Preparation of collagen substrates for cell attachment: effect of collagen concentration and phosphate buffer

Proteoglycans support proper granule formation in pancreatic acinar cells

Zymogen granules (ZG) are specialized organelles in the exocrine pancreas which allow digestive enzyme storage and regulated secretion. The molecular mechanisms of their biogenesis and the sorting of zymogens are still incompletely understood. Here, we investigated the role of proteoglycans in granule formation and secretion of zymogens in pancreatic AR42J cells, an acinar model system. Cupromeronic Blue cytochemistry and biochemical studies revealed an association of proteoglycans primarily with the granule membrane. Removal of proteoglycans by carbonate treatment led to a loss of membrane curvature indicating a supportive role in the maintenance of membrane shape and stability. Chemical inhibition of proteoglycan synthesis impaired the formation of normal electron-dense granules in AR42J cells and resulted in the formation of unusually small granule structures. These structures still contained the zymogen carboxypeptidase, a cargo molecule of secretory granules, but migrated to lighter fractions after density gradient centrifugation. Furthermore, the basal secretion of amylase was increased in AR42J cells after inhibitor treatment. In addition, irregular-shaped granules appeared in pancreatic lobules. We conclude that the assembly of a proteoglycan scaffold at the ZG membrane is supporting efficient packaging of zymogens and the proper formation of stimulus-competent storage granules in acinar cells of the pancreas.

Modulating zymogen granule formation in pancreatic AR42J cells

Zymogen granules (ZG) are specialized organelles in the exocrine pancreas which allow digestive enzyme storage and regulated secretion. To investigate ZG biogenesis, cargo sorting and packaging, suitable cellular model systems are required. Here, we demonstrate that granule formation in pancreatic AR42J cells, an acinar model system, can be modulated by altering the growth conditions in cell culture. We find that cultivation of AR42J cells in Panserin™ 401, a serum-free medium, enhances the induction of granule formation in the presence or absence of dexamethasone when compared to standard conditions including serum. Biochemical and morphological studies revealed an increase in ZG markers on the mRNA and protein level, as well as in granule size compared to standard conditions. Our data indicate that this effect is related to pronounced differentiation of AR42J cells. To address if enhanced expression of ZG proteins promotes granule formation, we expressed several zymogens and ZG membrane proteins in unstimulated AR42J cells and in constitutively secreting COS-7 cells. Neither single expression nor co-expression was sufficient to initiate granule formation in AR42J cells or the formation of granule-like structures in COS-7 cells as described for neuroendocrine cargo proteins. The importance of our findings for granule formation in exocrine cells is discussed.

Human umbilical cord stromal stem cell express CD10 and exert contractile properties

BACKGROUND

It has been demonstrated that human umbilical cord stromal stem cells (UCSSCs) are bio-equivalent to bone marrow mesenchymal stem cells. However, little is known about their tissue origin or in vivo functions, and data on their expansion properties are limited due to early senescence in the culture methods described to date.

METHODS

UC sections and cultured UCSSCs were analyzed with a panel of 12 antibodies. UCSSCs were grown in low-FCS containing medium at 5% or 21% oxygen and were assayed for their clonogenic properties, karyotype stability, expression of specific cellular markers, and multi-lineage potential. UCSSC contractile properties were evaluated by using collagen gel contraction assays under cytokine stimulus.

RESULTS

Immunohistochemistry studies showed that the UCSSCs were derived from the Wharton's jelly and not from the vascular smooth muscle sheath of the blood vessels. UCSSC growth properties were increased in a 5% oxygen atmosphere in comparison to normoxic culture conditions. In both culture conditions, UCSSCs were CD14-, CD34-, and CD45-negative while expressing high levels of CD73, CD90 and CD105 and maintaining their differentiation potentialities. UCSSCs expressed alpha smooth muscle actin and behaved as functional myofibroblasts when cellular contraction was challenged with appropriate stimuli.

CONCLUSIONS

UCSCs are mesenchymal stem cells that reside in the perivascular area of Wharton's jelly and are phenotypically and functionally related to myofibroblasts.

Analysis of low abundance membrane-associated proteins from rat pancreatic zymogen granules

Zymogen granules (ZG) are specialized storage organelles in the exocrine pancreas that allow the sorting, packaging, and regulated apical secretion of digestive enzymes. As there is a critical need for further understanding of the key processes in regulated secretion to develop new therapeutic options in medicine, we applied a suborganellar proteomics approach to identify peripheral membrane-associated ZG proteins. We focused on the analysis of a "basic" group (pH range 6.2-11) with about 46 spots among which 44 were identified by tandem mass spectrometry. These spots corresponded to 16 unique proteins, including rat mast cell chymase (RMCP-1) and peptidyl-prolyl cis-trans isomerase B (PpiB; cyclophilin B), an ER-resident protein. To confirm that these proteins were specific to zymogen granules and not contaminants of the preparation, we conducted a series of validation experiments. Immunoblotting of ZG subfractions revealed that chymase and PpiB behaved like bona fide peripheral membrane proteins. Their expression in rat pancreas was regulated by feeding behavior. Ultrastructural and immunofluorescence studies confirmed their ZG localization. Furthermore, a chymase-YFP fusion protein was properly targeted to ZG in pancreatic AR42J cells. Interestingly, for both proteins, proteoglycan-binding properties have been reported. The importance of our findings for sorting and packaging during ZG formation is discussed.

Contrasting effects of collagen and bFGF-2 on neural cell function in degradable synthetic PEG hydrogels

Injectable biodegradable cell carriers provide a potential means to improve transplanted cell viability in the nervous system by providing physical protection from compaction, shear forces, and the acute inflammatory response that occurs following transplantation into the host brain environment. Synthetic polyethylene glycol (PEG) hydrogels are ideal candidates for this purpose, as the degradation profile and mechanical properties of the gel can be controlled. Here we introduce biological components into the synthetic gel with the goal of improving neural cell function in the inert PEG environment. In this study, it was found that (1) bFGF-2 is a survival/mitogenic factor for neural precursor cells in degradable hydrogel cultures, (2) collagen has no measurable effect on cell survival, metabolic activity, or proliferation, and (3) co-application of collagen and bFGF-2 to hydrogel cultures targets cell survival and metabolic activity, an effect that is different than either applied individually. Because collagen and bFGF-2 support the survival and growth of neural cells and other cell types, the co-encapsulation approach and functional characterization described in this study can be extended to the development of an array of tissue engineering applications. These findings suggest the importance of understanding and developing strategies to control the chemical microenvironment surrounding cells in three-dimensional biomaterials.

Follicular dendritic cells are related to bone marrow stromal cell progenitors and to myofibroblasts

Follicular dendritic cells (FDC) are involved in the presentation of native Ags to B cells during the secondary immune response. Some authors consider FDC to be hemopoietic cells, whereas others believe them to be mesenchymal cells. The low proportion of FDC in the lymphoid follicle, together with technical difficulties in their isolation, make these cells difficult to study. We show that Fibroblast Medium can be used successfully to isolate and maintain FDC lines. In this culture medium, we obtained 18 FDC lines from human tonsils, which proliferated for as long as 18 wk and showed a stable Ag phenotype as detected by flow cytometry and RT-PCR. FDC lines were CD45-negative and expressed Ags associated to FDC (CD21, CD23, CD35, CD40, CD73, BAFF, ICAM-1, and VCAM-1) and Ags specific for FDC (DRC-1, CNA.42, and HJ2). These cell lines were also able to bind B cells and secrete CXCL13, functional activities characteristic of FDC. Nevertheless, the additional expression of STRO-1, together with CD10, CD13, CD29, CD34, CD63, CD73, CD90, ICAM-1, VCAM-1, HLA-DR, alkaline phosphatase, and alpha-smooth muscle actin (alpha-SM actin) indicated that FDC are closely related to bone marrow stromal cell progenitors. The expression of alpha-SM actin also relates FDC with myofibroblasts. Like myofibroblasts, FDC lines expressed stress fibers containing alpha-SM actin and were able to contract collagen gels under the effect of TGFbeta1 and platelet-derived growth factor. These findings suggest that FDC are a specialized form of myofibroblast and derive from bone marrow stromal cell progenitors.

Contractile activity of human decidual stromal cells. II. Effect of interleukin-10

CONTEXT

Human decidual stromal cells (DSC) are myofibroblast-like cells that express alpha-smooth muscle (alpha-SM) actin, a protein associated with cell contractility. Several lines of experimental evidence in humans and mice show that antiinflammatory cytokines favor normal pregnancy, whereas Th1 and inflammatory cytokines play a role in abortion. We previously demonstrated that IL-2, a Th1 cytokine, increased the contractility of human DSC.

OBJECTIVE

We studied the effect of the antiinflammatory cytokines IL-10 and IL-4 on the contractility of DSC from first-trimester pregnancy.

SETTING AND PATIENTS

We studied 10 healthy women who underwent elective vaginal termination of first-trimester pregnancy at Clínica El Sur, Málaga, and Clínica Ginegranada, Granada.

MAIN OUTCOME MEASURE(S)

After isolation of DSC, cell contractility was measured with the collagen gel contraction assay. alpha-SM actin was detected with Western blotting and immunofluorescence.

RESULTS

We found that IL-10, but not IL-4, increased the volume of the collagen gel matrixes in which the cytokine-treated DSC were cultured, showing that IL-10 decreased DSC contractility. By Western blotting we demonstrated that this effect was not related to an alteration in the synthesis of alpha-SM actin. Nevertheless, we observed by immunofluorescence microscopy that DSC treated with IL-10 exhibited stress fibers with a lower content of alpha-SM actin than untreated control DSC.

CONCLUSIONS

IL-10 relaxes DSC by reducing the incorporation of alpha-SM actin into their stress fibers. This relaxing activity may be of relevance for the maintenance of pregnancy.

Fibronectin fibrillogenesis on sulfonated polystyrene surfaces

Extracellular matrix (ECM) protein adsorption and organization serves as a critical first step in the development and organization of tissues. Advances in tissue engineering, therefore, will depend on the ability to control the rate and pattern of ECM formation. Fibronectin is a prominent component of the ECM, which undergoes fibrillogenesis in the presence of cells. Using sulfonated polysyrene surfaces, we showed that fibronectin undergoes a transition from monolayer to multilayer adsorption at calculated surface charge densities above 0.03 Coulombs (C)/m(2). At charge densities above approximately 0.08 C/m(2), distinct fibronectin fibrillar networks are observed to form with a fibril morphology similar to those observed to form in situ on cell surfaces. This self-organization process is time dependent, with the fibrils achieving dimensions of 30-40 microm in length and 1 microm in height after 72 h of incubation. We suggest that the polarization of charge domains on the polyampholytic fibronectin molecules near high charge density surfaces is sufficient to initiate the multilayer adsorption and the organization of these fibrillar structures. These results suggest that the nonlinear dependence of adsorption on surface charge density may play an important role in the self-organization of many matrix components.

Serglycin proteoglycan is sorted into zymogen granules of rat pancreatic acinar cells

Serglycin is known as a secretory granule proteoglyean in hematopoietic cells. In this study we identified a high-molecular-weight molecule in aggregated content proteins of zymogen granules of pancreatic acinar cells. The amino acid composition of the isolated protein showed high similarity to serglycin proteoglycan core protein. To confirm the expression of serglycin proteoglycan in pancreatic acinar cells we cloned the rat pancreas cDNA of serglycin core protein and detected the serglycin mRNA in pancreas tissue and AR4-2J cells by reverse transcription-PCR. In AR4-2J cells, transfected with serglycin fused to green fluorescent protein (EGFP), serglycin localized within a web-like pattern in the perinuclear space as well as with a punctate pattern distributed in the cytoplasm. The perinuclear structures colocalized with the Golgi membrane-associated protein p115 and the punctate structures with the secretory enzyme procarboxypeptidase A, indicating that the serglycin-EGFP fusion protein travels through compartments of the secretory pathway and is sorted into secretory granules. Using an antiserum against serglycin core protein immunofluorescence as well as immunogold electron microscopy analysis conrirmed the subcellular distribution of serglycin proteoglycan in zymogen granules of pancreatic acinar cells. To prevent glycosylation of serglycin core protein we incubated AR4-2J cells with 2 mM p-nitrophenyl-beta-D-xylopyranoside (PNP-xyloside), which serves as alternate substrate for glycosaminoglycan chain attachment. Furthermore, we deleted the serine/glycine repeat region in the serglycin core protein. In both approaches the transfected serglycin-EGFP fusion protein could be detected predominantly in perinuclear Golgi membrane structures, while in control cells the serglycin fusion protein was mostly sorted into the secretory granules. Additionally, we show that sorting of secretory enzymes like amylase

Hepatocyte encapsulation for enhanced cellular functions

An efficient bioartificial liver-assisted device can sustain the lives of patients with acute liver failure. Among different configurations of the bioreactor design, hepatocyte encapsulation has important features that satisfy most requirements of the device. We have encapsulated rat hepatocytes in a two-layer polymeric membrane by complex coacervation using a simple setup and demonstrated enhanced cellular functions up to three times higher than those of the monolayer control. These microcapsules of the functioning hepatocytes have a 2- to 3-microm outer layer of synthetic polymer with 25% 2-hydroxyethyl methacrylate, 25% methacrylic acid, and 50% methyl methacrylate and an inner layer of positively charged modified collagen as a suitable substrate for the enhanced cellular functions. Permeable only to small molecules up to albumin, the microcapsules should allow unimpeded exchange of nutrients, oxygen, growth factors, and metabolites but prevent attack by immunoglobulins of the immune system, and no "skin effect" of the collagen has been observed. Mechanical properties of the microcapsules measured with a nano-indentation method suggest that the microcapsules should be suitable for use in a bioartificial liver-assisted device.

LCC, a cerebroside from Lycium chinense, protects primary cultured rat hepatocytes exposed to galactosamine

Primary cultures of rat hepatocytes exposed to galactosamine (GalN) were used as a screening system to assess whether a new cerebroside, LCC, isolated from the fruits of Lycium chinense, exhibits hepatoprotective activity. Cultured rat hepatocytes injured with GalN routinely release glutamic pyruvic transaminase (GPT) and sorbitol dehydrogenase (SDH) into the culture medium. Treatment of these GalN-injured primary cultures with LCC markedly blocked the release of both GPT and SDH in a dose-dependent manner over concentrations of LCC ranging from 1 microM to 10 microM. To investigate the mechanism of action for the hepatoprotective activity of LCC, the extent of [(3)H]-uridine incorporation into RNA was measured in GalN-injured cultures of rat hepatocytes. [(3)H]-Uridine incorporation was significantly decreased in injured hepatocytes. LCC, however significantly restored the incorporation of [(3)H]-uridine into RNA in a dose-dependent manner over concentrations ranging from 1 microM to 10 microM. LCC also blocked the suppression of RNA synthesis caused by actinomycin D in a dose-dependent manner. These data suggest that LCC may have prominent hepatoprotective activity and that its therapeutic value should be investigated further.

Protective effects of bergenin, the major constituent of Mallotus japonicus, on D-galactosamine-intoxicated rat hepatocytes

This study was designed to investigate the effects of bergenin against D-galactosamine-induced injury in primary cultured rat hepatocytes. Bergenin (100 microM) decreased the release of glutamic pyruvic transaminase and sorbitol dehydrogenase by 62 and 50%, respectively, into hepatocyte medium incubated for 14 h with 1.5 mM galactosamine. Decreased RNA synthesis by 1.5 mM galactosamine was recovered 2.5 times compared with that of control hepatocytes at 100 microM bergenin. Therefore, the present results suggest that bergenin show hepatoprotective effects against galactosamine-intoxicated rat hepatocytes by inhibiting the release of glutamic pyruvic transaminase and sorbitol dehydrogenase as well as by increasing RNA synthesis.

Protection of rat hepatocytes exposed to CCl4 in-vitro by cynandione A, a biacetophenone from Cynanchum wilfordii

To identify hepatoprotective agents from plant sources we use primary cultures of rat hepatocytes injured by CCl4. The hepatoprotective agents are the compounds that mitigate the injury caused by CCl4. Using this system we have investigated the biochemical mechanisms involved in the hepatoprotective activity of cynandione A, a biacetopherone, isolated from the roots of Cynanchum wilfordii Hemsley (Asclepiadaceae). Cynandione A (50 microM) significantly reduced (approximately 50%) the release into the culture medium of glutamic pyruvic transaminase and sorbitol dehydrogenase from the primary cultures of rat hepatocytes exposed to CCl4. Glutathione, superoxide dismutase, catalase and glutathione reductase play important roles in the cellular defence against oxidative stress. Cynandione A appeared to protect primary cultured rat hepatocytes exposed to CCl4 from significant drops in the levels of each of these four specific markers. Cynandione A also ameliorated lipid peroxidation by up to 50% as demonstrated by a reduction in the production of malondialdehyde. These results suggest that cynandione A protected the hepatocytes from CCl4-injury by maintaining the level of glutathione and by inhibiting the production of malondialdehyde, due to its radical scavenging properties.

Antihepatotoxic activity of bergenin, the major constituent of Mallotus japonicus, on carbon tetrachloride-intoxicated hepatocytes

To determine the antihepatotoxic activity of bergenin from Mallotus japonicus, carbon tetrachloride (CCl4)-induced cytotoxicity in primary cultured rat hepatocytes has been adopted as an assay system. Bergenin significantly reduced the activities of glutamic pyruvic transaminase and sorbitol dehydrogenase released from the CCl4-intoxicated hepatocytes. The antihepatotoxicity of bergenin was also evidenced by elevating the activities of glutathione S-transferase and glutathione reductase, and content of glutathione in the CCl4-intoxicated hepatocytes. From these results, it is assumed that bergenin exerted antihepatotoxicity against CCl4-induced cytotoxicity through glutathione-mediated detoxification as well as free radical suppressing activity.

Sphingomyelinase, an enzyme implicated in atherogenesis, is present in atherosclerotic lesions and binds to specific components of the subendothelial extracellular matrix

Atherosclerotic lesions contain an extracellular sphingomyelinase (SMase) activity that hydrolyzes the sphingomyelin of subendothelial low density lipoprotein (LDL). This SMase activity may promote atherosclerosis by enhancing subendothelial LDL retention and aggregation, foam cell formation, and possibly other atherogenic processes. The results of recent cell-culture studies have led to the hypothesis that a specific molecule called secretory SMase (S-SMase) is responsible for the SMase activity known to be in lesions, although its presence in atheromata had not been examined directly. Herein we provide immunohistochemical and biochemical support for this hypothesis. First, 2 different antibodies against S-SMase detected extracellular immunoreactive protein in the intima of mouse, rabbit, and human atherosclerotic lesions. Much of this material in lesions appeared in association with the subendothelial matrix. Second, binding studies in vitro demonstrated that (125)I-S-SMase adheres to the extracellular matrix of cultured aortic smooth muscle and endothelial cells, specifically to the laminin and collagen components. Third, in its bound state, S-SMase retains substantial enzymatic activity against lipoprotein substrates. Overall, these data support the hypothesis that S-SMase is an extracellular arterial wall SMase that contributes to the hydrolysis of the sphingomyelin of subendothelial LDL. S-SMase may therefore be an important participant in atherogenesis through local enzymatic effects that stimulate subendothelial retention and aggregation of atherogenic lipoproteins.

A novel zymogen granule protein (ZG29p) and the nuclear protein MTA1p are differentially expressed by alternative transcription initiation in pancreatic acinar cells of the rat

Using a polyclonal antibody against purified zymogen granule membrane components from rat pancreas a cDNA coding for the 29 kDa protein (ZG29p) was identified by immunoscreening of a hormonally stimulated pancreas cDNA library. Western blot analysis suggests that ZG29p is a pancreas-specific protein and immunofluorescence shows that ZG29p is mainly associated with zymogen granules. Analysis of subcellular fraction applying immunoblotting revealed that ZG29p was localized mainly in the soluble fraction of zymogen granules and in a Golgi- and RER-enriched fraction, but was absent from the cytosol. In isolated zymogen granule content ZG29p was associated with protein complexes containing amylase as main constituent. The cDNA coding for ZG29p is homologous to the C-terminal region of the candidate metastasis-associated gene mta1. Northern blot analysis and RT-PCR showed that no MTA1 mRNA is present in pancreas from fasted rats and in the rat pancreas carcinoma cell line AR4-2J in its protodifferentiated state. Although no ZG29p specific mRNA was seen in the northern blot analysis, RT-PCR showed that ZG29p was expressed under both non-stimulated and stimulated conditions. The expression of MTA1 was up-regulated in the pancreas by endogenous cholecystokinin release and in AR4-2J after induction of cellular differentiation by dexamethasone. Western blotting and immunofluorescense studies indicated that MTA1p is localized in the nucleus in all tissues studied. Using genomic DNA in PCR analysis it was shown that two short introns are present flanking the sequences of the 5'end of ZG29p cDNA. One intron contains consensus elements required for pancreas specific transcription initiation, suggesting that MTA1 and ZG29 are differentially expressed by alternative transcription initiation in the pancreas. The localisation of MTA1p in the nucleus of most cell types could signify a general role in gene regulation, while the cell type specific and exclusive expression of ZG29p in pancreatic acinar cells could indicate a role in granule formation.

Human endothelial cells cultured on microporous filters used for leukocyte transmigration studies form monolayers on both sides of the filter

A growing number of studies on the mechanism of leukocyte transendothelial migration use endothelial cells grown on microporous filters as an in vitro model of endothelium. Ultrastructural examination of such a model system previously demonstrated that human pulmonary artery endothelial cells (HPAEC) formed confluent monolayers on both sides of the 3-microm-pore filter (Mackarel et al., 1999). To determine whether this was a characteristic specific to pulmonary artery endothelial cells, the growth characteristics of a human pulmonary microvascular endothelial cell type (HMVEC-L) and the widely used human umbilical vein endothelial cells (HUVEC) on 3-microm microporous filters were examined by transmission electron microscopy (TEM). Similar to HPAEC, HMVEC-L and HUVEC were also found to grow on both sides of the filter. All three endothelial cell types were capable of migrating through the 3 microm pores of the filter to form a monolayer on the filter underside. The endothelial cells on the underside were orientated in an inverted position with the luminal surface facing away from the filter. Such 'bilayer' formation was observed at a range of seeding densities and in different culture media. Despite the presence of a bilayer of endothelial cells, TEM demonstrated that neutrophils migrated successfully across the cell-filter-cell system. Previous transmigration reports in which an in vitro model similar to ours was used have often assumed only one layer of endothelial cells. The observations reported here indicate that while endothelial cells on microporous filters are useful models for examining leukocyte-endothelial interactions, they are not appropriate for studies examining endothelial cell 'sidedness.'

Hepatoprotective activity of scopoletin, a constituent of Solanum lyratum

Scopoletin (7-hydroxy-6-methoxycoumarin), a coumarin, was isolated from the aerial part of Solanum lyratum Thunb. by the activity-guided fractionation employing carbon tetrachloride-intoxicated primary cultured rat hepatocytes as a screening system. Its hepatoprotective activity was first evaluated by measuring the release of glutamic pyruvic transaminase and sorbitol dehydrogenase from carbon tetrachloride-intoxicated rat hepatocytes into the culture medium. Scopoletin significantly reduced the releases of glutamic pyruvic transaminase and sorbitol dehydrogenase from the carbon tetrachloride-intoxicated primary cultured rat hepatocytes by 53% and 58%, respectively, from the toxicity in a dose-dependent manner over concentration ranges of 1 microM to 50 microM. Further studies revealed that at the concentration of 10 microM, scopoletin significantly preserved glutathione content by 50% and the activity of superoxide dismutase by 36% and also inhibited the production of malondialdehyde to the degree as seen in the control.

Membrane dipeptidase and glutathione are major components of pig pancreatic zymogen granules

Membrane proteins of highly purified porcine zymogen granules were separated by two-dimensional gel electrophoresis in order to isolate proteins which are involved in intracellular trafficking of digestive enzymes in the exocrine pancreas. A 48-kDa glycoprotein was a major component in membrane preparations washed with 0.1 M Na2CO3 and 0.5 M NaCl. By N-terminal amino acid sequencing this protein was identified as membrane dipeptidase (MDP; EC 3.4.13.19). MDP mRNA levels in rat pancreas were increased threefold by feeding rats with FOY-305, which is a known stimulus of endogenous cholecystokinin release from the gut. Cholecystokinin then stimulates secretion in pancreatic acinar cells. In another set of experiments treatment of the rat pancreatic acinar tumor cell line AR42J with dexamethasone led to an eightfold increase in the expression of MDP. Thus, the expression pattern of the MDP gene in response to hormonal stimulation in vivo and in vitro resembles those found for most of the enzymes and proteins which are involved in secretion. Since MDP has been thought to have a role in glutathione (GSH) metabolism, we also measured GSH concentration in zymogen granules and found high levels of GSH. Based on our data we propose a working model for the function of MDP. According to this model, MDP might play a pivotal role in maintaining the oxidizing conditions in the ER, which are required for the correct folding of secretory proteins.

Heparin inhibits the attachment and growth of Balb/c-3T3 fibroblasts on collagen substrata

In investigating the role of cell-extracellular matrix interactions in cell adhesion and growth control, the effects of heparin on cell-collagen interactions were examined. Exponentially growing Balb/c-3T3 fibroblasts were radiolabelled with 3H-thymidine and detached from tissue culture surfaces using EDTA, and cell attachment to various types of collagen substrata was assayed in the presence or absence of heparin or other glycosaminoglycans (GAGs) or dextran sulfate (40 K). Cells attached readily (70-90%) to films of types I and V, but not to type III collagen. The number of cells bound to types I and V collagen films was inhibited by 10-50% when heparin was present from 0.1-100 micrograms/ml. Cell-collagen attachment was also inhibited by dextran sulfate, and to a lesser extent by dermatan sulfate, but chondroitin sulfates A and C and hyaluronic acid showed no effect. Heparin was active even at early time points in the adhesion assay, suggesting it may disrupt cell-collagen attachment. To study the effects of heparin in modulating cell growth on collagen, growth arrested cells cultured on type I collagen films were serum stimulated in the presence of heparin or other GAGs for 3 days. Growth was inhibited (greater than 40%) only by heparin and dextran sulfate. Interaction of heparin fragments (Mr less than or equal to 6KD) with type I collagen was analyzed by affinity co-electrophoresis (Lee and Lander, 1991) and showed higher affinity heparin binding to native as compared with denatured collagen. These data suggest that sites within native collagen may mediate Balb cell-collagen and heparin-collagen interactions, and such interactions may be relevant towards understanding heparin's antiproliferative activity in vivo and in vitro.

Decreases in local hormone biosynthesis and c-fos gene expression accompany differentiation of porcine preadipocytes

To better understand possible autocrine or paracrine mechanisms involved in adipose tissue development, we have studied the biosynthesis of insulinlike growth factor I (IGF-I) and prostaglandin E2 (PGE2) by cultured porcine preadipocytes in response to factors known to modulate cell growth and differentiation. The expression of c-fos was also monitored because of the potential role of that proto-oncogene in coordination of growth and differentiation. Preadipocytes were grown to confluence and then maintained in one of three media treatments: a) standard medium supplemented with 10% fetal bovine serum (FBS), b) FBS supplemented with dexamethasone (Dex), c) FBS supplemented with dibutyryladenosine 3'-5'-cyclic monophosphate. Indirect measurements of growth indicated that cell proliferation did not differ due to media type. Histochemical and enzymatic measurements of adipocyte development revealed that differentiation occurred only in those cultures exposed to Dex. The increase in adipocyte differentiation in response to Dex was associated with a decrease in c-fos and actin RNA expression whereas the decrease in c-fos RNA expression in response to Dex was small (approximately 40%); immunocytochemical analysis indicated that induction of Fos protein occurred only in undifferentiated cells. Thus, the cells responsible for the decrease in c-fos RNA expression are possibly those signaled to differentiate into adipocytes. Expression of IGF-I RNA and secretion of IGF-I and PGE2 were also decreased in response to Dex treatment. These data provide the first demonstration that biosynthesis of IGF-I by preadipocytes can be modulated by a potent inducer of adipocyte differentiation. The combined results indicate that glucocorticoids may stimulate adipocyte differentiation by suppressing intracellular and putative intercellular mitogenic signals.

Inhibition of the adrenergic phenotype in cultured neural crest cells by norepinephrine uptake inhibitors

Tricyclic antidepressants in combination with in vitro clonal analysis of quail neural crest cells were used to examine the role the norepinephrine uptake mechanism might play in the development of adrenergic neural crest derivatives. Norepinephrine (NE) uptake inhibitors blocked expression of the adrenergic phenotype by neural crest cells. The degree of inhibition of phenotypic expression correlated with the potency and specificity of the uptake inhibitors. The drugs acted during the early phase of in vitro development, i.e., several days before overt expression of the adrenergic phenotype in clonal culture. They were nontoxic, and a chronic exposure of the cells to NE uptake inhibitors was necessary to cause an effect. These observations suggest that norepinephrine and possibly related neurotransmitters play a direct or indirect role in the expression of the adrenergic phenotype by neural crest cells and that tricyclic antidepressants may affect neurogenesis during sensitive stages of embryonic development. The data may reflect in vivo mechanisms, since there are neurotransmitters present in the migratory pathway of presumptive sympathetic neurons and the norepinephrine uptake system is expressed in the embryo by these cells before they synthesize and accumulate catecholamines.

Primary cultures of stromal-vascular cells from pig adipose tissue: the influence of glucocorticoids and insulin as inducers of adipocyte differentiation

Porcine stromal-vascular (S-V) cells from perirenal and subcutaneous fat depots were studied in a primary culture system. The ability of S-V cells to differentiate into adipocytes in response to insulin and to glucocorticoid treatments was determined. Treatments were either hydrocortisone plus insulin, dexamethasone plus isobutylmethylxanthine, or insulin. Insulin did not affect glycerol phosphate dehydrogenase (GPDH) activity or cytodifferentiation in porcine S-V cultures. All cultures differentiated in response to glucocorticoid addition. Glycerol phosphate dehydrogenase specific activity increased an average of 42.5% and the number of cell clusters with multilocular fat cells markedly increased. Cells receiving insulin after dexamethasone-stimulated differentiation had no greater ability to respond to the insulin than cells from control cultures. Glucocorticoids promoted cytodifferentiation of porcine S-V cells to adipocytes in a qualitative manner similar to other preadipocyte models; quantitatively, however, the response was greatly diminished.

Fetal hypophysectomy causes a decrease in preadipocyte growth and insulin like growth factor-1 in pigs

Fetal pigs in one uterine horn of each of five gilts were hypophysectomized (HX) in utero by electrical cauterization at 72-74 days of gestation and sera collected at 110 days of gestation. Sera from HX fetuses had lower levels of insulin-like growth factor-1 compared to control littermates (P less than .05). Sera were tested for their effects on primary cultures of stromal-vascular cells from adipose tissue. The soluble protein concentration/dish was lower when pig cells were cultured in sera from HX fetuses compared to sera from control fetuses (P less than .01). Sera from HX fetuses inadequately supported growth of stromal-vascular cells so subsequent experiments utilized pooled sera from normal and HX adult pigs. Sera from HX and control fetuses were mixed with sera from the two adult pools and tested for incorporation of tritiated thymidine into rat preadipocytes and the appearance of adipocytes (determined histochemically) in pig stromal-vascular cultures. In cultures fed sera from HX fetuses there was a lower (P less than .05) number of pig fat cells/culture and a lower level (P less than .06) of preadipocyte proliferation in rat cell cultures when compared to control fetal sera. Fetal pig serum contains factors (adipogenic) which promote the proliferation and differentiation of adipocytes in culture. Serum from HX fetuses has a lower level of adipogenic factors.

Evidence that an RGD-dependent receptor mediates the binding of oligodendrocytes to a novel ligand in a glial-derived matrix

A simple adhesion assay was used to measure the interaction between rat oligodendrocytes and various substrata, including a matrix secreted by glial cells. Oligodendrocytes bound to surfaces coated with fibronectin, vitronectin and a protein component of the glial matrix. The binding of cells to all of these substrates was inhibited by a synthetic peptide (GRGDSP) modeled after the cell-binding domain of fibronectin. The component of the glial matrix responsible for the oligodendrocyte interaction is a protein which is either secreted by the glial cells or removed from serum by products of these cultures; serum alone does not promote adhesion to the same extent as the glial-derived matrix. The interaction of cells with this glial-derived matrix requires divalent cations and is not mediated by several known RGD-containing extracellular proteins, including fibronectin, vitronectin, thrombospondin, type I and type IV collagen, and tenascin.

Lipoprotein uptake in primary cell cultures of rabbit atherosclerotic lesions. A fluorescence microscopic and flow cytometric study

To characterize the lipoprotein metabolism of lipid-filled cells of atherosclerotic lesions, uptake of 3,3'-dioctadecylindocarbocyanine (DiI)-labelled low density lipoprotein (LDL), acetylated LDL (Ac-LDL) and beta-very low density lipoprotein (beta-VLDL) was studied by fluorescence microscopy and flow cytometry in primary cultures of enzymatically dispersed aortic cells from cholesterol-fed rabbits. Most of the foam cells were identified as macrophages on the basis of Fc-receptors and high activities of nonspecific esterase and acid lipase, although cholesteryl ester (CE) inclusions were found by filipin staining also in smooth muscle cells (SMCs). During the culture only SMCs proliferated and were confluent in about 1 week. After incubation with DiI-Ac-LDL most macrophage foam cells were brightly fluorescent, but also many SMCs accumulated fluorescence. In SMCs, an excess of LDL inhibited the uptake of DiI-beta-VLDL and DiI-LDL, indicating that these lipoproteins were taken up by the apoB,E receptor; the activity of this receptor was low 2 days after cell isolation but increased considerably during SMC proliferation. DiI-beta-VLDL was not taken up by the macrophage foam cells until after 7 days' culture, when their CE content had decreased, reflecting a feed-back regulation of these receptors as well. Our results indicate that, in primary cultures of enzyme-dispersed cells from rabbit atherosclerotic lesions, most of the foam cells have lipoprotein receptors resembling those described in macrophages and that also many SMCs accumulate Ac-LDL.

Evidence for neuroendocrine regulation of preadipocyte proliferation and differentiation

Cells in fetal adipose tissue and cells in vitro are characterized by rapid proliferation. Serum factors have been shown to be important for the rapid proliferation of cells in vitro. The present experiment was performed to determine if neuroendocrine regulatory mechanisms of the fetus can influence the actions of serum factors on preadipocyte proliferation and differentiation in vitro. Sera were obtained from decapitated fetal pigs and intact littermates during gestation. Sera were tested for their effects on primary cultures of preadipocytes and stromal-vascular cells derived from inguinal adipose tissue of young Sprague-Dawley rats. Coverslip cultures were used for histochemical analysis of enzymes after 12 days of incubation with test media. Analysis of growth curves produced from sequential [3H]-thymidine labeling indicated that fetal age influences rates of proliferation. Sera from decapitated fetal pigs specifically reduced the number of proliferating preadipocytes in culture. Sera from decapitated fetal pigs induced a minimum of 50% less differentiation of sn-glycerol-3-phosphate dehydrogenase activity than sera from intact pigs at all fetal ages. Histochemical staining for enzymes of differentiating preadipocytes was also reduced in cultures incubated with sera from decapitated fetal pigs in comparison to sera from intact pigs. The present study has demonstrated that the in vivo effect of decapitation on fetal adipose tissue development is a consequence of alterations in systemic factors present in serum in response to removal of central regulation by the hypothalamic-pituitary axis.

Interaction of embryonic chick calvarial bone cells with collagen substrata; attachment characteristics and growth behaviour

Freshly isolated bone cells from embryonic chick calvariae were found to attach to films of native monomeric type I or II collagen, to gels of native type I collagen and, to a lesser extent, to air-dried films of these collagens, in a fibronectin-independent manner, and with no requirement for collagen synthesis. Adhesion to type III collagen was relatively poor. Films of native monomeric type I or II collagen were preferred to the corresponding air-dried films as substrata for proliferation. Cis-hydroxyproline inhibited growth upon both plastic and type I and type II collagenous substrata, but this effect could largely be overcome by providing bone cell-conditioned medium, suggesting the possibility of a requirement in the growth process for synthesis of a collagen other than type I, the major form in bone matrix.

Use of extracellular matrix components for cell culture

Extracellular matrix components when used as a substratum in vitro can greatly influence cell behavior. The response observed is dependent on the type of cell and matrix used. Cells in vitro usually respond best to the matrix components with which they are normally in contact in vivo. More differentiated phenotypes are observed and cells generally survive longer on such matrices. In some cases, the presence of such matrices allows cells to be cultured in the absence of serum and growth factors. As more investigators try the matrices and matrix components described, as well as new components and combinations of them, it is anticipated that improvement in the culture of many cells can be expected.

Effects of fetal versus postnatal sera upon adipose tissue stromal-vascular cells in primary culture

This experiment was conducted to determine if serum factors are responsible for differences in cellularity of prenatal and postnatal pig adipose tissue as determined by in vitro measurement of cellular proliferation and enzyme-histochemical metabolic development. Cellular proliferation of stromal-vascular cells derived from rat inguinal adipose tissue was measured by [3H]-thymidine incorporation. Coverslip cultures were used for analysis of histochemical differentiation. Cells were incubated in media containing 10% fetal bovine, fetal pig, mature pig, or various combinations of these sera. Fetal bovine serum promoted more [3H]-thymidine incorporation than fetal or postnatal pig sera. Fetal pig sera also stimulated more [3H]-thymidine incorporation than mature pig sera. Sera from adult pigs promoted differentiation and lipid filling of adipocytes. Fetal pig sera stimulated histochemical expression of enzymes, but did not induce lipid filling. Fetal bovine serum produced histochemically undifferentiated cells. Addition of fetal bovine serum to media containing mature pig sera reduced lipid accumulation and histochemical reactivity of cells. This effect of fetal serum was thus due to specific inhibition of lipid deposition and not substrate restriction. These experiments demonstrated that serum factors have a major influence on morphological development of fetal and postnatal adipose tissue.

Target cell stimulation of dissociated serotonergic neurons in culture

Dissociated mesencephalic raphe cells from fetal rats (14-18 days) were grown in culture in 96 well Linbro plates. The maturation of serotonergic cells was qualitatively studied using immunocytochemistry with a serotonin antibody and quantitatively by measuring the retention of radioactivity following incubation in the presence of a low concentration of [3H]5-hydroxytryptamine (6 X 10(-8) M). The 5-hydroxytryptamine immunoreactive neurons showed specific staining in the perikaryon, nucleus, dendrites, axons and growth cones. These neurons formed varicose fibers and growth cones after 18 h in culture and survived for up to 21 days in culture. Each serotonergic neuron concentrated approximately 1 fmol of serotonin after 20 min of incubation. Maturation of mesencephalic serotonergic neurons was increased in co-cultures of both normal (hippocampus, cerebral cortex, olfactory bulb and striatum) and abnormal (spinal cord) target neurons. The best stimulation was produced by dissociated hippocampal neurons (14-18 days of gestation) on mesencephalic raphe cells (14 days of gestation) after 4 days in culture. This stimulation was seen in culture conditions which favored neuronal but not glial survival. Our results obtained using cultures of dissociated serotonergic cells are consistent with an expansive network pattern developed by this chemical transmitter system in the adult brain.

Adipocyte development in primary rat cell cultures: a scanning electron microscopy study

This study utilized scanning electron microscopy (SEM) techniques to observe primary cultures of stromal-vascular (SV) cells derived from postnatal rat inguinal adipose tissue. Cells were grown on collagen-coated, fibronectin-coated, or uncoated glass coverslips. Coverslips were normally fixed in glutaraldehyde, osmium tetroxide, dehydrated, and critical-point-dried. Other coverslips were frozen in isopentane (cooled in LN2) and dried or fixed in Baker's formalin for demonstration of inosine diphosphatase (IDPase) by X-ray microprobe analysis (XRMA). Adipocyte morphologies were similar on all substrates. At 2 days of culture, actin cables were detected extending from developing adipocytes. No difference in actin cable structure, cellular shape, or lipid accumulation was observed among the different substrates. Some stromal cells did not accumulate lipid but proliferated into a multilayer by 9 days in culture. Inosine diphosphatase was detected in the Golgi apparatus of developing adipocytes utilizing the technique of XRMA. This study demonstrates the potential for using SEM and XRMA techniques to define morphological features and cytochemical markers of adipocytes in vitro and the response of primary cultured rat SV cells to other attachment substrates.

The effect of substrate and epidermal growth factor on human placental trophoblast cells in culture

Attempts were made to select for trophoblast cells in cultures of mixed cell populations derived from preterm (7 to 12 wk) or term human placentas. Epidermal growth factor added to cultures on solid or porous supports caused proliferation of epithelial-type cells to give a confluent monolayer but did not increase the expression of differentiated function. The presence or absence of placental basement membrane collagen as substrate made little apparent difference; however a porous basement membrane collagen support led to increased differentiated function. Initial production of human chorionic gonadotrophin was increased and after 4 wk in culture a substantial proportion of the cells exhibited alkaline phosphatase activity. Epidermal growth factor and a substrate of placental basement membrane collagen on a porous support favorably influence the growth and differentiation of human trophoblast cells in culture.

Fibronectin-independent attachment of human gingival fibroblasts to interstitial and basement membrane collagens

We have studied the ability of human gingival fibroblasts (HGF) to attach to different interstitial (types I, II and III) and basement membrane (types IV and V) collagens. HGF cells were plated onto collagen-coated Petri dishes under various conditions and the percentage of cells attaching to the collagen was determined. HGF were found to attach to all the different types of native collagens, but attached poorly to the corresponding denatured collagens. When plated in the presence of 15% fetal bovine serum (FBS) or fibronectin-depleted FBS, similar percentages (approximately 85%) of cells attached to both interstitial and basement membrane collagens, demonstrating an attachment mechanism that is independent of plasma fibronectin. That the attachment in the presence of serum was also independent of cellular fibronectin was shown by the inability of fibronectin antibodies to block attachment to any of the collagen types. HGF were also capable of attaching to all of the collagen types in the complete absence of serum. In previous studies, investigators using cell lines have suggested that cell attachment in the absence of serum is non-physiological. However, the serum-free attachment of HGF to collagen was found to be dependent on cellular protein synthesis indicating that this attachment mechanism has biological significance.

Collagen can modulate cell interactions with fibronectin

We have examined the effects of soluble collagen on the function of fibronectin in baby hamster kidney (BHK) cells. Collagen and its purified alpha1(l) chain noncompetitively inhibited cell spreading on substrates precoated with fibronectin or a 75,000-D cell-binding fragment of fibronectin. Neither preincubation of cells with collagen followed by washing nor the addition of collagen to previously spread cells had any inhibitory effect on cell spreading, which indicates a requirement for the concurrent presence of collagen during the process of spreading. Treatment of collagen or alpha1(l) chain with collagenase abolished the inhibitory effect on fibronectin-mediated cell spreading. However, direct attachment of BHK cells to fibronectin-coated or 75,000-D fragment-coated substrates was not inhibited by collagen or by the alpha1(l) chain. Moreover, the binding of [3H]fibronectin or the 3'-75,000-D fragment to cell surfaces was not inhibited by the presence of soluble collagen, whereas soluble fibronectin inhibited binding. Although the binding of [3H]fibronectin-coated beads to BHK cell surfaces was also not inhibited by collagen, the phagocytosis of such beads was inhibited by the presence of collagen. On the other hand, soluble fibronectin partially inhibited the binding of fibronectin-coated beads but did not inhibit phagocytosis of the beads that did bind. The mechanism of the inhibition of fibronectin function by collagen and the possible interactions of two different kinds of receptors on the cell surface are discussed.

Matrix influence on the tumor cell stimulation of fibroblast collagenase production

Cocultures of rabbit fibroblasts and mouse B-16 melanoma cells produce increased levels of collagenase against type I collagen. This stimulatory effect was also found when fibroblasts were cultured in conditioned media from tumor cells. However, the level of the stimulatory factor in conditioned media was influenced by matrix deposited by fibroblasts. Thus, conditioned media collected from monolayers of B-16 plated on fibroblast matrix consistently showed high levels of the factor activity. The influence of the matrix on the level of the factor was not removed by treating the fibroblast matrix with collagenase or chondroitinase ABC and was not reproduced by collagen-coated dishes.

Effects of fibrinogen degradation products on glomerular mesangial cells in culture

We investigated effects of fibrin, fibrinogen, and fibrinogen degradation products (FDPs) on human glomerular mesangial cells in culture, using the methods of cell count, 3[H] thymidine uptake and 51Cr release. Incorporation of 3[H] thymidine by the cells was much the same with various concentrations of fibrin and similar to findings in the control without fibrin. Fibrinogen, FDP-D, -E, low molecular weight FDP (LMWFDP) fractions 1 and 3 had no promoting effects on mesangial cell proliferation. The LMWFDP fraction 2 showed a suppressive effect on the proliferation of cultured cells and increase of 51Cr release from the cells. The cytotoxic effect of this fraction was dose-dependent. These results suggest that while fibrin deposition in the renal glomeruli does not relate with mesangial hypercellularity, this deposition plays a role in mesangiolysis, through the production of FDPs.

Adhesive and migratory behavior of normal and sulfate-deficient sea urchin cells in vitro

Dissociated cells from different stage embryos of the sea urchin Lytechinus pictus were compared in their adhesion to various substrates. Micromeres from 16-cell stage embryos bind to tissue culture and Petri dishes but not to Petri dishes coated with human plasma fibronectin. Other cell types did not adhere to any of the substrates tested. By hatched blastula stage, about 28% of the cells adhered to fibronectin as well as to tissue culture dishes. By the mesenchyme blastula stage, there was a further increase in the proportion of cells adhering to these substrates. At no stage did cells adhere to native rat tail collagen. Primary mesenchymal cells were isolated by their selective adhesion to tissue culture dishes in the presence of horse serum. These cells were then examined for their migratory capacity. Cell spreading and migration followed adhesion and occurred on fibronectin but not on the other substrates tested. Based on analysis of video tapes, greater than 60% of these cells moved faster than 1 micron/min. On the other hand, cells from sulfate-deprived embryos, in which primary mesenchyme migration is blocked in situ, failed to spread and migrated little on the same substratum. This defect was reversed by a 6 h pretreatment of the cells in normal sea water. Thus, the in vitro migratory behavior parallels that observed in vivo. These results support the hypothesis that the primary mesenchymal cells produce a sulfate-dependent component that is required for cell spreading and migration.

Synthesis and effects of basement membrane components in cultured rat Schwann cells

Schwann cells, the myelin-forming cells of the peripheral nervous system, are surrounded by a basement membrane. Whether cultured rat Schwann cells synthesize the basement membrane-specific components, laminin and collagen type IV, and whether these components influence the adhesion, morphology, and growth of these cells have been investigated. Both laminin and collagen type IV were detected in the cytoplasm of Schwann cells by immunofluorescence. After ascorbate treatment, laminin and collagen type IV were both found in an extracellular fibrillar matrix bound to the Schwann cell surface. Laminin was further localized on the Schwann cell surface by electron microscopy using gold immunolabeling. Anti-laminin IgG-labeled gold particles were scattered over the cell surface, and linear rows of particles and small aggregates were found along the cell edges and at points of contact with other cells. When added to the culture medium, laminin acted as a potent adhesion factor, stimulating Schwann cell adhesion as much as eightfold above control levels on type IV collagen. In the presence of laminin, the cells became stellate and by 24 hr had extended long, thin processes. Laminin also stimulated cell growth in a dose-dependent manner and anti-laminin IgG completely inhibited cell attachment and growth in the absence of exogenous laminin. Thus, cultured Schwann cells synthesize laminin and collagen type IV, two major components of basement membrane, and laminin may trigger Schwann cell differentiation in vivo during early stages of axon-Schwann cell interaction before myelination.

The histochemistry of developing adipocytes in primary stromal-vascular cultures of rat adipose tissue

Histochemical analysis for NADP-dependent dehydrogenases, succinate dehydrogenase, NADH and NADPH- tetrazoleum reductases and esterase was conducted on primary cultures of adipose tissue stromal-vascular cells. Enzyme activities were restricted to clusters of lipid laden cells (adipocytes). The number of enzyme reactive adipocytes increased with length of culture. Coverslips were partially coated with collagen to allow comparisons of cell differentiation on coated (C-glass) and uncoated glass (U-glass) surface. There were no reactions for NADH- and NADPH- tetrazoleum reductases (TR) in cells on C-glass whereas adipocytes and stromal cells on U-glass were reactive. Glucose-6-phosphate (G6PDH) and 6-phosphogluconate (6PGDH) dehydrogenase activities were markedly demonstrated in both stromal cells and adipocytes on U-glass. Malate (MDH) and isocitrate (ICDH) dehydrogenase activities were higher in adipocytes than in stromal cells on the U-glass. Stromal cells on C-glass were either devoid of these enzymes (G6PDH, MDH, 6PGDH, ICDH) or activity was restricted to a small area of the cytoplasm. There were two levels of staining intensity in (MDH, ICDH, G6PDH, 6PGDH) adipocyte clusters on C-glass. Elimination of phenazine methosulphate from the NADP-dependent dehydrogenase medias and SDH media, caused a reduction in enzyme reactive adipocytes on the C-glass. This manipulation did not reduce the number of enzyme reactive cells on U-glass. Cells on C-glass and U-glass were distinctly different in esterase stained coverslips. These studies demonstrated enzyme histochemical reactions of adipocytes and stromal cells in primary culture that were dependent on the type of extracellular matrix. Furthermore, enzyme histochemistry was shown to be useful for delineating adipocytes from stromal cells in primary cultures.

Loss of adhesion of murine erythroleukemia cells to fibronectin during erythroid differentiation

Uninduced murine erythroleukemia cells specifically attached to fibronectin-coated dishes but not to dishes coated with laminin or type I or IV collagen. Dimethyl sulfoxide-induced differentiation of these cells caused a dramatic decrease in adhesion to fibronectin that was correlated with synthesis of the erythrocyte glycoprotein "band III," a membrane marker of the differentiated erythrocyte. Loss or modification of fibronectin binding sites on the cell surface during erythroid differentiation may cause the release of reticulocytes from the interstitial matrix of bone marrow into the blood.

A new microtechnique for quantitating cell movement in vitro using polystyrene bead monolayers

In this paper we describe a new and simple technique for studying cell movement in vitro. This method is based upon the migration of endothelial cells on polystyrene bead monolayers. It permits the rapid preparation and screening of multiple 96-well plates for effects on migration, requires fewer samples per test and has the potential for precise quantitation by digital image analysis. The locomotive response of endothelial cells in response to different protein matrices (fibrin, collagen, albumin, gelatin), as used by this technique, is also described. Experiments in progress have shown that this technique can be used to study the effect of different factors (monoclonal antibodies, lymphokines, etc.) on cell migration, and that it may be used with other cell types which exhibit cell migration on substrates in vitro.

Optimal conditions for long term storage of native collagens

Cryopreservation was used to maintain the biological activity of collagen, i.e., its fibril formation property, after isolation from tissues. Freezer temperatures commonly available in laboratories, -15 degrees C and -90 degrees C, and liquid nitrogen temperature, -196 degrees C, were compared for efficacy in preserving both type I collagen structure (amino acid and subunit composition, triple helix) and activity (fibril formation in vitro). Whether the collagen was stored dry or in acetic acid solution at -196 degrees C, the kinetics of fibril formation were completely stable for at least two and a half years, but decreased after several months storage at -15 degrees C or -90 degrees C. Types II and III collagens, also with intact nonhelical ends, are also completely stable in liquid nitrogen for at least two and a half years.

Immunoelectron microscopic demonstration of fibronectin in rheumatoid pannus and at the cartilage-pannus junction

The presence of fibronectin (Fn) in rheumatoid pannus was investigated by an immunoelectron microscopic method using horseradish peroxidase-conjugated antibody to stain Fn. Large amounts of Fn were demonstrated in the interstitial collagenous tissue of invasive rheumatoid pannus. Fn was also observed on the surface of both fibroblast-like and macrophage-like pannus cells, suggesting that it was secreted by these cells and that the secreted Fn might facilitate the spreading of the pannus cells over the cartilage matrix. However, decreased amounts of Fn were observed in areas of contact between pannus cells and the cartilage matrix. The reduction in the amount of Fn demonstrable at the cartilage-pannus junction may be a consequence either of proteolysis of Fn by enzymes secreted at the junction, inhibition of Fn synthesis in cells in contact with cartilage matrix, or transfer of Fn from the pannus cell surface to collagen of the cartilage matrix.

Changes in the distribution of fibronectin during limb regeneration in newts using immunocytochemistry

The distribution of fibronectin in regenerating newt limbs was studied using immunocytochemistry. At appropriate intervals after the initial amputation at the elbow (10-30 days), animals were reamputated at the shoulder and processed for light microscopy. The peroxidase-antiperoxidase technique was used to localize affinity-purified antibodies to fibronectin in limb tissues. At the amputation site, fibronectin was associated with basal laminae and connective tissues adjacent to dedifferentiating limb tissues destined to form the regeneration blastema. Accumulation and growth of the blastema was accompanied by the apparent de novo synthesis of fibronectin, where it appeared randomly in the interstitium between blastemal cells. The onset of chondrogenesis was characterized by a central condensation of prechondroblasts that formed the cartilage anlagen. Fibronectin formed an amorphous network between presumptive chondroblasts. As the mature cartilage phenotype was expressed and chondrocytes became isolated in lacunae, fibronectin was greatly reduced and then disappeared. The extracellular matrix surrounding undifferentiated blastemal cells still contained fibronectin. Fibronectin was also found in high concentrations between differentiating myoblasts. A condensation of fibronectin was also observed beneath the epidermis at the distal limb tip at the onset of digit formation. These observations are consistent with the hypothesis that fibronectin may play a key role in the morphogenetic events that result in the spatial organization and subsequent differentiation of cells during pattern formation in the regenerating limb.