Biomedical subjects

A M Delany

Publications and source records attributed to A M Delany.

24 records · Page 2Linked to original sources

PubMed1995

Transcriptional repression of insulin-like growth factor I by glucocorticoids in rat bone cells.

Insulin-like growth factor I (IGF-I) is an abundant autocrine and paracrine growth factor secreted by osteoblasts. It promotes osteoblast proliferation and expression of their differentiated phenotype. Glucocorticoids decrease IGF-I production by osteoblasts, which may mediate some actions of the steroid on bone in both normal and pathological states. The mechanisms by which the glucocorticoid cortisol down-regulates IGF-I transcripts were explored using cultures of osteoblast-enriched cells derived from fetal rat calvaria (Ob cells). Repression of IGF-I transcripts was apparent after 8 h of treatment, was sustained for at least 24 h, and was not altered by cotreatment with cycloheximide. Cortisol did not alter the stability of IGF-I messenger RNAs in transcriptionally arrested Ob cells. Cortisol decreased IGF-I heterogeneous nuclear RNA and gene transcription, as determined by reverse transcription-linked polymerase chain reaction and nuclear run-on assay, respectively. Transient transfection of Ob cells with constructs containing portions of the rat IGF-I exon 1 promoter and 5'-flanking DNA linked to the reporter gene luciferase were performed to determine glucocorticoid-responsive region of the rat IGF-I exon 1 promoter was localized to 34 to 192 relative to the first start site of transcription. In conclusion, cortisol inhibits the transcription of IGF-I in osteoblasts, an effect that may be relevant to the actions of cortisol in bone.

Animals↗

PubMed1995

Insulin-like growth factors inhibit interstitial collagenase synthesis in bone cell cultures.

Insulin-like growth factor-I (IGF-I) and IGF-II are among the most prevalent growth factors secreted by bone cells and are presumed to act as autocrine regulators of bone formation. We recently demonstrated that IGFs inhibit bone collagen degradation, and we postulated that they may either inhibit the expression of interstitial collagenase or stimulate the synthesis of tissue inhibitors of metalloproteinase-1 (TIMP-1), -2, or -3. We tested the effects of IGF-I and -II on collagenase and TIMP-1, -2, and -3 expression in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). Steady state messenger RNA (mRNA) levels were determined by Northern blot analysis, and collagenase concentrations were determined in the culture medium by a specific immunoassay. After 2-6 h of treatment, IGF-I and -II decreased collagenase transcripts by up to 80%. IGF-I was a more potent inhibitor than IGF-II, because it was active at doses as low as 10 nM, whereas a dose of 100 nM was required to observe the IGF-II effect. In addition, IGF-I and -II opposed the stimulatory effect of retinoic acid on collagenase transcripts. Immunoreactive collagenase levels were not detectable in control or IGF-treated cultures, but IGF-I and -II decreased the levels induced by retinoic acid by 70-90%. The protein synthesis inhibitor cycloheximide superinduced collagenase transcripts, and IGF-I or -II decreased this mRNA induction to levels similar to, but not lower than, those observed in control cultures. The effects of IGF-I and -II on collagenase transcripts were not modified by the DNA synthesis inhibitor hydroxyurea at 1 mM. Neither IGF-I nor IGF-II modified the expression of TIMP-1, -2, or -3 mRNA in Ob cells. TIMP protein levels were not determined, and our study does not exclude a translational or posttranslational effect of IGF. In conclusion, IGF-I and -II decrease interstitial collagenase transcripts as well as induced protease levels in Ob cells, and this effect may contribute to their inhibitory actions on bone collagen degradation.

Animals↗

PubMed1994

Cellular and clinical perspectives on skeletal insulin-like growth factor I.

Insulin-like growth factor (IGF) I, a polypeptide synthesized by skeletal cells, is presumed to act as an autocrine regulator of bone formation. IGF I stimulates bone replication of preosteoblastic cells and enhances the differentiated function of the osteoblast. The synthesis of skeletal IGF I is regulated by systemic hormones, most notably parathyroid hormone and glucocorticoids, as well as by locally produced factors, such as prostaglandins and other skeletal growth factors. Whereas hormones and growth factors regulate IGF I synthesis, the exact level of regulation has not been established and may involve both transcriptional and posttranscriptional mechanisms. The IGF I gene contains six exons, and both exon 1 and 2 contain transcription initiation sites. Extrahepatic tissues, including bone, express exon 1 transcripts, and regulation of the exon 1 promoter activity in osteoblasts is currently under study. It is apparent that the regulation of IGF I gene transcription as well as the regulation of mRNA stability is complex and tissue specific. It is possible that abnormalities in skeletal IGF I synthesis or activity play a role in the pathogenesis of bone disorders. In view of its important anabolic actions in bone, it is tempting to postulate the use of IGF I for the treatment of disorders characterized by decreased bone mass. An alternative could be the stimulation of the local production of IGF I in bone.

Animals↗

PubMed1994

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.

Animals↗

PubMed1993

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.

Animals↗

PubMed1992

Post-transcriptional regulation of collagenase and stromelysin gene expression by epidermal growth factor and dexamethasone in cultured human fibroblasts.

Epidermal growth factor (EGF) is a ubiquitous fibroblast mitogen which also stimulates the synthesis of the extracellular matrix degrading metalloproteinases, collagenase, and stromelysin. Using primary cultures of human skin fibroblast, we show that these metalloproteinase mRNAs are coordinately up-regulated by EGF; and that dexamethasone, a potent inhibitor of collagenase and stromelysin synthesis, coordinately down-regulates these EGF-induced mRNAs. Nuclear run-on assays showed that EGF increased transcription of collagenase and stromelysin approximately 2-fold over the untreated control, while repression by dexamethasone was difficult to detect. However, steady state mRNA levels were induced approximately 10-fold by EGF and co-treatment with dexamethasone decreased them to below control levels, suggesting modulation of mRNA stability. Thus, we measured the half-life of these mRNAs using "pulse-chase" methodology. Typically, the half-life of EGF-induced collagenase and stromelysin mRNAs was approximately 30 h, and co-treatment with dexamethasone decreased the half-life of these mRNAs by 30-50%. Additionally, we found that the transcription inhibitor DRB stabilized EGF-induced metalloproteinase mRNAs, suggesting an mRNA degradation pathway which requires transcription. Thus our data demonstrate that collagenase and stromelysin are coordinately regulated by EGF and by dexamethasone, primarily at the level of metalloproteinase mRNA stability.

Blotting, Northern↗