Induction of macrophage lysosomal hydrolase synthesis and secretion by beta-1,3-glucan

Studies were undertaken to elucidate the active component in zymosan necessary to induce the delayed-onset synthesis and secretion of representative lysosomal hydrolases, hexosaminidase, and beta-glucuronidase in macrophages. Resident mouse peritoneal macrophages were challenged with zymosan particles and particulate beta-1,3-glucan, the major subcomponent of zymosan. Zymosan was found to induce a rapid secretion of preformed hexosaminidase with maximal release (75%) occurring 6 hr after the addition of zymosan. By contrast, beta-1,3-glucan was totally inactive in this respect. However, both zymosan and beta-1,3-glucan were found to induce the delayed-onset synthesis and secretion of hexosaminidase and beta-glucuronidase while maintaining constant cellular enzyme levels over a 5-day period following the addition of stimulus. These late responses were almost totally blocked by a noncytolytic concentration of cycloheximide, indicating their dependence on de novo protein synthesis. Mannan, the second major subcomponent of zymosan, had no effect on either immediate secretion or delayed-onset synthesis and secretion of hexosaminidase. These results suggest that the induction of the delayed-onset synthesis and secretion of the lysosomal hydrolases by zymosan may be dependent on the glucan subcomponent of zymosan. Moreover, it would also appear that the release of preformed lysosomal enzymes is not the trigger for the delayed-onset synthesis and secretion of hexosaminidase.     

Intercellular exchange of lysosomal hydrolases between mutant human fibroblasts and other cell types

Human fibroblasts with a genetic deficiency of a single lysosomal enzyme and fibroblasts from a patient with ‘I-cell’ disease with a multiple deficiency of lysosomal hydrolases were used as recipient cells in studies on recognition and uptake of β-N-acetylhexosaminidase (hexosaminidase), β-glucuronidase and β-galactosidase. Normal human fibroblasts, and fibroblasts, hepatocytes and hepatoma cells from the rat were used as donor cells. The release of hexosaminidase was found to be similar among these different cell types, but the extracellular activities of β-glucuronidase and β-galactosidase were much higher in the rat cell cultures than in cultures of normal human fibroblasts. The enzymes released by rat fibroblasts were ingested by deficient human fibroblasts; enzyme from normal human fibroblasts was shown to be taken up by rat fibroblasts by means of electrophoresis. This indicates that reciprocal transfer of lysosomal hydrolases occurs between human and rat fibroblasts. Rat hepatocytes released hydrolases that were poorly taken up by human recipient fibroblasts and uptake of human fibroblast enzyme was not detected in the hepatocytes. Rat hepatoma cells, on the other hand, released lysosomal enzymes that were taken up by human deficient cells with a higher efficiency than those from fibroblasts. The uptake was subject to competitive inhibition by mannose 6-phosphate, the kinetics of which were comparable with those reported for ‘high-uptake’ forms of lysosomal enzymes [1–2]. Electrophoretic studies showed that rat hepatoma cells were not only capable of ingesting hexosaminidase from normal human fibroblasts, but also defectively processed enzyme [4–5] released by ‘I-cells’. These findings make rat hepatoma cells a useful model for the study of recognition and uptake of lysosomal enzymes.     

Leukocyte complement: interleukin-like properties of factor Bb

It has been previously shown that the activated form of Factor B (Factor Bb) of the alternative pathway of complement activation stimulates monocyte spreading and killing of xenogenic erythrocytes and staphylococci. Factor Bb also stimulates lymphocyte blastogenesis in vitro, and native (uncleaved) Factor B is a major constitutive product of murine macrophages. To evaluate the possible "monokine" or "lymphokine"-like properties of Factor Bb, a radioimmunoassay was developed to measure the quantities of Factor B in phytohemagglutinin (PHA)-mitogen-stimulated cultures of human peripheral blood mononuclear cells. Nonstimulated mononuclear cell cultures from human peripheral blood (containing 10-14% monocytes and greater than 85% lymphocytes) at a density of 3 X 10(6) cells/ml (in serum-free medium) released less than 7 X 10(-10) M/liter (60 ng/ml) of Factor B antigen in 24 hr at 37 degrees C, and when mononuclear cells were stimulated with PHA mitogen in serum-free medium, the levels of Factor B antigen in media at 24 hr were significantly higher 1-3 X 10(-8) M/liter (0.9-2.8 micrograms/ml). The molecular size of Factor B in these media was 50-65 kDa by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a size appropriate for Factor Bb (60 kDa). Since pathological effects of macrophages in autoimmune disease may result from the release of lysosomal hydrolases, the effects of purified Factor Bb on mononuclear phagocytes were investigated in an in vitro system of murine peritoneal exudate macrophages. Factor Bb induced secretion of marker lysosomal hydrolases N-acetyl-beta-D-glucosaminidase (hexosaminidase) and beta-glucuronidase from thioglycollate-elicited murine peritoneal exudate macrophages in a dose-response and kinetic manner. Hydrolase release was induced in serum-free medium without a known particulate activator at a concentration of 80-200 nM (5-13 micrograms/ml) Factor Bb. Maximal release occurred in 3-5 hr at 37 degrees C and extracellular enzyme activity of hexosaminidase and glucuronidase increased as intracellular enzyme levels decreased, suggesting that Factor Bb triggers release of these enzymes from intracellular lysosomal pools. These results provide an example of a complement protein which is synthesized, released, and activated during mononuclear cell culture and which induces release of lysosomal enzymes from macrophages. In conventional terminology, Factor B or Factor Bb might be termed a "lymphokine," "monokine," or "interleukin".     

Paraquat depresses the activity of angiotensin converting enzyme expressed by human umbilical vein endothelial cells in culture

The activity of angiotensin converting enzyme (ACE) in cell lysate of cultured human umbilical vein endothelial cells (HUVEC) after a 24-hour incubation with 10(-3) and 10(-4)M of paraquat (PQ) was decreased. However, LDH released into the culture medium of HUVEC during the 24-hour incubation with PQ was not increased. Many investigators show that the change in serum ACE activity reflects the impairment of vascular endothelial cells. We showed in this report that ACE was decreased even at an early stage of endothelial injury induced by PQ, when LDH release is not yet increased.     

Secretion of lysosomal hydrolases by cultured human amnion epithelial cells

Primary microcultures of human amnion epithelial cells were established, starting from sterile term placentae. Over a period of 1 week in culture, the epithelial cells release into the extracellular medium substantial amounts of some lysosomal hydrolases, such as sphingomyelinase, N-acetyl-beta-glucosaminidase, alpha-fucosidase, beta-glucuronidase, alpha-mannosidase, and arylsulfatase. Judging from experiments conducted with the protein synthesis inhibitor, cycloheximide, the enzymes released are not newly synthesized forms, but very likely derive from lysosomes. The constitutive secretion of lysosomal enzymes, coupled with lack of immunogenicity, makes amnion epithelial cells a convenient source of enzymes for implantation in attempts of enzyme replacement therapies.     

Synthesis of genistein derivatives and determination of their protective effects against vascular endothelial cell damages caused by hydrogen peroxide

A series of genistein derivatives, prepared by alkylation and difluoromethylation, were tested for their inhibitory effects on the hydrogen peroxide induced impairment in human umbilical vein endothelial (HUVE-12) cells in vitro. The HUVE-12 cells were pretreated with either the vehicle solvent (DMSO), genistein, or different amounts of the genistein derivatives for 30 min before exposed to 1 mM hydrogen peroxide for 24 h. Cell apoptosis was determined by flow cytometry with propidium iodide (PI) staining. Cellular injury was estimated by measuring the lactate dehydrogenase (LDH) release. Data suggested that the genistein derivatives possessed a protective effect on HUVE-12 cells from hydrogen peroxide induced apoptosis and reduced LDH release. Among these derivatives, 7-difluoromethyl-5,4'-dimethoxygenistein exhibited the strongest activity against hydrogen peroxide induced apoptosis of HUVE-12 cells.     

Endobrevin/VAMP8 mediates exocytotic release of hexosaminidase from rat basophilic leukaemia cells

Mast cells are important players in innate immunity and mediate allergic responses. Upon stimulation, they release biologically active mediators including histamine, cytokines and lysosomal hydrolases. We used permeabilized rat basophilic leukaemia cells as model to identify R-SNAREs (soluble NSF (N-ethylmaleimide-sensitive fusion protein)) mediating exocytosis of hexosaminidase from mast cells. Of a complete set of recombinant mammalian R-SNAREs, only vesicle associated membrane protein (VAMP8)/endobrevin consistently blocked hexosaminidase release, which was also insensitive to treatment with clostridial neurotoxins. Thus, VAMP8, which also mediates fusion of late endosomes and lysosomes, plays a major role in hexosaminidase release, strengthening the view that mast cell granules share properties of both secretory granules and lysosomes.     

Constitutive Secretion of Acid Hydrolases in Tetrahymena thermophila

THE role of lysosomal enzymes in intracellular digestion is now well established [11]. Most often we think of lysosomal hydrolases in catabolism of endogenous or foreign material taken up by endocytosis. There is however, a number of reports dealing with the release of acid hydrolases into the extracellular fluid in a variety of eukaryote cells. These cells range from Saccharomyces cerevisiae [15], Dictyostelium discoideum [10], Leishmania donovani [20], Acanthamoeba castellani [22], Entamoeba histolytica [12, 31], and species of Tetrahymena [1–3, 6] to mammalian cells in culture [49]. Concerning the latter, fibroblasts and hepatocytes in culture release acid hydrolases to the extracellular medium, but only if the synthesis of a specific recognition marker is impaired in the cells. This marker (man-nose-6-phosphate) is used for receptor mediated segregation of lysosomal enzymes into the lysosomal compartments. If the receptor or the marker are lacking, the hydrolases fail to enter the lysosomal compartment, and are secreted in immature form together with molecules belonging to the constitutive secretory pathway of the cells [8, 49]. Such a release of acid hydrolases seems to occur spontaneously from mammalian osteoclasts [4]. Macrophages, on the other hand, need a specific stimulation for their release process [40]. In lower eukaryotes the release may     

Does the induction of macrophage lysosomal enzyme secretion by zymosan involve the mannose receptor?

Secretion of the lysosomal enzyme hexosaminidase induced by zymosan is inhibited by mannose and by high concentrations of mannose-6-phosphate and 2-deoxy-glucose but not by mannan. Secretion of hexosaminidase from cells storing previously endocytosed zymosan is unaffected by mannose. Exposure of the cells to mannose does not affect secretion caused by subsequent exposure to zymosan. These findings suggest a role for the mannose-glycoprotein receptor in initiation of lysosomal enzyme secretion by zymosan.     

Distribution of acid hydrolases in subcellular fractions of proliferating vs non-proliferating fibroblasts

We have employed colloidal silica (Percoll) density-gradient subcellular fractionation technique to examine the distribution of lysosomal hydrolases between intermediate vesicles (primary lysosomes) and secondary lysosomes in contact-inhibited non-proliferating vs proliferating chicken embryo fibroblasts. We find that the activities of lysosomal specific enzymes from both phases of growth are distributed within two peaks; however, the relative amounts differ markedly. In normal, non-proliferating cells approx. 60% of the total activities of cathepsin B, beta-mannosidase, alpha-fucosidase, beta-galactosidase and hexosaminidase is recovered in the heavier density fraction corresponding to secondary lysosomes, while less than 9% of the enzyme activities are recovered in the light-density peak. With transformed cells, between 16 and 22% of activity for these enzymes are recovered in the lighter density intermediate vesicle fraction, when less than 40% of the enzyme activities recovered in the heavy density fraction. beta-Glucuronidase distribution was different from that of the above enzymes. First, a more even distribution between the two lysosomal fractions was found with non-proliferating normal cells (33% in heavy-density fraction and 21% in light-density fraction), whereas more than 40% of the total enzyme activity was recovered in the lighter density fraction from transformed cells. Also, the amount of cathepsin B contained in the vesicle fractions is increased severalfold relative to that of contact-inhibited normal cells. However, the apparent differences in enzyme distribution between confluent normal and transformed cells are not found when vesicles are prepared from subconfluent, actively proliferating cultures. We have also compared the Percoll density gradient patterns of membrane vesicles from proliferating and non-proliferating human fibroblasts, since most earlier studies utilized this system. Again, we find that the majority of beta-hexosaminidase activity (41%) of contact-inhibited, confluent cells is recovered in the heavier density fraction with less than 15% in the lighter density fraction. Also, the distribution of beta-hexosaminidase between the heavy density and light density vesicle fractions is altered in homogenates from exponentially growing cells, being 22% and 26% respectively. We conclude that the distribution of lysosomal hydrolases between the two vesicle populations is growth-phase dependent and is markedly heterogeneous in proliferating cells.     

Proteomic analysis of the secretome of human umbilical vein endothelial cells using a combination of free‐flow electrophoresis and nanoflow LC‐MS/MS

Human umbilical vein endothelial cells are the most widely used in vitro model for endothelial cells. Their secreted proteins, however, have not been comprehensively analysed so far. In this study, we accomplished to map the secretome of human umbilical vein endothelial cells by combining free‐flow electrophoresis with nanoflow LC‐MS/MS. This comprehensive analysis provides a basis for future comparative studies of protein secretion by endothelial cells in response to cardiovascular risk factors and is available on our website http://www.vascular‐proteomics.com .     

Biochemical heterogeneity in I-cell disease. Sucrose-loading test classifies two distinct subtypes

Since we observed the normalization of intracellular hydrolases in some cell lines of I-cell disease (ICD) by 88 mmol/l sucrose, we have hypothesized that the degree of responses of the hydrolases might be due to biochemical heterogeneity among ICD. In this study the changes of intracellular lysosomal enzymes as well as Golgi enzymes including N-acetylglucosaminyl phosphotransferase (GlcNAcPTase) and extracellular hexosaminidase (HEX) were investigated using normal and ICD fibroblasts. Sucrose loading induced the activities of intracellular HEX and GlcNAcPTase simultaneously only in responding-type ICD cells, and not in nonresponding-type ICD cells, indicating that two biochemical heterogeneous groups exist in ICD.     

Quantitative evaluation of the phagocytic activity of endothelial cells in culture

The phagocytic activity of endothelial cells (EC) from human umbilical vein was analysed quantitatively in primary culture. EC were incubated with fluorescent carboxylated microspheres (FCM) and the intensity of fluorescence was measured on spectrofluorimeter. It was found that EC phagocyted actively only FCM of limited diameter (not more than 0.26 mu). The most intensive phagocytosis occurred in the first 60 min of the experiment, the following incubation with FCM did not influence significantly the number of phagocyted particles but increased nonspecific binding. High doses of FCM stimulated phagocytosis within EC. The phagocytic activity of EC depended on the growth stage: it was maximum in proliferated cells and sharply decreased in confluent cultures. This method may be useful for the comparison of phagocytic activity of different cell types, as well as for drug testing.     

High glucose promotes the release and expression of novel vasoactive peptide, coupling factor 6, in human umbilical vein endothelial cells

As a novel vasoactive peptide, plasma coupling factor 6 (CF6) was shown to be elevated in patients with diabetes mellitus, yet the mechanism involved is unknown. We studied CF6 protein release and its potential mechanism in human umbilical vein endothelial cells (HUVECs) incubated with high glucose levels. High glucose level enhanced CF6 expression and peptide secretion in HUVECs in a time- and concentration-dependent manner, which was independent of increased osmolarity. PKC or p38 MAPK inhibition significantly suppressed high glucose-mediated CF6 release in HUVECs, and the inhibition rate was -45% and -30%, respectively. Also, high glucose-induced CF6 production was antagonized by insulin treatment. Hence, high glucose increases the expression and secretion of CF6 in endothelial cells and appears to be mediated by PKC and p38 MAPK activity.     

Two-chain high molecular weight kininogen induces endothelial cell apoptosis and inhibits angiogenesis: partial activity within domain 5.

We previously reported that the binding of two-chain high molecular weight kininogen (HKa) to endothelial cells may occur through interactions with endothelial urokinase receptors. Since the binding of urokinase to urokinase receptors activates signaling responses and may stimulate mitogenesis, we assessed the effect of HKa binding on endothelial cell proliferation. Unexpectedly, HKa inhibited proliferation in response to several growth factors, with 50% inhibition caused by approximately 10 nM HKa. This activity was Zn(2+) dependent and not shared by either single-chain high molecular weight kininogen (HK) or low molecular weight kininogen. HKa selectively inhibited the proliferation of human umbilical vein and dermal microvascular endothelial cells, but did not affect that of umbilical vein or human aortic smooth muscle cells, trophoblasts, fibroblasts, or carcinoma cells. Inhibition of endothelial proliferation by HKa was associated with endothelial cell apoptosis and unaffected by antibodies that block the binding of HK or HKa to any of their known endothelial receptors. Recombinant HK domain 5 displayed activity similar to that of HKa. In vivo, HKa inhibited neovascularization of subcutaneously implanted Matrigel plugs, as well as rat corneal angiogenesis. These results demonstrate that HKa is a novel inhibitor of angiogenesis, whose activity is dependent on the unique conformation of the two-chain molecule.     

Human endothelial cells selectively express large amounts of pancreatic-type ribonuclease (RNase 1)

Pyrimidine-specific ribonucleases are a superfamily of structurally related enzymes with distinct catalytic and biological properties. We used a combination of enzymatic and non-enzymatic assays to investigate the release of such enzymes by isolated cells in serum-free and serum-containing media. We found that human endothelial cells typically expressed large amounts of a pancreatic-type RNase that is related to, if not identical to, human pancreatic RNase. This enzyme exhibits pyrimidine-specific catalytic activity, with a marked preference for poly(C) substrate over poly(U) substrate. It was potently inhibited by placental RNase inhibitor, the selective pancreatic-type RNase inhibitor Inhibit-Ace, and a polyclonal antibody against human pancreatic RNase. The enzyme isolated from medium conditioned by immortalized umbilical vein endothelial cells (EA.hy926) possesses an amino-terminal sequence identical to that of pancreatic RNase, and shows molecular heterogeneity (molecular weights 18,000-26,000) due to different degrees of N-glycosylation. Endothelial cells from arteries, veins, and capillaries secreted up to 100 ng of this RNase daily per million cells, whereas levels were low or undetectable in media conditioned by other cell types examined. The corresponding messenger RNA was detected by RT-PCR in most cell types tested so far, and level of its expression was in keeping with the amounts of protein. The selective strong release of pancreatic-type RNase by endothelial cells suggests that it is endowed with non-digestive functions and involved in vascular homeostasis.     

The effect of second-line antirheumatic drugs on interleukin-8 mRNA synthesis and protein secretion in human endothelial cells.

Interactions between interleukin 8 (IL-8) and endothelial cells play an important role in the emigration of mononuclear cells from the blood into areas of inflammation. We examined the ability of specific second-line antirheumatic drugs to regulate (IL-8) gene expression and protein secretion in interleukin 1 (IL-1) stimulated human umbilical vein endothelial cells and peripheral blood mononuclear cells. The drugs sodium aurothiomalate, D-penicillamine and sulphasalazine were all able to modulate IL-8 mRNA synthesis in and protein secretion from endothelial cells. A bimodal effect was observed: at low concentrations IL-8 was suppressed, whereas higher concentrations resulted in an increased IL-8 production. In endothelial cells, treatment with hydrocortisone led to a linear suppression of IL-8 production in concentrations ranging from 0.5 micrograms/ml up to 500 micrograms/ml. Sulphapyridine, auranofin, hydroxychloroquine and methotrexate, had no effect on IL-8 secretion in endothelial cells. By contrast, 5-aminosalicylic acid induced a threefold increase in the IL-8 release. In peripheral blood mononuclear cells it was only possible to suppress the IL-8 production by hydrocortisone treatment. These results indicate that suppression of IL-8 production in endothelial cells could be an important factor in the mode of action for a number of second-line antirheumatic drugs.     

Effect of RNA and protein synthesis inhibitors on the release of inflammatory mediators by macrophages responding to phorbol myristate acetate

The interaction of phorbol myristate acetate with resident populations of mouse peritoneal macrophages causes an increased release of arachidonic acid followed by increased synthesis and secretion of prostaglandin E2 and 6-keto-prostaglandin F1 alpha. In addition, phorbol myristate acetate causes the selective release of lysosomal acid hydrolases from resident and elicited macrophages. These effects of phorbol myristate acetate on macrophages do not cause lactate dehydrogenase to leak into the culture media. The phorbol myristate acetate-induced release of arachidonic acid and increased synthesis and secretion of prostaglandins by macrophages can be inhibited by RNA and protein synthesis inhibitors, whereas the release of lysosomal hydrolases is unaffected. 0.1 microgram/ml actinomycin D blocked the increased prostaglandin production due to this inflammatory agent by more than 80%, and 3 microgram/ml cycloheximide blocked prostaglandin production by 78%. Similar results with these metabolic inhibitors were found with another stimulator of prostaglandin production, zymosan. However, these inhibitors do not interfere with lysosomal hydrolase releases caused by zymosan or phorbol myristate acetate. It appears that one of the results of the interaction of macrophages with inflammatory stimuli is the synthesis of a rapidly turning-over protein which regulates the production of prostaglandins. It is also clear that the secretion of prostaglandins and lysosomal hydrolases are independently regulated.     

A simple and biosafe method for isolation of human umbilical vein endothelial cells

Human umbilical vein endothelial cells (HUVEC_S) are used as an irreplaceable tool for the study of vascular diseases. However, the technicians who isolate HUVECs are largely exposed to potential infectious threats. Here we report the development of a specialized instrument to protect researchers from known or unknown infectious agents when they operate on human umbilical cords. This instrument can be assembled by common laboratory supplies and adapted to accommodate umbilical cords of different lengths. When the cord is enclosed within the instrument, the risk of sample contamination and operator infection is greatly reduced. Using our instrument, endothelial cells were successfully isolated from human umbilical veins without contamination. The cells were verified by their cobblestone-like morphology and by immunofluorescence staining (Factor VIII and CD31 positivity and α-SMA negativity). Our instrument simplifies and optimizes the cell extraction process, and most importantly elevates the biosafety to a higher level during the isolation of human umbilical vein endothelial cells.     

Adaptive Induction of Growth Differentiation Factor 15 Attenuates Endothelial Cell Apoptosis in Response to High Glucose Stimulus

Growth differentiation factor 15 (GDF15), a direct target gene of p53, is a multifunctional member of the TGF-β/BMP superfamily. GDF15 can be induced and is implicated as a key secretory cytokine in response to multiple cellular stimuli. Accumulating evidence indicates that GDF15 is associated with the development and prognosis of diabetes mellitus, while whether GDF15 can be induced by high glucose is unknown. In the present study, we revealed that high glucose could induce GDF15 expression and secretion in cultured human umbilical vein endothelial cells in a ROS- and p53-dependent manner. Inhibition of high glucose-induced GDF15 expression by siRNA demonstrated that adaptively induced GDF15 played a protective role against high glucose-induced human umbilical vein endothelial cell apoptosis via maintaining the active state of PI3K/Akt/eNOS pathway and attenuating NF-κB/JNK pathway activation. The protective effects of GDF15 were probably achieved by inhibiting ROS overproduction in high glucose-treated human umbilical vein endothelial cells in a negative feedback manner. Our results suggest that high glucose can promote GDF15 expression and secretion in human umbilical vein endothelial cells, which in turn attenuates high glucose-induced endothelial cell apoptosis.