An autophagy-enhancing drug promotes degradation of mutant alpha1-antitrypsin Z and reduces hepatic fibrosis

Recent Developments in mRNA-Based Protein Supplementation Therapy to Target Lung Diseases

Protein supplementation therapy using in vitro-transcribed (IVT) mRNA for genetic diseases contains huge potential as a new class of therapy. From the early ages of synthetic mRNA discovery, a great number of studies showed the versatile use of IVT mRNA as a novel approach to supplement faulty or absent protein and also as a vaccine. Many modifications have been made to produce high expressions of mRNA causing less immunogenicity and more stability. Recent advancements in the in vivo lung delivery of mRNA complexed with various carriers encouraged the whole mRNA community to tackle various genetic lung diseases. This review gives a comprehensive overview of cells associated with various lung diseases and recent advancements in mRNA-based protein replacement therapy. This review also covers a brief summary of developments in mRNA modifications and nanocarriers toward clinical translation.

The Activation and Function of Autophagy in Alcoholic Liver Disease

Autophagy is an important lysosome-mediated intracellular degradation pathway required for tissue homeostasis. Dysregulation of liver autophagy is closely associated with different liver diseases including alcoholic liver disease. Studies now indicate that autophagy may be induced or suppressed depending on the amount and the duration of ethanol treatment. Autophagy induced by ethanol serves as a protective mechanism, probably by selective degradation of the damaged mitochondria (mitophagy) and excess lipid droplets (lipophagy) and in turn attenuates alcohol-induced steatosis and liver injury. However, the detailed molecular mechanism of selective targeting of mitochondria and lipid is still unclear. Autophagy may possess other functions that protect hepatocytes from ethanol. Understanding these molecular entities would be essential in order to therapeutically module autophagy for treatment of alcoholic liver disease.

Role and mechanisms of autophagy in alcohol-induced liver injury

Alcoholic liver disease (ALD) is one of the major causes of chronic liver disease worldwide. Currently, no successful treatments are available for ALD. The pathogenesis of ALD is characterized as simple steatosis, fibrosis, cirrhosis, alcoholic hepatitis (AH), and eventually hepatocellular carcinoma (HCC). Autophagy is a highly conserved intracellular catabolic process, which aims at recycling cellular components and removing damaged organelles in response to starvation and stresses. Therefore, autophagy is considered as an important cellular adaptive and survival mechanism under various pathophysiological conditions. Recent studies from our lab and others suggest that chronic alcohol consumption may impair autophagy and contribute to the pathogenesis of ALD. In this chapter, we summarize recent progress on the role and mechanisms of autophagy in the development of ALD. Understanding the roles of autophagy in ALD may offer novel therapeutic avenues against ALD by targeting these pathways.

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

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.

Diverse Functions of Autophagy in Liver Physiology and Liver Diseases

Autophagy is a catabolic process by which eukaryotic cells eliminate cytosolic materials through vacuole-mediated sequestration and subsequent delivery to lysosomes for degradation, thus maintaining cellular homeostasis and the integrity of organelles. Autophagy has emerged as playing a critical role in the regulation of liver physiology and the balancing of liver metabolism. Conversely, numerous recent studies have indicated that autophagy may disease-dependently participate in the pathogenesis of liver diseases, such as liver hepatitis, steatosis, fibrosis, cirrhosis, and hepatocellular carcinoma. This review summarizes the current knowledge on the functions of autophagy in hepatic metabolism and the contribution of autophagy to the pathophysiology of liver-related diseases. Moreover, the impacts of autophagy modulation on the amelioration of the development and progression of liver diseases are also discussed.

Relevance of Autophagy in Parenchymal and Non-Parenchymal Liver Cells for Health and Disease

Autophagy is a highly conserved intracellular process for the ordered degradation and recycling of cellular components in lysosomes. In the liver, parenchymal cells (i.e., mainly hepatocytes) utilize autophagy to provide amino acids, glucose, and free fatty acids as sources of energy and biosynthesis functions, but also for recycling and controlling organelles such as mitochondria. Non-parenchymal cells of the liver, including endothelial cells, macrophages (Kupffer cells), and hepatic stellate cells (HSC), also employ autophagy, either for maintaining cellular homeostasis (macrophages, endothelium) or for providing energy for their activation (stellate cells). In hepatocytes, autophagy contributes to essential homeostatic functions (e.g., gluconeogenesis, glycogenolysis, fatty acid oxidation), but is also implicated in diseases. For instance, storage disorders (alpha 1 antitrypsin deficiency, Wilson's disease), metabolic (non-alcoholic steatohepatitis, NASH), and toxic (alcohol) liver diseases may benefit from augmenting autophagy in hepatocytes. In hepatic fibrosis, autophagy has been implicated in the fibrogenic activation of HSC to collagen-producing myofibroblasts. In hepatocellular carcinoma (HCC), autophagy may contribute to tumor surveillance as well as invasiveness, indicating a dual and stage-dependent function in cancer. As many drugs directly or indirectly modulate autophagy, it is intriguing to investigate autophagy-targeting, possibly even cell type-directed strategies for the treatment of hereditary liver diseases, NASH, fibrosis, and HCC.

A selective ER-phagy exerts procollagen quality control via a Calnexin-FAM134B complex

Autophagy is a cytosolic quality control process that recognizes substrates through receptor‐mediated mechanisms. Procollagens, the most abundant gene products in Metazoa, are synthesized in the endoplasmic reticulum (ER), and a fraction that fails to attain the native structure is cleared by autophagy. However, how autophagy selectively recognizes misfolded procollagens in the ER lumen is still unknown. We performed siRNA interference, CRISPR‐Cas9 or knockout‐mediated gene deletion of candidate autophagy and ER proteins in collagen producing cells. We found that the ER‐resident lectin chaperone Calnexin (CANX) and the ER‐phagy receptor FAM134B are required for autophagy‐mediated quality control of endogenous procollagens. Mechanistically, CANX acts as co‐receptor that recognizes ER luminal misfolded procollagens and interacts with the ER‐phagy receptor FAM134B. In turn, FAM134B binds the autophagosome membrane‐associated protein LC3 and delivers a portion of ER containing both CANX and procollagen to the lysosome for degradation. Thus, a crosstalk between the ER quality control machinery and the autophagy pathway selectively disposes of proteasome‐resistant misfolded clients from the ER.

Clinical and histologic features of adults with alpha-1 antitrypsin deficiency in a non-cirrhotic cohort

BACKGROUND & AIMS

Alpha-1 antitrypsin deficiency (AATD) is an uncommonly recognized cause of liver disease in adults, with descriptions of its natural history limited to case series and patient-reported data from disease registries. Liver pathology is limited to selected patients or unavailable. Therefore, we aimed to determine the prevalence and severity of liver fibrosis in an adult AATD population who were not known to have cirrhosis, while defining risk factors for fibrosis and testing non-invasive markers of disease.

METHODS

A total of 94 adults with classic genotype 'PI*ZZ' AATD were recruited from North America and prospectively enrolled in the study. Liver aminotransferases and markers of synthetic function, transient elastography, and liver biopsy were performed.

RESULTS

The prevalence of clinically significant liver fibrosis (F ≥ 2) was 35.1%. Alanine aminotransferase, aspartate aminotransferase and gamma-glutamyltransferase values were higher in the F ≥ 2 group. Metabolic syndrome was associated with the presence of clinically significant fibrosis (OR 14.2; 95% CI 3.7-55; p <0.001). Additionally, the presence of accumulated abnormal AAT in hepatocytes, portal inflammation, and hepatocellular degeneration were associated with clinically significant fibrosis. The accuracy of transient elastography to detect F ≥ 2 fibrosis was fair, with an AUC of 0.70 (95% CI 0.58-0.82).

CONCLUSIONS

Over one-third of asymptomatic and lung affected adults with 'PI*ZZ' AATD have significant underlying liver fibrosis. Liver biopsies demonstrated variable amounts of accumulated Z AAT. The risk of liver fibrosis increases in the presence of metabolic syndrome, accumulation of AAT in hepatocytes, and portal inflammation on baseline biopsy. The results support the hypothesis that liver disease in this genetic condition may be related to a "toxic gain of function" from accumulation of AAT in hepatocytes.

LAY SUMMARY

Individuals diagnosed with classic alpha-1 antitrypsin deficiency (ZZ) are at risk of liver injury and scarring, because of the accumulation of abnormal alpha-1 antitrypsin in the liver. A liver biopsy in ZZ individuals can demonstrate the accumulation of alpha-1 antitrypsin within the liver and identify if any associated liver scarring is present. Indviduals with large amounts of alpha-1 antitrypsin on biopsy may be at risk of liver injury and fibrosis. Additional common medical conditions of diabetes, obesity, high cholesterol, and hypertension (known as metabolic syndrome) are associated with a greater degree of liver injury. CLINICAL TRIAL NUMBER: clinicaltrials.gov NCT01810458.

Autophagy is a gatekeeper of hepatic differentiation and carcinogenesis by controlling the degradation of Yap

Activation of the Hippo pathway effector Yap underlies many liver cancers, however no germline or somatic mutations have been identified. Autophagy maintains essential metabolic functions of the liver, and autophagy-deficient murine models develop benign adenomas and hepatomegaly, which have been attributed to activation of the p62/Sqstm1-Nrf2 axis. Here, we show that Yap is an autophagy substrate and mediator of tissue remodeling and hepatocarcinogenesis independent of the p62/Sqstm1-Nrf2 axis. Hepatocyte-specific deletion of Atg7 promotes liver size, fibrosis, progenitor cell expansion, and hepatocarcinogenesis, which is rescued by concurrent deletion of Yap. Our results shed new light on mechanisms of Yap degradation and the sequence of events that follow disruption of autophagy, which is impaired in chronic liver disease.

Increased levels of the Yap oncoprotein stimulate liver growth and promote hepatocarcinogenesis. Here the authors show that hepatocyte-specific loss of Atg7 in mice leads to decreased autophagic degradation of Yap and liver overgrowth, and further establish this association in human liver cancer tissues.

Autophagy as an emerging target in cardiorenal metabolic disease: From pathophysiology to management

Although advances in medical technology and health care have improved the early diagnosis and management for cardiorenal metabolic disorders, the prevalence of obesity, insulin resistance, diabetes, hypertension, dyslipidemia, and kidney disease remains high. Findings from numerous population-based studies, clinical trials, and experimental evidence have consolidated a number of theories for the pathogenesis of cardiorenal metabolic anomalies including resistance to the metabolic action of insulin, abnormal glucose and lipid metabolism, oxidative and nitrosative stress, endoplasmic reticulum (ER) stress, apoptosis, mitochondrial damage, and inflammation. Accumulating evidence has recently suggested a pivotal role for proteotoxicity, the unfavorable effects of poor protein quality control, in the pathophysiology of metabolic dysregulation and related cardiovascular complications. The ubiquitin-proteasome system (UPS) and autophagy-lysosomal pathways, two major although distinct cellular clearance machineries, govern protein quality control by degradation and clearance of long-lived or damaged proteins and organelles. Ample evidence has depicted an important role for protein quality control, particularly autophagy, in the maintenance of metabolic homeostasis. To this end, autophagy offers promising targets for novel strategies to prevent and treat cardiorenal metabolic diseases. Targeting autophagy using pharmacological or natural agents exhibits exciting new strategies for the growing problem of cardiorenal metabolic disorders.

Alpha-1-Antitrypsin Deficiency Liver Disease

In homozygous ZZ alpha-1-antitrypsin (AAT) deficiency, the liver synthesizes large quantities of AAT mutant Z, which folds improperly during biogenesis and is retained within the hepatocytes and directed into intracellular proteolysis pathways. These intracellular polymers trigger an injury cascade, which can lead to liver injury. This is highly variable and not all patients develop liver disease. Although not fully described, there is likely a strong influence of genetic and environmental modifiers of the injury cascade and of the fibrotic response. With improved understanding of liver injury mechanisms, new strategies for treatment are now being explored.

Histone methyl-transferases and demethylases in the autophagy regulatory network: the emerging role of KDM1A/LSD1 demethylase

Macroautophagy/autophagy is a physiological mechanism that is essential for the maintenance of cellular homeostasis and stress adaptation. Defective autophagy is associated with many human diseases, including cancer and neurodegenerative disorders. The emerging implication of epigenetic events in the control of the autophagic process opens new avenues of investigation and offers the opportunity to develop novel therapeutic strategies in diseases associated with dysfunctional autophagy-lysosomal pathways. Accumulating evidence reveals that several methyltransferases and demethylases are essential regulators of autophagy, and recent studies have led to the identification of the lysine demethylase KDM1A/LSD1 as a promising drug target. KDM1A/LSD1 modulates autophagy at multiple levels, participating in the transcriptional control of several downstream effectors. This review summarizes our current understanding of the role of KDM1A/LSD1 in the autophagy regulatory network.

Liver fibrosis

Liver fibrosis is a wound-healing response generated against an insult to the liver that causes liver injury. It has the potential to progress into cirrhosis, and if not prevented, it may lead to liver cancer and liver failure. The activation of hepatic stellate cells (HSCs) is the central event underlying liver fibrosis. In addition to HSCs, numerous studies have supported the potential contribution of bone marrow-derived cells and myofibroblasts to liver fibrosis. The liver is a heterogeneous organ; thus, molecular and cellular events that underlie liver fibrogenesis are complex. This review aims to focus on major events that occur during liver fibrogenesis. In addition, important antifibrotic therapeutic approaches and experimental liver fibrosis models will be discussed.

Patient-Derived Induced Pluripotent Stem Cells for Alpha-1 Antitrypsin Deficiency Disease Modeling and Therapeutic Discovery

PIZZ alpha-1 antitrypsin deficiency (AATD) is an autosomal recessive disease affecting approximately 100,000 individuals in the United States and one of the most common hereditary causes of liver disease.¹ The most common form of the disease results from a single base pair mutation (Glu342Lys), known as the "Z" mutation, that encodes a mutant protein (Z alpha-1 antritypsin [AAT]) that is prone to misfolding and is retained in the endoplasmic reticulum (ER) rather than appropriately secreted. Some of the retained mutant protein attains an unusual aggregated or polymerized conformation. Retained polymeric ZAAT aggregates are hepatotoxic and lead to downstream liver disease in a subset of PiZZ neonates and adults through a gain-of-function mechanism. PiZZ individuals are likewise highly predisposed to developing chronic obstructive pulmonary disease (COPD)/emphysema as a result of low circulating levels of AAT protein and associated protease-antiprotease imbalance. Much of our understanding of the molecular pathogenesis of AATD is based on studies employing either transgenic mice that express the mutant human Z allele or immortalized cell lines transduced to overexpress ZAAT. While they have been quite informative, these models fail to capture the patient-to-patient variability in disease phenotype that clinicians observe in their AATD patients, raising the question of whether alternative models might provide new insight. Induced pluripotent stem cells (iPSCs), first described in 2006, have the capacity to differentiate into a broad array of cell types from all 3 germ layers, including hepatocytes. Disease-specific iPSCs have been derived from patients with a variety of monogenic disorders and have been found to faithfully recapitulate features of such diseases as spinal muscular atrophy, familial dysautonomia, Rett syndrome, polycythemia vera, type 1A glycogen storage disease, familial hypercholesterolemia, long QT syndrome, and others. This discussion reviews the potential applications of iPSCs for understanding AATD-associated liver disease as well as for development of potential therapeutic strategies.

Coordinate regulation of mutant NPC1 degradation by selective ER autophagy and MARCH6-dependent ERAD

Niemann–Pick type C disease is a fatal, progressive neurodegenerative disorder caused by loss-of-function mutations in NPC1, a multipass transmembrane glycoprotein essential for intracellular lipid trafficking. We sought to define the cellular machinery controlling degradation of the most common disease-causing mutant, I1061T NPC1. We show that this mutant is degraded, in part, by the proteasome following MARCH6-dependent ERAD. Unexpectedly, we demonstrate that I1061T NPC1 is also degraded by a recently described autophagic pathway called selective ER autophagy (ER-phagy). We establish the importance of ER-phagy both in vitro and in vivo, and identify I1061T as a misfolded endogenous substrate for this FAM134B-dependent process. Subcellular fractionation of I1061T Npc1 mouse tissues and analysis of human samples show alterations of key components of ER-phagy, including FAM134B. Our data establish that I1061T NPC1 is recognized in the ER and degraded by two different pathways that function in a complementary fashion to regulate protein turnover.

Niemann-Pick type C1 disease is most commonly caused by the allele NPC1 I1061T, which is misfolded in the ER and rapidly degraded by the ubiquitin proteasome system. Here the authors show that the I1061T mutant is also degraded by ER-phagy.

ER-to-lysosome-associated degradation of proteasome-resistant ATZ polymers occurs via receptor-mediated vesicular transport

Maintenance of cellular proteostasis relies on efficient clearance of defective gene products. For misfolded secretory proteins, this involves dislocation from the endoplasmic reticulum (ER) into the cytosol followed by proteasomal degradation. However, polypeptide aggregation prevents cytosolic dislocation and instead activates ill-defined lysosomal catabolic pathways. Here, we describe an ER-to-lysosome-associated degradation pathway (ERLAD) for proteasome-resistant polymers of alpha1-antitrypsin Z (ATZ). ERLAD involves the ER-chaperone calnexin (CNX) and the engagement of the LC3 lipidation machinery by the ER-resident ER-phagy receptor FAM134B, echoing the initiation of starvation-induced, receptor-mediated ER-phagy. However, in striking contrast to ER-phagy, ATZ polymer delivery from the ER lumen to LAMP1/RAB7-positive endolysosomes for clearance does not require ER capture within autophagosomes. Rather, it relies on vesicular transport where single-membrane, ER-derived, ATZ-containing vesicles release their luminal content within endolysosomes upon membrane:membrane fusion events mediated by the ER-resident SNARE STX17 and the endolysosomal SNARE VAMP8. These results may help explain the lack of benefits of pharmacologic macroautophagy enhancement that has been reported for some luminal aggregopathies.

ER-phagy at a glance

Selective autophagy represents the major quality control mechanism that ensures proper turnover of exhausted or harmful organelles, among them the endoplasmic reticulum (ER), which is fragmented and delivered to the lysosome for degradation via a specific type of autophagy called ER-phagy. The recent discovery of ER-resident proteins that bind to mammalian Atg8 proteins has revealed that the selective elimination of ER involves different receptors that are specific for different ER subdomains or ER stresses. FAM134B (also known as RETREG1) and RTN3 are reticulon-type proteins that are able to remodel the ER network and ensure the basal membrane turnover. SEC62 and CCPG1 are transmembrane ER receptors that function in response to ER stress signals. This task sharing reflects the complexity of the ER in terms of biological functions and morphology. In this Cell Science at a Glance article and the accompanying poster, we summarize the most recent findings about ER-phagy in yeast and in mammalian cells.

New Therapeutic Targets for Alpha-1 Antitrypsin Deficiency

Alpha-1antitrypsin deficiency (AATD) results from the intracellular polymerization and retention of mutant alpha-1antitrypsin (AAT) within the endoplasmic reticulum of hepatocytes. This causes cirrhosis whilst the deficiency of circulating AAT predisposes to early onset emphysema. This is an exciting time for researchers in the field with the development of novel therapies based on understanding the pathobiology of disease. I review here augmentation therapy to prevent the progression of lung disease and a range of approaches to treat the liver disease associated with the accumulation of mutant AAT: modifying proteostasis networks that are activated by Z AAT polymers, stimulating autophagy, small interfering RNA and small molecules to block intracellular polymerization, and stem cell technology to correct the genetic defect that underlies AATD.

Liver - master and servant of serum proteome

Hepatocytes synthesise the majority of serum proteins. This production occurs in the endoplasmic reticulum (ER) and is adjusted by complex local and systemic regulatory mechanisms. Accordingly, serum levels of hepatocyte-made proteins constitute important biomarkers that reflect both systemic processes and the status of the liver. For example, C-reactive protein is an established marker of inflammatory reaction, whereas transferrin emerges as a liver stress marker and an attractive mortality predictor. The high protein flow through the ER poses a continuous challenge that is handled by a complex proteostatic network consisting of ER folding machinery, ER stress response, ER-associated degradation and autophagy. Various disorders disrupt this delicate balance and result in protein accumulation in the ER. These include chronic hepatitis B infection with overproduction of hepatitis B surface antigen or inherited alpha1-antitrypsin deficiency that give rise to ground glass hepatocytes and alpha1-antitrypsin aggregates, respectively. We review these ER storage disorders and their downstream consequences. The interaction between proteotoxic stress and other ER challenges such as lipotoxicity is also discussed. Collectively, this article aims to sharpen our view of liver hepatocytes as the central hubs of protein metabolism.

NorUDCA promotes degradation of α1-antitrypsin mutant Z protein by inducing autophagy through AMPK/ULK1 pathway

Alpha-1 Antitrypsin (α1AT) Deficiency is a genetic disease in which accumulation of α1AT mutant Z (α1ATZ) protein in the ER of hepatocytes causes chronic liver injury, liver fibrosis, and hepatocellular carcinoma. No effective medical therapy is currently available for the disease. We previously found that norUDCA improves the α1AT deficiency associated liver disease by promoting autophagic degradation of α1ATZ protein in liver in a mouse model of the disease. The current study unravels the novel underlying cellular mechanism by which norUDCA modulates autophagy. HTOZ cells, modified from HeLa Tet-Off cells by transfection with the resulting pTRE1-ATZ plasmid and expressing mutant Z proteins, were studied in these experiments. The role of norUDCA in inducing autophagy, autophagy-mediated degradation of α1ATZ and the role of AMPK in norUDCA-induced autophagy were examined in the current report. NorUDCA promoted disposal of α1ATZ via autophagy-mediated degradation of α1ATZ in HTOZ cells. Activation of AMPK was required for norUDCA-induced autophagy and α1ATZ degradation. Moreover, mTOR/ULK1 was involved in norUDCA-induced AMPK activation and autophagy in HTOZ cells. Our results provide novel mechanistic insights into the therapeutic action of norUDCA in promoting the clearance of α1ATZ in vitro and suggest a novel therapeutic approach for the treatment of α1ATZ deficiency disease and its associated liver diseases.

Alpha-1 antitrypsin deficiency: outstanding questions and future directions

Background

Alpha-1 antitrypsin deficiency (AATD) is a rare hereditary condition that leads to decreased circulating alpha-1 antitrypsin (AAT) levels, significantly increasing the risk of serious lung and/or liver disease in children and adults, in which some aspects remain unresolved.

Methods

In this review, we summarise and update current knowledge on alpha-1 antitrypsin deficiency in order to identify and discuss areas of controversy and formulate questions that need further research.

Results

1) AATD is a highly underdiagnosed condition. Over 120,000 European individuals are estimated to have severe AATD and more than 90% of them are underdiagnosed.

Conclusions

2) Several clinical and etiological aspects of the disease are yet to be resolved. New strategies for early detection and biomarkers for patient outcome prediction are needed to reduce morbidity and mortality in these patients; 3) Augmentation therapy is the only specific approved therapy that has shown clinical efficacy in delaying the progression of emphysema. Regrettably, some countries reject registration and reimbursement for this treatment because of the lack of larger randomised, placebo-controlled trials. 4) Alternative strategies are currently being investigated, including the use of gene therapy or induced pluripotent stem cells, and non-augmentation strategies to prevent AAT polymerisation inside hepatocytes.

NFκB mitigates the pathological effects of misfolded α1-antitrypsin by activating autophagy and an integrated program of proteostasis mechanisms

Intrahepatocytic accumulation of misfolded α1-antitrypsin Z variant (ATZ) is responsible for liver disease in some individuals with α1-antitrypsin deficiency (ATD), characterized by fibrosis/cirrhosis and predisposition to carcinogenesis. Previous results showing that accumulation of ATZ in model systems activates the NFκB signaling pathway have led us to hypothesize that downstream targets of NFκB are elements of a proteostasis response network for this type of proteinopathy. Here we show that only a subset of downstream targets within the NFκB transcriptomic repertoire are activated in model systems of this proteinopathy. Breeding of the PiZ mouse model of ATD to two different mouse models with NFκB deficiency led to greater intrahepatocytic accumulation of ATZ, more severe hepatic fibrosis, decreased autophagy and hyperproliferation of hepatocytes with massive ATZ inclusions. Specific downstream targets of NFκB could be implicated in each pathological effect. These results suggest a new role for NFκB signaling in which specific downstream targets of this pathway mediate an integrated program of proteostatic responses designed to mitigate the pathologic effects of proteinopathy, including autophagic disposal of misfolded protein, degradation of collagen and prevention of hyperproliferation.

Chemical probes and drug leads from advances in synthetic planning and methodology

Screening of small-molecule libraries is a productive method for identifying both chemical probes of disease-related targets and potential starting points for drug discovery. In this article, we focus on strategies such as diversity-oriented synthesis that aim to explore novel areas of chemical space efficiently by populating small-molecule libraries with compounds containing structural features that are typically under-represented in commercially available screening collections. Drawing from more than a decade's worth of examples, we highlight how the design and synthesis of such libraries have been enabled by modern synthetic chemistry, and we illustrate the impact of the resultant chemical probes and drug leads in a wide range of diseases.

Substrate Insolubility Dictates Hsp104-Dependent Endoplasmic-Reticulum-Associated Degradation

Misfolded proteins in the endoplasmic reticulum (ER) are destroyed by ER-associated degradation (ERAD). Although the retrotranslocation of misfolded proteins from the ER has been reconstituted, how a polypeptide is initially selected for ERAD remains poorly defined. To address this question while controlling for the diverse nature of ERAD substrates, we constructed a series of truncations in a single ER-tethered domain. We observed that the truncated proteins exhibited variable degradation rates and discovered a positive correlation between ERAD substrate instability and detergent insolubility, which demonstrates that aggregation-prone species can be selected for ERAD. Further, Hsp104 facilitated degradation of an insoluble species, consistent with the chaperone's disaggregase activity. We also show that retrotranslocation of the ubiquitinated substrate from the ER was inhibited in the absence of Hsp104. Therefore, chaperone-mediated selection frees the ER membrane of potentially toxic, aggregation-prone species.

Knockdown of Z Mutant Alpha-1 Antitrypsin In Vivo Using Modified DNA Antisense Oligonucleotides

Alpha-1 antitrypsin (AAT) is a serum protease inhibitor, mainly expressed in and secreted from hepatocytes, important for regulating neutrophil elastase activity among other proteases. Various mutations in AAT cause alpha-1 antitrypsin deficiency (AATD), a rare hereditary disorder that results in liver disease due to accumulation of AAT aggregates and lung disease from excessive neutrophil elastase activity. PiZ transgenic mice contain the human AAT genomic region harboring the most common AATD mutation, the Glu342Lys (Z) point mutation. These mice effectively recapitulate the liver disease exhibited in AATD patients, including AAT protein aggregates, hepatocyte death, and eventual liver fibrosis. Previously, we demonstrated that modified antisense oligonucleotides (ASOs) can dramatically reduce Z-AAT RNA and protein levels in PiZ mice enabling inhibition, prevention, and reversal of the associated liver disease. Here, we describe in detail usage of AAT-ASOs to knock down Z-AAT in PiZ mice with a focus on preparation and in vivo delivery of ASOs, as well as detailed workflows pertaining to the analysis of Z-AAT mRNA, plasma protein, and soluble/insoluble liver protein levels following ASO administration.

Repurposing carbamazepine for the treatment of amyotrophic lateral sclerosis in SOD1-G93A mouse model

AIMS

To investigate the effect and mechanisms of carbamazepine (CBZ) on the onset and progression of amyotrophic lateral sclerosis (ALS) in SOD1-G93A mouse model.

METHODS

Starting from 64 days of age, SOD1-G93A mice were orally administered with CBZ at 200 mg/kg once daily until death. The disease onset and life span of SOD1-G93A mice were recorded. Motor neurons (MNs) in anterior horn of spinal cord were quantified by Nissl staining and SMI-32 immunostaining. Hematoxylin and eosin (H&E), nicotinamide adenine dinucleotide hydrogen (NADH), modified Gomori trichrome (MGT), and α-bungarotoxin-ATTO-488 staining were also performed to evaluate muscle and neuromuscular junction (NMJ) damage. Expressions of aggregated SOD1 protein and autophagy-related proteins were further detected by Western blot and immunofluorescent staining.

RESULTS

Carbamazepine treatment could delay the disease onset and extend life span of SOD1-G93A mice by about 14.5% and 13.9%, respectively. Furthermore, CBZ treatment reduced MNs loss by about 46.6% and ameliorated the altered muscle morphology and NMJ. Much more interestingly, mechanism study revealed that CBZ treatment activated autophagy via AMPK-ULK1 pathway and promoted the clearance of mutant SOD1 aggregation.

CONCLUSION

Our findings uncovered the therapeutic effects of CBZ against disease pathogenesis in SOD1-G93A mice, indicating a promising clinical utilization of CBZ in ALS therapy.

Endoplasmic reticulum turnover: ER-phagy and other flavors in selective and non-selective ER clearance

The endoplasmic reticulum (ER) is a highly dynamic organelle in eukaryotic cells. It is deputed to lipid and protein biosynthesis, calcium storage, and the detoxification of various exogenous and endogenous harmful compounds. ER activity and size must be adapted rapidly to environmental and developmental conditions or biosynthetic demand. This is achieved on induction of thoroughly studied transcriptional/translational programs defined as "unfolded protein responses" that increase the ER volume and the expression of ER-resident proteins regulating the numerous ER functions. Less understood are the lysosomal catabolic processes that maintain ER size at steady state, that prevent excessive ER expansion during ER stresses, or that ensure return to physiologic ER size during recovery from ER stresses. These catabolic processes may also be activated to remove ER subdomains where proteasome-resistant misfolded proteins or damaged lipids have been segregated. Insights into these catabolic mechanisms have only recently emerged with the identification of so-called ER-phagy receptors, which label specific ER subdomains for selective lysosomal delivery for clearance. Here, in eight chapters and one addendum, we comment on recent advances in ER turnover pathways induced by ER stress, nutrient deprivation, misfolded proteins, and live bacteria. We highlight the role of yeast (Atg39 and Atg40) and mammalian (FAM134B, SEC62, RTN3, and CCPG1) ER-phagy receptors and of autophagy genes in selective and non-selective catabolic processes that regulate cellular proteostasis by controlling ER size, turnover, and function.

Carbamazepine, a beta-cell protecting drug, reduces type 1 diabetes incidence in NOD mice

Pancreatic beta-cells are selectively destroyed by the host immune system in type 1 diabetes. Thus, drugs that preserve beta-cell mass and/or function have the potential to prevent or slow the progression of this disease. We recently reported that the use-dependent sodium channel blocker, carbamazepine, protects beta-cells from inflammatory cytokines in vitro. Here, we tested the effects of carbamazepine treatment in female non-obese diabetic (NOD) mice by supplementing LabDiet 5053 with 0.5% w/w carbamazepine to achieve serum carbamazepine levels of 14.98 ± 3.19 µM. Remarkably, diabetes incidence over 25 weeks, as determined by fasting blood glucose, was ~50% lower in carbamazepine treated animals. Partial protection from diabetes in carbamazepine-fed NOD mice was also associated with improved glucose tolerance at 6 weeks of age, prior to the onset of diabetes in our colony. Less insulitis was detected in carbamazepine treated NOD mice at 6 weeks of age, but we did not observe differences in CD4⁺ and CD8⁺ T cell composition in the pancreatic lymph node, as well as circulating markers of inflammation. Taken together, our results demonstrate that carbamazepine reduces the development of type 1 diabetes in NOD mice by maintaining functional beta-cell mass.

Antagonism of Interleukin-17A ameliorates experimental hepatic fibrosis by restoring the IL-10/STAT3-suppressed autophagy in hepatocytes

Interleukin-17A has been identified as a driver of hepatic stellate cell activation and plays a critical role in the pathogenesis of hepatic fibrosis. However, the underlining fibrosis-promoting mechanism of IL-17A is far from understood. Here we aimed to define whether hepatocytes directly respond to IL-17A stimulation and are associated with the development of hepatic fibrosis. The functional significance of IL-17A was evaluated in bile duct ligation (BDL) or thioacetamide (TAA) injection-induced mouse models of hepatic fibrosis. Human cirrhosis and control tissues were obtained from the patients with cirrhosis who received an open surgical repair process. Neutralizing IL-17A promoted the resolution of BDL or TAA-induced acute or chronic inflammation and fibrosis, resulted in a shift of the suppressive immune response in fibrotic liver toward a Th1-type immune response, and restored autophagy activity in both cholestatic and hepatotoxic liver injury induced fibrotic liver tissues, which was accompanied by a significant inhibition of STAT3 phosphorylation. Moreover, we found that IL-17A stimulated the concentration-and time-dependent phosphorylation of STAT3 in AML-12 liver cells. Blocking STAT3 with a specific inhibitor STATTIC or STAT3 siRNA protected from the IL-17A-induced autophagy suppression in AML-12 cells, indicating that STAT3 mediates IL-17A-suppressed autophagy. Administration of IL-10, which activated STAT3 and inhibited autophagy, reversed the therapeutic effect of IL-17A antagonism in vivo. Our study suggests that the IL-17A/STAT3 signaling pathway plays a crucial role in the pathogenesis of hepatic fibrosis through suppressing hepatocellular autophagy and that blocking this pathway may provide therapeutic benefits for the treatment of hepatic fibrosis.

Harnessing the mTOR Pathway for Tuberculosis Treatment

Tuberculosis (TB) remains as one of the leading killer infectious diseases of humans. At present, the standard therapeutic regimen to treat TB comprised of multiple antibiotics administered for a minimum of six months. Although these drugs are useful in controlling TB burden globally, they have not eliminated the disease. In addition, the lengthy duration of treatment with multiple drugs contributes to patient non-compliance that can result in the development of drug resistant strains (MDR and XDR) of Mycobacterium tuberculosis (Mtb), the causative agent of TB. Therefore, new and improved therapeutic strategies are urgently needed for effective control of TB worldwide. The intracellular survival of Mtb is regarded as a cumulative effect of the host immune response and the bacterial ability to resist or subvert this response. When the host innate defensive system is manipulated by Mtb for its survival and dissemination, the host develops disease conditions that are hard to overcome. The host intrinsic factors also contributes to the poor efficacy of anti-mycobacterial drugs and to the emergence of drug resistance. Hence, strengthening the immune repertoire involved in combating Mtb through host-directed therapeutics (HDT) can be one of the approaches for effective bacterial killing and clearance of infection/disease. Recently, more scientific research has been focused toward HDT strategies that empowers host cells for effective killing of Mtb, reduce the duration of treatment and/or alleviates the development of MDR/XDR, since Mtb cannot develop resistance against a drug that targets the host cell function. Autophagy is a conserved cellular process critical for maintaining cellular integrity and function. Autophagy is regulated by multiple pathways that are either dependent or independent of mTOR (mechanistic target of rapamycin; a.k.a. mammalian target of rapamycin), a master regulatory molecules that impacts several cellular functions. In this review, we summarize the role of autophagy in Mtb pathogenesis, the mTOR pathway and, modulating the mTOR pathway with inhibitors as potential adjunctive HDT, in combination with standard anti-TB antibiotics, to improve the outcome of current TB treatment.

New Concepts in Alpha-1 Antitrypsin Deficiency Disease Mechanisms

Alpha-1 antitrypsin deficiency is predominantly caused by point mutations that alter the protein's 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 cell's 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 cell's 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.

Endoplasmic reticulum stress in the pathogenesis of fibrotic disease

Eukaryotic cells contain an elegant protein quality control system that is crucial in maintaining cellular homeostasis; however, dysfunction of this system results in endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). Severe or prolonged ER stress is associated with the development of degenerative and fibrotic disorders in multiple organs, as evidenced by the identification of disease-causing mutations in epithelial-restricted genes that lead to protein misfolding or mistrafficking in familial fibrotic diseases. Emerging evidence implicates ER stress and UPR signaling in a variety of profibrotic mechanisms in individual cell types. In epithelial cells, ER stress can induce apoptosis, inflammatory signaling, and epithelial-mesenchymal transition. In other cell types, ER stress is linked to myofibroblast activation, macrophage polarization, and T cell differentiation. ER stress-targeted therapies have begun to emerge using approaches that range from global enhancement of chaperone function to selective targeting of activated ER stress sensors and other downstream mediators. As the complex regulatory mechanisms of this system are further clarified, there are opportunities to develop new disease-modifying therapeutic strategies in a wide range of chronic fibrotic diseases.

Resolution of organ fibrosis

Fibrosis is the excessive accumulation of extracellular matrix that often occurs as a wound healing response to repeated or chronic tissue injury, and may lead to the disruption of organ architecture and loss of function. Although fibrosis was previously thought to be irreversible, recent evidence indicates that certain circumstances permit the resolution of fibrosis when the underlying causes of injury are eradicated. The mechanism of fibrosis resolution encompasses degradation of the fibrotic extracellular matrix as well as elimination of fibrogenic myofibroblasts through their adaptation of various cell fates, including apoptosis, senescence, dedifferentiation, and reprogramming. In this Review, we discuss the present knowledge and gaps in our understanding of how matrix degradation is regulated and how myofibroblast cell fates can be manipulated, areas that may identify potential therapeutic approaches for fibrosis.

Design of Small Molecule Autophagy Modulators: A Promising Druggable Strategy

Autophagy is a lysosome-dependent mechanism of intracellular degradation for maintaining cellular homeostasis. Dysregulation of autophagy has been verified to be closely linked to a number of human diseases. Consequently, targeting autophagy has been highlighted as a novel therapeutic strategy for clinical utility. Mounting efforts have been done in recent years to elucidate the mechanisms of autophagy regulation and to identify potential modulators of autophagy. However, most of the compounds target complex and multifaceted pathway and proteins, which may limit the evaluation of therapeutic value and in depth studies as chemical tools. Therefore, the development of specific and active autophagy modulators becomes most desirable. Here, we briefly review the regulation of autophagy and then summarize the recent development of small molecules targeting the core autophagic machinery. Finally, we put forward our viewpoints on the current problems, with the aim to provide reference for future drug discovery and potential therapeutic perspectives on novel, potent, selective autophagy modulators.

Regulation of glycolytic metabolism by autophagy in liver cancer involves selective autophagic degradation of HK2 (hexokinase 2)

Impaired macroautophagy/autophagy and high levels of glycolysis are prevalent in liver cancer. However, it remains unknown whether there is a regulatory relationship between autophagy and glycolytic metabolism. In this study, by utilizing cancer cells with basal or impaired autophagic flux, we demonstrated that glycolytic activity is negatively correlated with autophagy level. The autophagic degradation of HK2 (hexokinase 2), a crucial glycolytic enzyme catalyzing the conversion of glucose to glucose-6-phosphate, was found to be involved in the regulation of glycolysis by autophagy. The Lys63-linked ubiquitination of HK2 catalyzed by the E3 ligase TRAF6 was critical for the subsequent recognition of HK2 by the autophagy receptor protein SQSTM1/p62 for the process of selective autophagic degradation. In a tissue microarray of human liver cancer, the combination of high HK2 expression and high SQSTM1 expression was shown to have biological and prognostic significance. Furthermore, 3-BrPA, a pyruvate analog targeting HK2, significantly decreased the growth of autophagy-impaired tumors in vitro and in vivo (p < 0.05). By demonstrating the regulation of glycolysis by autophagy through the TRAF6- and SQSTM1-mediated ubiquitination system, our study may open an avenue for developing a glycolysis-targeting therapeutic intervention for treatment of autophagy-impaired liver cancer.

Quantitative assessment of cell fate decision between autophagy and apoptosis

Autophagy and apoptosis are cellular processes that regulate cell survival and death, the former by eliminating dysfunctional components in the cell, the latter by programmed cell death. Stress signals can induce either process, and it is unclear how cells 'assess' cellular damage and make a 'life' or 'death' decision upon activating autophagy or apoptosis. A computational model of coupled apoptosis and autophagy is built here to analyze the underlying signaling and regulatory network dynamics. The model explains the experimentally observed differential deployment of autophagy and apoptosis in response to various stress signals. Autophagic response dominates at low-to-moderate stress; whereas the response shifts from autophagy (graded activation) to apoptosis (switch-like activation) with increasing stress intensity. The model reveals that cytoplasmic Ca²⁺ acts as a rheostat that fine-tunes autophagic and apoptotic responses. A G-protein signaling-mediated feedback loop maintains cytoplasmic Ca²⁺ level, which in turn governs autophagic response through an AMP-activated protein kinase (AMPK)-mediated feedforward loop. Ca²⁺/calmodulin-dependent kinase kinase β (CaMKKβ) emerges as a determinant of the competing roles of cytoplasmic Ca²⁺ in autophagy regulation. The study demonstrates that the proposed model can be advantageously used for interrogating cell regulation events and developing pharmacological strategies for modulating cell decisions.

Clinical and pathological characteristics of IgG4-related interstitial lung disease

IgG4-related interstitial lung disease (IgG4-RILD), which is characterized by increased IgG4 levels, IgG4⁺ plasma cell infiltration and irregular whorled fibrosis, is a recently described lung disorder that belongs to the group of systemic fibroinflammatory IgG4-related diseases (IgG4-RD). The aim of the present study was to improve the current knowledge regarding the specific clinical and histopathological characteristics of IgG4-RILD and to investigate its underlying immune mechanism in vivo. A total of 7 patients newly diagnosed with IgG4-RILD were enrolled in the present study (4 men and 3 women; mean age, 57 years; range, 29–71 years). Patients' clinical history was collected and serological indicators, including C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), antinuclear antibodies (ANAs) and tumor markers were measured. Serum immunoglobulin G (IgG), IgE and IgG4 levels were also evaluated. In addition, computed tomographic (CT) images and pathological examinations were used to determine the characteristics of lung lesions in all patients. The majority of patients presented with symptoms of fever, cough and dyspnea, while allergic symptoms were also encountered. The laboratory examination results revealed different degrees of increased CRP, ESR, tumor markers, ANA, serum IgE and IgG4. The CT images revealed diffuse ground glass opacities, bronchiectasis and thickened bronchovascular bundles. Histologically, the lung lesions were characterized by dense IgG4⁺ lymphoplasmacytic infiltrates intermixed with extensive fibrous tissue hyperplasia and an irregularly storiform pattern of fibrosis. The mean number of IgG4⁺ plasma cells was >10 cells/high power field. The ratio of IgG/IgG4⁺ plasma cells was >50% in inflamed lesions and the number of parenchymal cells was markedly reduced. Obliterative phlebitis or obliterative arteritis was observed in all patients. In conclusion, the clinicopathological similarities between IgG4-RILD and other IgG4-RD suggest that IgG4-related immunopathological processes may be associated with the pathogenesis of pulmonary lesions. Future studies based on the findings herein may elucidate the specific pathological process underlying the development of this fibroinflammatory disorder.

Ezetimibe ameliorates steatohepatitis via AMP activated protein kinase-TFEB-mediated activation of autophagy and NLRP3 inflammasome inhibition

Impairment in macroautophagy/autophagy flux and inflammasome activation are common characteristics of nonalcoholic steatohepatitis (NASH). Considering the lack of approved agents for treating NASH, drugs that can enhance autophagy and modulate inflammasome pathways may be beneficial. Here, we investigated the novel mechanism of ezetimibe, a widely prescribed drug for hypercholesterolemia, as a therapeutic option for ameliorating NASH. Human liver samples with steatosis and NASH were analyzed. For in vitro studies of autophagy and inflammasomes, primary mouse hepatocytes, human hepatoma cells, mouse embryonic fibroblasts with Ampk or Tsc2 knockout, and human or primary mouse macrophages were treated with ezetimibe and palmitate. Steatohepatitis and fibrosis were induced by feeding Atg7 wild-type, haploinsufficient, and knockout mice a methionine- and choline-deficient diet with ezetimibe (10 mg/kg) for 4 wk. Human livers with steatosis or NASH presented impaired autophagy with decreased nuclear TFEB and increased SQSTM1, MAP1LC3-II, and NLRP3 expression. Ezetimibe increased autophagy flux and concomitantly ameliorated lipid accumulation and apoptosis in palmitate-exposed hepatocytes. Ezetimibe induced AMPK phosphorylation and subsequent TFEB nuclear translocation, related to MAPK/ERK. In macrophages, ezetimibe blocked the NLRP3 inflammasome-IL1B pathway in an autophagy-dependent manner and modulated hepatocyte-macrophage interaction via extracellular vesicles. Ezetimibe attenuated lipid accumulation, inflammation, and fibrosis in liver-specific Atg7 wild-type and haploinsufficient mice, but not in knockout mice. Ezetimibe ameliorates steatohepatitis by autophagy induction through AMPK activation and TFEB nuclear translocation, related to an independent MTOR ameliorative effect and the MAPK/ERK pathway. Ezetimibe dampens NLRP3 inflammasome activation in macrophages by modulating autophagy and a hepatocyte-driven exosome pathway.

Increased intracellular proteolysis reduces disease severity in an ER stress-associated dwarfism

The short-limbed dwarfism metaphyseal chondrodysplasia type Schmid (MCDS) is linked to mutations in type X collagen, which increase ER stress by inducing misfolding of the mutant protein and subsequently disrupting hypertrophic chondrocyte differentiation. Here, we show that carbamazepine (CBZ), an autophagy-stimulating drug that is clinically approved for the treatment of seizures and bipolar disease, reduced the ER stress induced by 4 different MCDS-causing mutant forms of collagen X in human cell culture. Depending on the nature of the mutation, CBZ application stimulated proteolysis of misfolded collagen X by either autophagy or proteasomal degradation, thereby reducing intracellular accumulation of mutant collagen. In MCDS mice expressing the Col10a1.pN617K mutation, CBZ reduced the MCDS-associated expansion of the growth plate hypertrophic zone, attenuated enhanced expression of ER stress markers such as Bip and Atf4, increased bone growth, and reduced skeletal dysplasia. CBZ produced these beneficial effects by reducing the MCDS-associated abnormalities in hypertrophic chondrocyte differentiation. Stimulation of intracellular proteolysis using CBZ treatment may therefore be a clinically viable way of treating the ER stress–associated dwarfism MCDS.

Molecular genetics of the transcription factor GLIS3 identifies its dual function in beta cells and neurons

The GLIS family zinc finger 3 isoform (GLIS3) is a risk gene for Type 1 and Type 2 diabetes, glaucoma and Alzheimer's disease endophenotype. We identified GLIS3 binding sites in insulin secreting cells (INS1) (FDR q<0.05; enrichment range 1.40-9.11 fold) sharing the motif wrGTTCCCArTAGs, which were enriched in genes involved in neuronal function and autophagy and in risk genes for metabolic and neuro-behavioural diseases. We confirmed experimentally Glis3-mediated regulation of the expression of genes involved in autophagy and neuron function in INS1 and neuronal PC12 cells. Naturally-occurring coding polymorphisms in Glis3 in the Goto-Kakizaki rat model of type 2 diabetes were associated with increased insulin production in vitro and in vivo, suggestive alteration of autophagy in PC12 and INS1 and abnormal neurogenesis in hippocampus neurons. Our results support biological pleiotropy of GLIS3 in pathologies affecting β-cells and neurons and underline the existence of trans‑nosology pathways in diabetes and its co-morbidities.

Modeling Inborn Errors of Hepatic Metabolism Using Induced Pluripotent Stem Cells

Inborn errors of hepatic metabolism are because of deficiencies commonly within a single enzyme as a consequence of heritable mutations in the genome. Individually such diseases are rare, but collectively they are common. Advances in genome-wide association studies and DNA sequencing have helped researchers identify the underlying genetic basis of such diseases. Unfortunately, cellular and animal models that accurately recapitulate these inborn errors of hepatic metabolism in the laboratory have been lacking. Recently, investigators have exploited molecular techniques to generate induced pluripotent stem cells from patients' somatic cells. Induced pluripotent stem cells can differentiate into a wide variety of cell types, including hepatocytes, thereby offering an innovative approach to unravel the mechanisms underlying inborn errors of hepatic metabolism. Moreover, such cell models could potentially provide a platform for the discovery of therapeutics. In this mini-review, we present a brief overview of the state-of-the-art in using pluripotent stem cells for such studies.

Crosstalk and Interplay between the Ubiquitin-Proteasome System and Autophagy

Proteolysis in eukaryotic cells is mainly mediated by the ubiquitin (Ub)-proteasome system (UPS) and the autophagylysosome system (hereafter autophagy). The UPS is a selective proteolytic system in which substrates are recognized and tagged with ubiquitin for processive degradation by the proteasome. Autophagy is a bulk degradative system that uses lysosomal hydrolases to degrade proteins as well as various other cellular constituents. Since the inception of their discoveries, the UPS and autophagy were thought to be independent of each other in components, action mechanisms, and substrate selectivity. Recent studies suggest that cells operate a single proteolytic network comprising of the UPS and autophagy that share notable similarity in many aspects and functionally cooperate with each other to maintain proteostasis. In this review, we discuss the mechanisms underlying the crosstalk and interplay between the UPS and autophagy, with an emphasis on substrate selectivity and compensatory regulation under cellular stresses.

Liver Disease in Alpha-1 Antitrypsin Deficiency: Current Approaches and Future Directions

Purpose of Review

The aim of the study is to review the liver disease caused by alpha-1 antitrypsin deficiency (A1ATD), including pathogenesis, epidemiology, diagnostic testing, and recent therapeutic developments.

Recent Findings

Therapeutic approaches target several intracellular pathways to reduce the cytotoxic effects of the misfolded mutant globular protein (ATZ) on the hepatocyte. These include promoting ATZ transport out of the endoplasmic reticulum (ER), enhancing ATZ degradation, and preventing ATZ globule-aggregation.

Summary

A1ATD is the leading genetic cause of liver disease among children. It is a protein-folding disorder in which toxic insoluble ATZ proteins aggregate in the ER of hepatocytes leading to inflammation, fibrosis, cirrhosis, and increased risk of hepatocellular carcinoma. The absence of the normal A1AT serum protein also predisposes patients to pan lobar emphysema as adults. At this time, the only approved therapy for A1ATD-associated liver disease is orthotopic liver transplantation, which is curative. However, there has been significant recent progress in the development of small molecule therapies with potential both to preserve the native liver and prevent hepatotoxicity.

The endoplasmic reticulum: A hub of protein quality control in health and disease

One third of the eukaryotic proteome is synthesized at the endoplasmic reticulum (ER), whose unique properties provide a folding environment substantially different from the cytosol. A healthy, balanced proteome in the ER is maintained by a network of factors referred to as the ER quality control (ERQC) machinery. This network consists of various protein folding chaperones and modifying enzymes, and is regulated by stress response pathways that prevent the build-up as well as the secretion of potentially toxic and aggregation-prone misfolded protein species. Here, we describe the components of the ERQC machinery, investigate their response to different forms of stress, and discuss the consequences of ERQC break-down.