Polymerized Z-α-1 antitrypsin leads to lung injury in a murine model of emphysema

In α-1 antitrypsin (AAT) deficiency (AATD), emphysema is classically linked to protease-antiprotease imbalance caused by decreased antiprotease AAT due levels and function. This decrease is secondary to the impaired release of Z-AAT polymers from hepatocytes carrying Pi*Z, E342K mutation in SERPENA1 gene. Whether the accumulation of Z-AAT polymers in distal lungs contributes directly to emphysema pathogenesis has remained unexplored due to the lack of suitable model systems. We characterized lung injury and airspace enlargement in a Z-AAT-overexpressing murine model. We generated Z-AAT Serpina1Null mice overexpressing human (E342K) SERPENA1 in Serpina1Null mice and analyzed pulmonary phenotypes in young and aged animals, complemented by translational studies using primary cells, bronchoalveolar lavage fluid (BALf), and lung tissue from individuals who have never smoked and individuals with AATD. Young Z-AAT Serpina1Null mice accumulated Z-AAT polymers in hepatocytes, plasma, and BALf, exhibited spontaneous neutrophilic lung inflammation, increased alveolo-capillary permeability, and premature airspace enlargement, which was worse in older Z-AAT Serpina1Null mice. Moreover, Z-AAT polymers accumulated in alveolar type-2 epithelial (AT2) cells and lung macrophages, associated with endoplasmic reticulum (ER) stress, mitochondria dysfunction, and incomplete autophago-lysosomal fusion, which we recapitulated in lung samples from individuals with AATD. These findings support the pathogenic role of Z-AAT polymer accumulation in distal lung epithelium as a driver of epithelial, endothelial, and macrophage dysfunction linked to AATD emphysema.