Abstract
Severe deficiency of the major anti-elastase α1-antitrypsin (AT) due to Z (Glu342Lys) variant (Z-AT) (polymerizes within hepatocyte endoplasmic reticulum (ER)) is the commonest genetic reason for the development of COPD. F variant (Arg223Cys) of AT (F-AT) is linked with mild plasma deficiency. FZ heterozygote is linked to emphysema and cirrhosis. We assessed properties of F-AT in a cell-model. Human F-AT gene was transfected into lung epithelial (A549) cells and assessed supernatants, lysates or inclusion bodies at 24h and compared to normal non-polymerizing M-AT by ELISA/immunoblot. F-AT secretion was slightly lower, but comparable to M-AT secretion(1535±150pg/ml vs.1785±112, P=0.59). Secreted F-AT had reduced elastase inhibitory capacity (EIC) (0.5±0.1(OD@405nm) vs.1.2±0.1, P<0.001). F-AT formed insoluble aggregates of polymeric-AT(328±55pg/ml vs.undetectable), upregulated ER overload response (EOR) proteins; PERK(125KDa), ATF4(38KDa) and RGS16(29KDa), increased NF-κB(0.8±0.1(OD@450nm) vs.0.3±0.1, P<0.001), TNF-α(32±4pg/ml vs.12±3, P=0.04) and IL-6 (at 48h)(149±28pg/ml vs.27±15, P=0.004). All of which were inhibited by treatment with an inhibitor of polymerization (P<0.001 for all). Compared to polymerizing Z-AT, F-AT cells had greater F-AT secretion (P<0.001) but had reduced EIC (P=0.04), TNF-α (P=0.04), IL-6 (P=0.01), ER accumulated polymeric-AT, EOR protein expression and NF-κB (P<0.001 for all). M-AT cells do not have inclusion polymers or evidence of EOR activity. Conclusion, F-AT secretion was comparable to M-AT, but defective as an anti-elastase. F-AT aggregates as inclusion bodies and activates EOR mediated inflammation. This suggests that FZ phenotype may be at risk for lung disease.
- © 2014 ERS