Glucocorticosteroids up-regulate human elastin gene promoter activity in transgenic mice

Glycosaminoglycans Influence Extracellular Matrix of Human Trabecular Meshwork Cells Cultured on 3D Scaffolds

Glaucoma is a multifactorial progressive optic neuropathy characterized by the loss of retinal ganglion cells leading to irreversible blindness. It is the leading cause of global irreversible blindness and is currently affecting over 70 million people. Elevated intraocular pressure (IOP) is considered the only modifiable risk factor and is a target of numerous treatment modalities. Researchers have assigned this elevation of IOP to accumulation of extracellular matrix (ECM) components in the aqueous humor (AH) outflow pathway. The major drainage structure for AH outflow is the trabecular meshwork (TM). The ECM of the TM is important in regulating IOP in both normal and glaucomatous eyes. In this work, we have studied the role of exogeneous glycosaminoglycans (GAGs), glucocorticoids, and culture conditions on the expression of the ECM gene and proteins by human TM (hTM) cells cultured on biomaterial scaffolds. Gene and protein expression levels of elastin, laminin, and matrix metalloproteinase-2 (MMP-2) were evaluated using quantitative PCR and immunohistochemistry. Pressure gradient changes in cell-laden scaffolds in perfusion cultures were also monitored. Our findings show that GAGs and dexamethasone play an influencing role in hTM ECM turnover at both transcriptional and translational levels by altering expression levels of elastin, laminin, and MMP-2. Understanding the role of exogeneous factors on hTM cell behavior is helpful in gaining insights on glaucoma pathogenesis and ultimately pivotal in development of novel therapeutics against the disease.

The Glucocorticoid Receptor NR3C1 in Testicular Peritubular Cells is Developmentally Regulated and Linked to the Smooth Muscle-Like Cellular Phenotype

Whether glucocorticoids (GC) can directly affect human testicular functions is not well understood. A predominant site of GC receptor (GR; NR3C1) expression in the adult testis are peritubular smooth muscle-like cells, which express smooth muscle actin (ACTA2), contract and thereby are involved in sperm transport. In contrast to the adult, neither GR nor ACTA2, or elastin (ELN) were detected in the peritubular compartment before puberty in non-human primate testes. In isolated human testicular peritubular cells (HTPCs), activation of GR by dexamethasone (Dex) caused the translocation of GR to the nucleus and stimulated expression of ACTA2 and ELN, without affecting the expression of collagens. Cytoskeletal ACTA2-rearrangements were observed and were associated with an increased ability to contract. Our results indicate post-pubertal testicular roles of GC in the maintenance of the contractile, smooth muscle-like phenotype of peritubular cells.

Synthetic ligands of the elastin receptor induce elastogenesis in human dermal fibroblasts via activation of their IGF-1 receptors

BACKGROUND

We have previously reported that a mixture of peptides obtained after chemical or enzymatic degradation of bovine elastin, induced new elastogenesis in human skin.

OBJECTIVE

Now, we investigated the elastogenic potential of synthetic peptides mimicking the elastin-derived, VGVAPG sequence, IGVAPG sequence that we found in the rice bran, and a similar peptide, VGVTAG that we identified in the IGF-1-binding protein-1 (IGFBP-1).

RESULTS

We now demonstrate that treatment with each of these xGVxxG peptides (recognizable by the anti-elastin antibody), up-regulated the levels of elastin-encoding mRNA, tropoelastin protein, and the deposition of new elastic fibers in cultures of human dermal fibroblasts and in cultured explants of human skin. Importantly, we found that such induction of new elastogenesis may involve two parallel signaling pathways triggered after activation of IGF-1 receptor. In the first one, the xGVxxG peptides interact with the cell surface elastin receptor, thereby causing the downstream activation of the c-Src kinase and a consequent cross-activation of the adjacent IGF-1R, even in the absence of its principal ligand. In the second pathway their hydrophobic association with the N-terminal domain (VGVTAG) of the serum-derived IGFBP-1 induces conformational changes of this IGF-1 chaperone allowing for the release of its cargo and a consequent ligand-specific phosphorylation of IGF-1R.

CONCLUSION

We present a novel, clinically relevant mechanism in which products of partial degradation of dermal elastin may stimulate production of new elastic fibers by dermal fibroblasts. Our findings particularly encourage the use of biologically safe synthetic xGVxxG peptides for regeneration of the injured or aged human skin.

Sodium L-ascorbate enhances elastic fibers deposition by fibroblasts from normal and pathologic human skin

BACKGROUND

Vitamin C (L-ascorbic acid), a known enhancer of collagen deposition, has also been identified as an inhibitor of elastogenesis.

OBJECTIVE

Present studies explored whether and how the L-ascorbic acid derivative (+) sodium L-ascorbate (SA) would affect production of collagen and elastic fibers in cultures of fibroblasts derived from normal human skin and dermal fat, as well as in explants of normal human skin, stretch-marked skin and keloids.

METHODS

Effects of SA on the extracellular matrix production were assessed quantitatively by PCR analyses, western blots, biochemical assay of insoluble elastin and by immuno-histochemistry. We also evaluated effects of SA on production of the reactive oxygen species (ROS) and phosphorylation of IGF-I and insulin receptors.

RESULTS

SA, applied in 50-200 μM concentrations, stimulates production of both collagen and elastic fibers in all tested cultures. Moreover, combination of SA with a proline hydroxylase inhibitor induces a beneficial remodelling in explants of dermal scars, resulting in the inhibition of collagen deposition and induction of new elastogenesis. Importantly, we revealed that SA stimulates elastogenesis only after intracellular influx of non-oxidized ascorbate anions (facilitated by the sodium-dependent ascorbate transporter), that causes reduction of intracellular ROS, activation of c-Src tyrosine kinase and the enhancement of IGF-1-induced phosphorylation of the IGF-1 receptor that ultimately triggers elastogenic signalling pathway.

CONCLUSION

Our results endorse the use of this potent stimulator of collagen and elastin production in the treatment of wrinkled and stretch-marked skin. They also encourage inclusion of SA into therapeutic combinations with collagenogenesis inhibitors to prevent formation of dermal scars and keloids.

A transgenic zebrafish model for monitoring glucocorticoid receptor activity

Gene regulation resulting from glucocorticoid receptor and glucocorticoid response element interactions is a hallmark feature of stress response signaling. Imbalanced glucocorticoid production and glucocorticoid receptor activity have been linked to socioeconomically crippling neuropsychiatric disorders, and accordingly there is a need to develop in vivo models to help understand disease progression and management. Therefore, we developed the transgenic SR4G zebrafish reporter line with six glucocorticoid response elements used to promote expression of a short half-life green fluorescent protein following glucocorticoid receptor activation. Herein, we document the ability of this reporter line to respond to both chronic and acute exogenous glucocorticoid treatment. The green fluorescent protein expression in response to transgene activation was high in a variety of tissues including the brain, and provided single-cell resolution in the effected regions. The specificity of these responses is demonstrated using the partial agonist mifepristone and mutation of the glucocorticoid receptor. Importantly, the reporter line also modeled the temporal dynamics of endogenous stress response signaling, including the increased production of the glucocorticoid cortisol following hyperosmotic stress and the fluctuations of basal cortisol concentrations with the circadian rhythm. Taken together, these results characterize our newly developed reporter line for elucidating environmental or genetic modifiers of stress response signaling, which may provide insights to the neuronal mechanisms underlying neuropsychiatric disorders such as major depressive disorder.

Dexamethasone normalizes aberrant elastic fiber production and collagen 1 secretion by Loeys-Dietz syndrome fibroblasts: a possible treatment?

Loeys-Dietz syndrome (LDS) is an autosomal dominant connective tissue disorder characterized by facial dysmorphism, cleft palate, dilation of the aortic arch, blood vessel tortuosity and a high risk of aortic dissection. It is caused by mutations in the transforming growth factor β-receptor 1 and 2 (TGFβ-R1 and TGFβ-R2) genes. Fibroblasts derived from 12 Loeys-Dietz syndrome patients, six with TGFB-R1 mutations and six with TGFB-R2 mutations, were analyzed using RT-PCR, biochemical assays, immunohistochemistry and electron microscopy for production of elastin, fibrillin 1, fibulin 1 and fibulin 4 and deposition of collagen type I. All LDS fibroblasts with TGFβ-R1 mutations demonstrated decreased expression of elastin and fibulin 1 genes and impaired deposition of elastic fibers. In contrast, fibroblasts with TGFβ-R2 mutations consistently demonstrated intracellular accumulation of collagen type I in the presence of otherwise normal elastic fiber production. Treatment of the cell cultures with dexamethasone induced remarkable upregulation in the expression of tropoelastin, fibulin 1- and fibulin 4-encoding mRNAs, leading to normalization of elastic fiber production in fibroblasts with TGFβ-R1 mutations. Treatment with dexamethasone also corrected the abnormal secretion of collagen type I from fibroblasts with TGFβ-R2 gene mutations. As the organogenesis-relevant elastic fiber production occurs exclusively in late fetal and early neonatal life, these findings may have implications for treatment in early life. Further studies are required to determine if dexamethasone treatment of fetuses prenatally diagnosed with LDS would prevent or alleviate the connective tissue and vascular defects seen in this syndrome.

Elastin in lung development and disease

Elastic fibres are present in lung structures including alveoli, alveolar ducts, airways, vasculature and pleura. The rate of lung elastin synthesis is greatest during fetal and neonatal development, and is minimal in the healthy adult. We have determined that glucocorticoids up-regulate fetal lung tropoelastin expression while concomitantly accelerating terminal airspace maturation. Because there is minimal turnover of elastin in healthy adult lung, the elastin incorporated into the lung early in development supports lung function for the normal lifespan. However, in the adult lung, in pathological circumstances such as emphysema or pulmonary fibrosis there may be reactivation of elastin expression. We have found in silica-induced pulmonary fibrosis that expression of tropoelastin is primarily increased in the walls and the septal tips of the alveolus, with modest increases in other compartments which normally express tropoelastin during development. This finding suggests that the mesenchymal cell of the alveolar wall increases tropoelastin expression during fibrotic disorders. In emphysema and fibrosis, elastin is present in abnormal-appearing, probably non-functional, elastic fibres, suggesting that the adult lung cannot recapitulate the elastic fibre assembly mechanisms operative during normal lung growth.

Skin elastic fibres: regulation of human elastin promoter activity in transgenic mice

Elastic fibres form an extracellular network which provides elasticity and resilience to tissues such as the skin. To study the regulation of human elastin gene expression, we have developed a line of transgenic mice which harbour 5.2 kb of human elastin gene promoter region in their genome. This promoter is linked to the chloramphenicol acetyltransferase (CAT) reporter gene which allows determination of the expression of human elastin promoter in different tissues. The highest CAT activity was found in the lungs and aorta, tissues rich in elastin, while lower levels were detected in a variety of other tissues, including skin. Assay of CAT activity in the lungs of fetal and newborn animals revealed high activity which progressively declined during the postnatal period up to six months. Thus, there was evidence of tissue-specific and developmentally regulated expression of the human elastin promoter activity in these mice. These animals were then used to examine the expression of the elastin gene by a variety of factors which have previously shown to alter elastin gene expression, as determined at the mRNA or protein levels. First, injection of transforming growth factor beta 1 (100 ng) subcutaneously into the transgenic animals resulted in a time-dependent elevation of the promoter activity up to 10-fold after a single injection. Secondly, enhancement of the human elastin promoter activity by interleukin 1 beta injected subcutaneously resulted in an approximately 10-fold elevation of the CAT activity. Finally, subcutaneous injection of these animals with triamcinolone acetonide or dexamethasone, two glucocorticosteroids in clinical use, resulted in marked enhancement of human elastin promoter activity. Similar changes were noted in fibroblast cultures established from the transgenic animals. These data indicate that the 5.2 kb upstream segment of the human elastin gene contains cis-elements which allow tissue-specific and developmentally regulated expression of the human elastin promoter. Furthermore, this segment of the gene contains responsive elements to a variety of cytokines and pharmacological agents. Collectively, these data indicate that elastin gene expression in the skin in vivo can be regulated at the transcriptional level.

Positive transcriptional regulatory element located within exon 1 of elastin gene

Elastin gene transcription is cell type specific and developmentally regulated, but the promoter often exhibits relatively weak activity in transient transfections of cells that express elastin at high levels. To search for positive-acting regulatory sequences, we isolated genomic clones spanning the mouse elastin gene and extensive 5'- and 3'-flanking regions. Restriction fragments of potential regulatory regions were ligated 5' or 3' relative to the active promoter to test for enhancer activity in transient transfections of fetal rat lung fibroblasts, which express elastin at high levels, and distal lung epithelial cells, which do not express detectable elastin. Fragments of intron 1 did not exhibit significant enhancer activity. Inclusion of the 84-bp exon 1 and adjacent 5'-untranslated region increased activity of the elastin promoter approximately sixfold compared with parental constructs. Transfections with constructs of varying promoter length showed that as little as 40 bp of the 5' end of exon 1 confers enhanced activity in elastin-expressing rat lung fibroblasts, but these constructs had variable activity in lung epithelial cell lines. This region, localized between the transcription start site and extending into exon 1, binds Sp1 in nuclear extracts from elastin-expressing cells. These studies indicate a role for the 5' end of the first exon of the elastin gene in regulating strong transcriptional activity in elastogenic cells.

All-trans-retinoic acid down-regulates elastin promoter activity elevated by ultraviolet B irradiation in cultured skin fibroblasts

Topical tretinoin therapy produces clinical improvements in the fine wrinkling of photodamaged skin, possibly by enhancement of collagen synthesis. A major biochemically and histologically detectable change in photodamaged skin is the accumulation of abnormal elastic fibers (elastotic material). However, little is known about the effects of retinoic acid and ultraviolet B (UVB) on elastin gene expression. Consequently, we examined the effects of all-trans-retinoic acid (t-RA) and UVB on elastin gene expression in cultured human skin fibroblasts in vitro. Elastin mRNA gene expression was up-regulated in response to UVB by approximately equal to 3-fold, in a dose dependent manner, between 3 and 10 mJ/cm2 doses. Similar results were obtained by chloramphenicol acetyltransferase assay, in which a maximal promoter activation more than 5.4-fold that in nonirradiated controls occurred after a single dose of 20 mJ/cm2. Also t-RA inhibited the increase in elastin mRNA level following a single exposure to UVB by approximately 16%, and the increase in promotor activity by about 65%. The inhibitory effect of t-RA on elastin induced by UVB was also demonstrated by indirect immunofluorescence studies. Taken together, t-RA down-regulated human elastin gene expression elevated by a single exposure to UVB at transcriptional and possibly protein levels. These results suggest that the anti-photoaging effect of t-RA may be related, at least in part, to down-regulation of elastin gene expression elevated by UVB.

Evaluation of sunscreens with various sun protection factors in a new transgenic mouse model of cutaneous photoaging that measures elastin promoter activation

BACKGROUND

Long-term sun exposure can cause major alterations in the papillary dermis, resulting in the deposition of massive amounts of abnormal elastic material, termed solar elastosis. Previous work has demonstrated that this type of photodamage is accompanied by an increase in elastin and fibrillin messenger RNAs and elastin promoter activity.

OBJECTIVE

Our purpose was to develop a rapid and sensitive in vivo method for evaluating compounds offering protection against cutaneous photodamage.

METHODS

Using a line of transgenic mice that expresses the human elastin promoter linked to a chloramphenicol acetyltransferase reporter gene, we applied sunscreens with various sun protection factors to 5-day-old mice followed by 30 minimal erythema doses of solar simulating radiation for three consecutive days.

RESULTS

Solar simulating radiation alone resulted in a fivefold increase in elastin promoter activity. Sun protection factors of 2, 4, 8, and 15 yielded a reduction in promoter activity by 2.8%, 42.5%, 58.1%, and 70.3%, respectively.

CONCLUSION

These results confirm the use of this system as a rapid and sensitive in vivo model for evaluating compounds that protect against photodamage.

8-methoxypsoralen and ultraviolet a radiation activate the human elastin promoter in transgenic mice: in vivo and in vitro evidence for gene induction

Treatment of skin diseases with the combination of 8-methoxypsoralen and ultraviolet A radiation (PUVA) results in clinical alterations in treated skin that resemble those observed in chronically photodamaged skin. The PUVA-treated patients develop nonmelanoma skin cancers, pigmentary alterations and wrinkling characteristic of sun-induced changes. The major alteration in the dermis of sun-damaged skin is the deposition of abnormal elastic fibers, termed solar elastosis. Up-regulation of elastin promoter activity in dermal fibroblasts explains the excess elastic tissue but not the reason for the aberrant morphology of the elastotic material. In order to study photoaging in an experimental system, we utilized a transgenic mouse line that expresses the human elastin promoter/chloramphenicol acetyltransferase construct in a tissue-specific and developmentally regulated manner. Although UVB radiation has been demonstrated to increase promoter activity in vitro, UVA fails to demonstrate a similar effect at the doses utilized. In this study, we demonstrate the ability of PUVA treatment to up-regulate elastin promoter activity both in vitro and in vivo. These data help to explain the development of photoaging in sun-protected PUVA-treated skin. We attribute the up-regulation of elastin promoter activity in response to PUVA to the formation of DNA photoadducts, which do not occur in response to UVA radiation alone.

Ultraviolet radiation activates the human elastin promoter in transgenic mice: a novel in vivo and in vitro model of cutaneous photoaging

The major alteration in photoaged skin is the deposition of massive amounts of abnormal elastic material, termed solar elastosis. In previous work, it has been shown that solar elastosis is accompanied by increased abundance of elastin and fibrillin mRNAs and upregulation of elastin promoter activity. Using a transgenic mouse line, which expresses the human elastin promoter, linked to a chloramphenicol acetyltransferase reporter gene, in a tissue-specific and developmentally regulated manner, we investigated the effects of ultraviolet A radiation and ultraviolet B radiation on human elastin promoter activity in vivo and in vitro. Irradiation of mice with a single dose of ultraviolet B radiation (491.4 mJ/cm2) resulted in an increase up to 8.5-fold in promoter activity, whereas a more modest increase of 1.8-fold was measured with ultraviolet A radiation (38.2 J/cm2). In addition, in vitro studies revealed over a thirtyfold increase in elastin promoter activity in response to ultraviolet B radiation (5.5 mJ/cm2), whereas no change was measured in response to ultraviolet A radiation (2.2 J/cm2). These results confirm the role of ultraviolet B radiation in elastin promoter activation in photoaging, and identify ultraviolet A radiation as a contributing factor. This system should serve as a useful in vivo and in vitro model to study cutaneous photoaging, and for testing compounds that may protect against cutaneous photodamage.