria, some enzymatic activities related to energy transduction (citrate synthase, malate dehydrogenase, total NADH-cytochromec reductase, cytochrome oxidase and glutamate dehydrogenase) were measured. For DNA labeling [methyl-³H]thymidine was added to the culture medium at different days after plating. During the culture times studied the specific activity of total, nuclear, and mitochondrial DNA decreased from 8 days in vitro (DIV) to 21 DIV and increased at 30 DIV. The specific activity of nuclear DNA was always higher than that of mitochondrial DNA. The specific activity of the above mentioned mitochondrial enzymes increased from 8 DIV up to 21 DIV and decreased at 30 DIV, suggesting a relationship between the energy metabolism and the differentiation of glial cells in culture.The AA. would like to dedicate this paper to the memory of Dr. Ida Serra, Associate Professor of Biochemistry at the Medical Faculty, University of Catania, who prematurely died, after this paper was submitted for publication.     

Effects of serum and insulin on hyaluronate synthesis by cultures of chondrocytes from the Swarm rat chondrosarcoma

Incorporation of [3H]glucosamine into hyaluronate synthesized by chondrocyte cultures was dependent on the concentration of foetal calf serum in the culture medium. [3H]Hyaluronate levels in cultures supplemented with 2% serum, or maintained without serum, were about 60 and 43%, respectively, of that in cultures maintained with 15% serum. Addition of insulin to cultures maintained with 15% serum had no significant effect on [3H]hyaluronate synthesis. Addition of the hormone to cultures maintained with 2% serum increased [3H]hyaluronate synthesis to levels either the same (1 ng insulin/ml), or greater than (100 ng insulin/ml) that in cultures maintained with 15% serum. The [3H]hyaluronate synthesized by the cultures was of very high molecular weight irrespective of the level of synthesis. [3H]Hyaluronate formed about 12% of the total [3H]glycosaminoglycan synthesized under all culture conditions. Synthesis of 35S, 3H-labelled proteoglycan was reduced, or increased, by the same relative amounts as [3H]hyaluronate, under the different culture conditions. Incorporation of [3H]glucosamine into hyaluronate by near confluent cultures of fibroblasts derived from the Swarm rat chondrosarcoma was reduced by 50% in cultures treated with 2% foetal calf serum compared to those maintained with 15% serum. [3H]Hyaluronate synthesis by fibroblast cultures treated with 2% serum was not stimulated by addition of insulin.     

On the phospholipid metabolism of glial cell primary cultures

Primary cultures prepared from newborn rat brain, consisted after 16 or 17 days mainly of astrocytes and of oligodendrocytes. 1-Alkenyl-sn-glycero-3-phosphoethanolamine (lysoplasmalogen) was used as substrate for studies on the metabolism of ethanolamine-glycerophospholipids. After 3 hr incubation two main products were observed: a) 1-alkenyl-2-acyl-sn-glycero-3-phosphoethanolamine (=ethanolamine plasmalogen) and b) 1-alkenyl-2-acyl-sn-glycero-3-phosphocholine (=choline plasmalogen). The acylation rate reached saturation at about 10 nmol substrate/mg cell protein with aV _max of 30 nmol×mg cell protein^–1×3 hr^–1. This acylated compound amounted to almost 60% of all radioactivity internalized, whereas the second product, choline plasmalogen, came to 20%. Unchanged substrate was found within the cells only in small amounts, even at maximum substrate internalization. These results were discussed in comparison with those obtained with 1-alkyl-sn-glycero-3-phosphoethanolamine under the same conditions (25).     

Effect of ferric nitrilotriacetate on predominately cortical glial cell cultures

Cultured glial cells were exposed to ferric nitrilotriacetate (Fe-NTA) at varying concentrations. Studies of the exposed glial cells were performed at days 29 and 36 post-conceptional age (culture days 8 and 15). In addition to morphologic studies, biochemical assays including [³H]-flunitrazepam (FLU) specific binding, Ro5-4864-displaceable³H-FLU binding, and protein determinations were performed. At day 29 post-conceptional age, significant decreases in³H-FLU specific binding, Ro5-4864-displaceable³H-FLU binding, and protein determinations were discernible only in the presence of 100 M Fe-NTA. At day 36 post-conceptional age³H-FLU specific binding was significantly decreased at 20, 60, and 100 M Fe-NTA concentrations, while Ro5-4864-displaceable³H-FLU binding and protein determinations were significantly reduced at 60 and 100 M Fe-NTA concentrations. The effects of Fe-NTA exposure appear to be both concentration and duration-of-exposure related. When compared to previously reported neuronal cell culture, studies utilizing³H-FLU specific binding, Ro5-4864-displaceable³H-FLU binding, and protein determinations, glial cells appear to be significantly more resistant to chelated iron exposure.     

Effects of brefeldin A on the synthesis of chondroitin 4-sulfate by cultures of mouse mastocytoma cells.

Mouse mastocytoma cells were cultured with brefeldin A in medium containing [35S]sulfate and [3H]glucosamine in order to determine the effects of this fungal metabolite on the formation of chondroitin 4-sulfate by these cells. There was a marked reduction in the incorporation of [35S]sulfate into the glycosaminoglycan which was approximately equal to the reduction in the incorporation of [3H]hexosamine into the same molecule. The chondroitin 4-sulfate chain size was greatly diminished, while the number of chains appeared to remain relatively constant, indicating that the brefeldin A partially disrupted the polymerizing system, but had little effect upon movement of the nascent proteochondroitin to the site for chondroitin polymerization and sulfation.