Recruitment of type I collagen producing cells from the microvasculature in vitro

We have previously suggested that microvascular pericytes can differentiate into fibroblast-like, type I collagen-producing cells during excessive dermal scarring in vivo (Sundberg, C., Ivarsson, M., Gerdin, B., and Rubin, K., Lab. Invest. 74, 454-468, 1996). Here we have investigated to what extent pericytes derived from microvessels of full-term human placenta exhibited this capacity in vitro. Vascular fragments of human term placenta were isolated by enzymatic digestion and separation in Percoll. Their microvascular origin was ascertained by confocal microscopy using antibodies specific for endothelial cells (PAL-E) and pericytes (high-molecular-weight-melanoma-associated antigen). When vascular fragments were cultured in vitro, large cells with irregular edges migrated out from the fragments. After 4-6 days in culture, these cells started to proliferate and reached near confluence after approximately 8 days. The cultures were not overgrown by clones of cells with a high proliferative capacity, as demonstrated by cell membrane fluorescence staining and Ki67 expression. Expression of PAL-E, high-molecular-weight-melanoma-associated antigen, smooth muscle alpha-actin, desmin, and collagen synthesis (prolyl-4-hydroxylase and type I procollagen, as well as collagen pro-alpha1(I) mRNA) were followed during a culture period of 8 days. The cells were PAL-E negative but expressed high-molecular-weight-melanoma-associated antigen, smooth muscle alpha-actin, and desmin. Based on morphology and expression of the various markers, the outgrowing cells were identified as pericytes. With time in culture the cells decreased their expression of all these markers and increased their expression of prolyl-4-hydroxylase, type I procollagen, and collagen pro-alpha1(I) mRNA. Metabolic labeling and SDS-PAGE analysis of labeled proteins revealed that type I collagen was the major collagen species synthesized in the cultures. Our results support the hypotheses that pericytes can leave the vasculature and differentiate into collagen-producing cells and that cultured "fibroblasts" are derived from pericytes.

A novel physiological function for platelet-derived growth factor-BB in rat dermis

1. The present experiments describe a role for platelet-derived growth factor-BB and cellular adhesion receptors towards extracellular matrix molecules (beta 1-integrins) in control of interstitial fluid pressure (Pif). 2. Pif was measured in rat skin with sharpened glass capillaries (3-7 microns) connected to a servocontrolled counter-pressure system. 3. The collagen and laminin-binding alpha 2 beta 1-integrin is involved in the control of Pif since subdermal injection (5 microliters) of monoclonal hamster anti-rat alpha 2 beta 1-integrin IgG (anti-alpha 2 beta 1) resulted in increased negativity of Pif. Control Pif averaged -0.88 +/- 0.23 mmHg (+/- S.D.) and decreased to -2.50 +/- 0.35 mmHg (P < 0.05) and -3.88 +/- 1.45 mmHg (P < 0.05) at anti-alpha 2 beta 1 concentrations of 0.56 and 1.12 mg ml-1, respectively. 4. The effect of anti-alpha 2 beta 1 was abolished when platelet-derived growth factor-BB (PDGF-BB) (200 ng ml-1) was injected together with anti-alpha 2 beta 1. 5. The time- and dose-responses of PDGF-BB to counteract increased negativity of Pif were studied further using dextran anaphylaxis as an experimental model inducing increased negativity of Pif in skin. Control Pif averaged -0.33 +/- 0.43 mmHg and fell to -4.10 +/- 1.47 mmHg within 10 min after dextran (P < 0.01). Subsequent subdermal injection of PDGF-BB at 200 ng ml-1 normalized Pif in 10-20 min which became -1.37 +/- 1.23 mmHg (P < 0.01 versus dextran, P > 0.05 versus control). PDGF-BB had little or no effect at 50 ng ml-1. PDGF-AA and basic fibroblast growth factor had no effect on Pif. 6. The in vivo function reported for PDGF-BB has not been described previously and provides further evidence for active participation of connective tissue cells in control of Pif by altering tension on extracellular matrix structures.

Colon-cancer cell variants producing regressive tumors in syngeneic rats, unlike variants yielding progressive tumors, attach to interstitial collagens through integrin alpha2beta1

Nine clones of tumor cells, derived from a single rat colon carcinoma, were analyzed for their adhesive properties and in vivo growth patterns. Four clones (denoted REG) gave rise to regressively growing tumors. Cells from the 4 REG clones attached significantly better to collagen types I and III than did cells from the 5 clones (denoted PRO) which grew progressively in vivo. In contrast, REG and PRO clones did not differ in their attachment to collagen type IV, laminin or fibronectin. The attachment of REG cells to collagen was dependent on Mg2+, but not Ca2+. Monospecific rabbit IgG to rat integrin beta 1-chain inhibited REG cell attachment to collagen, demonstrating involvement of a beta 1 integrin in this process. PRO and REG cells expressed an underglycosylated beta 1 chain (Mr approximately 105,000) that was somewhat smaller than beta 1-chains described previously on rat fibroblasts and hepatocytes (Mr approximately 115,000). Monoclonal IgG to rat integrin alpha 2 beta 1, but not to alpha 1 beta 1, readily inhibited REG cell attachment to collagen, demonstrating the involvement of integrin alpha 2 beta 1. However, beta 1 and alpha 2 integrin subunits were found in purified glycoproteins from both PRO and REG cells. This suggests that alpha 2 beta 1 integrin is expressed by both cell variants, but is functional as a collagen receptor on REG cells only. In this system of tumor-cell variants, the clear-cut differences in attachment to interstitial collagens of the 9 clones suggest a possible relationship between this attachment and the capacity to induce progressive or regressive tumors.

Stimulation of beta1 integrins on fibroblasts induces PDGF independent tyrosine phosphorylation of PDGF beta-receptors

We report that integrin-mediated signaling induces a rapid and transient tyrosine phosphorylation of platelet-derived growth factor (PDGF) beta-receptors in human diploid foreskin AG 1518 fibroblasts. A transient tyrosine phosphorylation of PDGF beta-receptors was evident one and two hours after cells had been plated on collagen type I and fibronectin, as well as on immobilized anti-integrin subunit IgG, but not on poly-L-lysine. In contrast EGF or PDGF alpha-receptors were not phosphorylated on tyrosine residues under these conditions. Tyrosine phosphorylation of PDGF beta-receptors induced by plating on collagen type I was inhibited by cytochalasin D and herbimycin A, unaffected by cycloheximide and enhanced by orthovanadate. Furthermore, a transient phosphorylation of PDGF beta-receptors occurred when AG 518 fibroblasts were cultured in three-dimensional collagen lattices or exposed to external strain exerted through centrifugation. The latter effect was evident already after two minutes. Clustering of cell surface beta1 integrins led to PDGF beta-receptor phosphorylation both in suspended and firmly attached AG 1518 fibroblasts. Plating of cells on collagen type I, fibronectin, and anti-beta1-integrin IgG resulted in the formation of PDGF beta-receptor aggregates as detected by immunofluorescence. Suramin or anti-PDGF-BB IgG had no effect on the plating-induced tyrosine phosphorylation of PDGF beta-receptors. PDGF-B chain mRNA, or protein, were not detected in AG 1518 fibroblasts. Our data suggest that a ligand-independent PDGF beta-receptor activation during cell adhesion and early phases of cell spreading is involved in integrin-mediated signaling in fibroblasts, and constitutes parts of a mechanism for cells to respond during the dynamic phases of externally applied tension as well as fibroblast-mediated tension during cell adhesion and collagen gel contraction.

Pericytes as collagen-producing cells in excessive dermal scarring

Immunohistochemistry and image analysis were performed on sections from excessive dermal scar formation to investigate the potential of pericytes to differentiate into collagen-producing cells. Expression of the prolyl-4-hydroxylase beta-subunit (P-4-H) was used as a marker for collagen synthesis as the distribution of this protein was identical to the distribution of procollagen type I C-propeptide and similar to the distribution of cells expressing pro alpha 1(I) collagen mRNA. Double immunofluorescence stainings using combinations of monoclonal antibodies specific for activated pericytes in vivo (high molecular weight-melanoma associated antigen (HMW-MAA)), P-4-H, smooth muscle alpha-actin (SMA), endothelial cells (PAL-E), platelet-derived growth factor (PDGF) beta-receptor, and the integrin alpha 5 subunit were performed. Stained sections were analyzed by computerized image analysis allowing for a quantification of the degree of colocalization between pairs of antigens on the same tissue section. Four different subpopulations of HMW-MAA expressing cells were discerned. The first subpopulation corresponded to intramural pericytes, juxtapositioned to the endothelium, that expressed HMW-MAA, SMA, integrin alpha 5 subunit and the PDGF beta-receptor, but not P-4-H. The second subpopulation was partly dissociated from the microvascular wall and exhibited a similar antigen expression except for a decrease in expression of SMA. Cells in the third subpopulation were located in the perivascular space and expressed P-4-H, integrin alpha 5 subunit, the PDGF beta-receptor and, albeit less pronounced, HMW-MAA, but not SMA. The fourth subpopulation expressed integrin alpha 5 subunit, HMW-MAA and the PDGF beta-receptor, no expression of SMA and a strong expression of P-4-H. Moreover, an in vitro analysis of cells derived from isolated microvascular fragments from human dermis revealed a similar pattern of phenotypical change. Taken together the data suggest that a population of intramural pericytes migrate into the perivascular space and develop into collagen-synthesizing fibroblasts during fibrosis.

Effect of atmospheric composition and pressure on the laser ablation of (GeTe)(85)Sn(15) chalcogenide thin films

Laser ablation of (GeTe)(85)Sn(15) thin films as a function of atmospheric exposure was monitored in real time by transient reflectivity. The observed optical changes were correlated with microstructural analysis. Among the key findings were that the presence of water in the atmosphere during laser irradiation of a thin-film structure reduced the incident laser power required for ablation by as much as a factor of 2. The magnitude of the effect was dependent on both H(2)O vapor pressure and duration of exposure to the vapor. The reduction of laser power necessary to ablate was partially reversed by exposure of the thin-film structure to vacuum. Significantly, exposure to other (dry) gases such as N(2) did not change the ablation threshold from that observed in vacuum. We determined that dome formation and ablation occurred at lower temperatures in the presence of water. In addition, the power necessary to crystallize the amorphous chalcogenide layer in the structure was independent of atmospheric composition or pressure. Microstructure analysis showed the presence of H(2)O fostered the formation of a nonuniform distribution of the chalcogenide material in the ablated region. The experimental results are consistent with our model that ablation is assisted by high pressures produced by vaporization of absorbed liquid water.

Collagen type I is not under autocrine control by transforming growth factor-beta 1 in normal and scleroderma fibroblasts

BACKGROUND

The ability of transforming growth factor-beta (TGF-beta) to induce synthesis of extracellular matrix proteins stimulated this study in which we address the hypothesis that TGF-beta can induce, in normal fibroblasts, the sustained, elevated collagen synthesis characteristic of the scleroderma fibroblast.

EXPERIMENTAL DESIGN

Fibroblasts were studied for synthesis of and responsiveness to TGF-beta. Secreted TGF-beta levels were determined in a bioassay and at the transcriptional level in a series of scleroderma (SSc) and normal fibroblasts. The ability of cells to interact functionally with a 3-dimensional collagen matrix after TGF-beta treatment was examined. The kinetics of TGF-beta-induced fibrosis in fibroblasts was studied.

RESULTS

SSc fibroblasts were not characterized by elevated TGF-beta synthesis. There was no evidence of coordinate regulation of TGF-beta and collagen over passage number. Repeated pulses of 200 pM of TGF-beta did not significantly induce sustained procollagen alpha 1(I) mRNA synthesis in normal fibroblasts, and this treatment did not significantly alter the characteristics of normal fibroblasts in a collagen gel. mRNA for both collagen and TGF-beta type II receptor was induced by TGF-beta in both SSc and control cells. SSc fibroblasts were found to have an impaired ability to activate the small latent complex of TGF-beta.

CONCLUSIONS

Our data give no support to the hypothesis that TGF-beta can maintain the SSc phenotype in vitro or that it is able to induce this phenotype. The inducibility of TGF-beta receptor mRNA in SSc fibroblasts after exposure to TGF-beta suggests that the lack of sustained elevation in collagen synthesis is not due to lack of responsiveness by the fibroblasts but is rather a reflection of the transient nature of TGF-beta-induced fibrosis.

Platelet-derived growth factor-BB stimulates synthesis of the integrin alpha 2-subunit in human diploid fibroblasts

Platelet-derived growth factor (PDGF)-BB stimulates fibroblast-mediated contraction of collagen gels, as well as migration of fibroblasts through collagen-coated membranes. In the present study we examined effects of PDGF-BB stimulation on the synthesis of collagen-binding beta 1 integrins by human diploid fibroblasts (AG 1518). PDGF-BB stimulation led to an increase in the rare of integrin alpha 2-subunit synthesis. In contrast, synthesis of the integrin alpha 1- or alpha 3-subunits were not affected by PDGF-BB stimulation. Furthermore, levels of alpha 2-subunit mRNA relative to levels of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA increased after PDGF-BB stimulation. The latter finding is compatible with PDGF-BB stimulating transcription of the alpha 2-subunit gene. PDGF-BB stimulation did not influence the relation between levels of integrin beta 1-subunit mRNA and GAPDH mRNA. In addition, the rate of synthesis or post-translational processing of the integrin beta 1-subunit were not, or only marginally, affected by PDGF-BB stimulation. It is likely that the motility response elicited in fibroblasts by PDGF-BB involves such alterations in the synthesis of the alpha 2-subunit of the alpha 2 beta 1 collagen-binding integrin.

The anti-inflammatory agent alpha-trinositol exerts its edema-preventing effects through modulation of beta 1 integrin function

Edema formation in acute inflammation can be induced through lowering of interstitial fluid pressure (Pif) and seems to involve dynamic beta 1 integrin-mediated interactions between dermal cells and extracellular matrix fibers. The present experiments investigate the role of beta 1 integrins in the control of Pif. The anti-inflammatory drug alpha-trinositol (1,2,6-D-myo-inositol trisphosphate) stabilizes Pif in acute inflammation. Pretreatment with 5 mg IV alpha-trinositol in pentobarbital-anesthetized rats inhibited the lowering in Pif and the edema formation induced by subdermal injection of anti-beta 1 integrin IgG. This stabilization of the beta 1 integrin function in vivo was paralleled by effects of alpha-trinositol on contraction of fibroblast-populated three-dimensional collagen lattices in vitro. alpha-Trinositol was additive to the known stimulatory effect of platelet-derived growth factor-BB on the final gel size in the collagen gel contraction assay. Furthermore, alpha-trinositol counteracted the inhibitory effect of anti-beta 1 integrin Fab fragments on collagen gel contraction. Finally, subdermal injection of dibutyryl-cAMP (db-cAMP) induced increased negativity of Pif to the same extent as did anti-beta 1 integrin antibodies, and in vitro db-cAMP reduced the ability of fibroblasts to contract collagen gels. The latter effect was opposed by alpha-trinositol. The data demonstrate that alpha-trinositol modulates beta 1 integrin function and may do so via intracellular pathways in turn affecting the function and/or cell surface expression of beta 1 integrins and suggest that alpha-trinositol can serve as a tool to study integrin function. Furthermore, the data indicate that the collagen contraction assays may provide important information of the control of Pif in vivo.

Vitronectin in colorectal adenocarcinoma--synthesis by stromal cells in culture

We have investigated the expression and cellular source of vitronectin in colorectal adenocarcinoma. Immunofluorescence staining of tissue sections revealed the presence of vitronectin in the stroma of the 11 tumors studied, but not in adjacent normal colon. A method was devised for the isolation from colorectal adenocarcinomas of fibroblast-like cells that stained positive for vimentin but negative for cytokeratin. These tumor-derived stromal cells synthesized and secreted vitronectin, as revealed by metabolic labeling and immunoprecipitation. This was confirmed by Southern blot analysis of polymerase chain reaction amplification products from reverse-transcribed RNA. Normal skin fibroblasts did not synthesize vitronectin. Immunofluorescence staining showed vitronectin deposited at focal contact sites in the tumor-derived cells, where it colocalized with vinculin and the alpha v integrin subunit. The deposition of vitronectin into focal contact sites was not dependent on the presence of serum. The finding that vitronectin can be synthesized and secreted by tumor-derived fibroblast-like cells in culture indicates that vitronectin expression can be promoted by as yet unknown signals provided in disease states, such as cancer.

Purification of a bone sialoprotein-binding protein from Staphylococcus aureus

Bone sialoprotein (BSP) is selectively bound by Staphylococcus aureus cells isolated from patients suffering from infections of bone and joint tissues [Rydén C., Maxe, I., Franzén, A., Ljungh, A., Heinegård, D. & Rubin, K. (1987) Lancet II, 515]. We now report on the purification of a cell-wall protein from Staphylococcus aureus, strain O24, that possesses affinity for bone sialoprotein. Staphylococcal cell-wall components with capacity to inhibit binding of 125I-labeled BSP to staphylococcal cells were solubilized with LiCl (1.0 M, pH 5.0). Preparative SDS/PAGE and protein-overlay experiments revealed that inhibitory activity present in LiCl extracts resided in a fraction of polypeptides with M(r) 75,000-110,000. Staphylococcal proteins solubilized with LiCl were chromatographed on a Mono-Q anion-exchange column. Inhibitory activity was eluted at 0.6-0.8 M NaCl and could be further purified by affinity chromatography on BSP-Sepharose. Elution of the affinity matrix with 0.1 M glycine, pH 3.0, specifically eluted inhibitory activity. Analysis by SDS/PAGE revealed a single M(r) 97,000 polypeptide in the eluate. The purified M(r) 97,000 protein bound BSP in protein-overlay experiments. LiCl extracts from S. aureus, strain E514 or Staphylococcus epidermidis, strain 7686, both lacking the capacity to bind BSP did not contain the M9r) 97,000 protein. Our data demonstrate the presence of a S. aureus cell-surface BSP-binding protein. This protein could be involved in bacterial tropism in osteomyelitis.

Anti-beta 1 integrin IgG inhibits pulmonary macrometastasis and the size of micrometastases from a murine mammary carcinoma

In the present report, we investigated the possible importance of beta 1 integrins in the growth and metastasis of a murine mammary carcinoma, SP1, and a metastatic variant, SP1-3M in vivo. CBA/J female mice bearing SP1 tumor transplants were injected with anti-beta 1 integrin IgG or control nonimmune IgG (200 micrograms per mouse; i.p.) every two days. Animals received anti-CD4 antibody (100 micrograms per mouse) at time zero to suppress immunity against rabbit IgG. Outgrowth of macroscopic metastases from SP1, but not from SP1-3M primary tumors, was markedly inhibited in animals receiving anti-beta 1 integrin IgG but not nonimmune IgG. To assess the stage(s) in the metastatic cascade affected, we examined the number and diameter of micrometastatic nodules in treated and untreated groups. The diameter of micrometastases was significantly reduced in SP1-tumor-bearing mice treated with anti-beta 1 integrin IgG compared to control IgG, although the number of nodules per cm2 of lung sections examined remained unchanged. No change in the number or size of micrometastases in SP1-3M tumor-bearing mice was observed. No difference in the binding, or complement-mediated and antibody-dependent cell-mediated cytotoxicity of anti-beta 1 integrin IgG with SP1 and SP1-3M cells was detected. The results suggest that under these conditions anti-beta 1 integrin inhibits metastatic tumor growth in lung tissue, but has minimal effect on intravasation, adhesion to target organs and extravasation.

Predictors of axial and peripheral bone mineral density in healthy children and adolescents, with special attention to the role of puberty

The role of various physical and lifestyle factors in determining axial bone mineral density (BMD) at the lumbar segment of the spine, as measured by dual-photon absorptiometry, and peripheral BMD at the distal third of the radius, as measured by single-photon absorptiometry, was assessed in 299 healthy white children of both sexes, aged 6 to 18 years. The BMD measurements were correlated with age, height, weight, body mass index, and pubertal status. Peripheral and axial BMD were highly correlated with age, height, weight, and pubertal stage, and more weakly with body mass index. Approximately 76% of the observed changes in peripheral BMD were accounted for by age, height, weight, and pubertal stage, with weight being the single strongest predictor. Up to 80% of the variation in axial BMD was explained by weight and pubertal stage, with pubertal stage being the strongest single predictor. After adjustment for weight, the effect of puberty on axial BMD in both sexes was greatest between middle and late puberty. These data indicate that a large amount of the observed changes on BMD is accounted for by standard measures of growth and development, which are largely genetically determined. Peripheral BMD rose steadily with age. Axial BMD increased steadily before puberty, followed by accelerated increases during puberty, beginning at 10 years of age in girls and 13 years of age in boys. A significant positive effect of dietary calcium intake on peripheral BMD and of physical activity on axial BMD indicated a potentially important impact of physical activity and calcium intake on peak bone mass.

Stromal expression of platelet-derived growth factor beta-receptor and platelet-derived growth factor B-chain in colorectal cancer

BACKGROUND

The importance of growth factors, such as platelet-derived growth factor (PDGF), for stromal activation in colorectal cancer is unclear.

EXPERIMENTAL DESIGN

The expression of beta-receptors for PDGF, and PDGF B-chain (PDGF AB and PDGF BB) was investigated by immunohistologic techniques in full-thickness biopsies from 210 colorectal cancers. These antigens were detected by the monoclonal antibodies PDGFR-B2 and PDGF 007, respectively.

RESULTS

All tumors contained granular clusters of PDGF beta-receptor expressing stromal cells, whereas tumor epithelium was invariably negative. The staining was most prominent in vascular cells. There were several cells in the tumor stroma that expressed PDGF AB/BB. Double immunofluorescence stainings in specimens from four patients performed in order to characterize PDGF beta-receptor- and PDGF AB/BB expressing cells showed that cells expressing PDGF beta-receptors did not express PDGF AB/BB. About 20% of cells in the stroma expressing PDGF AB/BB were macrophages (CD68-positive cells), whereas the nature of the remaining stromal cells expressing PDGF AB/BB could not be disclosed. Furthermore, about 30% of CD68-positive macrophages expressed PDGF AB/BB, but not PDGF beta-receptors. The extent of clusters of PDGF beta-receptor expressing cells varied considerably between tumors, and its prognostic value was considered in the entire tumor material. The number of clusters did, however, not correlate to tumor differentiation, tumor stage according to Dukes', or outcome.

CONCLUSIONS

The presence of cells expressing PDGF beta-receptor and PDGF AB/BB respectively, i.e., expression of the receptor and its ligand, fulfills two of the prerequisites for a role of PDGF in the activation of stromal cells in colorectal cancers. The data suggest that stromal activation, characterized by clusters of PDGF beta-receptor expressing cells, is of importance for the formation of tumor stroma per se. However, the expression of the PDGF beta-receptor has no potential as a prognostic marker.

Microvascular pericytes express platelet-derived growth factor-beta receptors in human healing wounds and colorectal adenocarcinoma

The expression of platelet-derived growth factor- beta (PDGF-beta) receptors in the microvasculature of human healing wounds and colorectal adenocarcinoma was investigated. Frozen sections were subjected to double immunofluorescence staining using monoclonal antibodies (MAbs) specific for pericytes (MAb 225.28 recognizing the high-molecular weight-melanoma-associated antigen, expressed by activated pericytes during angiogenesis), endothelial cells (MAb PAL-E), laminin, as well as PDGF-beta receptors (MAb PDGFR-B2) and its ligand PDGF-B chain (MAb PDGF 007). Stained sections were analyzed by computer-aided imaging processing that allowed for a numerical quantification of the degree of colocalization of the investigated antigens. An apparent background colocalization, varying between 23 and 35%, between markers for cells not expected to co-localize was recorded. This background could be due to limitations of camera resolution, to out-of-focus fluorescence, and to interdigitations of the investigated structures. In all six tumor specimens, co-localization of PDGF-beta receptors and PAL-E was not different from the background co-localization, whereas that of PDGF-beta receptors and high-molecular weight-melanoma-associated antigen was significantly higher with mean values between 57 and 71%. Qualitatively, the same pattern was obtained in the two investigated healing wounds. PDGF-B chain did not co-localize with either PAL-E or high-molecular weight-melanoma-associated antigen, but PDGF-B chain-expressing cells were, however, frequently found juxtaposed to the microvasculature. The expression of PDGF-beta receptors on pericytes in activated microvessels and the presence of PDGF-B chain-expressing cells in close proximity to the microvasculature of healing wounds and colorectal adenocarcinoma is compatible with a role for PDGF in the physiology of the microvasculature in these conditions.

Impaired regulation of collagen pro-alpha 1(I) mRNA and change in pattern of collagen-binding integrins on scleroderma fibroblasts

We explored the hypothesis that dermal fibroblasts isolated from patients suffering from systemic sclerosis are disturbed in their ability to interact functionally with native collagen fibers. Additionally, we investigated the expression of one collagen-binding integrin matrix receptor, alpha 1 beta 1 on those cells. Two populations of primary dermal fibroblasts were established, one from patients with systemic sclerosis and one from normal subjects. When cultured for 24 h in free-floating collagen gels, both types of fibroblasts down-regulated the cellular content of collagen pro-alpha 1(I) messenger ribonucleic acid, the systemic sclerosis fibroblasts less markedly than the normals. In normal, but not in systemic sclerosis fibroblasts, the kinetics of collagen gel contraction were directly proportional to the extent of the down-regulation. Fetal bovine serum stimulated collagen gel contraction in both populations. When grown in collagen gels in the presence of fetal bovine serum, no difference between systemic sclerosis and normal fibroblasts in capacity to down-regulate pro-alpha 1(I) was observed. Collagen-binding beta 1 integrins mediate the functional interactions between fibroblasts and the collagen fibers. To assess the cell surface expression of collagen-binding beta 1 integrins on fibroblasts, we labeled cells with 125I and subjected Triton X-100 extracts from them to immunoprecipitation with anti-beta 1 integrin immunoglobulin G. Among the systemic sclerosis fibroblasts, a larger number of isolates expressed low amount of alpha 1 beta 1 than did the fibroblasts isolated from normal individuals. Our data are compatible with the hypothesis that systemic sclerosis fibroblasts have a disturbed interaction with collagen fibers; this disturbance may in part be the result of an aberrant expression of collagen-binding beta 1 integrins.

Tissue localization of beta receptors for platelet-derived growth factor and platelet-derived growth factor B chain during wound repair in humans

The expression and localization of PDGF beta receptors and PDGF-AB/BB in human healing wounds was evaluated by immunohistochemical techniques and in situ hybridization. Expression of PDGF beta receptor protein and PDGF-AB/BB were analyzed in wound margin biopsies using the PDGFR-B2 and PDGF 007 antibodies. PDGF beta receptor expression was minor in normal skin. An increased expression of PDGF beta receptor protein was prominent in vessels in the proliferating tissue zone in wounds as early as 1 d after surgery and was apparent < or = 4 wk after surgery. There was also a concordant increase in PDGF beta receptor mRNA detected by in situ hybridization. PDGF-AB/BB was present in healing wounds as well as in normal skin. In normal skin, expression of PDGF-AB/BB was confined to peripheral nerve fibers and to solitary cells of the epidermis and of the superficial dermis. In wounds, infiltrating mononuclear cells also stained for PDGF-AB/BB. To identify cell types expressing PDGF AB/BB and PDGF beta receptors, respectively, we performed double immunofluorescence stainings. PDGF beta receptors were expressed by vascular smooth muscle cells and cells in capillary walls; the receptor protein could not be detected in neurofilament containing structures, T lymphocytes, or CD68 expressing macrophages. PDGF-AB/BB colocalized with neurofilaments, it was present in Langerhans cells of the epidermis and in HLA-DR positive cells located in the epidermal/dermal junction area. Of the macrophages infiltrating the wound, 43 +/- 18% stained positively for PDGF AB/BB. Since PDGF-AB/BB and PDGF beta receptors are expressed in the healing wound, two essential prerequisites for a role of PDGF in wound healing are fulfilled.

Interconnection of integrins alpha 2 and alpha 3 and structure of the basal membrane in colorectal cancer: relation to survival

The expression and distribution of integrin subunits alpha 2 and alpha 3 and two of their putative ligands, type IV collagen and laminin, were examined by immunohistochemistry in specimens from 33 consecutive patients operated on for colorectal adenocarcinomas. Both tumour cells and normal epithelium expressed the alpha 2 and alpha 3 subunits. Two typical patterns of expression could be discerned; a basolateral expression and a diffuse cytoplasmic expression. The stained tumour specimens were assessed according to (i) distribution of integrin expression (diffusely cytoplasmic or basolateral), (ii) continuity in basolateral integrin expression, and (iii) interconnection of integrin expression and expression of type IV collagen and laminin. These parameters were then related to tumour differentiation, tumour stage according to Dukes' classification, DNA-ploidy and patient survival (median observation time was 30 months; range 24-35). The continuity in the basolateral expression of alpha 3 but not of alpha 2, correlated with the basal membrane expression of type IV collagen (P < 0.001). Loss of continuity in the basolateral expression of both integrins was significantly related to impaired tumour differentiation (alpha 2 P = 0.02; alpha 3 P = 0.01), more advanced Dukes' stage (alpha 2 = 0.07, alpha 3 P < 0.001), survival rate (both integrins P < 0.05), but not to DNA-ploidy. These data suggest that determination of the pattern of expression of the integrin subunits alpha 2 and alpha 3 in the preoperative biopsy and the surgical specimen could be used as a prognostic indicator.

Analysis of alpha 1 beta 1, alpha 2 beta 1 and alpha 3 beta 1 integrins in cell--collagen interactions: identification of conformation dependent alpha 1 beta 1 binding sites in collagen type I

Integrins can mediate the attachment of cells to collagen type I. In the present study we have investigated the possible differences in collagen type I recognition sites for the alpha 1 beta 1 and alpha 2 beta 1 integrins. Different cyanogen bromide (CB) fragments of the alpha 1 (I) collagen chain were used in cell attachment experiments with three rat cell types, defined with regard to expression of collagen binding integrins. Primary rat hepatocytes expressed alpha 1 beta 1, primary rat cardiac fibroblasts alpha 1 beta 1 and alpha 2 beta 1, and Rat-1 cells only alpha 2 beta 1. All three cell types expressed alpha 3 beta 1 but this integrin did not bind to collagen--Sepharose or to immobilized collagen type I in a radioreceptor assay. Hepatocytes and cardiac fibroblasts attached to substrata coated with alpha 1(I)CB3 and alpha 1(I)CB8; Rat-1 cells attached to alpha 1(I)CB3 but only poorly to alpha 1(I)CB8-coated substrata. Cardiac fibroblasts and Rat-1 cells spread and formed beta 1-integrin-containing focal adhesions when grown on substrata coated with native collagen or alpha 1(I)CB3; focal adhesions were also detected in cardiac fibroblasts cultured on alpha 1(I)CB8. The rat alpha 1 specific monoclonal antibody 3A3 completely inhibited hepatocyte attachment to alpha 1(I)CB3 and alpha 1(I)CB8, as well as the attachment of cardiac fibroblasts to alpha 1(I)CB8, but only partially inhibited the attachment of cardiac fibroblasts to alpha 1(I)CB3. 3A3 IgG did not inhibit the attachment of Rat-1 cells to collagen type I or to alpha 1(I)CB3.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of beta 1-integrins in skin causes edema through lowering of interstitial fluid pressure

The increased capillary fluid filtration required to rapidly create edema in acute inflammation can be generated by increased negativity of the interstitial fluid pressure (Pif). This observation suggests that connective tissues can "actively" enhance capillary fluid filtration. We now show that in vivo blockade of beta 1-integrin adhesion receptors in rat skin causes local edema concomitant with increased negativity of Pif. Experiments were performed on the dorsal side of the hind paw, and Pif was measured with sharpened glass capillaries (tip diameter, 3-7 microns) connected to a servo-controlled counterpressure system. Measurements were made after circulatory arrest had been induced with intracardiac potassium chloride in pentobarbital anesthesia. This procedure prevents the vascular phenomena of increased fluid and protein flux leading to edema formation, which in turn can increase Pif and therefore potentially mask an increased negativity of Pif. Control Pif averaged -0.58 +/- 0.81 (mean +/- SD) mm Hg (n = 37). Subdermal injection of 5 microliters monospecific rabbit anti-rat integrin beta 1-subunit immunoglobulin G caused increased negativity of Pif to average values between -4 and -6 mm Hg within 10 minutes after injection. Subdermal injection of 0.9% NaCl, preimmune immunoglobulin G, rat anti-fibronectin, and peptides with Arg-Gly-Asp and Arg-Gly-Glu sequences did not change Pif significantly. In another series of experiments, 5 microliters anti-beta 1 integrin immunoglobulin G was injected subdermally in rats with intact circulation and resulted in an increase in total tissue water corresponding to a doubling of the interstitial fluid volume in 10 minutes (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Neuritogenesis on collagen substrates. Involvement of integrin-like matrix receptors in retinal fibre outgrowth on collagen

Extracellular matrix molecules such as laminin, fibronectin and collagen promote neurite outgrowth in vitro. We have investigated the capacity of hydrated gels of collagen types I-III and monomeric collagen types I-VI on plastic surfaces to support neuritogenesis. The attachment and survival of explants from the day 6 chick embryo were studied and neurite outgrowth measured as mean elongation rate and maximal neurite length. Collagen types I and III, both as three-dimensional gels or as native monomers supported neuritogenesis equal to or better than laminin. Collagen type V also supported neurite out-growth although less effectively. Collagen types II, IV and VI, as well as denatured collagens of all types tested, did not support outgrowth. The monoclonal anti-beta 1 integrin antibody (CSAT), as well as rabbit polyclonal antibodies directed to the integrin beta 1-chain, effectively inhibited neurite outgrowth on permissive collagenous substrata, indicating that collagen-binding integrins were involved in the neuritogenesis. These beta 1-integrins were independent of Arg-Gly-Asp (RGD) since neurite formation proceeded in the presence of synthetic RGD-containing peptides. Fluorescence immunohistochemistry revealed the presence of the integrin beta 1-chain on the outgrowing neurites. The results suggest a possible function of collagen and collagen-binding integrins in the development of the visual system.