Effects of Fine Particulate Matter (PM2.5) on the Larynx in a Mouse Model

Introduction: Exposure to fine particulate matter (PM2.5), a major air pollutant generated by wildfires and other sources, is increasing worldwide. While PM2.5 is known to adversely affect the lower airway, its interactions with the upper airway remain poorly understood. We describe a murine model of laryngeal PM2.5 exposure and characterize cellular and molecular responses in the vocal folds (VF) and subglottic (SG) larynx.

Methods: Forty-four male C57BL/6J mice were randomized to control or PM2.5 exposure groups for acute (2-day) or subacute (10-day) exposure schedules. PM2.5 mice underwent daily direct laryngoscopy with nebulized PM2.5 (NIST 2786; 2.5 mg/mL in saline) applied to the VF; controls received nebulized saline alone. VF and SG epithelial thickness and SG submucosal gland area were quantified histologically in harvested larynges. Expression of mucin, inflammatory, and epithelial structural genes was assessed using quantitative PCR. Groups were compared using the Mann–Whitney test (p < 0.05).

Results: Subacute PM2.5 exposure significantly increased VF epithelial thickness (p=0.0079), SG epithelial thickness (p=0.0079), and SG submucosal gland area (p=0.008), with PM2.5 particles visualized within the airway and submucosal glands. Subacutely exposed mice demonstrated significantly increased MUC5AC expression and significantly decreased TNF-α, β-catenin, and CXCL-1 expression. Acute PM2.5 exposures resulted in significantly increased IL-1β expression only.

Conclusions: We successfully established a mouse model of laryngeal PM2.5 exposures, revealing the measurable acute and subacute impacts of PM2.5 on the VF and SG. Persistent exposures to PM2.5 demonstrate increased structural and transcriptional impacts on the murine larynx. This work reveals the anatomic location and types of cells at risk during these exposures, highlights the vulnerability of the upper airway to PM2.5, and provides a foundation for further investigation into the laryngeal health effects of PM2.5.