Pretranslational regulation of type I collagen, fibronectin, and a 50-kilodalton noncollagenous extracellular protein by dexamethasone in rat fibroblasts

Effects of different pre-operative doses of dexamethasone on alveolar repair in rats

Dexamethasone has been widly used in oral and maxillofacial surgery for controlling of postoperative surgical inflammation. Despite its clinical effectiveness, several studies have demonstrated the negative impact of this drug on the healing of soft and hard tissues. This study aimed to assess the effects of different pre-operative doses of dexamethasone on alveolar repair. Sixty rats were divided into four groups of 15 animals each. Single pre-operative doses of dexamethasone equivalent to human doses of 4 mg (Group 4 mg), 8 mg (Group 8 mg), and 12 mg (Group 12 mg), calculated by allometric dose extrapolation, were administered; and rats in the Control Group were injected with saline solution. The animals were anesthetized, and their left mandibular first molars (M1) were removed. After three, seven, and 40 days, 5 animals from each group were euthanized, and bone samples of M1 alveolus were collected for radipgraphic, histomorphological and histometric evaluation of the early and late phases of alveolar healing. At three days, Group 12 mg presented reduced radiographic density, percentage of collagen, and connective matrix compared with the Control Group. At 7 days, the percentage of bone was increased in the Control Group compared to Groups 8 mg and 12 mg (P < 0.05). It can be concluded that a single pre-operative dose of 12 mg of dexamethasone affected the early stages of alveolar repair in rats.

The effect of skin thickness and time in the absorption of dexamethasone in human tendons using iontophoresis

STUDY DESIGN

Experimental laboratory study.

OBJECTIVES

To measure the transmission of dexamethasone sodium phosphate (DEX-P) using iontophoresis as a function of skinfold tissue thickness and time elapsed between treatment and tissue extraction.

BACKGROUND

Iontophoresis is a modality used in physical therapy with the intent to drive medications through the skin to underlying tissues using a direct electrical current. DEX-P is the most commonly used medication with iontophoresis and is used to treat a variety of connective tissue conditions.

METHODS AND MEASURES

Sixteen adults undergoing anterior cruciate ligament reconstructive surgery using the semitendinosis/gracilis autograft received a 40-mA-min dose of iontophoresis with 0.4% DEX-P superficial to a slip of the distal semitendinosis tendon prior to surgery. The tendon slip was extracted within 4 hours. Time between treatment and tissue extraction and skinfold thickness were measured. Analysis was performed on the slip of the semitendinosis using high-performance liquid chromatography mass spectrum.

RESULTS

Of the 16 subjects (10 female, 6 male; mean age, 33 years), 7 had measurable amounts of DEX-P in the tendon slip (4 female, 3 male; mean age, 34 years). The average concentration in the 16 subjects was 2.9 ng/g of tendon tissue. There was no correlation between DEX-P absorbed and skinfold thickness (r = -0.08, P = .79) or time elapsed (r = 0.25, P = .38). In a subset of the 7 individuals that showed measurable levels of DEX-P absorbed, the average concentration of DEX-P was 6.6 ng/g of tendon tissue, and there was a relationship between DEX-P concentrations and time elapsed that did not reach statistical significance (r = 0.71, P = .11).

CONCLUSIONS

Iontophoresis appears to facilitate the transmission of dexamethasone to connective tissues in humans with skinfold thickness up to at least 30 mm. The absorption of the dexamethasone seemed to continue to occur for up to 4 hours after delivery. It is not clear why DEX-P was measured in only 7 of the 16 subjects.

LEVEL OF EVIDENCE

Therapy, level 5.

Absorption of dexamethasone sodium phosphate in human connective tissue using iontophoresis

BACKGROUND

Iontophoresis ostensibly facilitates the delivery of medications through the skin to underlying tissues using a direct electrical current. Dexamethasone is the most commonly used medication with iontophoresis to treat a variety of connective tissue disorders.

HYPOTHESIS

Iontophoresis will facilitate the absorption of dexamethasone into connective tissue compared with diffusion.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-nine adults undergoing anterior cruciate ligament reconstructive surgery using the semitendinosus/gracilis autograft were randomly assigned to either a true iontophoresis (TI) or sham iontophoresis (SI). In the TI group, a 40-mA/min dose of iontophoresis using a 0.4% (4 mg/mL) solution of dexamethasone was used targeting the semitendinosus tendon just before surgery. The SI group underwent the same treatment, but the machine was not turned on. Tissue was extracted within 4 hours of treatment and analyzed for dexamethasone. In addition, 2 control samples were sent to the laboratory for analysis.

RESULTS

There was a statistically significant difference in dexamethasone concentrations between the groups (P = .0216). Of the 16 samples in the TI group, 8 had measurable amounts of dexamethasone, with an average concentration of 2.906 ng/g of tendon tissue. In the SI group, 1 of the 13 samples had measurable amounts of dexamethasone with an average concentration of 0.205 ng/g of tendon tissue. The control samples contained no dexamethasone.

CONCLUSION

Iontophoresis facilitates the transmission of dexamethasone to connective tissues in humans.

CLINICAL RELEVANCE

Iontophoresis can deliver dexamethasone to connective tissues in humans.

Proliferating keratinocytes are putative sources of the psoriasis susceptibility-related EDA+ (extra domain A of fibronectin) oncofetal fibronectin

The extra domain A of fibronectin (EDA+ oncofetal isoform of fibronectin was recently reported to be overexpressed in psoriatic uninvolved epidermis. It has been proposed that the abnormal presence of EDA+ oncofetal protein at the dermal-epidermal junction in the uninvolved skin may provide the "psoriatic" environment in which keratinocytes are in a preactivated state with regard to mitogenic signals (e.g., T cell lymphokines). To determine the possible sources of cellular fibronectin in the non-lesional psoriatic skin, we aimed to investigate whether keratinocytes could produce the EDA+ oncofetal form of fibronectin. RT-PCR studies revealed that both cultured normal keratinocytes and HaCaT cells express the EDA+ splice variant of fibronectin mRNA, and in HaCaT cells the EDA+/EDA- transcript ratio was elevated compared with normal keratinocytes. Cultured keratinocytes and HaCaT cells showed intracytoplasmic staining with an EDA+ fibronectin-specific antibody and among the positively stained cells many showed mitosis. Using RT-PCR, western blot analysis, and flow cytometry, we showed that in synchronized HaCaT cells the amount of both total fibronectin and its EDA+ isoform change with the proliferation/differentiation state of HaCaT cells and peak in highly proliferating cells. We show that in short-term ex vivo cultures, a small population of EDA+ fibronectin containing cell population appear among psoriatic uninvolved, but not normal epidermal cells. We also demonstrate that cell attachment has a strong influence on the expression of both total and EDA+ fibronectin. Our results suggest that proliferating keratinocytes could be the sources of the psoriasis susceptibility-related EDA+ oncofetal fibronectin in the epidermis.

Les glucocorticoïdes et leur récepteur : mécanismes d'action et conséquences cliniques

BACKGROUND

Glucocorticoids are used as anti-inflammatory, immuno-modulatory, anti-proliferative and cytotoxic drugs, but they also trigger important side-effects. These hormones bind to glucocorticoid receptor alpha (GRalpha), an intracellular protein, which acts essentially in the nucleus.

MAIN POINTS

GRalpha is a ligand-activated transcription factor that positively or negatively regulates gene expression by distinct mechanisms. Stimulation of gene transcription occurs after direct binding of the receptor to specific responsive DNA elements. Gene activation by glucocorticoids is mainly responsible for certain adverse effects. In contrast, the therapeutic effects of glucocorticoids are predominantly mediated through repression of genes encoding inflammatory mediators. Inhibitory protein-protein interaction between the hormone-activated receptor and the transcription factors NF-kappaB and AP-1 was found to be the underlying mechanism. However, inhibition of other transcription factors may account for deleterious effects of glucocorticoids, such as adrenal suppression and osteoporosis. GRalpha also mediates rapid non-genomic effects of glucocorticoids. Side-effects are reduced by using topical glucocorticoids which have a low systemic bioavailability. Moreover, it is important to determine the lowest effective maintenance dose of systemic and topical glucocorticoids to further decrease the risk of adverse effects. This is particularly justified because inhibition of AP-1 and NF-kappaB activities, that is the anti-inflammatory effect, occurs at much lower hormone concentrations than transactivation.

PERSPECTIVES

Clinical use of glucocorticoids is limited by occurrence of severe adverse effects. Therefore, the current aim is to design GRalpha ligands that retain only the anti-inflammatory activities of GC.

APC0576 decreases production of pro-inflammatory chemokine and extracellular matrix by human Tenon's capsule fibroblasts

PURPOSE

To control intraocular pressure in patients treated by trabeculectomy, progressive inflammation, fibroblast proliferation, and the enhanced expression of extracellular matrix (ECM), causes of scar formation at the bleb, must be prevented. Using human Tenon's capsule fibroblasts (TCFs), we examined the effect of APC0576, a suppressor of NF-kappaB-dependent gene activation of human vascular endothelial cells that does not adversely affect cell viability, on the production of pro-inflammatory chemokine and ECM. Its effect on TCF proliferation was also assessed.

METHODS

Enzyme-linked immunosorbent assay was used to detect the pro-inflammatory cytokines IL-8 and MCP-1 in the supernatant of TCFs stimulated with IL-1alpha in the presence or absence of APCO576 and ECM proteins, COOH-terminal peptide of type I procollagen (PIP), fibronectin (FN), and laminin (LN) in supernatants and lysates of TCFs stimulated with IL-1alpha or TGF-beta. The proliferative response of IL-1alpha-stimulated TCFs was examined using the SF formazan solution reaction.

RESULTS

APC0576 significantly suppressed the production by TCFs of IL-8 (p<0.0001), MCP-1(p<0.0001), PIP (supernatants: p<0.0001, cell lysates: p<0.0001), LN (supernatants: p<0.0001, lysates: p<0.0001), and FN (supernatants: p<0.0001, lysates: p<0.0001) as well as their proliferation (p<0.0001).

CONCLUSIONS

APC0576 suppressed pro-inflammatory chemokine and ECM production in TCFs as well as their proliferation. It may represent a novel candidate for the postoperative management of patients treated by trabeculectomy.

Molecular basis of the alteration in skin collagen metabolism in response to in vivo dexamethasone treatment: effects on the synthesis of collagen type I and III, collagenase, and tissue inhibitors of metalloproteinases

BACKGROUND

Glucocorticoids are widely used for the treatment of various diseases, despite known side-effects such as skin atrophy. Many studies have shown that the status of collagen fibres in the skin is affected by glucocorticoid treatment. However, the molecular mechanism underlying the alteration of collagen metabolism in the skin by glucocorticoid treatment remains unknown.

OBJECTIVES

To characterize the molecular mechanisms related to the deterioration of the dermis in response to glucocorticoids, the status of two major types of collagen, collagenase, and tissue inhibitors of metalloproteinases (TIMPs) in the dorsal skin of rats was studied at the protein and mRNA levels.

METHODS

Samples of rat dorsal skin were obtained after daily (1 mg kg-1) subcutaneous injections of dexamethasone (DEX) for 8 days. mRNA levels of two types of collagen and of TIMPs were measured by a lysate RNase protection assay. mRNA levels of collagenase were measured by a quantitative polymerase chain reaction. Protein levels of collagen and collagenase were measured by an immunoblot analysis.

RESULTS

Levels of type I tropocollagen and type III tropocollagen were drastically reduced in response to DEX. The effects of DEX treatment were more severe on type III than type I collagen: it also produced a significant decrease in fibril collagen of type III collagen. DEX treatment was found to decrease both active and latent forms of collagenase as well as its mRNA levels. Among TIMPs, mRNA levels of TIMP-1 and TIMP-2 were decreased in response to DEX treatment, whereas those of TIMP-3 were not affected.

CONCLUSIONS

These results suggest that DEX treatment strongly interferes with both the synthesis and degradation of type I collagen and, more drastically, type III collagen, the molecule that is known to play a major role in the initiation of wound healing. The present study may provide a molecular basis for the deterioration of skin function, impaired wound healing, and skin atrophy caused by glucocorticoid treatment.

Regulation of mRNA stability in mammalian cells

The regulation of mRNA decay is a major control point in gene expression. The stability of a particular mRNA is controlled by specific interactions between its structural elements and RNA-binding proteins that can be general or mRNA-specific. Regulated mRNA stability is achieved through fluctuations in half-lives in response to developmental or environmental stimuli like nutrient levels, cytokines, hormones and temperature shifts as well as environmental stresses like hypoxia, hypocalcemia, viral infection, and tissue injury. Furthermore, in specific disorders like some forms of neoplasia, thalassemia and Alzheimer's disease, deregulated mRNA stability can lead to the aberrant accumulation of mRNAs and the proteins they encode. This review presents a discussion of some recently identified examples of regulated and deregulated mRNA stability in order to illustrate the diversity of genes regulated by alterations in the degradation rates of their mRNAs.

Dexamethasone stimulates ribosomal protein L32 gene transcription in rat myoblasts

Incubation of rat L6 myoblasts for 24 h with 10(-7) M dexamethasone, a glucocorticoid analogue, resulted in a 2.5-fold increase in the rate of ribosomal protein L32 (rpL32) gene transcription with a corresponding increase in the level of rpL32 mRNA. The increased rate of transcription was accompanied by a dramatic enhancement in binding of the delta, but not beta and gamma, factors to the rpL32 gene promoter as measured by gel mobility shift assays. This increased binding reflects a change in the activity of the delta factor since its level is unchanged by dexamethasone treatment. The presence of the glucocorticoid analogue RU38486 reversed the stimulating effect of dexamethasone on rpL32 gene transcription and binding of the delta factor to the delta element. These results suggest that the mechanism which enhances rpL32 gene transcription in dexamethasone-treated rat L6 myoblasts involves glucocorticoid-receptor mediated changes in the activity of the delta factor.

Post-transcriptional and post-translational regulation of insulin-like growth factor binding protein-3 and -4 by insulin-like growth factor-I in uterine myometrial cells

Involution of the uterus induced by oestrogen depletion is associated with a decrease in uterine insulin-like growth factor (IGF)-I and an increase in IGF binding protein (IGFBP) gene expression. We examined the effects of IGF-I on primary uterine myometrial cell proliferation, and on IGFBP-3 and IGFBP-4 gene expression. IGF-I enhanced DNA synthesis in these cells. In conditioned media, IGF-I increased IGFBP-3 accumulation by release of cell associated IGFBP-3. A low dose of IGF-I increased IGFBP-4 accumulation, and a high dose caused IGFBP-4 to disappear. In cell-free conditioned media IGF-I protected IGFBP-3 and enhanced IGFBP-4 proteolysis. Co-incubation of [(125)I]-IGFBP-4 with cell-free conditioned media cleaved IGFBP-4 into 18 and 12 kDa fragments. Northern blot analysis indicated that IGF-I increased IGFBP-4 mRNA accumulation by stabilizing the mRNA while IGFBP-3 gene expression was slightly decreased. The results demonstrate that IGF-I regulates IGFBP-4 post-trancriptionally and post-translationally, whereas IGFBP-3 is only affected post-translationally. By enhancing IGFBP-4 proteolysis, increasing cell-associated IGFBP-3 and stabilizing IGFBP-3, IGF-I may initiate a mitogenic response.

Dexamethasone abrogates the fibrogenic effect of transforming growth factor-beta in rat granuloma and granulation tissue fibroblasts

Administration of TGF-beta, a fibrogenic inflammatory growth factor, promotes fibrosis and scarring. Dexamethasone, an anti-inflammatory steroid, inhibits wound healing and reduces fibrosis. The current studies were initiated to determine whether the co-administration of dexamethasone was able to abrogate the fibrogenic effect of TGF-beta. Polyvinyl alcohol sponges were implanted subcutaneously on the abdominal area of rats and directly injected with vehicle, dexamethasone, TGF-beta, or dexamethasone plus TGF-beta. Dexamethasone was able to block the fibrogenic effect of TGF-beta. Collagen and noncollagen protein synthesis was measured as a function of TGF-beta or dexamethasone concentrations in fibroblasts isolated from granulation tissue. Addition of dexamethasone to cultures treated simultaneously with TGF-beta blocked the fibrogenic response of TGF-beta. To study the molecular regulation of collagen gene expression by TGF-beta or dexamethasone, fibroblasts derived from granulation tissue were stably transfected with the ColCat 3.6 plasmid, which contains the rat pro alpha1(I) collagen promoter linked to the chloramphenicol acetyltransferase (CAT) gene. Dexamethasone decreased CAT activity whereas TGF-beta increased the activity of this reporter gene. The increase in CAT activity observed with TGF-beta treatment was significantly decreased when dexamethasone was added to the cultures, although CAT activity did not return to control level. Since collagen synthesis in fibroblasts treated simultaneously with dexamethasone and TGF-beta1 was found to be the same as that of untreated samples, the data indicate that there is a dexamethasone-mediated posttranscriptional regulation of pro alpha1(I) collagen mRNA. These studies demonstrate that at the in vivo level, the cellular level, and the molecular level, dexamethasone is able to block the fibrogenic effect of TGF-beta.

Dexamethasone suppresses in vivo levels of bone collagen synthesis in neonatal mice

The objective of this study was to determine the acute effects of glucocorticoids on in vivo levels of bone collagen synthesis in neonatal mice. Mice were injected with vehicle or dexamethasone at the start of the experiment. At 22 h, mice were given a 10 microCi injection of [3H]proline. At 24 h, the mice were sacrificed and the incorporation of [3H]proline into collagenase-digestible CDP labeling) and noncollagen (NCP labeling) protein in calvariae were determined by digestion with bacterial collagenase. Calvarial RNA was analyzed for COL 1A1 and osteocalcin mRNA levels by Northern blotting. After 24 h, vehicle-treated mice showed a 9.8 +/- 1.0% weight gain while dexamethasone-treated mice (1 mg/kg) had a 7.4 +/- 0.8% weight loss. Dexamethasone (1 mg/kg) decreased CDP and NCP labeling in calvariae by 51 +/- 4% and 17 +/- 4%, respectively (13 experiments). The inhibitory effect on protein labeling was selective for collagen since dexamethasone decreased the percent collagen synthesis from 25.4 +/- 1.6% to 16.6 +/- 1.0% (13 experiments). Dexamethasone at 3 mg/kg also decreased CDP labeling and the percent collagen synthesis in calvariae. There was a 30% reduction in COL1A1 mRNA levels and a 67% decrease in osteocalcin mRNA levels. To determine the reversibility of the inhibition of collagen synthesis, mice were given a single injection of dexamethasone (1 mg/kg) and then injected with [3H]proline 2 h prior to sacrifice at 24, 48, or 72 h. The reduction in CDP labeling observed at 24 h was fully reversed by 48-72 h. Moreover, by 72 h, the-rate of weight gain by dexamethasone-treated mice was similar to vehicle-treated controls. These data show that administration of dexamethasone to neonatal mice leads to a selective decrease in bone collagen synthesis within 24 h that is accompanied by down-regulation of osteocalcin and COL1A1 mRNA levels. This model will be useful in determining mechanisms by which high dose glucocorticoids inhibit bone formation in vivo.

Up-regulation of the low density lipoprotein receptor-related protein by dexamethasone in HepG2 cells

Dexamethasone has been shown to decrease the expression of the low density lipoprotein (LDL) receptor, but its effect on other members of the LDL receptor family is not known. We studied the effect of dexamethasone in HepG2 cells on the expression of the LDL receptor family members using radiolabeled receptor associated protein (RAP) which binds to all the members of the family. Treatment of HepG2 cells with increasing concentrations of dexamethasone resulted in a 2-fold increase in the binding and degradation of RAP. To identify the receptor responsible for the increased binding and degradation of RAP, we used specific ligands. For LDL receptor, we used LDL itself. For the LDL receptor-related protein/alpha 2-macroglobulin receptor, we used activated alpha 2-macroglobulin. The binding of LDL to HepG2 cells was decreased, whereas binding and degradation of activated alpha 2-macroglobulin was increased by 2-fold suggesting that dexamethasone increased LRP expression. Increased LRP expression was positively correlated with the increase in the steady-state levels and transcript numbers of the LRP mRNA; no changes in RAP or gamma-actin mRNA levels were observed. Increased mRNA levels were not due to an increased rate of transcription of the gene as assessed by nuclear run-on experiments. These studies indicate that dexamethasone increases cell-surface LRP activity in HepG2 cells by increasing the steady state mRNA levels and suggest that post-transcriptional mechanisms play a role in controlling LRP mRNA levels.

Effect of low-power laser irradiation on procollagen synthesis in human fibroblasts

The conflicting views of the effect of low-power laser (LPL) irradiation on procollagen synthesis have existed at the present time, whereas many clinical studies have tested usefulness of LPL irradiation for the wound healing. To evaluate the effect of LPL irradiation on the procollagen synthesis of human fibroblasts in vitro, LPL irradiation on human fibroblast was carried out using two different culture medium, serum-starved medium and fetal calf serum (FCS)-contained medium. In addition, to investigate the mechanism of the LPL on the procollagen synthesis of human fibroblasts, dexamethasone and methylene blue contained medium were used for inhibition of procollagen product at the pretranslational level and cGMP-mediated processes, respectively. Enhanced effect of LPL was consistently observed in the serum-starved medium (50% increase by a 3 min irradiation), not in the FCS-contained medium. The LPL enhanced effect was not blocked by dexamethasone (3% inhibition) but methylene blue (40% inhibition). Our data suggest that some factors in FCS might interfere with the enhanced effect of LPL on procollagen synthesis and the LPL might act as a direct stimulator of the procollagen synthesis. It seems probable that the LPL enhanced effects might be occurred at the translational level or at the pretranslational level, which is not affected by dexamethasone and cGMP, might be involved in the LPL enhanced effect of the procollagen synthesis in fibroblast.

Okadaic acid-induced transcriptional downregulation of type I collagen gene expression is mediated by protein phosphatase 2A

Expression of type I collagen genes is highly regulated and becomes abnormal in various pathological conditions, from excessive collagen production in fibrotic diseases to their downregulation in transformed cells. Some inflammatory cytokines and other ligands, capable of eliciting intracellular phosphorylation, can profoundly alter collagen gene expression. We investigated the role of serine/threonine protein phosphatases (PP) in the regulation of collagen gene expression. Biosynthesis of the endogenous type I procollagen, and expression of Pro alpha 1(I) promoter-luciferase (Luc) constructs transfected in NIH3T3 fibroblasts, were evaluated in response to PP2A and PP1 inhibitor okadaic acid (OA) and exogenously expressed PP catalytic subunits. OA suppressed type I collagen gene expression as judged by reduced rates of protein synthesis, steady state levels of Pro alpha 1(I) collagen mRNA and expression of Luc driven by Pro alpha 1 (I) collagen promoter in OA-treated cells. Co-transfection of Pro alpha 1(I)-Luc with expression vectors containing PP2A, but not PP1, stimulated collagen promoter activity. These results strongly suggest that OA acts via PP2A-mediated dephosphorylation of an unidentified transcription factor(s) or cofactor(s) needed to activate Pro alpha 1(I) collagen promoter.

Glucocorticoids coordinately regulate type I collagen pro alpha 1 promoter activity through both the glucocorticoid and transforming growth factor beta response elements: a novel mechanism of glucocorticoid regulation of eukaryotic genes

Glucocorticoids have previously have shown to decrease Type I collagen synthesis in vivo and in fibroblast cell culture. Several studies have demonstrated that glucocorticoids decrease Type I procollagen gene expression. These latter studies have included uridine incorporation into pro alpha 1 (I) and pro alpha 2 (I) mRNAs and nuclear run-off experiments. Using the ColCat 3.6 plasmid, which contains part of the 5' flanking region of the pro alpha 1 (I) collagen gene and the reporter gene, chloramphenicol acetyltransferase, the present studies demonstrate by stable transfection of fetal rat skin fibroblasts that dexamethasone down regulates the promoter activity of the pro alpha 1 (I) collagen gene. The glucocorticoid-mediated down-regulation of procollagen gene expression was demonstrated using the ColCat 3.6, 2.4, 1.7, or 0.9 plasmid. In addition, competitive oligonucleotide transfection experiments and site specific mutation of the glucocorticoid response element (GRE) in the whole ColCat 3.6 plasmid did not eliminate the effect. The possibility existed that another cis-element in the 5' flanking region of the pro alpha 1 (I) collagen gene was also required for the collagen glucocorticoid-mediated down-regulation of procollagen gene expression, since TGF-beta has been shown to stimulate in a decrease of transforming growth factor-beta (TGF-beta) secretion into the media. Gel mobility studies demonstrated that glucocorticoid treatment of rat skin fibroblasts decreased glucocorticoid receptor binding to the GRE and TGF-beta activator protein to the TGF-beta element which were brought back to control values by coordinate exogenous TGF-beta treatment. Thus the interaction of these TGF-beta molecules with cellular membrane receptors and subsequent transduction is dramatically decreased resulting in less signals to regulate collagen gene expression. These data indicate that glucocorticoids coordinately regulate procollagen gene expression through both the GRE and TGF-beta elements. Depression of procollagen gene expression by glucocorticoids through the TGF-beta element is mediated by decreased TGF-beta secretion, possibly involving a secondary effect on regulatory protein(s) encoded by noncollagenous protein gene(s). The present studies provide the basis for a novel mechanism of glucocorticoid-mediator regulation of eukaryotic genes containing the TGF-beta element.

Glucocorticoids regulate V1a vasopressin receptor expression by increasing mRNA stability in vascular smooth muscle cells

Enhancement of vascular responsiveness is considered to be one of the major contributing factors observed in glucocorticoid-induced hypertension. We examined the effects of glucocorticoids on V1a arginine vasopressin receptor mRNA and protein levels in vascular smooth muscle cells. Dexamethasone (1 mumol/L) produced a 1.8-fold increase in V1a receptor density without changing its affinity. Steady-state values of V1a receptor mRNA, analyzed by Northern blotting, increased 2.7-fold after a 12-hour exposure to dexamethasone. This effect of dexamethasone was blocked by the glucocorticoid antagonist RU38486 and did not occur in the presence of the protein synthesis inhibitor cycloheximide. The V1a receptor gene transcription rate, determined by nuclear run-off assays, was unchanged in cells treated with dexamethasone for 12 hours. Dexamethasone increased the half-life of V1a receptor mRNA by 2.2-fold. These findings suggest that dexamethasone upregulates the expression of the V1a receptor by increasing mRNA stability rather than by gene transcription and that de novo protein synthesis is involved in this regulation.

Cortisol downregulates osteoblast alpha 1 (I) procollagen mRNA by transcriptional and posttranscriptional mechanisms

Glucocorticoids decrease osteoblast proliferation and type I collagen production, and this may play a role in the development of glucocorticoid-induced osteoporosis. Osteoblast-enriched cultures derived from fetal rat calvaria were used to determine the mechanisms by which cortisol decreases alpha 1 (I) procollagen expression in bone cells. A 24 h treatment with cortisol decreased collagen synthesis in these cultures in a dose-dependent manner. Cortisol decreased alpha 1 (I) procollagen transcripts in a dose- and time-dependent manner as well. Repression of alpha 1 (I) procollagen transcripts was evident as early as 2 h of treatment and was maximal after 48 h of treatment. Nuclear run-off assays showed that cortisol downregulated transcription of the alpha 1 (I) procollagen gene. In addition, pretreatment with cortisol decreased the stability of alpha 1 (I) procollagen mRNA in transcription-arrested osteoblast cultures. The ability of cortisol to downregulate alpha 1 (I) procollagen transcripts was sensitive to cycloheximide treatment, suggesting that the gene is under "secondary control" by glucocorticoids. Since cortisol decreases alpha 1 (I) procollagen gene transcription in osteoblasts but does not affect alpha 1 (I) procollagen gene transcription in fibroblasts, we suggest that the mechanisms controlling glucocorticoid repression of collagen expression are cell-type specific.

Mechanisms of glucocorticoid action in bone cells

Glucocorticoids play an important role in the normal regulation of bone remodeling; however continued exposure of bone to glucocorticoid excess results in osteoporosis. In vivo, glucocorticoids stimulate bone resorption and decrease bone formation, and in vitro studies have shown that while glucocorticoids stimulate osteoblastic differentiation, they have important inhibitory actions on bone formation. Glucocorticoids have many effects on osteoblast gene expression, including down-regulation of type I collagen and osteocalcin, and up-regulation of interstitial collagenase. The synthesis and activity of osteoblast growth factors can be modulated by glucocorticoids as well. For example, insulin-like growth factor I (IGF-I) is an important stimulator of osteoblast function, and expression of IGF-I is decreased by glucocorticoids. The activity of IGF I can be modified by IGF binding proteins (IGFBPs), and their synthesis is also regulated by glucocorticoids. Thus, glucocorticoid action on osteoblasts can be direct, by activating or repressing osteoblast gene expression, or indirect by altering the expression or activity of osteoblast growth factors. Further investigation of the mechanisms by which glucocorticoids modulate gene expression in bone cells will contribute to our understanding of steroid hormone biology and will provide a basis for the design of effective treatments for glucocorticoid-induced osteoporosis.

Upstream regulatory elements necessary for expression of the rat COL1A1 promoter in transgenic mice

The activity of fusion genes containing fragments of the COL1A1 promoter was measured in tissues from 6- to 8-day-old transgenic mice. ColCAT3.6 contains approximately 3.6 kb (-3521 to 115 bp) of the rat COL1A1 gene, the chloramphenicol acetyltransferase (CAT) reporter gene, and the SV40 splice and polyadenylation sequences. ColCAT2.3 and ColCAT1.7 are deletion constructs that contain 2296 and 1667 bp of COL1A1 upstream from the RNA start site, respectively. For each transgene, up to six lines of mice were characterized. Both ColCAT3.6 and ColCAT2.3 had similar activity in bone and tooth; ColCAT1.7 was inactive. In transgenic calvariae, levels of transgene mRNA paralleled levels of CAT activity. In tendon, the activity of ColCAT2.3 was 3- to 4-fold lower than that of ColCAT3.6, and the activity ColCAT1.7 was 16-fold lower than that of ColCAT2.3. There was little activity of the ColCAT constructs in liver and brain. These data show that DNA sequences between -2.3 and -1.7 kb are required for COL1A1 promoter expression in bone and tooth; sequences that control expression in tendon are distributed between -3.5 and -1.7 kb of the promoter, with sequences downstream of -1.7 kb still capable of directing expression to this tissue. The cis elements that govern basal expression of COL1A1 in transgenic calvariae appear to be different from those required for optimal expression of the COL1A1 promoter in stably transfected osteoblastic cells.

The synthetic retinoid (4-hydroxyphenyl)retinamide decreases collagen expression in vitro and in the tight-skin mouse

OBJECTIVE

We documented the effect of the retinoid (4-hydroxyphenyl)retinamide on collagen expression in a tissue culture and in an animal model of scleroderma.

METHODS

We used RNA analysis, chloramphenicol acetyltransferase assays, organ culture, and histologic evaluation.

RESULTS

We showed that (4-hydroxyphenyl)retinamide decreases alpha 1(I) collagen messenger RNA and transcription in cultured cells, and decreases collagen levels in the dermis of tight-skin mice.

CONCLUSION

These results provide a basis for further experiments to address the efficacy of (4-hydroxyphenyl)retinamide in the treatment of scleroderma.

Regulation of expression of the type I collagen genes

The identification and functional analysis of DNA-protein interactions in the intronic and 5' flanking regions of the type I collagen genes has begun to define a series of cis-elements and trans-acting factors which regulate transcription of these genes. Studies such as these will eventually be expected to elucidate the mechanisms responsible for coordinate transcription of the alpha 1 and alpha 2 genes, a question which remains central to the field of collagen research. Although it is relatively straightforward to define sites of DNA-protein binding, interpretation of the functional importance of such interactions can be extremely complex. Furthermore, while mutation or deletion of a particular binding site may alter the functional activity of a construct transfected into cultured cells, there is no guarantee that a similar change will have the same effect in vivo, where the entire gene locus is present in its native chromosomal context. Nevertheless, these kinds of in vitro studies offer the best current approach to defining and isolating transcription factors that control expression of the alpha 1 and alpha 2 genes. Ultimately, it will be necessary to test the activity of such factors (and their respective cis-elements) in defined systems in vivo.

Glucocorticoid receptors in leukemias, lymphomas and myelomas of young and old

In this paper we have briefly reviewed the nature of leukemias and lymphomas in the old and the young. We surveyed in general the ways in which lymphoid cells and other hematologic elements respond to glucocorticoids, mentioning that there may be direct or indirect effects on their growth by these ligands. We have reviewed the current general model for the action of glucocorticoids in all cells, namely the fact that the actions of these steroids are mediated to a large extent through binding with ligand-activated transcription factors, their receptors. The growing wealth of detail about the nature of the interaction of these receptors with regulatory sites in the genome is discussed. Finally, we have described our results with lines of tissue culture cells representing clones from a typical leukemia of the young, and of myeloma, a typical hematologic malignancy of the elderly. Several features of the effects of glucocorticoids on these cells point up areas that would be pertinent to explore in aging and in the relationship of hematologic diseases to survival and response to therapy in the older versus the younger patient.

Glucocorticoid and retinoid regulation of alpha-2 type I procollagen promoter activity

Glucocorticoids decrease type I procollagen synthesis by decreasing the steady state levels of procollagen mRNAs and mRNA synthesis. The present studies were undertaken to determine the functional sequences of the pro alpha 2(I) collagen gene required for the glucocorticoid-mediated decrease of type I procollagen mRNA synthesis. Embryonic mouse fibroblasts were stably transfected with the pR40 DNA CAT construct containing the 5' flanking region fragment from -2048 to +54 and the intronic fragment from +418 to +1524 of the mouse alpha 2(I) collagen gene. Dexamethasone treatment of these pR40 transfected fibroblasts resulted in a significant decrease in CAT activity which agrees with the glucocorticoid-mediated decrease of the steady state levels of type I procollagen mRNAs. To determine the possible role of the first intron fragment in the dexamethasone-mediated decrease of CAT activity, pR36, a CAT plasmid containing the first intron fragment and the SV40 early promoter, was transfected into mouse fibroblasts and treated with dexamethasone. No significant decrease in CAT activity was observed. The dexamethasone-mediated response was then localized within the 5' flanking region by preparing a series of constructs containing internal deletions and transfecting these plasmids into mouse fibroblasts. The regions -2048 to -981 and -506 to -351 were required for the dexamethasone response of gene activity. However, the DNA stretch from -981 to -506 was not. Analysis of the DNA sequences of these regions revealed a single GRE at -1023 to -1018 and a modified doublet at -873 to -856.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that an iron chelator regulates collagen synthesis by decreasing the stability of procollagen mRNA

Iron chelation has been shown previously to decrease collagen synthesis at a posttranslational level by inhibiting prolyl 4-hydroxylase, one of the key enzymes in collagen metabolism. On the other hand, recent in vivo studies of iron overload in rats suggest that iron could specifically activate collagen gene expression in liver tissues. These findings led us to investigate whether iron chelation might also affect collagen gene expression and posttranslational modification. Our data indicate that alpha,alpha'-dipyridyl, an iron chelator, at a concentration of 1 mmol/L, decreased steady-state levels of type I procollagen messenger RNA by 42% (p less than 0.001) without affecting beta-actin messenger RNA levels. Nuclear runoff studies demonstrated that transcription of the type I procollagen gene was unchanged by alpha,alpha'-dipyridyl. However, the turnover rate of type I procollagen messenger RNA was increased by 30%. This pretranslational inhibition of collagen synthesis was not due to decreased lipid peroxidation, because thiobarbituric acid-reactive substances were unchanged by alpha,alpha'-dipyridyl. However, cycloheximide totally abolished the effect, indicating that de novo protein synthesis was required.

Fibrogenesis in cirrhosis. Potential for therapeutic intervention

Liver cirrhosis is an end stage of several diseases that affect the liver chronically. It is characterized, among other things, by excess collagen deposition, distortion of liver architecture, tissue malfunction and hemodynamic alterations. Many of the complications of cirrhosis may result from excess matrix-deposition. Therefore, prevention of collagen accumulation or removal of collagen deposits could ameliorate the disease. In this article we discuss the pathophysiology of liver fibrosis and we describe various compounds with antiinflammatory and antifibrogenic activity. We discuss their possible mechanism of action and we describe animal and clinical studies in which these compounds have been utilized.

Effect of transforming growth factor beta and basic fibroblast growth factor on steroid-impaired healing intestinal wounds

A longitudinal intestinal wound model in the pig was used to assess the effect of parenteral steroids (betamethasone 12 mg 50 kg-1 intramuscularly twice daily) on breaking load. Steroid treatment significantly decreased the breaking load of wounds in the ileum and colon in comparison with wounds from saline-treated animals. In a further group of animals receiving steroids, paired longitudinal wounds were constructed. One wound of a pair was treated with a local application of transforming growth factor beta (TGF-beta) (5 micrograms per wound) or basic fibroblast growth factor (5 micrograms per wound) in a collagen suspension. The other wound was treated with a collagen suspension alone. Ileal wounds treated with TGF-beta were significantly stronger than collagen-treated controls at 7 days. The steroid-induced impairment of breaking load in intestinal wounds is partially reversed by a local application of TGF-beta in a collagen suspension at the time of surgery.

Effects of methylprednisolone on glomerular and medullary mRNA levels for extracellular matrices in puromycin aminonucleoside nephrosis

We examined the effects of methylprednisolone (MPSL) on type IV collagen, laminin and heparan sulfate proteoglycan (HSPG) mRNA levels in the renal glomeruli and medulla of puromycin aminonucleoside (PAN) nephrosis. mRNA levels encoding for type IV collagen and laminin increased markedly, whereas those for HSPG decreased significantly in glomeruli of PAN nephrosis. Administration of MPSL partially ameliorated the abnormal gene expression for basement membrane components. Furthermore, we showed that medullary mRNA levels for all these basement membrane components decreased with age in PAN nephrosis with or without MPSL treatment, suggesting that neither PAN nor MPSL has any effect on basement membrane component mRNA levels in the renal medulla. In contrast, mRNA levels for the interstitial collagens including alpha 1 (I) and alpha 1 (III) chains in glomeruli showed little change with or without MPSL treatment, whereas those in medulla increased significantly in PAN nephrosis when compared with the control. MPSL ameliorated the abnormal gene expression of alpha 1 (I) and alpha 1 (III) collagen in renal medulla. These results indicate that PAN affects both glomerular mRNA encoding for basement membrane components and medullary mRNA encoding for interstitial collagens, and that MPSL has marked effects on the amelioration of abnormal gene expression in both glomeruli and medulla of PAN nephrosis.

Dexamethasone modulates alpha 2-macroglobulin and apolipoprotein E gene expression in cultured rat liver fat-storing (Ito) cells

Fat-storing (Ito) cells are perisinusoidal liver cells thought to play a central role in vitamin A metabolism and fibrongenesis. Glucocorticoids have been shown to be beneficial in the treatment of certain types of liver diseases by delaying the development of cirrhosis. To study the regulatory effects of dexamethasone on Ito cell gene expression, Ito cells were isolated from normal rat liver and primary cultures were established. The effect of dexamethasone on the synthesis of alpha 2-macroglobulin, apolipoprotein E, fibronectin and actin was examined. Protein synthesis was studied both at the protein level and at the RNA level by means of biosynthetic labeling, immunoprecipitation followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by Northern blot analysis of total RNA. After exposure to dexamethasone for 20 hr, alpha 2-macroglobulin protein synthesis was increased threefold, whereas apolipoprotein E expression was decreased 80%. Biosynthesis of fibronectin remained unaffected by hormone treatment. The dexamethasone effect became detectable 5 hr after beginning the exposure. Deinduction kinetic experiments showed that the glucocorticoid effect was detectable more than 12 hr after the replacement of the dexamethasone-containing culture medium by medium without the hormone. Corresponding to the data obtained at the protein level, dexamethasone increased the steady-state levels of alpha 2-macroglobulin-specific messenger RNA and reduced apolipoprotein E-specific transcripts, whereas fibronectin and actin messenger mRNA remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptide growth factors and wound healing

Growth factors and cytokines are important signal transducers in wound microenvironments. Experimental data are accumulating rapidly which demonstrate their ability to influence populations of polymorphs and macrophages to migrate to the wound, subsequently to be replaced by synthetic cells which produce collagen and matrix; these events are controlled sequentially at cell receptor level by a variety of locally delivered (paracrine and autocrine) peptides. Preliminary results from clinical trials using recombinant human growth factors to improve cutaneous healing are encouraging. Current research aims to produce growth preparations which can be applied to a wound to accelerate healing.

Dopamine D2-receptor mRNA level in rat striatum after chronic haloperidol treatment

Chronic treatment with haloperidol, a D2-receptor antagonist and a neuroleptic, increases the number of D2-receptors in rat striatum. However, there have been inconsistent reports on the D2-receptor mRNA level, one showing the increase in the mRNA level and another detecting no changes. Furthermore, they did not distinguish the two isoforms of D2-receptor, D2A and D2B. In the present work, both D2- and DeA-receptor mRNA levels in rat striatum were estimated after chronic administration of haloperidol. There was, within the sensitivity of the assay, no significant increase in either of them between 3 and 24 h after the last administration. This suggests that chronic haloperidol treatment does not affect the transcriptional regulation of the D2-receptor gene or the alternative splicing process of its transcripts.

The role of DNA synthesis in the responses of fetal rat calvariae to cortisol

To determine the extent to which the effects of cortisol on collagen synthesis in 21 day fetal rat calvariae are linked to its effects on cell replication, calvariae were cultured for 24-72 h with 0.1 and 1 microM cortisol in the presence or absence of 1 mM hydroxyurea (HU) or 30 microM aphidicolin (APC), inhibitors of DNA synthesis. The incorporation of [3H]proline into collagenase-digestible protein (CDP) and [3H]thymidine into DNA were measured during the last 2 h of culture. At 24 h HU and APC decreased thymidine incorporation by greater than 90%, and this remained low for the duration of culture. In contrast, cortisol reduced thymidine incorporation by only 44% at 72 h. Although cortisol caused a 24 h stimulatory effect and a 48 and 72 h inhibitory effect on CDP labeling and the percentage of collagen being synthesized (PCS), HU, and APC had no effect on basal CDP labeling or PCS over the 72 h culture period. Cortisol caused parallel alterations in the steady-state levels of alpha-1(I) procollagen mRNA, suggesting that its effects occur at the pretranslational level. At 24 h HU and APC did not prevent the stimulatory effect of cortisol on CDP labeling and PCS. At 48 h the inhibitory effects of cortisol on CDP labeling and PCS were observed in the presence of APC but not in the presence of HU. At 72 h the inhibitory effects of cortisol on CDP labeling and PCS were still observed in the presence of HU and APC.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet-derived growth factor-induced destabilization of smooth muscle alpha-actin mRNA

We have previously shown that treatment of postconfluent, quiescent rat vascular smooth muscle cells (SMC) with platelet-derived growth factor (PDGF) dramatically reduced smooth muscle (SM) alpha-actin synthesis and SM alpha-actin mRNA abundance, suggesting a role for this mitogen in the control of SMC differentiation. In the present studies, we explored the molecular mechanisms whereby PDGF decreases SM alpha-actin mRNA levels. Treatment of postconfluent SMC with both platelet PDGF and recombinant PDGF-BB resulted in a dramatic and concentration-dependent decrease in SM alpha-actin mRNA levels. We observed no differences in efficacy between platelet PDGF and PDGF-BB, indicating that the PDGF-A chain is not required for the effect. The rate of decrease in SM alpha-actin mRNA abundance in PDGF-treated SMC was greater than that observed in cells treated with the transcriptional inhibitor, actinomycin D, with or without PDGF, indicating that PDGF induced a transcriptionally dependent destabilization of the cytosolic SM alpha-actin mRNA pool. This effect appeared selective for SM alpha-actin, in that there was no evidence of a similar change in non-muscle (NM) beta-actin mRNA stability following PDGF treatment. Results of nuclear run-on analyses showed no differences in SM alpha-actin transcription between PDGF- and vehicle-treated SMC at either 4 or 24 hours following treatment, demonstrating that decreases in transcription of the SM alpha-actin gene did not contribute to PDGF-induced changes in SM alpha-actin mRNA abundance. Results of these studies support a possible role for PDGF in regulation of SMC differentiation via a post-transcriptional control mechanism.

Differential regulation of corticotropin-releasing hormone mRNA in rat brain

Corticotropin-releasing hormone (CRH), a major hypothalamic component of the hypothalamic-pituitary-adrenal axis, has been localized to both the paraventricular nucleus (PVN) and cerebral cortex. Adrenalectomy causes an increase in PVN CRH content, whereas its effect on cortical CRH content is not clear. In the present study, adrenalectomy resulted in a threefold rise in the CRH mRNA content of anatomic micropunches of the PVN of individual rats (P less than 0.001), which was abolished by dexamethasone replacement. In parietal cortex, adrenalectomy did not affect CRH mRNA content, whereas hypophysectomy resulted in a twofold rise in CRH mRNA content (P less than 0.02), which was not significantly reduced by dexamethasone replacement. These results demonstrate that the CRH gene is negatively regulated by glucocorticoid in the PVN but not in cerebral cortex and that the increase in cortical CRH mRNA content after hypophysectomy may be evidence for negative regulation of cortical CRH gene expression by a second pituitary-dependent factor other than glucocorticoid.

Proliferative vitreoretinopathy membranes. An immunohistochemical study

Proliferative vitreoretinopathy (PVR) is the leading cause of failure after retinal detachment surgery. Therefore, both the extracellular matrix and cellular components of preretinal membranes from 23 eyes with PVR were characterized immunohistochemically. The membrane stroma was composed primarily of types I, II, and III collagen. Laminin and both heparan sulfate proteoglycans and collagens types IV and V were co-distributed in discrete regions within the stroma. Glial and retinal pigment epithelial (RPE) cell populations were identified in these membranes using specific immunohistochemical markers as was a small but significant macrophage population. Double-labeling experiments indicated that RPE cells in these membranes expressed the class II histocompatibility antigen HLA-DR, although neither the RPE monolayer in situ nor cultured RPE cells was HLA-DR positive unless induced by gamma interferon. Only rare isolated vascular endothelial cells were detected in 5 of the 23 membranes.

Differential regulation of glycosaminoglycan, fibronectin, and collagenase production in cultured human dermal fibroblasts by interferon-alpha, -beta, and -gamma

In order to determine whether interferons (IFNs) play a universal role in terminating the fibrotic response by inhibiting other fibroblast functions in addition to growth and collagen production, we investigated the effect of human recombinant (hu-r) IFN-alpha, -beta, and -gamma on the glycosaminoglycan, fibronectin, and collagenase production of cultured human dermal fibroblasts. Our results show that short-term (48 h) treatment of confluent fibroblast cultures with hu-r-IFN-alpha 2 and hu-r-IFN-beta-ser17 causes a concentration (1 to 1 x 10(5) U/ml)-dependent inhibition of glycosaminoglycan production, has no effect on fibronectin production, and markedly increases collagenase production. In contrast, hu-r-IFN-gamma not only causes a concentration-dependent increase in collagenase production but also increases both glycosaminoglycan and fibronectin production. These results demonstrate that IFNs differently regulate fibroblast functions rather than universally inhibit all functions, and show that IFN-alpha and -beta exhibit a broader antifibrotic spectrum that IFN-gamma.

Effect of dexamethasone on the expression of interleukin-2 in a mouse T cell line

1. The effect of the synthetic glucocorticoid, dexamethasone (dex), on the production of interleukin-2 (IL-2) and IL-2 mRNA was examined in the mouse T cell line, LBRM-33.4A2. 2. Treatment of Concanavalin A (Con A)-stimulated LBRM-33 cells with low concentrations of dex (10nM) inhibited the production of IL-2 activity by approx. 70%, with a corresponding decrease in IL-2 mRNA levels. 3. In contrast, much higher concentrations of dex (up to 10 microM) inhibited the level of another Con A-inducible mRNA, c-myc mRNA, by only 30%, and did not affect beta-tubulin mRNA levels at all. 4. Thus it appears that inhibition by dex in stimulated LBRM-33 cells is specific for the expression of IL-2 mRNA. 5. Experiments with actinomycin D suggest that dex does not mediate its suppression of IL-2 mRNA accumulation by decreasing the stability of this message; rather, it appears that dex inhibits transcription of the IL-2 gene.

Hormonal regulation of collagen gene expression in osteoblastic cell-overview and new findings

Type I collagen synthesis in osteoblasts is regulated by a variety of systemic hormones, growth factors and locally produced factors. With the use of cDNA probes and hybridization analysis, it appears that many of these agents alter collagen synthesis by a pretranslational mechanism.