Marie E. Egan

In vitro pharmacologic restoration of CFTR-mediated chloride transport with sodium 4-phenylbutyrate in cystic fibrosis epithelial cells containing delta F508-CFTR.

The most common cystic fibrosis transmembrane conductance regulator mutation, delta F508-CFTR, is a partially functional chloride channel that is retained in the endoplasmic reticulum and degraded. We hypothesize that a known transcriptional regulator, sodium 4-phenylbutyrate (4PBA), will enable a greater fraction of delta F508-CFTR to escape degradation and appear at the cell surface. Primary cultures of nasal polyp epithelia from CF patients (delta F508 homozygous or heterozygous), or the CF bronchial epithelial cell line IB3-1 (delta F508/W1282X) were exposed to 4PBA for up to 7 d in culture. 4PBA treatment at concentrations of 0.1 and 2 mM resulted in the restoration of forskolin-activated chloride secretion. Protein kinase A-activated, linear, 10 pS chloride channels appeared at the plasma membrane of IB3-1 cells at the tested concentration of 2.5 mM. Treatment of IB3-1 cells with 0.1-1 mM 4PBA and primary nasal epithelia with 5 mM 4PBA also resulted in the appearance of higher molecular mass forms of CFTR consistent with addition and modification of oligosaccharides in the Golgi apparatus, as detected by immunoblotting of whole cell lysates with anti-CFTR antisera. Immunocytochemistry in CF epithelial cells treated with 4PBA was consistent with increasing amounts of delta F508-CFTR. These data indicate that 4PBA is a promising pharmacologic agent for inducing correction of the CF phenotype in CF patients carrying the delta F508 mutation.

Calcium-pump inhibitors induce functional surface expression of Delta F508-CFTR protein in cystic fibrosis epithelial cells.

The most common mutation in cystic fibrosis, ΔF508, results in a cystic fibrosis transmembrane conductance regulator (CFTR) protein that is retained in the endoplasmic reticulum (ER). Retention is dependent upon chaperone proteins, many of which require Ca++ for optimal activity. Interfering with chaperone activity by depleting ER Ca++ stores might allow functional ΔF508-CFTR to reach the cell surface. We exposed several cystic fibrosis cell lines to the ER Ca++ pump inhibitor thapsigargin and evaluated surface expression of ΔF508-CFTR. Treatment released ER-retained ΔF508-CFTR to the plasma membrane, where it functioned effectively as a Cl− channel. Treatment with aerosolized calcium-pump inhibitors reversed the nasal epithelial potential defect observed in a mouse model of ΔF508-CFTR expression. Thus, ER calcium-pump inhibitors represent a potential target for correcting the cystic fibrosis defect.

Pseudomonas aeruginosa chronic colonization in cystic fibrosis patients.

Purpose of review Chronic infection with Pseudomonas aeruginosa is a leading cause of morbidity and mortality in individuals with cystic fibrosis despite the aggressive use of antibiotics. P. aeruginosa employs a number of strategies that promote chronic pulmonary colonization instead of acute infection. These include biofilm formation, evasion of the host immune system, and conversion to a mucoid phenotype. This review discusses recent advances regarding P. aeruginosa pathogenesis and biofilm behavior in the setting of chronic pulmonary disease. Recent findings Biofilm formation in the cystic fibrosis lung likely occurs under anaerobic conditions, is controlled by bacterial quorum-sensing mechanisms, and is enhanced by environmental components in the cystic fibrosis airway. P. aeruginosa possesses regulatory pathways that recognize environmental cues to favor either acute infection or chronic colonization. P. aeruginosa that inhabit the respiratory tract accumulate mutations favoring chronic colonization. Azithromycin, a macrolide with clinical benefit in cystic fibrosis, alters P. aeruginosa biofilm formation. Promising new therapies that target biofilm formation include molecules that disrupt quorum sensing. Summary Eradication of P. aeruginosa in cystic fibrosis patients remains problematic. As more information emerges about P. aeruginosa behavior in vivo, potential therapeutics directed against biofilms and mucoid P. aeruginosa are being developed.

Macrophages Directly Contribute to the Exaggerated Inflammatory Response in Cystic Fibrosis Transmembrane Conductance Regulator−/− Mice

Pulmonary infection with an exaggerated inflammatory response is the major cause of morbidity and mortality in cystic fibrosis (CF). The objective of this study was to determine whether differences in the innate immune system underlie the exaggerated immune response in CF. We established a model that recapitulates the exaggerated immune response in a CF mouse model by exposure to Pseudomonas aeruginosa LPS and assessed the pulmonary cellular and cytokine responses of wild-type (WT) and CF mice. Compared with WT mice, CF mice had increased numbers of neutrophils and increased proinflammatory cytokines in their bronchoalveolar lavage fluid after LPS exposure. Based on the increased levels of IL-1alpha, IL-6, granulocyte colony-stimulating factor (G-CSF), and keratinocyte chemoattractant, all of which are known to be produced by macrophages, we tested whether two populations of macrophages, bone marrow-derived macrophages and alveolar macrophages, directly contribute to the elevated cytokine response of CF mice to LPS. After in vitro stimulation of bone marrow-derived macrophages and alveolar macrophages with LPS, IL-1alpha, IL-6, G-CSF, and monocyte chemoattractant protein-1 were higher in CF compared with WT cell supernatants. Quantitative analyses for IL-6 and keratinocyte chemoattractant revealed that LPS-stimulated CF macrophages have higher mRNA and intracellular protein levels compared with WT macrophages. Our data support the hypothesis that macrophages play a role in the exuberant cytokine production and secretion that characterizes CF, suggesting that the macrophage response may be an important therapeutic target for decreasing the morbidity of CF lung disease.

Partial correction of cystic fibrosis defects with PLGA nanoparticles encapsulating curcumin.

Cystic fibrosis (CF) is a common life threatening genetic disease (incidence: approximately 1 in 2500 live births). CF is caused by mutations in CFTR, a chloride channel involved in epithelial secretion of fluid and electrolytes. The most common mutation entails the deletion of a phenylalanine in position 508 that causes protein misfolding and abnormal CFTR processing. The DeltaF508 mutation accounts for approximately 70% of all CF alleles, and about 90% of CF patients carry at least one copy of DeltaF508 CFTR. Curcumin, a natural constituent of Curcuma longa (turmeric spice), is a nontoxic low-affinity SERCA (sarco (endo)plasmic reticulum calcium ATPase) pump inhibitor thought to permit DeltaF508 CFTR escape from the ER. The compound has been shown to be capable of correcting the defect in cell lines and mice expressing DeltaF508 CFTR. In this work, poly lactic-co-glycolic acid (PLGA) nanoparticles encapsulating curcumin were synthesized and used to treat two different CF mouse strains in an effort to correct the defects associated with CF by improving bioavailability of the compound, which has previously been a challenge in treatment with curcumin. Our results suggest that oral administration of PLGA nanoparticles encapsulating curcumin enhances the effects of curcumin therapy in CF mice, as compared to delivery of nonencapsulated curcumin.

Abnormal Trafficking and Degradation of TLR4 Underlie the Elevated Inflammatory Response in Cystic Fibrosis

Morbidity and mortality in cystic fibrosis (CF) are due not only to abnormal epithelial cell function, but also to an abnormal immune response. We have shown previously that macrophages lacking CF transmembrane conductance regulator (CFTR), the gene mutated in CF, contribute significantly to the hyperinflammatory response observed in CF. In this study, we show that lack of functional CFTR in murine macrophages causes abnormal TLR4 subcellular localization. Upon LPS stimulation, CFTR macrophages have prolonged TLR4 retention in the early endosome and reduced translocation into the lysosomal compartment. This abnormal TLR4 trafficking leads to increased LPS-induced activation of the NF-κB, MAPK, and IFN regulatory factor-3 pathways and decreased TLR4 degradation, which affects downregulation of the proinflammatory state. In addition to primary murine cells, mononuclear cells isolated from CF patients demonstrate similar defects in response to LPS. Moreover, specific inhibition of CFTR function induces abnormal TLR4 trafficking and enhances the inflammatory response of wild-type murine cells to LPS. Thus, functional CFTR in macrophages influences TLR4 spatial and temporal localization and perturbs LPS-mediated signaling in both murine CF models and patients with CF.

Engraftment of donor-derived epithelial cells in multiple organs following bone marrow transplantation into newborn mice.

Bone marrow‐derived cells (BMDCs) can engraft as epithelial cells throughout the body, including in the lung, liver, and gastrointestinal (GI) tract following transplantation into lethally irradiated adult recipients. Except for rare disease models in which marrow‐derived epithelial cells have a survival advantage over endogenous cells, the currently attained levels of epithelial engraftment of BMDCs are too low to be of therapeutic benefit. Here we tested whether the degree of bone marrow to epithelial engraftment would be higher if bone marrow transplantation (BMT) were performed on 1‐day‐old mice, when tissues are undergoing rapid growth and remodeling. BMT into newborn mice after multiple different regimens allowed for robust hematopoietic engraftment, as well as the development of rare donor‐derived epithelial cells in the GI tract and lung but not in the liver. The highest epithelial engraftment (0.02%) was obtained in mice that received a preparative regimen of two doses of busulfan in utero. When BMDCs were transplanted into myelosuppressed newborn mice that lacked expression of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, the chloride channel that is not functional in patients with cystic fibrosis, the engrafted mice showed partial restoration of CFTR channel activity, suggesting that marrow‐derived epithelial cells in the GI tract were functional. However, BMT into newborn mice, regardless of the myeloablative regimen used, did not increase the number of bone marrow‐derived epithelial cells over that which occurs after BMT into lethally irradiated adult mice.

CFTR is functionally active in GnRH-expressing GT1-7 hypothalamic neurons.

We have demonstrated the expression of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, mRNA, and protein within the rat and human brains, in areas regulating sexual differentiation and function. We have found that GT1-7, a gonadotropin-releasing hormone (GnRH)-secreting hypothalamic neuronal cell line, expresses the CFTR gene, mRNA, and protein and cAMP-dependent 36Cl efflux. A linear 7-pS Cl- conductance, which is stimulated by ATP and cAMP analogs and inhibited by glibenclamide, consistent with CFTR activity, has been identified in GT1-7 cells. Antisense oligo(dN) generated against exon 10 of the CFTR gene transcript (mRNA) inhibit GnRH secretion into media [312 ± 73, 850 ± 150, 963 ± 304, and 912 ± 74 pg GnRH/4 × 106 cells for antisense, sense, missense, and no oligo(dN), respectively; P < 0.029 for antisense oligo(dN)-treated vs. normal cells]. No changes in intracellular synthesis of GnRH were noted [1,400 ± 371 and 1,395 ± 384 pg GnRH/4 × 106 cells for antisense and sense oligo(dN), respectively]. Antisense oligo(dN), but not sense or missense oligo(dN), inhibited cAMP-dependent36Cl efflux. The expression of CFTR protein, detected by Western blotting, was also inhibited 68% by preincubation of cells with antisense oligo(dN). GT1-7 hypothalamic neurons express the CFTR gene, mRNA, and protein, which modulate neurosecretion. Abnormal neuropeptide vesicle trafficking by mutant CFTR may help to explain some of the diverse manifestations of cystic fibrosis.We have demonstrated the expression of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, mRNA, and protein within the rat and human brains, in areas regulating sexual differentiation and function. We have found that GT1-7, a gonadotropin-releasing hormone (GnRH)-secreting hypothalamic neuronal cell line, expresses the CFTR gene, mRNA, and protein and cAMP-dependent (36)Cl efflux. A linear 7-pS Cl- conductance, which is stimulated by ATP and cAMP analogs and inhibited by glibenclamide, consistent with CFTR activity, has been identified in GT1-7 cells. Antisense oligo(dN) generated against exon 10 of the CFTR gene transcript (mRNA) inhibit GnRH secretion into media [312 +/- 73, 850 +/- 150, 963 +/- 304, and 912 +/- 74 pg GnRH/4 x 10(6) cells for antisense, sense, missense, and no oligo(dN), respectively; P < 0. 029 for antisense oligo(dN)-treated vs. normal cells]. No changes in intracellular synthesis of GnRH were noted [1,400 +/- 371 and 1,395 +/- 384 pg GnRH/4 x 10(6) cells for antisense and sense oligo(dN), respectively]. Antisense oligo(dN), but not sense or missense oligo(dN), inhibited cAMP-dependent 36Cl efflux. The expression of CFTR protein, detected by Western blotting, was also inhibited 68% by preincubation of cells with antisense oligo(dN). GT1-7 hypothalamic neurons express the CFTR gene, mRNA, and protein, which modulate neurosecretion. Abnormal neuropeptide vesicle trafficking by mutant CFTR may help to explain some of the diverse manifestations of cystic fibrosis.

CFTR is required for PKA-regulated ATP sensitivity of Kir1.1 potassium channels in mouse kidney

The cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel plays vital roles in fluid transport in many epithelia. While CFTR is expressed along the entire nephron, its function in renal tubule epithelial cells remains unclear, as no specific renal phenotype has been identified in cystic fibrosis. CFTR has been proposed as a regulator of the 30 pS, ATP-sensitive renal K channel (Kir1.1, also known as renal outer medullar K [ROMK]) that is critical for K secretion by cells of the thick ascending limb (TAL) and distal nephron segments responsive to aldosterone. We report here that both ATP and glibenclamide sensitivities of the 30 pS K channel in TAL cells were absent in mice lacking CFTR and in mice homozygous for the deltaF508 mutation. Curcumin treatment in deltaF508-CFTR mice partially reversed the defect in ATP sensitivity. We demonstrate that the effect of CFTR on ATP sensitivity was abrogated by increasing PKA activity. We propose that CFTR regulates the renal K secretory channel by providing a PKA-regulated functional switch that determines the distribution of open and ATP-inhibited K channels in apical membranes. We discuss the potential physiological role of this functional switch in renal K handling during water diuresis and the relevance to renal K homeostasis in cystic fibrosis.

A functional CFTR-NBF1 is required for ROMK2-CFTR interaction

In a previous study on inside-out patches of Xenopus oocytes, we demonstrated that the cystic fibrosis transmembrane conductance regulator (CFTR) enhances the glibenclamide sensitivity of a coexpressed inwardly rectifying K+ channel, ROMK2 (C. M. McNicholas, W. B. Guggino, E. M. Schwiebert, S. C. Hebert, G. Giebisch, and M. E. Egan. Proc. Natl. Acad. Sci. USA 93: 8083-8088, 1996). In the present study, we used the two-microelectrode voltage-clamp technique to measure whole cell K+ currents in Xenopus oocytes, and we further characterized the enhanced sensitivity of ROMK2 to glibenclamide by CFTR. Glibenclamide inhibited K+currents by 56% in oocytes expressing both ROMK2 and CFTR but only 11% in oocytes expressing ROMK2 alone. To examine the role of the first nucleotide binding fold (NBF1) of CFTR in the ROMK2-CFTR interaction, we studied the glibenclamide sensitivity of ROMK2 when coexpressed with CFTR constructs containing mutations in or around the NBF1 domain. In oocytes coinjected with ROMK2 and a truncated construct of CFTR with an intact NBF1 (CFTR-K593X), glibenclamide inhibited K+ currents by 46%. However, in oocytes coinjected with ROMK2 and a CFTR mutant truncated immediately before NBF1 (CFTR-K370X), glibenclamide inhibited K+ currents by 12%. Also, oocytes expressing both ROMK2 and CFTR mutants with naturally occurring NBF1 point mutations, CFTR-G551D or CFTR-A455E, display glibenclamide-inhibitable K+currents of only 14 and 25%, respectively. Because CFTR mutations that alter the NBF1 domain reduce the glibenclamide sensitivity of the coexpressed ROMK2 channel, we conclude that the NBF1 motif is necessary for the CFTR-ROMK2 interaction that confers sulfonylurea sensitivity.