Density-dependent expression of ganglioside GM3 by human skin fibroblasts in an all-or-none fashion, as a possible modulator of cell growth in vitro

Cell density-dependent reduction of dihydroceramide desaturase activity in neuroblastoma cells

We applied a metabolic approach to investigate the role of sphingolipids in cell density-induced growth arrest in neuroblastoma cells. Our data revealed that sphingolipid metabolism in neuroblastoma cells significantly differs depending on the cells' population context. At high cell density, cells exhibited G0/G1 cell-cycle arrest and reduced ceramide, monohexosylceramide, and sphingomyelin, whereas dihydroceramide was significantly increased. In addition, our metabolic-labeling experiments showed that neuroblastoma cells at high cell density preferentially synthesized very long chain (VLC) sphingolipids and dramatically decreased synthesis of sphingosine-1-phosphate (S1P). Moreover, densely populated neuroblastoma cells showed increased message levels of both anabolic and catabolic enzymes of the sphingolipid pathway. Notably, our metabolic-labeling experiments indicated reduced dihydroceramide desaturase activity at confluence, which was confirmed by direct measurement of dihydroceramide desaturase activity in situ and in vitro. Importantly, we could reduce dihydroceramide desaturase activity in low-density cells by applying conditional media from high-density cells, as well as by adding reducing agents, such as DTT and L-cysteine to the media. In conclusion, our data suggest a role of the sphingolipid pathway, dihydroceramides desaturase in particular, in confluence-induced growth arrest in neuroblastoma cells.

Role of gangliosides in the association of ErbB2 with lipid rafts in mammary epithelial HC11 cells

We analyzed the role of gangliosides in the association of the ErbB2 receptor tyrosine-kinase (RTK) with lipid rafts in mammary epithelial HC11 cells. Scanning confocal microscopy experiments revealed a strict ErbB2-GM3 colocalization in wild-type cells. In addition, analysis of membrane fractions obtained using a linear sucrose gradient showed that ErbB2, epidermal growth factor receptor (EGFR) and Shc-p66 (proteins correlated with the ErbB2 signal transduction pathway) were preferentially enriched in lipid rafts together with gangliosides. Blocking of endogenous ganglioside synthesis by (+/-)-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol hydrochloride ([D]-PDMP) induced a drastic cell-surface redistribution of ErbB2, EGFR and Shc-p66, within the Triton-soluble fractions, as revealed by linear sucrose-gradient analysis. This redistribution was partially reverted when exogenous GM3 was added to ganglioside-depleted HC11 cells. The results point out the key role of ganglioside GM3 in retaining ErbB2 and signal-transduction-correlated proteins in lipid rafts.

Cell density-dependent expression of EDG family receptors and mesangial cell proliferation: role in lysophosphatidic acid-mediated cell growth

Lysophosphatidic acid (LPA), a major member of the bioactive lysophospholipids in serum, possesses diverse physiological activities including cell proliferation. Recently, three endothelial differentiation gene (EDG) family receptors, including EDG-2 (LPA1), EDG-4 (LPA2), and EDG-7 (LPA3), have been identified as LPA receptors. The role of LPA and their receptors in mesangial cell physiology is not clearly understood. This study examined the expression profile of EDG receptors as a function of cell density and the participation of EDG receptors in human mesangial cell proliferation by LPA. We showed that mesangial cells express all three EDG family LPA receptors in a cell density-dependent manner. EDG-7 maximally expressed at sparse cell density and minimally expressed in dense cell population. The EDG-2 expression pattern was opposite to the EDG-7. No changes in EDG-4 expression as a function of cell density were noted. DNA synthetic rate was greater in sparse cell density compared with dense cell population and followed a similar pattern with EDG-7 expression. Comparative studies in sparse and dense cell density indicated that EDG-7 was positively associated, whereas EDG-2 was negatively associated with cell proliferation rate. LPA induced mesangial cell proliferation by 1.5- to 3.5-fold. Dioctanoylglycerol pyrophosphate, an antagonist for EDG-7, almost completely inhibited mesangial cell proliferation induced by LPA. We suggest that EDG-7 regulates LPA-mediated mesangial cell proliferation. Additionally, these data suggest that EDG-7 and EDG-2 LPA receptors play a diverse role as proliferative and antiproliferative, respectively, in mesangial cells. Regulation of EDG family receptors may be importantly linked to mesangial cell-proliferative processes.

Inhibition of fibroblast proliferation in cardiac myocyte cultures by surface microtopography

Cardiac myocyte cultures usually require pharmacological intervention to prevent overproliferation of contaminating nonmyocytes. Our aim is to prevent excessive fibroblast cell proliferation without the use of cytostatins. We have produced a silicone surface with 10-microm vertical projections that we term "pegs," to which over 80% of rat neonatal cardiac fibroblasts attach within 48 h after plating. There was a 50% decrease in cell proliferation by 5 days of culture compared with flat membranes (P < 0.001) and a concomitant 60% decrease (P < 0.01) in cyclin D1 protein levels, suggesting a G1/S1 cell cycle arrest due to microtopography. Inhibition of Rho kinase with 5 or 20 microM Y-27632 reduced attachment of fibroblasts to the pegs by over 50% (P < 0.001), suggesting that this signaling pathway plays an important role in the process. Using mobile and immobile 10-microm polystyrene spheres, we show that reactive forces are important for inhibiting fibroblast cell proliferation, because mobile spheres failed to reduce cell proliferation. In primary myocyte cultures, pegs also inhibit fibroblast proliferation in the absence of cytostatins. The ratio of aminopropeptide of collagen protein from fibroblasts to myosin from myocytes was significantly reduced in cultures from pegged surfaces (P < 0.01), suggesting an increase in the proportion of myocytes on the pegged surfaces. Connexin43 protein expression was also increased, suggesting improved myocyte-myocyte interaction in the presence of pegs. We conclude that this microtextured culture system is useful for preventing proliferation of fibroblasts in myocyte cultures and may ultimately be useful for tissue engineering applications in vivo.

Differential expression of receptors for Shiga and Cholera toxin is regulated by the cell cycle

Cholera and Shiga toxin bind to the cell surface via glycolipid receptors GM1 and Gb3, respectively. Surprisingly, the majority of Vero cells from a non-synchronized population bind either Cholera or Shiga toxin but not both toxins. The hypothesis that the differential expression of toxin receptors is regulated by the cell cycle was tested. We find that Cholera toxin binds preferentially in G0/G1, with little binding through S-phase to telophase,whereas Shiga toxin binds maximally through G2 to telophase but does not bind during G0/G1 and S-phase. The changes result from the corresponding changes in Gb3 and GM1 synthesis, not from variations of receptor transport to the cell surface. The changes do not reflect competition of Gb3 and GM1 synthesis for lactosylceramide. Cells as diverse as Vero cells, PC12 cells and astrocytes show the same cell-cycle-dependent regulation of glycosphingolipid receptors,suggesting that this novel phenomenon is based on a conserved regulatory mechanism.

Emerging targets: molecular mechanisms of cell contact-mediated growth control

Contact inhibition of cell proliferation evokes a unique cellular program of growth arrest compared with stress, age, or other physical constraints. The last decade of research on genes activated by cell-cell contact has uncovered features of transmembrane signaling, cytoskeletal reorganization, and transcriptional control that initiate and maintain a quiescent phenotype. This review will focus on mechanisms controlling contact inhibition of cell proliferation, highlighting specific gene expression responses that are activated by cell-cell contact. Although a temporal framework for imposition of these mechanisms has not yet been well described, contact inhibition of cell proliferation clearly requires their coordinated function. Novel targets for intervention in proliferative disorders are emerging from these studies.

Immunohistological and flow cytometric analysis of glycosphingolipid expression in mouse lymphoid tissues

Expression of neutral glycosphingolipids (GSLs) and gangliosides in normal lymphoid tissues and cells has been studied mostly by biochemical and immunochemical analysis of lipid extracts separated by thin-layer chromatography. GSLs and gangliosides involved in the GM1b biosynthetic pathway were assigned to T-lymphocytes, whereas B-cell gangliosides and GSLs have been poorly characterized in former publications. We used specific polyclonal antibodies in immunohistochemistry and flow cytometry to analyze the distribution of globotriaosylceramide (Gb(3)Cer), globoside (Gb(4)Cer), gangliotriaosylceramide (Gg(3)Cer), gangliotetraosylceramide (Gg(4)Cer), and gangliosides GM3 and GalNAc-GM1b in the mouse thymus, spleen, and lymph node. Immature thymocytes expressed epitopes recognized by all antibodies, except for anti-Gb(4)Cer. Mature thymocytes bound only antibodies to GalNAc-GM1b, Gg(4)Cer, and Gb(4)Cer. In secondary lymphoid organs, antibodies to globo-series GSLs bound to vascular spaces of secondary lymphoid organs, whereas the ganglio-series GSL antibodies recognized lymphocyte-containing regions. In a Western blotting analysis, only GalNAc-GM1b antibody recognized a specific protein band in all three organs. Flow cytometric analysis of spleen and lymph node cells revealed that B-cells carried epitopes recognized by all antibodies, whereas the T-cell GSL repertoire was mostly oriented to ganglio-series-neutral GSLs and GM1b-type gangliosides. The results of immunohistochemistry and flow cytometry were not always identical, possibly because of crossreactivity to glycoprotein-linked oligosaccharides and/or differences between cell surface carbohydrate profiles of isolated cells and cells in a tissue environment.

Sphingolipids as receptor modulators. An overview

Glycosphingolipids are amphipathic compounds that exist mainly in the plasmalemma with their oligosaccharide portion protruding into the extracellular environment. In this position they are admirably situated for interacting with both ligands and receptors. Binding studies have demonstrated that specific glycolipids function as receptors for some microorganisms and bacterial toxins. Specific oligosaccharides on both glycolipids and glycoproteins bind members of the selection families, and some gangliosides facilitate integrins binding to their ligands. Gangliosides modulate the trophic factor-stimulated dimerization, tyrosine phosphorylation, and subsequent signal transduction events of several tyrosine kinase receptors. GM3 inhibits both the epidermal growth factor receptor and basic fibroblast factor receptor; several gangliosides except GM3 inhibit the platelet-derived growth-factor receptor; GM1 enhances nerve growth-factor-stimulated activation of TrkA; insulin receptor is inhibited to varying degrees by several gangliosides, but 2-->3 sialosylparagloboside is most effective. Activities of the beta(1)-adrenergic and delta-opioid receptors are modulated by GM1. Available information suggests that glycolipids serve as coordinators of multiple receptor functions.

Large scale purification of gangliosides GM3(Neu5Ac) and GM3(Neu5Gc) by trimethylaminoethyl-Fractogel high-performance liquid chromatography

A preparative anion-exchange high-performance liquid chromatographic method for the separation of the closely allied monosialogangliosides GM3(Neu5Ac) and GM3(Neu5Gc) has been developed. Hybridoma cells, readily available material derived from industrial monoclonal antibody production, were used as ganglioside source and led to fractions with pure GM3(Neu5Ac) and GM3(Neu5Gc) in high milligram quantities. The crude ganglioside extract was loaded onto columns filled with the strong anion-exchanger trimethylaminoethyl (TMAE)-Fractogel. Gangliosides were eluted from the stationary phase with a gradient system of ammonium acetate in methanol. The scaled-up approach ranged over more than one order of magnitude from 20 to 500 mg batches of GM3 gangliosides. Thus, the high-resolution power of the strong anion-exchanger TMAE-Fractogel allowed the preparative isolation by one-step column chromatography of two GM3 specimens which only differ in one hydroxyl group at position 5 of the neuraminic acid (N-acetyl-versus N-glycolylneuraminic acid).

Deletion of complex gangliosides of human glioma cells during mitotic cell division

Glycolipid compositions of the human glioma cell line T98G were studied during each phase of the cell cycle to see if those cell surface molecules are concerned with cell proliferation. In vitro cultured non-synchronized T98G cells are composed of ceramidemonohexoside (CMH), ceramidedihexoside (CDH), ceramidetrihexoside (CTH) and neolactotetraosylceramide (nLc4Cer) as neutral glycolipids, and of sulfatide (CS), gangliosides GM3, GM2, GD1a and several other gangliosides as acidic ones. While total glycolipid content per cellular weight was shown to be increased during the M phase, deletion of complex gangliosides particularly b-series gangliosides was recognized (p < 0.05). The glycolipid profile in other phases was fairly consistent, and there was no glycolipid molecule specific to a certain phase of the cell cycle. Relative enhancement of simple gangliosides with a decrease of complex ones during mitotic division may imply the functional involvement of complex gangliosides in cell-cell or cell-matrix attachment, which may have to be abandoned during the process of detachment from the matrix or cellular cleavage.

Effects of oestrogen on the extracellular matrix in the endometrium of postmenopausal women

AIM

To obtain insight into the effects of oestrogen on extracellular matrix (ECM) in the postmenopausal endometrium.

METHODS

The distribution of the components of the ECM, including collagen types I, III, IV, and VI, and laminin, was investigated in the human postmenopausal endometrium by an indirect immunofluorescence method with specific monoclonal antibodies and a polyclonal antibody. Collagens were also extracted from the endometrial tissues of postmenopausal women who had or had not been treated with oestrogen for three weeks.

RESULTS

Immunohistochemical studies demonstrated that type I collagen was the predominant interstitial collagen, and that types III and VI collagens were absent or very sparsely distributed in the stroma of the postmenopausal endometrium. However, types I, III, and VI collagens were diffusely localised in the stroma of the postmenopausal endometrium after administration of oestrogen. Even though type IV collagen was not seen in the basement membrane of the endometrial glands in the endometrium of postmenopausal women in the absence of oestrogen treatment, both type IV collagen and laminin were localised exclusively in the basement membrane of the endometrial glands in the postmenopausal endometrium after three weeks of oestrogen treatment. The level of type III collagen relative to that of type I collagen was significantly increased (p < 0.01) in the endometrium of oestrogen treated postmenopausal women compared with non-treated postmenopausal women.

CONCLUSIONS

Conjugated equine oestrogen might induce changes in the distribution of components and in the composition of the ECM in the endometrium of postmenopausal women.

Cell density regulates crypticity of GM3 ganglioside on human glioma cells

Human glioma cell line KG-1C contains GM3 ganglioside as its sole glycolipid. The degree of M2590 antibody binding to GM3 was found to be regulated by the cell density; the percentage of positive cells in FACS analysis decreased from approximately 20% to close to none as the cells increased their density from sparse to confluent. The contents of GM3 with different cell densities were consistent, being more than 0.4 micromol/g of the cellular weight, which was high enough to be recognized by the antibody. Trypsin treatment of the cells did not increase antibody reactivity. The extracted GM3 retained its antigenicity, being intensely stained with M2590 on a TLC plate; there was no change in chromatographic mobility either, indicating no modification of its chemical structure. The fluorescent microscope disclosed scattered dot-like staining of GM3, particularly at the periphery of the cells. We were able to expose cryptic GM3 fully within 12 h by dispersion of the cells to a sparse density. Surface labeling of GM3 with the use of limited sodium periodate oxidation of sialylated residue equally labeled GM3 either from the confluent cells or the sparse cells. Disassembly of actin filaments with cytochalasin B (10 microM) partially exposed cryptic GM3 of confluent cells, indicating reversibility of the crypticity. All together, the results indicate that cryptic GM3 actually exists on the cell surface, hidden from the surface not by other molecules but by other mechanisms associated with the cellular architecture. We are beginning to explore the possibility of selective localization of GM3 in small caves or folds of the cell membrane produced upon cell-to-cell contact.

Increase in the relative level of type V collagen during development and ageing of the placenta

AIM

To obtain some insight into the extracellular matrix in the placenta, changes in the composition of collagens during placental development were investigated.

METHODS

Collagen was extracted from placentas (group 1, 25-30 weeks, n = 21; group 2, 31-36 weeks, n = 32; and group 3, 37-41 weeks of gestation, n = 40) and the relative concentrations of various collagens were evaluated by SDS-PAGE.

RESULTS

The ratio of the intensity of the alpha 1 (III) band to that of alpha 1 (I) chain collagen in group 3 placentas were lower than those in group 1 placentas. In contrast, the ratio of the intensity of the alpha 1 (V) band to that of alpha 1 (I) chain collagen in group 3 placentas were higher than those in group 1 and group 2 placentas.

CONCLUSIONS

These results suggest that type V collagen might play an important role in the function of the placenta and that an increased relative concentration of type V collagen might be closely associated with the development and ageing of the placenta.

Overexpression of monosialoganglioside GM3 on lymphocyte plasma membrane in patients with HIV infection

SUMMARY

This study was undertaken to analyze both the GM3 expression on peripheral blood lymphocytes of HIV-infected patients and the relationship between ganglioside content and anti-GM3 reactivity. GM3 expression was determined as a percentage of lipid-bound sialic acid and by cytofluorimetric analysis in 25 AIDS patients, 20 anti-HIV+ asymptomatic subjects, 25 patients with different viral disease, and 25 healthy donors. GM3 distribution was analyzed by immunofluorescence and immunoelectron microscopy. A follow-up study to detect anti-lymphocytic GM3 antibodies was performed in progressive and nonprogressive anti-HIV+ subjects. Lymphocytes from HIV-infected patients showed a significant increase of plasma membrane GM3 content; no difference was found between CD4+ and CD8+ cells. Immunofluorescence and immunoelectron microscopic analysis showed that GM3 was distributed in large clusters over the cell plasma membrane. The follow-up study revealed that the occurrence of anti-lymphocytic GM3 antibodies was significantly higher in patients with progressive disease, compared with asymptomatic non-progressive subjects. These findings revealed that (1) the increased GM3 content in HIV-infected patients is detected at the plasma membrane level, (2) GM3 overexpression is able to induce an increased reactivity with anti-GM3 antibodies, and (3) the appearance of anti-lymphocytic GM3 antibodies in asymptomatic anti-HIV+ subjects could have prognostic relevance for the risk of developing AIDS.

Prosaposin and prosaptide, a peptide from prosaposin, induce an increase in ganglioside content on NS20Y neuroblastoma cells

Prosaposin has been recently identified as a neurotrophic factor eliciting differentiation in neuronal cultured cells (NS20Y). In this paper we investigate whether prosaposin and its active peptide (prosaptide) may modify the ganglioside pattern in neuroblastoma cells. The analysis by high performance thin layer chromatography did not reveal qualitative changes in the ganglioside pattern of NS20Y cells incubated in the presence of prosaposin, compared to control cells, but it did reveal an increase of the content of all three major resorcinol positive bands (GM3, GM2, GD1a). Cytofluorimetric and immunofluorescence microscopic analysis revealed that the increase of the ganglioside content was at the plasma membrane level. These findings suggest that the neurotrophic activity of prosaposin on NS20Y neuroblastoma cells might be mediated in part by the increase of cell surface gangliosides.

Role of gangliosides in tumour progression: a molecular target for cancer therapy?

In a number of patients with tumours of either neuroectodermal or epithelial origin, polysialylated gangliosides (e.g. GD3) are over-expressed. The mechanism of ganglioside over-expression may be different for the two classes of tumour and could represent distinct secondary genetic mutations or epigenetic changes affecting the enzymes (transferases and/or hydrolases) controlling the metabolic interconversions of these gangliosides. Tumour cells of neuroectodermal origin (e.g. melanomas and brain tumours) are known to produce and shed polysialylated gangliosides, whereas paracrine signal(s) from tumour cells of epithelial origin (e.g. carcinomas of cervix, lung, prostate, breast, head and neck, colon and ovary) may stimulate over-expression and shedding from tumour infiltrating mesenchymal cells (e.g. macrophages and/or fibroblasts). This cellular membrane over-expression and shedding of acidic glycosphingolipids into the interstitial spaces and blood of cancer patients may play a central role in increased tumour cell growth, lack of immune cell recognition and neovascularization and could represent a molecular target for cancer therapy.

Significant inhibition of hybridoma cells by exogenous application of ganglioside GM3, a possible modulator of cell growth in vitro

Gangliosides of the mouse-rat hybridoma cell line 187.1, which secretes an antibody against kappa-light chain of mouse IgG, were isolated and structurally characterized by biochemical and immunological methods (overlay technique), and fast atom bombardment-mass spectrometry. Exclusively GM3, substituted with C24:1 and C16:0 fatty acid and C18:1 sphingosine, was found in this B cell derived cell line. A GM3(NeuGc) to GM3(NeuAc) ratio (80 to 20), was characteristic for 187.1 cells, and absolute GM3 amounts of about 0.3 mg 10(-9) viable cells were determined. Exogenous application of GM3, which has been isolated from large cell preparations, to 187.1 cells showed growth inhibition in a concentration dependent manner. Using the MTT-assay and the [3H]thymidine incorporation assay, the cells exhibited a strong reduction in metabolic and proliferative activity, respectively, after exposure of cells to GM3. GM3 was applied in concentrations between 3 microM and 30 microM, giving evidence for strong inhibitory effects at 30 microM GM3 and less but significant suppression after application of GM3 concentrations lower than 20 microM. No cellular response was observed at the lowest concentration (3 microM) used in this study. Hybridoma cells as well as other cell types like fibroblasts, muscle cells and endothelial cells, are in general characterized by high expression of the GM3 ganglioside, which is known to act as a modulator of cellular growth in monolayer cultures of adherent cells. Since gangliosides are released to the culture medium by cell lysis, i.e. cell death, and/or by active membrane shedding, the results obtained in this study suggest a growth regulatory role of GM3 in high density hybridoma cell cultures.

Cyclic AMP causes differentiation and decreases the expression of neutral glycosphingolipids in cell cultures derived from a malignant glioma

Cultures derived from a malignant glioma (U-87 MG) were treated with 3 mM dibutyryl cAMP. The treatment resulted in morphological differentiation of the cultures and a decrease in cell proliferation. Biochemically, dibutyryl cAMP treatment caused a general reduction in the concentration of neutral glycosphingolipids in the U-87 MG cells. The concentration of individual neutral glycosphingolipids in the untreated cells was 1.8- to 3.0-fold higher than in cells treated for 72 h with 3 mM dibutyryl cAMP. Cells were labeled with [3H]galactose to monitor synthesis of the neutral glycosphingolipids. Decreased synthesis was noted in cells treated with dibutyryl cAMP as compared with untreated cells as indicated by decreased uptake of [3H]galactose label. The ganglioside composition of the cells was essentially unchanged after dibutyryl cAMP treatment.

The ganglioside GD1 alpha' IV3Neu5Ac, III6Neu5Ac-GgOse4Cer, is a major disialoganglioside in the highly metastatic murine lymphoreticular tumour cell line MDAY-D2

The aim of the present study was to investigate the ganglioside expression of the highly metastatic murine lymphoreticular tumour cell line MDAY-D2. Cells were propagated under controlled pH conditions and oxygen supply in bioreactors of 1 and 7.5 l volumes by repeated batch fermentation. Gangliosides were isolated from 2.7 x 10(11) cells, purified by silica gel chromatography and separated into mono- and disialoganglioside fractions by preparative DEAE anion exchange high performance liquid chromatography. Individual gangliosides were obtained by preparative thin layer chromatography. Their structural features were established by immunostaining, fast atom bombardment and gas chromatography mass spectrometry. In addition to gangliosides of the GM1a-pathway (GM2, GM1a and GD1a) and GM1b (IV3Neu5Ac-GgOse4Cer) and GalNAc-GM1b of the Gm1b-pathway, the disialoganglioside GD1 alpha (IV3Neu5Ac, III6Neu5Ac-GgOse4Cer) was found in equal amounts compared to GD1a (IV3Neu5Ac, II3Neu5Ac-GgOse4Cer). All gangliosides were substituted with C24:0, 24:1 and C16:0 fatty acids, sphingosine and N-acetylneuraminic acid as the sole sialic acid.

Ganglioside alterations in YAC-1 cells cultivated in serum-supplemented and serum-free growth medium

Gangliosides of the 'GM1b-pathway' (GM1b and GalNAc-GM1b) have been found to be highly expressed by the mouse T lymphoma YAC-1 grown in serum-supplemented medium, whereas GM2 and GM1 ('GM1a-pathway') occurred only in low amounts [Müthing, J., Peter-Katalinić, J., Hanisch, F.-G., Neumann, U. (1991) Glycoconjugate J 8:414-23]. Considerable differences in the ganglioside composition of YAC-1 cells grown in serum-supplemented and in well defined serum-free medium were observed. After transfer of the cells from serum-supplemented medium (RPMI 1640 with 10% fetal calf serum) to serum-free medium (RPMI 1640 with well defined supplements), GM1b and GalNAc-GM1b decreased and only low amounts of these gangliosides could be detected in serum-free growing cells. The expression of GM1a was also diminished but not as strongly as that of GM1b and GalNAc-GM1b. These growth medium mediated ganglioside alterations were reversible, and the original ganglioside expression was achieved by readaptation of serum-free growing cells to the initial serum-supplemented medium. On the other hand, a 'new' ganglioside, supposed to represent GalNAc-GD1a and not expressed by serum-supplemented growing cells, was induced during serum-free cultivation, and increased strongly after readaptation. These observations reveal that the ganglioside composition of in vitro cultivated cells can be modified by the extracellular environment due to different supplementation of the basal growth medium.

Gangliosides and neuronal differentiation

Using the GD3-specific mAb R24 we demonstrate by immunohistochemistry that the first embryonic cells of chicken expressing GD3 represent heavily proliferating cells of mesodermal origin (mesenchymal stem and endothelial cells). At this developmental stage (E1-1.5) neuroectodermal cells of the forming neural tube are not stained by R24 or any other available anti-ganglioside antibodies. These cells of the neural tube start to express GD3 at around E1.5 in parallel with increasing proliferative activity. Likewise proliferating and migrating neuronal crest derivates as well as undifferentiated retinal cells, the forming lens and otic placodes increasingly express GD3 in an organ-specific pattern following the spatiotemporal increase in mitotic activity. Immunostaining of GD1b (mAb D21b) or c-pathway polysialogangliosides (mAb Q211) is not obtained before E2.5, is nervous tissue specific and restricted to "new-born" neurons, which start to migrate and form first neurites. This striking change in ganglioside synthesis and expression also occurs in primary cell cultures (after or without previous Q211-mediated complement kill of neurons) during differentiation of mitotic progenitor cells to neurons (neurogenesis). In cell culture, the fluorescence staining is evenly distributed over the whole neuronal surface including filopodia at the growth cones. Monensin (10(-8) M) prevents expression of GD1b and c-polysialogangliosides and simultaneously differentiation of neuronal morphology (neurogenesis). The presence of exogenous gangliosides from bovine brain leads to a decrease of the monensin effect or even abolishes it.

Cell surface distribution of endogenous and effects of exogenous gangliosides on neuronal survival, cell shape and growth in vitro

In vitro immunostaining of neurons from spinal cord or brain of embryonic chicken by means of monoclonal anti-ganglioside antibodies (Q211, D21b) revealed a fluorescence-labeling of c-polysialogangliosides and GD1b evenly distributed over the entire neuronal surface including filopodia at the growth cones. On electronmicroscopical level the gold-stained ganglioside-antigens were found more or less densely packed in small adjacent areas suggesting a concentration in local "domains". Survival in serum-free or serum-containing medium of embryonic spinal cord motoneurons, which normally died if not cultivated in muscle conditioned medium or in contact to myotubes, was remarkably improved in the presence of a ganglioside mixture (10 microM) from bovine brain. If embryonic neurons from optic lobes were cultivated at low Ca(2+)-concentration (< 20 microM) they developed flat, broad cell bodies with many filopodia and only a few flat-shaped short processes. A very weak cytoskeleton-staining by means of rhodamine-linked phalloidine indicated that polymerization of actin was impaired in these neurons. At the same low Ca(2+)-concentration of < 20 microM but in the presence of ganglioside GM1 (up to 100 microM) most of the neurons developed a "normal" cell shape with rounded perikarya and thin neurites with "normal" shaped growth cones. In this case rhodamine-linked phalloidine revealed a much more intense staining mainly concentrated within the growing tips. The morphology and growth of the ganglioside-treated neurons resembled that of neurons cultivated at a higher Ca(2+)-concentration of at least 600 microM.

Mitogenic effects of bacterial neuroaminidase and lactosylceramide on human cultured fibroblasts

Exogenously added bacterial neuraminidase and lactosylceramide both stimulated the growth of cultured human skin fibroblasts. Neuraminidase (100 units/ml) increased DNA synthesis 1.9-fold and cell density 1.4-fold after 24 and 48 h, respectively, in culture. Treated fibroblasts contained less ganglioside NeuAc alpha 2-3Gal beta 1-4GlcCer (GM3), presumably due to neuraminidase-catalyzed hydrolysis to lactosylceramide. Addition of lactosylceramide (100 microM) to the fibroblast culture medium also increased DNA synthesis threefold within 24 h and cell density twofold after 48 h. These findings are compatible with a mechanism by which the proliferation of human fibroblasts is regulated by the relative levels of GM3 and lactosylceramide in the plasma membrane.

Lipid modulators of epidermal proliferation and differentiation

The importance of lipids within the skin as components of the permeability barrier has been appreciated for quite some time. However, the more recent work reviewed here suggests numerous alternative bioactive functions for lipid molecules within the skin and other tissues. The precise roles of lipids in epidermal proliferation and differentiation have only begun to be studied and are far from being defined.