Jennifer A. Dickens

COPD association and repeatability of blood biomarkers in the ECLIPSE cohort

BackgroundThere is a need for biomarkers to better characterise individuals with COPD and to aid with the development of therapeutic interventions. A panel of putative blood biomarkers was assessed in a subgroup of the Evaluation of COPD Longitudinally to Identify Surrogate Endpoints (ECLIPSE) cohort.MethodsThirty-four blood biomarkers were assessed in 201 subjects with COPD, 37 ex-smoker controls with normal lung function and 37 healthy non-smokers selected from the ECLIPSE cohort. Biomarker repeatability was assessed using baseline and 3-month samples. Intergroup comparisons were made using analysis of variance, repeatability was assessed through Bland-Altman plots, and correlations between biomarkers and clinical characteristics were assessed using Spearman correlation coefficients.ResultsFifteen biomarkers were significantly different in individuals with COPD when compared to former or non-smoker controls. Some biomarkers, including tumor necrosis factor-α and interferon-γ, were measurable in only a minority of subjects whilst others such as C-reactive protein showed wide variability over the 3-month replication period. Fibrinogen was the most repeatable biomarker and exhibited a weak correlation with 6-minute walk distance, exacerbation rate, BODE index and MRC dyspnoea score in COPD subjects. 33% (66/201) of the COPD subjects reported at least 1 exacerbation over the 3 month study with 18% (36/201) reporting the exacerbation within 30 days of the 3-month visit. CRP, fibrinogen interleukin-6 and surfactant protein-D were significantly elevated in those COPD subjects with exacerbations within 30 days of the 3-month visit compared with those individuals that did not exacerbate or whose exacerbations had resolved.ConclusionsOnly a few of the biomarkers assessed may be useful in diagnosis or management of COPD where the diagnosis is based on airflow obstruction (GOLD). Further analysis of more promising biomarkers may reveal utility in subsets of patients. Fibrinogen in particular has emerged as a potentially useful biomarker from this cohort and requires further investigation.Trial RegistrationSCO104960, clinicaltrials.gov identifier NCT00292552

The molecular and cellular pathology of α1-antitrypsin deficiency

Since its discovery 50 years ago, α₁-antitrypsin deficiency has represented a case study in molecular medicine, with careful clinical characterisation guiding genetic, biochemical, biophysical, structural, cellular, and in vivo studies. Here we highlight the milestones in understanding the disease mechanisms and show how they have spurred the development of novel therapeutic strategies. α₁-Antitrypsin deficiency is an archetypal conformational disease. Its pathogenesis demonstrates the interplay between protein folding and quality control mechanisms, with aberrant conformational changes causing liver and lung disease through combined loss- and toxic gain-of-function effects. Moreover, α₁-antitrypsin exemplifies the ability of diverse proteins to self-associate into a range of morphologically distinct polymers, suggesting a mechanism for protein and cell evolution.

Why has it been so difficult to prove the efficacy of alpha-1-antitrypsin replacement therapy? Insights from the study of disease pathogenesis.

Alpha-1-antitrypsin is the most abundant circulating protease inhibitor. It is mainly produced by the liver and secreted into the circulation where it acts to prevent excessive proteolytic damage in the lungs by the enzyme neutrophil elastase. The most common severe deficiency allele is the Z mutation, which causes the protein to self-associate into ordered polymers. These polymers accumulate within hepatocytes to cause liver damage. The resulting lack of circulating α1-antitrypsin predisposes the Z homozygote to proteolytic lung damage and emphysema. Other pathways may also contribute to the development of lung disease. In particular, polymers of Z α1-antitrypsin can form within the lung where they act as a pro-inflammatory stimulus that may exacerbate protease-mediated lung damage. Researchers recognized in the 1980s that plasma α1-antitrypsin levels could be restored by intravenous infusions of purified human protein. Alpha-1-antitrypsin replacement therapy was introduced in 1987 but subsequent clinical trials have produced conflicting results, and to date there remains no widely accepted clinical evidence of the efficacy of α1-antitrypsin replacement therapy. This review addresses our current understanding of disease pathogenesis in α1-antitrypsin deficiency and questions why this treatment in isolation may not be effective. In particular it discusses the possible role of α1-antitrypsin polymers in exacerbating intrapulmonary inflammation and attenuating the efficacy of α1-antitrypsin replacement therapy.

Circulating polymers in α1-antitrypsin deficiency

To the Editor: Most individuals carry two wild-type M alleles of the SERPINA1 gene which encodes α1-antitrypsin. 95% of severe deficiency of α1-antitrypsin is associated with the Z allele (Glu342Lys; denoted PiZZ in the homozygote), and with the retention and polymerisation of α1-antitrypsin within hepatocytes [1]. These polymers are contained within periodic acid–Schiff-positive, diastase-resistant inclusions that are associated with neonatal hepatitis, cirrhosis and hepatocellular carcinoma. The concomitant lack of circulating α1-antitrypsin predisposes the Z α1-antitrypsin homozygote to early-onset emphysema. Polymers of α1-antitrypsin form within the lung as a result of local inflammation and exposure to cigarette smoke [2]. They have also been identified in the skin of an individual with α1-antitrypsin deficiency and panniculitis [3] and in a renal biopsy from an individual with α1-antitrypsin deficiency and vasculitis [4]. It is unknown whether these polymers form locally or are deposited in these tissues from a circulating source, and whether extrahepatic polymers are associated with any disease phenotypes. We have assessed whether polymers of α1-antitrypsin are present within serum, from where they originate, and whether they are associated with clinical features in individuals with PiZZ α1-antitrypsin deficiency. In this investigation we used ELISA with the anti-α1-antitrypsin polymer monoclonal antibody (2C1) [5] to assess the presence of polymers in the plasma of 1) 518 individuals with PiZZ α1-antitrypsin deficiency; 2) an individual with α1-antitrypsin deficiency who underwent liver transplantation; and 3) 293 individuals with a mixture of α1-antitrypsin phenotypes. The specificity of the 2C1 antibody was confirmed by using it to immunoprecipitate polymers from the plasma of individuals with and without a positive signal …

A single-chain variable fragment intrabody prevents intracellular polymerization of Z α1-antitrypsin while allowing its antiproteinase activity

Mutant Z α1‐antitrypsin (E342K) accumulates as polymers within the endoplasmic reticulum (ER) of hepatocytes predisposing to liver disease, whereas low levels of circulating Z α1‐antitrypsin lead to emphysema by loss of inhibition of neutrophil elastase. The ideal therapy should prevent polymer formation while preserving inhibitory activity. Here we used mAb technology to identify interactors with Z α1‐antitrypsin that comply with both requirements. We report the generation of an mAb (4B12) that blocked α1‐antitrypsin polymerization in vitro at a 1:1 molar ratio, causing a small increase of the stoichiometry of inhibition for neutrophil elastase. A single‐chain variable fragment (scFv) intrabody was generated based on the sequence of mAb4B12. The expression of scFv4B12 within the ER (scFv4B12KDEL) and along the secretory pathway (scFv4B12) reduced the intracellular polymerization of Z α1‐antitrypsin by 60%. The scFv4B12 intrabody also increased the secretion of Z α1‐antitrypsin that retained inhibitory activity against neutrophil elastase. MAb4B12 recognized a discontinuous epitope probably located in the region of helices A/C/G/H/I and seems to act by altering protein dynamics rather than binding preferentially to the native state. This novel approach could reveal new target sites for small‐molecule intervention that may block the transition to aberrant polymers without compromising the inhibitory activity of Z α1‐antitrypsin.—Ordóñez, A., Pérez, J., Tan, L., Dickens, J. A., Motamedi‐Shad, N., Irving, J. A., Haq, I., Ekeowa, U., Marciniak, S. J., Miranda, E., Lomas, D. A. A single‐chain variable fragment intrabody prevents intracellular polymerization of Z α1‐antitrypsin while allowing its antiproteinase activity. FASEB J. 29, 2667‐2678 (2015). www.fasebj.org

Increased ERK signalling promotes inflammatory signalling in primary airway epithelial cells expressing Z α1-antitrypsin

Overexpression of Z α1-antitrypsin is known to induce polymer formation, prime the cells for endoplasmic reticulum stress and initiate nuclear factor kappa B (NF-κB) signalling. However, whether endogenous expression in primary bronchial epithelial cells has similar consequences remains unclear. Moreover, the mechanism of NF-κB activation has not yet been elucidated. Here, we report excessive NF-κB signalling in resting primary bronchial epithelial cells from ZZ patients compared with wild-type (MM) controls, and this appears to be mediated by mitogen-activated protein/extracellular signal-regulated kinase, EGF receptor and ADAM17 activity. Moreover, we show that rather than being a response to protein polymers, NF-κB signalling in airway-derived cells represents a loss of anti-inflammatory signalling by M α1-antitrypsin. Treatment of ZZ primary bronchial epithelial cells with purified plasma M α1-antitrypsin attenuates this inflammatory response, opening up new therapeutic options to modulate airway inflammation in the lung.

Characterising the association of latency with α1-antitrypsin polymerisation using a novel monoclonal antibody

α1-Antitrypsin is primarily synthesised in the liver, circulates to the lung and protects pulmonary tissues from proteolytic damage. The Z mutant (Glu342Lys) undergoes inactivating conformational change and polymerises. Polymers are retained within the hepatocyte endoplasmic reticulum (ER) in homozygous (PiZZ) individuals, predisposing the individuals to hepatic cirrhosis and emphysema. Latency is an analogous process of inactivating, intra-molecular conformational change and may co-occur with polymerisation. However, the relationship between latency and polymerisation remained unexplored in the absence of a suitable probe. We have developed a novel monoclonal antibody specific for latent α1-antitrypsin and used it in combination with a polymer-specific antibody, to assess the association of both conformers in vitro, in disease and during augmentation therapy. In vitro kinetics analysis showed polymerisation dominated the pathway but latency could be promoted by stabilising monomeric α1-antitrypsin. Polymers were extensively produced in hepatocytes and a cell line expressing Z α1-antitrypsin but the latent protein was not detected despite manipulation of the secretory pathway. However, α1-antitrypsin augmentation therapy contains latent α1-antitrypsin, as did the plasma of 63/274 PiZZ individuals treated with augmentation therapy but 0/264 who were not receiving this medication (p < 10−14). We conclude that latent α1-antitrypsin is a by-product of the polymerisation pathway, that the intracellular folding environment is resistant to formation of the latent conformer but that augmentation therapy introduces latent α1-antitrypsin into the circulation. A suite of monoclonal antibodies and methodologies developed in this study can characterise α1-antitrypsin folding and conformational transitions, and screen methods to improve augmentation therapy.

Altered native stability is the dominant basis for susceptibility of α1-antitrypsin mutants to polymerization.

Serpins are protease inhibitors whose most stable state is achieved upon transition of a central 5-stranded β-sheet to a 6-stranded form. Mutations, low pH, denaturants and elevated temperatures promote this transition, which can result in a growing polymer chain of inactive molecules. Different types of polymer are possible, but, experimentally only heat has been shown to generate polymers in vitro consistent with ex vivo pathological specimens. Many mutations that alter the rate of heat-induced polymerization have been described, but interpretation is problematic because discrimination is lacking between the effect of global changes in native stability and specific effects on structural mechanism. We show that the temperature midpoint (Tm) of thermal denaturation reflects the transition of α1-antitrypsin to the polymerization intermediate, and determine the relationship with fixed-temperature polymerization half-times (t0.5) in the presence of stabilizing additives [TMAO (trimethylamine N-oxide), sucrose and sodium sulfate], point mutations and disulfide bonds. Combined with a retrospective analysis of 31 mutants characterized in the literature, the results of the present study show that global changes to native state stability are the predominant basis for the effects of mutations and osmolytes on heat-induced polymerization, summarized by the equation: ln(t0.5,mutant/t0.5,wild-type)=0.34×ΔTm. It is deviations from this relationship that hold key information about the polymerization process.

The endoplasmic reticulum remains functionally connected by vesicular transport after its fragmentation in cells expressing Z-α1-antitrypsin

α1‐Antitrypsin is a serine protease inhibitor produced in the liver that is responsible for the regulation of pulmonary inflammation. The commonest pathogenic genemutation yields Z‐α1‐antitrypsin, which has a propensity to self‐associate forming polymers that become trapped in inclusions of endoplasmic reticulum (ER). It is unclear whether these inclusions are connected to the main ER network in Z‐α1‐antitrypsin‐expressing cells. Using live cell imaging, we found that despite inclusions containing an immobile matrix of polymeric α1‐antitrypsin, small ER resident proteins can diffuse freely within them. Inclusions havemany features to suggest they represent fragmented ER, and some are physically separated from the tubular ER network, yetwe observed cargo to be transported between them in a cytosol‐dependent fashion that is sensitive to N‐ethylmaleimide and dependent on Sar1 and sec22B. We conclude that protein recycling occurs between ER inclusions despite their physical separation.—Dickens, J. A., Ordóñez, A., Chambers, J. E., Beckett, A. J., Patel, V., Malzer, E., Dominicus, C.S., Bradley, J., Peden, A.A., Prior, I. A., Lomas, D. A., Marciniak, S. J. The endoplasmic reticulum remains functionally connected by vesicular transport after its fragmentation in cells expressing Z‐a1‐antitrypsin. FASEB J. 30, 4083–4097 (2016). www.fasebj.org

New Concepts in Alpha-1 Antitrypsin Deficiency Disease Mechanisms

Alpha-1 antitrypsin deficiency is predominantly caused by point mutations that alter the proteins folding. These mutations fall into two broad categories: those that destabilize the protein dramatically and lead to its post-translational degradation and those that affect protein structure more subtly to promote protein polymerization within the endoplasmic reticulum (ER). This distinction is important because it determines the cells response to each mutant. The severely misfolded mutants trigger an unfolded protein response (UPR) that promotes improved protein folding but can kill the cell in the chronic setting. In contrast, mutations that permit polymer formation fail to activate the UPR but instead promote a nuclear factor-κB-mediated ER overload response. The ability of polymers to increase a cells sensitivity to ER stress likely explains apparent inconsistencies in the alpha-1 antitrypsin-signaling literature that have linked polymers with the UPR. In this review we discuss the use of mutant serpins to dissect each signaling pathway.