CFTR Cl− channel function in native human colon correlates with the genotype and phenotype in cystic fibrosis

BACKGROUND & AIMS: Cystic fibrosis (CF) is caused by over 1000 mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and presents with a widely variable phenotype. Genotype-phenotype studies identified CFTR mutations that were associated with pancreatic sufficiency (PS). Residual Cl- channel function was shown for selected PS mutations in heterologous cells. However, the functional consequences of most CFTR mutations in native epithelia are not well established. METHODS: To elucidate the relationships between epithelial CFTR function, CFTR genotype, and patient phenotype, we measured cyclic adenosine monophosphate (cAMP)-mediated Cl- secretion in rectal biopsy specimens from 45 CF patients who had at least 1 non-DeltaF508 mutation carrying a wide spectrum of CFTR mutations. We compared CFTR genotypes and clinical manifestations of CF patients who expressed residual CFTR-mediated Cl- secretion with patients in whom Cl- secretion was absent. RESULTS: Residual anion secretion was detected in 40% of CF patients, and was associated with later disease onset (P < 0.0001), higher frequency of PS (P < 0.0001), and less severe lung disease (P < 0.05). Clinical outcomes correlated with the magnitude of residual CFTR activity, which was in the range of approximately 12%-54% of controls. CONCLUSIONS: Specific CFTR mutations confer residual CFTR function to rectal epithelia, which is related closely to a mild disease phenotype. Quantification of rectal CFTR-mediated Cl- secretion may be a sensitive test to predict the prognosis of CF disease and identify CF patients who would benefit from therapeutic strategies that would increase residual CFTR activity

Modulation of Ca2+-activated Cl- secretion by basolateral K+ channels in human normal and cystic fibrosis airway epithelia

Human airway epithelia express Ca-activated Cl channels (CaCC) that are activated by extracellular nucleotides (ATP and UTP). CaCC is preserved and seems to be up-regulated in the airways of cystic fibrosis (CF) patients. In the present study, we examined the role of basolateral K channels in CaCC-mediated Cl secretion in native nasal tissues from normal individuals and CF patients by measuring ion transport in perfused micro Ussing chambers. In the presence of amiloride, UTP-mediated peak secretory responses were increased in CF compared with normal nasal tissues. Activation of the cAMP pathway further increased CaCC-mediated secretion in CF but not in normal nasal mucosa. CaCC-dependent ion transport was inhibited by the chromanol 293B, an inhibitor of cAMP-activated hKvLQT1 K channels, and by clotrimazole, an inhibitor of Ca-activated hSK4 K channels. The K channel opener 1-ethyl-2-benzimidazolinone further increased CaCC-mediated Cl secretion in normal and CF tissues. Expression of hSK4 as well as hCACC-2 and hCACC-3 but not hCACC-1 was demonstrated by reverse transcriptase PCR on native nasal tissues. We conclude that Ca-activated Cl secretion in native human airway epithelia requires activation of Ca-dependent basolateral K channels (hSK4). Co-activation of hKvLQT1 improves CaCC-mediated Cl secretion in native CF airway epithelia, and may have a therapeutic effect in the treatment of CF lung disease

Role of K(V)LQT1 in cyclic adenosine monophosphate-mediated C1- secretion in human airway epithelia

Ion transport defects underlying cystic fibrosis (CF) lung disease are characterized by impaired cyclic adenosine monophosphate (cAMP)-dependent CI conductance. Activation of Cl secretion in airways depends on simultaneous activation of luminal CI channels and basolateral K channels. We determined the role of basolateral K conductance in cAMP-dependent Cl secretion in native human airway epithelium obtained from non-CF and CF patients. CF tissues showed typical alterations of short-circuit currents with enhanced amiloride-sensitive Na conductance and defective cAMP-mediated Cl conductance. In non-CF tissues, Cl secretion was significantly inhibited by the chromanol 293B (10 μmol/liter), a specific inhibitor of K(V)LQT1 K channels. Inhibition was increased after cAMP-dependent stimulation. Similar effects were obtained with Ba (5 mmol/liter). In patch-clamp experiments with a human bronchial epithelial cell line, stimulation with forskolin (10 μmol/liter) simultaneously activated Cl and K conductance. The K conductance was reversibly inhibited by Ba and 293B. Analysis of reverse-transcribed messenger RNA from non-CF and CF airways showed expression of human K(V)LQT1. We conclude that the K channel K(V)LQT1 is important in maintaining cAMP-dependent Cl secretion in human airways. Activation of K(V)LQT1 in CF airways in parallel with stimulation of residual CF transmembrane conductance regulator Cl channel activity or alternative Cl channels could help to circumvent the secretory defect

Identification of a New Gene Locus for Adolescent Nephronophthisis, on Chromosome 3q22 in a Large Venezuelan Pedigree

Nephronophthisis, an autosomal-recessive cystic kidney disease, is the most frequent monogenic cause for renal failure in childhood. Infantile and juvenile forms of nephronophthisis are known to originate from separate gene loci. We describe here a new disease form, adolescent nephronophthisis, that is clearly distinct by clinical and genetic findings. In a large, 340-member consanguineous Venezuelan kindred, clinical symptoms and renal pathology were evaluated. Onset of terminal renal failure was compared with that in a historical sample of juvenile nephronophthisis. Onset of terminal renal failure in adolescent nephronophthisis occurred significantly later (median age 19 years, quartile borders 16.0 and 25.0 years) than in juvenile nephronophthisis (median age 13.1 years, quartile borders 11.3 and 17.3 years; Wilcoxon test P=.0069). A total-genome scan of linkage analysis was conducted and evaluated by LOD score and total-genome haplotype analyses. A gene locus for adolescent nephronophthisis was localized to a region of homozygosity by descent, on chromosome 3q22, within a critical genetic interval of 2.4 cM between flanking markers D3S1292 and D3S1238. The maximum LOD score for D3S1273 was 5.90 (maximum recombination fraction .035). This locus is different than that identified for juvenile nephronophthisis. These findings will have implications for diagnosis and genetic counseling in hereditary chronic renal failure and provide the basis for identification of the responsible gene

Human adolescent nephronophthisis: Gene locus synteny with polycystic kidney disease in pcy mice

Human adolescent nephronophthisis: Gene locus synteny with polycystic kidney disease in pcy mice Omran, Heymut; Häffner, Karsten; Burth, Suse; Fernandez, Carmen; Fargier, Bernardo; Villaquiran, Aminta; Nothwang, Hans-Gerd; Schnittger, Susanne; Lehrach, Hans; Woo, David; Brandis, Matthias; Sudbrak, Ralf and Hildebrandt, Friedhelm Abstract In a large Venezuelan kindred, a new type of nephronophthisis was recently identified: Adolescent nephronophthisis (NPH3) is a late-onset recessive renal cystic disorder of the nephronophthisis/medullary cystic group of diseases causing end-stage renal disease at a median age of 19 yr. With the use of a homozygosity mapping strategy, the gene (NPHP3) was previously localized to chromosome 3q22 within a critical interval of 2.4 cM. In the current study, the NPHP3 genetic region was cloned and seven genes, eight expressed sequence-tagged sites, and seven microsatellites were physically localized within the critical disease interval. By humanmouse synteny analysis based on expressed genes, synteny between the human NPHP3 locus on chromosome 3q and the pcy locus on mouse chromosome 9 was clearly demonstrated, thus providing the first evidence of synteny between a human and a spontaneous murine renal cystic disease. By fluorescence in situ hybridization the chromosomal assignment of NPHP3 to chromosome 3q21-q22 was refined. Renal pathology in NPH3 was found to consist of tubular basement membranes changes, tubular atrophy and dilation, and sclerosing tubulointerstitial nephropathy. This pathology clearly resembled findings observed in the recessive pcy mouse model of late-onset polycystic kidney disease. In analogy to pcy, renal cyst development at the corticomedullary junction was found to be an early sign of the disease. Through cloning of the NPH3 critical region and mapping of expressed genes, synteny between human NPH3 and murine pcy was established, thus generating the hypothesis that both diseases are caused by recessive mutations of homologous genes. Artículo Publicado en: Journal of the American Society of Nephrology. J Am Soc Nephrol 12: 107-113, 2001 Copyright © 2001 by the American Society of [email protected]@hotmail.comNivel monográfic