Relation of Cholesterol to Oligodendroglial Differentiation in C-6 Glial Cells

Abstract: The relation of cellular cholesterol content to a biochemical expression of oligodendroglial differentiation was studied in cultured C-6 glial cells. Induction of the oligodendroglial marker enzyme 2′: 3′-cyclic nucleotide 3′-phosphohydrolase (CNP) was determined after alteration of the sterol content of cellular membranes by exposure to compactin, a specific inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol synthesis. The sterol content and as a consequence, the sterol/phospholipid molar ratio of C-6 glial cells were decreased by treating the cells, in 10% lipoprotein-poor serum, with various concentrations of compactin for 24 h. The degrees of sterol depletion thus produced were maintained for 48 h after removal of the compactin if the cells were maintained in serum-free medium, the culture conditions necessary for induction of CNP in untreated cells. Forty-eight hours after removal of serum, no induction of CNP occurred in cells previously treated with 0.5 μg/ml of compactin, whereas untreated cells exhibited a three- to fourfold increase in CNP activity. Intermediate degrees of sterol depletion resulted in intermediate degrees of inhibition of the CNP induction. Moreover, the morphological expressions of glial differentiation observed in the untreated cells did not occur in the sterol-depleted cells. That the effect of compactin on the induction of CNP relates to depletion of sterol was indicated by the finding that when low-density lipoprotein was added to the compactin-treated cells, the induction of CNP, the morphological expressions of differentiation and the sterol/phospholipid molar ratios were preserved. The degree of sterol depletion that totally prevented the induction of CNP had no effect on (Na⁺+ K⁺)-activated ATPase activity, total protein synthesis and cell viability. The data define a critical role for sterol in oligodendroglial differentiation in this model system.     

Coordinate regulation of cholesterol synthesis and 3-hydroxy-3-methylglutaryl coenzyme A synthase but not 3-hydroxy-3-methylglutaryl coenzyme A reductase in C-6 glia

The effects on cholesterol biosynthesis of growth of cultured C-6 glial cells in serumfree medium ± supplementation with linoleic or linolenic acid were studied. Markedly higher activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase, EC 1.1.1.34) were observed in cells grown in linoleate- or linolenate-supplemented versus nonsupplemented medium. After 48 h HMG-CoA reductase activities were two-and four-fold higher in cells supplemented with 20 and 100 μm linoleate, respectively. The increase in activity became apparent after 24 h and was marked after 48 h. Rates of incorporation of [¹⁴C]acetate or ³H₂O into sterols did not reflect the changes in reductase activity. Thus, in cells supplemented with 50 μm linoleate for 24 and 48 h rates of incorporation of [¹⁴C]acetate were 75–80% lower than rates in nonsupplemented cells. This difference resulted because over the first 24 h of the experiment a fivefold increase in the rate of sterol synthesis occurred in the nonsupplemented cells, whereas essentially no change occurred in the linoleate-supplemented cells; little further change occurred between 24 and 48 h in the nonsupplemented and the linoleate-supplemented cells. That the difference in sterol synthesis under these experimental conditions could be mediated at the level of HMG-CoA synthase (EC 4.1.3.5) was suggested by two series of findings, i.e., first, similar quantitative and temporal changes in the activity of this enzyme, and, second, no change in the activity of acetoacetyl-CoA thiolase (EC 2.3.1.9) or the incorporation of [¹⁴C]mevalonate into sterols. Thus, the data suggest that HMG-CoA synthase, and not HMG-CoA reductase, may direct the rate of cholesterol biosynthesis under these conditions of serum-free growth ± supplementation with polyunsaturated fatty acid.     

Aneurysms of the Internal Carotid Artery Simulating Pituitary Tumours: Report of Two Cases

Two patients suffering from aneurysms of the internal carotid artery simulating pituitary tumours are reported. One of these was a 17-year-old boy with a mycotic aneurysm of the right internal carotid artery causing failure of growth and pubertal maturation. The second was a 53-year-old woman with a left internal carotid artery aneurysm, probably of atherosclerotic origin, who had evidence of anterior pituitary insufficiency.In both cases there was paresis of extraocular muscles and one patient had bitemporal hemianopsia. While lateral radiographs of the skull suggested intrasellar calcification in each case, further roentgenological investigation established that this calcification was actually extrasellar, and carotid arteriograms demonstrated the presence of an internal carotid aneurysm in each case. Investigations of the endocrine system confirmed the presence of anterior pituitary insufficiency in both patients, and diabetes insipidus became evident in one patient after cortisone therapy was commenced.This lesion, while rare, may be difficult to differentiate from a pituitary tumour. It is likely that this syndrome depends on aneurysmal expansion to the region of the sella turcica with compression of the pituitary gland itself, as well as the optic fibres.     

The effect of phenothiazines on Ca2+ fluxes in skeletal muscle sarcoplasmic reticulum

The effect of phenothiazines (trifluoperazine, chlorpromazine, methochlorpromazine, and imipramine) on Ca2+ fluxes in light and heavy sarcoplasmic reticulum (SR) isolated from rabbit fast-twitch skeletal muscle was investigated. These drugs inhibited Ca2+ loading and (Ca2+,Mg2+)-ATPase activity, but had no effect on unidirectional Ca2+ efflux from vesicles loaded either actively or passively with Ca2+. Chlorpromazine, which is membrane permeable, and its quaternary analog, methochlorpromazine, which is membrane impermeable, gave identical results. It is concluded that (a) the enhancement of net Ca2+ release by phenothiazines is due to inhibition of Ca2+ influx mediated by the Ca2+ pump rather than to the opening of a Ca2+ channel; and (b) phenothiazines act at the outer (myoplasmic) face of the SR membrane.     

Rapidly exchanging Ca2+ stores of non-muscle cells

The rapid and transient redistribution of calcium from intracellular stores is a key event of cell activation. The nature and molecular composition of intracellular Ca2+ stores of non-muscle cells are the object of intense investigation. In this paper, we review: (a) the experimental evidence in favor of the existence of intracellular, membrane-bound compartments specialized for uptake, storage and release of calcium, (b) the main protein components of rapidly exchanging Ca2+ stores, i.e. Ca2+ pump, intralumenal Ca2+ binding proteins (calsequestrin, calreticulin, etc.) and Ca2+ channels sensitive to either inositol 1,4,5-trisphosphate or Ca2+, caffeine and ryanodine, and (c) the relationship between Ca2+ stores and the endoplasmic reticulum.     

Effect of culture conditions on spore shelf life of the biocontrol agent Trichoderma harzianum

The influence of pH, carbon:nitrogen (C:N) ratio, carbon content and harvesting time on spore attributes of the biocontrol agent Trichoderma harzianum was evaluated. The effect of these culture parameters on viability, shelf-life and ultrastucture was also assessed. pH was a key parameter to manipulate for both growth and sporulation, while carbon concentration and C:N ratio strongly affected spore production time. At fixed pH, the C:N ratio had a limited influence on production yield, but was critical for spore shelf-life. The highest spore longevity was found in a medium with a C:N ratio of 14 and a pH of 7.0, when most resulting spores were still alive after 45 d storage. These spores also remained viable during storage under a broad range of relative humidities, indicating that they would be more sustainable in the field.