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Calreticulin enhances the secretory trafficking of a misfolded α-1-antitrypsin.

ABSTRACT: α1-antitrypsin (AAT) regulates the activity of multiple proteases in the lungs and liver. A mutant of AAT (E342K) called ATZ forms polymers that are present at only low levels in the serum and induce intracellular protein inclusions, causing lung emphysema and liver cirrhosis. An understanding of factors that can reduce the intracellular accumulation of ATZ is of great interest. We now show that calreticulin (CRT), an endoplasmic reticulum (ER) glycoprotein chaperone, promotes the secretory trafficking of ATZ, enhancing the media:cell ratio. This effect is more pronounced for ATZ than with AAT and is only partially dependent on the glycan-binding site of CRT, which is generally relevant to substrate recruitment and folding by CRT. The CRT-related chaperone calnexin does not enhance ATZ secretory trafficking, despite the higher cellular abundance of calnexin-ATZ complexes. CRT deficiency alters the distributions of ATZ-ER chaperone complexes, increasing ATZ-BiP binding and inclusion body formation and reducing ATZ interactions with components required for ER-Golgi trafficking, coincident with reduced levels of the protein transport protein Sec31A in CRT-deficient cells. These findings indicate a novel role for CRT in promoting the secretory trafficking of a protein that forms polymers and large intracellular inclusions. Inefficient secretory trafficking of ATZ in the absence of CRT is coincident with enhanced accumulation of ER-derived ATZ inclusion bodies. Further understanding of the factors that control the secretory trafficking of ATZ and their regulation by CRT could lead to new therapies for lung and liver diseases linked to AAT deficiency.

SUBMITTER: Mohan HM

PROVIDER: S-EPMC7864070 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Calreticulin enhances the secretory trafficking of a polymerogenic alpha1-antitrypsin

Project description:α-1-antitrypsin (AAT) regulates protease activity in the lungs and liver. The presence of one or more copies of a mutant Z allele (AAT (E342K), called ATZ), results in low serum levels of ATZ along with intracellular inclusions of polymeric forms, causing lung emphysema and liver cirrhosis. Our experiments show that calreticulin (CRT), an endoplasmic reticulum (ER) glycoprotein chaperone, promotes the secretory trafficking of ATZ, enhancing the media to cell ratio. This effect is more specific for ATZ compared with AAT, and is only partially dependent on the glycan-binding site of CRT. The CRT-related chaperone calnexin (CNX) does not promote enhanced ATZ secretory trafficking, despite the higher cellular abundance of CNX-ATZ complexes. CRT deficiency alters the distributions of ATZ-ER chaperone complexes, increasing ATZ-BiP binding and inclusion body (IB) formation, and reducing ATZ interactions with components required for ER-Golgi trafficking. These findings indicate a novel role for CRT in promoting the secretory trafficking of a polymerogenic protein. Inefficient secretory trafficking of ATZ in the absence of CRT is coincident with enhanced accumulation of ER-derived ATZ IBs.

2020-09-24 | PXD020562 | Pride

An analog of glibenclamide selectively enhances autophagic degradation of misfolded α1-antitrypsin Z.

Project description:The classical form of α1-antitrypsin deficiency (ATD) is characterized by intracellular accumulation of the misfolded variant α1-antitrypsin Z (ATZ) and severe liver disease in some of the affected individuals. In this study, we investigated the possibility of discovering novel therapeutic agents that would reduce ATZ accumulation by interrogating a C. elegans model of ATD with high-content genome-wide RNAi screening and computational systems pharmacology strategies. The RNAi screening was utilized to identify genes that modify the intracellular accumulation of ATZ and a novel computational pipeline was developed to make high confidence predictions on repurposable drugs. This approach identified glibenclamide (GLB), a sulfonylurea drug that has been used broadly in clinical medicine as an oral hypoglycemic agent. Here we show that GLB promotes autophagic degradation of misfolded ATZ in mammalian cell line models of ATD. Furthermore, an analog of GLB reduces hepatic ATZ accumulation and hepatic fibrosis in a mouse model in vivo without affecting blood glucose or insulin levels. These results provide support for a drug discovery strategy using simple organisms as human disease models combined with genetic and computational screening methods. They also show that GLB and/or at least one of its analogs can be immediately tested to arrest the progression of human ATD liver disease.

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Active trafficking of alpha 1 antitrypsin across the lung endothelium.

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Polymerization of misfolded Z alpha-1 antitrypsin protein lowers CX3CR1 expression in human PBMCs.

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The endosomal protein-sorting receptor sortilin has a role in trafficking α-1 antitrypsin.

Project description:Up to 1 in 3000 individuals in the United States have α-1 antitrypsin deficiency, and the most common cause of this disease is homozygosity for the antitrypsin-Z variant (ATZ). ATZ is inefficiently secreted, resulting in protein deficiency in the lungs and toxic polymer accumulation in the liver. However, only a subset of patients suffer from liver disease, suggesting that genetic factors predispose individuals to liver disease. To identify candidate factors, we developed a yeast ATZ expression system that recapitulates key features of the disease-causing protein. We then adapted this system to screen the yeast deletion mutant collection to identify conserved genes that affect ATZ secretion and thus may modify the risk for developing liver disease. The results of the screen and associated assays indicate that ATZ is degraded in the vacuole after being routed from the Golgi. In fact, one of the strongest hits from our screen was Vps10, which can serve as a receptor for the delivery of aberrant proteins to the vacuole. Because genome-wide association studies implicate the human Vps10 homolog, sortilin, in cardiovascular disease, and because hepatic cell lines that stably express wild-type or mutant sortilin were recently established, we examined whether ATZ levels and secretion are affected by sortilin. As hypothesized, sortilin function impacts the levels of secreted ATZ in mammalian cells. This study represents the first genome-wide screen for factors that modulate ATZ secretion and has led to the identification of a gene that may modify disease severity or presentation in individuals with ATZ-associated liver disease.

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Modulation of calreticulin expression reveals a novel exosome-mediated mechanism of Z variant α<sub>1</sub>-antitrypsin disposal.

Project description:α1-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 position 342 in the mature protein, resulting in the Z mutation of the AAT gene (ZAAT). This substitution is associated with misfolding and accumulation of ZAAT in the endoplasmic reticulum (ER) of hepatocytes, causing a toxic gain of function. ERdj3 is an ER luminal DnaJ homologue, which, along with calreticulin, directly interacts with misfolded ZAAT. We hypothesize that depletion of each of these chaperones will change the fate of ZAAT polymers. Our study demonstrates that calreticulin modulation reveals a novel ZAAT degradation mechanism mediated by exosomes. Using human PiZZ hepatocytes and K42, a mouse calreticulin-deficient fibroblast cell line, our results show ERdj3 and calreticulin directly interact with ZAAT in PiZZ hepatocytes. Silencing calreticulin induces calcium independent ZAAT-ERdj3 secretion through the exosome pathway. This co-secretion decreases ZAAT aggregates within the ER of hepatocytes. We demonstrate that calreticulin has an inhibitory effect on exosome-mediated ZAAT-ERdj3 secretion. This is a novel ZAAT degradation process that involves a DnaJ homologue chaperone bound to ZAAT. In this context, calreticulin modulation may eliminate the toxic gain of function associated with aggregation of ZAAT in lung and liver, thus providing a potential new therapeutic approach to the treatment of AATD-related liver disease.

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Alpha 1-antitrypsin reduces inflammation and enhances mouse pancreatic islet transplant survival.

Project description:The promise of islet cell transplantation cannot be fully realized in the absence of improvements in engraftment of resilient islets. The marginal mass of islets surviving the serial peritransplant insults may lead to exhaustion and thereby contribute to an unacceptably high rate of intermediate and long-term graft loss. Hence, we have studied the effects of treatment with alpha 1-antitrypsin (AAT) in a syngeneic nonautoimmune islet graft model. A marginal number of syngeneic mouse islets were transplanted into nonautoimmune diabetic hosts and islet function was analyzed in control and AAT treated hosts. In untreated controls, marginal mass islet transplants did not restore euglycemia. Outcomes were dramatically improved by short-term AAT treatment. Transcriptional profiling identified 1,184 differentially expressed transcripts in AAT-treated hosts at 3 d posttransplantation. Systems-biology-based analysis revealed AAT down-regulated regulatory hubs formed by inflammation-related molecules (e.g., TNF-?, NF-?B). The conclusions yielded by the systems-biology analysis were rigorously confirmed by QRT-PCR and immunohistology. These data suggest that short-term AAT treatment of human islet transplant recipients may be worthy of a clinical trial.

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Hypoxia Enhances Oxidative Stress in Neutrophils from ZZ Alpha-1 Antitrypsin Deficiency Patients.

Project description:Alpha-1 antitrypsin deficiency (AATD) is a neutrophilic inflammatory disorder that may result in local hypoxia, reactive oxygen and nitrogen species (ROS/RNS) production, and increased damage in adjacent tissues. This study aims to determine the impact of hypoxia on neutrophil oxidative stress profile in AATD patients. Neutrophils were isolated from AATD patients and control volunteers and exposed to hypoxia (1% O2 for 4 h), ROS/RNS, mitochondrial parameters, and non-enzymatic antioxidant defenses measured by flow cytometry. The expression of enzymatic antioxidant defenses was determined by qRT-PCR. Our results indicate that ZZ-AATD neutrophils produce higher amounts of hydrogen peroxide, peroxynitrite, and nitric oxide and decreased levels of the antioxidant enzymes catalase, superoxide dismutase, and glutathione reductase. Likewise, our results show a decrease in mitochondrial membrane potential, indicating that this organelle could be involved in the production of the reactive species observed. No decrease in glutathione and thiol levels were observed. The accumulation of substances with high oxidative capacity would explain the greater oxidative damage observed in proteins and lipids. In conclusion, our results indicate that, compared to MM control individuals, ZZ-AATD neutrophils show increased ROS/RNS production under hypoxic conditions opening a new rationale for using antioxidant therapies to treat the disease.

| S-EPMC10135227 | biostudies-literature

α-1 Antitrypsin Enhances Islet Engraftment by Suppression of Instant Blood-Mediated Inflammatory Reaction.

Project description:Islet cell transplantation has limited effectiveness because of an instant blood-mediated inflammatory reaction (IBMIR) that occurs immediately after cell infusion and leads to dramatic β-cell death. In intraportal islet transplantation models using mouse and human islets, we demonstrated that α-1 antitrypsin (AAT; Prolastin-C), a serine protease inhibitor used for the treatment of AAT deficiency, inhibits IBMIR and cytokine-induced inflammation in islets. In mice, more diabetic recipients reached normoglycemia after intraportal islet transplantation when they were treated with AAT compared with mice treated with saline. AAT suppressed blood-mediated coagulation pathways by diminishing tissue factor production, reducing plasma thrombin-antithrombin complex levels and fibrinogen deposition on islet grafts, which correlated with less graft damage and apoptosis. AAT-treated mice showed reduced serum tumor necrosis factor-α levels, decreased lymphocytic infiltration, and decreased nuclear factor (NF)-κB activation compared with controls. The potent anti-inflammatory effect of AAT is possibly mediated by suppression of c-Jun N-terminal kinase (JNK) phosphorylation. Blocking JNK activation failed to further reduce cytokine-induced apoptosis in β-cells. Taken together, AAT significantly improves islet graft survival after intraportal islet transplantation by mitigation of coagulation in IBMIR and suppression of cytokine-induced JNK and NF-κB activation. AAT-based therapy has the potential to improve graft survival in human islet transplantation and other cellular therapies on the horizon.

| S-EPMC5360304 | biostudies-literature

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