Calcium-modulated chloride pathways contribute to chloride flux in murine cystic fibrosis-affected macrophages

Colonic Fluid and Electrolyte Transport 2022: An Update

Colonic epithelial cells are responsible for maintaining a delicate balance between luminal secretion and the absorption of fluids and ions. This review aims to discuss and update the model of colonic electrolyte secretion and absorption via the cystic fibrosis transmembrane regulator (CFTR), epithelial sodium channel (ENaC), Na-K-Cl cotransporters (NKCC1 and 2), Na-H exchangers (NHE1–4), colonic H,KATPase, and several other key components involved in multi-level transepithelial ion transport. Developments in our understanding of the activity, regulation, localization, and relationships of these ion transporters and their interactions have helped forge a more robust understanding of colonic ion movement that accounts for the colonic epithelium’s role in mucosal pH modulation, the setting of osmotic gradients pivotal for fluid retention and secretion, and cell death regulation. Deviations from homeostatic ion transport cause diarrhea, constipation, and epithelial cell death and contribute to cystic fibrosis, irritable bowel syndrome (IBS), ulcerative colitis, and cancer pathologies. Signal transduction pathways that regulate electrolyte movement and the regulatory relationships between various sensors and transporters (CFTR as a target of CaSR regulation and as a regulator of ENaC and DRA, for example) are imperative aspects of a dynamic and comprehensive model of colonic ion homeostasis.

Macrophage dysfunction in cystic fibrosis: Nature or nurture?

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) affect the homeostasis of chloride flux by epithelial cells. This has deleterious consequences, especially in respiratory epithelia, where the defect results in mucus accumulation distinctive of cystic fibrosis. CFTR is, however, also expressed in phagocytic cells, like macrophages. Immune cells are highly sensitive to conditioning by their environment; thus, CFTR dysfunction in epithelia influences macrophages by affecting the lung milieu, but the mutations also appear to be directly consequential for intrinsic macrophage functions. Particular mutations can alter CFTR's folding, traffic of the protein to the membrane and function. As such, understanding the intrinsic effects of CFTR mutation requires distinguishing the secondary effects of misfolded CFTR on cell stress pathways from the primary defect of CFTR dysfunction/absence. Investigations into CFTR's role in macrophages have exploited various models, each with their own advantages and limitations. This review summarizes these methodologic approaches, discussing their physiological correspondence and highlighting key findings. The controversy surrounding CFTR-dependent acidification is used as a case study to highlight difficulties in commensurability across model systems. Recent work in macrophage biology, including polarization and host-pathogen interaction studies, brought into the context of CFTR research, offers potential explanations for observed discrepancies between studies. Moreover, the rapid advancement of novel gene editing technologies and new macrophage model systems makes this assessment of the field's models and methodologies timely.

Role of IRE1α/XBP-1 in Cystic Fibrosis Airway Inflammation

Cystic fibrosis (CF) pulmonary disease is characterized by chronic airway infection and inflammation. The infectious and inflamed CF airway environment impacts on the innate defense of airway epithelia and airway macrophages. The CF airway milieu induces an adaptation in these cells characterized by increased basal inflammation and a robust inflammatory response to inflammatory mediators. Recent studies have indicated that these responses depend on activation of the unfolded protein response (UPR). This review discusses the contribution of airway epithelia and airway macrophages to CF airway inflammatory responses and specifically highlights the functional importance of the UPR pathway mediated by IRE1/XBP-1 in these processes. These findings suggest that targeting the IRE1/XBP-1 UPR pathway may be a therapeutic strategy for CF airway disease.

Cystic Fibrosis Lung Immunity: The Role of the Macrophage

Cystic fibrosis (CF) pathophysiology is hallmarked by excessive inflammation and the inability to efficiently resolve lung infections, contributing to major morbidity and eventually the mortality of patients with this disease. Macrophages (MΦs) are major players in lung homeostasis through their diverse contributions to both the innate and adaptive immune networks. The setting of MΦ function and activity in CF is multifaceted, encompassing the response to the unique environmental cues in the CF lung as well as the intrinsic changes resulting from CFTR dysfunction. The complexity is further enhanced with the identification of modifier genes, which modulate the CFTR contribution to disease, resulting in epigenetic and transcriptional shifts in MΦ phenotype. This review focuses on the contribution of MΦ to lung homeostasis, providing an overview of the diverse literature and various perspectives on the role of these immune guardians in CF.

Cholangiocytes derived from human induced pluripotent stem cells for disease modeling and drug validation

The study of biliary disease has been constrained by a lack of primary human cholangiocytes. Here we present an efficient, serum-free protocol for directed differentiation of human induced pluripotent stem cells into cholangiocyte-like cells (CLCs). CLCs show functional characteristics of cholangiocytes, including bile acids transfer, alkaline phosphatase activity, γ-glutamyl-transpeptidase activity and physiological responses to secretin, somatostatin and vascular endothelial growth factor. We use CLCs to model in vitro key features of Alagille syndrome, polycystic liver disease and cystic fibrosis (CF)-associated cholangiopathy. Furthermore, we use CLCs generated from healthy individuals and patients with polycystic liver disease to reproduce the effects of the drugs verapamil and octreotide, and we show that the experimental CF drug VX809 rescues the disease phenotype of CF cholangiopathy in vitro. Our differentiation protocol will facilitate the study of biological mechanisms controlling biliary development, as well as disease modeling and drug screening.

Nanoparticles that deliver triplex-forming peptide nucleic acid molecules correct F508del CFTR in airway epithelium

Cystic fibrosis (CF) is a lethal genetic disorder most commonly caused by the F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. It is not readily amenable to gene therapy because of its systemic nature and challenges including in vivo gene delivery and transient gene expression. Here, we use triplex-forming PNA molecules and donor DNA in biodegradable polymer nanoparticles to correct F508del. We confirm modification with sequencing and a functional chloride efflux assay. In vitro correction of chloride efflux occurs in up to 25% of human cells. Deep sequencing reveals negligible off-target effects in partially homologous sites. Intranasal application of nanoparticles in CF mice produces changes in nasal epithelium potential differences consistent with corrected CFTR, with gene correction also detected in lung tissue. This work represents facile genome engineering in vivo with oligonucleotides using a nanoparticle system to achieve clinically relevant levels of gene editing without off-target effects.

New findings concerning vertebrate porin II--on the relevance of glycine motifs of type-1 VDAC

New findings concerning vertebrate porin part I was published in 1997, then summarizing early data and reflections regarding the molecular structure of vertebrate voltage-dependent anion-selective channels, VDAC/eukaryotic porin, and the extra-mitochondrial expression pattern of human type-1 VDAC. Meanwhile, endeavors of different laboratories confirmed and widened this beginning by encircling the function of the channels. Regarding the function of mitochondrial outer membrane-standing VDACs the channels are established parts of the intrinsic apoptotic pathway and thus therapeutic targets in studies on several diseases: cancer, Alzheimer's disease, Down Syndrome, Parkinson's disease, Amyotrophic Lateral Sclerosis, cystic fibrosis and malaria. Regarding cell membrane-integrated type-1 VDAC it has been documented by different approaches that this porin channel is engaged in cell volume regulation, trans-membrane electron transport and apoptosis. Furthermore, new data insinuate a bridging of extrinsic and intrinsic apoptotic pathways, putatively gaining relevance in Alzheimer research. Mammalian type-1 VDAC, a β-barrel, is basically built up by nineteen β-sheets connected by peptide stretches of varying lengths. The molecule also comprises an N-terminal stretch of some twenty amino acids which, according to biochemical data, traverses the channel lumen towards the cytosolic surface of outer mitochondrial membranes or the plasma lemma, respectively and works as voltage sensor in channel gating. In artificial lipid bilayers VDACs figure as anion or cation-channels, as VDACs are permeable to both cations and anions, with voltage shifts changing the relative permeability. Type-1 VDAC carries several motifs where glycine residues are in critical positions. Motifs of this type, on the on hand, are established nucleotide binding sites. On the other hand, the GxxxG motifs are also discussed as relevant peptide dimerization/aggregation/membrane perturbation motifs. Finally, GxxxG motifs bind cholesterol. Type-1 VDAC shows one such GxxxG motif at the proximal end of its N-terminal voltage sensor while amyloid Aβ peptides include three of them in series. Noteworthy, two additional may be modified versions, GxxxGxG and GxxGxxxG, are found on β-sheet 19 or 9, respectively. Recent data have allowed speculating that amyloid Aβ induces apoptosis via opening type-1 VDAC in cell membranes of hypo-metabolic neurons, a process most likely running over life time--as leaves fall from trees in the tropics--and ending in Alzheimer's disease whenever critical brain regions are affected. The expression of GxxxG motifs on either reactant under consideration is in line with this model of Alzheimer's disease pathogenesis, which clearly differs from the amyloid Aβ cascade theory, and which can, furthermore, be understood as a basic model for apoptosis induction. However, to assume randomly distributed interactions of body wide found amyloid Aβ peptides with the N-terminal voltage sensors of ubiquitously expressed cell membrane-standing human type-1 VDAC opens up a new view on Alzheimer's disease, which might even include a clue on systemic aspects of the disease. While elaborating this concept, my focus was at first only on the GxxxG motif at the proximal end of the N-terminal voltage sensor of type-1 VDAC. Here, I include a corresponding sequence stretch on the channel's β-sheet 19, too.