Neue Konzepte zur Pathophysiologie und Therapie der Mukoviszidose

Today, the majority of cystic fibrosis (CF) patients treated in Germany have reached adulthood. However, with increasing age the morbidity and frequency of severe pulmonary complications continues to rise. Further optimization of conventional therapy alone will be insufficient to compensate for this development. In recent years, there has been impressive progress in our understanding of the molecular basis of the CF gene and its product, the cystic fibrosis transmembrane conductance regulator (CFTR). This knowledge can now be applied to develop new therapeutic strategies. However, important questions remain to be solved, i. e., little is known about the pathways that link the malfunctioning of the CFTR protein with the observed clinical phenotype. This review briefly touches on CF genetics as it applies to lung disease and will focus on the current hypotheses of CFTR (dys)function and its impact on pulmonary fluid homeostasis. New treatment options that target the molecular basis of the disease will be discussed.

Activation of PPARγ is not involved in butyrate-induced epithelial cell differentiation

Histone deacetylase-inhibitors affect growth and differentiation of intestinal epithelial cells by inducing expression of several transcription factors, e.g. Peroxisome proliferator-activated receptor gamma (PPARgamma) or vitamin D receptor (VDR). While activation of VDR by butyrate mainly seems to be responsible for cellular differentiation, the activation of PPARgamma in intestinal cells remains to be elucidated. The aim of this study was to determine the role of PPARgamma in butyrate-induced cell growth inhibition and differentiation induction in Caco-2 cells. Treatment with PPARgamma ligands ciglitazone and BADGE (bisphenol A diglycidyl) enhanced butyrate-induced cell growth inhibition in a dose- and time-dependent manner, whereas cell differentiation was unaffected after treatment with PPARgamma ligands rosiglitazone and MCC-555. Experiments were further performed in dominant-negative PPARgamma mutant cells leading to an increase in cell growth whereas butyrate-induced cell differentiation was again unaffected. The present study clearly demonstrated that PPARgamma is involved in butyrate-induced inhibition of cell growth, but seems not to play an essential role in butyrate-induced cell differentiation.

Incorporation of biodegradable nanoparticles into human airway epithelium cells-in vitro study of the suitability as a vehicle for drug or gene delivery in pulmonary diseases

PURPOSE

Nanoparticles are able to enhance drug or DNA stability for purposes of optimised deposition to targeted tissues. Surface modifications can mediate drug targeting. The suitability of nanoparticles synthesised out of porcine gelatin, human serum albumin, and polyalkylcyanoacrylate as drug and gene carriers for pulmonary application was investigated in vitro on primary airway epithelium cells and the cell line 16HBE14o-.

METHODS

The uptake of nanoparticles into these cells was examined by confocal laser scan microscopy (CLSM) and flow cytometry (FACS). Further the cytotoxicity of nanoparticles was evaluated by an LDH-release-test and the inflammatory potential of the nanoparticles was assessed by measuring IL-8 release.

RESULTS

CLSM and FACS experiments showed that the nanoparticles were incorporated into bronchial epithelial cells provoking little or no cytotoxicity and no inflammation as measured by IL-8 release.

CONCLUSIONS

Based on their low cytotoxicity and the missing inflammatory potential in combination with an efficient uptake in human bronchial epithelial cells, protein-based nanoparticles are suitable drug and gene carriers for pulmonary application.

Melanocytes respond to mechanical stretch by activation of mitogen-activated protein kinases (MAPK)

Cells of human epidermis are permanently targeted by mechanical stimuli. Besides mechanical forces from external sources the body itself generates mechanical forces via muscle contractions and growth processes. Recently, it was demonstrated that mechanical stretch is connected to enhanced proliferation in epidermal cells. The underlying biochemical events are still a matter of debate. Here we show that mechanical stretch leads to activation of both ERK1/2 and SAPK/JNK in human melanocytes and keratinocytes. In response to a 5 min single stretch ERK1/2 becomes moderately induced in melanocytes and peaked 30 min after the stimulus. In keratinocytes strong activation of ERK1/2 is present directly after the stimulus. SAPK/JNK shows the same activation pattern in both cell species--a slow but steady activation. The different kinetics of both MAPK suggest that different signalling cascades were activated. Future studies should evaluate the relevance of stretch-dependent MAPK activation in triggering the cell proliferation.

Signaling of mechanical stretch in human keratinocytes via MAP kinases

Cells within human skin are permanently exposed to mechanical stretching. Here we present evidence that alterations in cell shape trigger biochemical signaling via MAP kinases in human keratinocytes. In an in vitro attempt we demonstrate a fast but transient activation of extracellular signal-regulated kinases 1/2 in response to cell stretch. This activation is reversed by preincubation with functional blocking antibodies directed towards beta1-integrins. As a second member of MAP kinases, stress-activated protein kinase/c-JUN NH2-terminal kinase was activated in a slower fashion, peaking at 1 h after the initial stimulus. The delay in signal transmission suggests that extracellular signal-regulated kinases 1/2 and stress-activated protein kinase/c-JUN NH2-terminal kinase do not share the same signaling pathway. p38 was not activated by cell stretching. The contribution of cytoskeletal elements in signal perception and transduction was evaluated by selective disruption of either actin filaments, microtubules, or keratin filaments but showed no clear effect on stretch-induced activation of extracellular signal-regulated kinases 1/2 and stress-activated protein kinase/c-JUN NH2-terminal kinase. In conclusion we found evidence of a cell-shape-dependent activation of MAP kinases in human keratinocytes disclosing beta1-integrins as putative mechano-transducers. It is likely that alterations of skin mechanics in vivo underlying pathogenic processes like wound formation and healing trigger physiologic responses via the MAP kinase pathway.

Effects of short-term inhaled fluticasone on oxidative burst of sputum cells in cystic fibrosis patients

Inhaled corticosteroids have been proposed to decrease pulmonary inflammation in cystic fibrosis (CF). In this study the effects of therapy with inhaled fluticasone on clinical and sputum outcomes (leukocyte count, activity of myeloperoxidase, superoxide anion release) in adult CF patients were investigated in an open label design. Twenty-six stable patients (median+/-SD forced expiratory volume in one second (FEV1) 58.1+/-19.9% pred.) were randomly assigned to the study group (500 microg b.i.d., for three weeks) or the control group (n=14; nonsteroid medication). Sputum samples were obtained during inhalation of hypertonic saline (3%, 20 min), which was found not to alter the investigated sputum parameters. No significant changes in clinical parameters, sputum leukocyte count, activity of myeloperoxidase, and baseline superoxide anion release where observed following therapy. Surprisingly, stimulated superoxide anion release increased significantly after therapy (34.1+/-17.7 versus 25.2+/-17.4 nmol x hr(-1) x 10(6) cells, p<0.03) and exceeded spontaneous variability of this parameter (p=0.02 versus control group). In conclusion, in adult cystic fibrosis patients short-term fluticasone therapy had no evident effect on clinical and sputum parameters. Further investigations are necessary to evaluate whether the observed up-regulation of oxidative capacity of inflammatory cells is of concern or benefit in these patients.

Cyclic stretch up-regulates proliferation and heat shock protein 90 expression in human melanocytes

Human skin is repeatedly exposed to mechanical stretching in vivo, but in an ordinary culture of skin cells this prominent feature has been neglected. In order to study whether mechanical stretching plays a role for human melanocytes, we have established a culture technique to mimic this physical stretching: primary cultures of human melanocytes were plated on silicon supports, which undergo a stretching of about 10% of the initial length. After application of repeated stretching and relaxation for 4 days, cell count was significantly (about 40%) enhanced. In addition, we found approximately 2-fold increase in heat shock protein (HSP) 90, both at the protein and mRNA level. HSP 90 is known to bind to Raf-1 and, therefore, may contribute to the Raf-1-MEK (mitogen-activated protein-kinase kinase)-MAPK (mitogen-activated protein-kinase) signaling pathway. Disruption of the Raf-1-HSP 90 multimolecular complex by geldanamycin lead to a considerable decrease in melanocyte cell count. However, geldanamycin did not reverse the stretch-induced growth stimulation. Therefore, the stretch-mediated up-regulation of HSP 90 expression in melanocytes appears to be independent of stretch-mediated growth stimulation. These findings have strong implications for the in vitro cultivation of melanocytes for transplantation purposes.

Modulation of cystic fibrosis transmembrane conductance regulator gene - expression by elevation of intracellular cyclic AMP

Cystic fibrosis (CF) is caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Its product is a cyclic AMP-dependent Cl- channel, that is defective in CF. Since cAMP regulates the expression of many genes and since the 5'-flanking region of the CFTR gene contains cAMP response elements, we hypothesized that intracellular cAMP might modulate not only the cAMP-dependent Cl- channel CFTR, but also CFTR gene expression in epithelial cells. To accomplish this, we investigated Cl- secretion and CFTR-mRNA levels in HT-29 and T84 colon carcinoma epithelial cells before and after exposure to forskolin and 8-bromo-cAMP for 12 hr. While resting T84 cells increased Cl- secretion in response to forskolin strongly and immediately, HT-29 cells did not, although both cell lines showed highly increased Cl- efflux in response to A23187, a calcium ionophore. Interestingly, prolonged exposure to forskolin (12 hr) induced a clear decrease of CFTR-mRNA levels in T84 cells, but an increase of CFTR-mRNA levels in HT-29 cells, thus demonstrating different behaviour of CFTR gene regulation in different epithelial cells in response to intracellular cAMP. These results suggest that cells with an effective cAMP-dependent Cl- channel (CFTR) respond to prolonged stimulation of this channel with down-regulation of CFTR gene expression, while cells with no effective cAMP-dependent Cl--secretion respond with an up-regulation of CFTR gene expression.

Quantification of tyrosinase, TRP-1, and Trp-2 transcripts in human melanocytes by reverse transcriptase-competitive multiplex PCR--regulation by steroid hormones

We have introduced a reverse transcriptase polymerase chain reaction based method to measure mRNA levels of the melanogenesis enzymes tyrosinase, tyrosinase-related-protein 1 (TRP-1), and tyrosinase-related-protein 2 (TRP-2). Expression was determined by reverse transcriptase-competitive multiplex polymerase chain reaction of (i) melanogenesis enzyme transcripts and the "housekeeping" gene glyceraldehyde-3-phosphate dehydrogenase, and (ii) two internal standards consisting of mutated melanogenesis enzyme cDNA and mutated gene glyceraldehyde-3-phosphate dehydrogenase cDNA. This was investigated on in vitro cultured melanocytes in the presence of three different steroids; one glucocorticoid (betamethasone-17-valerate) and two sex steroids (diethylstilbestrol and estradiol). All three steroids lead to an increase of about 1.5-2.5-fold of tyrosinase transcripts. The amount of TRP-1 transcripts was likewise enhanced, but only moderately (approximately 1.5-fold). In contrast, TRP-2 transcripts were reduced by approximately 40% in number after betamethasone-17-valerate treatment, whereas the two sex steroids, diethylstilbestrol and estradiol, caused an upregulation of about 20-fold of the initial TRP-2 transcript level. We therefore suggest that hyperpigmentation during pregnancy or under contraceptive treatment is mediated by a direct induction of melanogenesis via sex steroids.

Candida albicans suppresses transcription of melanogenesis enzymes in cultured melanocytes

Human skin can be colonized by different yeasts that may have an impact on skin pigmentation. In order to study this effect normal human melanocytes were cultured with different yeasts. Reverse transcription polymerase chain reaction (RT-PCR) analysis gives evidence that Candida albicans suppresses the transcription of melanogenesis enzymes.