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Balderacchi AM, Bignotti M, Ottaviani S, Denardo A, Barzon V, Ben Khlifa E, Vailati G, Piloni D, Benini F, Corda L, Corsico AG, Ferrarotti I, Fra A. Quantification of circulating alpha-1-antitrypsin polymers associated with different SERPINA1 genotypes. Clin Chem Lab Med 2024; 0:cclm-2023-1348. [PMID: 38407261 DOI: 10.1515/cclm-2023-1348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2023] [Accepted: 02/15/2024] [Indexed: 02/27/2024]
Abstract
OBJECTIVES Alpha-1-antitrypsin deficiency is a genetic disorder caused by mutations in the SERPINA1 gene encoding alpha-1-antitrypsin (AAT), the major serine protease inhibitor in plasma. Reduced AAT levels are associated with elevated risk of developing emphysema mainly due to uncontrolled activity of neutrophil elastase in the lungs. The prevalent Z-AAT mutant and many rare pathogenic AAT variants also predispose to liver disease due to their accumulation as polymeric chains in hepatocytes. Part of these polymers are secreted into the bloodstream and could represent biomarkers of intra-hepatic accumulation. Moreover, being inactive, they further lower lung protection against proteases. Aim of our study is to accurately quantify the percentage of circulating polymers (CP) in a cohort of subjects with different SERPINA1 genotypes. METHODS CP concentration was measured in plasma or Dried Blood Spot (DBS) by a sensitive sandwich ELISA based on capture by the polymer-specific 2C1 monoclonal antibody. RESULTS CP were significantly elevated in patients with the prevalent PI*SZ and PI*ZZ genotypes, with considerable intra-genotype variability. Notably, higher percentage of polymers was observed in association with elevated C-reactive protein. CP levels were also increased in carriers of the Mmalton variant, and of Mprocida, I, Plowell and Mherleen in heterozygosity with Z-AAT. CONCLUSIONS These findings highlight the importance of implementing CP quantification in a clinical laboratory. Indeed, the variable amount of CP in patients with the same genotype may correlate with the variable severity of the associated lung and liver diseases. Moreover, CP can reveal the polymerogenic potential of newly discovered ultrarare AAT variants.
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Affiliation(s)
- Alice M Balderacchi
- Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, UOC Pulmonology, 18631Fondazione IRCCS Policlinico San Matteo, Pavia, Italy
| | - Mattia Bignotti
- Experimental Oncology and Immunology, Department of Molecular and Translational Medicine, 9297University of Brescia, Brescia, Italy
| | - Stefania Ottaviani
- Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, UOC Pulmonology, 18631Fondazione IRCCS Policlinico San Matteo, Pavia, Italy
| | - Andrea Denardo
- Experimental Oncology and Immunology, Department of Molecular and Translational Medicine, 9297University of Brescia, Brescia, Italy
| | - Valentina Barzon
- Department of Internal Medicine and Therapeutics, Pulmonology Unit, 19001University of Pavia, Pavia, Italy
| | - Emna Ben Khlifa
- Experimental Oncology and Immunology, Department of Molecular and Translational Medicine, 9297University of Brescia, Brescia, Italy
| | - Guido Vailati
- Referral Centre for Alpha-1 Antitrypsin Deficiency, 18515 Spedali Civili , Brescia, Italy
| | - Davide Piloni
- Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, UOC Pulmonology, 18631Fondazione IRCCS Policlinico San Matteo, Pavia, Italy
| | - Federica Benini
- Referral Centre for Alpha-1 Antitrypsin Deficiency, 18515 Spedali Civili , Brescia, Italy
| | - Luciano Corda
- Referral Centre for Alpha-1 Antitrypsin Deficiency, 18515 Spedali Civili , Brescia, Italy
| | - Angelo G Corsico
- Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, UOC Pulmonology, 18631Fondazione IRCCS Policlinico San Matteo, Pavia, Italy
- Department of Internal Medicine and Therapeutics, Pulmonology Unit, 19001University of Pavia, Pavia, Italy
| | - Ilaria Ferrarotti
- Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, UOC Pulmonology, 18631Fondazione IRCCS Policlinico San Matteo, Pavia, Italy
- Department of Internal Medicine and Therapeutics, Pulmonology Unit, 19001University of Pavia, Pavia, Italy
| | - Annamaria Fra
- Experimental Oncology and Immunology, Department of Molecular and Translational Medicine, 9297University of Brescia, Brescia, Italy
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Barzon V, Ferrarotti I, Ottaviani S. Sanger and Next-Generation Sequencing of AAT. Methods Mol Biol 2024; 2750:57-67. [PMID: 38108967 DOI: 10.1007/978-1-0716-3605-3_6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Sequencing of DNA is normally the final procedure carried out to determine the actual pathogenic variants when the techniques used for genotyping are unable to provide complete identification of both AAT alleles. Gene sequencing of complete SERPINA1 gene by using the Sanger method or next-generation sequencing (NGS) is crucial to enable correct diagnosis in patients with alpha1-antitrypsin deficiency caused by uncommon AAT variants.This protocol explains how to correctly sequence SERPINA1 gene both with Sanger method and NGS.
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Affiliation(s)
- Valentina Barzon
- Department of Internal Medicine and Therapeutics, Pulmonology Unit, University of Pavia, Pavia, Italy
| | - Ilaria Ferrarotti
- Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, UOC Pulmonology, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy.
| | - Stefania Ottaviani
- Centre for Diagnosis of Inherited Alpha-1 Antitrypsin Deficiency, UOC Pulmonology, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy
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Denardo A, Ben Khlifa E, Bignotti M, Giuliani R, D'Acunto E, Miranda E, Irving JA, Fra A. Probing of the reactive center loop region of alpha-1-antitrypsin by mutagenesis predicts new type-2 dysfunctional variants. Cell Mol Life Sci 2023; 81:6. [PMID: 38087060 PMCID: PMC11073084 DOI: 10.1007/s00018-023-05059-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 10/25/2023] [Accepted: 11/22/2023] [Indexed: 12/18/2023]
Abstract
Lung disease in alpha-1-antitrypsin deficiency (AATD) mainly results from insufficient control of the serine proteases neutrophil elastase (NE) and proteinase-3 due to reduced plasma levels of alpha-1-antitrypsin (AAT) variants. Mutations in the specificity-determining reactive center loop (RCL) of AAT would be predicted to minimally affect protein folding and secretion by hepatocytes but can impair anti-protease activity or alter the target protease. These properly secreted but dysfunctional 'type-2' variants would not be identified by common diagnostic protocols that are predicated on a reduction in circulating AAT. This has potential clinical relevance: in addition to the dysfunctional Pittsburgh and Iners variants reported previously, several uncharacterized RCL variants are present in genome variation databases. To prospectively evaluate the impact of RCL variations on secretion and anti-protease activity, here we performed a systematic screening of amino acid substitutions occurring at the AAT-NE interface. Twenty-three AAT variants that can result from single nucleotide polymorphisms in this region, including 11 present in sequence variation databases, were expressed in a mammalian cell model. All demonstrated unaltered protein folding and secretion. However, when their ability to form stable complexes with NE was evaluated by western blot, enzymatic assays, and a novel ELISA developed to quantify AAT-NE complexes, substrate-like and NE-binding deficient dysfunctional variants were identified. This emphasizes the ability of the RCL to accommodate inactivating substitutions without impacting the integrity of the native molecule and demonstrates that this class of molecule violates a generally accepted paradigm that equates circulating levels with functional protection of lung tissue.
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Affiliation(s)
- Andrea Denardo
- Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy
| | - Emna Ben Khlifa
- Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy
| | - Mattia Bignotti
- Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy
| | - Roberta Giuliani
- Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy
| | - Emanuela D'Acunto
- Department of Biology and Biotechnologies 'Charles Darwin', Sapienza University of Rome, Rome, Italy
| | - Elena Miranda
- Department of Biology and Biotechnologies 'Charles Darwin', Sapienza University of Rome, Rome, Italy
| | - James A Irving
- UCL Respiratory and the Institute of Structural and Molecular Biology, University College London, London, UK
| | - Annamaria Fra
- Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy.
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