Transcytosis maintains CFTR apical polarity in the face of constitutive and mutation-induced basolateral missorting.

Apical polarity of cystic fibrosis transmembrane conductance regulator (CFTR) is essential for solute and water transport in secretory epithelia and can be impaired in human diseases. Maintenance of apical polarity in the face of CFTR non-polarized delivery and inefficient apical retention of mutant CFTRs lacking PDZ-domain protein (NHERF1, also known as SLC9A3R1) interaction, remains enigmatic. Here, we show that basolateral CFTR delivery originates from biosynthetic (∼35%) and endocytic (∼65%) recycling missorting. Basolateral channels are retrieved via basolateral-to-apical transcytosis (hereafter denoted apical transcytosis), enhancing CFTR apical expression by two-fold and suppressing its degradation. In airway epithelia, CFTR transcytosis is microtubule-dependent but independent of Myo5B, Rab11 proteins and NHERF1 binding to its C-terminal DTRL motif. Increased basolateral delivery due to compromised apical recycling and accelerated internalization upon impaired NHERF1-CFTR association is largely counterbalanced by efficient CFTR basolateral internalization and apical transcytosis. Thus, transcytosis represents a previously unrecognized, but indispensable, mechanism for maintaining CFTR apical polarity that acts by attenuating its constitutive and mutation-induced basolateral missorting.

Mutation-specific downregulation of CFTR2 variants by gating potentiators.

Approximately 50% of cystic fibrosis (CF) patients are heterozygous with a rare mutation on at least one allele. Several mutants exhibit functional defects, correctable by gating potentiators. Long-term exposure (≥24 h) to the only available potentiator drug, VX-770, leads to the biochemical and functional downregulation of F508del-CFTR both in immortalized and primary human airway cells, and possibly other CF mutants, attenuating its beneficial effect. Based on these considerations, we wanted to determine the effect of chronic VX-770 exposure on the functional and biochemical expression of rare CF processing/gating mutants in human airway epithelia. Expression of CFTR2 mutants was monitored in the human bronchial epithelial cell line (CFBE41o-) and in patient-derived conditionally reprogrammed bronchial and nasal epithelia by short-circuit current measurements, cell surface ELISA and immunoblotting in the absence or presence of CFTR modulators. The VX-770 half-maximal effective (EC50) concentration for G551D-CFTR activation was ∼0.63 µM in human nasal epithelia, implying that comparable concentration is required in the lung to attain clinical benefit. Five of the twelve rare CFTR2 mutants were susceptible to ∼20-70% downregulation by chronic VX-770 exposure with an IC50 of ∼1-20 nM and to destabilization by other investigational potentiators, thereby diminishing the primary functional gain of CFTR modulators. Thus, chronic exposure to VX-770 and preclinical potentiators can destabilize CFTR2 mutants in human airway epithelial models in a mutation and compound specific manner. This highlights the importance of selecting potentiator drugs with minimal destabilizing effects on CF mutants, advocating a precision medicine approach.

Extracellular oxidation in cystic fibrosis airway epithelium causes enhanced EGFR/ADAM17 activity.

The EGF receptor (EGFR)/a disintegrin and metalloproteinase 17 (ADAM17) signaling pathway mediates the shedding of growth factors and secretion of cytokines and is involved in chronic inflammation and tissue remodeling. Since these are hallmarks of cystic fibrosis (CF) lung disease, we hypothesized that CF transmembrane conductance regulator (CFTR) deficiency enhances EGFR/ADAM17 activity in human bronchial epithelial cells. In CF bronchial epithelial CFBE41o- cells lacking functional CFTR (iCFTR-) cultured at air-liquid interface (ALI) we found enhanced ADAM17-mediated shedding of the EGFR ligand amphiregulin (AREG) compared with genetically identical cells with induced CFTR expression (iCFTR+). Expression of the inactive G551D-CFTR did not have this effect, suggesting that active CFTR reduces EGFR/ADAM17 activity. This was confirmed in CF compared with normal differentiated primary human bronchial epithelial cells (HBEC-ALI). ADAM17-mediated AREG shedding was tightly regulated by the EGFR/MAPK pathway. Compared with iCFTR+ cells, iCFTR- cells displayed enhanced apical presentation and phosphorylation of EGFR, in accordance with enhanced EGFR/ADAM17 activity in CFTR-deficient cells. The nonpermeant natural antioxidant glutathione (GSH) strongly inhibited AREG release in iCFTR and in primary HBEC-ALI, suggesting that ADAM17 activity is directly controlled by extracellular redox potentials in differentiated airway epithelium. Furthermore, the fluorescent redox probe glutaredoxin 1-redox-sensitive green fluorescent protein-glycosylphosphatidylinositol (Grx1-roGFP-GPI) indicated more oxidized conditions in the extracellular space of iCFTR- cells, consistent with the role of CFTR in GSH transport. Our data suggest that in CFTR-deficient airway epithelial cells a more oxidized state of the extracellular membrane, likely caused by defective GSH secretion, leads to enhanced activity of the EGFR/ADAM17 signaling axis. In CF lungs this could contribute to tissue remodeling and hyperinflammation.

Epithelial Anion Transport as Modulator of Chemokine Signaling.

The pivotal role of epithelial cells is to secrete and absorb ions and water in order to allow the formation of a luminal fluid compartment that is fundamental for the epithelial function as a barrier against environmental factors. Importantly, epithelial cells also take part in the innate immune system. As a first line of defense they detect pathogens and react by secreting and responding to chemokines and cytokines, thus aggravating immune responses or resolving inflammatory states. Loss of epithelial anion transport is well documented in a variety of diseases including cystic fibrosis, chronic obstructive pulmonary disease, asthma, pancreatitis, and cholestatic liver disease. Here we review the effect of aberrant anion secretion with focus on the release of inflammatory mediators by epithelial cells and discuss putative mechanisms linking these transport defects to the augmented epithelial release of chemokines and cytokines. These mechanisms may contribute to the excessive and persistent inflammation in many respiratory and gastrointestinal diseases.

Functional effects of 13 rare PRSS1 variants presumed to cause chronic pancreatitis.

OBJECTIVE: Hereditary pancreatitis is caused by mutations in human cationic trypsinogen (PRSS1) which lead to increased autoactivation by altering chymotrypsin C (CTRC)-dependent trypsinogen activation and degradation. Exceptions are some cysteine mutations which cause misfolding, intracellular retention and endoplasmic reticulum stress. Clinical relevance of many PRSS1 variants found in patients with sporadic chronic pancreatitis is unknown but often assumed by analogy with known disease-causing mutations. Functional comparison of PRSS1 variants found in sporadic and hereditary cases is needed to resolve this dilemma. DESIGN: Here, we investigated the functional phenotype of 13 published PRSS1 variants with respect to autoactivation in the presence of CTRC and cellular secretion. RESULTS: Only mutation p.D100H increased trypsinogen autoactivation, but this gain in function was offset by a marked reduction in secretion. Five mutants (p.P36R, p.G83E, p.I88N, p.V123M, p.S124F) showed decreased autoactivation due to increased degradation by CTRC. Five mutants exhibited strongly (p.D100H, p.C139F) or moderately (p.K92N, p.S124F, p.G208A) reduced secretion, whereas mutant p.K170E showed slightly increased secretion. Mutant p.I88N was also secreted to higher levels but was rapidly degraded by CTRC. Finally, three mutants (p.Q98K, p.T137M, p.S181G) had no phenotypic alterations relative to wild-type trypsinogen. CONCLUSIONS: Rare PRSS1 variants found in sporadic chronic pancreatitis do not stimulate autoactivation but may cause increased degradation, impaired secretion or no functional change. Variants with reduced secretion are likely pathogenic due to mutation-induced misfolding and consequent endoplasmic reticulum stress.

Heavy metals in cigarette smoke strongly inhibit pancreatic ductal function and promote development of chronic pancreatitis.

BACKGROUND AND AIMS: Smoking is recognised as an independent risk factor in the development of chronic pancreatitis (CP). Cystic fibrosis transmembrane conductance regulator (CFTR) function and ductal fluid and bicarbonate secretion are also known to be impaired in CP, so it is crucial to understand the relationships between smoking, pancreatic ductal function and the development of CP. METHODS: We measured sweat chloride (Cl-) concentrations in patients with and without CP, both smokers and non-smokers, to assess CFTR activity. Serum heavy metal levels and tissue cadmium concentrations were determined by mass spectrometry in smoking and non-smoking patients. Guinea pigs were exposed to cigarette smoke, and cigarette smoke extract (CSE) was prepared to characterise its effects on pancreatic HCO3 - and fluid secretion and CFTR function. We administered cerulein to both the smoking and non-smoking groups of mice to induce pancreatitis. RESULTS: Sweat samples from smokers, both with and without CP, exhibited elevated Cl- concentrations compared to those from non-smokers, indicating a decrease in CFTR activity due to smoking. Pancreatic tissues from smokers, regardless of CP status, displayed lower CFTR expression than those from non-smokers. Serum levels of cadmium and mercury, as well as pancreatic tissue cadmium, were increased in smokers. Smoking, CSE, cadmium, mercury and nicotine all hindered fluid and HCO3 - secretion and CFTR activity in pancreatic ductal cells. These effects were mediated by sustained increases in intracellular calcium ([Ca2+]i), depletion of intracellular ATP (ATPi) and mitochondrial membrane depolarisation. CONCLUSION: Smoking impairs pancreatic ductal function and contributes to the development of CP. Heavy metals, notably cadmium, play a significant role in the harmful effects of smoking. KEY POINTS: Smoking and cigarette smoke extract diminish pancreatic ductal fluid and HCO3 - secretion as well as the expression and function of CFTR Cd and Hg concentrations are significantly higher in the serum samples of smokers Cd accumulates in the pancreatic tissue of smokers.

Na+/Ca2+ exchangers regulate the migration and proliferation of human gastric myofibroblasts.

Gastrointestinal myofibroblasts are contractile, electrically nonexcitable, transitional cells that play a role in extracellular matrix production, in ulcer healing, and in pathophysiological conditions they contribute to chronic inflammation and tumor development. Na+/Ca2+ exchangers (NCX) are known to have a crucial role in Ca2+ homeostasis of contractile cells, however, no information is available concerning the role of NCX in the proliferation and migration of gastrointestinal myofibroblasts. In this study, our aim was to investigate the role of NCX in the Ca2+ homeostasis, migration, and proliferation of human gastrointestinal myofibroblasts, focusing on human gastric myofibroblasts (HGMs). We used microfluorometric measurements to investigate the intracellular Ca2+ and Na+ concentrations, PCR analysis and immunostaining to show the presence of the NCX, patch clamp for measuring NCX activity, and proliferation and migration assays to investigate the functional role of the exchanger. We showed that 53.0±8.1% of the HGMs present Ca2+ oscillations, which depend on extracellular Ca2+ and Na+, and can be inhibited by NCX inhibitors. NCX1, NCX2, and NCX3 were expressed at both mRNA and protein levels in HGMs, and they contribute to the intracellular Ca2+ and Na+ homeostasis as well, regardless of the oscillatory activity. NCX inhibitors significantly blocked the basal and insulin-like growth factor II-stimulated migration and proliferation rates of HGMs. In conclusion, we showed that NCX plays a pivotal role in regulating the Ca2+ homeostasis, migration, and proliferation of HGMs. The inhibition of NCX activity may be a potential therapeutic target in hyperproliferative gastric diseases.

NHE1 activity contributes to migration and is necessary for proliferation of human gastric myofibroblasts.

Myofibroblasts play central roles in wound healing, deposition of the extracellular matrix and epithelial function. Their functions depend on migration and proliferation within the subepithelial matrix, which results in accelerated cellular metabolism. Upregulated metabolic pathways generate protons which need to be excreted to maintain intracellular pH (pH(i)). We isolated human gastric myofibroblasts (HGMs) from surgical specimens of five patients. Then we characterized, for the first time, the expression and functional activities of the Na(+)/H(+) exchanger (NHE) isoforms 1, 2 and 3, and the functional activities of the Na(+)/HCO(3)(-) cotransporter (NBC) and the anion exchanger (AE) in cultured HGMs using microfluorimetry, immunocytochemistry, reverse transcription polymerase chain reaction and immunoblot analysis. We showed that NHE1-3, NBC and AE activities are present in HGMs and that NHE1 is the most active of the NHEs. In scratch wound assays we also demonstrated (using the selective NHE inhibitor HOE-642) that carbachol and insulin like growth factor II (IGF-II) partly stimulate migration of HGMs in a NHE1-dependent manner. EdU incorporation assays revealed that IGF-II induces proliferation of HGMs which is inhibited by HOE-642. The results indicate that NHE1 is necessary for IGF-II-induced proliferation response of HGMs. Overall, we have characterized the pH(i) regulatory mechanisms of HGMs. In addition, we demonstrated that NHE1 activity contributes to both IGF-II- and carbachol-stimulated migration and that it is obligatory for IGF-II-induced proliferation of HGMs.

Trypsin reduces pancreatic ductal bicarbonate secretion by inhibiting CFTR Cl⁻ channels and luminal anion exchangers.

BACKGROUND & AIMS: The effects of trypsin on pancreatic ductal epithelial cells (PDECs) vary among species and depend on the localization of proteinase-activated receptor 2 (PAR-2). We compared PAR-2 localization in human and guinea-pig PDECs, and used isolated guinea pig ducts to study the effects of trypsin and a PAR-2 agonist on bicarbonate secretion. METHODS: PAR-2 localization was analyzed by immunohistochemistry in guinea pig and human pancreatic tissue samples (from 15 patients with chronic pancreatitis and 15 without pancreatic disease). Functionally, guinea pig PDECs were studied by microperfusion of isolated ducts, measurements of intracellular pH and intracellular Ca(2+) concentration, and patch clamp analysis. The effect of pH on trypsinogen autoactivation was assessed using recombinant human cationic trypsinogen. RESULTS: PAR-2 localized to the apical membrane of human and guinea pig PDECs. Trypsin increased intracellular Ca(2+) concentration and intracellular pH and inhibited secretion of bicarbonate by the luminal anion exchanger and the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. Autoactivation of human cationic trypsinogen accelerated when the pH was reduced from 8.5 to 6.0. PAR-2 expression was strongly down-regulated, at transcriptional and protein levels, in the ducts of patients with chronic pancreatitis, consistent with increased activity of intraductal trypsin. Importantly, in PAR-2 knockout mice, the effects of trypsin were markedly reduced. CONCLUSIONS: Trypsin reduces pancreatic ductal bicarbonate secretion via PAR-2-dependent inhibition of the apical anion exchanger and the CFTR Cl(-) channel. This could contribute to the development of chronic pancreatitis by decreasing luminal pH and promoting premature activation of trypsinogen in the pancreatic ducts.

Establishment and characterization of a novel human induced pluripotent stem cell line stably expressing the iRFP720 reporter.

Stem cell therapy has great potential for replacing beta-cell loss in diabetic patients. However, a key obstacle to cell therapy's success is to preserve viability and function of the engrafted cells. While several strategies have been developed to improve engrafted beta-cell survival, tools to evaluate the efficacy within the body by imaging are limited. Traditional labeling tools, such as GFP-like fluorescent proteins, have limited penetration depths in vivo due to tissue scattering and absorption. To circumvent this limitation, a near-infrared fluorescent mutant version of the DrBphP bacteriophytochrome, iRFP720, has been developed for in vivo imaging and stem/progenitor cell tracking. Here, we present the generation and characterization of an iRFP720 expressing human induced pluripotent stem cell (iPSC) line, which can be used for real-time imaging in various biological applications. To generate the transgenic cells, the CRISPR/Cas9 technology was applied. A puromycin resistance gene was inserted into the AAVS1 locus, driven by the endogenous PPP1R12C promoter, along with the CAG-iRFP720 reporter cassette, which was flanked by insulator elements. Proper integration of the transgene into the targeted genomic region was assessed by comprehensive genetic analysis, verifying precise genome editing. Stable expression of iRFP720 in the cells was confirmed and imaged by their near-infrared fluorescence. We demonstrated that the reporter iPSCs exhibit normal stem cell characteristics and can be efficiently differentiated towards the pancreatic lineage. As the genetically modified reporter cells show retained pluripotency and multilineage differentiation potential, they hold great potential as a cellular model in a variety of biological and pharmacological applications.

Integration of nano- and biotechnology for beta-cell and islet transplantation in type-1 diabetes treatment.

Regenerative medicine using human or porcine ß-cells or islets has an excellent potential to become a clinically relevant method for the treatment of type-1 diabetes. High-resolution imaging of the function and faith of transplanted porcine pancreatic islets and human stem cell-derived beta cells in large animals and patients for testing advanced therapy medicinal products (ATMPs) is a currently unmet need for pre-clinical/clinical trials. The iNanoBIT EU H2020 project is developing novel highly sensitive nanotechnology-based imaging approaches allowing for monitoring of survival, engraftment, proliferation, function and whole-body distribution of the cellular transplants in a porcine diabetes model with excellent translational potential to humans. We develop and validate the application of single-photon emission computed tomography (SPECT) and optoacoustic imaging technologies in a transgenic insulin-deficient pig model to observe transplanted porcine xeno-islets and in vitro differentiated human beta cells. We are progressing in generating new transgenic reporter pigs and human-induced pluripotent cell (iPSC) lines for optoacoustic imaging and testing them in transplantable bioartificial islet devices. Novel multifunctional nanoparticles have been generated and are being tested for nuclear imaging of islets and beta cells using a new, high-resolution SPECT imaging device. Overall, the combined multidisciplinary expertise of the project partners allows progress towards creating much needed technological toolboxes for the xenotransplantation and ATMP field, and thus reinforces the European healthcare supply chain for regenerative medicinal products.

Phosphorylation-dependent modulation of CFTR macromolecular signalling complex activity by cigarette smoke condensate in airway epithelia.

Genetic and acquired loss-of-function defect of the cystic fibrosis transmembrane conductance regulator (CFTR) compromise airway surface liquid homeostasis and mucociliary clearance (MCC), culminating in recurrent lung inflammation/infection. While chronic cigarette smoke (CS), CS extract (CSE; water-soluble compounds) and CS condensate (CSC; particulate, organic fraction) exposure inhibit CFTR activity at transcriptional, biochemical, and functional levels, the acute impact of CSC remains incompletely understood. We report that CSC transiently activates CFTR chloride secretion in airway epithelia. The comparable CFTR phospho-occupancy after CSC- and forskolin-exposure, determined by affinity-enriched tandem mass spectrometry and pharmacology, suggest that localised cAMP-dependent protein kinase (PKA) stimulation by CSC causes the channel opening. Due to the inhibition of the MRP4/ABCC4, a cAMP-exporter confined to the CFTR macromolecular signalling-complex, PKA activation is accomplished by the subcompartmentalised elevation of cytosolic cAMP. In line, MRP4 inhibition results in CFTR activation and phospho-occupancy similar to that by forskolin. In contrast, acute CSC exposure reversibly inhibits the phosphorylated CFTR both in vivo and in phospholipid bilayers, without altering its cell surface density and phospho-occupancy. We propose that components of CSC elicit both a transient protective CFTR activation, as well as subsequent channel block in airway epithelia, contributing to the subacute MCC defect in acquired CF lung diseases.

Variants in CPA1 are strongly associated with early onset chronic pancreatitis.

Chronic pancreatitis is an inflammatory disorder of the pancreas. We analyzed CPA1, encoding carboxypeptidase A1, in subjects with nonalcoholic chronic pancreatitis (cases) and controls in a German discovery set and three replication sets. Functionally impaired variants were present in 29/944 (3.1%) German cases and 5/3,938 (0.1%) controls (odds ratio (OR) = 24.9, P = 1.5 × 10(-16)). The association was strongest in subjects aged ≤ 10 years (9.7%; OR = 84.0, P = 4.1 × 10(-24)). In the replication sets, defective CPA1 variants were present in 8/600 (1.3%) cases and 9/2,432 (0.4%) controls from Europe (P = 0.01), 5/230 (2.2%) cases and 0/264 controls from India (P = 0.02) and 5/247 (2.0%) cases and 0/341 controls from Japan (P = 0.013). The mechanism by which CPA1 variants confer increased pancreatitis risk may involve misfolding-induced endoplasmic reticulum stress rather than elevated trypsin activity, as is seen with other genetic risk factors for this disease.

New therapeutic targets in ulcerative colitis: the importance of ion transporters in the human colon.

BACKGROUND: The absorption of water and ions (especially Na(+) and Cl(-)) is an important function of colonic epithelial cells in both physiological and pathophysiological conditions. Despite the comprehensive animal studies, there are only scarce available data on the ion transporter activities of the normal and inflamed human colon. METHODS: In this study, 128 healthy controls and 69 patients suffering from ulcerative colitis (UC) were involved. We investigated the expressional and functional characteristics of the Na(+)/H(+) exchangers (NHE) 1-3, the epithelial sodium channel (ENaC), and the SLC26A3 Cl(-)/HCO 3- exchanger downregulated in adenoma (DRA) in primary colonic crypts isolated from human biopsy and surgical samples using microfluorometry, patch clamp, and real-time reverse-transcription polymerase chain reaction (RT-PCR) techniques. RESULTS: Data collected from colonic crypts showed that the activities of electroneutral (via NHE3) and the electrogenic Na(+) absorption (via ENaC) are in inverse ratio to each other in the proximal and distal colon. We found no significant differences in the activity of NHE2 in different segments of the colon. Surface cell Cl(-)/HCO 3- exchange is more active in the distal part of the colon. Importantly, both sodium and chloride absorptions are damaged in UC, whereas NHE1, which has been shown to promote immune response, is upregulated by 6-fold. CONCLUSIONS: These results open up new therapeutic targets in UC.