Sulfated glycosaminoglycans synthesized by fibroblast, smooth muscle and endothelium-like cells grown in culture

Stroma-mediated granulocyte-macrophage colony-stimulating factor (GM-CSF) control of myelopoiesis: spatial organisation of intercellular interactions

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is one of the major cytokines involved in control of haemopoiesis both in bone marrow and in extramedullar sites. Its biological activity depends upon the composition and physicochemical properties of the microenvironment provided by the supporting stroma. GM-CSF activity is modulated and controlled by the stromal heparan-sulphate proteoglycans, but their optimal interaction occurs only at low pH. We questioned whether the microenvironment organisation of the interface between stroma and haemopoietic cells provides such conditions. We studied myeloid progenitor proliferation in contact with bone marrow-derived and extramedullar stromas using electron microscopy and selective labelling of pericellular components. We present evidence that, upon interaction, the two cell types reorganise their interface both in shape and molecular composition. Haemopoietic cells extend projections that considerably increase the area of intercellular contact, and stromal cells form lamellipodia and carry out a redistribution of membrane-associated sialylated glycoconjugates and proteoglycans. Such rearrangements lead to extensive capping of negatively charged molecules at the interface between the supporting stroma and the haemopoietic cells, leading potentially to a local decrease in pH. Our results indicate that the distribution of negative charges at the cellular interface may be responsible for the selectivity of cell response to GM-CSF.

Thymic epithelial cells synthesize a heparan sulfate with a highly sulfated region

Epithelial cells are important components of the thymus microenvironment and are involved in thymocyte differentiation. The production and secretion of sulfated glycosaminoglycans by these cells grown in culture were investigated using labeling with radioactive 35S-Na2SO4 and 3H-glucosamine. The major glycosaminoglycans synthesized by these cells are heparan sulfate and hyaluronic acid. The structure of the heparan sulfate was investigated by the pattern of degradation products formed by deaminative cleavage with nitrous acid. The ratio 35S-sulfate/ H-glucosamine is high in the segments of the heparan sulfate released during the deaminative cleavage with nitrous acid but low in the resistant portion of the molecule. Thus, the heparan sulfate synthesized by the thymic epithelial cells contains a highly sulfated region. Digestion with heparitinase reveals that this highly sulfated region is a heparin-like segment of the molecule. The heparan sulfate is rapidly incorporated into the cell surface but its secretion to the extracellular medium requires a longer incubation period. Finally, heparin was used to mimic the possible effect of this heparan sulfate with a highly sulfated region, as ascertained by its ability to modulate thymocyte adhesion to thymic epithelial cells. Since heparin actually enhanced thymocyte adhesion, it is suggested that the heparan sulfate described herein, secreted by the thymic epithelium, may play a role upon intrathymic heterotypic cellular interactions.

Compartmental distribution of sulfated glycosaminoglycans in lateral and medial midbrain astroglial cultures

Sulfated glycosaminoglycans (S-GAGs) were isolated from the pericellular (P), intracellular (I), and extracellular (E) compartments of astrocytes cultures from lateral (L) and medial (M) sectors of embryonic mouse midbrain; these sectors differ in their ability to support neurite growth (L, permissive, M, non-permissive for growth) and laminin deposition patterns (L, fibrillar; M, punctate pattern). The total amount of S-GAGs in M cultures was twice that in L cultures and was particularly high in the P compartment of M glia. Both glial cultures showed heparan sulfate (HS) in the three cellular compartments but chondroitin sulfate (CS) GAGs were vestigial in I and P compartments of L glia. Our results suggest that M and L astrocytes are heterogeneous concerning the ability to synthesize GAGs and distribute them among the different cellular compartments. Together with other data (Garcia-Abreu et al: J Neurosci Res 40:471, 1995; Garcia-Abreu et al: Neuroreport 6:761, 1995), the present results suggest that this heterogeneous features might be at least partially responsible for the differential effects of L and M glial cultures on the growth of midbrain neurons and may also be involved in complex ways in the guidance of axons at the brain midline.

Interaction of high molecular weight chondroitin sulfate from human aorta with plasma low density lipoproteins

Aortic glycosaminoglycans were separated into fractions of increasing molecular weights containing heparan sulfate or chondroitin 4/6-sulfate + dermatan sulfate. When these fractions were added to plasma low density lipoproteins (LDL) in the presence of Ca2+, only chondroitin 4/6 sulfate + dermatan sulfate of high relative molecular weight produced turbidity. Treatment with testicular hyaluronidase abolished totally the formation of insoluble complex. When these glycosaminoglycans were applied to LDL-affinity columns in the presence of Ca2+, higher NaCl concentrations were necessary for the elution of the high relative molecular weight chondroitin sulfate. Heparan sulfate fractions did not produce turbidity when added to LDL solutions and were eluted from LDL-affinity columns at low NaCl concentrations. All these results suggest that besides the structure (or charge density), the molecular weight of the chondroitin sulfate chains is a relevant factor for the binding of this compound to LDL.

Sulfated glycosaminoglycans synthesized by human smooth muscle cells isolated from different organs

The sulfated glycosaminoglycans synthesized by human smooth muscle cells isolated from different organs were identified on the basis of electrophoretic mobility, enzymatic degradation with specific mucopolysaccharidases and by the type of degradation products formed. The results obtained indicated that chondroitin sulfate and heparan sulfate were the main glycosaminoglycans found, that most of the labeled glycosaminoglycans were found in the pericellular pool, and that no marked differences were observed in the sulfated glycosaminoglycan composition of the smooth muscle cells obtained from different organs. 'Liver connective tissue cells', isolated from pathological livers (which had been shown to possess biochemical and physiological features typical of smooth muscle cells) showed a pattern of glycosaminoglycan synthesis similar to that of the smooth muscle cells.

Macrophage interaction with very-low-density lipoproteins results in triacylglycerol-enriched smooth muscle cells

Macrophage-conditioned medium containing very-low-density lipoproteins (VLDL) and its effects on smooth muscle cell triacylglycerol metabolism was investigated. Macrophages exposed to VLDL from normolipemic rats accumulated high levels of intracellular triacylglycerol, while similarly treated smooth muscle cells showed only slight changes. Medium, initially composed of VLDL and albumin, contained substantial levels of free fatty acids after exposure to macrophages. In the presence of albumin, the loss of VLDL triacylglycerol from the medium and the appearance of medium free fatty acids was consistent with a precursor-product relationship. The extent of medium fatty acid accumulation was dependent on the length of time of incubation with macrophages and was proportional to the concentration of VLDL and albumin added to the culture dish. This macrophage-conditioned medium, when given to smooth muscle cells, promoted a 6-12-fold increase in smooth muscle cell triacylglycerol levels over that produced by fresh VLDL and albumin. Similar increases in cell triacylglycerol levels could be produced using fresh medium approximating the oleate concentration and the fatty acid to albumin molar ratios found in macrophage-conditioned medium. In macrophage-conditioned medium with VLDL but without albumin, little free fatty acid was found. Other factors produced by macrophages did not seem to affect the metabolism of VLDL by smooth muscle cells since, in the absence of albumin, media with VLDL caused comparable responses in smooth muscle cell triacylglycerol accumulation whether or not the medium was previously exposed to macrophages. Thus, the minor changes in triacylglycerol content in smooth muscle cells promoted by medium containing VLDL and albumin were substantially enhanced by a prior exposure of the medium to macrophages, primarily due to the free fatty acids present in the macrophage-conditioned medium.

Sulfated glycosaminoglycans in cultured endothelial cells from capillaries and large vessels of human and bovine origin

The [35S]glycosaminoglycans ([35S]GAG) synthesized by capillary endothelial cells were analyzed and compared to GAG synthesized by endothelial cells cultured from 4 larger vessels. Two separate cultures of endothelial cells were established from bovine fat capillaries and from 4 larger vessels of human origin (umbilical vein) and bovine origin (pulmonary artery, pulmonary vein and aorta). After incubation with 35SO4 for 72 h, the [35S]glycosaminoglycans (GAG) composition of the media, pericellular and cellular fractions of each culture were determined by selective degradation with nitrous acid, chondroitinase ABC and chondroitinase AC. All endothelial cells produced large amounts of [35S]GAG with increased proportions of heparinoids (heparan sulfate and heparin) in the cellular and pericellular fractions. Each culture showed a distinct distribution of [35S]GAG in the media, pericellular and cellular fractions with several specific differences found among the 5 cultures. The differences in GAG content were confirmed in a second group of separate cultures from each of the 5 vessels indicating that, although having several features of GAG metabolism in common, each endothelial cell culture demonstrated a characteristic complement of synthesized, secreted and cell surface-sulfated glycosaminoglycans.

A comparison of glycosaminoglycan synthesis by human fibroblasts from normal skin, normal scar, and hypertrophic scar

Fibroblasts isolated from normal skin, normal scar, and hypertrophic scar tissues were compared with respect to their growth curves, protein contents, and abilities to synthesize glycosaminoglycans (GAGs). While no significant differences were found with respect to protein content or population doubling times, we did find significant differences in the proportions of radiolabel incorporated into the various GAGs among the 3 groups of cell lines. Using a dual-label technique to label both hyaluronic acid and the sulfated GAGs, we isolated labeled constituents from the extracellular, the pericellular, and the cellular fractions by pronase digestion and gel filtration and identified the various GAGs by electrophoresis and selective digestion with enzymes. Of the GAGs isolated from the extracellular fraction, hypertrophic scar fibroblasts incorporated proportionately more 35S into chondroitin sulfate and less into heparan sulfate and more [3H]glucosamine into hyaluronic acid than did normal skin fibroblasts. Of the GAGs isolated from the cellular fraction, hypertrophic scar fibroblasts incorporated proportionately more 35S into heparin and less into dermatan sulfate and more [3H]glucosamine into hyaluronic acid than did normal skin fibroblasts. These differences in biosynthesis may help to explain the differences in GAG content in skin and scars found in vivo and to give insight into the development of hypertrophic scars.