Variants in autophagy genes MTMR12 and FAM134A are putative modifiers of the hepatic phenotype in α1-antitrypsin deficiency

BACKGROUND AND AIMS

In the classical form of α1-antitrypsin deficiency, a misfolded variant α1-antitrypsin Z accumulates in the endoplasmic reticulum of liver cells and causes liver cell injury by gain-of-function proteotoxicity in a sub-group of affected homozygotes but relatively little is known about putative modifiers. Here, we carried out genomic sequencing in a uniquely affected family with an index case of liver failure and 2 homozygous siblings with minimal or no liver disease. Their sequences were compared to sequences in well-characterized cohorts of homozygotes with or without liver disease, and then candidate sequence variants were tested for changes in the kinetics of α1-antitrypsin variant Z degradation in iPS-derived hepatocyte-like cells derived from the affected siblings themselves.

APPROACH AND RESULTS

Specific variants in autophagy genes MTMR12 and FAM134A could each accelerate the degradation of α1-antitrypsin variant Z in cells from the index patient, but both MTMR12 and FAM134A variants were needed to slow the degradation of α1-antitrypsin variant Z in cells from a protected sib, indicating that inheritance of both variants is needed to mediate the pathogenic effects of hepatic proteotoxicity at the cellular level. Analysis of homozygote cohorts showed that multiple patient-specific variants in proteostasis genes are likely to explain liver disease susceptibility at the population level.

CONCLUSIONS

These results validate the concept that genetic variation in autophagy function can determine susceptibility to liver disease in α1-antitrypsin deficiency and provide evidence that polygenic mechanisms and multiple patient-specific variants are likely needed for proteotoxic pathology.

Multiple Genes Core to ERAD, Macroautophagy and Lysosomal Degradation Pathways Participate in the Proteostasis Response in α1-Antitrypsin Deficiency

BACKGROUND & AIMS

In the classic form of α1-antitrypsin deficiency (ATD), the misfolded α1-antitrypsin Z (ATZ) variant accumulates in the endoplasmic reticulum (ER) of liver cells. A gain-of-function proteotoxic mechanism is responsible for chronic liver disease in a subgroup of homozygotes. Proteostatic response pathways, including conventional endoplasmic reticulum-associated degradation and autophagy, have been proposed as the mechanisms that allow cellular adaptation and presumably protection from the liver disease phenotype. Recent studies have concluded that a distinct lysosomal pathway called endoplasmic reticulum-to-lysosome completely supplants the role of the conventional macroautophagy pathway in degradation of ATZ. Here, we used several state-of-the-art approaches to characterize the proteostatic responses more fully in cellular systems that model ATD.

METHODS

We used clustered regularly interspaced short palindromic repeats (CRISPR)-mediated genome editing coupled to a cell selection step by fluorescence-activated cell sorter to perform screening for proteostasis genes that regulate ATZ accumulation and combined that with selective genome editing in 2 other model systems.

RESULTS

Endoplasmic reticulum-associated degradation genes are key early regulators and multiple autophagy genes, from classic as well as from ER-to-lysosome and other newly described ER-phagy pathways, participate in degradation of ATZ in a manner that is temporally regulated and evolves as ATZ accumulation persists. Time-dependent changes in gene expression are accompanied by specific ultrastructural changes including dilation of the ER, formation of globular inclusions, budding of autophagic vesicles, and alterations in the overall shape and component parts of mitochondria.

CONCLUSIONS

Macroautophagy is a critical component of the proteostasis response to cellular ATZ accumulation and it becomes more important over time as ATZ synthesis continues unabated. Multiple subtypes of macroautophagy and nonautophagic lysosomal degradative pathways are needed to respond to the high concentrations of misfolded protein that characterizes ATD and these pathways are attractive candidates for genetic variants that predispose to the hepatic phenotype.

Longitudinal modeling of human neuronal aging reveals the contribution of the RCAN1-TFEB pathway to Huntington's disease neurodegeneration

Aging is a common risk factor in neurodegenerative disorders. Investigating neuronal aging in an isogenic background stands to facilitate analysis of the interplay between neuronal aging and neurodegeneration. Here we perform direct neuronal reprogramming of longitudinally collected human fibroblasts to reveal genetic pathways altered at different ages. Comparative transcriptome analysis of longitudinally aged striatal medium spiny neurons (MSNs) in Huntington's disease identified pathways involving RCAN1, a negative regulator of calcineurin. Notably, RCAN1 protein increased with age in reprogrammed MSNs as well as in human postmortem striatum and RCAN1 knockdown rescued patient-derived MSNs of Huntington's disease from degeneration. RCAN1 knockdown enhanced chromatin accessibility of genes involved in longevity and autophagy, mediated through enhanced calcineurin activity, leading to TFEB's nuclear localization by dephosphorylation. Furthermore, G2-115, an analog of glibenclamide with autophagy-enhancing activities, reduced the RCAN1-calcineurin interaction, phenocopying the effect of RCAN1 knockdown. Our results demonstrate that targeting RCAN1 genetically or pharmacologically can increase neuronal resilience in Huntington's disease.

Longitudinal modeling of human neuronal aging identifies RCAN1-TFEB pathway contributing to neurodegeneration of Huntington's disease

Aging is a common risk factor in neurodegenerative disorders and the ability to investigate aging of neurons in an isogenic background would facilitate discovering the interplay between neuronal aging and onset of neurodegeneration. Here, we perform direct neuronal reprogramming of longitudinally collected human fibroblasts to reveal genetic pathways altered at different ages. Comparative transcriptome analysis of longitudinally aged striatal medium spiny neurons (MSNs), a primary neuronal subtype affected in Huntington's disease (HD), identified pathways associated with RCAN1, a negative regulator of calcineurin. Notably, RCAN1 undergoes age-dependent increase at the protein level detected in reprogrammed MSNs as well as in human postmortem striatum. In patient-derived MSNs of adult-onset HD (HD-MSNs), counteracting RCAN1 by gene knockdown (KD) rescued HD-MSNs from degeneration. The protective effect of RCAN1 KD was associated with enhanced chromatin accessibility of genes involved in longevity and autophagy, mediated through enhanced calcineurin activity, which in turn dephosphorylates and promotes nuclear localization of TFEB transcription factor. Furthermore, we reveal that G2-115 compound, an analog of glibenclamide with autophagy-enhancing activities, reduces the RCAN1-Calcineurin interaction, phenocopying the effect of RCAN1 KD. Our results demonstrate that RCAN1 is a potential genetic or pharmacological target whose reduction-of-function increases neuronal resilience to neurodegeneration in HD through chromatin reconfiguration.

Resolution of hepatic fibrosis after ZFN-mediated gene editing in the PiZ mouse model of human α1-antitrypsin deficiency

BACKGROUND

α1-antitrypsin deficiency is most commonly caused by a mutation in exon-7 of SERPINA1 (SA1-ATZ), resulting in hepatocellular accumulation of a misfolded variant (ATZ). Human SA1-ATZ-transgenic (PiZ) mice exhibit hepatocellular ATZ accumulation and liver fibrosis. We hypothesized that disrupting the SA1-ATZ transgene in PiZ mice by in vivo genome editing would confer a proliferative advantage to the genome-edited hepatocytes, enabling them to repopulate the liver.

METHODS

To create a targeted DNA break in exon-7 of the SA1-ATZ transgene, we generated 2 recombinant adeno-associated viruses (rAAV) expressing a zinc-finger nuclease pair (rAAV-ZFN), and another rAAV for gene correction by targeted insertion (rAAV-TI). PiZ mice were injected i.v. with rAAV-TI alone or the rAAV-ZFNs at a low (7.5×1010vg/mouse, LD) or a high dose (1.5×1011vg/mouse, HD), with or without rAAV-TI. Two weeks and 6 months after treatment, livers were harvested for molecular, histological, and biochemical analyses.

RESULTS

Two weeks after treatment, deep sequencing of the hepatic SA1-ATZ transgene pool showed 6%±3% or 15%±4% nonhomologous end joining in mice receiving LD or HD rAAV-ZFN, respectively, which increased to 36%±12% and 36%±12%, respectively, 6 months after treatment. Two weeks postinjection of rAAV-TI with LD or HD of rAAV-ZFN, repair by targeted insertion occurred in 0.10%±0.09% and 0.25%±0.14% of SA1-ATZ transgenes, respectively, which increased to 5.2%±5.0% and 33%±13%, respectively, 6 months after treatment. Six months after rAAV-ZFN administration, there was a marked clearance of ATZ globules from hepatocytes, and resolution of liver fibrosis, along with reduction of hepatic TAZ/WWTR1, hedgehog ligands, Gli2, a TIMP, and collagen content.

CONCLUSIONS

ZFN-mediated SA1-ATZ transgene disruption provides a proliferative advantage to ATZ-depleted hepatocytes, enabling them to repopulate the liver and reverse hepatic fibrosis.

Age-related Huntington's disease progression modeled in directly reprogrammed patient-derived striatal neurons highlights impaired autophagy

Huntington's disease (HD) is an inherited neurodegenerative disorder with adult-onset clinical symptoms, but the mechanism by which aging drives the onset of neurodegeneration in patients with HD remains unclear. In this study we examined striatal medium spiny neurons (MSNs) directly reprogrammed from fibroblasts of patients with HD to model the age-dependent onset of pathology. We found that pronounced neuronal death occurred selectively in reprogrammed MSNs from symptomatic patients with HD (HD-MSNs) compared to MSNs derived from younger, pre-symptomatic patients (pre-HD-MSNs) and control MSNs from age-matched healthy individuals. We observed age-associated alterations in chromatin accessibility between HD-MSNs and pre-HD-MSNs and identified miR-29b-3p, whose age-associated upregulation promotes HD-MSN degeneration by impairing autophagic function through human-specific targeting of the STAT3 3' untranslated region. Reducing miR-29b-3p or chemically promoting autophagy increased the resilience of HD-MSNs against neurodegeneration. Our results demonstrate miRNA upregulation with aging in HD as a detrimental process driving MSN degeneration and potential approaches for enhancing autophagy and resilience of HD-MSNs.

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.

Mechanisms of Action of Autophagy Modulators Dissected by Quantitative Systems Pharmacology Analysis

Autophagy plays an essential role in cell survival/death and functioning. Modulation of autophagy has been recognized as a promising therapeutic strategy against diseases/disorders associated with uncontrolled growth or accumulation of biomolecular aggregates, organelles, or cells including those caused by cancer, aging, neurodegeneration, and liver diseases such as α1-antitrypsin deficiency. Numerous pharmacological agents that enhance or suppress autophagy have been discovered. However, their molecular mechanisms of action are far from clear. Here, we collected a set of 225 autophagy modulators and carried out a comprehensive quantitative systems pharmacology (QSP) analysis of their targets using both existing databases and predictions made by our machine learning algorithm. Autophagy modulators include several highly promiscuous drugs (e.g., artenimol and olanzapine acting as activators, fostamatinib as an inhibitor, or melatonin as a dual-modulator) as well as selected drugs that uniquely target specific proteins (~30% of modulators). They are mediated by three layers of regulation: (i) pathways involving core autophagy-related (ATG) proteins such as mTOR, AKT, and AMPK; (ii) upstream signaling events that regulate the activity of ATG pathways such as calcium-, cAMP-, and MAPK-signaling pathways; and (iii) transcription factors regulating the expression of ATG proteins such as TFEB, TFE3, HIF-1, FoxO, and NF-κB. Our results suggest that PKA serves as a linker, bridging various signal transduction events and autophagy. These new insights contribute to a better assessment of the mechanism of action of autophagy modulators as well as their side effects, development of novel polypharmacological strategies, and identification of drug repurposing opportunities.

Identification of Polycystic Kidney Disease 1 Like 1 Gene Variants in Children With Biliary Atresia Splenic Malformation Syndrome

Biliary atresia (BA) is the most common cause of end-stage liver disease in children and the primary indication for pediatric liver transplantation, yet underlying etiologies remain unknown. Approximately 10% of infants affected by BA exhibit various laterality defects (heterotaxy) including splenic abnormalities and complex cardiac malformations-a distinctive subgroup commonly referred to as the biliary atresia splenic malformation (BASM) syndrome. We hypothesized that genetic factors linking laterality features with the etiopathogenesis of BA in BASM patients could be identified through whole-exome sequencing (WES) of an affected cohort. DNA specimens from 67 BASM subjects, including 58 patient-parent trios, from the National Institute of Diabetes and Digestive and Kidney Diseases-supported Childhood Liver Disease Research Network (ChiLDReN) underwent WES. Candidate gene variants derived from a prespecified set of 2,016 genes associated with ciliary dysgenesis and/or dysfunction or cholestasis were prioritized according to pathogenicity, population frequency, and mode of inheritance. Five BASM subjects harbored rare and potentially deleterious biallelic variants in polycystic kidney disease 1 like 1 (PKD1L1), a gene associated with ciliary calcium signaling and embryonic laterality determination in fish, mice, and humans. Heterozygous PKD1L1 variants were found in 3 additional subjects. Immunohistochemical analysis of liver from the one BASM subject available revealed decreased PKD1L1 expression in bile duct epithelium when compared to normal livers and livers affected by other noncholestatic diseases. Conclusion: WES identified biallelic and heterozygous PKD1L1 variants of interest in 8 BASM subjects from the ChiLDReN data set; the dual roles for PKD1L1 in laterality determination and ciliary function suggest that PKD1L1 is a biologically plausible, cholangiocyte-expressed candidate gene for the BASM syndrome.

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.

α1-antitrypsin Deficiency: A Misfolded Secretory Protein Variant with Unique Effects on the Endoplasmic Reticulum

In the classical form of α1-antitrypsin deficiency (ATD) a point mutation leads to accumulation of a misfolded secretory glycoprotein in the endoplasmic reticulum (ER) of liver cells and so ATD has come to be considered a prototypical ER storage disease. It is associated with two major types of clinical disorders, chronic obstructive pulmonary disease (COPD) by loss-of-function mechanisms and hepatic cirrhosis and carcinogenesis by gain-of-function mechanisms. The lung disease predominantly results from proteolytic damage to the pulmonary connective tissue matrix because of reduced levels of protease inhibitor activity of α1-anitrypsin (AT) in the circulating blood and body fluids. Cigarette smoking is a powerful disease-promoting modifier but other modifiers are known to exist because variation in the lung disease phenotype is still found in smoking and non-smoking homozygotes. The liver disease is highly likely to be caused by the proteotoxic effects of intracellular misfolded protein accumulation and a high degree of variation in the hepatic phenotype among affected homozygotes has been hypothetically attributed to genetic and environmental modifiers that alter proteostasis responses. Liver biopsies of homozygotes show intrahepatocytic inclusions with dilation and expansion of the ER and recent studies of iPS-derived hepatocyte-like cells from individuals with ATD indicate that the changes in the ER directly vary with the hepatic phenotype i.e there is much lesser alteration in the ER in cells derived from homozygotes that do not have clinically significant liver disease. From a signaling perspective, studies in mammalian cell line and animal models expressing the classical α1-antitrypsin Z variant (ATZ) have found that ER signaling is perturbed in a relatively unique way with powerful activation of autophagy and the NFκB pathway but relatively limited, if any, UPR signaling. It is still not known how much these unique structural and functional changes and the variation among affected homozygotes relate to the tendency of this variant to polymerize and aggregate and/or to the repertoire of proteostasis mechanisms that are activated.

Is severe progressive liver disease caused by alpha-1-antitrypsin deficiency more common in children or adults?

The classical form of alpha-1-antitrypsin deficiency (A1ATD) is known to cause liver disease in children and adults, but there is relatively little information about the risk of severe, progressive liver disease and the need for liver transplantation. To better understand how newly evolving pharmacological, genetic, and cellular therapies may be targeted according to risk for progressive liver disease, we sought to determine the age distribution of A1ATD as a cause of severe liver disease, as defined by the need for liver transplantation. Using 3 US liver transplantation databases for the period 1991-2012, we found 77.2% of 1677 liver transplants with a reported diagnosis of A1ATD were adults. The peak age range was 50-64 years. Using 2 of the databases which included specific A1AT phenotypes, we found that many of these adults who undergo liver transplantation with A1ATD as the diagnosis are heterozygotes and have other potential causes of liver disease, most notably obesity and ethanol abuse. However, even when these cases are excluded and only ZZ and SZ phenotypes are considered, severe liver disease requiring transplantation is more than 2.5 times as likely in adults. The analysis also showed a markedly increased risk for males. In the pediatric group, almost all of the transplants are done in children less than 5 years of age. In conclusion, A1ATD causes progressive liver disease most commonly in adults with males in the highest risk category. In the pediatric group, children less than 5 years of age are highest in risk. These results suggest that A1ATD most commonly causes liver disease by mechanisms similar to age-dependent degenerative diseases and more rarely in children by powerful modifiers. Liver Transplantation 22 886-894 2016 AASLD.

Deficient and Null Variants of SERPINA1 Are Proteotoxic in a Caenorhabditis elegans Model of α1-Antitrypsin Deficiency

α1-antitrypsin deficiency (ATD) predisposes patients to both loss-of-function (emphysema) and gain-of-function (liver cirrhosis) phenotypes depending on the type of mutation. Although the Z mutation (ATZ) is the most prevalent cause of ATD, >120 mutant alleles have been identified. In general, these mutations are classified as deficient (<20% normal plasma levels) or null (<1% normal levels) alleles. The deficient alleles, like ATZ, misfold in the ER where they accumulate as toxic monomers, oligomers and aggregates. Thus, deficient alleles may predispose to both gain- and loss-of-function phenotypes. Null variants, if translated, typically yield truncated proteins that are efficiently degraded after being transiently retained in the ER. Clinically, null alleles are only associated with the loss-of-function phenotype. We recently developed a C. elegans model of ATD in order to further elucidate the mechanisms of proteotoxicity (gain-of-function phenotype) induced by the aggregation-prone deficient allele, ATZ. The goal of this study was to use this C. elegans model to determine whether different types of deficient and null alleles, which differentially affect polymerization and secretion rates, correlated to any extent with proteotoxicity. Animals expressing the deficient alleles, Mmalton, Siiyama and S (ATS), showed overall toxicity comparable to that observed in patients. Interestingly, Siiyama expressing animals had smaller intracellular inclusions than ATZ yet appeared to have a greater negative effect on animal fitness. Surprisingly, the null mutants, although efficiently degraded, showed a relatively mild gain-of-function proteotoxic phenotype. However, since null variant proteins are degraded differently and do not appear to accumulate, their mechanism of proteotoxicity is likely to be different to that of polymerizing, deficient mutants. Taken together, these studies showed that C. elegans is an inexpensive tool to assess the proteotoxicity of different AT variants using a transgenic approach.

Enhancing Autophagy with Drugs or Lung-directed Gene Therapy Reverses the Pathological Effects of Respiratory Epithelial Cell Proteinopathy

Recent studies have shown that autophagy mitigates the pathological effects of proteinopathies in the liver, heart, and skeletal muscle but this has not been investigated for proteinopathies that affect the lung. This may be due at least in part to the lack of an animal model robust enough for spontaneous pathological effects from proteinopathies even though several rare proteinopathies, surfactant protein A and C deficiencies, cause severe pulmonary fibrosis. In this report we show that the PiZ mouse, transgenic for the common misfolded variant α1-antitrypsin Z, is a model of respiratory epithelial cell proteinopathy with spontaneous pulmonary fibrosis. Intracellular accumulation of misfolded α1-antitrypsin Z in respiratory epithelial cells of the PiZ model resulted in activation of autophagy, leukocyte infiltration, and spontaneous pulmonary fibrosis severe enough to elicit functional restrictive deficits. Treatment with autophagy enhancer drugs or lung-directed gene transfer of TFEB, a master transcriptional activator of the autophagolysosomal system, reversed these proteotoxic consequences. We conclude that this mouse is an excellent model of respiratory epithelial proteinopathy with spontaneous pulmonary fibrosis and that autophagy is an important endogenous proteostasis mechanism and an attractive target for therapy.

Induced pluripotent stem cells model personalized variations in liver disease resulting from α1-antitrypsin deficiency

In the classical form of α1-antitrypsin deficiency (ATD), aberrant intracellular accumulation of misfolded mutant α1-antitrypsin Z (ATZ) in hepatocytes causes hepatic damage by a gain-of-function, "proteotoxic" mechanism. Whereas some ATD patients develop severe liver disease (SLD) that necessitates liver transplantation, others with the same genetic defect completely escape this clinical phenotype. We investigated whether induced pluripotent stem cells (iPSCs) from ATD individuals with or without SLD could model these personalized variations in hepatic disease phenotypes. Patient-specific iPSCs were generated from ATD patients and a control and differentiated into hepatocyte-like cells (iHeps) having many characteristics of hepatocytes. Pulse-chase and endoglycosidase H analysis demonstrate that the iHeps recapitulate the abnormal accumulation and processing of the ATZ molecule, compared to the wild-type AT molecule. Measurements of the fate of intracellular ATZ show a marked delay in the rate of ATZ degradation in iHeps from SLD patients, compared to those from no liver disease patients. Transmission electron microscopy showed dilated rough endoplasmic reticulum in iHeps from all individuals with ATD, not in controls, but globular inclusions that are partially covered with ribosomes were observed only in iHeps from individuals with SLD.

CONCLUSION

iHeps model the individual disease phenotypes of ATD patients with more rapid degradation of misfolded ATZ and lack of globular inclusions in cells from patients who have escaped liver disease. The results support the concept that "proteostasis" mechanisms, such as intracellular degradation pathways, play a role in observed variations in clinical phenotype and show that iPSCs can potentially be used to facilitate predictions of disease susceptibility for more precise and timely application of therapeutic strategies.

Worming our way to novel drug discovery with the Caenorhabditis elegans proteostasis network, stress response and insulin-signaling pathways

INTRODUCTION

Many human diseases result from a failure of a single protein to achieve the correct folding and tertiary conformation. These so-called 'conformational diseases' involve diverse proteins and distinctive cellular pathologies. They all engage the proteostasis network (PN), to varying degrees in an attempt to mange cellular stress and restore protein homeostasis. The insulin/insulin-like growth factor signaling (IIS) pathway is a master regulator of cellular stress response, which is implicated in regulating components of the PN.

AREAS COVERED

This review focuses on novel approaches to target conformational diseases. The authors discuss the evidence supporting the involvement of the IIS pathway in modulating the PN and regulating proteostasis in Caenorhabditis elegans. Furthermore, they review previous PN and IIS drug screens and explore the possibility of using C. elegans for whole organism-based drug discovery for modulators of IIS-proteostasis pathways.

EXPERT OPINION

An alternative approach to develop individualized therapy for each conformational disease is to modulate the global PN. The involvement of the IIS pathway in regulating longevity and response to a variety of stresses is well documented. Increasing data now provide evidence for the close association between the IIS and the PN pathways. The authors believe that high-throughput screening campaigns, which target the C. elegans IIS pathway, may identify drugs that are efficacious in treating numerous conformational diseases.

A genome-wide RNAi screen identifies potential drug targets in a C. elegans model of α1-antitrypsin deficiency

α1-Antitrypsin deficiency (ATD) is a common genetic disorder that can lead to end-stage liver and lung disease. Although liver transplantation remains the only therapy currently available, manipulation of the proteostasis network (PN) by small molecule therapeutics offers great promise. To accelerate the drug-discovery process for this disease, we first developed a semi-automated high-throughput/content-genome-wide RNAi screen to identify PN modifiers affecting the accumulation of the α1-antitrypsin Z mutant (ATZ) in a Caenorhabditis elegans model of ATD. We identified 104 PN modifiers, and these genes were used in a computational strategy to identify human ortholog-ligand pairs. Based on rigorous selection criteria, we identified four FDA-approved drugs directed against four different PN targets that decreased the accumulation of ATZ in C. elegans. We also tested one of the compounds in a mammalian cell line with similar results. This methodology also proved useful in confirming drug targets in vivo, and predicting the success of combination therapy. We propose that small animal models of genetic disorders combined with genome-wide RNAi screening and computational methods can be used to rapidly, economically and strategically prime the preclinical discovery pipeline for rare and neglected diseases with limited therapeutic options.

A C. elegans model of human α1-antitrypsin deficiency links components of the RNAi pathway to misfolded protein turnover

The accumulation of serpin oligomers and polymers within the endoplasmic reticulum (ER) causes cellular injury in patients with the classical form α1-antitrypsin deficiency (ATD). To better understand the cellular and molecular genetic aspects of this disorder, we generated transgenic C. elegans strains expressing either the wild-type (ATM) or Z mutant form (ATZ) of the human serpin fused to GFP. Animals secreted ATM, but retained polymerized ATZ within dilated ER cisternae. These latter animals also showed slow growth, smaller brood sizes and decreased longevity; phenotypes observed in ATD patients or transgenic mouse lines expressing ATZ. Similar to mammalian models, ATZ was disposed of by autophagy and ER-associated degradation pathways. Mutant strains defective in insulin signaling (daf-2) also showed a marked decrease in ATZ accumulation. Enhanced ATZ turnover was associated with the activity of two proteins central to systemic/exogenous (exo)-RNAi pathway: the dsRNA importer, SID-1 and the argonaute, RDE-1. Animals with enhanced exo-RNAi activity (rrf-3 mutant) phenocopied the insulin signaling mutants and also showed increased ATZ turnover. Taken together, these studies allude to the existence of a novel proteostasis pathway that mechanistically links misfolded protein turnover to components of the systemic RNAi machinery.

Mysteries of α1-antitrypsin deficiency: emerging therapeutic strategies for a challenging disease

The classical form of α1-antitrypsin deficiency (ATD) is an autosomal co-dominant disorder that affects ~1 in 3000 live births and is an important genetic cause of lung and liver disease. The protein affected, α1-antitrypsin (AT), is predominantly derived from the liver and has the function of inhibiting neutrophil elastase and several other destructive neutrophil proteinases. The genetic defect is a point mutation that leads to misfolding of the mutant protein, which is referred to as α1-antitrypsin Z (ATZ). Because of its misfolding, ATZ is unable to efficiently traverse the secretory pathway. Accumulation of ATZ in the endoplasmic reticulum of liver cells has a gain-of-function proteotoxic effect on the liver, resulting in fibrosis, cirrhosis and/or hepatocellular carcinoma in some individuals. Moreover, because of reduced secretion, there is a lack of anti-proteinase activity in the lung, which allows neutrophil proteases to destroy the connective tissue matrix and cause chronic obstructive pulmonary disease (COPD) by loss of function. Wide variation in the incidence and severity of liver and lung disease among individuals with ATD has made this disease one of the most challenging of the rare genetic disorders to diagnose and treat. Other than cigarette smoking, which worsens COPD in ATD, genetic and environmental modifiers that determine this phenotypic variability are unknown. A limited number of therapeutic strategies are currently available, and liver transplantation is the only treatment for severe liver disease. Although replacement therapy with purified AT corrects the loss of anti-proteinase function, COPD progresses in a substantial number of individuals with ATD and some undergo lung transplantation. Nevertheless, advances in understanding the variability in clinical phenotype and in developing novel therapeutic concepts is beginning to address the major clinical challenges of this mysterious disorder.

C. elegans in high-throughput drug discovery

Caenorhabditis elegans has been proven to be a useful model organism for investigating molecular and cellular aspects of numerous human diseases. More recently, investigators have explored the use of this organism as a tool for drug discovery. Although earlier drug screens were labor-intensive and low in throughput, recent advances in high-throughput liquid workflows, imaging platforms and data analysis software have made C. elegans a viable option for automated high-throughput drug screens. This review will outline the evolution of C. elegans-based drug screening, discuss the inherent challenges of using C. elegans, and highlight recent technological advances that have paved the way for future drug screens.

α1-antitrypsin deficiency and the hepatocytes - an elegans solution to drug discovery

Hepatocytes are metabolically active cells of the liver that play an important role in the biosynthesis of proteins including α1-antitrypsin. Mutations in the α1-antitrypsin gene can lead to protein misfolding, polymerization/aggregation and retention of protein within the endoplasmic reticulum of hepatocytes. The intracellular accumulation of α1-antitrypsin aggregates can lead to liver disease and increased likelihood of developing hepatocellular carcinomas. Of note, only ~10% of individuals with α1-antitrypsin-deficiency develop severe liver disease suggesting that there are other genetic and/or environmental factors that determine disease outcome. The nematode, Caenorhabditis elegans, is a powerful genetic model organism to study molecular aspects of human disease. In this review, we discuss the functional similarities between the intestinal cells of C. elegans and human hepatocytes and how a C. elegans model of α1-antitrypsin-deficiency can be used as a tool for identifying genetic modifiers and small molecule drugs.

Fluphenazine reduces proteotoxicity in C. elegans and mammalian models of alpha-1-antitrypsin deficiency

The classical form of α1-antitrypsin deficiency (ATD) is associated with hepatic fibrosis and hepatocellular carcinoma. It is caused by the proteotoxic effect of a mutant secretory protein that aberrantly accumulates in the endoplasmic reticulum of liver cells. Recently we developed a model of this deficiency in C. Elegans and adapted it for high-content drug screening using an automated, image-based array scanning. Screening of the Library of Pharmacologically Active Compounds identified fluphenazine (Flu) among several other compounds as a drug which reduced intracellular accumulation of mutant α1-antitrypsin Z (ATZ). Because it is representative of the phenothiazine drug class that appears to have autophagy enhancer properties in addition to mood stabilizing activity, and can be relatively easily re-purposed, we further investigated its effects on mutant ATZ. The results indicate that Flu reverses the phenotypic effects of ATZ accumulation in the C. elegans model of ATD at doses which increase the number of autophagosomes in vivo. Furthermore, in nanomolar concentrations, Flu enhances the rate of intracellular degradation of ATZ and reduces the cellular ATZ load in mammalian cell line models. In the PiZ mouse model Flu reduces the accumulation of ATZ in the liver and mediates a decrease in hepatic fibrosis. These results show that Flu can reduce the proteotoxicity of ATZ accumulation in vivo and, because it has been used safely in humans, this drug can be moved rapidly into trials for liver disease due to ATD. The results also provide further validation for drug discovery using C. elegans models that can be adapted to high-content drug screening platforms and used together with mammalian cell line and animal models.

Targeting intracellular degradation pathways for treatment of liver disease caused by α1-antitrypsin deficiency

The classic form of α1-antitrypsin deficiency (ATD) is a well-known genetic cause of severe liver disease in childhood. A point mutation alters the folding of a hepatic secretory glycoprotein such that the protein is prone to misfolding and polymerization. Liver injury, characterized predominantly by fibrosis/cirrhosis and carcinogenesis, is caused by the proteotoxic effect of polymerized mutant α1-antitrypsin Z (ATZ), which accumulates in the endoplasmic reticulum (ER) of hepatocytes. Several intracellular pathways have been shown to be responsible for disposal of ATZ after it accumulates in the ER, but autophagy appears to be specialized for disposal of insoluble ATZ polymers. Recently, we have found that drugs that enhance the activity of the autophagic pathway reduce the cellular load of mutant ATZ and reverse hepatic fibrosis in a mouse model of ATD. Because several of these autophagy enhancers have been used safely in humans for other reasons, we have been able to initiate a clinical trial of one of these drugs, carbamazepine, to determine its efficacy in severe liver disease due to ATD. In this review, we discuss the autophagy enhancer drugs as a new therapeutic strategy that targets cell biological mechanisms integral to the pathogenesis of liver disease due to ATD.

Functions of autophagy in normal and diseased liver

Autophagy has emerged as a critical lysosomal pathway that maintains cell function and survival through the degradation of cellular components such as organelles and proteins. Investigations specifically employing the liver or hepatocytes as experimental models have contributed significantly to our current knowledge of autophagic regulation and function. The diverse cellular functions of autophagy, along with unique features of the liver and its principal cell type the hepatocyte, suggest that the liver is highly dependent on autophagy for both normal function and to prevent the development of disease states. However, instances have also been identified in which autophagy promotes pathological changes such as the development of hepatic fibrosis. Considerable evidence has accumulated that alterations in autophagy are an underlying mechanism of a number of common hepatic diseases including toxin-, drug- and ischemia/reperfusion-induced liver injury, fatty liver, viral hepatitis and hepatocellular carcinoma. This review summarizes recent advances in understanding the roles that autophagy plays in normal hepatic physiology and pathophysiology with the intent of furthering the development of autophagy-based therapies for human liver diseases.

Clathrin pit-mediated endocytosis of neutrophil elastase and cathepsin G by cancer cells

Neutrophil elastase (NE) is a neutrophil-derived serine proteinase with broad substrate specificity. We have recently demonstrated that NE is capable of entering tumor cell endosomes and processing novel intracellular substrates. In the current study, we sought to determine the mechanism by which NE enters tumor cells. Our results show that NE enters into early endosomal antigen-1(+) endosomes in a dynamin- and clathrin-dependent but flotillin-1- and caveolin-1-independent fashion. Cathepsin G (but not proteinase-3) also enters tumor endosomes via the same mechanism. We utilized (125)I-labeled NE to demonstrate that NE binds to the surface of cancer cells. Incubation of radiolabeled NE with lung cancer cells displays a dissociation constant (K(d)) of 284 nm. Because NE is known to bind to heparan sulfate- and chondroitin sulfate-containing proteoglycans, we treated cells with glycanases to remove these confounding factors, which did not significantly diminish cell surface binding or endosomal entry. Thus, NE and CG bind to the surface of cancer cells, presumably to a cell surface receptor, and subsequently undergo clathrin pit-mediated endocytosis.

A pro-cathepsin L mutant is a luminal substrate for endoplasmic-reticulum-associated degradation in C. elegans

Endoplasmic-reticulum associated degradation (ERAD) is a major cellular misfolded protein disposal pathway that is well conserved from yeast to mammals. In yeast, a mutant of carboxypeptidase Y (CPY*) was found to be a luminal ER substrate and has served as a useful marker to help identify modifiers of the ERAD pathway. Due to its ease of genetic manipulation and the ability to conduct a genome wide screen for modifiers of molecular pathways, C. elegans has become one of the preferred metazoans for studying cell biological processes, such as ERAD. However, a marker of ERAD activity comparable to CPY* has not been developed for this model system. We describe a mutant of pro-cathepsin L fused to YFP that no longer targets to the lysosome, but is efficiently eliminated by the ERAD pathway. Using this mutant pro-cathepsin L, we found that components of the mammalian ERAD system that participate in the degradation of ER luminal substrates were conserved in C. elegans. This transgenic line will facilitate high-throughput genetic or pharmacological screens for ERAD modifiers using widefield epifluorescence microscopy.

Guidelines for the use and interpretation of assays for monitoring autophagy

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.

Novel treatment strategies for liver disease due to α1-antitrypsin deficiency

Alpha1-antitrypsin (AT) deficiency is the most common genetic cause of liver disease in children and is also a cause of chronic hepatic fibrosis, cirrhosis, and hepatocellular carcinoma in adults. Recent advances in understanding how mutant AT molecules accumulate within hepatocytes and cause liver cell injury have led to a novel strategy for chemoprophylaxis of this liver disease. This strategy involves a class of drugs, which enhance the intracellular degradation of mutant AT and, because several of these drugs have been used safely in humans for other indications, the strategy can be moved immediately into clinical trials. In this review, we will also report on advances that provide a basis for several other strategies that could be used in the future for treatment of the liver disease associated with AT deficiency.

Alpha-1-antitrypsin deficiency: importance of proteasomal and autophagic degradative pathways in disposal of liver disease-associated protein aggregates

Alpha-1-antitrypsin (AT) deficiency is the most common genetic cause of liver disease in children. The primary pathological issue is a point mutation that renders an abundant hepatic secretory glycoprotein prone to altered folding and a tendency to polymerize and aggregate. However, the expression of serious liver damage among homozygotes is dependent on genetic and/or environmental modifiers. Several studies have validated the concept that endogenous hepatic pathways for disposal of aggregation-prone proteins, including the proteasomal and autophagic degradative pathways, could play a key role in the variation in hepatic damage and be the target of the modifiers. Exciting recent results have shown that a drug that enhances autophagy can reduce the hepatic load of aggregated protein and reverse fibrosis in a mouse model of this disease.

Spontaneous hepatic repopulation in transgenic mice expressing mutant human α1-antitrypsin by wild-type donor hepatocytes

α1-Antitrypsin deficiency is an inherited condition that causes liver disease and emphysema. The normal function of this protein, which is synthesized by the liver, is to inhibit neutrophil elastase, a protease that degrades connective tissue of the lung. In the classical form of the disease, inefficient secretion of a mutant α1-antitrypsin protein (AAT-Z) results in its accumulation within hepatocytes and reduced protease inhibitor activity, resulting in liver injury and pulmonary emphysema. Because mutant protein accumulation increases hepatocyte cell stress, we investigated whether transplanted hepatocytes expressing wild-type AAT might have a competitive advantage relative to AAT-Z-expressing hepatocytes, using transgenic mice expressing human AAT-Z. Wild-type donor hepatocytes replaced 20%-98% of mutant host hepatocytes, and repopulation was accelerated by injection of an adenovector expressing hepatocyte growth factor. Spontaneous hepatic repopulation with engrafted hepatocytes occurred in the AAT-Z-expressing mice even in the absence of severe liver injury. Donor cells replaced both globule-containing and globule-devoid cells, indicating that both types of host hepatocytes display impaired proliferation relative to wild-type hepatocytes. These results suggest that wild-type hepatocyte transplantation may be therapeutic for AAT-Z liver disease and may provide an alternative to protein replacement for treating emphysema in AAT-ZZ individuals.

Hepatic fibrosis and carcinogenesis in α1-antitrypsin deficiency: a prototype for chronic tissue damage in gain-of-function disorders

In α1-antitrypsin (AT) deficiency, a point mutation renders a hepatic secretory glycoprotein prone to misfolding and polymerization. The mutant protein accumulates in the endoplasmic reticulum of liver cells and causes hepatic fibrosis and hepatocellular carcinoma by a gain-of-function mechanism. Genetic and/or environmental modifiers determine whether an affected homozygote is susceptible to hepatic fibrosis/carcinoma. Two types of proteostasis mechanisms for such modifiers have been postulated: variation in the function of intracellular degradative mechanisms and/or variation in the signal transduction pathways that are activated to protect the cell from protein mislocalization and/or aggregation. In recent studies we found that carbamazepine, a drug that has been used safely as an anticonvulsant and mood stabilizer, reduces the hepatic load of mutant AT and hepatic fibrosis in a mouse model by enhancing autophagic disposal of this mutant protein. These results provide evidence that pharmacological manipulation of endogenous proteostasis mechanisms is an appealing strategy for chemoprophylaxis in disorders involving gain-of-function mechanisms.

Automated high-content live animal drug screening using C. elegans expressing the aggregation prone serpin α1-antitrypsin Z

The development of preclinical models amenable to live animal bioactive compound screening is an attractive approach to discovering effective pharmacological therapies for disorders caused by misfolded and aggregation-prone proteins. In general, however, live animal drug screening is labor and resource intensive, and has been hampered by the lack of robust assay designs and high throughput work-flows. Based on their small size, tissue transparency and ease of cultivation, the use of C. elegans should obviate many of the technical impediments associated with live animal drug screening. Moreover, their genetic tractability and accomplished record for providing insights into the molecular and cellular basis of human disease, should make C. elegans an ideal model system for in vivo drug discovery campaigns. The goal of this study was to determine whether C. elegans could be adapted to high-throughput and high-content drug screening strategies analogous to those developed for cell-based systems. Using transgenic animals expressing fluorescently-tagged proteins, we first developed a high-quality, high-throughput work-flow utilizing an automated fluorescence microscopy platform with integrated image acquisition and data analysis modules to qualitatively assess different biological processes including, growth, tissue development, cell viability and autophagy. We next adapted this technology to conduct a small molecule screen and identified compounds that altered the intracellular accumulation of the human aggregation prone mutant that causes liver disease in α1-antitrypsin deficiency. This study provides powerful validation for advancement in preclinical drug discovery campaigns by screening live C. elegans modeling α1-antitrypsin deficiency and other complex disease phenotypes on high-content imaging platforms.

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

In the classical form of alpha1-antitrypsin (AT) deficiency, a point mutation in AT alters the folding of a liver-derived secretory glycoprotein and renders it aggregation-prone. In addition to decreased serum concentrations of AT, the disorder is characterized by accumulation of the mutant alpha1-antitrypsin Z (ATZ) variant inside cells, causing hepatic fibrosis and/or carcinogenesis by a gain-of-toxic function mechanism. The proteasomal and autophagic pathways are known to mediate degradation of ATZ. Here we show that the autophagy-enhancing drug carbamazepine (CBZ) decreased the hepatic load of ATZ and hepatic fibrosis in a mouse model of AT deficiency-associated liver disease. These results provide a basis for testing CBZ, which has an extensive clinical safety profile, in patients with AT deficiency and also provide a proof of principle for therapeutic use of autophagy enhancers.

Microvascular Decompression in Patient With Atypical Features of Hemifacial Spasm Secondary to Compression by a Tortuous Vertebrobasilar System

OBJECTIVE

We report a case of hemifacial spasm in a patient who had associated hearing loss, numbness throughout the face, tinnitus, and vertigo, all of which occurred when turning his head to the left. To our knowledge, these symptoms have not occurred in this pattern and with a single trigger.

CLINICAL PRESENTATION

A 45-year-old man presented with a 3-year history of right-sided hemifacial spasm initially treated with botulinum toxin. One month before presentation, he had an episode of acute hearing loss in the right ear when turning his head to the left, followed by multiple episodes of transient hearing loss in his right ear, numbness in his right face in all distributions of the trigeminal nerve, tinnitus, and vertigo. He was found to have decreased sensation in nerves V1 to V3 and House-Brackmann grade 3/6 weakness in his right face, despite not having botulinum toxin injections in more than a year. Magnetic resonance imaging/angiography showed an ectatic vertebrobasilar system causing compression of the fifth, seventh, and eighth cranial nerves.

INTERVENTION

The patient underwent a retromastoid craniotomy and microvascular decompression. Postoperatively, he had complete resolution of his symptoms except for his facial weakness. The benefit has been long-lasting.

CONCLUSION

Multiple, simultaneous cranial neuropathies from vascular compression are rare, but this case is an example of safe and effective treatment with microvascular decompression with durable results.

Modeling molecular and cellular aspects of human disease using the nematode Caenorhabditis elegans

As an experimental system, Caenorhabditis elegans offers a unique opportunity to interrogate in vivo the genetic and molecular functions of human disease-related genes. For example, C. elegans has provided crucial insights into fundamental biologic processes, such as cell death and cell fate determinations, as well as pathologic processes such as neurodegeneration and microbial susceptibility. The C. elegans model has several distinct advantages, including a completely sequenced genome that shares extensive homology with that of mammals, ease of cultivation and storage, a relatively short lifespan and techniques for generating null and transgenic animals. However, the ability to conduct unbiased forward and reverse genetic screens in C. elegans remains one of the most powerful experimental paradigms for discovering the biochemical pathways underlying human disease phenotypes. The identification of these pathways leads to a better understanding of the molecular interactions that perturb cellular physiology, and forms the foundation for designing mechanism-based therapies. To this end, the ability to process large numbers of isogenic animals through automated work stations suggests that C. elegans, manifesting different aspects of human disease phenotypes, will become the platform of choice for in vivo drug discovery and target validation using high-throughput/content screening technologies.

Autophagic disposal of the aggregation-prone protein that causes liver inflammation and carcinogenesis in alpha-1-antitrypsin deficiency

Alpha-1-antitrypsin (AT) deficiency is a relatively common autosomal co-dominant disorder, which causes chronic lung and liver disease. A point mutation renders aggregation-prone properties on a hepatic secretory protein in such a way that the mutant protein is retained in the endoplasmic reticulum of hepatocytes rather than secreted into the blood and body fluids where it ordinarily functions as an inhibitor of neutrophil proteases. A loss-of-function mechanism allows neutrophil proteases to degrade the connective tissue matrix of the lung causing chronic emphysema. Accumulation of aggregated mutant AT in the endoplasmic reticulum of hepatocytes causes liver inflammation and carcinogenesis by a gain-of-toxic function mechanism. However, genetic epidemiology studies indicate that many, if not the majority of, affected homozygotes are protected from liver disease by unlinked genetic and/or environmental modifiers. Studies performed over the last several years have demonstrated the importance of autophagy in disposal of mutant, aggregated AT and raise the possibility that predisposition to, or protection from, liver injury and carcinogenesis is determined by the balance of de novo biogenesis of the mutant AT molecule and its autophagic disposal.

Regulation of complement protein biosynthesis in mononuclear phagocytes

Proteins of the complement system (with the exception of the terminal components C6-9) are synthesized in mononuclear phagocytes. The extrahepatic macrophage is therefore an important local source of the complement proteins which may serve as a first-line host defence mechanism. Net synthesis and secretion of complement by these cells is a function of maturation of the mononuclear phagocytic series, the tissue from which the cells are isolated, and the state of macrophage activation. To define some of the mechanisms for regulation of complement gene expression in mononuclear phagocytes, the major histocompatibility complex class III genes and C3 have been investigated. These genes are expressed constitutively in hepatocytes and monocytes/macrophages. In the mononuclear phagocyte, interferon-gamma, at physiological concentrations, effects a dose- and time-dependent increase in factor B and C2 mRNA and a corresponding increase in factor B and C2 biosynthesis. This effect is specific inasmuch as the expression of other genes (e.g. C3) is decreased by interferon-gamma, and interferon-alpha and beta at concentrations one to two logs greater have only a minimal effect on C2 and factor B gene expression. Endotoxin acting directly on monocytes has qualitatively different effects on expression of the complement genes. These complex regulatory mechanisms are being investigated with the use of murine fibroblasts transfected with human DNA bearing the relevent complement genes.

Guidelines for the use and interpretation of assays for monitoring autophagy in higher eukaryotes

Research in autophagy continues to accelerate,(1) and as a result many new scientists are entering the field. Accordingly, it is important to establish a standard set of criteria for monitoring macroautophagy in different organisms. Recent reviews have described the range of assays that have been used for this purpose.(2,3) There are many useful and convenient methods that can be used to monitor macroautophagy in yeast, but relatively few in other model systems, and there is much confusion regarding acceptable methods to measure macroautophagy in higher eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers of autophagosomes versus those that measure flux through the autophagy pathway; thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from fully functional autophagy that includes delivery to, and degradation within, lysosomes (in most higher eukaryotes) or the vacuole (in plants and fungi). Here, we present a set of guidelines for the selection and interpretation of the methods that can be used by investigators who are attempting to examine macroautophagy and related processes, as well as by reviewers who need to provide realistic and reasonable critiques of papers that investigate these processes. This set of guidelines is not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to verify an autophagic response.