Loop-sheet polymerization: the mechanism of alpha1-antitrypsin deficiency

Erdj3 Has an Essential Role for Z Variant Alpha-1-Antitrypsin Degradation

Alpha‐1‐antitrypsin deficiency (AATD) is an inherited disease characterized by emphysema and liver disease. AATD is most often caused by a single amino acid substitution at amino acid 342 in the mature protein, resulting in the Z mutation of the alpha‐1‐antitrypsin gene (ZAAT). This substitution is associated with misfolding and accumulation of ZAAT in the endoplasmic reticulum (ER) of hepatocytes and monocytes, causing a toxic gain of function. Retained ZAAT is eliminated by ER‐associated degradation and autophagy. We hypothesized that alpha‐1‐antitrypsin (AAT)‐interacting proteins play critical roles in quality control of human AAT. Using co‐immunoprecipitation, we identified ERdj3, an ER‐resident Hsp40 family member, as a part of the AAT trafficking network. Depleting ERdj3 increased the rate of ZAAT degradation in hepatocytes by redirecting ZAAT to the ER calreticulin‐EDEM1 pathway, followed by autophagosome formation. In the Huh7.5 cell line, ZAAT ER clearance resulted from enhancing ERdj3‐mediated ZAAT degradation by silencing ERdj3 while simultaneously enhancing autophagy. In this context, ERdj3 suppression may eliminate the toxic gain of function associated with polymerization of ZAAT, thus providing a potential new therapeutic approach to the treatment of AATD‐related liver disease. J. Cell. Biochem. 118: 3090–3101, 2017. © 2017 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals Inc.

Prevalence of PI*Z and PI*S alleles of alpha-1-antitrypsin deficiency in Finland

The prevalence of PI*Z and PI*S alleles of SERPINA1 gene related to alpha-1-antitrypsin deficiency has previously been estimated to be lower in Finland than in the other countries of Northern Europe. The prevalence of PI*M (Malton) has not been studied in Finland before. We determined alpha-1-antitrypsin PI*Z and PI*S and PI*M (Malton) genotypes from a representative population sample. The number of subjects was 6,354 in the PI*S and PI*M (Malton) genotyping. PI*Z genotyping was performed in a subsample of 2,482 subjects. The allele frequencies were PI*Z 19.7/1,000 and PI*S 10.2/1,000. No PI*M (Malton) was found. The number of carriers of PI*Z and PI*S is significantly higher than previously estimated. The prevalences are in line with the findings in the neighboring countries.

Discovery of an inhibitor of Z-alpha1 antitrypsin polymerization

Polymerization of the Z variant alpha-1-antitrypsin (Z-α1AT) results in the most common and severe form of α1AT deficiency (α1ATD), a debilitating genetic disorder whose clinical manifestations range from asymptomatic to fatal liver and/or lung disease. As the altered conformation of Z-α1AT and its attendant aggregation are responsible for pathogenesis, the polymerization process per se has become a major target for the development of therapeutics. Based on the ability of Z-α1AT to aggregate by recruiting the reactive center loop (RCL) of another Z-α1AT into its s4A cavity, we developed a high-throughput screening assay that uses a modified 6-mer peptide mimicking the RCL to screen for inhibitors of Z-α1AT polymer growth. A subset of compounds from the Library of Pharmacologically Active Compounds (LOPAC) with molecular weights ranging from 300 to 700 Da, was used to evaluate the assay's capabilities. The inhibitor S-(4-nitrobenzyl)-6-thioguanosine was identified as a lead compound and its ability to prevent Z-α1AT polymerization confirmed by secondary assays. To further investigate the binding location of S-(4-nitrobenzyl)-6-thioguanosine, an in silico strategy was pursued and the intermediate α1AT M* state modeled to allow molecular docking simulations and explore various potential binding sites. Docking results predict that S-(4-nitrobenzyl)-6-thioguanosine can bind at the s4A cavity and at the edge of β-sheet A. The former binding site would directly block RCL insertion whereas the latter site would prevent β-sheet A from expanding between s3A/s5A, and thus indirectly impede RCL insertion. Altogether, our investigations have revealed a novel compound that inhibits the formation of Z-α1AT polymers, as well as in vitro and in silico strategies for identifying and characterizing additional blocking molecules of Z-α1AT polymerization.

Distinguishing alpha1-antitrypsin deficiency from asthma

OBJECTIVE

To explore the relations that exist between α1-antitrypsin deficiency (AATD) and asthma and to evaluate practices for screening patients with asthma for this genetically determined condition in the context of current guidelines.

DATA SOURCES

English-language articles were selected from a PubMed search using combinations of the following search terms: alpha1-antitrypsin, screening, and asthma.

STUDY SELECTIONS

Studies to be included in this review were based on the authors' expert opinions.

RESULTS

Asthma and AATD are 2 distinct conditions yet they can coexist. Although AATD has a variable symptomatology and some patients may be asymptomatic, many can present with symptoms that are similar to those of asthma, such as dyspnea, wheezing, cough, and mucus production, which can cause confusion at diagnosis. A simple genetic test exists for AATD, which is a single-gene disorder, and the American Thoracic Society and European Respiratory Society guidelines recommend the screening of patients with asthma who exhibit chronic airflow obstruction. Patients with AATD are seen by internal medicine, family medicine, allergy, and pulmonary clinicians, yet there is a generalized lack of awareness of testing among all specialties. This leads to a delayed diagnosis for patients with AATD, typically by 8.3 years.

CONCLUSION

A greater awareness of AATD among clinicians who regularly manage patients with asthma symptoms could increase diagnosis rates, thus optimizing interventions and management strategies to improve patient outcomes.

In vivo post-transcriptional gene silencing of alpha-1 antitrypsin by adeno-associated virus vectors expressing siRNA

alpha-1 Antitrypsin (AAT) deficiency is one of the most common genetic diseases in North America, with a carrier frequency of approximately 4% in the US population. Homozygosity for the most common mutation (Glu342Lys, PI(*)Z) leads to the synthesis of a mutant protein, which accumulates and polymerizes within hepatocytes rather than being efficiently secreted. This lack of secretion causes severe serum deficiency predisposing to chronic lung disease. Twelve to fifteen percent of patients with PI(*)ZZ also develop liver disease, which can be severe, even in infancy. This is thought to be due to toxic effects of the accumulated mutant Z-AAT within the hepatocyte. Thus, an approach to reduce AAT-deficient liver disease will likely require some mechanism to decrease the amount of Z-AAT within hepatocytes. In this report, we describe studies of small-interfering RNAs (siRNAs) designed to downregulate endogenous AAT within hepatocytes. Three different siRNA sequences were identified and cloned into a recombinant adeno-associated virus (rAAV) backbone, either singly or as a trifunctional (3X) construct. Each had activity independently, but the levels of AAT expression in cell culture models showed the greatest decrease with the 3X construct, resulting in levels that were five-fold lower than controls. The rAAV-3X-siRNA was then packaged into AAV8 capsids and used in vivo to transduce the livers of human Z-AAT overexpressing transgenic mice. Those studies showed a decrease in total human AAT, a clearing of Z-AAT accumulation by immunohistochemistry, and a decrease in monomer Z-AAT within the liver within 3 weeks after vector injection. The rAAV8-3X-siRNA vector may hold promise as a potential therapy for patients with AAT liver disease.

Alpha-1-antitrypsin replacement therapy: current status

PURPOSE OF REVIEW

Alpha-1-antitrypsin deficiency is a relatively common genetic disease that predisposes to the development of early-onset emphysema and, in some instances, liver disease. The use of alpha-1-antitrypsin replacement therapy in the treatment of alpha-1-antitrypsin deficiency related emphysema is much debated and the purpose of this review is to examine the results of recent studies. We will comment briefly on the pathogenesis and epidemiology of the disease together with new therapeutic approaches currently under intense research.

RECENT FINDINGS

Several nonrandomized observational studies and one meta-analysis on the clinical effectiveness of alpha-1-antitrypsin replacement treatment showed a favourable result towards reducing forced expiratory volume in 1 s (FEV1) deterioration in alpha-1-antitrypsin-deficient individuals with moderate lung disease or accelerated FEV1 decline. Improved ways of monitoring disease progression, including computed tomography scanning and exacerbations, are being proposed as primary endpoints. Apart from one small randomized, placebo-controlled trial using computed tomography scanning, which showed a trend toward preservation of lung density on scanning with treatment, the literature lacks proof of effectiveness from large randomized trials.

SUMMARY

There might be a possible, but so far unproven, role of alpha-1-antitrypsin augmentation therapy in reducing the progression of emphysema in subsets of patients with alpha-1-antitrypsin deficiency. Placebo-controlled, randomized clinical trials are required to draw firm conclusions. Recent advances in the understanding of the molecular pathology provide opportunities for development of new therapeutic targets for this genetic disorder.

Alpha-antitrypsin genotypes in Korean patients with chronic obstructive pulmonary disease

OBJECTIVE

Alpha1-antitrypsin (AAT) deficiency is a recognized susceptible factor for chronic obstructive pulmonary disease (COPD) in Western countries, but its importance in Korea is unclear. To date, no definitive case of alpha1-antitrypsin deficiency has been reported in Korea. This study aimed to clarify whether alpha1-antitrypsin deficiency exists and to determine the distribution of alpha1-antitrypsin alleles in the Korean population.

METHODOLOGY

The serum concentrations of alpha1-antitrypsin were determined and polymorphisms of the alpha1-antitrypsin gene in 114 COPD patients and in 196 healthy controls were examined. Phenotyping by isoelectric focusing and the genotyping of alpha1-antitrypsin gene by polymerase chain reaction and restriction fragment length polymorphism were performed.

RESULTS

No alpha1-antitrypsin level abnormality was found in the patients. M1(Val)/M1(Val) was found to be the most frequent genotype in both groups (69.2% and 66.8%, respectively), and M1(Val) the most frequent allele. The distributions of alpha1-antitrypsin alleles were similar in the patient and control groups, and no S or Z allele was found.

CONCLUSION

Alpha1-antitrypsin deficiency is unlikely to be an important cause of chronic obstructive pulmonary disease in the Korean population.

AAT as a diagnostic tool

Serum alpha-1-antitrypsin (AAT) concentration can be affected by both inflammatory and non-inflammatory conditions. This paper characterizes the nature of AAT in physiology and pathologic deficiency and increasing states. The relationships between the AAT concentration in different clinical materials (serum, urine, faeces) and various diseases connected with different organs were analyzed.

Effects of hydrofluoroalkane formulations of ciclesonide 400 microg once daily vs fluticasone 250 microg twice daily on methacholine hyper-responsiveness in mild-to-moderate persistent asthma

AIMS

There are no data comparing the relative efficacy of hydrofluoroalkane (HFA) formulations of ciclesonide (CIC) and fluticasone propionate (FP) on airway hyper-responsiveness, in mild-to-moderate persistent asthma. We therefore elected to evaluate the comparative efficacy of HFA pressurized metered-dose inhaler formulations of CIC and FP, assessing methacholine challenge, in addition to exhaled nitric oxide, lung function, diary cards and quality of life.

METHODS

Nineteen mild-to-moderate asthmatic patients completed the study per protocol in randomized, double-blind, double-dummy, crossover fashion. Patients were required to stop their usual inhaled corticosteroid therapy for the duration of the study. Patients were commenced instead on salmeterol (SM) 50 microg one puff twice daily + montelukast (ML) 10 mg once daily for 2-week washout periods prior to each randomized treatment, in order to prevent dropouts. Patients received 4 weeks of either CIC 200 microg two puffs once daily (08.00 h) + CIC-placebo (PL) two puffs once daily (20.00 h) + FP-PL two puffs twice daily (08.00 h and 20.00 h), or FP 125 microg two puffs twice daily (08.00 h and 20.00 h) + CIC-PL two puffs twice daily (08.00 h and 20.00 h). SM + ML were withheld for 72 h prior to post-washout visits and CIC or FP was withheld for 24 h prior to study visits.

RESULTS

There was no significant difference between CIC vs. FP for the primary outcome of methacholine PC20 as doubling dilution (dd) shift from respective baseline; mean difference: 0.4 dd (95% CI -0.4, 1.2). Moreover, there was no difference between treatments for the sequence of CIC first vs FP second; mean difference: 0.2 dd (95% CI -1.3, 1.7) or FP first vs CIC second; mean difference: 0.9 dd (95% CI -0.1, 1.8). There were also no differences for other secondary outcomes between treatments, either respective or irrespective of sequence, as change from baseline.

CONCLUSIONS

There were no differences between 4 weeks of CIC 400 microg once daily and FP 250 microg twice daily on methacholine hyper-responsiveness in mild-to-moderate persistent asthma. Longer-term studies are indicated to evaluate their relative efficacy on asthma exacerbations.

Role of the M-loop and reactive center loop domains in the folding and bridging of nucleosome arrays by MENT

MENT is a developmentally regulated heterochromatin-associated protein that condenses chromatin in terminally differentiated avian blood cells. Its homology to the serpin protein family suggests that the conserved serpin reactive center loop (RCL) and the unique M-loop are important for its function. To examine the role of these domains, we studied the interaction of wild-type and mutant MENT with naked DNA and biochemically defined nucleosome arrays reconstituted from 12-mer repeats containing nucleosome positioning sequences. Wild-type MENT folded the naked DNA duplexes into closely juxtaposed parallel structures ("tramlines"). Deletion of the M-loop, but not inactivation of the RCL, prevented tramline formation and the cooperative interaction of MENT with DNA. Reconstitution of wild-type MENT with nucleosome arrays caused their tight folding and self-association. M-loop deletion inhibited nucleosome array folding, whereas the inactive RCL mutant was competent to fold the nucleosome arrays, but had a significantly impaired ability to cause their self-association. Bifunctional chemical cross-linking of MENT revealed oligomerization of wild-type MENT in the presence of chromatin and DNA. This oligomerization was severely reduced in the RCL mutant. We propose that the mechanism of MENT-induced heterochromatin formation involves two independent events: bringing together nucleosome linkers within a chromatin fiber and formation of protein bridges between chromatin fibers. Ordered binding of MENT to linker DNA via its unique M-loop domain promotes the folding of chromatin, whereas bridging of chromatin fibers is facilitated by MENT oligomerization mediated by the RCL.

Detection of circulating and endothelial cell polymers of Z and wild type alpha 1-antitrypsin by a monoclonal antibody

Globular inclusions of abnormal alpha1-antitrypsin (AAT) in the endoplasmic reticulum of hepatocytes are a characteristic feature of AAT deficiency of the PiZZ phenotype. Monoclonal antibodies, which contain constant specificity and affinity, are often used for the identification of Z-mutation carriers. A mouse monoclonal antibody (ATZ11) raised against PiZZ hepatocytic AAT was successfully used in enzyme-linked immunosorbent assays (ELISA) and in identification of Z-related AAT globular inclusions by immunohistochemical techniques. Using electrophoresis, Western blotting, and ELISA procedures, we have shown in the present study that this monoclonal antibody specifically detects a conformation-dependent neoepitope on both polymerized and elastase-complexed molecular forms of AAT. The antibody has no apparent affinity for native, latent, or cleaved forms of AAT. The antibody ATZ11 illustrates the structural resemblance between the polymerized form of AAT and its complex with elastase and provides evidence that Z-homozygotes beyond the native form may have at least one more circulating molecular form of AAT, i.e. its polymerized form. In addition, staining of endothelial cells with ATZ11 antibody in both M- and Z-AAT individuals shows that AAT attached to endothelial cells is in a polymerized form. The antibody can be a powerful tool for the study of the molecular profile of AAT, not only in Z-deficiency cases but also in other (patho)physiological conditions.

Inhibitory activity of a heterochromatin-associated serpin (MENT) against papain-like cysteine proteinases affects chromatin structure and blocks cell proliferation

MENT (Myeloid and Erythroid Nuclear Termination stage-specific protein) is a developmentally regulated chromosomal serpin that condenses chromatin in terminally differentiated avian blood cells. We show that MENT is an effective inhibitor of the papain-like cysteine proteinases cathepsins L and V. In addition, ectopic expression of MENT in mammalian cells is apparently sufficient to inhibit a nuclear papain-like cysteine proteinase and prevent degradation of the retinoblastoma protein, a major regulator of cell proliferation. MENT also accumulates in the nucleus, causes a strong block in proliferation, and promotes condensation of chromatin. Variants of MENT with mutations or deletions within the M-loop, which contains a nuclear localization signal and an AT-hook motif, reveal that this region mediates nuclear transport and morphological changes associated with chromatin condensation. Non-inhibitory mutants of MENT were constructed to determine whether its inhibitory activity has a role in blocking proliferation. These mutations changed the mode of association with chromatin and relieved the block in proliferation, without preventing transport to the nucleus. We conclude that the repressive effect of MENT on chromatin is mediated by its direct interaction with a nuclear protein that has a papain-like cysteine proteinase active site.

Stable therapeutic serum levels of human alpha-1 antitrypsin (AAT) after portal vein injection of recombinant adeno-associated virus (rAAV) vectors

Previous work from our group showed that recombinant adeno-associated virus (rAAV) vectors mediated long-term secretion of therapeutic serum levels of human alpha-1 antitrypsin (hAAT) after a single injection in murine muscle. We hypothesized that hepatocyte transduction could be even more efficient, since these cells represent the natural site of AAT production and secretion. To test this hypothesis, rAAV vectors containing the hAAT cDNA driven by either the human elongation factor 1 alpha promoter, the human cytomegalovirus immediate-early promoter (CMV), or the CMV-chicken beta actin hybrid (CB) promoter were injected into the portal or tail veins of adult C57Bl/6 mice. Potentially therapeutic serum levels of hAAT (600 microg/ml) were achieved after portal vein injection of doses of 4 x 10(9) infectious units (IU), a 10-fold lower dose than that required for similar levels of expression via the i.m. route. Serum levels greater than 1 mg/ml were achieved at doses of 3 x 10(10) IU. Southern blotting of liver DNA revealed the presence of circular episomal vector genomes. Immunostaining showed that transgene expression was scattered throughout the liver parenchyma. Similar results were obtained with a rAAV-CB-green fluorescent protein (GFP) vector. There was no evidence of hepatic toxicity. These data indicate that liver-directed rAAV-based gene therapy is effective in the murine model, and hence might be feasible for treatment of human AAT deficiency.