Periostin expression in the U-BIOPRED severe asthma bronchoscopy cohort

Periostin (POSTN) is secreted basolaterally by bronchial epithelial cells in asthma and is expressed in the extracellular matrix where it is thought to play a role in fibrosis and is associated with airway eosinophilia.In this study we have assessed the protein expression of POSTN in bronchial biopsies by immunohistochemistry, in serum by the Elecsys Periostin Immunoassay and measured gene expression by Affymetrix arrays in bronchial biopsies, bronchial brushings and in sputum in the U-BIOPRED severe asthma study in the bronchoscopy sub-cohort, which included 4 groups; severe non-smoker asthmatics (SAns), current / ex-smoker severe asthmatics (SAs), mild-moderate asthmatics (MMA) and non-asthmatic healthy controls (HC).Subepithelial protein expression in the bronchial biopsies was higher (p=0.02) in SAns, 9.2% (IQR 5.8-12.6)(n=44) compared to SAs 6.2% (3-9.2)(n=16), and in MMA 11% (7.5-12.6)(n=32) compared to SAs (p=0.002) or HC 7.1% (5.5-10.3)(p=0.01)(n=39). There was no difference between SAns and MMA. Gene expression was higher in biopsies from SAns (n=30), -0.044 (IQR -0.425-0.508), compared to both the SAs (n=9), -0.274 (-0.590-0.200), (p=0.02) and HC (n=21), -0.377 (-0.583-0.125), (p=0.008), but similar in MMA. There was no difference between the groups in POSTN serum levels or in gene expression in bronchial brushings or sputum. In asthmatics, the biopsy protein expression correlated with the biopsy gene expression, and both correlated with eosinophils numbers in the biopsies and blood, exhaled NO, and thickness of the lamina reticularis. These results highlight the potential relevance of tissue POSTN to asthma pathophysiology however, this does not appear to be reflected by serum POSTN measures.