Accumulation of PiZ alpha 1-antitrypsin causes liver damage in transgenic mice

Impact of PNPLA3 I148M on alpha-1 antitrypsin deficiency-dependent liver disease progression

BACKGROUND AND AIMS

Genetic risk factors are major determinants of chronic liver disease (CLD) progression. Patatin-like phospholipase domain-containing protein 3 (PNPLA3) I148M polymorphism and alpha-1 antitrypsin (AAT) E342K variant, termed PiZ, are major modifiers of metabolic CLD. Both variants are known to affect metabolic CLD through increased endoplasmic reticulum stress, but their combined effect on CLD progression remains largely unknown. Here, we aimed to test our working hypothesis that their combined incidence triggers CLD disease progression.

APPROACH AND RESULTS

We showed that patients with PiZZ/PNPLA3 I148M from the European alpha-1-antitrypsin deficiency (AATD) liver consortium and the UK Biobank had a trend towards higher liver enzymes, but no increased liver fat accumulation was evident between subgroups. After generating transgenic mice that overexpress the PiZ variant and simultaneously harbor the PNPLA3 I148M knockin (designated as PiZ/PNPLA3 I148M ), we observed that animals with PiZ and PiZ/PNPLA3 I148M showed increased liver enzymes compared to controls during aging. However, no significant difference between PiZ and PiZ/PNPLA3 I148M groups was observed, with no increased liver fat accumulation over time. To further study the impact on CLD progression, a Western-styled diet was administered, which resulted in increased fat accumulation and fibrosis in PiZ and PiZ/PNPLA3 I148M livers compared to controls, but the additional presence of PNPLA3 I148M had no impact on liver phenotype. Notably, the PiZ variant protected PNPLA3 I148M mice from liver damage and obesity after Western-styled diet feeding.

CONCLUSION

Our results demonstrate that the PNPLA3 polymorphism in the absence of additional metabolic risk factors is insufficient to drive the development of advanced liver disease in severe AATD.

Biodistribution and safety of a single rAAV3B-AAT vector for silencing and replacement of alpha-1 antitrypsin in Cynomolgus macaques

Alpha-1 antitrypsin deficiency (AATD) is characterized by both chronic lung disease due to loss of wild-type AAT (M-AAT) antiprotease function and liver disease due to toxicity from delayed secretion, polymerization, and aggregation of misfolded mutant AAT (Z-AAT). The ideal gene therapy for AATD should therefore comprise both endogenous Z-AAT suppression and M-AAT overexpression. We designed a dual-function rAAV3B (df-rAAV3B) construct, which was effective at transducing hepatocytes, resulting in a considerable decrease of Z-AAT levels and safe M-AAT augmentation in mice. We optimized df-rAAV3B and created two variants, AAV3B-E12 and AAV3B-G3, to simultaneously enhance the concentration of M-AAT in the bloodstream to therapeutic levels and silence endogenous AAT liver expression in cynomolgus monkeys. Our results demonstrate that AAV3b-WT, AAV3B-E12, and AAV3B-G3 were able to transduce the monkey livers and achieve high M-AAT serum levels efficiently and safely. In this nondeficient model, we did not find downregulation of endogenous AAT. However, the dual-function vector did serve as a potentially "liver-sparing" alternative for high-dose liver-mediated AAT gene replacement in the context of underlying liver disease.

The p24-family and COPII subunit SEC24C facilitate the clearance of alpha1-antitrypsin Z from the endoplasmic reticulum to lysosomes

A subpopulation of the alpha-1-antitrypsin misfolding Z mutant (ATZ) is cleared from the endoplasmic reticulum (ER) via an ER-to-lysosome-associated degradation (ERLAD) pathway. Here, we report that the COPII subunit SEC24C and the p24-family of proteins facilitate the clearance of ATZ via ERLAD. In addition to the previously reported ERLAD components calnexin and FAM134B, we discovered that ATZ coimmunoprecipitates with the p24-family members TMP21 and TMED9. This contrasts with wild type alpha1-antitrypsin, which did not coimmunoprecipitate with FAM134B, calnexin or the p24-family members. Live-cell imaging revealed that ATZ and the p24-family members traffic together from the ER to lysosomes. Using chemical inhibitors to block ER exit or autophagy, we demonstrated that p24-family members and ATZ co-accumulate at SEC24C marked ER-exit sites or in ER-derived compartments, respectively. Furthermore, depletion of SEC24C, TMP21, or TMED9 inhibited lysosomal trafficking of ATZ and resulted in the increase of intracellular ATZ levels. Conversely, overexpression of these p24-family members resulted in the reduction of ATZ levels. Intriguingly, the p24-family members coimmunoprecipitate with ATZ, FAM134B, and SEC24C. Thus, we propose a model in which the p24-family functions in an adaptor complex linking SEC24C with the ERLAD machinery for the clearance of ATZ.

Approaches to Therapeutic Gene Editing in Alpha-1 Antitrypsin Deficiency

Five distinct gene therapy approaches have been developed for treating AATD. These approaches include knockout of the mutant (PiZ) allele by introduction of double-strand breaks (DSBs) and subsequent creation of insertions and deletions (indels) by DSB repair, homology-directed repair (HDR) targeted to the mutation site, base editing, prime editing, and alternatively targeted knock-in techniques. Each approach will be discussed and a brief summary of a standard CRISPR-Cas9 targeting method will be presented.

Increased expression or activation of TRPML1 reduces hepatic storage of toxic Z alpha-1 antitrypsin

Mutant Z alpha-1 antitrypsin (ATZ) accumulates in globules in the liver and is the prototype of proteotoxic hepatic disease. Therapeutic strategies aiming at clearance of polymeric ATZ are needed. Transient receptor potential mucolipin-1 (TRPML1) is a lysosomal Ca2+ channel that maintains lysosomal homeostasis. In this study, we show that by increasing lysosomal exocytosis, TRPML1 gene transfer or small-molecule-mediated activation of TRPML1 reduces hepatic ATZ globules and fibrosis in PiZ transgenic mice that express the human ATZ. ATZ globule clearance induced by TRPML1 occurred without increase in autophagy or nuclear translocation of TFEB. Our results show that targeting TRPML1 and lysosomal exocytosis is a novel approach for treatment of the liver disease due to ATZ and potentially other diseases due to proteotoxic liver storage.

RNAi therapeutics for diseases involving protein aggregation: fazirsiran for alpha-1 antitrypsin deficiency-associated liver disease

INTRODUCTION

Therapeutic agents that prevent protein misfolding or promote protein clearance are being studied to treat proteotoxic diseases. Among them, alpha-1 antitrypsin deficiency (AATD) is caused by mutations in the alpha-1 antitrypsin (SERPINA1) gene. Fazirsiran is a small interfering RNA (siRNA) that is intended to address the underlying cause of liver disease associated with AATD through the RNA interference (RNAi) mechanism.

AREAS COVERED

This article describes the role of misfolded proteins and protein aggregates in disease and options for therapeutic approaches. The RNAi mechanism is discussed, along with how the siRNA therapeutic fazirsiran for the treatment of AATD was developed. We also describe the implications of siRNA therapeutics in extrahepatic diseases.

EXPERT OPINION

Using RNAi as a therapeutic approach is well suited to treat disease in conditions where an excess of a protein or the effect of an abnormal mutated protein causes disease. The results observed for the first few siRNA therapeutics that were approved or are in development provide an important promise for the development of future drugs that can address such conditions in a specific and targeted way. Current developments should enable the use of RNAi therapeutics outside the liver, where there are many more possible diseases to address.

Cleaning up alpha-1 antitrypsin deficiency related liver disease

PURPOSE OF REVIEW

Alpha-1 antitrypsin deficiency (AATD) is one of the most common genetic disorders arising due to mutations in alpha-1 antitrypsin (AAT) gene affecting primarily the lung and the liver. This review summarizes the pathophysiology and clinical manifestation of different AATD genotypes and discusses the recent therapeutic developments. The focus is on the severe, rare homozygous Pi∗ZZ and the common heterozygous Pi∗MZ genotype.

RECENT FINDINGS

Pi∗ZZ individuals harbor an up to 20 times higher risk of liver fibrosis and cirrhosis than noncarriers and liver transplantation is currently the only available therapeutic option. AATD constitutes a proteotoxic disorder arising from hepatic AAT accumulation and the currently most promising data come from a phase 2, open-label trial of fazirsiran, a hepatocyte-targeted siRNA. Pi∗MZ subjects display an increased risk of advanced liver disease and at the latter stage, a faster deterioration than individuals without AAT mutation.

SUMMARY

Although the fazirsiran data offer a glimpse of hope to AATD patients, a consensus on appropriate study endpoint, a careful patient selection as well as monitoring of long-term safety will be essential for an approval.

Cellular therapies in liver and pancreatic diseases

Over the past two decades, developments in regenerative medicine in gastroenterology have been greatly enhanced by the application of stem cells, which can self-replicate and differentiate into any somatic cell. The discovery of induced pluripotent stem cells has opened remarkable perspectives on tissue regeneration, including their use as a bridge to transplantation or as supportive therapy in patients with organ failure. The improvements in DNA manipulation and gene editing strategies have also allowed to clarify the physiopathology and to correct the phenotype of several monogenic diseases, both in vivo and in vitro. Further progress has been made with the development of three-dimensional cultures, known as organoids, which have demonstrated morphological and functional complexity comparable to that of a miniature organ. Hence, owing to its protean applications and potential benefits, cell and organoid transplantation has become a hot topic for the management of gastrointestinal diseases. In this review, we describe current knowledge on cell therapies in hepatology and pancreatology, providing insight into their future applications in regenerative medicine.

Human iPSC-hepatocyte modeling of alpha-1 antitrypsin heterozygosity reveals metabolic dysregulation and cellular heterogeneity

Individuals homozygous for the "Z" mutation in alpha-1 antitrypsin deficiency are known to be at increased risk for liver disease. It has also become clear that some degree of risk is similarly conferred by the heterozygous state. A lack of model systems that recapitulate heterozygosity in human hepatocytes has limited the ability to study the impact of a single Z alpha-1 antitrypsin (ZAAT) allele on hepatocyte biology. Here, we describe the derivation of syngeneic induced pluripotent stem cells (iPSCs) engineered to determine the effects of ZAAT heterozygosity in iPSC-hepatocytes (iHeps). We find that heterozygous MZ iHeps exhibit an intermediate disease phenotype and share with ZZ iHeps alterations in AAT protein processing and downstream perturbations including altered endoplasmic reticulum (ER) and mitochondrial morphology, reduced mitochondrial respiration, and branch-specific activation of the unfolded protein response in cell subpopulations. Our model of MZ heterozygosity thus provides evidence that a single Z allele is sufficient to disrupt hepatocyte homeostatic function.

Fazirsiran for Liver Disease Associated with Alpha1-Antitrypsin Deficiency

BACKGROUND

Alpha₁-antitrypsin (AAT) deficiency results from carriage of a homozygous SERPINA1 "Z" mutation (proteinase inhibitor [PI] ZZ). The Z allele produces a mutant AAT protein called Z-AAT, which accumulates in hepatocytes and can lead to progressive liver disease and fibrosis. This open-label, phase 2 trial investigated the safety and efficacy of fazirsiran, an RNA interference therapeutic, in patients with liver disease associated with AAT deficiency.

METHODS

We assigned adults with the PI ZZ genotype and liver fibrosis to receive fazirsiran at a dose of 200 mg (cohorts 1 [4 patients] and 2 [8 patients]) or 100 mg (cohort 1b [4 patients]) subcutaneously on day 1 and week 4 and then every 12 weeks. The primary end point was the change from baseline to week 24 (cohorts 1 and 1b) or week 48 (cohort 2) in liver Z-AAT concentrations, which were measured by means of liquid chromatography-mass spectrometry.

RESULTS

All the patients had reduced accumulation of Z-AAT in the liver (median reduction, 83% at week 24 or 48). The nadir in serum was a reduction of approximately 90%, and treatment was also associated with a reduction in histologic globule burden (from a mean score of 7.4 [scores range from 0 to 9, with higher scores indicating a greater globule burden] at baseline to 2.3 at week 24 or 48). All cohorts had reductions in liver enzyme concentrations. Fibrosis regression was observed in 7 of 15 patients and fibrosis progression in 2 of 15 patients after 24 or 48 weeks. There were no adverse events leading to trial or drug discontinuation. Four serious adverse events (viral myocarditis, diverticulitis, dyspnea, and vestibular neuronitis) resolved.

CONCLUSIONS

In this small trial, fazirsiran was associated with a strong reduction of Z-AAT concentrations in the serum and liver and concurrent improvements in liver enzyme concentrations. (Funded by Arrowhead Pharmaceuticals; AROAAT-2002 ClinicalTrials.gov number, NCT03946449.).

Regulation of PGC1α Downstream of the Insulin Signaling Pathway Plays a Role in the Hepatic Proteotoxicity of Mutant α1-Antitrypsin Deficiency Variant Z

BACKGROUND & AIMS

Insulin signaling is known to regulate essential proteostasis mechanisms.

METHODS

The analyses here examined effects of insulin signaling in the PiZ mouse model of α1-antitrypsin deficiency in which hepatocellular accumulation and proteotoxicity of the misfolded α1-antitrypsin Z variant (ATZ) causes liver fibrosis and cancer.

RESULTS

We first studied the effects of breeding PiZ mice to liver-insulin-receptor knockout (LIRKO) mice (with hepatocyte-specific insulin-receptor gene disruption). The results showed decreased hepatic ATZ accumulation and liver fibrosis in PiZ x LIRKO vs PiZ mice, with reversal of those effects when we bred PiZ x LIRKO mice onto a FOXO1-deficient background. Increased intracellular degradation of ATZ mediated by autophagy was identified as the likely mechanism for diminished hepatic proteotoxicity in PiZ x LIRKO mice and the converse was responsible for enhanced toxicity in PiZ x LIRKO x FOXO1-KO animals. Transcriptomic studies showed major effects on oxidative phosphorylation and autophagy genes, and significant induction of peroxisome proliferator-activated-receptor-γ-coactivator-1α (PGC1α) expression in PiZ-LIRKO mice. Because PGC1α plays a key role in oxidative phosphorylation, we further investigated its effects on ATZ proteostasis in our ATZ-expressing mammalian cell model. The results showed PGC1α overexpression or activation enhances autophagic ATZ degradation.

CONCLUSIONS

These data implicate suppression of autophagic ATZ degradation by down-regulation of PGC1α as one mechanism by which insulin signaling exacerbates hepatic proteotoxicity in PiZ mice, and identify PGC1α as a novel target for development of new human α1-antitrypsin deficiency liver disease therapies.

Therapeutic applications of gene editing in chronic liver diseases: an update

Innovative genome editing techniques developed in recent decades have revolutionized the biomedical research field. Liver is the most favored target organ for genome editing owing to its ability to regenerate. The regenerative capacity of the liver enables ex vivo gene editing in which the mutated gene in hepatocytes isolated from the animal model of genetic disease is repaired. The edited hepatocytes are injected back into the animal to mitigate the disease. Furthermore, the liver is considered as the easiest target organ for gene editing as it absorbs almost all foreign molecules. The mRNA vaccines, which have been developed to manage the COVID-19 pandemic, have provided a novel gene editing strategy using Cas mRNA. A single injection of gene editing components with Cas mRNA is reported to be efficient in the treatment of patients with genetic liver diseases. In this review, we first discuss previously reported gene editing tools and cases managed using them, as well as liver diseases caused by genetic mutations. Next, we summarize the recent successes of ex vivo and in vivo gene editing approaches in ameliorating liver diseases in animals and humans.

Evaluation of cytosine base editing and adenine base editing as a potential treatment for alpha-1 antitrypsin deficiency

Alpha-1 antitrypsin deficiency (AATD) is a rare autosomal codominant disease caused by mutations within the SERPINA1 gene. The most prevalent variant in patients is PiZ SERPINA1, containing a single G > A transition mutation. PiZ alpha-1 antitrypsin (AAT) is prone to misfolding, leading to the accumulation of toxic aggregates within hepatocytes. In addition, the abnormally low level of AAT secreted into circulation provides insufficient inhibition of neutrophil elastase within the lungs, eventually causing emphysema. Cytosine and adenine base editors enable the programmable conversion of C⋅G to T⋅A and A⋅T to G⋅C base pairs, respectively. In this study, two different base editing approaches were developed: use of a cytosine base editor to install a compensatory mutation (p.Met374Ile) and use of an adenine base editor to mediate the correction of the pathogenic PiZ mutation. After treatment with lipid nanoparticles formulated with base editing reagents, PiZ-transgenic mice exhibited durable editing of SERPINA1 in the liver, increased serum AAT, and improved liver histology. These results indicate that base editing has the potential to address both lung and liver disease in AATD.

Ferret models of alpha-1 antitrypsin deficiency develop lung and liver disease

Alpha-1 antitrypsin deficiency (AATD) is the most common genetic cause and risk factor for chronic obstructive pulmonary disease, but the field lacks a large-animal model that allows for longitudinal assessment of pulmonary function. We hypothesized that ferrets would model human AATD-related lung and hepatic disease. AAT-knockout (AAT-KO) and PiZZ (E342K, the most common mutation in humans) ferrets were generated and compared with matched controls using custom-designed flexiVent modules to perform pulmonary function tests, quantitative computed tomography (QCT), bronchoalveolar lavage (BAL) proteomics, and alveolar morphometry. Complete loss of AAT (AAT-KO) led to increased pulmonary compliance and expiratory airflow limitation, consistent with obstructive lung disease. QCT and morphometry confirmed emphysema and airspace enlargement, respectively. Pathway analysis of BAL proteomics data revealed inflammatory lung disease and impaired cellular migration. The PiZ mutation resulted in altered AAT protein folding in the liver, hepatic injury, and reduced plasma concentrations of AAT, and PiZZ ferrets developed obstructive lung disease. In summary, AAT-KO and PiZZ ferrets model the progressive obstructive pulmonary disease seen in AAT-deficient patients and may serve as a platform for preclinical testing of therapeutics including gene therapy.

HRD1-mediated METTL14 degradation regulates m6A mRNA modification to suppress ER proteotoxic liver disease

Accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) lumen triggers an unfolded protein response (UPR) for stress adaptation, the failure of which induces cell apoptosis and tissue/organ damage. The molecular switches underlying how the UPR selects for stress adaptation over apoptosis remain unknown. Here, we discovered that accumulation of unfolded/misfolded proteins selectively induces N6-adenosine-methyltransferase-14 (METTL14) expression. METTL14 promotes C/EBP-homologous protein (CHOP) mRNA decay through its 3' UTR N6-methyladenosine (m6A) to inhibit its downstream pro-apoptotic target gene expression. UPR induces METTL14 expression by competing against the HRD1-ER-associated degradation (ERAD) machinery to block METTL14 ubiquitination and degradation. Therefore, mice with liver-specific METTL14 deletion are highly susceptible to both acute pharmacological and alpha-1 antitrypsin (AAT) deficiency-induced ER proteotoxic stress and liver injury. Further hepatic CHOP deletion protects METTL14 knockout mice from ER-stress-induced liver damage. Our study reveals a crosstalk between ER stress and mRNA m6A modification pathways, termed the ERm6A pathway, for ER stress adaptation to proteotoxicity.

The Mechanism of Mitochondrial Injury in Alpha-1 Antitrypsin Deficiency Mediated Liver Disease

Alpha-1 antitrypsin deficiency (AATD) is caused by a single mutation in the SERPINA1 gene, which culminates in the accumulation of misfolded alpha-1 antitrypsin (ZAAT) within the endoplasmic reticulum (ER) of hepatocytes. AATD is associated with liver disease resulting from hepatocyte injury due to ZAAT-mediated toxic gain-of-function and ER stress. There is evidence of mitochondrial damage in AATD-mediated liver disease; however, the mechanism by which hepatocyte retention of aggregated ZAAT leads to mitochondrial injury is unknown. Previous studies have shown that ER stress is associated with both high concentrations of fatty acids and mitochondrial dysfunction in hepatocytes. Using a human AAT transgenic mouse model and hepatocyte cell lines, we show abnormal mitochondrial morphology and function, and dysregulated lipid metabolism, which are associated with hepatic expression and accumulation of ZAAT. We also describe a novel mechanism of ZAAT-mediated mitochondrial dysfunction. We provide evidence that misfolded ZAAT translocates to the mitochondria for degradation. Furthermore, inhibition of ZAAT expression restores the mitochondrial function in ZAAT-expressing hepatocytes. Altogether, our results show that ZAAT aggregation in hepatocytes leads to mitochondrial dysfunction. Our findings suggest a plausible model for AATD liver injury and the possibility of mechanism-based therapeutic interventions for AATD liver disease.

In vivo somatic cell base editing and prime editing

Recent advances in genome editing technologies have magnified the prospect of single-dose cures for many genetic diseases. For most genetic disorders, precise DNA correction is anticipated to best treat patients. To install desired DNA changes with high precision, our laboratory developed base editors (BEs), which can correct the four most common single-base substitutions, and prime editors, which can install any substitution, insertion, and/or deletion over a stretch of dozens of base pairs. Compared to nuclease-dependent editing approaches that involve double-strand DNA breaks (DSBs) and often result in a large percentage of uncontrolled editing outcomes, such as mixtures of insertions and deletions (indels), larger deletions, and chromosomal rearrangements, base editors and prime editors often offer greater efficiency with fewer byproducts in slowly dividing or non-dividing cells, such as those that make up most of the cells in adult animals. Both viral and non-viral in vivo delivery methods have now been used to deliver base editors and prime editors in animal models, establishing that base editors and prime editors can serve as effective agents for in vivo therapeutic genome editing in animals. This review summarizes examples of in vivo somatic cell (post-natal) base editing and prime editing and prospects for future development.

Involvement of Autophagy in Ageing and Chronic Cholestatic Diseases

Autophagy is a “housekeeping” lysosomal degradation process involved in numerous physiological and pathological processes in all eukaryotic cells. The dysregulation of hepatic autophagy has been described in several conditions, from obesity to diabetes and cholestatic disease. We review the role of autophagy, focusing on age-related cholestatic diseases, and discuss its therapeutic potential and the molecular targets identified to date. The accumulation of toxic BAs is the main cause of cell damage in cholestasis patients. BAs and their receptor, FXR, have been implicated in the regulation of hepatic autophagy. The mechanisms by which cholestasis induces liver damage include mitochondrial dysfunction, oxidative stress and ER stress, which lead to cell death and ultimately to liver fibrosis as a compensatory mechanism to reduce the damage. The stimulation of autophagy seems to ameliorate the liver damage. Autophagic activity decreases with age in several species, whereas its basic extends lifespan in animals, suggesting that it is one of the convergent mechanisms of several longevity pathways. No strategies aimed at inducing autophagy have yet been tested in cholestasis patients. However, its stimulation can be viewed as a novel therapeutic strategy that may reduce ageing-dependent liver deterioration and also mitigate hepatic steatosis.

Living with the enemy: from protein-misfolding pathologies we know, to those we want to know

Conformational diseases are caused by the aggregation of misfolded proteins. The risk for such pathologies develops years before clinical symptoms appear, and is higher in people with alpha-1 antitrypsin (AAT) polymorphisms. Thousands of people with alpha-1 antitrypsin deficiency (AATD) are underdiagnosed. Enemy-aggregating proteins may reside in these underdiagnosed AATD patients for many years before a pathology for AATD fully develops. In this perspective review, we hypothesize that the AAT protein could exert a new and previously unconsidered biological effect as an endogenous metal ion chelator that plays a significant role in essential metal ion homeostasis. In this respect, AAT polymorphism may cause an imbalance of metal ions, which could be correlated with the aggregation of amylin, tau, amyloid beta, and alpha synuclein proteins in type 2 diabetes mellitus (T2DM), Alzheimer's and Parkinson's diseases, respectively.

Up-regulation of miR-34b/c by JNK and FOXO3 protects from liver fibrosis

α1-Antitrypsin (AAT) deficiency is a common genetic disease presenting with lung and liver diseases. AAT deficiency results from pathogenic variants in the SERPINA1 gene encoding AAT and the common mutant Z allele of SERPINA1 encodes for Z α1-antitrypsin (ATZ), a protein forming hepatotoxic polymers retained in the endoplasmic reticulum of hepatocytes. PiZ mice express the human ATZ and are a valuable model to investigate the human liver disease of AAT deficiency. In this study, we investigated differential expression of microRNAs (miRNAs) between PiZ and control mice and found that miR-34b/c was up-regulated and its levels correlated with intrahepatic ATZ. Furthermore, in PiZ mouse livers, we found that Forkhead Box O3 (FOXO3) driving microRNA-34b/c (miR-34b/c) expression was activated and miR-34b/c expression was dependent upon c-Jun N-terminal kinase (JNK) phosphorylation on Ser⁵⁷⁴ Deletion of miR-34b/c in PiZ mice resulted in early development of liver fibrosis and increased signaling of platelet-derived growth factor (PDGF), a target of miR-34b/c. Activation of FOXO3 and increased miR-34c were confirmed in livers of humans with AAT deficiency. In addition, JNK-activated FOXO3 and miR-34b/c up-regulation were detected in several mouse models of liver fibrosis. This study reveals a pathway involved in liver fibrosis and potentially implicated in both genetic and acquired causes of hepatic fibrosis.

The Recruitment-Secretory Block ("R-SB") Phenomenon and Endoplasmic Reticulum Storage Diseases

In this article, we review the biological and clinical implication of the Recruitment-Secretory Block (“R-SB”) phenomenon. The phenomenon refers to the reaction of the liver with regard to protein secretion in conditions of clinical stimulation. Our basic knowledge of the process is due to the experimental work in animal models. Under basal conditions, the protein synthesis is mainly carried out by periportal (zone 1) hepatocytes that are considered the “professional” synthesizing protein cells. Under stimulation, midlobular and centrolobular (zones 2 and 3) hepatocytes, are progressively recruited according to lobular gradients and contribute to the increase of synthesis and secretion. The block of secretion, operated by exogenous agents, causes intracellular retention of all secretory proteins. The Pi MZ phenotype of Alpha-1-antitrypsin deficiency (AATD) has turned out to be the key for in vivo studies of the reaction of the liver, as synthesis and block of secretion are concomitant. Indeed, the M fraction of AAT is stimulated for synthesis and regularly exported while the Z fraction is mostly retained within the cell. For that reason, the phenomenon has been designated “Recruitment-Secretory Block” (“R-SB”). The “R-SB” phenomenon explains why: (a) the MZ individuals can correct the serum deficiency; (b) the resulting immonohistochemical and electron microscopic (EM) patterns are very peculiar and specific for the diagnosis of the Z mutation in tissue sections in the absence of genotyping; (c) the term carrier is no longer applicable for the heterozygous condition as all Pi MZ individuals undergo storage and the storage predisposes to liver damage. The storage represents the true elementary lesion and consequently reflects the phenotype-genotype correlation; (d) the site and function of the extrahepatic AAT and the relationship between intra and extracellular AAT; (e) last but not least, the concept of Endoplasmic Reticulum Storage Disease (ERSD) and of a new disease, hereditary hypofibrinogenemia with hepatic storage (HHHS). In the light of the emerging phenomenon, described in vitro, namely that M and Z AAT can form heteropolymers within hepatocytes as well as in circulation, we have reviewed the whole clinical and experimental material collected during forty years, in order to evaluate to what extent the polymerization phenomenon occurs in vivo. The paper summarizes similarities and differences between AAT and Fibrinogen as well as between the related diseases, AATD and HHHS. Indeed, fibrinogen gamma chain mutations undergo an aggregation process within the RER of hepatocytes similar to AATD. In addition, this work has clarified the intriguing phenomenon underlying a new syndrome, hereditary hypofibrinogenemia and hypo-APO-B-lipoproteinemia with hepatic storage of fibrinogen and APO-B lipoproteins. It is hoped that these studies could contribute to future research and select strategies aimed to simultaneously correct the hepatocytic storage, thus preventing the liver damage and the plasma deficiency of the two proteins.

Hepatic and Extrahepatic Sources and Manifestations in Endoplasmic Reticulum Storage Diseases

Alpha-1-antitrypsin (AAT) and fibrinogen are secretory acute phase reactant proteins. Circulating AAT and fibrinogen are synthesized exclusively in the liver. Mutations in the encoding genes result in conformational abnormalities of the two molecules that aggregate within the rough endoplasmic reticulum (RER) instead of being regularly exported. That results in AAT-deficiency (AATD) and in hereditary hypofibrinogenemia with hepatic storage (HHHS). The association of plasma deficiency and liver storage identifies a new group of pathologies: endoplasmic reticulum storage disease (ERSD).

Therapeutic Potential of Alpha-1 Antitrypsin in Type 1 and Type 2 Diabetes Mellitus

Alpha-1 antitrypsin (AAT) has established anti-inflammatory and immunomodulatory effects in chronic obstructive pulmonary disease but there is increasing evidence of its role in other inflammatory and immune-mediated conditions, like diabetes mellitus (DM). AAT activity is altered in both developing and established type 1 diabetes mellitus (T1DM) as well in established type 2 DM (T2DM). Augmentation therapy with AAT appears to favorably impact T1DM development in mice models and to affect β-cell function and inflammation in humans with T1DM. The role of AAT in T2DM is less clear, but AAT activity appears to be reduced in T2DM. This article reviews these associations and emerging therapeutic strategies using AAT to treat DM.

Improved prime editors enable pathogenic allele correction and cancer modelling in adult mice

Prime editors (PEs) mediate genome modification without utilizing double-stranded DNA breaks or exogenous donor DNA as a template. PEs facilitate nucleotide substitutions or local insertions or deletions within the genome based on the template sequence encoded within the prime editing guide RNA (pegRNA). However, the efficacy of prime editing in adult mice has not been established. Here we report an NLS-optimized SpCas9-based prime editor that improves genome editing efficiency in both fluorescent reporter cells and at endogenous loci in cultured cell lines. Using this genome modification system, we could also seed tumor formation through somatic cell editing in the adult mouse. Finally, we successfully utilize dual adeno-associated virus (AAVs) for the delivery of a split-intein prime editor and demonstrate that this system enables the correction of a pathogenic mutation in the mouse liver. Our findings further establish the broad potential of this genome editing technology for the directed installation of sequence modifications in vivo, with important implications for disease modeling and correction.

Dual proteotoxic stress accelerates liver injury via activation of p62-Nrf2

Protein accumulation is the hallmark of various neuronal, muscular, and other human disorders. It is also often seen in the liver as a major protein-secretory organ. For example, aggregation of mutated alpha1-antitrypsin (AAT), referred to as PiZ, is a characteristic feature of AAT deficiency, whereas retention of hepatitis B surface protein (HBs) is found in chronic hepatitis B (CHB) infection. We investigated the interaction of both proteotoxic stresses in humans and mice. Animals overexpressing both PiZ and HBs (HBs-PiZ mice) had greater liver injury, steatosis, and fibrosis. Later they exhibited higher hepatocellular carcinoma load and a more aggressive tumor subtype. Although PiZ and HBs displayed differing solubility properties and distinct distribution patterns, HBs-PiZ animals manifested retention of AAT/HBs in the degradatory pathway and a marked accumulation of the autophagy adaptor p62. Isolation of p62-containing particles revealed retained HBs/AAT and the lipophagy adapter perilipin-2. p62 build-up led to activation of the p62-Nrf2 axis and emergence of reactive oxygen species. Our results demonstrate that the simultaneous presence of two prevalent proteotoxic stresses promotes the development of liver injury due to protein retention and activation of the p62-Nrf2 axis. In humans, the PiZ variant was over-represented in CHB patients with advanced liver fibrosis (unadjusted odds ratio = 9.92 [1.15-85.39]). Current siRNA approaches targeting HBs/AAT should be considered for these individuals. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Advances in Alpha-1 Antitrypsin Gene Therapy

AAT (alpha-1 antitrypsin) deficiency (AATD), characterized by low levels of circulating serine protease inhibitor AAT, results in emphysematous destruction of the lung. Inherited serum deficiency disorders, such as hemophilia and AATD, have been considered ideal candidates for gene therapy. Although viral vector-meditated transduction of the liver has demonstrated utility in hemophilia, similar success has not been achieved for AATD. The challenge for AAT gene therapy is achieving protective levels of AAT locally in the lung and mitigating potential liver toxicities linked to systemically administered viral vectors. Current strategies with ongoing clinical trials involve different routes of adeno-associated virus administrations, such as intramuscular and intrapleural injections, to provide consistent therapeutic levels from nonhepatic organ sites. Nevertheless, exploration of alternative methods of nonhepatic sourcing of AAT has been of great interest in the field. In this regard, pulmonary endothelium-targeted adenovirus vector could be a key technical mandate to achieve local augmentation of AAT within the lower respiratory tract, with the potential benefit of circumventing liver toxicities. In addition, incorporation of the CRISPR/Cas9 (CRISPR-associated protein 9) nuclease system into gene-delivery technologies has provided adjunctive technologies that could fully realize a one-time treatment for sustained, lifelong expression of AAT in patients with AATD. This review will focus on the adeno-associated virus- and adenoviral vector-mediated gene therapy strategies for the pulmonary manifestations of AATD and show that endeavoring to use genome-editing techniques will advance the current strategy to one fully compatible with direct human translation.

Regulation of autophagy by bile acids and in cholestasis - CholestoPHAGY or CholeSTOPagy

Autophagy is a lysosomal degradation pathway in which the cell self-digests its own components to provide nutrients in harsh environmental conditions. It also represents an opportunity to rid the cell of superfluous and damaged organelles, misfolded proteins or invaded microorganisms. Liver autophagy contributes to basic hepatic functions such as lipid, glycogen and protein turnover. Deregulated hepatic autophagy has been linked to many liver diseases including alpha-1-antitrypsin deficiency, alcoholic and non-alcoholic fatty liver diseases, hepatitis B and C infections, liver fibrosis as well as liver cancer. Recently, bile acids and the bile acid receptor FXR have been implicated in the regulation of hepatic autophagy, which implies a role of autophagy also for cholestatic liver diseases. This review summarizes the current evidence of bile acid mediated effects on autophagy and how this affects cholestatic liver diseases. Although detailed studies are lacking, we suggest a concept that the activity of autophagy in cholestasis depends on the disease stage, where autophagy may be induced at early stages ("cholestophagy") but may be impaired in prolonged cholestatic states ("cholestopagy").

Alpha-1 antitrypsin deficient individuals have circulating extracellular vesicles with profibrogenic cargo

Background

Alpha-1 antitrypsin deficiency (AATD)-mediated liver disease is a toxic “gain-of-function” inflammation in the liver associated with intracellular retention of mutant alpha-1 antitrypsin. The clinical presentation of the disease includes fibrosis, cirrhosis and liver failure. However, the pathogenic mechanism of AATD-mediated liver disease is not well understood. Here, we investigated the role of plasma extracellular vesicles (EVs) in progression of AATD-mediated liver disease.

Methods

EVs were isolated from plasma of AATD individuals with liver disease and healthy controls. Their cytokines and miRNA content were examined by multiplex assay and small RNA sequencing. The bioactivity of EVs was assessed by qPCR, western blot analysis and immunofluorescent experiments using human hepatic stellate cells (HSCs) treated with EVs isolated from control or AATD plasma samples.

Results

We have found that AATD individuals have a distinct population of EVs with pathological cytokine and miRNA contents. When HSCs were cultured with AATD plasma derived-EVs, the expression of genes related to the development of fibrosis were significantly amplified compared to those treated with healthy control plasma EVs.

Conclusion

AATD individuals have a distinct population of EVs with abnormal cytokine and miRNA contents and the capacity to activate HSCs and mediate fibrosis. Better understanding of the components which cause liver inflammation and fibrogenesis, leading to further liver injury, has the potential to lead to the development of new treatments or preventive strategies to prevent AATD-mediated liver disease.

Gene Therapy in Rare Respiratory Diseases: What Have We Learned So Far?

Gene therapy is an alternative therapy in many respiratory diseases with genetic origin and currently without curative treatment. After five decades of progress, many different vectors and gene editing tools for genetic engineering are now available. However, we are still a long way from achieving a safe and efficient approach to gene therapy application in clinical practice. Here, we review three of the most common rare respiratory conditions-cystic fibrosis (CF), alpha-1 antitrypsin deficiency (AATD), and primary ciliary dyskinesia (PCD)-alongside attempts to develop genetic treatment for these diseases. Since the 1990s, gene augmentation therapy has been applied in multiple clinical trials targeting CF and AATD, especially using adeno-associated viral vectors, resulting in a good safety profile but with low efficacy in protein expression. Other strategies, such as non-viral vectors and more recently gene editing tools, have also been used to address these diseases in pre-clinical studies. The first gene therapy approach in PCD was in 2009 when a lentiviral transduction was performed to restore gene expression in vitro; since then, transcription activator-like effector nucleases (TALEN) technology has also been applied in primary cell culture. Gene therapy is an encouraging alternative treatment for these respiratory diseases; however, more research is needed to ensure treatment safety and efficacy.

Liver Phenotypes of European Adults Heterozygous or Homozygous for Pi∗Z Variant of AAT (Pi∗MZ vs Pi∗ZZ genotype) and Noncarriers

BACKGROUND & AIMS

Homozygosity for the Pi∗Z variant of the gene that encodes the alpha-1 antitrypsin peptide (AAT), called the Pi∗ZZ genotype, causes a liver and lung disease called alpha-1 antitrypsin deficiency. Heterozygosity (the Pi∗MZ genotype) is a risk factor for cirrhosis in individuals with liver disease. Up to 4% of Europeans have the Pi∗MZ genotype; we compared features of adults with and without Pi∗MZ genotype among persons without preexisting liver disease.

METHODS

We analyzed data from the European Alpha-1 Liver Cohort, from 419 adults with the Pi∗MZ genotype, 309 adults with the Pi∗ZZ genotype, and 284 individuals without the variant (noncarriers). All underwent a comprehensive evaluation; liver stiffness measurements (LSMs) were made by transient elastography. Liver biopsies were analyzed to define histologic and biochemical features associated with the Pi∗Z variant. Levels of serum transaminases were retrieved from 444,642 participants, available in the United Kingdom biobank.

RESULTS

In the UK biobank database, levels of serum transaminases were increased in subjects with the Pi∗MZ genotype compared with noncarriers. In the Alpha-1 Liver Cohort, adults with Pi∗MZ had lower levels of gamma-glutamyl transferase in serum and lower LSMs than adults with the Pi∗ZZ variant, but these were higher than in noncarriers. Ten percent of subjects with the Pi∗MZ genotype vs 4% of noncarriers had LSMs of 7.1 kPa or more (adjusted odds ratio, 4.8; 95% confidence interval, 2.0-11.8). Obesity and diabetes were the most important factors associated with LSMs ≥7.1 kPa in subjects with the Pi∗MZ genotype. AAT inclusions were detected in liver biopsies of 63% of subjects with the Pi∗MZ genotype, vs 97% of subjects with the Pi∗ZZ genotype, and increased with liver fibrosis stages. Subjects with the Pi∗MZ genotype did not have increased hepatic levels of AAT, whereas levels of insoluble AAT varied among individuals.

CONCLUSIONS

Adults with the Pi∗MZ genotype have lower levels of serum transaminases, fewer AAT inclusions in liver, and lower liver stiffness than adults with the Pi∗ZZ genotype, but higher than adults without the Pi∗Z variant. These findings should help determine risk of subjects with the Pi∗MZ genotype and aid in counseling.

CHOP and c-JUN up-regulate the mutant Z α1-antitrypsin, exacerbating its aggregation and liver proteotoxicity

α₁-Antitrypsin (AAT) encoded by the SERPINA1 gene is an acute-phase protein synthesized in the liver and secreted into the circulation. Its primary role is to protect lung tissue by inhibiting neutrophil elastase. The Z allele of SERPINA1 encodes a mutant AAT, named ATZ, that changes the protein structure and leads to its misfolding and polymerization, which cause endoplasmic reticulum (ER) stress and liver disease through a gain-of-function toxic mechanism. Hepatic retention of ATZ results in deficiency of one of the most important circulating proteinase inhibitors and predisposes to early-onset emphysema through a loss-of-function mechanism. The pathogenetic mechanisms underlying the liver disease are not completely understood. C/EBP-homologous protein (CHOP), a transcription factor induced by ER stress, was found among the most up-regulated genes in livers of PiZ mice that express ATZ and in human livers of patients homozygous for the Z allele. Compared with controls, juvenile PiZ/Chop ^-/- mice showed reduced hepatic ATZ and a transcriptional response indicative of decreased ER stress by RNA-Seq analysis. Livers of PiZ/Chop ^-/- mice also showed reduced SERPINA1 mRNA levels. By chromatin immunoprecipitations and luciferase reporter-based transfection assays, CHOP was found to up-regulate SERPINA1 cooperating with c-JUN, which was previously shown to up-regulate SERPINA1, thus aggravating hepatic accumulation of ATZ. Increased CHOP levels were detected in diseased livers of children homozygous for the Z allele. In summary, CHOP and c-JUN up-regulate SERPINA1 transcription and play an important role in hepatic disease by increasing the burden of proteotoxic ATZ, particularly in the pediatric population.

Alpha-1 Antitrypsin Deficiency-Mediated Liver Toxicity: Why Do Some Patients Do Poorly? What Do We Know So Far?

Alpha-1 antitrypsin deficiency (AATD) is a rare genetic disease caused by mutations in the SERPINA1 gene and is associated with a decreased level of circulating alpha-1 antitrypsin (AAT). Among all the known mutations in the SERPINA1 gene, homozygous for the Z allele is well-known to result in both lung and liver disease. Unlike the lung injury that occurs in adulthood with the environment (notably, tobacco) as a co-factor, the hepatic damage is more complicated. Despite a common underlying gene mutation, the liver disease associated with AATD presents a considerable variability in the age-of-onset and severity, ranging from transient neonatal cholestasis (in early childhood) to cirrhosis and liver cancer (in childhood and adulthood). Given that all the cofactors- genetics and/or environmental- have not been fully identified, it is still impossible to predict which individuals with AATD may develop severe liver disease. The discovery of these modifiers represents the major challenge for the detection, diagnosis, and development of new therapies to provide alternative options to liver transplantation. The aim of this current review is to provide an updated overview of our knowledge on why some AATD patients associated with liver damage progress poorly.

Development of an RNAi therapeutic for alpha-1-antitrypsin liver disease

The autosomal codominant genetic disorder alpha-1 antitrypsin (AAT) deficiency (AATD) causes pulmonary and liver disease. Individuals homozygous for the mutant Z allele accumulate polymers of Z-AAT protein in hepatocytes, where AAT is primarily produced. This accumulation causes endoplasmic reticulum (ER) stress, oxidative stress, damage to mitochondria, and inflammation, leading to fibrosis, cirrhosis, and hepatocellular carcinoma. The magnitude of AAT reduction and duration of response from first-generation intravenously administered RNA interference (RNAi) therapeutic ARC-AAT and then with next-generation subcutaneously administered ARO-AAT were assessed by measuring AAT protein in serum of the PiZ transgenic mouse model and human volunteers. The impact of Z-AAT reduction by RNAi on liver disease phenotypes was evaluated in PiZ mice by measuring polymeric Z-AAT in the liver; expression of genes associated with fibrosis, autophagy, apoptosis, and redox regulation; inflammation; Z-AAT globule parameters; and tumor formation. Ultrastructure of the ER, mitochondria, and autophagosomes in hepatocytes was evaluated by electron microscopy. In mice, sustained RNAi treatment reduced hepatic Z-AAT polymer, restored ER and mitochondrial health, normalized expression of disease-associated genes, reduced inflammation, and prevented tumor formation. RNAi therapy holds promise for the treatment of patients with AATD-associated liver disease. ARO-AAT is currently in phase II/III clinical trials.

A transgenic zebrafish model of hepatocyte function in human Z α1-antitrypsin deficiency

In human α1-antitrypsin deficiency, homozygous carriers of the Z (E324K) mutation in the gene SERPINA1 have insufficient circulating α1-antitrypsin and are predisposed to emphysema. Misfolding and accumulation of the mutant protein in hepatocytes also causes endoplasmic reticulum stress and underpins long-term liver damage. Here, we describe transgenic zebrafish (Danio rerio) expressing the wildtype or the Z mutant form of human α1-antitrypsin in hepatocytes. As observed in afflicted humans, and in rodent models, about 80% less α1-antitrypsin is evident in the circulation of zebrafish expressing the Z mutant. Although these zebrafish also show signs of liver stress, they do not accumulate α1-antitrypsin in hepatocytes. This new zebrafish model will provide useful insights into understanding and treatment of α1-antitrypsin deficiency.

Genome editing technologies to treat rare liver diseases

Liver has a central role in protein and lipid metabolism, and diseases involving hepatocytes have often repercussions on multiple organs and systems. Hepatic disorders are frequently characterized by production of defective or non-functional proteins, and traditional gene therapy approaches have been attempted for years to restore adequate protein levels through delivery of transgenes. Recently, many different genome editing platforms have been developed aimed at correcting at DNA level the defects underlying the diseases. In this Review we discuss the latest applications of these tools applied to develop therapeutic strategies for rare liver disorders, in particular updating the literature with the most recent strategies relying on base editors technology.

Mitophagy in the Pathogenesis of Liver Diseases

Autophagy is a catabolic process involving vacuolar sequestration of intracellular components and their targeting to lysosomes for degradation, thus supporting nutrient recycling and energy regeneration. Accumulating evidence indicates that in addition to being a bulk, nonselective degradation mechanism, autophagy may selectively eliminate damaged mitochondria to promote mitochondrial turnover, a process termed “mitophagy”. Mitophagy sequesters dysfunctional mitochondria via ubiquitination and cargo receptor recognition and has emerged as an important event in the regulation of liver physiology. Recent studies have shown that mitophagy may participate in the pathogenesis of various liver diseases, such as liver injury, liver steatosis/fatty liver disease, hepatocellular carcinoma, viral hepatitis, and hepatic fibrosis. This review summarizes the current knowledge on the molecular regulations and functions of mitophagy in liver physiology and the roles of mitophagy in the development of liver-related diseases. Furthermore, the therapeutic implications of targeting hepatic mitophagy to design a new strategy to cure liver diseases are discussed.

The Biological Effects of Double-Dose Alpha-1 Antitrypsin Augmentation Therapy. A Pilot Clinical Trial

Rationale: Augmentation therapy with intravenous AAT (alpha-1 antitrypsin) is the only specific therapy for individuals with pulmonary disease from AAT deficiency (AATD). The recommended standard dose (SD; 60 mg/kg/wk) elevates AAT trough serum levels to around 50% of normal; however, outside of slowing emphysema progression, its effects in other clinical outcomes have not been rigorously proven.

Objectives: To evaluate the biological effects of normalizing AAT trough levels with double-dose (DD) therapy (120 mg/kg/wk) in subjects with AATD already receiving SD therapy.

Methods: Clinically stable subjects were evaluated after 4 weeks of SD therapy, followed by 4 weeks of DD therapy, and 4 weeks after return to SD therapy. At the end of each phase, BAL fluid (BALF) and plasma samples were obtained.

Measurements and Main Results: DD therapy increased trough AAT levels to normal and, compared with SD therapy, reduced serine protease activity in BALF (elastase and cathepsin G), plasma elastase footprint (Aα-Val³⁶⁰), and markers of elastin degradation (desmosine/isodesmosine) in BALF. DD therapy also further downregulated BALF ILs and cytokines including Jak-STAT (Janus kinases–signal transducer and activator of transcription proteins), TNFα (tumor necrosis factor-α), and T-cell receptor signaling pathways, cytokines involved in macrophage migration, eosinophil recruitment, humoral and adaptive immunity, neutrophil activation, and cachexia. On restarting SD after DD treatment, a possible carryover effect was seen for several biological markers.

Conclusions: Subjects with AATD on SD augmentation therapy still exhibit inflammation, protease activity, and elastin degradation that can be further improved by normalizing AAT levels. Higher AAT dosing than currently recommended may lead to enhanced clinical benefits and should be explored further.

Clinical trial registered with www.clinicaltrials.gov (NCT 01669421).

Animal Modeling of Pediatric Liver Cancer

Hepatoblastoma (HB) is the most common pediatric liver malignancy. Management of HB requires multidisciplinary efforts. The 5-year overall survival of this disease is about 80% in developed countries. Despite advances in the care of these patients, survival in recurrent or treatment-refractory disease is lower than 50%. This is due to more complex tumor biology, including hepatocellular carcinoma (HCC)-like mutations and expression of aggressive gene signatures leading to chemoresistance, vascular invasion, and metastatic spread. The current treatment protocols for pediatric liver cancer do not incorporate targeted therapies, and the ability to test these therapies is limited due to the inaccessibility of cell lines and mouse models. In this review, we discuss the current status of preclinical animal modeling in pediatric liver cancer, primarily HB. Although HB is a rare cancer, the research community has worked together to develop a range of interesting and relevant mouse models for diverse preclinical studies.

A Novel Small Molecule Inhibits Intrahepatocellular Accumulation of Z-Variant Alpha 1-Antitrypsin In Vitro and In Vivo

Alpha 1-antitrypsin deficiency (AATD) is the most common genetic cause of liver disease in children and is associated with early-onset chronic liver disease in adults. AATD associated liver injury is caused by hepatotoxic retention of polymerized mutant alpha 1-antitrypsin molecules within the endoplasmic reticulum. Currently, there is no curative therapy for AATD. In this study, we selected small molecules with the potential to bind mutant alpha 1-antitrypsin (Z-variant) to inhibit its accumulation in hepatocytes. We used molecular docking to select candidate compounds that were validated in cell and animal models of disease. A crystal structure of polymerized alpha 1-antitrypsin molecule was used as the basis for docking 139,735 compounds. Effects of the top scoring compounds were investigated in a cell model that stably expresses Z-variant alpha 1-antitrypsin and in PiZ mice expressing Z-variant human alpha 1-antitrypsin (Z-hAAT), encoded by SERPINA1*E342K. 4′,′5-(Methylenedioxy)-2-nitrocinnamic acid was predicted to bind cleaved alpha 1-antitrypsin at the polymerization interface, and observed to co-localize with Z-hAAT, increase Z-hAAT degradation, inhibit intracellular accumulation of Z-hAAT, and alleviate liver fibrosis.

Mild Iron Overload as Seen in Individuals Homozygous for the Alpha-1 Antitrypsin Pi*Z Variant Does Not Promote Liver Fibrogenesis in HFE Knockout Mice

The presence of the homozygous 'Pi*Z' variant of alpha-1 antitrypsin (AAT) ('Pi*ZZ' genotype) predisposes to liver fibrosis development, but the role of iron metabolism in this process remains unknown. Therefore, we assessed iron metabolism and variants in the Homeostatic Iron Regulator gene (HFE) as the major cause of hereditary iron overload in a large cohort of Pi*ZZ subjects without liver comorbidities. The human cohort comprised of 409 Pi*ZZ individuals and 254 subjects without evidence of an AAT mutation who were recruited from ten European countries. All underwent a comprehensive work-up and transient elastography to determine liver stiffness measurements (LSM). The corresponding mouse models (Pi*Z overexpressors, HFE knockouts, and double transgenic [DTg] mice) were used to evaluate the impact of mild iron overload on Pi*Z-induced liver injury. Compared to Pi*Z non-carriers, Pi*ZZ individuals had elevated serum iron, transferrin saturation, and ferritin levels, but relevant iron overload was rare. All these parameters were higher in individuals with signs of significant liver fibrosis (LSM ≥ 7.1 kPa) compared to those without signs of significant liver fibrosis. HFE knockout and DTg mice displayed similar extent of iron overload and of fibrosis. Loss of HFE did not alter the extent of AAT accumulation. In Pi*ZZ individuals, presence of HFE mutations was not associated with more severe liver fibrosis. Taken together, Pi*ZZ individuals display minor alterations in serum iron parameters. Neither mild iron overload seen in these individuals nor the presence of HFE mutations (C282Y and H63D) constitute a major contributor to liver fibrosis development.

Liver Fibrosis and Metabolic Alterations in Adults With alpha-1-antitrypsin Deficiency Caused by the Pi*ZZ Mutation

BACKGROUND & AIMS

Alpha-1 antitrypsin deficiency (AATD) is among the most common genetic disorders. Severe AATD is caused by a homozygous mutation in the SERPINA1 gene that encodes the Glu342Lys substitution (called the Pi*Z mutation, Pi*ZZ genotype). Pi*ZZ carriers may develop lung and liver diseases. Mutation-associated lung disorders have been well studied, but less is known about the effects in liver. We assessed the liver disease burden and associated features in adults with this form of AATD.

METHODS

We collected data from 554 Pi*ZZ adults (403 in an exploratory cohort, 151 in a confirmatory cohort), in 9 European countries, with AATD who were homozygous for the Pi*Z mutation, and 234 adults without the Pi*Z mutation (controls), all without pre-existing liver disease. We collected data on demographic parameters, comorbidities, lung- and liver-related health, and blood samples for laboratory analysis. Liver fibrosis was assessed non-invasively via the serum tests Aspartate Aminotransferase to Platelet Ratio Index and HepaScore and via transient elastography. Liver steatosis was determined via transient elastography-based controlled attenuation parameter. We performed histologic analyses of livers from transgenic mice that overexpress the AATD-associated Pi*Z variant.

RESULTS

Serum levels of liver enzymes were significantly higher in Pi*ZZ carriers vs controls. Based on non-invasive tests for liver fibrosis, significant fibrosis was suspected in 20%-36% of Pi*ZZ carriers, whereas signs of advanced fibrosis were 9- to 20-fold more common in Pi*ZZ carriers compared to non-carriers. Male sex; age older than 50 years; increased levels of alanine aminotransferase, aspartate aminotransferase, or γ-glutamyl transferase; and low numbers of platelets were associated with higher liver fibrosis burden. We did not find evidence for a relationship between lung function and liver fibrosis. Controlled attenuation parameter ≥280 dB/m, suggesting severe steatosis, was detected in 39% of Pi*ZZ carriers vs 31% of controls. Carriers of Pi*ZZ had lower serum concentrations of triglyceride and low- and very-low-density lipoprotein cholesterol than controls, suggesting impaired hepatic secretion of lipid. Livers from Pi*Z-overexpressing mice had steatosis and down-regulation of genes involved in lipid secretion.

CONCLUSIONS

In studies of AATD adults with the Pi*ZZ mutation, and of Pi*Z-overexpressing mice, we found evidence of liver steatosis and impaired lipid secretion. We identified factors associated with significant liver fibrosis in patients, which could facilitate hepatologic assessment and counseling of individuals who carry the Pi*ZZ mutation. ClinicalTrials.gov Number NCT02929940.

Targeting the site encoded by SERPINA1*E342K for treating alpha-1 antitrypsin deficiency-associated liver diseases

Alpha1-antitrypsin (AAT) deficiency predisposes individuals to emphysema and liver diseases such as cirrhosis and hepatocellular carcinoma. The deficiency results from mutations in the SERPIN1A gene encoding AAT molecules that cause hepatotoxic retention within the endoplasmic reticulum. Since the E342K mutation is the basis for destabilization leading to lung and liver pathologies, we used the crystal structure of the mutated AAT as the basis for molecular docking selection of candidate compounds that may bind and stabilize the 342K structural pocket. We identified compounds that inhibited intracellular accumulation of AAT in hepatocytes in vitro. These data suggest that drug binding to a structural site encoded by a mutation associated with AAT deficiency has the potential for clinical utility by modulating conformational transitions.

A combined in silico and in vitro study on mouse Serpina1a antitrypsin-deficiency mutants

Certain point-mutations in the human SERPINA1-gene can cause severe α1-antitrypsin-deficiency (A1AT-D). Affected individuals can suffer from loss-of-function lung-disease and from gain-of-function liver-disease phenotypes. However, age of onset and severity of clinical appearance is heterogeneous amongst carriers, suggesting involvement of additional genetic and environmental factors. The generation of authentic A1AT-D mouse-models has been hampered by the complexity of the mouse Serpina1-gene locus and a model with concurrent lung and liver-disease is still missing. Here, we investigate point-mutations in the mouse Serpina1a antitrypsin-orthologue, which are homolog-equivalent to ones known to cause severe A1AT-D in human. We combine in silico and in vitro methods and we find that analyzed mutations do introduce potential disease-causing properties into Serpina1a. Finally, we show that introduction of the King’s-mutation causes inactivation of neutrophil elastase inhibitory-function in both, mouse and human antitrypsin, while the mouse Z-mutant retains activity. This work paves the path to generation of better A1AT-D mouse-models.

Role for Cela1 in Postnatal Lung Remodeling and Alpha-1 Antitrypsin-Deficient Emphysema

Alpha-1 antitrypsin (AAT) deficiency-related emphysema is the fourth leading indication for lung transplant. Chymotrypsin-like elastase 1 (Cela1) is a digestive protease that is expressed during lung development in association with regions of elastin remodeling, exhibits stretch-dependent expression during lung regeneration, and binds lung elastin in a stretch-dependent manner. AAT covalently neutralizes Cela1 in vitro. We sought to determine the role of Cela1 in postnatal lung physiology, whether it interacted with AAT in vivo, and to detect any effects it may have in the context of AAT deficiency. The lungs of Cela1^-/- mice had aberrant lung elastin structure and higher elastance as assessed with the flexiVent system. On the basis of in situ zymography with ex vivo lung stretch, Cela1 was solely responsible for stretch-inducible lung elastase activity. By mass spectrometry, Cela1 degraded mature elastin similarly to pancreatic elastase. Cela1 promoter and protein sequences were phylogenetically distinct in the placental mammal lineage, suggesting an adaptive role for lung-expressed Cela1 in this clade. A 6-week antisense oligonucleotide mouse model of AAT deficiency resulted in emphysema with increased Cela1 mRNA and reduction of approximately 70 kD Cela1, consistent with covalent binding of Cela1 by AAT. Cela1^-/- mice were completely protected against emphysema in this model. Cela1 was increased in human AAT-deficient emphysema. Cela1 is important in physiologic and pathologic stretch-dependent remodeling processes in the postnatal lung. AAT is an important regulator of this process. Our findings provide proof of concept for the development of anti-Cela1 therapies to prevent and/or treat AAT-deficient emphysema.

Russell-Like Bodies in Plant Seeds Share Common Features With Prolamin Bodies and Occur Upon Recombinant Protein Production

Although many recombinant proteins have been produced in seeds at high yields without adverse effects on the plant, endoplasmic reticulum (ER) stress and aberrant localization of endogenous or recombinant proteins have also been reported. The production of murine interleukin-10 (mIL-10) in Arabidopsis thaliana seeds resulted in the de novo formation of ER-derived structures containing a large fraction of the recombinant protein in an insoluble form. These bodies containing mIL-10 were morphologically similar to Russell bodies found in mammalian cells. We confirmed that the compartment containing mIL-10 was enclosed by ER membranes, and 3D electron microscopy revealed that these structures have a spheroidal shape. Another feature shared with Russell bodies is the continued viability of the cells that generate these organelles. To investigate similarities in the formation of Russell-like bodies and the plant-specific protein bodies formed by prolamins in cereal seeds, we crossed plants containing ectopic ER-derived prolamin protein bodies with a line accumulating mIL-10 in Russell-like bodies. This resulted in seeds containing only one population of protein bodies in which mIL-10 inclusions formed a central core surrounded by the prolamin-containing matrix, suggesting that both types of protein aggregates are together removed from the secretory pathway by a common mechanism. We propose that, like mammalian cells, plant cells are able to form Russell-like bodies as a self-protection mechanism, when they are overloaded with a partially transport-incompetent protein, and we discuss the resulting challenges for recombinant protein production.

Making gene editing a therapeutic reality

This review discusses current bottlenecks in making CRISPR-Cas9-mediated genome editing a therapeutic reality and it outlines recent strategies that aim to overcome these hurdles as well as the scope of current clinical trials that pioneer the medical translation of CRISPR-Cas9. Additionally, this review outlines the specifics of disease-modifying gene editing in recessive versus dominant genetic diseases with the focus on genetic myopathies that are exemplified by Duchenne muscular dystrophy and myotonic dystrophies.

Phospholipid transfer protein and alpha-1 antitrypsin regulate Hck kinase activity during neutrophil degranulation

Excessive neutrophil degranulation is a common feature of many inflammatory disorders, including alpha-1 antitrypsin (AAT) deficiency. Our group has demonstrated that phospholipid transfer protein (PLTP) prevents neutrophil degranulation but serine proteases, which AAT inhibits, cleave PLTP in diseased airways. We propose to identify if airway PLTP activity can be restored by AAT augmentation therapy and how PLTP subdues degranulation of neutrophils in AAT deficient subjects. Airway PLTP activity was lower in AAT deficient patients but elevated in the airways of patients on augmentation therapy. Functional AAT protein (from PiMM homozygotes) prevented PLTP cleavage unlike its mutated ZZ variant (PiZZ). PLTP lowered leukotriene B4 induced degranulation of primary, secondary and tertiary granules from neutrophils from both groups (n = 14/group). Neutrophils isolated from Pltp knockout mice have enhance neutrophil degranulation. Both AAT and PLTP reduced neutrophil degranulation and superoxide production, possibly though their inhibition of the Src tyrosine kinase, Hck. Src kinase inhibitors saracatinib and dasatinib reduced neutrophil degranulation and superoxide production. Therefore, AAT protects PLTP from proteolytic cleavage and both AAT and PLTP mediate degranulation, possibly via Hck tyrosine kinase inhibition. Deficiency of AAT could contribute to reduced lung PLTP activity and elevated neutrophil signaling associated with lung disease.