Cigarette smoke exposure alters phosphodiesterases in human structural lung cells

What every clinician should know about inflammation in COPD

Inflammation drives COPD pathogenesis and exacerbations. Although the conceptual framework and major players in the inflammatory milieu of COPD have been long established, the nuances of cellular interactions and the etiological differences that create heterogeneity in inflammatory profiles and treatment response continue to be revealed. This wealth of data and understanding is not only a boon to the researcher but also provides guidance to the clinician, moving the field closer to precision medicine. It is through this lens that this review seeks to describe the inflammatory processes at play in COPD, relating inflammation to pathological and functional changes, identifying patient-specific and disease-related factors that may influence clinical observations, and providing current insights on existing and emerging anti-inflammatory treatments and treatment targets, including biological therapies and phosphodiesterase (PDE) inhibitors.

Nicotine Impairs Smooth Muscle cAMP Signaling and Vascular Reactivity

OBJECTIVE

This study aimed to determine nicotine's impact on receptor-mediated cyclic adenosine monophosphate (cAMP) synthesis in vascular smooth muscle (VSM). We hypothesize that nicotine impairs β adrenergic-mediated cAMP signaling in VSM, leading to altered vascular reactivity.

METHODS

The effects of nicotine on cAMP signaling and vascular function were systematically tested in aortic VSM cells and acutely isolated aortas from mice expressing the cAMP sensor TEpacVV (Camper), specifically in VSM (e.g., CamperSM).

RESULTS

Isoproterenol (ISO)-induced β-adrenergic production of cAMP in VSM was significantly reduced in cells from second-hand smoke (SHS)-exposed mice and cultured wild-type VSM treated with nicotine. The decrease in cAMP synthesis caused by nicotine was verified in freshly isolated arteries from a mouse that had cAMP sensor expression in VSM (e.g., CamperSM mouse). Functionally, the changes in cAMP signaling in response to nicotine hindered ISO-induced vasodilation, but this was reversed by immediate PDE3 inhibition.

CONCLUSIONS

These results imply that nicotine alters VSM β adrenergic-mediated cAMP signaling and vasodilation, which may contribute to the dysregulation of vascular reactivity and the development of vascular complications for nicotine-containing product users.

Diesel exhaust particles alter mitochondrial bioenergetics and cAMP producing capacity in human bronchial epithelial cells

Introduction: Air pollution from diesel combustion is linked in part to the generation of diesel exhaust particles (DEP). DEP exposure induces various processes, including inflammation and oxidative stress, which ultimately contribute to a decline in lung function. Cyclic AMP (cAMP) signaling is critical for lung homeostasis. The impact of DEP on cAMP signaling is largely unknown. Methods: We exposed human bronchial epithelial (BEAS-2B) cells to DEP for 24-72 h and evaluated mitochondrial bioenergetics, markers of oxidative stress and inflammation and the components of cAMP signaling. Mitochondrial bioenergetics was measured at 72 h to capture the potential and accumulative effects of prolonged DEP exposure on mitochondrial function. Results: DEP profoundly altered mitochondrial morphology and network integrity, reduced both basal and ATP-linked respiration as well as the glycolytic capacity of mitochondria. DEP exposure increased gene expression of oxidative stress and inflammation markers such as interleukin-8 and interleukin-6. DEP significantly affected mRNA levels of exchange protein directly activated by cAMP-1 and -2 (Epac1, Epac2), appeared to increase Epac1 protein, but left phospho-PKA levels unhanged. DEP exposure increased A-kinase anchoring protein 1, β2-adrenoceptor and prostanoid E receptor subtype 4 mRNA levels. Interestingly, DEP decreased mRNA levels of adenylyl cyclase 9 and reduced cAMP levels stimulated by forskolin (AC activator), fenoterol (β2-AR agonist) or PGE2 (EPR agonist). Discussion: Our findings suggest that DEP induces mitochondrial dysfunction, a process accompanied by oxidative stress and inflammation, and broadly dampens cAMP signaling. These epithelial responses may contribute to lung dysfunction induced by air pollution exposure.

Cigarette Smoke Mediates Nasal Epithelial Barrier Dysfunction via TNF-α

BACKGROUND

Extensive data suggest that exposure to cigarette smoke can induce pulmonary epithelial barrier dysfunction. However, the effects of cigarette smoke on the nasal epithelial barrier are still unclear. Here, we investigated the consequence and mechanism of cigarette smoke on the nasal epithelial barrier.

METHODS

Sprague Dawley rats were exposed to cigarette smoke for 3 or 6 months, and changes in inflammatory markers and nasal barrier function were evaluated. Moreover, underlying mechanisms were explored. Finally, normal human bronchial epithelial cells were cultured with or without tumor necrosis factor-alpha (TNF-α) in vitro, and the levels of continuity and tight junction-associated proteins were measured.

RESULTS

In vivo experiments showed that the nasal mucosal barrier function of rats exposed to cigarette smoke was disturbed. Indeed, proteins associated with tight junctions were decreased, and the levels of inflammatory factors, such as IL-8, IL-6, and TNF-α, were dramatically increased in comparison to those of control animals. In vitro, TNF-α was shown to disrupt the continuity of proteins associated with tight junctions and to downregulate the expression of these proteins in bronchial epithelial cells.

CONCLUSIONS

We found that cigarette smoke disrupted the nasal mucosal barrier, and the extent of the damage was correlated with the duration of cigarette smoke exposure. We showed that TNF-α can disrupt the continuity and attenuate the expression of tight junction proteins in human bronchial epithelial cells. Therefore, cigarette smoke may induce nasal epithelial barrier dysfunction through TNF-α.

Nicotine promotes renal interstitial fibrosis via upregulation of XIAP in an alpha7-nAChR-dependent manner

Renal fibrosis, characterized by excessive accumulation of the extracellular matrix in the renal tubulointerstitium, can lead to chronic kidney disease (CKD), resulting in a heavy burden on families and society. Clinical studies have shown that smoking is closely associated with CKD deterioration in patients with diabetes, hypertension, polycystic kidney disease, and kidney transplantation. However, the mechanism of action of nicotine in renal fibrosis pathogenesis remains largely unknown. X-linked inhibitor of apoptosis (XIAP), a member of the inhibitor of apoptosis protein (IAP) family, is involved in apoptosis, necroptosis, autophagy, and immune response. Here, the upregulated expression of XIAP and α7 nicotine acetylcholine receptor (α7-nAChR) was determined in the kidneys of the CKD smoking group in human and animal studies. A significant positive correlation between XIAP and cotinine was observed. In addition, the nuclear translocation and transcriptional activity of SP1 were promoted when nicotine bound to α7-nAChR, resulting in XIAP overexpression and renal interstitial fibrosis progression. This phenotype can be reversed by the nicotine receptor subtype α7-nAChR antagonists methyllycaconitine. Our results revealed the complex underlying mechanism of nicotine in promoting renal fibrosis by altering SP1 nucleocytoplasmic translocation and regulating XIAP expression. These results provide novel insights into the pathogenesis and treatment of CKD.

Impact of Particles on Pulmonary Endothelial Cells

According to the WHO, air quality affects around 40 million people, contributing to around 21,000 premature deaths per year. Severe respiratory diseases, such as asthma and chronic obstructive pulmonary disorder, can be promoted by air pollution, which has already been documented; this is one of the reasons why air quality is a very relevant factor for human health and well-being. Aerosols are an aggregation of solid or liquid particles dispersed in the air and can be found in the form of dust or fumes. Aerosols can be easily inhaled or absorbed by the skin, which can lead to adverse health effects according to their sizes that range from the nanometre to the millimetre scale. Based on the PRISMA methodology and using the Rayyan QCRI platform, it was possible to assess more than four hundred research articles. This systematic review study aimed to understand the impact of particles on pulmonary endothelial cells, namely particulate matter in different sizes, cigarette smoke, diesel exhaust particles and carbon black. The main conclusions were that particles induce multiple health effects on endothelial cells, namely endothelial dysfunction, which can lead to apoptosis and necrosis, and it may also cause necroptosis in lung structure.

High miR203a-3p and miR-375 expression in the airways of smokers with and without COPD

Smoking is a leading cause of chronic obstructive pulmonary disease (COPD). It is known to have a significant impact on gene expression and (inflammatory) cell populations in the airways involved in COPD pathogenesis. In this study, we investigated the impact of smoking on the expression of miRNAs in healthy and COPD individuals. We aimed to elucidate the overall smoking-induced miRNA changes and those specific to COPD. In addition, we investigated the downstream effects on regulatory gene expression and the correlation to cellular composition. We performed a genome-wide miRNA expression analysis on a dataset of 40 current- and 22 ex-smoking COPD patients and a dataset of 35 current- and 38 non-smoking respiratory healthy controls and validated the results in an independent dataset. miRNA expression was then correlated with mRNA expression in the same patients to assess potential regulatory effects of the miRNAs. Finally, cellular deconvolution analysis was used to relate miRNAs changes to specific cell populations. Current smoking was associated with increased expression of three miRNAs in the COPD patients and 18 miRNAs in the asymptomatic smokers compared to respiratory healthy controls. In comparison, four miRNAs were lower expressed with current smoking in asymptomatic controls. Two of the three smoking-related miRNAs in COPD, miR-203a-3p and miR-375, were also higher expressed with current smoking in COPD patients and the asymptomatic controls. The other smoking-related miRNA in COPD patients, i.e. miR-31-3p, was not present in the respiratory healthy control dataset. miRNA-mRNA correlations demonstrated that miR-203a-3p, miR-375 and also miR-31-3p expression were negatively associated with genes involved in pro-inflammatory pathways and positively associated with genes involved in the xenobiotic pathway. Cellular deconvolution showed that higher levels of miR-203a-3p were associated with higher proportions of proliferating-basal cells and secretory (club and goblet) cells and lower levels of fibroblasts, luminal macrophages, endothelial cells, B-cells, amongst other cell types. MiR-375 expression was associated with lower levels of secretory cells, ionocytes and submucosal cells, but higher levels of endothelial cells, smooth muscle cells, and mast cells, amongst other cell types. In conclusion, we identified two smoking-induced miRNAs (miR-375 and miR-203a-3p) that play a role in regulating inflammation and detoxification pathways, regardless of the presence or absence of COPD. Additionally, in patients with COPD, we identified miR-31-3p as a miRNA induced by smoking. Our identified miRNAs should be studied further to unravel which smoking-induced inflammatory mechanisms are reactive and which are involved in COPD pathogenesis.

Photoreceptor phosphodiesterase (PDE6): activation and inactivation mechanisms during visual transduction in rods and cones

Rod and cone photoreceptors of the vertebrate retina utilize cGMP as the primary intracellular messenger for the visual signaling pathway that converts a light stimulus into an electrical response. cGMP metabolism in the signal-transducing photoreceptor outer segment reflects the balance of cGMP synthesis (catalyzed by guanylyl cyclase) and degradation (catalyzed by the photoreceptor phosphodiesterase, PDE6). Upon light stimulation, rapid activation of PDE6 by the heterotrimeric G-protein (transducin) triggers a dramatic drop in cGMP levels that lead to cell hyperpolarization. Following cessation of the light stimulus, the lifetime of activated PDE6 is also precisely regulated by additional processes. This review summarizes recent advances in the structural characterization of the rod and cone PDE6 catalytic and regulatory subunits in the context of previous biochemical studies of the enzymological properties and allosteric regulation of PDE6. Emphasis is given to recent advances in understanding the structural and conformational changes underlying the mechanism by which the activated transducin α-subunit binds to-and relieves inhibition of-PDE6 catalysis that is controlled by its intrinsically disordered, inhibitory γ-subunit. The role of the regulator of G-protein signaling 9-1 (RGS9-1) in regulating the lifetime of the transducin-PDE6 is also briefly covered. The therapeutic potential of pharmacological compounds acting as inhibitors or activators targeting PDE6 is discussed in the context of inherited retinal diseases resulting from mutations in rod and cone PDE6 genes as well as other inherited defects that arise from excessive cGMP accumulation in retinal photoreceptor cells.

Why new biology must be uncovered to advance therapeutic strategies for chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by the destruction of alveolar tissue (in emphysema) and airway remodeling (leading to chronic bronchitis), which cause difficulties in breathing. It is a growing public health concern with few therapeutic options that can reverse disease progression or mortality. This is in part because current treatments mainly focus on ameliorating symptoms induced by inflammatory pathways as opposed to curing disease. Hence, emerging research focused on upstream pathways are likely to be beneficial in the development of efficient therapeutics to address the root causes of disease. Some of these pathways include mitochondrial function, cytoskeletal structure and maintenance, and airway hydration, which are all affected by toxins that contribute to COPD. Because of the complexity of COPD and unknown targets for disease onset, simpler model organisms have proved to be useful tools in identifying disease-relevant pathways and targets. This review summarizes COPD pathology, current treatments, and therapeutic discovery research, with a focus on the aforementioned pathways that can advance the therapeutic landscape of COPD.

Phosphodiesterase Inhibitors: Could They Be Beneficial for the Treatment of COVID-19?

In March 2020, the World Health Organization declared the severe acute respiratory syndrome corona virus 2 (SARS-CoV2) infection to be a pandemic disease. SARS-CoV2 was first identified in China and, despite the restrictive measures adopted, the epidemic has spread globally, becoming a pandemic in a very short time. Though there is growing knowledge of the SARS-CoV2 infection and its clinical manifestations, an effective cure to limit its acute symptoms and its severe complications has not yet been found. Given the worldwide health and economic emergency issues accompanying this pandemic, there is an absolute urgency to identify effective treatments and reduce the post infection outcomes. In this context, phosphodiesterases (PDEs), evolutionarily conserved cyclic nucleotide (cAMP/cGMP) hydrolyzing enzymes, could emerge as new potential targets. Given their extended distribution and modulating role in nearly all organs and cellular environments, a large number of drugs (PDE inhibitors) have been developed to control the specific functions of each PDE family. These PDE inhibitors have already been used in the treatment of pathologies that show clinical signs and symptoms completely or partially overlapping with post-COVID-19 conditions (e.g., thrombosis, inflammation, fibrosis), while new PDE-selective or pan-selective inhibitors are currently under study. This review discusses the state of the art of the different pathologies currently treated with phosphodiesterase inhibitors, highlighting the numerous similarities with the disorders linked to SARS-CoV2 infection, to support the hypothesis that PDE inhibitors, alone or in combination with other drugs, could be beneficial for the treatment of COVID-19.

Nanodomains in cardiopulmonary disorders and the impact of air pollution

Air pollution is a major environmental threat and each year about 7 million people reported to die as a result of air pollution. Consequently, exposure to air pollution is linked to increased morbidity and mortality world-wide. Diesel automotive engines are a major source of urban air pollution in the western societies encompassing particulate matter and diesel exhaust particles (DEP). Air pollution is envisioned as primary cause for cardiovascular dysfunction, such as ischemic heart disease, cardiac dysrhythmias, heart failure, cerebrovascular disease and stroke. Air pollution also causes lung dysfunction, such as chronic obstructive pulmonary disease (COPD), asthma, idiopathic pulmonary fibrosis (IPF), and specifically exacerbations of these diseases. DEP induces inflammation and reactive oxygen species production ultimately leading to mitochondrial dysfunction. DEP impair structural cell function and initiate the epithelial-to-mesenchymal transition, a process leading to dysfunction in endothelial as well as epithelial barrier, hamper tissue repair and eventually leading to fibrosis. Targeting cyclic adenosine monophosphate (cAMP) has been implicated to alleviate cardiopulmonary dysfunction, even more intriguingly cAMP seems to emerge as a potent regulator of mitochondrial metabolism. We propose that targeting of the mitochondrial cAMP nanodomain bear the therapeutic potential to diminish air pollutant — particularly DEP — induced decline in cardiopulmonary function.

A Novel, Pan-PDE Inhibitor Exerts Anti-Fibrotic Effects in Human Lung Fibroblasts via Inhibition of TGF-β Signaling and Activation of cAMP/PKA Signaling

Phosphodiesterase (PDE) inhibitors are currently a widespread and extensively studied group of anti-inflammatory and anti-fibrotic compounds which may find use in the treatment of numerous lung diseases, including asthma and chronic obstructive pulmonary disease. Several PDE inhibitors are currently in clinical development, and some of them, e.g., roflumilast, are already recommended for clinical use. Due to numerous reports indicating that elevated intracellular cAMP levels may contribute to the alleviation of inflammation and airway fibrosis, new and effective PDE inhibitors are constantly being sought. Recently, a group of 7,8-disubstituted purine-2,6-dione derivatives, representing a novel and prominent pan-PDE inhibitors has been synthesized. Some of them were reported to modulate transient receptor potential ankyrin 1 (TRPA1) ion channels as well. In this study, we investigated the effect of selected derivatives (832—a pan-PDE inhibitor, 869—a TRPA1 modulator, and 145—a pan-PDE inhibitor and a weak TRPA1 modulator) on cellular responses related to airway remodeling using MRC-5 human lung fibroblasts. Compound 145 exerted the most considerable effect in limiting fibroblast to myofibroblasts transition (FMT) as well as proliferation, migration, and contraction. The effect of this compound appeared to depend mainly on its strong PDE inhibitory properties, and not on its effects on TRPA1 modulation. The strong anti-remodeling effects of 145 required activation of the cAMP/protein kinase A (PKA)/cAMP response element-binding protein (CREB) pathway leading to inhibition of transforming growth factor type β₁ (TGF-β₁) and Smad-dependent signaling in MRC-5 cells. These data suggest that the TGF-β pathway is a major target for PDE inhibitors leading to inhibitory effects on cell responses involved in airway remodeling. These potent, pan-PDE inhibitors from the group of 7,8-disubstituted purine-2,6-dione derivatives, thus represent promising anti-remodeling drug candidates for further research.

Phosphodiesterase isoforms and cAMP compartments in the development of new therapies for obstructive pulmonary diseases

The second messenger molecule 3'5'-cyclic adenosine monophosphate (cAMP) imparts several beneficial effects in lung diseases such as asthma, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). While cAMP is bronchodilatory in asthma and COPD, it also displays anti-fibrotic properties that limit fibrosis. Phosphodiesterases (PDEs) metabolize cAMP and thus regulate cAMP signaling. While some existing therapies inhibit PDEs, there are only broad family specific inhibitors. The understanding of cAMP signaling compartments, some centered around lipid rafts/caveolae, has led to interest in defining how specific PDE isoforms maintain these signaling microdomains. The possible altered expression of PDEs, and thus abnormal cAMP signaling, in obstructive lung diseases has been poorly explored. We propose that inhibition of specific PDE isoforms can improve therapy of obstructive lung diseases by amplifying specific cAMP signals in discreet microdomains.