A Review of Alpha-1 Antitrypsin Binding Partners for Immune Regulation and Potential Therapeutic Application.

Alpha-1 antitrypsin (AAT) is the canonical serine protease inhibitor of neutrophil-derived proteases and can modulate innate immune mechanisms through its anti-inflammatory activities mediated by a broad spectrum of protein, cytokine, and cell surface interactions. AAT contains a reactive methionine residue that is critical for its protease-specific binding capacity, whereby AAT entraps the protease on cleavage of its reactive centre loop, neutralises its activity by key changes in its tertiary structure, and permits removal of the AAT-protease complex from the circulation. Recently, however, the immunomodulatory role of AAT has come increasingly to the fore with several prominent studies focused on lipid or protein-protein interactions that are predominantly mediated through electrostatic, glycan, or hydrophobic potential binding sites. The aim of this review was to investigate the spectrum of AAT molecular interactions, with newer studies supporting a potential therapeutic paradigm for AAT augmentation therapy in disorders in which a chronic immune response is strongly linked.

d-Galactose treatment increases ACE2, TMPRSS2, and FURIN and reduces SERPINA1 mRNA expression in A549 human lung epithelial cells.

Several comorbidities including diabetes, immune deficiency, and chronic respiratory disorders increase the risk of severe Covid-19 and fatalities among SARS-CoV-2 infected individuals. Severe Covid-19 risk among diabetes patients may reflect reduced immune response to viral infections. SARS-CoV-2 initially infects respiratory tract epithelial cells by binding to the host cell membrane ACE2, followed by proteolytic priming for cell entry by the host cell membrane serine protease TMPRSS2. Additionally, the protease FURIN facilitates cell exit of mature SARS-CoV-2 virions. Alpha-1 antitrypsin (AAT), the major plasma serine protease inhibitor, encoded by SERPINA1, is known to promote immune response to viral infections. AAT inhibits neutrophil elastase, a key inflammatory serine protease implicated in alveolar cell damage during respiratory infections, and AAT deficiency is associated with susceptibility to lung infections. AAT is implicated in Covid-19 as it inhibits TMPRSS2, a protease essential for SARS-CoV-2 cell entry. Here we show that treatment of A549 human lung epithelial cells for 7 days with 25 mM d-galactose, an inducer of diabetic-like and oxidative stress cellular phenotypes, leads to increased mRNA levels of ACE2, TMPRSS2, and FURIN, along with reduced SERPINA1 mRNA. Together, the dysregulated transcription of these genes following d-galactose treatment suggests that chronic diabetic-like conditions may facilitate SARS-CoV-2 infection of lung epithelial cells. Our findings may in part explain the higher severe Covid-19 risk in diabetes, and highlight the need to develop special treatment protocols for diabetic patients.

Insights into the potential role of alpha1-antitrypsin in COVID-19 patients: Mechanisms, current update, and future perspectives.

In this work, we provide an up-to-date summary of the available molecular- and cell-related mechanisms by which alpha1-antitrypsin (AAT) protein could be of benefit in treating COVID-19 patients. As well, we demonstrate the current status in terms of the ongoing clinical trials using AAT in COVID-19 patients. Finally, we touch on the potential role gene therapy and stem cell-based gene therapy could have in such emerging and serious condition caused by the SARS-CoV-2 virus.

SARS-CoV-2 infection in alpha1-antitrypsin deficiency.

Alpha1-antitrypsin deficiency arises due to mutations in alpha1-antitrypsin (AAT) gene and represents the most prominent genetic predisposition to chronic obstructive pulmonary disease and emphysema. Since AAT plays important immunomodulatory and tissue-protective roles and since it was suggested to protect from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, we assessed this association in United Kingdom Biobank, a community-based cohort with >500,000 participants. The most common, mild AATD genotypes were associated neither with increased SARS-CoV-2 infection rates nor with increased SARS-CoV-2 fatalities, while the numbers of severe AATD cases were too low to allow definitive conclusions.

SARS-CoV-2 mutation 614G creates an elastase cleavage site enhancing its spread in high AAT-deficient regions.

SARS-CoV-2 was first reported from China. Within three months, it evolved to 10 additional subtypes. Two evolved subtypes (A2 and A2a) carry a non-synonymous Spike protein mutation (D614G). We conducted phylodynamic analysis of over 70,000 SARS-CoV-2 coronaviruses worldwide, sequenced until July2020, and found that the mutant subtype (614G) outcompeted the pre-existing type (614D), significantly faster in Europe and North-America than in East Asia. Bioinformatically and computationally, we identified a novel neutrophil elastase (ELANE) cleavage site introduced in the G-mutant, near the S1-S2 junction of the Spike protein. We hypothesised that elevation of neutrophil elastase level at the site of infection will enhance the activation of Spike protein thus facilitating host cell entry for 614G, but not the 614D, subtype. The level of neutrophil elastase in the lung is modulated by its inhibitor α1-antitrypsin (AAT). AAT prevents lung tissue damage by elastase. However, many individuals exhibit genotype-dependent deficiency of AAT. AAT deficiency eases host-cell entry of the 614G virus, by retarding inhibition of neutrophil elastase and consequently enhancing activation of the Spike protein. AAT deficiency is highly prevalent in European and North-American populations, but much less so in East Asia. Therefore, the 614G subtype is able to infect and spread more easily in populations of the former regions than in the latter region. Our analyses provide a molecular biological and evolutionary model for the higher observed virulence of the 614G subtype, in terms of causing higher morbidity in the host (higher infectivity and higher viral load), than the non-mutant 614D subtype.

Host genomics of COVID-19: Evidence point towards Alpha 1 antitrypsin deficiency as a putative risk factor for higher mortality rate.

Corona Virus Disease 2019 (COVID-19) has emerged as a pandemic leading to unprecedented disruption of global health and economy. Transmembrane protease serine 2 (TMPRSS2) has been found to be critical in priming the viral spike protein and the host ACE2 receptor before the virus enters into the host cell. Recent studies have experimentally demonstrated that Alpha 1 antitrypsin (encoded by SERPINA1 gene) is an inhibitor of TMPRSS2 and provided support to the already approved therapy as a candidate for COVID-19. Interestingly Alpha 1 antitrypsin deficiency is common among Europeans. Here we have provided in silico evidence that Alpha 1 antitrypsin can interact with TMPRSS2 and both of them are co-expressed in the human liver and lung. We then analyzed the gnomAD dataset to show that Europeans and Latinos have a substantially higher carrier frequency of Alpha 1 Antitrypsin Deficiency (~12%) compared to other large ethnicities. Therefore, we hypothesize that Alpha 1 antitrypsin deficiency might be a risk factor for severe infection with SARS-CoV-2. We propose Alpha 1 antitrypsin status as a potential prognostic predictor of COVID-19 outcome.

Ethnic differences in alpha-1 antitrypsin deficiency allele frequencies may partially explain national differences in COVID-19 fatality rates.

Infection rates, severity, and fatalities due to COVID-19, the pandemic mediated by SARS-CoV-2, vary greatly between countries. With few exceptions, these are lower in East and Southeast Asian and Sub-Saharan African countries compared with other regions. Epidemiological differences may reflect differences in border closures, lockdowns, and social distancing measures taken by each county, and by cultural differences, such as common use of face masks in East and Southeast Asian countries. The plasma serine protease inhibitor alpha-1 antitrypsin was suggested to protect from COVID-19 by inhibiting TMPRSS2, a cell surface serine protease essential for the SARS-CoV-2 cell entry. Here, we present evidence that population differences in alpha-1 antitrypsin deficiency allele frequencies may partially explain national differences in the COVID-19 epidemiology. Our study compared reported national estimates for the major alpha-1 antitrypsin deficiency alleles PiZ and PiS (SERPINA1 rs28929474 and rs17580, respectively) with the Johns Hopkins University Coronavirus Resource Center dataset. We found a significant positive correlation (R = .54, P = 1.98e-6) between the combined frequencies of the alpha-1 antitrypsin PiZ and PiS deficiency alleles in 67 countries and their reported COVID-19 mortality rates. Our observations suggest that alpha-1 antitrypsin deficiency alleles may contribute to national differences in COVID-19 infection, severity, and mortality rates. Population-wide screening for carriers of alpha-1 antitrypsin deficiency alleles should be considered for prioritizing individuals for stricter social distancing measures and for receiving a SARS-CoV-2 vaccine once it becomes available.