Cysteinyl leukotriene D₄ (LTD₄) promotes airway epithelial cell inflammation and remodelling

Cysteinyl leukotrienes (CysLTs), a group of inflammatory lipid mediators, are found elevated in obese-asthmatic patients. Leukotriene D₄ (LTD₄), a representative CysLT, is implicated in promoting lung inflammation and remodelling in allergic asthma, but its role in non-allergic asthma, especially in obese-asthmatic patients, is not known. Here, using primary human small airway epithelial cells (SAECs) we have investigated the mechanism of LTD₄-induced inflammation and remodelling and assessed high proneness of obese mice to develop asthma upon challenge with allergen ovalbumin (OVA).

Primary human small airway epithelial cells (SAECs) were stimulated with different concentrations of LTD₄ for different time intervals and various inflammatory markers were measured through cytokine array, membrane-based ELISA and Western blotting. An air-liquid interface (ALI) model of SAECs was used to study the effects of LTD₄-induced remodelling in SAECs using Western blotting, H&E staining and PAS staining. Further, OVA-based murine model was used to examine the propensity of high-fat diet (HFD)-fed obese mice to develop asthma symptoms by studying the infiltration of inflammatory cells (assessed by bronchioalveolar lavage (BAL) cytology) and airway remodelling (assessed by histopathology) upon allergen exposure.

The human primary small airway epithelial cells (SAECs) treated with LTD₄ showed significant alterations in the levels of inflammatory markers such as GM-CSF, TNF-α, IL-1β, EGF and eotaxin in dose- and time-dependent manner. Further, LTD₄ enhanced the activation of inflammasomes as evidenced by increased levels of NALP3, cleaved caspase-1 and IL-1β. LTD₄ also enhanced inflammation by increasing the expression of COX-2 in SAECs. The airway remodelling markers Vimentin and Muc5AC were found elevated in ALI culture of SAECs when stimulated with LTD₄, as it also increased TGF-β levels and activation of Smad2/3 phosphorylation in SAECs. Last, sensitization and challenge of HFD-fed obese mice with OVA showed increased infiltration of inflammatory cells in BAL and enhanced levels of remodeling phenotypes like loss of cilia, mucus cell metaplasia and collagen deposition in mice lung tissues.

The results suggest that LTD₄ could induce inflammatory response in human airway epithelial cell by activating NALP3 inflammasome. LTD₄ could further promote airway epithelial cells' remodelling through TGF-β/smad2/3-mediated pathway. Our in vivo results suggested that obesity predisposed the OVA challenged mice to develop lung inflammation and remodelling akin to asthma-like phenotypes during obesity.