RNA synthesis in rat liver cells with different DNA contents

Continuous transport of a small fraction of plasma membrane cholesterol to endoplasmic reticulum regulates total cellular cholesterol

Cells employ regulated transport mechanisms to ensure that their plasma membranes (PMs) are optimally supplied with cholesterol derived from uptake of low-density lipoproteins (LDL) and synthesis. To date, all inhibitors of cholesterol transport block steps in lysosomes, limiting our understanding of post-lysosomal transport steps. Here, we establish the cholesterol-binding domain 4 of anthrolysin O (ALOD4) as a reversible inhibitor of cholesterol transport from PM to endoplasmic reticulum (ER). Using ALOD4, we: (1) deplete ER cholesterol without altering PM or overall cellular cholesterol levels; (2) demonstrate that LDL-derived cholesterol travels from lysosomes first to PM to meet cholesterol needs, and subsequently from PM to regulatory domains of ER to suppress activation of SREBPs, halting cholesterol uptake and synthesis; and (3) determine that continuous PM-to-ER cholesterol transport allows ER to constantly monitor PM cholesterol levels, and respond rapidly to small declines in cellular cholesterol by activating SREBPs, increasing cholesterol uptake and synthesis.

A cullin gene is induced in tomato roots forming arbuscular mycorrhizae

We have isolated a cDNA clone, Le-MI-13 (Lycopersicon esculentum mycorrhizal induced) by differential screening of a cDNA library prepared from mRNA extracted from tomato roots colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae. The Le-MI-13 clone encodes a polypeptide that shows a high degree of amino acid sequence similarity with members of the recently identified multigene family, the cullins. Northern blot analyses demonstrated that the Le-MI-13 transcript accumulated in tomato roots forming arbuscular mycorrhizal symbiosis. Only very little Le-MI-13 transcript was detected in control roots. Tomato roots infected by the pathogenic fungus Phytophthora nicotianae var. parasitica did not accumulate Le-MI-13 transcript, indicating that upregulation of the Le-MI-13 gene is specific to roots forming arbuscular mycorrhizal symbiosis. Indirect evidence suggesting that a Le-MI-13-mediated cell-cycle-like control might operate in AM-colonized cells came from flow cytometry and static micro fluorimetry analysis. There was a strong correlation between nuclear polyploidization and AM colonization.Key words: tomato, arbuscular mycorrhizae, Phytophthora, cullins, polyploidy.

Potential mechanisms of metabolic imprinting that lead to chronic disease

This review synthesizes a subset of human epidemiologic and experimental animal studies that suggest that early nutrition affects susceptibility to chronic diseases in adulthood. These studies provide evidence that biological mechanisms may exist to "memorize" the metabolic effects of early nutritional environments. However, hypothesis-driven investigations of potential mechanisms have been scant. Thus, our understanding of the biology underlying metabolic imprinting is incomplete. A working definition of metabolic imprinting is proposed, emphasizing the adaptive nature and limited ontogenic window of the mechanisms putatively responsible for these relations. Five specific candidate mechanisms of metabolic imprinting are elaborated: 1) induced variations in organ structure, 2) alterations in cell number, 3) clonal selection, 4) metabolic differentiation, and 5) hepatocyte polyploidization. Last, experimental approaches for probing potential mechanisms with animal models are discussed.

Changes in numbers of pancreatic acinar cell nuclei and in DNA content during raw soya flour feeding in mice

Nuclei of pancreatic cells were isolated by trypsin-detergent digestion of fresh tissue and stained with propidium iodide, and nuclear DNA was measured by flow cytometry. Samples were isolated from mice fed either chow or raw soya flour (RSF) for periods ranging from 1 day to 48 weeks, beginning at 4 weeks of age. In chow-fed mice, the pancreas contained about 80% diploid (2N) and 20% tetraploid (4N) cells at the start of the study, but tetraploidy gradually increased to about 40% 2 weeks later (6 weeks of age) and remained at this level from that time onwards. Low levels of octaploid nuclei (8N) were also present in some animals after 2 weeks. In RSF-fed mice, about 20% tetraploid nuclei were also present for 1 and 2 days after starting RSF, but by 4 days tetraploidy had increased significantly to 40% and by 14 days had further increased to 50%. This level was significantly higher than that seen in chow-fed animals and was maintained for up to 48 weeks. Significantly higher numbers of octaploid nuclei were also present in the RSF-fed animals. In both chow- and RSF-fed mice, most cells were mononuclear, averaging 70% in chow-fed and 64% in RSF-fed animals. This difference was significant. This study shows that the mouse pancreas differs from the rat pancreas in the absence of a large population of binucleate acinar cells and the presence of considerable nuclear tetraploidy. Raw soya flour feeding leads to significant changes in these features, but in this species these changes do not appear to predispose to neoplasia.

Immunocytochemical determination of ploidy class-dependent bromodeoxyuridine incorporation in rat liver parenchymal cells after partial hepatectomy

Immunocytochemistry of bromodeoxyuridine (BrdU) incorporated in DNA was performed on cryostat sections of rat liver and on isolated hepatocytes after partial hepatectomy using a two-step labeling technique. The method enabled the detection of S-phase nuclei in both tissue preparations. Quantification of the number of labeled nuclei in sections showed that the number of nuclei in S-phase increased from 0.3% in control liver to about 36% at 24 h after partial hepatectomy. The detection of BrdU in isolated hepatocytes showed the same labeling index of binuclear diploid, mononuclear tetraploid and binuclear tetraploid cells. A special role for mononuclear diploid cells in proliferation did not seem to occur.

Leucine aminopeptidase activity of polyploid cells after centrifugal elutriation of rat hepatocytes of various ages

Rat hepatocytes were isolated by the perfusion method, and further separated with centrifugal elutriation into diploid cells and polyploid cells. The ploidy class and amount of polyploid (octaploid) cells increased with increasing flow rate. At higher flow rates of centrifugal elutriation, older rats contained much more octaploid cells than younger rats. Activity of acid phosphatase and leucine aminopeptidase increased with increasing flow rate (increasing ploidy class). Protein components of hepatocytes in octaploid cells were different from those of tetraploid cells. From these results, it is suggested that the function of the higher ploidy class hepatocytes is greater than that of lower ploidy class hepatocytes.

Long-term protein and calorie restriction: alterations in nucleic acid levels of organs of male rats

The effects of dietary restriction (calorie and/or protein) imposed at weaning on tissue concentrations of nucleic acids and protein were determined in young (one year) and old (two year) rats. In liver, calorie restriction increased protein concentration and decreased RNA/DNA and RNA/protein, while protein restriction elevated liver DNA and reduced protein and protein/DNA. These changes are consistent with decreased liver cell size in response to protein, but not calorie, restriction. Age also influenced these parameters, since DNA (elevated), RNA/protein (elevated), protein (reduced), and protein/DNA (reduced) differed in livers of old as compared to young rats. In kidney, DNA concentrations were unaffected by age or dietary restriction. Although protein and nucleic acid concentrations are commonly used as baselines for expressing other biochemical parameters, our results indicate that in liver, these factors vary both with age and nutritional status.

Changes in pancreatic acinar cell nuclear number and DNA content during aging in the rat

Pancreatic acinar cells from rats 5 to 658 days (94 weeks) of age were isolated by enzymatic dissociation and stained with the DNA specific fluorochrome Hoechst 33258. The nuclear DNA content and the incidence of binucleation were estimated in these cells. Total pancreatic weight, RNA, protein and DNA, and the incorporation of 3H-thymidine into pancreatic acinar cell DNA were also estimated in similar animals as measures of pancreatic growth. From 5 to 17 days after birth, 95% of the cells were mononucleate diploid and 5% were binucleate diploid; but during the period of rapid pancreatic growth over the following 39 days, acinar cells became increasingly binucleate. By 56 days after birth, 64% of cells were binucleate with a diploid DNA content per nucleus; and the incidence of binucleation then remained constant. At 28 days of age, 4% of mononucleate cells were tetraploid, increasing to 6% at 658 days of age. At this time 3% of binucleate cells contained dual tetraploid nuclei. There is thus a rapid development towards diploid binucleate acinar cells in the growing, postnatal pancreas; and in the adult pancreas a small proportion of these cells develop tetraploid nuclei.

Detection of metabolic changes in hepatocytes by quantitative cytochemistry

Studies by means of quantitative histochemistry and cytochemistry have greatly contributed to the knowledge of metabolic changes in liver parenchymal cells. In the present paper recent work along this line is reviewed with emphasis on three topics, polyploidy as a source of metabolic heterogeneity, proteolysis in the regulation of hepatocyte cell mass and ischemic injury of hepatocytes. In all three fields, accuracy and precision of information obtained by quantitative histochemical means has been greatly enhanced by a thorough knowledge of the mechanisms of histochemical reactions obtained by fundamental work on matrix chemistry, and well-considered application of optical measuring tools and conditions of measurement. These are the principles put forward by van Duijn since the pioneer period of histochemistry and to whom this review is dedicated.

Mechanisms regulating cell resistance to adriamycin. Evidence that drug accumulation in resistant cells is modulated by phosphorylation of a plasma membrane glycoprotein

Incubation of adriamycin resistant Chinese hamster lung cells with the calmodulin inhibitor trifluoperazine (TFP) resulted in a significant increase in the cellular accumulation of drug. When resistant cells were prelabeled with 32Pi and then treated with TFP, a major increase also occurred in the phosphorylation of a plasma membrane glycoprotein (P-180). The concentration of TFP required for inducing the superphosphorylation of this protein correlated well with the TFP concentration required for inducing an increase in drug accumulation in resistant cells. In addition to TFP, the Ca2+ channel blocker verapamil also induced drug uptake and enhanced the phosphorylation level of P-180. Additional studies showed that, when resistant cells reverted to drug sensitivity, there was a parallel loss in the TFP-induced P-180 phosphorylation. The results of this study indicate that the trifluoperazine-induced uptake of drug in resistant cells is mediated by a mechanism which involves an enhanced phosphorylation of P-180. It is suggested that, when this protein is superphosphorylated, it becomes biologically inactive, and that this results in the conversion of the resistant cell to one having a drug sensitive phenotype.

Growth and aging in the rat: changes in total protein, cellularity, and polyploidy in various organs

The objectives of this study were to determine the influence of growth and aging on ploidy, cell number, and protein content of various organs. Tissue homogenates were prepared at 3, 8, 25, 50, and 100 weeks of age. Samples were analyzed for DNA per nucleus (by flow cytofluorometry), nuclei number, and protein content. Livers of 8- and 100-week-old animals were also perfused with collagenase and the released cells separated into parenchymal and nonparenchymal populations by unit gravity sedimentation. Nuclei of these cells were also analyzed for DNA. In all four zones of the kidney and in thyroid, 4n nuclei diminished in percentage between 3 and 50 weeks and increased at 100 weeks. In the growth phase these probably are cycling cells and after 50 weeks represent an increasing population of nuclei arrested after synthesis of DNA. Constant levels of ploidy were found in brain, heart, rectus abdominis, and adrenal throughout the 3-100 weeks. A dramatic increase in 4n nuclei occurred between 3 and 8 weeks in liver with little change occurring thereafter. Ploidy is a property of only parenchymal cells in liver and this probably is also true in other organs. The 4n nuclei that remain in constant proportion to the total population are established early in life and are not related to aging. They are probably tetraploid and replicate into 4n daughter cells during growth. Cerebrum shows no changes in nuclei number but exhibits a 70% increase in protein between 3 and 100 weeks. Although kidney, liver and adrenal show large increases in number of nuclei (approximately equal to fourfold) with growth, these are not as great as increases in body weight (approximately equal to 11-fold). With regard to organ protein, only liver shows increases approximating those in body weight. Increases in organ nuclei appear to occur in concert for adrenal, kidney, and liver whereas increases in organ protein bear no relationship to each other. Protein content remains at stable levels in organs of 100-week-old animals and little (adrenal, liver) or no (brain, kidney) diminution occurs in nuclei numbers.

Ploidy class-dependent variations during 24 h of glucose-6-phosphate and succinate dehydrogenase activity and single-stranded RNA content in isolated rat hepatocytes

The time-dependent variations over 24 h of glucose-6-phosphate dehydrogenase (G6PDH) activity, succinate dehydrogenase (SDH) activity and single-stranded RNA (ssRNA) content have been investigated by cytophotometric analysis of cytochemically stained isolated hepatocytes of different ploidy classes from adult male rats. A marked variation of 48% over the day in G6PDH activity of the mononuclear diploid cells was revealed, but no significant variation in the binuclear tetraploid cells. The cells of the inbetween ploidy classes showed an amplitude of variation of 38% (binuclear diploid cells) and 24% (mononuclear tetraploid cells), respectively. All cells showed a maximum activity of the enzyme at the middle of the day and a minimum during the night. The relative enzyme activity per mononuclear diploid cell was significantly higher than the relative activity in the other cells, especially at its maximum. The variation of the SDH activity in hepatocytes isolated from the same rats was similar in all cells, irrespective of their ploidy class. The activity was highest at the end of the activity phase of the animals. The SDH activity per cell was directly proportional to the quantity of genome copies. The ssRNA content of the hepatocytes showed a time-dependent variation with a maximum during the resting phase of the animals and a minimum during their activity phase. The variation was larger in the mononuclear diploid cells than in the cells of other ploidy classes and the ssRNA content was also significantly higher in these cells than in the hepatocytes of other ploidy classes when calculated on the basis of genome copies. It is concluded that the large amplitude of variation over the day and the high relative amount of G6PDH activity and ssRNA content in mononuclear diploid cells is related to the function of these cells as stem cells of the liver parenchyma.

Histochemistry and cytochemistry of glucose-6-phosphate dehydrogenase

Histochemistry and cytochemistry of glucose-6-phosphate dehydrogenase has found many applications in biomedical research. However, up to several years ago, the methods used often appeared to be unreliable because many artefacts occurred during processing and staining of tissue sections or cells. The development of histochemical methods preventing loss or redistribution of the enzyme by using either polyvinyl alcohol as a stabilizer or a semipermeable membrane interposed between tissue section and incubation medium, has lead to progress in the topochemical localization of glucose-6-phosphate dehydrogenase. Optimization of incubation conditions has further increased the precision of histochemical methods. Precise cytochemical methods have been developed either by the use of a polyacrylamide carrier in which individual cells have been incorporated before staining or by including polyvinyl alcohol in the incubation medium. In the present text, these methods for the histochemical and cytochemical localization of glucose-6-phosphate dehydrogenase for light microscopical and electron microscopical purposes are extensively discussed along with immunocytochemical techniques. Moreover, the validity of the staining methods is considered both for the localization of glucose-6-phosphate dehydrogenase activity in cells and tissues and for cytophotometric analysis. Finally, many applications of the methods are reviewed in the fields of functional heterogeneity of tissues, early diagnosis of carcinoma, effects of xenobiotics on cellular metabolism, diagnosis of inherited glucose-6-phosphate dehydrogenase deficiency, analysis of steroid-production in reproductive organs, and quality control of oocytes of mammals. It is concluded that the use of histochemistry and cytochemistry of glucose-6-phosphate dehydrogenase is of highly significant value in the study of diseased tissues. In many cases, the first pathological change is an increase in glucose-6-phosphate dehydrogenase activity and detection of these early changes in a few cells by histochemical means only, enables prediction of other subsequent abnormal metabolic events. Analysis of glucose-6-phosphate dehydrogenase deficiency in erythrocytes has been improved as well by the development of cytochemical tools. Heterozygous deficiency can now be detected in a reliable way. Cell biological studies of development or maturation of various tissues or cells have profited from the use of histochemistry and cytochemistry of glucose-6-phosphate dehydrogenase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

mRNA population in the liver, kidney and brain of young and senescent mice: analysis of in vitro translation products

Possible alterations in the population of poly(A)(+)mRNA during ageing were investigated by translation in vitro of poly(A)(+)mRNA from the liver, kidney and brain of male ddY mice of different ages. [35S]Methionine-labeled translation products were analysed by two-dimensional polyacrylamide gel electrophoresis followed by fluorography. A protein product with a molecular weight of 30 000 and isoelectric point of 6.5 was reproducibly observed only in the fluorograms of translation products of poly(A)(+)mRNA derived from the livers of senescent mice (24.5 months old). However, no age-related change was detected in the translation products of the kidney and brain. These results suggest that gene expression in liver cells changes at the level of the population of cytoplasmic poly(A)(+)mRNA during ageing.

Albumin secretion and protein synthesis by cultured diploid and tetraploid rat hepatocytes separated by elutriation

Diploid and tetraploid rat hepatocyte subpopulations were isolated by elutriation and cultured for 24 h. Albumin secretion and protein synthesis rates were two-fold lower in 2n than in 4n hepatocytes. [35S]methionine-labelled proteins analysed by acrylamide gel electrophoresis showed a strikingly similar pattern in the two cell subpopulations. No differences in cellular proteins or in the intensity of labelling were observed. These results show (1) that viable diploid and tetraploid hepatocyte subpopulations can be separated by elutriation under sterile conditions and then cultured; and (2) strongly suggest that the same genes are transcribed and further translated at the same rate in both hepatocyte subpopulations.

Liver polyploidy: influence of age and of dietary restriction

Polyploidy increases with age in mammalian liver. Since dietary restriction increases lifespan, the question posed in this study was whether liver polyploidy would be influenced by dietary protein restriction. Restricted mice were fed a 4% protein diet, while control mice received a 26% protein diet. Polyploidy was determined from measurements of nuclear diameter on liver of 3 week, 1 1/2, 3, 10, 20 and 24-1/2 month old Swiss albino mice. The percentage of polyploid cells increased steadily with age. The rate of increase, expressed as the polyploidization index, was greater in the fully fed control animals as compared to the animals on protein restriction. Protein restriction thus retards the age associated process of polyploidization of liver nuclei. Nuclear diameter increased slightly with age, but was not influenced by protein restriction.

Age-related changes in isolated rat hepatocytes. Comparison of size, morphology, binucleation, and protein content

Hepatocytes isolated from 6-, 12-, 18-, and 30-month-old female Fischer F344 rats were examined by scanning electron microscopy. No significant change in cell size with age was observed. However, the surface morphology of the cells isolated from the older animals exhibited a significant increase in surface folds. This feature did not exceed 10% of the cell population until 12 months of age and continued to increase to 31% of the cells in 30-month-old rats. From 6 to 12 months of age, there was a significant increase in protein content of the hepatocytes. No further increase in protein content occurred during senescence. An increase in percentage of binuclear cells occurred after 24 months of age. Because ploidy and binucleation increase with increasing age, it appears that the nuclear/cytoplasmic ratio changes as a function of age.

Long chain polyenoic acid levels in viably sorted, highly enriched mouse testis cells

Twenty- and 22-carbon fatty acids of the linoleic (n-6) and linolenic (n-3) acid families were measured in murine spermatogonia and preleptotene spermatocytes (early), pachytene primary spermatocytes (1 degree), round spermatids (RS), condensing spermatids (CS) and Leydig cells enriched by staput velocity sedimentation at 1 G, followed by viable microflow sorting on the basis of light scatter and DNA content. 22:5(n-6) increased progressively from 2 to 20% of total fatty acid in the progression of germinal cell differentiation, early leads to 1 degree leads to RS leads to CS, but decreased in mature sperm. The precursor 20:4(n-6) showed a roughly reciprocal relationship. 22:6(n-3) showed no significant correlation with cell type. 22:5(n-6) was found highest in triglycerides of later differentiation stages whereas 20:4(n-6) and 22:6(n-3) were found primarily in phospholipid in all cell fractions.

Variability of short-term cultures of HeLa S-3 cells: changes in DNA distributions and rates of DNA synthesis

DNA distributions of HeLa S-3 cells in spinner culture exhibit significant time-dependent changes. The major differences appear to occur in the S-phase region. Significant changes in the rates of DNA synthesis in several S-phase subcompartments correlated well with the changes in the DNA distributions. It is proposed that fluctuations in these rates of DNA synthesis are a reflection of the inherent instability of these abnormal, heteroploid cells.

A comparison of protein synthesis by liver parenchymal cells isolated from Fischer F344 rats of various ages

Rates of protein synthesis by intact liver parenchymal cells isolated from male Fischer F344 rats ranging in age from 2.5 to 30 months were determined by measuring the incorporation of [3H] valine into acid-insoluble material and the specific activity of the extracellular valine. The rate of protein synthesis decreased 44% from 2.5 to 18 months and then increased slightly (18%) from 18 to 30 months. There was no dramatic change in the types of proteins synthesized by isolated liver parenchymal cells isolated from 2- or 18-month-old rats as determined by SDS-polyacrylamide gel electrophoresis. The ribosomal-transit time by liver parenchymal cells isolated from 18-month-old rats was 60% higher than the ribosomal-transit time of liver parenchymal cells isolated from 4-month-old rats. The fidelity of protein synthesis by parenchymal cells isolated from 4- and 18-month old rats was compared by measuring the incorporation of p-fluorophenyl alanine (an analogue of phenylalanine) into acid-insoluble material. Although protein synthesis decreased significantly from 4 to 18 months, the fidelity of protein synthesis remained constant.