Hair cycle and wound healing in mice with a keratinocyte-restricted deletion of FAK

Focal adhesion kinase (FAK) is a critical component in transducing signals downstream of both integrins and growth factor receptors. To determine how the loss of FAK affects the epidermis in vivo, we have generated a mouse model with a keratinocyte-restricted deletion of fak (FAKK5 KO mice). FAK(K5 KO) mice displayed three major phenotypes--irregularities of hair cycle, sebaceous glands hypoplasia, and a thinner epidermis--pointing to defects in the proliferative capacity of multipotent stem cells found in the bulge. FAK-null keratinocytes in conventional primary culture undergo massive apoptosis hindering further analyses, whereas the defects observed in vivo do not shorten the mouse lifespan. These results suggest that the structure and the signaling environment of the native tissue may overcome the lack of signaling through FAK. Our findings point to the importance of in vivo and three-dimensional in vitro models in analyses of cell migration, proliferation, and survival. Surprisingly, the difference between FAKloxP/+ and FAKK5 KO mice in wound closure was not statistically significant, suggesting that in vivo loss of FAK does not affect migration/proliferation of basal keratinocytes in the same way as it affects multipotent stem cells of the skin.

Resistance of differentiated human airway epithelium to infection by rhinovirus

Virtually all in vitro studies of the effects of rhinovirus on human airway epithelium have used cells grown under conditions known to produce low levels of differentiation. The relevance of the results to native epithelium is questionable. Here we grew primary cultures of human tracheal or nasal epithelium under three conditions. One condition produced pseudostratified, mucociliary cells virtually indistinguishable from native epithelium. The other two conditions produced undifferentiated squamous cells lacking cilia. Cells were infected for 6 h with rhinovirus-16. After a 24-h incubation period, we determined levels of viral RNA in the cells, numbers of infectious viral particles released in the mucosal medium, expression of a variety of epithelial cytokines and other proteins, release of IL-6 and IL-8, and transepithelial electrical resistance and voltage. After infection, levels of viral RNA in the poorly differentiated cells were 30 or 130 times those in the differentiated. Furthermore, expression of mRNA for inflammatory cytokines, release of infectious particles, and release of IL-6 and IL-8 were closely correlated with the degree of viral infection. Thus well-differentiated cells are much more resistant to viral infection and its functional consequences than are poorly differentiated cells from the same source.

Interleukin-13 induces dramatically different transcriptional programs in three human airway cell types

Interleukin (IL)-13, a cytokine released by T lymphocytes during immediate hypersensitivity responses, is a central mediator of asthma. Because IL-13 induces phenotypic features of asthma in mice deficient in T and B lymphocytes, it is likely that this cytokine contributes to the development of asthma by acting directly on resident airway cells. To analyze the global effects of IL-13 on gene expression in airway cells that could contribute to the phenotypic features of asthma, we used Genechip HuGene FL arrays (Affymetrix, Santa Clara, CA) that contain probes for approximately 6,500 human genes. Despite activating a common signaling pathway, IL-13 induced dramatically different patterns of gene expression in primary cultures of airway epithelial cells, airway smooth muscle cells, and lung fibroblasts, with little overlap among cell types. The most prominent effects of IL-13 were on airway smooth muscle, but several genes induced in airway epithelial cells and fibroblasts are also candidates that may contribute to phenotypic features of asthma. These results suggest that the in vivo response to IL-13 in the airways likely results from a combination of distinct effects on each of several resident airway cell types.

Mild and moderate asthma is associated with airway goblet cell hyperplasia and abnormalities in mucin gene expression

Excessive airway mucus is an important cause of morbidity and mortality in asthma, but the relationship between accumulation of mucus and goblet cell size, number, and function is incompletely understood. To address these questions, stored mucin in the epithelium and goblet cell size and number were measured morphometrically, and mucin gene expression was measured by polymerase chain reaction and immunohistochemistry in endobronchial biopsies from 13 subjects with mild and moderate asthma and from 12 healthy control subjects. Secreted mucin was measured in induced sputum. We found that stored mucin in the airway epithelium was three times higher than normal in the subjects with asthma (p < 0.005). Goblet cell size was similar in both groups, but goblet cell number was significantly higher in the subjects with asthma (93,043 +/- 15,824 versus 41,959 +/- 9,230/mm3, p < 0.05). In mild asthma (FEV1 > or = 80% pred, n = 7), the level of stored mucin was as high as in moderate asthma (FEV1 < 80% pred, n = 6), but the level of secreted mucin was significantly lower (28.4 +/- 6.3 versus 73.5 +/- 47.5 microg/ml, p < 0.05). Secreted mucin was inversely correlated with stored mucin for the whole asthma group (rs = -0.78, p = 0.007). MUC5AC was the predominant mucin gene expressed in healthy subjects and subjects with asthma, and MUC5AC protein was increased in the subjects with asthma. We conclude that even mild asthma is associated with goblet cell hyperplasia and increased stored mucin in the airway epithelium, whereas moderate asthma is associated with increased stored mucin and secreted mucin. These findings suggest that acute degranulation of hyperplastic goblet cells may represent a mechanism for asthma exacerbations in mild and moderate asthma and that chronic degranulation of goblet cells may contribute to chronic airway narrowing in moderate asthma.

Coexpression of the interleukin-13 and interleukin-4 genes correlates with their physical linkage in the cytokine gene cluster on human chromosome 5q23-31

Interleukin-13 (IL-13) and IL-4 are cytokines produced by T cells that are encoded by the q23-31 region of human chromosome 5. To investigate the regulation of IL-13 gene expression by T cells, we isolated and sequenced the human IL-13 gene, analyzed its 5'-flanking region for potential transcriptional activation elements, and examined its expression in nontransformed T-lineage cell populations. The human IL-13 gene was located 12.5-kb upstream of the IL-4 gene and 2-kb downstream of a CpG island. The IL-13 gene 5' flank region included a segment with sequence homology to P elements of the IL-4 promoter involved in transcriptional activation in T cells. Mutation of the IL-13 P element site significantly reduced IL-13 promoter activity in response to T-cell activation. Oligonucleotides containing the IL-13 or IL-4 P element sites specifically bound the transcriptional activator protein, nuclear factor-activated T cells, preformed (NF-ATp), when incubated with nuclear protein extracts from activated T cells. Similar to IL-4, IL-13 mRNA expression was highest in T-cell populations enriched for cells that had previously been primed in vivo or in vitro, indicating that priming increases the expression of the IL-13 and IL-4 genes in a coordinate manner. Because the primed T cells contain higher levels of nuclear NF-ATp, capable of binding to P elements of the IL-4 and IL-13 promoters, than do freshly-isolated T cells, the NF-AT-binding P elements are attractive candidates to mediate the coordinate expression of these two cytokine genes.

Detection of three rare frameshift mutations in the cystic fibrosis gene in an African-American (CF444delA), an Italian (CF2522insC), and a Soviet (CF3821delT)

We have identified three new frameshift mutations in the CFTR gene in patients with cystic fibrosis (CF). The first one involves the deletion of an adenine nucleotide in exon 4 in an African-American patient (CF444delA), the second involves the insertion of a cytosine nucleotide in exon 13 in an Italian patient (CF2522insC), and the third results from the deletion of a thymidine nucleotide in exon 19 in a Soviet patient (CF3821delT). Each mutation is predicted to result in premature termination of the CFTR protein.