Phosphodiesterase 8A Regulates CFTR Activity in Airway Epithelial Cells

The follicle-stimulating hormone triggers rapid changes in mitochondrial structure and function in porcine cumulus cells

Oocyte maturation is a key process during which the female germ cell undergoes resumption of meiosis and completes its preparation for embryonic development including cytoplasmic and epigenetic maturation. The cumulus cells directly surrounding the oocyte are involved in this process by transferring essential metabolites, such as pyruvate, to the oocyte. This process is controlled by cyclic adenosine monophosphate (cAMP)-dependent mechanisms recruited downstream of follicle-stimulating hormone (FSH) signaling in cumulus cells. As mitochondria have a critical but poorly understood contribution to this process, we defined the effects of FSH and high cAMP concentrations on mitochondrial dynamics and function in porcine cumulus cells. During in vitro maturation (IVM) of cumulus-oocyte complexes (COCs), we observed an FSH-dependent mitochondrial elongation shortly after stimulation that led to mitochondrial fragmentation 24 h later. Importantly, mitochondrial elongation was accompanied by decreased mitochondrial activity and a switch to glycolysis. During a pre-IVM culture step increasing intracellular cAMP, mitochondrial fragmentation was prevented. Altogether, the results demonstrate that FSH triggers rapid changes in mitochondrial structure and function in COCs involving cAMP.

Therapeutic Targets and Precision Medicine in COPD: Inflammation, Ion Channels, Both, or Neither?

The development of a wider range of therapeutic options is a key objective in drug discovery for chronic obstructive pulmonary disease (COPD). Fundamental advances in lung biology have the potential to greatly expand the number of therapeutic targets in COPD. The recently reported successful Phase 3 clinical trial of the first biologic agent for COPD, the monoclonal antibody dupilumab, adds additional support to the importance of targeting inflammatory pathways in COPD. However, numerous other cellular mechanisms are important targets in COPD therapeutics, including airway remodeling, the CFTR ion channel, and mucociliary function. Some of these emerging targets can be exploited by the expanded use of existing COPD drugs, such as roflumilast, while targeting others will require the development of novel molecular entities. The identification of additional therapeutic targets and agents has the potential to greatly expand the value of using clinical and biomarker data to classify COPD into specific subsets, each of which can be predictive of an enhanced response to specific subset(s) of targeted therapies. The author reviews established and emerging drug targets in COPD and uses this as a framework to define a novel classification of COPD based on therapeutic targets. This novel classification has the potential to enhance precision medicine in COPD patient care and to accelerate clinical trials and pre-clinical drug discovery efforts.

Ionocyte-Specific Regulation of Cystic Fibrosis Transmembrane Conductance Regulator

CFTR (cystic fibrosis transmembrane conductance regulator) is a tightly regulated anion channel that mediates chloride and bicarbonate conductance in many epithelia and in other tissues, but whether its regulation varies depending on the cell type has not been investigated. Epithelial CFTR expression is highest in rare cells called ionocytes. We studied CFTR regulation in control and ionocyte-enriched cultures by transducing bronchial basal cells with adenoviruses that encode only eGFP or FOXI1 (forkhead box I1) + eGFP as separate polypeptides. FOXI1 dramatically increased the number of transcripts for ionocyte markers ASCL3 (Achaete-Scute Family BHLH Transcription Factor 3), BSND, ATP6V1G3, ATP6V0D2, KCNMA1, and CFTR without altering those for secretory (SCGB1A1), basal (KRT5, KRT6, TP63), goblet (MUC5AC), or ciliated (FOXJ1) cells. The number of cells displaying strong FOXI1 expression was increased 7-fold, and there was no evidence for a broad increase in background immunofluorescence. Total CFTR mRNA and protein levels increased 10-fold and 2.5-fold, respectively. Ionocyte-enriched cultures displayed elevated basal current, increased adenylyl cyclase 5 expression, and tonic suppression of CFTR activity by the phosphodiesterase PDE1C, which has not been shown previously to regulate CFTR activity. The results indicate that CFTR regulation depends on cell type and identifies PDE1C as a potential target for therapeutics that aim to increase CFTR function specifically in ionocytes.

It Takes Two to Tango! Protein-Protein Interactions behind cAMP-Mediated CFTR Regulation

Over the last fifteen years, with the approval of the first molecular treatments, a breakthrough era has begun for patients with cystic fibrosis (CF), the rare genetic disease caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). These molecules, known as CFTR modulators, have led to unprecedented improvements in the lung function and quality of life of most CF patients. However, the efficacy of these drugs is still suboptimal, and the clinical response is highly variable even among individuals bearing the same mutation. Furthermore, not all patients carrying rare CFTR mutations are eligible for CFTR modulator therapies, indicating the need for alternative and/or add-on therapeutic approaches. Because the second messenger 3',5'-cyclic adenosine monophosphate (cAMP) represents the primary trigger for CFTR activation and a major regulator of different steps of the life cycle of the channel, there is growing interest in devising ways to fine-tune the cAMP signaling pathway for therapeutic purposes. This review article summarizes current knowledge regarding the role of cAMP signalosomes, i.e., multiprotein complexes bringing together key enzymes of the cAMP pathway, in the regulation of CFTR function, and discusses how modulating this signaling cascade could be leveraged for therapeutic intervention in CF.

Cell signaling and regulation of CFTR expression in cystic fibrosis cells in the era of high efficiency modulator therapy

Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP- and protein kinase A (PKA)-regulated channel, expressed on the luminal surface of secretory and absorptive epithelial cells. CFTR has a complex, cell-specific regulatory network playing a major role in cAMP- and Ca2+-activated secretion of electrolytes. It secretes intracellular Cl- and bicarbonate and regulates absorption of electrolytes by differentially controlling the activity of the epithelial Na+ channel (ENaC) in colon, airways, and sweat ducts. The CFTR gene expression is regulated by cell-specific, time-dependent mechanisms reviewed elsewhere [1]. This review will focus on the transcriptional, post-transcriptional, and translational regulation of CFTR by cAMP-PKA, non-coding (nc)RNAs, and TGF-β signaling pathways in cystic fibrosis (CF) cells.