The heterogeneity of human fibroblasts as determined from the effects of hydrocortisone on cell growth and specific dexamethasone binding

Tudor staphylococcal nuclease drives chemoresistance of non-small cell lung carcinoma cells by regulating S100A11

Lung cancer is the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC), the major lung cancer subtype, is characterized by high resistance to chemotherapy. Here we demonstrate that Tudor staphylococcal nuclease (SND1 or TSN) is overexpressed in NSCLC cell lines and tissues, and is important for maintaining NSCLC chemoresistance. Downregulation of TSN by RNAi in NSCLC cells led to strong potentiation of cell death in response to cisplatin. Silencing of TSN was accompanied by a significant decrease in S100A11 expression at both mRNA and protein level. Downregulation of S100A11 by RNAi resulted in enhanced sensitivity of NSCLC cells to cisplatin, oxaliplatin and 5-fluouracil. AACOCF₃, a phospholipase A₂ (PLA₂) inhibitor, strongly abrogated chemosensitization upon silencing of S100A11 suggesting that PLA₂ inhibition by S100A11 governs the chemoresistance of NSCLC. Moreover, silencing of S100A11 stimulated mitochondrial superoxide production, which was decreased by AACOCF₃, as well as N-acetyl-L-cysteine, which also mimicked the effect of PLA₂ inhibitor on NSCLC chemosensitization upon S100A11 silencing. Thus, we present the novel TSN-S100A11-PLA₂ axis regulating superoxide-dependent apoptosis, triggered by platinum-based chemotherapeutic agents in NSCLC that may be targeted by innovative cancer therapies.

Pharmacotherapy and airway remodelling in asthma?

Over the last few decades attention has largely focused on airway inflammation in asthma, but more recently it has been appreciated that there are important structural airway changes which have been grouped together under the term "airway remodelling". It is only now that questions have been asked about the impact of treatment on these structural changes. This review examines the nature of these structural airway changes, the mechanisms of their generation, their potential consequences, and what is known about the ability of anti-asthma treatments to modulate these changes.

Chronic in vivo exposure to glucocorticoids prolongs cellular lifespan: the case of Cushing's syndrome-patients' fibroblasts

Glucocorticoid (GC) hypersecretion constitutes the major hormonal response to stress. In an effort to investigate the impact of a long-lasting exposure to high GC levels in vivo on cellular longevity, we have studied the lifespan of skin fibroblasts from patients suffering from Cushing's syndrome, who are characterised by chronic endogenous GC excess. Interestingly, we have observed that these cells exhibit a significant increase in their proliferative lifespan when cultured in vitro, under standard conditions, compared to fibroblasts from normal donors. In parallel, these cells secrete lower levels of transforming growth factor-beta, known to be implicated in stress-induced premature senescence. Furthermore, they also exhibit an intense stress reaction (near 2-fold, compared to normal cells) in terms of heat-shock protein-70 induction. These results support the hypothesis that stress response may have beneficial consequences in cellular longevity, as well as in tissue homeostasis.

IL-4, IL-13, and dexamethasone augment fibroblast proliferation in asthma

BACKGROUND

IL-4 and IL-13 have been shown to be critical for expression of the asthma phenotype in a murine model and may modulate human fibroblast function.

OBJECTIVE

We hypothesized that IL-4 and IL-13 would increase airway fibroblast proliferation and reduce the ability of dexamethasone to decrease this proliferation.

METHODS

Six subjects with severe asthma, 5 subjects with mild asthma, and 5 healthy subjects underwent bronchoscopy with endobronchial biopsy. Biopsy specimens were placed in Dulbecco modified Eagle medium and cultured, and only fibro-blasts from the first and second passages were evaluated. Cells were incubated with IL-4 (50 ng/mL), IL-13 (10 ng/mL), and the combination for 48 hours in the presence and absence of dexamethasone, 10(-7) mol/L, and 10(-8) mol/L. Fibroblasts were also incubated with IFN-gamma at 50 ng/mL to assess the response of a T(H)1 cytokine on proliferation.

RESULTS

Fibroblast proliferation, determined by (3)H-thymidine incorporation, was significantly increased by IL-4 in subjects with mild asthma as compared with IL-4 in subjects with severe asthma and healthy subjects (P =.003), IL-13 (P =.011), and the combination (P =.004). Dexamethasone also increased proliferation in the group with mild asthma as compared with the group with severe asthma and the healthy group (10(-7) mol/L, P =.02; 10(-8) mol/L, P =.02). IFN-gamma did not significantly alter airway fibroblast proliferation.

CONCLUSION

IL-4, IL-13, and dexamethasone all significantly increased fibroblast proliferation in subjects with mild asthma.

Synergistic action of endothelin (ET)-1 on the activation of bronchial fibroblast isolated from normal and asthmatic subjects

Bronchial subepithelial fibrosis is an histological characteristic of asthma. Cytokines and other mediators, such as PDGF-BB, TGF-beta1 and ET-1 found in the asthmatic submucosa can potentially activate a repair process that leads to fibroblast proliferation and collagen synthesis. The mechanisms of modulation of the repair process leading to extracellular matrix deposition are still to be documented. In this study, we assessed the in vitro proliferation and collagen synthesis of bronchial fibroblasts isolated from normal and asthmatic subjects in response to ET-1, platelet-derived growth factor (PDGF)-BB and transforming growth factor (TGF)-beta1 alone or in combination, in the presence or absence of dexamethasone. The combination of ET-1 with one of the other two growth factors, or the triple combination, significantly increased DNA synthesis and collagen production of bronchial fibroblasts isolated from both normal and asthmatic subjects, but the same growth factors used separately had no significant effect on the same parameters. These results suggest that the simultaneous presence of ET-1, PDGF-BB and TGF-beta1 in both normal and asthmatic subjects is necessary to activate bronchial fibroblast proliferation and collagen synthesis. As these mediators are present in the submucosa of the asthmatic bronchi, they could be responsible, at least in part, for the accumulation of collagen in the mucosa.

Inter- and intra-site heterogeneity in the expression of fetal-like phenotypic characteristics by gingival fibroblasts: potential significance for wound healing

We have previously reported that fetal and adult skin fibroblasts display distinctive migratory phenotypes on 3-D collagen substrata and that these behavioural characteristics may be quantified by a function defined as the cell density migration index (CDMI). Subsequent work indicated that this difference in migratory phenotype was due to the production by fetal fibroblasts of a migration stimulating factor (MSF) that is not produced by normal adult skin fibroblasts. We now present data indicating that: (a) unselected fibroblasts obtained from 14/14 (100%) of adult gingival explants expressed fetal-like CDMI values compared to only 1/10 (10%) of similarly explanted paired skin cells; (b) 12/12 (100%) of these gingival fibroblast lines also produced detectable quantities of MSF compared to 0/9 (0%) of the tested skin cells; (c) by microdissection studies, gingival fibroblasts obtained from different anatomical microdomains consisted of behaviourally distinct subpopulations, with cells derived from the papillary tips (PAP fibroblasts) displaying fetal-like CDMI values and persistent MSF production, whilst cells obtained from the deeper reticular tissue (RET fibroblasts) were adult-like with respect to these two criteria; (d) PAP fibroblasts were also smaller and achieved higher saturation cell densities compared to paired RET cells; (e) PAP fibroblasts passaged in vitro underwent a fetal-to-adult phenotypic transition characterized by the adoption of various RET cell characteristics, including the acquisition of CDMI values falling within the adult range and cessation in MSF production; and (f) early passage PAP fibroblasts incubated in the presence of an affinity-purified anti-MSF rabbit polyclonal antibody were induced to alter their migratory phenotype and exhibited CDMI values falling within the adult range. Statistical analysis indicated a highly significant correlation between the expression of a fetal-like CDMI and production of MSF (P < 0.00001, using the Fisher exact contingency test). Taken together, these observations suggest that the production of MSF by PAP fibroblasts is responsible for their characteristically fetal-like migratory behaviour. The existence of such inter- and intra-site phenotypic heterogeneity in populations of skin and gingival fibroblasts is discussed in the context of fibroblast lineage relationships and the possible contribution of persistently fetal-like fibroblast subpopulations to connective tissue function in wound healing.

Cloning and characterization of human gingival and periodontal ligament fibroblasts

Fibroblast heterogeneity in human periodontal tissues was characterized by cloning and immuno-histochemical techniques. Cell suspensions from primary cultures gingival (GF) and PDL fibroblasts (PF) were cloned. The relative intensity of double-labeled immunofluorescence, using specific antibodies to the extracellular matrix (ECM) molecules collagen type I (CI), type III (CIII), and fibronectin (Fn), was measured by photometry. Most clones derived from either GF or PF showed positive intracellular staining for both CI and Fn, and CIII and Fn. However, there were variations in fluorescence intensity for CI and Fn, ranging from relatively weak to strongly positive. The fluorescence for CI and CIII was relatively weak in most isolated GF clones in contrast to their PF clones. These observations coupled with studies of growth and cellular morphology in individual clones suggest that: 1) GF and PF contain functionally heterogeneous subpopulations; and 2) the synthesis and expression of extracellular matrix molecules of GF may be essentially different from that of PF.

Corticosteroids induce proliferation but do not influence TNF- or IL-1 beta-induced ICAM-1 expression of human dermal microvascular endothelial cells in vitro

The effects of hydrocortisone, dexamethasone, betamethasone 17-valerate and clobetasol propionate at concentrations of 10(-5)-10(-12) M on the proliferation of human dermal microvascular endothelial cells (HDMEC) were studied in vitro. In addition, confluent HDMEC were treated with TNF (1000 U/ml) or IL-1 beta (1000 U/ml) alone or in combination with the corticosteroids (10(-5) M, 10(-6) M) for 24 h, and cytokine-induced expression of intercellular adhesion molecule-1 (ICAM-1) was assessed by immunocytochemistry. Controls were treated either with growth medium or with the corticosteroids alone. All tested corticosteroids stimulated HDMEC growth after 4 and 6 days of treatment in a dose-dependent manner, as assessed by 3H-thymidine incorporation and the 4-methyl-umbelliferyl heptanoate (MUH) assay. The minimal effective concentration was 10(-9) M for hydrocortisone, 10(-10) M for dexamethasone and betamethasone, and 10(-12) M for clobetasol. In untreated and in corticosteroid-treated cultures, less than 5% of the cells expressed ICAM-1. TNF and IL-1 beta were strong inducers of ICAM-1 expression on 74% and 82% of the cells, respectively. None of the tested corticosteroids significantly influenced cytokine-induced ICAM-1 expression, suggesting that the anti-inflammatory effects of corticosteroids are not related to ICAM-1 modulation on HDMEC.

Alpha-smooth muscle actin is expressed in a subpopulation of cultured and cloned fibroblasts and is modulated by gamma-interferon

Clinical and experimental investigations have shown that, during wound healing and fibrocontractive diseases, fibroblasts acquire, more or less permanently according to the situation, morphological and biochemical features of smooth muscle (SM) cells including the expression of alpha-SM actin. Primary and passaged cultures of rat and human fibroblasts contain a subpopulation of cells expressing alpha-SM actin. These cells could derive from SM cells and/or pericytes present in the tissue from which cultures have been produced or represent bona fide fibroblasts. We have investigated the presence of alpha-SM actin in fibroblast cultures, clones, and subclones. In all cases the fibroblastic populations studied showed a proportion of alpha-SM actin expressing cells. Even after cloning, we never obtained populations negative for alpha-SM actin. We conclude that alpha-SM actin expression in fibroblastic cultures is not due to contaminant cells but is a feature of fibroblasts themselves. Our results support the view that fibroblastic cells are a heterogeneous population. It has been previously shown that gamma-interferon (gamma-IFN) decreases alpha-SM actin expression in SM cells. In rat and human fibroblasts, gamma-IFN decreases alpha-SM actin protein and mRNA expression as well as proliferation. The properties of this cytokine make it a good candidate for exerting an anti-fibrotic activity in vivo.

Biosynthetic and proliferative characteristics of tubulointerstitial fibroblasts probed with paracrine cytokines

Fibroblasts in parenchymal organs potentially contribute extracellular matrix to local fibrogenic processes. This contribution, in some circumstances, may be initiated by cytokines disseminated from inflammatory lesions. Different populations of fibroblasts, however, might respond distinctively to this cytokine bath depending on the microenvironment in which they reside. We have begun to explore this issue using syngeneic, low-passage fibroblasts cultured in serum-free media that were derived originally from the dermis (DFBs) and from tubulointerstitium (TFBs) of the kidney. Our findings indicate that, while fibroblasts from each compartment appear similar at the ultrastructural level, there are a variety of functional differences which distinguish their proliferative response, and their collagen secretory response (types I, III, IV, and V) following challenge with various doses of immune-relevant cytokines (TGF beta, EGF, IL-1, IL-2 and gamma IFN) in culture. DFBs, for example, express more surface EGF receptors than do TFBs, and, as a consequence, exhibit a more robust proliferative response to EGF in serum-free media. Unstimulated DFBs also secrete more collagen types I and III than TFBs, while unstimulated TFBs secrete more types IV and V. The expression of these collagens in TFBs was confirmed by Northern blot hybridization. When these sets of fibroblasts were further stimulated by cytokines, some of the cytokines not only differentially effect the secretion of various species of collagens within the same group of cells, but also between cells from populations which are anatomically distinct. DFBs, furthermore, at mid-level doses of cytokine, demonstrated a general trend towards less secretion of all types of collagen (particularly for TGF beta, EGF, and IL-2), while TFBs seemed less repressive. In TFBs the cytokine-induced responses for collagen types I and III tended to be discordant, and for types I and IV EGF inhibited, while TGF beta stimulated the secretory process. These findings speak collectively for the presence of a functional heterogeneity among organ-based populations of syngeneic fibroblasts in normal tissues.

Effect of cell density on induction of growth hormone receptors by dexamethasone in primary cultured rat hepatocytes

The effect of cell density on the regulation of growth hormone (GH) receptors was studied by measuring specific binding of [125I]hGH to primary cultured hepatocytes with or without dexamethasone, which induces GH receptors. In cell cultures without dexamethasone, the cell density did not affect the level of binding of labeled GH appreciably. On the other hand, in the presence of dexamethasone, which induced an increase in the level of GH receptors on the cells, GH-binding by cultured cells at low cell density (3.3 x 10(4) cells/cm2) was about one-third of that of cells at high cell density (10(5) cells/cm2). Scatchard plot analysis showed that the cell-density dependent change in induction of GH binding, by dexamethasone was due to change in the number of binding sites without significant change in their affinity. The binding capacity of glucocorticoid receptors, measured as specific binding of [3H]dexamethasone to the hepatocytes, was not significantly affected by cell density. These results suggest that cell density modulates GH receptor induction by dexamethasone via events after glucocorticoid receptor binding.

Suppression of protein kinase C and the stimulation of glucocorticoid receptor synthesis by dexamethasone in human fibroblasts derived from tumor tissue

Exposure of fibroblasts derived from keloid tissues, desmoid and dermal tissue from individuals with Gardner's syndrome (GS) to dexamethasone resulted in the suppression of protein kinase C (PKC) activity and [3H]thymidine incorporation into DNA, and a 20-fold induction of glutamine synthetase activity. Treatment of GS and keloid fibroblasts with 0.1 microM dexamethasone for 36 h increased glucocorticoid receptor (GR) synthesis, as determined by [35S]methionine labeling and immunoprecipitation with a monoclonal antibody to the human GR. The suppression of PKC activity by dexamethasone was shown to result from a loss of protein mass as determined by immunoblotting using an antibody to PKC type III. In contrast to these results, exposure of fibroblasts isolated from normal tissues to dexamethasone did not result in the suppression PKC and [3H]thymidine incorporation, there was only a sixfold induction of glutamine synthetase, and a decrease of GR synthesis. As no primary receptor binding defect could be detected, the altered response of tumor cells to steroid-occupied receptor indicates a partial post-receptor binding defect in GS and keloid cells.

The influence of glucocorticoids on the growth of a human leiomyosarcoma cell line SK-LMS-1

A cell line derived from a human leiomyosarcoma, SK-LMS-I, has cystolic [Bmax 201.6 +/- 39.7, means +/- SD, fm/mg cytosol protein KD 14.6 +/- 7.8 nM (n = 8)] and nuclear [Bmax 189.2 +/- 87.3 fM/mg DNA, KD 4.8 +/- 0.26 nM (n = 5)] glucocorticoid receptor, by Scatchard analysis of tumors grown in male athymic mice. Tumor growth of SK-LMS-I cells in male athymic mice is inhibited by daily s.c. injection of DEX 5 micrograms, DEX 25 micrograms, DEX 5 micrograms with 5 mu RU-486 and 5 micrograms RU-486. In sharp contrast, in vitro, glucocorticoid markedly stimulates the growth (as determined by cell number) of SK-LMS-I cells, principally at higher cell densities (days 10-21 of growth carried on over a 21- to 23-day period), the greatest stimulation being seen with DEX 10(-6) to 10(-8) M, and no stimulation being seen with DEX 10(-9) and 10(-10) M. In vitro, glucocorticoids with higher affinity for the GR stimulate growth, steroids with lower affinity inhibit growth. No alterations in cell-cycle distribution (percent G0/G1, S, or G2/m) could be found by flow cytometric analysis of glucocorticoid-stimulated asynchronously growing cultures. Single, isolated, untreated SK-LMS-I cells form colonies in soft agar with an efficiency of 1.78 +/- 0.10%. Pre-treatment of cells with DEX 10(-7) M increases this to 3.24 +/- 0.17%, while cells pre-treated with both DEX 10(-7) M RU-486 10(7) M form colonies with the same efficiency as untreated cells. Glucocorticoids have inhibitory effects on in vivo growth and stimulatory effects on in vitro growth of a GR-positive human leiomyosarcoma cell line.

Characterization of two major populations of lung fibroblasts: distinguishing morphology and discordant display of Thy 1 and class II MHC

We have determined that murine lung fibroblasts are divisible into two major subpopulations based on expression of Thy 1. Twenty-four to fifty-three percent of freshly isolated lung cells displayed Thy 1 and were separated using FACS into Thy 1+ and Thy 1- fractions for morphologic examination. Analysis by electron microscopy revealed that both the Thy 1+ and Thy 1- fractions contained fibroblasts. Freshly isolated lung cells cultured for 2 wk consisted of greater than 95% fibroblasts, with 28 to 49% displaying Thy 1. These cells were sorted by FACS into Thy 1+ and Thy 1- lines that maintained a stable phenotype over many weeks and that were used as a source to obtain stable fibroblast clones. Adherent pulmonary fibroblasts are not phagocytic and lack the markers of macrophages, dendritic cells, B lymphocytes, and T lymphocytes (with the exception of Thy 1). Interestingly, the Thy 1- fibroblasts spread more and contained a more extensive microfilament and microtubule network than did the spindly and often lipid-containing Thy 1+ population. Both populations of fibroblasts synthesized collagen. Class I MHC expression was very low on Thy 1+ and Thy 1- fibroblasts, but high levels were displayed after gamma-IFN treatment. Most exciting was the unexpected finding that only the Thy 1- lines and clones displayed class II MHC (Ia) in response to treatment with gamma-IFN. Moreover, only the Thy 1- fraction (gamma-IFN-treated) presented antigen to T lymphocyte clones, an observation that suggests that this subset of cells may be involved primarily in promoting chronic lung inflammation, which is associated with developing fibrosis. Thus, two populations of pulmonary fibroblasts exist, defined by the expression of Thy 1, distinguishing morphology, inducibility for Ia expression, and antigen-presenting function. It should now be possible, using these characteristics, to ascertain the role of pulmonary fibroblast subpopulations in developing fibrosis.

Effects of serum from human subjects of different ages on migration in vitro of human fibroblasts

A study was carried out to determine whether human serum from older subjects inhibited cell migration. Sera of both sexes from subjects in their 60s (60-64 years) tended to be more inhibitory (8-14%) to the migration of human fetal lung fibroblasts, TIG-1, than serum from subjects in their 20s (20-29 years). In the case of females, the effects of serum on cell migration were significantly (P less than 0.05) different between the younger and older groups. Next, cell migration-stimulatory activity of serum was measured using human skin fibroblasts from young adult (age 21) and elderly (age 65) donors. The results were similar to those obtained with TIG-1 cells. However, the cell migration-stimulatory activity of serum was not significantly different between the two age groups. A study on the effects of concentration of human serum on the migration of TIG-1 cells showed that cell migration-stimulatory activity of serum declined linearly with increasing concentrations of sera from subjects in their teens (16-19 years) and 50s (50-59 years), and was the same between the two age groups. These results imply that substance(s) inhibitory to cell migration may not have accumulated in serum during the ageing process in humans, although human serum contained substance(s) inhibitory to cell migration.

Effects of serum from human subjects of various ages on proliferation of human lung and skin fibroblasts

We carried out a study to determine whether serum from old human subjects inhibited cell proliferation. The results showed that serum from old subjects of either sex did not greatly inhibit the proliferation of human fetal lung fibroblast TIG-1 cells, even when serum from subjects in their 80s was used. The same results were obtained when the effects of serum on cell proliferation were examined up to a serum concentration of 50%. It was also found that serum from old subjects did not inhibit proliferation of human skin fibroblasts from a young adult to any greater degree than serum from young adult subjects, and that serum from young adult subjects did not stimulate proliferation of skin fibroblasts from an elderly donor to any greater degree than serum from old subjects.

Role of platelet factors and serum complement in growth of fibroblasts with high-affinity Clq complement receptors

Cultures of human diploid fibroblasts are heterogeneous in that a subpopulation interacts via high-affinity receptors with the globular head regions of the Clq complement protein. Growth and synthetic properties of these cells are characteristic of cells residing in healing wounds and inflammatory lesions. At these sites, fibroblasts are exposed to regulatory molecules such as complement components and factors released from blood platelets. We assessed the effects of native complement proteins and platelet-derived factors on proportions and phenotypic stability of high-affinity and low-affinity receptor cells generated from explants of adult and embryonic connective tissue, using radioligand binding assays and immunofluorescence analysis by flow cytometry. Fibroblasts expressing high-affinity Clq receptors could be generated from explants only when factors from platelets were present in the medium; native complement proteins were not essential. High-affinity receptor cells could be generated only from tissue; they could not be generated by incubating cultures of the low-affinity receptor phenotype in medium containing platelet-derived factors. High-affinity receptor cells, once established from explants in the presence of platelet-derived factors, persisted through many replications in the absence of platelets. We obtained the same fibroblast phenotypes from embryonic skin as from adult gingiva, but the proportion of high-affinity receptor cells from skin was much greater. We conclude that factors derived from platelets are essential for generating cultures containing fibroblasts expressing high-affinity Clq receptors, but not for their maintenance. High-affinity receptor cells may comprise a rapidly dividing subpopulation giving rise only to like progeny or to other, more differentiated cells.

Dexamethasone inhibits feedback regulation of the mitogenic activity of tumor necrosis factor, interleukin-1, and epidermal growth factor in human fibroblasts

Tumor necrosis factor (TNF), interleukin-1 (IL-1), and epidermal growth factor (EGF) were mitogenic for human diploid FS-4 fibroblasts. Dexamethasone amplified the growth-stimulating action of all three agents. Amplification of the growth-stimulating action was maximal when dexamethasone was added along with TNF or EGF; no amplification was seen if the addition of dexamethasone was delayed for more than 3 hr. Prolonged simultaneous treatment with TNF and EGF resulted in less growth stimulation than treatment with EGF alone. Dexamethasone abolished this apparent antagonistic interaction between TNF and EGF. Dexamethasone also inhibited the antiviral action of TNF against encephalomyocarditis (EMC) virus in FS-4 cells. TNF and IL-1 increased the steady state level of interferon (IFN)-beta 2 mRNA but failed to induce detectable levels of IFN-beta 1 mRNA in FS-4 cells. Dexamethasone inhibited the increase of IFN-beta 2 mRNA levels by IL-1 or TNF. Inhibition of IFN-beta synthesis is likely to be responsible for the inhibition of the TNF-induced antiviral state by dexamethasone. Since IFNs suppress cell growth, inhibition of endogenous IFN-beta synthesis may also be responsible for the amplification by dexamethasone of the growth-stimulating action of TNF and IL-1. Amplification of the mitogenic action of EGF by dexamethasone appears to be mediated by different mechanism.

Mitogenic activity of cementum components to gingival fibroblasts

Cementum forms the interface between root dentin and periodontal ligament through which periodontal connective tissue is attached to root surfaces. We have examined how cementum components influence the biological activities of gingival fibroblasts. Cementum was harvested from freshly extracted human teeth and extracted sequentially with 0.5 mol/L acetic acid, 4 mol/L guanidine-0.5 mol/L EDTA, and bacterial collagenase. The extracts were concentrated and analyzed for mitogenic activity to human gingival fibroblasts. DNA synthesis was assayed by measurement of [3H]thymidine incorporation by quiescent fibroblasts activated to divide, and cell growth was determined by the counting of cells over a 10-day period. Results showed that extracts of cementum stimulated quiescent gingival fibroblasts to synthesize DNA and grow. The stimulation was dose-dependent, and most of the stimulatory activity was extracted by acid. Addition of small quantities of serum potentiated the mitogenic activity to levels greater than those of control cultures containing 10% fetal calf serum. The mitogenic activity was heat-stable, but it was destroyed by trypsin. Neither platelet-derived growth factor (PDGF) nor epidermal growth factor (EGF) was detectable in the cementum extract, and extracts of human dentin and skin contained very little mitogenic activity. We conclude that cementum contains substances capable of regulating the growth of gingival fibroblasts, and that these substances may play an important role in gingival connective tissue formation and regeneration.

Effect of corticosteroids on the morphology and proliferation of two salmonid cell lines

In medium with cortisol at 5 ng/ml and greater, cells of the rainbow trout cell line, RTG-2, lost their fibroblast-like morphology and became flattened and epithelial-like. This also occurred with dexamethasone triamcinolone acetonide, and fluocinolone acetonide but not with cortisone, progesterone, estradiol, or testosterone. Maintenance in medium with cortisol but not with cortisone caused these cells to adhere more tightly to the growth surface. The addition of cortisol at 100 ng/ml to RTG-2 cultures reduced the saturation densities that were achieved after monolayers had formed but had no effect on the times to reach confluency. Cortisone had no influence on cell population growth. Neither cortisol nor cortisone altered the morphology, adhesion, or proliferation of the Chinook salmon embryo cells, CHSE-214.