The persistent inflammation in COPD: is autoimmunity the core mechanism?

COPD poses a significant global public health challenge, primarily characterised by irreversible airflow restriction and persistent respiratory symptoms. The hallmark pathology of COPD includes sustained airway inflammation and the eventual destruction of lung tissue structure. While multiple risk factors are implicated in the disease's progression, the underlying mechanisms remain largely elusive. The perpetuation of inflammation is pivotal to the advancement of COPD, emphasising the importance of investigating these self-sustaining mechanisms for a deeper understanding of the pathogenesis. Autoimmune responses constitute a critical mechanism in maintaining inflammation, with burgeoning evidence pointing to their central role in COPD progression; yet, the intricacies of these mechanisms remain inadequately defined. This review elaborates on the evidence supporting the presence of autoimmune processes in COPD and examines the potential mechanisms through which autoimmune responses may drive the chronic inflammation characteristic of the disease. Moreover, we attempt to interpret the clinical manifestations of COPD through autoimmunity.

Cigarette smoke-initiated autoimmunity facilitates sensitisation to elastin-induced COPD-like pathologies in mice.

It is currently not understood whether cigarette smoke exposure facilitates sensitisation to self-antigens and whether ensuing auto-reactive T cells drive chronic obstructive pulmonary disease (COPD)-associated pathologies.To address this question, mice were exposed to cigarette smoke for 2 weeks. Following a 2-week period of rest, mice were challenged intratracheally with elastin for 3 days or 1 month. Rag1-/- , Mmp12-/- , and Il17a-/- mice and neutralising antibodies against active elastin fragments were used for mechanistic investigations. Human GVAPGVGVAPGV/HLA-A*02:01 tetramer was synthesised to assess the presence of elastin-specific T cells in patients with COPD.We observed that 2 weeks of cigarette smoke exposure induced an elastin-specific T cell response that led to neutrophilic airway inflammation and mucus hyperproduction following elastin recall challenge. Repeated elastin challenge for 1 month resulted in airway remodelling, lung function decline and airspace enlargement. Elastin-specific T cell recall responses were dose dependent and memory lasted for over 6 months. Adoptive T cell transfer and studies in T cells deficient Rag1-/- mice conclusively implicated T cells in these processes. Mechanistically, cigarette smoke exposure-induced elastin-specific T cell responses were matrix metalloproteinase (MMP)12-dependent, while the ensuing immune inflammatory processes were interleukin 17A-driven. Anti-elastin antibodies and T cells specific for elastin peptides were increased in patients with COPD.These data demonstrate that MMP12-generated elastin fragments serve as a self-antigen and drive the cigarette smoke-induced autoimmune processes in mice that result in a bronchitis-like phenotype and airspace enlargement. The study provides proof of concept of cigarette smoke-induced autoimmune processes and may serve as a novel mouse model of COPD.

MTOR Suppresses Cigarette Smoke-Induced Epithelial Cell Death and Airway Inflammation in Chronic Obstructive Pulmonary Disease.

Airway epithelial cell death and inflammation are pathological features of chronic obstructive pulmonary disease (COPD). Mechanistic target of rapamycin (MTOR) is involved in inflammation and multiple cellular processes, e.g., autophagy and apoptosis, but little is known about its function in COPD pathogenesis. In this article, we illustrate how MTOR regulates cigarette smoke (CS)-induced cell death, airway inflammation, and emphysema. Expression of MTOR was significantly decreased and its suppressive signaling protein, tuberous sclerosis 2 (TSC2), was increased in the airway epithelium of human COPD and in mouse lungs with chronic CS exposure. In human bronchial epithelial cells, CS extract (CSE) activated TSC2, inhibited MTOR, and induced autophagy. The TSC2-MTOR axis orchestrated CSE-induced autophagy, apoptosis, and necroptosis in human bronchial epithelial cells; all of which cooperatively regulated CSE-induced inflammatory cytokines IL-6 and IL-8 through the NF-κB pathway. Mice with a specific knockdown of Mtor in bronchial or alveolar epithelial cells exhibited significantly augmented airway inflammation and airspace enlargement in response to CS exposure, accompanied with enhanced levels of autophagy, apoptosis, and necroptosis in the lungs. Taken together, these data demonstrate that MTOR suppresses CS-induced inflammation and emphysema-likely through modulation of autophagy, apoptosis, and necroptosis-and thus suggest that activation of MTOR may represent a novel therapeutic strategy for COPD.

Endoplasmic reticulum chaperone GRP78 mediates cigarette smoke-induced necroptosis and injury in bronchial epithelium.

Introduction: Bronchial epithelial cell death and airway inflammation induced by cigarette smoke (CS) have been involved in the pathogenesis of COPD. GRP78, belonging to heat shock protein 70 family, has been implicated in cell death and inflammation, while little is known about its roles in COPD. Here, we demonstrate that GRP78 regulates CS-induced necroptosis and injury in bronchial epithelial cells. Materials and methods: GRP78 and necroptosis markers were examined in human bronchial epithelial (HBE) cell line, primary mouse tracheal epithelial cells, and mouse lungs. siRNA targeting GRP78 gene and necroptosis inhibitor were used. Expression of inflammatory cytokines, mucin MUC5AC, and related signaling pathways were detected. Results: Exposure to CS significantly increased the expression of GRP78 and necroptosis markers in HBE cell line, primary mouse tracheal epithelial cells, and mouse lungs. Inhibition of GRP78 significantly suppressed CS extract (CSE)-induced necroptosis. Furthermore, GRP78-necroptosis cooperatively regulated CSE-induced inflammatory cytokines such as interleukin 6 (IL6), IL8, and mucin MUC5AC in HBE cells, likely through the activation of nuclear factor (NF-κB) and activator protein 1 (AP-1) pathways, respectively. Conclusion: Taken together, our results demonstrate that GRP78 promotes CSE-induced inflammatory response and mucus hyperproduction in airway epithelial cells, likely through upregulation of necroptosis and subsequent activation of NF-κB and AP-1 pathways. Thus, inhibition of GRP78 and/or inhibition of necroptosis could be the effective therapeutic approaches for the treatment of COPD.

Efficacy and safety of bronchoscopic lung volume reduction therapy in patients with severe emphysema: a meta-analysis of randomized controlled trials.

BACKGROUND: Increasing randomized controlled trials (RCTs) indicate that bronchoscopic lung volume reduction (BLVR) is effective for severe emphysema. In this meta-analysis, we investigated the efficacy and safety of BLVR in patients with severe emphysema. METHODS: PubMed, Embase and the Cochrane Library and reference lists of related articles were searched, and RCTs that evaluated BLVR therapy VS conventional therapy were included. Meta-analysis was performed only when included RCTs ≥ 2 trials. RESULTS: In total, 3 RCTs for endobronchial coils, 6 RCTs for endobronchial valves (EBV) and 2 RCTs for intrabronchial valves (IBV) were included. Compared with conventional therapy, endobronchial coils showed better response in minimal clinically important difference (MCID) for forced expiratory volume in 1s (FEV1) (RR = 2.37, 95% CI = 1.61 - 3.48, p < 0.0001), for 6-min walk test (6MWT) (RR = 2.05, 95% CI = 1.18 - 3.53, p = 0.01), and for St. George's Respiratory Questionnaire (SGRQ) (RR = 2.32, 95% CI = 1.77 - 3.03, p < 0.00001). EBV therapy also reached clinically significant improvement in FEV1 (RR = 2.96, 95% CI = 1.49 - 5.87, p = 0.002), in 6MWT (RR = 2.90, 95% CI = 1.24 - 6.79, p = 0.01), and in SGRQ (RR = 1.53, 95% CI = 1.22 - 1.92, p = 0.0002). Both coils and EBV treatment achieved statistically significant absolute change in FEV1, 6MWT, and SGRQ from baseline, also accompanied by serious adverse effects. Furthermore, subgroup analysis showed there was no difference between homogeneous and heterogeneous emphysema in coils group. However, IBV group failed to show superior to conventional group. CONCLUSIONS: Current meta-analysis indicates that coils or EBV treatment could significantly improve pulmonary function, exercise capacity, and quality of life compared with conventional therapy. Coils treatment could be applied in homogeneous emphysema, but further trials are needed.

Autophagy inhibitors suppress environmental particulate matter-induced airway inflammation.

Particulate matter (PM) is a significant risk factor for airway injury. We have recently demonstrated a pivotal role of autophagy in mediating PM-induced airway injury. In the present study, we examined the possible effects of autophagy inhibitors spautin-1 and 3-Methyladenine (3-MA) in protection of PM-induced inflammatory responses. We observed that PM triggered autophagy in human bronchial epithelial (HBE) cells and in mouse airways. Spautin-1 or 3-MA inhibited PM-induced expression of inflammatory cytokines in HBE cells, and decreased the neutrophil influx and proinflammatory cytokines induced by PM in vivo. We further illustrated that autophagy inhibitors suppressed the inflammation responses via inhibition of the nuclear factor-кB (NF-кB) pathway. Thus, this study shows a paradigm that autophagy inhibitors effectively decrease the PM-induced airway inflammation via suppressing the NF-кB pathway, which may provide novel preventive and/or protective approaches for PM-related airway injury.

Early growth response factor 1 is essential for cigarette smoke-induced MUC5AC expression in human bronchial epithelial cells.

Early growth response factor 1 (Egr-1) is a zinc finger transcription factor which responses rapidly to a variety of extracellular stimuli. Previous studies have suggested that Egr-1 exerts pathological functions in chronic obstructive pulmonary disease (COPD) by regulation of cigarette smoking-induced autophagy, cell death, and inflammation. However, little is known about the role of Egr-1 in regulation of mucus production in airway epithelium. In this study, we observed that cigarette smoke extract (CSE) induced a successive expression of Egr-1 and MUC5AC in human bronchial epithelial (HBE) cells. Knockdown of Egr-1 markedly attenuated CSE-induced MUC5AC production, and chromatin immunoprecipitation revealed that Egr-1 transcriptionally bound to MUC5AC promoter upon CSE stimulation. Concurrently, CSE increased the expression of c-Jun and c-Fos, two subunits of activator protein 1 (AP-1) which also critically regulates CSE-induced MUC5AC in HBE cells. CSE also induced a physical interaction of Egr-1 and AP-1, and knockdown of Egr-1 significantly decreased CSE-induced expression of c-Fos and c-Jun. Furthermore, knockdown of c-Fos remarkably attenuated the CSE-induced Egr-1 binding to MUC5AC promoter. These data taken together demonstrate that Egr-1 is essential for CSE-induced MUC5AC production in HBE cells likely through interaction with and modulation of AP-1, and re-emphasize targeting Egr-1 as a novel therapeutic strategy for COPD.

Autophagy as a double-edged sword in pulmonary epithelial injury: a review and perspective.

Pulmonary epithelial cells form the first line of defense of human airways against foreign irritants and also represent as the primary injury target of these pathogenic assaults. Autophagy is a revolutionary conserved ubiquitous process by which cytoplasmic materials are delivered to lysosomes for degradation when facing environmental and/or developmental changes, and emerging evidence suggests that autophagy plays pivotal but controversial roles in pulmonary epithelial injury. Here we review recent studies focusing on the roles of autophagy in regulating airway epithelial injury induced by various stimuli. Articles eligible for this purpose are divided into two groups according to the eventual roles of autophagy, either protective or deleterious. From the evidence summarized in this review, we draw several conclusions as follows: 1) in all cases when autophagy is decreased from its basal level, autophagy is protective; 2) when autophagy is deleterious, it is generally upregulated by stimulation; and 3) a plausible conclusion is that the endosomal/exosomal pathways may be associated with the deleterious function of autophagy in airway epithelial injury, although this needs to be clarified in future investigations.

Neutrophilic Inflammation in the Immune Responses of Chronic Obstructive Pulmonary Disease: Lessons from Animal Models.

Chronic obstructive pulmonary disease (COPD) is a major cause of mortality worldwide, which is characterized by chronic bronchitis, destruction of small airways, and enlargement/disorganization of alveoli. It is generally accepted that the neutrophilic airway inflammation observed in the lungs of COPD patients is intrinsically linked to the tissue destruction and alveolar airspace enlargement, leading to disease progression. Animal models play an important role in studying the underlying mechanisms of COPD as they address questions involving integrated whole body responses. This review aims to summarize the current animal models of COPD, focusing on their advantages and disadvantages on immune responses and neutrophilic inflammation. Also, we propose a potential new animal model of COPD, which may mimic the most characteristics of human COPD pathogenesis, including persistent moderate-to-high levels of neutrophilic inflammation.

Autophagy plays an essential role in cigarette smoke-induced expression of MUC5AC in airway epithelium.

Mucus hypersecretion is a common pathological feature of chronic airway inflammatory diseases including chronic obstructive pulmonary disease (COPD). However, the molecular basis for this condition remains incompletely understood. We have previously demonstrated a critical role of autophagy in COPD pathogenesis through mediating apoptosis of lung epithelial cells. In this study, we aimed to investigate the function of autophagy as well as its upstream and downstream signals in cigarette smoke-induced mucus production in human bronchial epithelial (HBE) cells and in mouse airways. Cigarette smoke extract (CSE), as well as the classical autophagy inducers starvation or Torin-1, significantly triggered MUC5AC expression, and inhibition of autophagy markedly attenuated CSE-induced mucus production. The CSE-induced autophagy was mediated by mitochondrial reactive oxygen species (mitoROS), which regulated mucin expression through the JNK and activator protein-1 pathway. Epidermal growth factor receptor (EGFR) was also required for CSE-induced MUC5AC in HBE cells, but it exerted inconsiderable effects on the autophagy-JNK signaling cascade. Airways of mice with dysfunctional autophagy-related genes displayed a markedly reduced number of goblet cells and attenuated levels of Muc5ac in response to cigarette smoke exposure. These results altogether suggest that mitoROS-dependent autophagy is essential for cigarette smoke-induced mucus hyperproduction in airway epithelial cells, and reemphasize autophagy inhibition as a novel therapeutic strategy for chronic airway diseases.

Autophagy is essential for ultrafine particle-induced inflammation and mucus hyperproduction in airway epithelium.

Environmental ultrafine particulate matter (PM) is capable of inducing airway injury, while the detailed molecular mechanisms remain largely unclear. Here, we demonstrate pivotal roles of autophagy in regulation of inflammation and mucus hyperproduction induced by PM containing environmentally persistent free radicals in human bronchial epithelial (HBE) cells and in mouse airways. PM was endocytosed by HBE cells and simultaneously triggered autophagosomes, which then engulfed the invading particles to form amphisomes and subsequent autolysosomes. Genetic blockage of autophagy markedly reduced PM-induced expression of inflammatory cytokines, e.g. IL8 and IL6, and MUC5AC in HBE cells. Mice with impaired autophagy due to knockdown of autophagy-related gene Becn1 or Lc3b displayed significantly reduced airway inflammation and mucus hyperproduction in response to PM exposure in vivo. Interference of the autophagic flux by lysosomal inhibition resulted in accumulated autophagosomes/amphisomes, and intriguingly, this process significantly aggravated the IL8 production through NFKB1, and markedly attenuated MUC5AC expression via activator protein 1. These data indicate that autophagy is required for PM-induced airway epithelial injury, and that inhibition of autophagy exerts therapeutic benefits for PM-induced airway inflammation and mucus hyperproduction, although they are differentially orchestrated by the autophagic flux.

Interaction of caveolin-1 with ATG12-ATG5 system suppresses autophagy in lung epithelial cells.

Autophagy plays a pivotal role in cellular homeostasis and adaptation to adverse environments, although the regulation of this process remains incompletely understood. We have recently observed that caveolin-1 (Cav-1), a major constituent of lipid rafts on plasma membrane, can regulate autophagy in cigarette smoking-induced injury of lung epithelium, although the underlying molecular mechanisms remain incompletely understood. In the present study we found that Cav-1 interacted with and regulated the expression of ATG12-ATG5, an ubiquitin-like conjugation system crucial for autophagosome formation, in lung epithelial Beas-2B cells. Deletion of Cav-1 increased basal and starvation-induced levels of ATG12-ATG5 and autophagy. Biochemical analyses revealed that Cav-1 interacted with ATG5, ATG12, and their active complex ATG12-ATG5. Overexpression of ATG5 or ATG12 increased their interactions with Cav-1, the formation of ATG12-ATG5 conjugate, and the subsequent basal levels of autophagy but resulted in decreased interactions between Cav-1 and another molecule. Knockdown of ATG12 enhanced the ATG5-Cav-1 interaction. Mutation of the Cav-1 binding motif on ATG12 disrupted their interaction and further augmented autophagy. Cav-1 also regulated the expression of ATG16L, another autophagy protein associating with the ATG12-ATG5 conjugate during autophagosome formation. Altogether these studies clearly demonstrate that Cav-1 competitively interacts with the ATG12-ATG5 system to suppress the formation and function of the latter in lung epithelial cells, thereby providing new insights into the molecular mechanisms by which Cav-1 regulates autophagy and suggesting the important function of Cav-1 in certain lung diseases via regulation of autophagy homeostasis.

Caveolin-1 inhibits expression of antioxidant enzymes through direct interaction with nuclear erythroid 2 p45-related factor-2 (Nrf2).

The Nrf2 (nuclear erythroid 2 p45-related factor-2) signaling pathway is known to play a pivotal role in a variety of oxidative stress-related human disorders. It has been reported recently that the plasma membrane resident protein caveolin-1 (Cav-1) can regulate expression of certain antioxidant enzymes and involves in the pathogenesis of oxidative lung injury, but the detailed molecular mechanisms remain incompletely understood. Here, we demonstrated that Cav-1 inhibited the expression of antioxidant enzymes through direct interaction with Nrf2 and subsequent suppression of its transcriptional activity in lung epithelial Beas-2B cells. Cav-1 deficiency cells exhibited higher levels of antioxidant enzymes and were more resistant to oxidative stress induced cytotoxicity, whereas overexpression of Cav-1 suppressed the induction of these enzymes and further augmented the oxidative cell death. Cav-1 constitutively interacted with Nrf2 in both cytosol and nucleus. Stimulation of 4-hydroxynonenol increased the Cav-1-Nrf2 interaction in cytosol but disrupted their association in the nucleus. Knockdown of Cav-1 also disassociated the interaction between Nrf2 and its cytoplasmic inhibitor Keap1 (Kelch-like ECH-associated protein 1) and increased the Nrf2 transcription activity. Mutation of the resembling Cav-1 binding motif on Nrf2 effectively attenuated their interaction, which exhibited higher transcription activity and induced higher levels of antioxidant enzymes relative to the wild-type control. Altogether, these studies clearly demonstrate that Cav-1 inhibits cellular antioxidant capacity through direct interaction with Nrf2 and subsequent suppression of its activity, thereby implicating in certain oxidative stress-related human pathologies.