Role of disulphide interactions in the ER retention of alpha1-antitrypsin deficiency variants

Alpha1 antitrypsin (AAT) mutants are normally retained within the Endoplasmic Reticulum (ER) of hepatocytes leading to plasma AAT deficiency (AATD), uncontrolled elastase activity in the lung and eventually emphysema. A subgroup of AAT mutants, including the common Z variant, tends to form ordered polymers in the ER which accumulate as inclusion bodies causing hepatotoxicity and liver disease. Notably, Z AAT polymers have also been found in the plasma and in the lung interstitium where they have local pro-inflammatory effects. Other rare AAT deficiency variants behave as polymerogenic similarly to Z AAT. Riccardo?s research group is now involved in the characterization of rare AAT deficiency mutants which, based on preliminary data, display non-classic retention / polymeriza tion mechanisms. A study was undertaken involving three variants including I (Mahadeva et al. 1999 JCI 103:999), F (Okayama et al. 1991 A. J. Hum. Genet. 48:1154) and a new one named Brixia. These contain an additional cysteine residue compared to wild type AAT where a single cysteine is present (Cys232). The preliminary results suggest that these form aberrant disulphide linked complexes in the ER of hepatic cells; this likely contributes to their intracellular retention or degradation by a novel mechanism.

Aims:

1. The first aim of this proposal is to further investigate these complexes, their composition, their sub cellular localization as well as the cell stress responses possibly activated by these mutants.
2. The major aim of this proposal is to investigate the actual contribution of disulphide interactions to the ER retention and the secretory defect of AAT variants including Z. To this aim the behavior of M and Z will be compared with their Cys232Ser counterparts and the ER redox state will be modulated by different strategies. These include treatments with reducing agents and the modulation (by over expression or RNAi) of ER components such as PDI and EroI alpha known to regulate disulphide interchange and ER redox homeostasis.

Curriculum Vitae Dr. Riccardo Ronzoni

Riccardo has dedicated most of his research activity to cell biology studies with a particular interest in ER storage diseases.
In the Department of Biomedical Sciences and Biotechnology at the University of Brescia he has been involved in projects on the role and characterization of rare variants causing Alpha-1- antitrypsin (AAT) deficiency. In particular, he has contributed to investigate a group of AAT variants bearing amino acid substitutions in the C-terminal region. His results show that their mutations promote accumulation of these variants within hepatocytes as order polymeric structures resembling Z AAT polymers. (Fra et al. PLoS, 2012).

His eALTA research project "Role of disulphide interactions in the ER retention of alpha1-antitrypsin deficiency variants" focuses on understanding the pathogenesis of the AATD in those patients who carry AAT mutants with an additional cysteine. This project may also reveal important novel aspects of the folding and quality control of the common M and Z AAT within hepatocytes.
Moreover, these studies may have a broader interest in the field of ER conformational diseases since "gain of cysteine" variants, or aberrant pairing of cysteines secondary to other mutations, may occur in different genetic diseases.

Contact
University of Brescia
Dept. Biomedical Sciences and Biotechnology
viale Europa 11
I-25123 Brescia
Italy