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What Causes Cystic Fibrosis (References)

References cystic fibrosis and cell hypoxia (low oxygen levels)

Yeger H, Pan J, Fu XW, Bear C, Cutz E, Expression of CFTR and Cl(-) conductances in cells of pulmonary neuroepithelial bodies, Am J Physiol Lung Cell Mol Physiol. 2001 Sep;281(3):L713-21.
The pulmonary neuroendocrine cell system comprises solitary neuroendocrine cells and clusters of innervated cells or neuroepithelial bodies (NEBs). NEBs figure prominently during the perinatal period when they are postulated to be involved in physiological adaptation to air breathing. Previous studies have documented hyperplasia of NEBs in cystic fibrosis (CF) lungs and increased neuropeptide (bombesin) content produced by these cells, possibly secondary to chronic hypoxia related to CF lung disease...

Zheng W, Kuhlicke J, Jäckel K, Eltzschig HK, Singh A, Sjöblom M, Riederer B, Weinhold C, Seidler U, Colgan SP, Karhausen J, Hypoxia inducible factor-1 (HIF-1)-mediated repression of cystic fibrosis transmembrane conductance regulator (CFTR) in the intestinal epithelium, FASEB J. 2009 Jan; 23(1): 204-13.
Diarrhea is widespread in intestinal diseases involving ischemia and/or hypoxia. Since hypoxia alters stimulated Cl(-) and water flux, we investigated the influence of such a physiologically and pathophysiologically important signal on expression of the cystic fibrosis transmembrane conductance regulator (CFTR). Located on the apical membrane, this cAMP-activated Cl(-) channel determines salt and fluid transport across mucosal surfaces. Our studies revealed depression of CFTR mRNA, protein, and function in hypoxic epithelia. Chromatin immunoprecipitation identified a previously unappreciated binding site for the hypoxia inducible factor-1 (HIF-1), and promoter studies established its relevance by loss of repression following point mutation. Consequently, HIF-1 overexpressing cells exhibited significantly reduced transport capacity in colorimetric Cl(-) efflux studies, altered short circuit measurements, and changes in transepithelial fluid movement. Whole-body hypoxia in wild-type mice resulted in significantly reduced small intestinal fluid and HCO(3)(-) secretory responses to forskolin. Experiments performed in Cftr(-/-) and Nkcc1(-/-) mice underlined the role of altered CFTR expression for these functional changes, and work in conditional Hif1a mutant mice verified HIF-1-dependent CFTR regulation in vivo. In summary, our study clarifies CFTR regulation and introduces the concept of a HIF-1-orchestrated response designed to regulate ion and fluid movement across hypoxic intestinal epithelia.

Bebök Z, Tousson A, Schwiebert LM, Venglarik CJ, Improved oxygenation promotes CFTR maturation and trafficking in MDCK monolayers, Am J Physiol Cell Physiol. 2001 Jan; 280(1): C135-45.
Culturing airway epithelial cells with most of the apical media removed (air-liquid interface) has been shown to enhance cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl(-) secretory current. Thus we hypothesized that cellular oxygenation may modulate CFTR expression. We tested this notion using type I Madin-Darby canine kidney cells that endogenously express low levels of CFTR. Growing monolayers of these cells for 4 to 5 days with an air-liquid interface caused a 50-fold increase in forskolin-stimulated Cl(-) current, compared with conventional (submerged) controls. Assaying for possible changes in CFTR by immunoprecipitation and immunocytochemical localization revealed that CFTR appeared as an immature 140-kDa form intracellularly in conventional cultures. In contrast, monolayers grown with an air-liquid interface possessed more CFTR protein, accompanied by increases toward the mature 170-kDa form and apical membrane staining. Culturing submerged monolayers with 95% O(2) produced similar improvements in Cl(-) current and CFTR protein as air-liquid interface culture, while increasing PO(2) from 2.5% to 20% in air-liquid interface cultures yielded graded enhancements. Together, our data indicate that improved cellular oxygenation can increase endogenous CFTR maturation and/or trafficking.

Guimbellot JS, Fortenberry JA, Siegal GP, Moore B, Wen H, Venglarik C, Chen YF, Oparil S, Sorscher EJ, Hong JS, Role of oxygen availability in CFTR expression and function, Am J Respir Cell Mol Biol. 2008 Nov; 39(5): 514-21.
The cystic fibrosis transmembrane conductance regulator (CFTR) serves a pivotal role in normal epithelial homeostasis; its absence leads to destruction of exocrine tissues, including those of the gastrointestinal tract and lung. Acute regulation of CFTR protein in response to environmental stimuli occurs at several levels (e.g., ion channel phosphorylation, ATP hydrolysis, apical membrane recycling). However, less information is available concerning the regulatory pathways that control levels of CFTR mRNA. In the present study, we investigated regulation of CFTR mRNA during oxygen restriction, examined effects of hypoxic signaling on chloride transport across cell monolayers, and related these findings to a possible role in the pathogenesis of chronic hypoxic lung disease. CFTR mRNA, protein, and function were robustly and reversibly altered in human cells in relation to hypoxia. In mice subjected to low oxygen in vivo, CFTR mRNA expression in airways, gastrointestinal tissues, and liver was repressed. CFTR mRNA expression was also diminished in pulmonary tissues taken from hypoxemic subjects at the time of lung transplantation. Environmental factors that induce hypoxic signaling regulate CFTR mRNA and epithelial Cl(-) transport in vitro and in vivo.

Clerici C, Matthay MA, Hypoxia regulates gene expression of alveolar epithelial transport proteins, J Appl Physiol. 2000 May;88(5):1890-6.

Karle C, Gehrig T, Wodopia R, Höschele S, Kreye VA, Katus HA, Bärtsch P, Mairbäurl H, Hypoxia-induced inhibition of whole cell membrane currents and ion transport of A549 cells, Am J Physiol Lung Cell Mol Physiol. 2004 Jun; 286(6): L1154-60.
In excitable cells, hypoxia inhibits K channels, causes membrane depolarization, and initiates complex adaptive mechanisms... These results indicate that hypoxia, membrane depolarization, and K-channel inhibition decrease whole cell membrane currents and transport activity. It appears, therefore, that a hypoxia-induced change in membrane conductance and membrane potential might be a link between hypoxia and alveolar ion transport inhibition.

Mairbaurl H, Mayer K, Kim KJ, Borok Z, Bartsch P, and Crandall ED, Hypoxia decreases active Na transport across primary rat alveolar epithelial cell monolayers, Am J Physiol Lung Cell Mol Physiol 282:
L659–L665, 2002.

Mairbaurl H, Wodopia R, Eckes S, Schulz S, and Bartsch P, Impairment of cation transport in A549 cells and rat alveolar epithelial cells by hypoxia, Am J Physiol Lung Cell Mol Physiol 273: L797–L806, 1997.

Planes C, Escoubet B, BlotChabaud M, Friedlander G, Farman N, and Clerici C, Hypoxia downregulates expression and activity of epithelial sodium channels in rat alveolar epithelial cells, Am J Respir Cell Mol Biol 17: 508–518, 1997.

Wodopia R, Ko HS, Billian J, Wiesner R, Ba¨rtsch P, and Mairbaurl, H. Hypoxia decreases proteins involved in transepithelial electrolyte transport of A549 cells and rat lung, Am J Physiol Lung Cell Mol Physiol 279: L1110–L1119, 2000.

Am J Clin Nutr 1999;69:913–9.
Energy expenditure and substrate utilization in adults with cystic fibrosis and diabetes mellitus
Ward SA, Tomezsko JL, Holsclaw DS, Paolone AM
... Results: In all 3 periods, minute ventilation was higher in the CF and CFDM groups than in the control subjects (P < 0.01).

Chest. 1990 Jun;97(6):1317-21.
Importance of respiratory rate as an indicator of respiratory dysfunction in patients with cystic fibrosis.
Browning IB, D'Alonzo GE, Tobin MJ.
... Respiratory frequency was increased in the patients with cystic fibrosis compared with a group of healthy control subjects, as was minute ventilation and mean inspiratory flow. Respiratory frequency was a sensitive predictor of respiratory dysfunction, being significantly (p less than 0.05) correlated with airway obstruction (r = 0.76), hyperinflation (r = 0.52), arterial oxygenation (r = -0.59), rib cage-abdominal discoordination (r = 0.54), and maximum ventilation during exercise (r = 0.66).

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