Muc5b-deficient mice develop early histological lung abnormalities

Bleomycin-Induced Pulmonary Fibrosis in Transgenic Mice Carrying the Human MUC5B rs35705950 Variant

Idiopathic pulmonary fibrosis (IPF) is a progressive, often fatal lung disease characterized by tissue scarring and declining lung function. The MUC5B promoter polymorphism rs35705950, a significant genetic predisposition for IPF, paradoxically associates with better survival and slower disease progression than other IPF genotypes. This study investigates the potential paradoxical protective effects of this MUC5B variant in lung fibrosis. For this purpose, we developed a transgenic mouse model overexpressing the human MUC5B rs35705950 variant in the proximal large airways. Lung fibrosis was induced through subcutaneous injection of bleomycin. Results demonstrated significantly reduced lung fibrosis severity in transgenic mice compared to wild-type mice, assessed by trichrome staining, Ashcroft scoring, and hydroxyproline levels. Additionally, transgenic mice showed significantly lower levels of inflammatory cells and cytokines (TNFα, IL-6, IFNγ) and growth factors (PDGF, CTGF, IL-13) in the bronchoalveolar lavage fluid and lung tissues. There was also a significant decrease in mRNA expressions of fibrosis-related markers (periostin, fibronectin, Col1a1). In summary, this study reveals that mucin overexpression related to the MUC5B rs35705950 variant in the large airways significantly attenuates lung fibrosis and inflammatory responses in transgenic mice. These findings suggest that the rs35705950 variant modulates inflammatory and fibrotic responses in the proximal airways, which may contribute to the slower disease progression observed in IPF patients carrying this variant. Our study offers a possible explanation for the paradoxical beneficial effects of the MUC5B variant despite its role as a significant predisposing factor for IPF.

Time-course transcriptome analysis of a double challenge bleomycin-induced lung fibrosis rat model uncovers ECM homoeostasis-related translationally relevant genes

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is an irreversible disorder with a poor prognosis. The incomplete understanding of IPF pathogenesis and the lack of accurate animal models is limiting the development of effective treatments. Thus, the selection of clinically relevant animal models endowed with similarities with the human disease in terms of lung anatomy, cell biology, pathways involved and genetics is essential. The bleomycin (BLM) intratracheal murine model is the most commonly used preclinical assay to evaluate new potential therapies for IPF. Here, we present the findings derived from an integrated histomorphometric and transcriptomic analysis to investigate the development of lung fibrosis in a time-course study in a BLM rat model and to evaluate its translational value in relation to IPF.

METHODS

Rats were intratracheally injected with a double dose of BLM (days 0-4) and sacrificed at days 7, 14, 21, 28 and 56. Histomorphometric analysis of lung fibrosis was performed on left lung sections. Transcriptome profiling by RNAseq was performed on the right lung lobes and results were compared with nine independent human gene-expression IPF studies.

RESULTS

The histomorphometric and transcriptomic analyses provided a detailed overview in terms of temporal gene-expression regulation during the establishment and repair of the fibrotic lesions. Moreover, the transcriptomic analysis identified three clusters of differentially coregulated genes whose expression was modulated in a time-dependent manner in response to BLM. One of these clusters, centred on extracellular matrix (ECM)-related process, was significantly correlated with histological parameters and gene sets derived from human IPF studies.

CONCLUSIONS

The model of lung fibrosis presented in this study lends itself as a valuable tool for preclinical efficacy evaluation of new potential drug candidates. The main finding was the identification of a group of persistently dysregulated genes, mostly related to ECM homoeostasis, which are shared with human IPF.

Modeling mucus physiology and pathophysiology in human organs-on-chips

The surfaces of human internal organs are lined by a mucus layer that ensures symbiotic relationships with commensal microbiome while protecting against potentially injurious environmental chemicals, toxins, and pathogens, and disruption of this layer can contribute to disease development. Studying mucus biology has been challenging due to the lack of physiologically relevant human in vitro models. Here we review recent progress that has been made in the development of human organ-on-a-chip microfluidic culture models that reconstitute epithelial tissue barriers and physiologically relevant mucus layers with a focus on lung, colon, small intestine, cervix and vagina. These organ-on-a-chip models that incorporate dynamic fluid flow, air-liquid interfaces, and physiologically relevant mechanical cues can be used to study mucus composition, mechanics, and structure, as well as investigate its contributions to human health and disease with a level of biomimicry not possible in the past.

Azithromycin inhibits mucin secretion, mucous metaplasia, airway inflammation and airways hyperresponsiveness in mice exposed to house dust mite extract

Excessive production, secretion and retention of abnormal mucus is a pathologic feature of many obstructive airways diseases including asthma, chronic obstructive pulmonary disease, cystic fibrosis and bronchiectasis. Azithromycin is an antibiotic that also possesses immunomodulatory and mucoregulatory activities, which may contribute to the clinical effectiveness of azithromycin in these obstructive airway diseases. The current study investigated these non-antibiotic activities of azithromycin (or saline) in mice exposed daily to intranasal house dust mite (HDM) extract (or SHAM inoculation) for 10 days. HDM-exposed mice exhibited airways hyperresponsiveness to aerosolised methacholine, a pronounced mixed eosinophilic and neutrophilic inflammatory response, increased airway smooth muscle (ASM) thickness and elevated levels of epithelial mucin staining (compared to SHAM mice). Azithromycin (50 mg/kg s.c., 2 h prior to each HDM exposure) significantly attenuated HDM-induced airways hyperresponsiveness to methacholine, airways inflammation (bronchoalveolar lavage eosinophil and neutrophils numbers, and cytokine/chemokine levels), and epithelial mucin staining (mucous metaplasia) (P<0.05, 2-way ANOVA). Isolated tracheal segments of HDM-exposed mice secreted Muc5ac and Muc5b (above baseline levels) in response to exogenous ATP. Moreover, ATP-induced secretion of mucins was significantly attenuated in segments obtained from azithromycin-treated, HDM-exposed mice (P<0.05, 2-way ANOVA). In additional ex vivo studies, ATP-induced secretion of Muc5ac from HDM-exposed tracheal segments was inhibited by in vitro exposure to azithromycin. In vitro azithromycin also inhibited ATP-induced secretion of Muc5ac and Muc5b in tracheal segments from IL-13-exposed mice. In summary, azithromycin inhibited ATP-induced mucin secretion and airways inflammation in HDM-exposed mice, both of which are likely to contribute to suppression of airways hyperresponsiveness.

MUC5B regulates goblet cell differentiation and reduces inflammation in a murine COPD model

Background

Airway mucus hypersecretion is one of the important pathological features of chronic obstructive pulmonary disease (COPD). MUC5B is the main mucin expressed in the airways of COPD patients and has been indicated to play an important role in airway defense. However, the specific biological function of MUC5B in COPD and the possible mechanism are not clear.

Methods

We established a COPD model with 24-week-old MUC5B^−/− mice exposed to cigarette smoke and tested our hypothesis through lung function tests, HE and PAS staining, immunohistochemistry (IHC), western blot, q-PCR and ELISA.

Results

Compared with MUC5B^+/+ mice, MUC5B^−/− mice had worse general condition and lung function, increased inflammatory infiltration, reduced goblet cell differentiation as indicated by decreased PAS staining (PAS grade: 1.8 ± 0.24 vs. 0.6 ± 0.16), reduced MUC5AC expression (ELISA: 0.30 ± 0.01 vs. 0.17 ± 0.01 mg/ml, q-PCR: 9.4 ± 1.7 vs. 4.1 ± 0.1 fold, IHC score: 3.1 ± 0.9 vs. 1.6 ± 0.7), increased macrophage secretion of inflammatory factors (TNF-α and IL-6) and expression of downstream pathway factors (ERK1/2 and NF-κB), decreased expression of SPDEF and STAT6, and increased expression of FOXA2.

Conclusion

The protective effect of MUC5B in the development of COPD was mediated by the promotion of goblet cell differentiation and the inhibition of inflammation. The role of MUC5B in regulating inflammation was related to macrophage function, and goblet cell differentiation was promoted by the induced expression of STAT6 and SPDEF. This study describes a mechanism of mucus hypersecretion and identifies MUC5B as a new target for the treatment of mucus hypersecretion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01920-8.

Genetics and animal models of familial pulmonary fibrosis

Pulmonary fibrosis is caused by the interplay between genetic and environmental factors. Recent studies have revealed various genes associated with idiopathic pulmonary fibrosis, as well as the causative genes for familial pulmonary fibrosis. Although increased death or dysfunction of type 2 alveolar epithelial (AT2) cells has been detected in lung specimens from pulmonary fibrosis patients, it remains unclear whether and how AT2 cell death or dysfunction is responsible for the progression of pulmonary fibrosis. A recent study showed that increased AT2 cell necroptosis is the initial event in pulmonary fibrosis by analyzing patients with familial pulmonary fibrosis and an animal model that harbors the same mutation as patients. The contribution of AT2 cell necroptosis to the pathogenesis of pulmonary fibrosis has not been identified in animal model studies, which validates the effectiveness of genetic analysis of familial diseases to uncover unknown pathogeneses. Thus, further extensive genetic studies of pulmonary fibrosis along with functional studies based on genetic analysis will be crucial not only in elucidating the precise disease process but also, ultimately, in identifying novel treatment strategies for both familial and non-familial pulmonary fibrosis.

The Known Unknowns of the Immune Response to Coccidioides

Coccidioidomycosis, otherwise known as Valley Fever, is caused by the dimorphic fungi Coccidioides immitis and C. posadasii. While most clinical cases present with self-limiting pulmonary infection, dissemination of Coccidioides spp. results in prolonged treatment and portends higher mortality rates. While the structure, genome, and niches for Coccidioides have provided some insight into the pathogenesis of disease, the underlying immunological mechanisms of clearance or inability to contain the infection in the lung are poorly understood. This review focuses on the known innate and adaptive immune responses to Coccidioides and highlights three important areas of uncertainty and potential approaches to address them. Closing these gaps in knowledge may enable new preventative and therapeutic strategies to be pursued.

The Cervicovaginal Mucus Barrier

Preterm births are a global health priority that affects 15 million babies every year worldwide. There are no effective prognostic and therapeutic strategies relating to preterm delivery, but uterine infections appear to be a major cause. The vaginal epithelium is covered by the cervicovaginal mucus, which is essential to health because of its direct involvement in reproduction and functions as a selective barrier by sheltering the beneficial lactobacilli while helping to clear pathogens. During pregnancy, the cervical canal is sealed with a cervical mucus plug that prevents the vaginal flora from ascending toward the uterine compartment, which protects the fetus from pathogens. Abnormalities of the cervical mucus plug and bacterial vaginosis are associated with a higher risk of preterm delivery. This review addresses the current understanding of the cervicovaginal mucus and the cervical mucus plug and their interactions with the microbial communities in both the physiological state and bacterial vaginosis, with a focus on gel-forming mucins. We also review the current state of knowledge of gel-forming mucins contained in mouse cervicovaginal mucus and the mouse models used to study bacterial vaginosis.

Antisense Oligonucleotides Targeting Jagged 1 Reduce House Dust Mite-induced Goblet Cell Metaplasia in the Adult Murine Lung

Goblet cell metaplasia, excessive mucus production, and inadequate mucus clearance accompany and exacerbate multiple chronic respiratory disorders, such as asthma and chronic obstructive pulmonary disease. Notch signaling plays a central role in controlling the fate of multiple cell types in the lung, including goblet cells. In the present study, we explored the therapeutic potential of modulating the Notch pathway in the adult murine lung using chemically modified antisense oligonucleotides (ASOs). To this end, we designed and characterized ASOs targeting the Notch receptors Notch1, Notch2, and Notch3 and the Notch ligands Jag1 (Jagged 1) and Jag2 (Jagged 2). Pulmonary delivery of ASOs in healthy mice or mice exposed to house dust mite, a commonly used mouse model of asthma, resulted in a significant reduction of the respective mRNAs in the lung. Furthermore, ASO-mediated knockdown of Jag1 or Notch2 in the lungs of healthy adult mice led to the downregulation of the club cell marker Scgb1a1 and the concomitant upregulation of the ciliated cell marker FoxJ1 (forkhead box J1). Similarly, ASO-mediated knockdown of Jag1 or Notch2 in the house dust mite disease model led to reduced goblet cell metaplasia and decreased mucus production. Because goblet cell metaplasia and excessive mucus secretion are a common basis for many lung pathologies, we propose that ASO-mediated inhibition of JAG1 could provide a novel therapeutic path for the treatment of multiple chronic respiratory diseases.

Infectivity and Progression of COVID-19 Based on Selected Host Candidate Gene Variants

Introduction: Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) has spread around the globe. Susceptibility has been associated with age, biological sex, and other prior existing health conditions. However, host genes are involved in viral infectivity and pathogenicity, and polymorphisms in these could be responsible for the interethnic/interindividual variability observed in infection and progression of COVID-19. Materials and Methods: Clinical exome data of 103 individuals was analyzed to identify sequence variants in five selected candidate genes: ACE2, TMPRSS2, CD209, IFITM3, and MUC5B to assess their prevalence and role to understand the COVID-19 infectivity and progression in our population. Results: A total of 497 polymorphisms were identified in the five selected genes in the exomes analyzed. Thirty-eight polymorphisms identified in our cohort have been reported earlier in literature and have functional significance or association with health conditions. These variants were classified into three groups: protective, susceptible, and responsible for comorbidities. Discussion and Conclusion: The two polymorphisms described in literature as risk inducing are rs35705950 in MUC5B gene and TMPRSS2 haplotype (rs463727, rs34624090, rs55964536, rs734056, rs4290734, rs34783969, rs11702475, rs35899679, and rs35041537) were absent in our cohort explaining the slower infectivity of the disease in this part of India. The 38 functional variants identified can be used as a predisposition panel for the COVID-19 infectivity and progression and stratify individuals as "high or low risk," which would help in planning appropriate surveillance and management protocols. A larger study from different regions of India is warranted to validate these results.