Pulmonary ORMDL3 is critical for induction of Alternaria-induced allergic airways disease

Abstract

BackgroundGenome-wide association studies have identified the ORM (yeast)-like protein isoform 3 (ORMDL3) gene locus on human chromosome 17q to be a highly significant risk factor for childhood-onset asthma.ObjectiveWe sought to investigate in vivo the functional role of ORMDL3 in disease inception.MethodsAn Ormdl3-deficient mouse was generated and the role of ORMDL3 in the generation of allergic airways disease to the fungal aeroallergen Alternaria alternata was determined. An adeno-associated viral vector was also used to reconstitute ORMDL3 expression in airway epithelial cells of Ormdl3 knockout mice.ResultsOrmdl3 knockout mice were found to be protected from developing allergic airways disease and showed a marked decrease in pathophysiology, including lung function and airway eosinophilia induced by Alternaria. Alternaria is a potent inducer of cellular stress and the unfolded protein response, and ORMDL3 was found to play a critical role in driving the activating transcription factor 6–mediated arm of this response through Xbp1 and downstream activation of the endoplasmic reticulum–associated degradation pathway. In addition, ORMDL3 mediated uric acid release, another marker of cellular stress. In the knockout mice, reconstitution of Ormdl3 transcript levels specifically in the bronchial epithelium resulted in reinstatement of susceptibility to fungal allergen–induced allergic airways disease.ConclusionsThis study demonstrates that ORMDL3, an asthma susceptibility gene identified by genome-wide association studies, contributes to key pathways that promote changes in airway physiology during allergic immune responses.

Cutting Edge: Targeting Epithelial ORMDL3 Increases, Rather than Reduces, Airway Responsiveness and Is Associated with Increased Sphingosine-1-Phosphate

“…There are several potential reasons why this was not the case including a) differences in hORMDL3 zp3-Cre mice compared to Ormdl3 Δ2-3/Δ2- 3 CC10 mice in cell types expressing or not expressing ORMDL3 (increased expression in all cells vs selectively deficient in airway epithelium), b) AHR differences detected with no allergen challenge (hORMDL3 zp3-Cre mice vs WT mice) vs AHR differences detected with an allergen challenge (OVA + Ormdl3 Δ2-3/Δ2- 3 CC10 vs OVA + WT mice), and c) potential different ORMDL3 downstream pathways mediating increased AHR (S1P derived from airway epithelium in Ormdl3 Δ2-3/Δ2- 3 CC10 mice vs SERCA2b in airway smooth muscle in hORMDL3 zp3-Cre mice). Studies have also demonstrated that universal ORMDL3 deficient mice have reduced AHR when challenged with Alternaria, but have not examined whether selective epithelial inactivation of ORMDL3 as in this study effects AHR (14). Thus, further studies are needed to determine which cell types expressing ORMDL3 contribute to increased AHR and through which of several downstream pathways regulated by ORMDL3 (ATF6α, SERCA2b, S1P, chemokines, remodeling genes, or other pathways)(2, 3) this may be mediated.…”

A pathophysiological role of PDE3 in allergic airway inflammation

“…We decided to measure the albumin content directly in BAL fluid and not via the indirect method of Evans blue dye (52,56). By measuring albumin in lavage or in tissue, we could clearly see a close correlation between inflammation and albumin concentration.…”

“…The next step in this study was to demonstrate this endothelial permeability by analysis of the leakage of large serum proteins like albumin (52,53). When endothelial barrier function is impaired, more albumin will leak through the airway's endothelium into the lung mucosal tissue (edema), which in turn is responsible for additional airway narrowing in asthmatics (54).…”

“…The PDE3 inhibitor cilostazol has been shown to improve barrier function by reducing leakage of albumin in vitro (55). We studied albumin leakage in both lung tissue and alveolar lumen by ELISA, which is reliable, instead of indirect Evans blue dye techniques (52,53,56). Initially, PBS-treated WT, PDE3A -/-, and PDE3B -/-mice had albumin levels that are within the normal range.…”

Advances in environmental and occupational disorders in 2016

“…Loser et al used murine models to demonstrate that an asthma susceptibility gene, ORMDL3 , contributed to key pathways promoting airway inflammation induced by Alternaria . (26)…”