No abstract

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, is strongly expressed by epidermal keratinocytes during wound healing, in psoriasis, and in bullous diseases such as erythema multiforme and bullous pemphigoid. All of these disorders are characterized by increased microvascular permeability and angiogenesis. Since the development of erythema as a result of hyperpermeable blood vessels is also a common feature after excess sun exposure, we speculated about an up-regulation of VEGF expression by ultraviolet (UV) light. To test this hypothesis, we analyzed the effect of UVB irradiation on VEGF expression in cultured keratinocytes. Thereby we found a large increase in VEGF mRNA and protein levels upon irradiation of quiescent keratinocytes with sublethal and physiologically relevant doses of UVB. Although H2O2 was also a potent inducer of VEGF expression, the effect of UVB irradiation is unlikely to be mediated by reactive oxygen species as determined by the use of antioxidants. Further experiments revealed that the UVB-induced overexpression of VEGF is dependent on de novo protein synthesis and might occur via release of soluble mediators, which subsequently turn on VEGF expression. In summary, our results suggest a novel role of VEGF in the induction of erythema after excess sun exposure.

Due to its potent effect on fibroblast proliferation and extracellular matrix deposition, connective tissue growth factor (CTGF) seems to play an important role in the pathogenesis of fibrotic disease. Since glucocorticoids are frequently used for the therapy of these disorders, we determined a potential effect of these steroids on CTGF expression. In cultured fibroblasts, a striking induction of CTGF expression was observed after dexamethasone treatment and occurred in a time-and dosedependent manner. This effect was obviously not mediated by the CTGF inducer transforming growth factor-␤1, since expression of this factor was down-regulated by the glucocorticoid. Most importantly, CTGF expression levels also increased substantially in various tissues and organs by systemic glucocorticoid treatment of mice. After cutaneous injury, a strong induction of CTGF expression was seen in the wounds of nontreated mice. However, no further increase in the levels of CTGF mRNA occurred in wounded skin compared with unwounded skin of glucocorticoid-treated animals, suggesting the presence of other factors in the wound that might compensate for the effect of the steroids. Tumor necrosis factor-␣ was identified as a possible mediator of this effect because this factor suppressed CTGF expression in cultured fibroblasts and also blocked the glucocorticoid-induced CTGF production by these cells. These findings indicate that glucocorticoids stimulate CTGF expression in normal tissues and organs but not in highly inflamed areas.

No abstract

No abstract

Keratinocyte growth factor (KGF) has been implicated in wound re-epithelialization and branching morphogenesis of several organs. To determine whether KGF induces these effects via induction of matrix metalloproteinase expression we have analysed the effect of KGF on the expression of stromelysin-2 in cultured HaCaT keratinocytes. Here we show a strong induction of stromelysin-2 mRNA within 5-8 h of stimulation of these cells with KGF. The degree of induction was similar to that achieved by treatment with epidermal growth factor or tumour necrosis factor alpha, whereas the stimulatory effect of transforming growth factor beta 1 was even stronger. To determine whether the induction of stromelysin-2 expression by growth factors and cytokines might be important for wound healing, we analysed the expression of this gene during the healing process of full-thickness excisional wounds in mice. Whereas stromelysin-2 mRNA could hardly be detected in unwounded skin, a biphasic induction was seen after injury and highest levels were found at days 1 and 5 after wounding. Hybridization in situ revealed the presence of stromelysin-2 mRNA in basal keratinocytes at the wound edge but not in the underlying mesenchymal tissue. During impaired wound healing as seen in glucocorticoid-treated mice, stromelysin-2 expression was significantly increased compared with untreated control mice. Taken together, these results suggest that correct regulation of this broad-spectrum metalloproteinase might be important for normal repair.

Tristetraprolin (TTP) is a zinc finger protein that has been implicated in the control of tumor necrosis factor (TNF) mRNA stability. We show here that TTP protein has a suppressive effect on promoter elements from TNF-alpha and interleukin-8 and that lipopolysaccharide (LPS) stimulation can release this suppression. The release in LPS-stimulated cells was found to be primarily mediated by the p38 pathway because activation of p38 is sufficient to remove the suppressive effect of TTP. Indeed, TTP seems to be a direct substrate of p38 in vivo since it is an excellent substrate of p38 in vitro, and mutation of potential phosphorylation sites in TTP prevents release of the suppression imposed on TNF transcription. We found TTP protein to be present at low levels in the resting macrophage cell line RAW 264.7 and to be quickly induced after LPS stimulation. The kinetics of TTP induction suggests a potential role of TTP as an important player in switching off LPS-induced genes after induction. In conclusion, TTP plays an important role in maintaining gene quiescence, and this quenching effect on transcription can be released by p38 phosphorylation of TTP.

Several growth factors have been suggested to play a crucial role in liver regeneration, but a functional proof is still missing. Since fibroblast growth factors are important for the initiation of mammalian liver development, we determined the roles of these mitogens in liver repair by targeted expression of a dominant-negative fibroblast growth factor receptor (FGFR) in hepatocytes of transgenic mice. The liver of young animals appeared histologically normal, and liver function was not obviously impaired. In aged transgenic mice, the frequency of fatty liver development was strongly increased compared to control animals. Following partial hepatectomy, transgenic mice showed markedly reduced hepatocyte proliferation because of an arrest in the late G 1 phase of the cell cycle. These data demonstrate a key role of FGFR signalling in repair after liver injury.