Small-Airway Dysfunction is Involved in the Pathogenesis of Asthma: Evidence from Two Mouse Models

Abstract

Background

There has been growing evidence of small-airway dysfunction in patients with asthma. Few studies have evaluated the mechanism of small-airway dysfunction in mouse models of asthma.

Purpose

We explored the correlation between small-airway spirometric variables and large-airway function or inflammation in different endotypes of asthma.

Methods

Ovalbumin (OVA) sensitization/challenge was used to produce a type 2 (T2)-high asthma model, and OVA combined with ozone exposure (OVA + ozone) was used for the T2-low asthma model with increased neutrophils. Spirometry, airway responsiveness, cytokine levels in bronchoalveolar lavage fluid (BALF), and pathological analyses of lung slices stained with hematoxylin-eosin, periodic acid–Schiff, and Masson’s trichrome stain were all determined. Muc5ac expression in lung tissue was evaluated by the reverse transcription-polymerase chain reaction (RT-PCR), and alpha-smooth muscle actin was measured by immunohistochemistry.

Results

Inflammatory cells infiltrated the lung tissue and inflammatory cytokines were increased in the BALF of both the OVA and OVA + ozone groups, compared with the control group. Peribronchial hypersecretion and collagen deposition were evident in the models. The OVA + ozone group showed greater neutrophilic infiltration and peribronchial smooth muscle proliferation than the OVA group. Large-airway obstruction, small-airway dysfunction, and airway hyperresponsiveness were confirmed in both models. Small-airway functional variables, such as MMEF (mean midexpiratory flow, average flow from 25 to 75% forced vital capacity [FVC]) and FEF50 (forced expiratory flow at 50% of FVC), were positively correlated with large-airway function and had a stronger negative correlation with airway inflammation, mucus secretion, and responsiveness than large-airway function.

Conclusion

Small-airway dysfunction was evident in the two endotypes of asthma and was correlated with severe airway inflammation, mucus hypersecretion, and airway hyperresponsiveness. The small airways may be an important target in asthma treatment, and further research in the role of small-airway variables in the pathogenesis of asthma is warranted.

Keywords:

• small airway
• spirometry
• airway inflammation
• asthma
• airway hyperresponsiveness

Abbreviations

α-SMA, α-smooth muscle actin; BALF, Bronchoalveolar lavage fluid; BHR, Bronchial hyperresponsiveness; ELISA, Enzyme-linked immunosorbent assay; FEV0.1, Volume expired in first 0.1s of fast expiration; FEV1, Volume expired in first 1s of fast expiration; FEF75, Forced Expiratory Flow at 75% of Forced Vital Capacity; FEF50, Forced Expiratory Flow at 50% of Forced Vital Capacity; FEF25, Forced Expiratory Flow at 25% of Forced Vital Capacity; FENO, Fractional exhaled nitric oxide; FEV25, Volume expired in first 25ms of fast expiration; FEV50, Volume expired in first 50ms of fast expiration; FEV75, Volume expired in first 75ms of fast expiration; FVC, Forced vital capacity; HE, Hematoxylin-Eosin; ICS, Inhaled corticosteroids; MMEF, Forced expiratory flow between 25 and 75% FVC; OVA, ovalbumin; PAS, Periodic Acid-Schiff; PC20, the concentration of methacholine that induces a 20% decline in FEV1; PC100, the ACh concentration demanded to elevate R_L by 100% from baseline was calculated; R5-R20, peripheral airway resistance as the difference between 5 and 20 Hz; R_L, lung resistance.

Study Approval and Ethics Statement

The study was approved by the Ethics Committee for Animal Studies at Shanghai General Hospital, China (IACUC: 2019-A011-01) and carried out in accordance with the Guide for the Care and Use of Laboratory Animals (National Academies Press, 2011). All surgeries were performed under anesthesia, and all efforts were made to minimize the suffering of animals. The experimental protocols were approved by Shanghai General Hospital Institutional Review Board, Shanghai, China.

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

The study was supported by National Natural Science Foundation of China (Grant No. 81873402); Appropriate technique application Program of Shanghai Municipal Health System (Grant No.2019SY042); Scientific and Technological Innovation program funded by Science and Technology Commission of Shanghai municipality (Grant No. 20Y11902400); Program of Shanghai Municipal Health System (Grant No.201740039).