Temporal regulation of CFTR expression during ovine lung development: implications for CF gene therapy

Abstract

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a small conductance chloride ion channel that may interact directly with other channels including the epithelial sodium channel (ENaC). CFTR is known to be more abundant in the airway epithelium during the second trimester of human development than after birth. This could be a consequence of the change in function of the respiratory epithelium from chloride secretion to sodium absorption near term. Alternatively it might reflect an additional role for CFTR in the developing airway epithelium. Though the lung epithelia of CF fetuses and infants rarely show gross histological abnormalities, there is often evidence of inflammation. Our aim was to establish whether CFTR expression levels correlated with specific developmental stages or differentiated functions in the ovine fetal lung. We evaluated CFTR expression using a quantitative assay of mRNA at 14 time points through gestation and showed highest levels at the start of the second trimester followed by a gradual decline through to term. In contrast, ENaC expression increased from the start of the third trimester. These results support a role for CFTR in differentiation of the respiratory epithelium and suggest that its expression levels are not merely reflecting major changes in the sodium/chloride bulk flow close to term. These observations may have significant implications for the likely success of CF gene therapy in the postnatal lung.

Cystic fibrosis transmembrane conductance regulator (CFTR) dependent cytoskeletal tension during lung organogenesis

“…This is consistent with a growing body of evidence that CF patient lungs are abnormal at birth (Sharp, 2002;Farrell et al, 2003); that CFTR heterozygous and knockout lungs are different from homozygous normal mice (Cohen et al, 2004a); that in utero CFTR can reverse the CFTR knockout phenotype in the lungs (Fig. 9) and intestines (Larson et al, 1997); that CFTR is expressed at high levels in the developing lung (Broackes-Carter et al, 2002); and finally that transient in utero knockout of CFTR results in a CF phenotype in animals with a nor- mal CFTR genotype (Cohen and Larson, 2005).…”

“…Additional evidence for the role of CFTR in lung organogenesis was obtained in expression studies in the fetal lung (Broackes-Carter et al, 2002). Expression of cftr-specific mRNA is approximately 75-fold greater in the fetal lung than in the adult lung (Broackes-Carter et al, 2002), and is distributed in temporal and tissuespecific patterns (Tizzano et al, 1993(Tizzano et al, , 1994Trezise et al, 1993).…”

“…Expression of cftr-specific mRNA is approximately 75-fold greater in the fetal lung than in the adult lung (Broackes-Carter et al, 2002), and is distributed in temporal and tissuespecific patterns (Tizzano et al, 1993(Tizzano et al, , 1994Trezise et al, 1993). CFTR is primarily expressed in the undifferentiated multipotent stem cells of the first-and second-trimester pulmonary epithelium, an indicator of its role in differentiation.…”

Transcription factors and miRNAs that regulate fetal to adultCFTRexpression change are new targets for cystic fibrosis

“…Expression studies carried out in humans, mice and goats have revealed that the CFTR gene is developmentally regulated [10,[12][13][14]45]. The most well-known site of developmentally regulated CFTR expression is the airway surface epithelium, with relatively high expression during embryonic and fetal development, followed by a marked decrease in expression after birth [45].…”

“…The most well-known site of developmentally regulated CFTR expression is the airway surface epithelium, with relatively high expression during embryonic and fetal development, followed by a marked decrease in expression after birth [45]. Despite extensive studies, the mechanisms accounting for this switch in CFTR expression remain unknown.…”