Role of Alpha1-Z-AT polymers in the lung

Alpha-1-Antitrypsin (AAT) is the main proteinase inhibitor within the lung. It is produced primarily by hepatocytes. The normal AAT protein is known as M-AAT. There are more than 100 variants described of which the Z variant is the most clinically relevant. The Z mutant of AAT is inactive and prone to polymerization. Polymers of Z-AAT aggregate within the producer cells.
Z-AAT homozygotes are characterized by severe plasma deficiency of the protein and by premature panacinar emphysema. The pathogenesis of emphysema in Z-AAT homozygotes is complex but two main mechanisms have been reported: severe deficiency of AAT within the alveoli allows tissue destruction because of uncontrolled proteolytic attack and Z-AAT protein is less efficient at inhibiting neutrophil elastase than normal M-AAT.
However, one additional explanation may be the pro-inflammatory effect of Z-AAT polymers in the lungs. Recent studies have indicated that polymers of AAT can be detected in Z-AAT homozygotes BALF and that, in vitro, they are chemotactic to neutrophils. Moreover Mahadeva et al. demonstrated the co-localization of Z-AAT polymers with neutrophils in the alveoli of individuals with Z-AAT and showed that these polymers are pro-inflammatory in cell and mouse models of the disease. These data raised the novel hypothesis that Z-AAT undergoes a conformational transition to polymers within the lungs and this transforms AAT into a local pro-inflammatory stimulus. These data provide an explanation for the excessive number of neutrophils in the lungs of Z-AAT homozygotes and the progression of disease despite adequate 1-AAT replacement.
Mechanisms that drive production of Z-AAT polymers in the lung and their cellular origin are still unknown. These polymers could be produced by local respiratory cells. We know that AAT can be synthesized and secreted by epithelial bronchial cells, especially during inflammation, but little is known about the ability of epithelial bronchial cells to synthesize and secrete mutant Z-AAT. There is also a lack of knowledge about potential Z-AAT intraepithelial polymerization and accumulation, the hypothetical cytotoxic effect (direct or in correlation with neutrophils) of polymer accumulation in airway epithelial cells and about the amount of these proteins' secretion by epithelial cells.
In this project, we will analyze synthesis, accumulation and secretion of Z-AAT protein (or its polymers). In preliminary experiments, we will use an epithelial bronchial cell line engineered to express human Z-AAT or the wild type M-AAT as a control and will examine ex-vivo cell cultures obtained from patients' epithelial brushing. We will also analyse Z-AAT secretion by epithelial bronchial cells in the presence of inflammatory cytokines to support the concept that an inflammatory state may exacerbate polymer formation and lung damage in Z-AAT patients.
Moreover we will perform immunohistochemical studies on bronchial biopsies from Z-AAT patients to detect the presence of Z-AAT polymers in epithelial bronchial cells, by using a specific monoclonal antibody for the polymeric conformation of Z-AAT protein. The possible presence of polymers in epithelial bronchial cells will be correlated to inflammatory indices such as neutrophil tissue infiltration.
Results obtained could be crucial for the therapeutic approach to AAT Deficiency related diseases. Studies are now investigating treatments capable of preventing polymer formation, and/or affecting their elimination. Development of an antipolymer drug may be highly relevant to treat both liver and lung diseases resulting from Z-AAT.

Curriculum Vitae of Laura Pini
Since 2004, Dr. Laura Pini holds an Assistant Professor position in Internal Medicine at the University Hospital of Brescia, Italy. Within her scientific career, in Italy and in Canada, Dr. Pini obtained a doctoral degree in medicine and a post-doctoral degree in respiratory medicine. She has many years of experience in the field of bronchial asthma and chronic obstructive respiratory diseases with emphasis on lung emphysema and the hereditary Alpha- 1-Antitrypsin Deficiency.
To date her scientific activities have resulted in more than 70 publications. She is member of several national and international thoracic societies such as the European Respiratory Society. Since 5 years, the main focus of her research has been on airway remodelling in asthma and chronic obstructive respiratory diseases. Her current work is focused on the presence of Z-AAT polymers in epithelial bronchial cells and on their possible local pro-inflammatory effect.

Contact
Laura Pini, MD
Medicina Interna I e Clinica Medica
Piazzale Spedali Civili 1
25125 Brescia
Italy