Intestinal CFTR expression alleviates meconium ileus in cystic fibrosis pigs

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The ΔF508 mutation causes CFTR misprocessing and cystic fibrosis-like disease in pigs

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel. The most common CF-associated mutation is ΔF508, which deletes a phenylalanine in position 508. In vitro studies indicate that the resultant protein, CFTR-ΔF508, is misprocessed, although the in vivo consequences of this mutation remain uncertain. To better understand the effects of the ΔF508 mutation in vivo, we produced CFTR ΔF508/ΔF508 pigs. Our biochemical, immunocytochemical, and electrophysiological data on CFTR-ΔF508 in newborn pigs paralleled in vitro predictions. They also indicated that CFTR ΔF508/ΔF508 airway epithelia retain a small residual CFTR conductance, with maximal stimulation producing ∼6% of wild-type function. Cyclic adenosine 3′,5′-monophosphate (cAMP) agonists were less potent at stimulating current in CFTR ΔF508/ΔF508 epithelia, suggesting that quantitative tests of maximal anion current may overestimate transport under physiological conditions. Despite residual CFTR function, four older CFTR ΔF508/ΔF508 pigs developed lung disease similar to human CF. These results suggest that this limited CFTR activity is insufficient to prevent lung or gastrointestinal disease in CF pigs. These data also suggest that studies of recombinant CFTR-ΔF508 misprocessing predict in vivo behavior, which validates its use in biochemical and drug discovery experiments. These findings help elucidate the molecular pathogenesis of the common CF mutation and will guide strategies for developing new therapeutics.link_to_subscribed_fulltex

Processing and function of CFTR-ΔF508 are species-dependent

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis. The most common mutation, a deletion of the phenylalanine at position 508 (ΔF508), disrupts processing of the protein. Nearly all human CFTR-ΔF508 is retained in the endoplasmic reticulum and degraded, preventing maturation to the plasma membrane. In addition, the F508 deletion reduces the activity of single CFTR channels. Human CFTR-ΔF508 has been extensively studied to better understand its defects. Here, we adopted a cross-species comparative approach, examining human, pig, and mouse CFTR-ΔF508. As with human CFTR-ΔF508, the ΔF508 mutation reduced the single-channel activity of the pig and mouse channels. However, the mutant pig and mouse proteins were at least partially processed like their wild-type counterparts. Moreover, pig and mouse CFTR-ΔF508 partially restored transepithelial Cl− transport to CF airway epithelia. Our data, combined with earlier work, suggest that there is a gradient in the severity of the CFTR-ΔF508 processing defect, with human more severe than pig or mouse. These findings may explain some previously puzzling observations in CF mice, they have important implications for evaluation of potential therapeutics, and they suggest new strategies for discovering the mechanisms that disrupt processing of human CFTR-ΔF508