Circumventing the packaging limit of AAV-mediated gene replacement therapy for neurological disorders

INTRODUCTION

Gene therapy provides the exciting opportunity of a curative single treatment for devastating diseases, eradicating the need for chronic medication. Adeno-associated viruses (AAVs) are among the most attractive vector carriers for gene replacement in vivo. Yet, despite the success of recent AAV-based clinical trials, the clinical use of these vectors has been limited. For instance, the AAV packaging capacity is restricted to ~4.7 kb, making it a substantial challenge to deliver large gene products.

AREAS COVERED

In this review, we explore established and emerging strategies that circumvent the packaging limit of AAVs to make them effective vehicles for gene replacement therapy of monogenic disorders, with a particular focus on diseases affecting the nervous system. We report historical references, design remarks, as well as strengths and weaknesses of these approaches. We additionally discuss examples of neurological disorders for which such strategies have been attempted.

EXPERT OPINION

The field of AAV-gene therapy has experienced enormous advancements in the last decade. However, there is still ample space for improvement aimed at overcoming existing challenges that are slowing down the progressive trajectory of this field.

C9ORF72-derived poly-GA DPRs undergo endocytic uptake in iAstrocytes and spread to motor neurons

Dipeptide repeat (DPR) proteins are aggregation-prone polypeptides encoded by the pathogenic GGGGCC repeat expansion in the C9ORF72 gene, the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. In this study, we focus on the role of poly-GA DPRs in disease spread. We demonstrate that recombinant poly-GA oligomers can directly convert into solid-like aggregates and form characteristic β-sheet fibrils in vitro. To dissect the process of cell-to-cell DPR transmission, we closely follow the fate of poly-GA DPRs in either their oligomeric or fibrillized form after administration in the cell culture medium. We observe that poly-GA DPRs are taken up via dynamin-dependent and -independent endocytosis, eventually converging at the lysosomal compartment and leading to axonal swellings in neurons. We then use a co-culture system to demonstrate astrocyte-to-motor neuron DPR propagation, showing that astrocytes may internalise and release aberrant peptides in disease pathogenesis. Overall, our results shed light on the mechanisms of poly-GA cellular uptake and propagation, suggesting lysosomal impairment as a possible feature underlying the cellular pathogenicity of these DPR species.

SMN-deficient cells exhibit increased ribosomal DNA damage

Spinal muscular atrophy, the leading genetic cause of infant mortality, is a motor neuron disease caused by low levels of survival motor neuron (SMN) protein. SMN is a multifunctional protein that is implicated in numerous cytoplasmic and nuclear processes. Recently, increasing attention is being paid to the role of SMN in the maintenance of DNA integrity. DNA damage and genome instability have been linked to a range of neurodegenerative diseases. The ribosomal DNA (rDNA) represents a particularly unstable locus undergoing frequent breakage. Instability in rDNA has been associated with cancer, premature ageing syndromes, and a number of neurodegenerative disorders. Here, we report that SMN-deficient cells exhibit increased rDNA damage leading to impaired ribosomal RNA synthesis and translation. We also unravel an interaction between SMN and RNA polymerase I. Moreover, we uncover an spinal muscular atrophy motor neuron-specific deficiency of DDX21 protein, which is required for resolving R-loops in the nucleolus. Taken together, our findings suggest a new role of SMN in rDNA integrity.

OUP accepted manuscript

Hereditary spastic paraplegia type 15 (HSP15) is a neurodegenerative condition caused by the inability to produce SPG15 protein, which leads to lysosomal swelling. However, the link between lysosomal aberrations and neuronal death is poorly explored. To uncover the functional consequences of lysosomal aberrations in disease pathogenesis, we analyze human dermal fibroblasts from HSP15 patients as well as primary cortical neurons derived from an SPG15 knockout (KO) mouse model. We find that SPG15 protein loss induces defective anterograde transport, impaired neurite outgrowth, axonal swelling and reduced autophagic flux in association with the onset of lysosomal abnormalities. Additionally, we observe lipid accumulation within the lysosomal compartment, suggesting that distortions in cellular lipid homeostasis are intertwined with lysosomal alterations. We further demonstrate that SPG15 KO neurons exhibit synaptic dysfunction, accompanied by augmented vulnerability to glutamate-induced excitotoxicity. Overall, our study establishes an intimate link between lysosomal aberrations, lipid metabolism and electrophysiological impairments, suggesting that lysosomal defects are at the core of multiple neurodegenerative disease processes in HSP15.

TMOD-10. THE ROLE OF IDH1 R132H MUTATION IN GLIOMA – AN INVESTIGATION BY GENOME-EDITING IN HUMAN INDUCED PLURIPOTENT STEM CELLS

BACKGROUND

Hot-spot mutations in the Isocitrate dehydrogenase 1 (IDH1) cause a new catalytic function resulting in the production of 2-HG, a hallmark in the development of low-grade glioma. The tumorigenic mechanism of this mutation as well as the cell of origin are not known and there is a lack of suitable disease models. Thus, we aim to create a model mimicking glioma development by introducing the IDH1 R132H into human induced pluripotent stem cells (hiPSC) and investigate the influence on stem cell properties and cell differentiation in neuronal progenitor cells.

MATERIAL AND METHODS

We use CRISPR/Cas9 based genome editing to induce the IDH1 R132H mutation into healthy-control-derived hiPSCs. Successful introduction of the mutation was confirmed on DNA, RNA and protein level. The hiPSCs are then differentiated into cerebral organoids and characterized using transcriptome sequencing and methylation arrays.

RESULTS

We successfully introduced the IDH1 R132H mutation into hiPSCs and confirmed expression of the mutated protein by Western Blot. Metabolite measurement using liquid chromatography tandem mass spectrometry (LC-MS/MS) showed a forty times increased concentration of 2-HG in IDH-mutated compared to the wildtype hiPSCs, proving that the mutated enzyme is functional. To investigate effects of IDH1 R132H on cell differentiation, we generated cerebral organoids from our iPSC-models. The IDH1 R132H mutation did not inhibit cell differentiation or maturation of cerebral organoids but led to a downregulation of splicosome, proteasome and DNA repair enzymes as well as an upregulation of ECM components.

CONCLUSION AND OUTLOOK

hiPSCs with R132H mutation pose a promising model for investigations on early glioma development. We are currently step-wise including TP53 and ATRX loss of function mutations in our hiPSC models to recapitulating tumor development in vivo.

Proteostatic imbalance and protein spreading in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder whose exact causative mechanisms are still under intense investigation. Several lines of evidence suggest that the anatomical and temporal propagation of pathological protein species along the neural axis could be among the main driving mechanisms for the fast and irreversible progression of ALS pathology. Many ALS-associated proteins form intracellular aggregates as a result of their intrinsic prion-like properties and/or following impairment of the protein quality control systems. During the disease course, these mutated proteins and aberrant peptides are released in the extracellular milieu as soluble or aggregated forms through a variety of mechanisms. Internalization by recipient cells may seed further aggregation and amplify existing proteostatic imbalances, thus triggering a vicious cycle that propagates pathology in vulnerable cells, such as motor neurons and other susceptible neuronal subtypes. Here, we provide an in-depth review of ALS pathology with a particular focus on the disease mechanisms of seeding and transmission of the most common ALS-associated proteins, including SOD1, FUS, TDP-43, and C9orf72-linked dipeptide repeats. For each of these proteins, we report historical, biochemical, and pathological evidence of their behaviors in ALS. We further discuss the possibility to harness pathological proteins as biomarkers and reflect on the implications of these findings for future research.

Muscleblind acts as a modifier of FUS toxicity by modulating stress granule dynamics and SMN localization

Mutations in fused in sarcoma (FUS) lead to amyotrophic lateral sclerosis (ALS) with varying ages of onset, progression and severity. This suggests that unknown genetic factors contribute to disease pathogenesis. Here we show the identification of muscleblind as a novel modifier of FUS-mediated neurodegeneration in vivo. Muscleblind regulates cytoplasmic mislocalization of mutant FUS and subsequent accumulation in stress granules, dendritic morphology and toxicity in mammalian neuronal and human iPSC-derived neurons. Interestingly, genetic modulation of endogenous muscleblind was sufficient to restore survival motor neuron (SMN) protein localization in neurons expressing pathogenic mutations in FUS, suggesting a potential mode of suppression of FUS toxicity. Upregulation of SMN suppressed FUS toxicity in Drosophila and primary cortical neurons, indicating a link between FUS and SMN. Our data provide in vivo evidence that muscleblind is a dominant modifier of FUS-mediated neurodegeneration by regulating FUS-mediated ALS pathogenesis.

FUS pathology in ALS is linked to alterations in multiple ALS-associated proteins and rescued by drugs stimulating autophagy

Amyotrophic lateral sclerosis (ALS) is a lethal disease characterized by motor neuron degeneration and associated with aggregation of nuclear RNA-binding proteins (RBPs), including FUS. How FUS aggregation and neurodegeneration are prevented in healthy motor neurons remain critically unanswered questions. Here, we use a combination of ALS patient autopsy tissue and induced pluripotent stem cell-derived neurons to study the effects of FUS mutations on RBP homeostasis. We show that FUS’ tendency to aggregate is normally buffered by interacting RBPs, but this buffering is lost when FUS mislocalizes to the cytoplasm due to ALS mutations. The presence of aggregation-prone FUS in the cytoplasm causes imbalances in RBP homeostasis that exacerbate neurodegeneration. However, enhancing autophagy using small molecules reduces cytoplasmic FUS, restores RBP homeostasis and rescues motor function in vivo. We conclude that disruption of RBP homeostasis plays a critical role in FUS-ALS and can be treated by stimulating autophagy.

Dual Inhibition of GSK3β and CDK5 Protects the Cytoskeleton of Neurons from Neuroinflammatory-Mediated Degeneration In Vitro and In Vivo

Neuroinflammation is a hallmark of neurological disorders and is accompanied by the production of neurotoxic agents such as nitric oxide. We used stem cell-based phenotypic screening and identified small molecules that directly protected neurons from neuroinflammation-induced degeneration. We demonstrate that inhibition of CDK5 is involved in, but not sufficient for, neuroprotection. Instead, additional inhibition of GSK3β is required to enhance the neuroprotective effects of CDK5 inhibition, which was confirmed using short hairpin RNA-mediated knockdown of CDK5 and GSK3β. Quantitative phosphoproteomics and high-content imaging demonstrate that neurite degeneration is mediated by aberrant phosphorylation of multiple microtubule-associated proteins. Finally, we show that our hit compound protects neurons in vivo in zebrafish models of motor neuron degeneration and Alzheimer's disease. Thus, we demonstrate an overlap of CDK5 and GSK3β in mediating the regulation of the neuronal cytoskeleton and that our hit compound LDC8 represents a promising starting point for neuroprotective drugs.

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Phenotypic screening identifies CDK inhibitors protecting neurons from inflammation

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Inhibition of CDK5 is involved in neuroprotection but is not sufficient

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Dual inhibition of CDK5 and GSK3β is neuroprotective in vitro and in vivo

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Quantitative phosphoproteomics links neuroprotection to microtubule dynamics

Phenotypic Screening Using Mouse and Human Stem Cell-Based Models of Neuroinflammation and Gene Expression Analysis to Study Drug Responses

High-throughput phenotypic screening enables the identification of new therapeutic targets even when the molecular mechanism underlying the disease is unknown. In the case of neurodegenerative disease, there is a dire need to identify new targets that can ameliorate, halt, or reverse degeneration. Stem cell-based disease models are particularly powerful tools for phenotypic screening because they use the same cell type affected in patients. Here, we describe the expansion of mouse stem cells and human induced pluripotent stem cells as well as the differentiation of these cells into neural lineages that, when exposed to neuroinflammatory stress, can be used for compound screening followed by hit identification, validation, and target deconvolution.

RNA buffers the phase separation behavior of prion-like RNA binding proteins

Prion-like RNA binding proteins (RBPs) such as TDP43 and FUS are largely soluble in the nucleus but form solid pathological aggregates when mislocalized to the cytoplasm. What keeps these proteins soluble in the nucleus and promotes aggregation in the cytoplasm is still unknown. We report here that RNA critically regulates the phase behavior of prion-like RBPs. Low RNA/protein ratios promote phase separation into liquid droplets, whereas high ratios prevent droplet formation in vitro. Reduction of nuclear RNA levels or genetic ablation of RNA binding causes excessive phase separation and the formation of cytotoxic solid-like assemblies in cells. We propose that the nucleus is a buffered system in which high RNA concentrations keep RBPs soluble. Changes in RNA levels or RNA binding abilities of RBPs cause aberrant phase transitions.

Generation of iPSCs carrying a common LRRK2 risk allele for in vitro modeling of idiopathic Parkinson's disease

Induced pluripotent stem cells (iPSCs) have recapitulated several aspects of Parkinson’s disease (PD), but most iPSCs are derived from familial cases, which account for only about 15% of patients. Thus, while the emphasis has justifiably been on using iPSCs to model rare familial cases, models for the most common forms of PD are critically lacking. Here, we report the generation of an iPSC-based model of idiopathic PD (iPD) with or without RS1491923, which is a common risk variant in the LRRK2 locus. Consistent with GWA studies, we found large variability in our datasets. However, iPSC-derived neurons carrying the risk allele emerged for displaying subtle disturbances of cellular degradative systems, in line with familial PD models. We also observed that treatment with the LRRK2 inhibitor CZC-25146 slightly reduced a marker of aSYN pathology in all iPD lines. Future iPSC-based studies may need to be structured similarly to large GWA studies in order to obtain relevant statistical power. However, results from this pilot study suggest that iPSC-based modeling represents an attractive way to investigate idiopathic diseases.

Isogenic FUS-eGFP iPSC Reporter Lines Enable Quantification of FUS Stress Granule Pathology that Is Rescued by Drugs Inducing Autophagy

Perturbations in stress granule (SG) dynamics may be at the core of amyotrophic lateral sclerosis (ALS). Since SGs are membraneless compartments, modeling their dynamics in human motor neurons has been challenging, thus hindering the identification of effective therapeutics. Here, we report the generation of isogenic induced pluripotent stem cells carrying wild-type and P525L FUS-eGFP. We demonstrate that FUS-eGFP is recruited into SGs and that P525L profoundly alters their dynamics. With a screening campaign, we demonstrate that PI3K/AKT/mTOR pathway inhibition increases autophagy and ameliorates SG phenotypes linked to P525L FUS by reducing FUS-eGFP recruitment into SGs. Using a Drosophila model of FUS-ALS, we corroborate that induction of autophagy significantly increases survival. Finally, by screening clinically approved drugs for their ability to ameliorate FUS SG phenotypes, we identify a number of brain-penetrant anti-depressants and anti-psychotics that also induce autophagy. These drugs could be repurposed as potential ALS treatments.

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Generation of isogenic WT and P525L FUS-eGFP reporter iPSCs

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P525L FUS-eGFP SGs are more numerous, more intense, and larger than WT

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Increasing PI3K/AKT/mTOR-regulated autophagy reduces FUS-eGFP recruitment to SGs

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Brain-penetrant drugs that induce autophagy ameliorate the FUS SG phenotype

Primary Spinal OPC Culture System from Adult Zebrafish to Study Oligodendrocyte Differentiation In Vitro

Endogenous oligodendrocyte progenitor cells (OPCs) are a promising target to improve functional recovery after spinal cord injury (SCI) by remyelinating denuded, and therefore vulnerable, axons. Demyelination is the result of a primary insult and secondary injury, leading to conduction blocks and long-term degeneration of the axons, which subsequently can lead to the loss of their neurons. In response to SCI, dormant OPCs can be activated and subsequently start to proliferate and differentiate into mature myelinating oligodendrocytes (OLs). Therefore, researchers strive to control OPC responses, and utilize small molecule screening approaches in order to identify mechanisms of OPC activation, proliferation, migration and differentiation. In zebrafish, OPCs remyelinate axons of the optic tract after lysophosphatidylcholine (LPC)-induced demyelination back to full thickness myelin sheaths. In contrast to zebrafish, mammalian OPCs are highly vulnerable to excitotoxic stress, a cause of secondary injury, and remyelination remains insufficient. Generally, injury induced remyelination leads to shorter internodes and thinner myelin sheaths in mammals. In this study, we show that myelin sheaths are lost early after a complete spinal transection injury, but are re-established within 14 days after lesion. We introduce a novel, easy-to-use, inexpensive and highly reproducible OPC culture system based on dormant spinal OPCs from adult zebrafish that enables in vitro analysis. Zebrafish OPCs are robust, can easily be purified with high viability and taken into cell culture. This method enables to examine why zebrafish OPCs remyelinate better than their mammalian counterparts, identify cell intrinsic responses, which could lead to pro-proliferating or pro-differentiating strategies, and to test small molecule approaches. In this methodology paper, we show efficient isolation of OPCs from adult zebrafish spinal cord and describe culture conditions that enable analysis up to 10 days in vitro. Finally, we demonstrate that zebrafish OPCs differentiate into Myelin Basic Protein (MBP)-expressing OLs when co-cultured with human motor neurons differentiated from induced pluripotent stem cells (iPSCs). This shows that the basic mechanisms of oligodendrocyte differentiation are conserved across species and that understanding the regulation of zebrafish OPCs can contribute to the development of new treatments to human diseases.

Outcomes associated with fetal hepatobiliary cysts: systematic review and meta-analysis

OBJECTIVE

To explore the outcomes associated with fetal hepatobiliary cysts.

METHODS

MEDLINE and EMBASE were searched for studies reporting on outcomes of fetal hepatobiliary cysts. Outcomes observed were resolution/reduction and increase in cyst size, associated congenital anomalies of the biliary tract and liver, abnormal postnatal liver function tests, clinical symptoms, need for surgery, postsurgical complications and predictive accuracy of prenatal ultrasound in identifying correctly hepatobiliary cysts. Meta-analysis of proportions was used to analyze the data.

RESULTS

The search identified 1498 articles, and 22 studies (252 fetuses) were included in the systematic review. For fetal hepatic cysts, resolution or reduction in cyst size either pre- or postnatally occurred in 59.3% (95% CI, 30.9-84.7%) of cases, while an increase in cyst size occurred in 8.7% (95% CI, 1.1-22.4%). No case of hepatic cyst had associated malformations of the biliary tract at birth. Clinical symptoms occurred in 14.8% (95% CI, 6.3-26.1%) of cases and, in 5.4% (95% CI, 0.9-13.6%), they were related to the presence of bile obstruction due to compression of the cyst on the biliary tract. No case of hepatic cyst had abnormal liver function at birth. For fetal biliary cysts, resolution or reduction in cyst size occurred in 8.7% (95% CI, 2.7-17.5%) of cases and an increase in size occurred in 34.4% (95% CI, 20.5-49.8%). Congenital anomalies of the biliary tract and liver, such as fibrosis, occurred in 21.5% (95% CI, 10.2-35.6%) and 17.4% (95% CI, 5.4-34.4%) of cases, respectively. 57.3% (95% CI, 33.9-79.0%) of cases showed impairment in liver function after birth, while 55.0% (95% CI, 37.5-71.9%) showed clinical symptoms, mainly due to bile obstruction (47.9% (95% CI, 29.4-66.7%)). Postsurgical complications occurred in 10.9% (95% CI, 3.7-21.3%) of operated cases. Risk assessment according to different cut-offs of cyst size could not be performed in view of the very small number of included studies.

CONCLUSIONS

Fetal hepatic cysts are benign, with a low likelihood of associated anomalies of the hepatobiliary tract, abnormal liver function or clinical symptoms. Congenital biliary cysts are associated with a high rate of progression, abnormal liver function after birth and clinical symptoms. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Outcome of fetal ovarian cysts diagnosed on prenatal ultrasound examination: systematic review and meta-analysis

OBJECTIVE

To explore the outcome of fetuses with a prenatal diagnosis of ovarian cyst.

METHODS

The electronic databases MEDLINE and EMBASE were searched using keywords and word variants for 'ovarian cysts', 'ultrasound' and 'outcome'. The following outcomes in fetuses with a prenatal diagnosis of ovarian cyst were explored: resolution of the cyst, change of ultrasound pattern of the cyst, occurrence of ovarian torsion and intracystic hemorrhage, need for postnatal surgery, need for oophorectomy, accuracy of prenatal ultrasound examination in correctly identifying ovarian cyst, type of ovarian cyst at histopathological analysis and intrauterine treatment. Meta-analyses using individual data random-effects logistic regression and meta-analyses of proportions were performed. Quality assessment of the included studies was performed using the Newcastle-Ottawa Scale.

RESULTS

Thirty-four studies (954 fetuses) were included. In 53.8% (95% CI, 46.0-61.5%) of cases for which resolution of the cyst was evaluated (784 fetuses), the cyst regressed either during pregnancy or after birth. The likelihood of resolution was significantly lower in complex vs simple cysts (odds ratio (OR), 0.15 (95% CI, 0.10-0.23)) and in cysts measuring ≥ 40 mm vs < 40 mm (OR, 0.03 (95% CI, 0.01-0.06)). Change in ultrasound pattern of the cyst was associated with an increased risk of ovarian loss (surgical removal or autoamputation) (pooled proportion, 57.7% (95% CI, 42.9-71.8%)). The risk of ovarian torsion was significantly higher for cysts measuring ≥ 40 mm compared with < 40 mm (OR, 30.8 (95% CI, 8.6-110.0)). The likelihood of having postnatal surgery was higher in patients with cysts ≥ 40 mm compared with < 40 mm (OR, 64.4 (95% CI, 23.6-175.0)) and in complex compared with simple cysts, irrespective of cyst size (OR, 14.6 (95% CI, 8.5-24.8)). In cases undergoing prenatal aspiration of the cyst, rate of recurrence was 37.9% (95% CI, 14.8-64.3%), ovarian torsion and intracystic hemorrhage were diagnosed after birth in 10.8% (95% CI, 4.4-19.7%) and 12.8% (95% CI, 3.8-26.0%), respectively, and 21.8% (95% CI, 0.9-40.0%) had surgery after birth.

CONCLUSION

Size and ultrasound appearance are the major determinants of perinatal outcome in fetuses with ovarian cysts. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Systematic review and meta-analysis of persistent left superior vena cava on prenatal ultrasound: associated anomalies, diagnostic accuracy and postnatal outcome

OBJECTIVES

To quantify the prevalence of chromosomal anomalies in fetuses with persistent left superior vena cava (PLSVC), assess the strength of the association between PLSVC and coarctation of the aorta and ascertain the diagnostic accuracy of antenatal ultrasound in correctly identifying isolated cases of PLSVC.

METHODS

MEDLINE, EMBASE, CINHAL and the Cochrane databases were searched from the year 2000 onwards using combinations of keywords 'left superior vena cava' and 'outcome'. Two authors reviewed all abstracts independently. Quality assessment of the included studies was performed using the Newcastle-Ottawa Scale for cohort studies. The rates of the following outcomes were analyzed: chromosomal abnormalities; associated intracardiac anomalies (ICAs) and extracardiac anomalies (ECAs) diagnosed prenatally; additional ICAs and ECAs detected only at postnatal imaging or clinical evaluation but missed at prenatal imaging; and association of PLSVC and coarctation of the aorta. Meta-analyses of proportions were used to combine data.

RESULTS

In total, 2708 articles were identified and 13 (n = 501) were included in the systematic review. Associated ICAs and ECAs were detected at the prenatal ultrasound examination or at a follow-up assessment in 60.7% (95% CI, 44.2-75.9%) and 37.8% (95% CI, 31.0-44.8%) of cases, respectively. Chromosomal anomalies occurred in 12.5% (95% CI, 9.0-16.4%) of cases in the overall population of fetuses with PLSVC and in 7.0% (95% CI, 2.7-13.0%) of isolated cases. Additional ICAs and ECAs were detected only after birth and missed at ultrasound in 2.4% (95% CI, 0.5-5.8%) and 6.7% (95% CI, 2.2-13.2%) of cases, respectively. Coarctation of the aorta was associated with isolated PLSVC in 21.3% (95% CI, 13.6-30.3%) of cases.

CONCLUSIONS

PLSVC is commonly associated with ICAs, ECAs and chromosomal anomalies. Fetuses with isolated PLSVC should be followed up throughout pregnancy in order to rule out coarctation of the aorta. As most of the data in this review were derived from high-risk pregnancies, the rate of associated abnormalities is likely to be higher than that in the general population of fetuses with PLSVC, for which more data are needed. Revisión sistemática y metaanálisis de la persistencia de la vena cava superior izquierda en la ecografía prenatal: anomalías asociadas, precisión del diagnóstico y resultado postnatal RESUMEN OBJETIVOS: Cuantificar la prevalencia de anomalías cromosómicas en fetos con vena cava superior izquierda persistente (VCSIP), evaluar la solidez de la asociación entre la VCSIP y la coartación aórtica, y determinar la precisión del diagnóstico de la ecografía prenatal como método para identificar correctamente casos aislados de VCSIP. MÉTODOS: Se buscó en las bases de datos de MEDLINE, EMBASE, CINHAL y Cochrane artículos publicados desde el año 2000 en adelante, usando combinaciones de las palabras clave "vena cava superior izquierda" y "resultado". Dos de los autores revisaron de forma independiente todos los resúmenes encontrados. La evaluación de calidad de los estudios incluidos se realizó mediante la escala Newcastle-Ottawa para estudios de cohortes. Se analizaron las tasas de los siguientes resultados: anomalías cromosómicas; anomalías intracardíacas (AIC) y anomalías extracardíacas (AEC) asociadas diagnosticadas prenatalmente; AIC y AEC adicionales detectadas sólo en ecografías postnatales o mediante evaluación clínica, pero no observadas en ecografías prenatales; y la asociación entre la VCSIP y la coartación aórtica. Se utilizó un meta-análisis de proporciones para combinar los datos.

RESULTADOS

En total, se identificaron 2708 artículos y se incluyeron 13 (n = 501) en la revisión sistemática. En la ecografía prenatal o en una revisión de seguimiento se detectaron AIC y AEC asociadas en el 60,7% (IC 95%, 44,2-75,9%) y el 37,8% (IC 95%, 31,0-44,8%) de los casos, respectivamente. Se produjeron anomalías cromosómicas en el 12,5% (IC 95%, 9,0-16,4%) de los casos en la población general de fetos con VCSIP y en el 7,0% (IC 95%, 2,7-13,0%) de casos aislados. Las AIC y AEC adicionales sólo se detectaron después del nacimiento y en el 6,7% (IC 95%, 2,2-13,2%) de los casos, respectivamente. La coartación aórtica se encontró asociada con la VCSIP aislada en un 21,3% (IC 95%, 13,6-30,3%) de los casos.

CONCLUSIONES

La VCSIP está comúnmente asociada a AIC, AEC y anomalías cromosómicas. Los fetos con VCSIP aislada deben ser objeto de seguimiento durante todo el embarazo, con el fin de descartar la coartación aórtica. Como la mayoría de los datos de esta revisión proceden de embarazos de alto riesgo, es probable que la tasa de anomalías asociadas sea más alta que la de la población general de fetos con VCSIP, por lo que se necesitan más datos.

Adoptive T-cell therapy in the treatment of viral and opportunistic fungal infections

Viral infections and opportunistic fungal pathogens represent a major menace for immunocompromised patients. Despite the availability of antifungal and antiviral drugs, mortality in these patients remains high, underlining the need of novel therapeutic options based on completely different strategies. This review describes the potential of several T-cell-based therapeutic approaches in the prophylaxis and treatment of infectious diseases with a particular focus on persistent viral infections and opportunistic fungal infections, as these mostly affect immunocompromised patients.

Oxygen Tension Within the Neurogenic Niche Regulates Dopaminergic Neurogenesis in the Developing Midbrain

Oxygen tension is an important factor controlling stem cell proliferation and maintenance in various stem cell populations with a particular relevance in midbrain dopaminergic progenitors. Further studies have shown that the oxygen-dependent transcription factor hypoxia-inducible factor 1α (HIF-1α) is involved in these processes. However, all available studies on oxygen effects in dopaminergic neuroprogenitors were performed in vitro and thus it remains unclear whether tissue oxygen tension in the embryonic midbrain is also relevant for the regulation of dopaminergic neurogenesis in vivo. We thus dissect here the effects of oxygen tension in combination with HIF-1α conditional knockout on dopaminergic neurogenesis by using a novel experimental design allowing for the control of oxygen tension within the microenvironment of the neurogenic niche of the murine fetal midbrain in vivo. The microenvironment of the midbrain dopaminergic neurogenic niche was detected as hypoxic with oxygen tensions below 1.1%. Maternal oxygen treatment of 10%, 21%, and 75% atmospheric oxygen tension for 48 h translates into robust changes in fetal midbrain oxygenation. Fetal midbrain hypoxia hampered the generation of dopaminergic neurons and is accompanied with restricted fetal midbrain development. In contrast, induced hyperoxia stimulated proliferation and differentiation of dopaminergic progenitors during early and late embryogenesis. Oxygen effects were not directly mediated through HIF-1α signaling. These data--in agreement with in vitro data-indicate that oxygen is a crucial regulator of developmental dopaminergic neurogenesis. Our study provides the initial framework for future studies on molecular mechanisms mediating oxygen regulation of dopaminergic neurogenesis within the fetal midbrain as its natural environment.

Brain oxygen tension controls the expansion of outer subventricular zone-like basal progenitors in the developing mouse brain

The mammalian neocortex shows a conserved six-layered structure that differs between species in the total number of cortical neurons produced owing to differences in the relative abundance of distinct progenitor populations. Recent studies have identified a new class of proliferative neurogenic cells in the outer subventricular zone (OSVZ) in gyrencephalic species such as primates and ferrets. Lissencephalic brains of mice possess fewer OSVZ-like progenitor cells and these do not constitute a distinct layer. Most in vitro and in vivo studies have shown that oxygen regulates the maintenance, proliferation and differentiation of neural progenitor cells. Here we dissect the effects of fetal brain oxygen tension on neural progenitor cell activity using a novel mouse model that allows oxygen tension to be controlled within the hypoxic microenvironment in the neurogenic niche of the fetal brain in vivo. Indeed, maternal oxygen treatment of 10%, 21% and 75% atmospheric oxygen tension for 48 h translates into robust changes in fetal brain oxygenation. Increased oxygen tension in fetal mouse forebrain in vivo leads to a marked expansion of a distinct proliferative cell population, basal to the SVZ. These cells constitute a novel neurogenic cell layer, similar to the OSVZ, and contribute to corticogenesis by heading for deeper cortical layers as a part of the cortical plate.

Structural studies of the final enzyme in the alpha-aminoadipate pathway-saccharopine dehydrogenase from Saccharomyces cerevisiae

The 1.64 A structure of the apoenzyme form of saccharopine dehydrogenase (SDH) from Saccharomyces cerevisiae shows the enzyme to be composed of two domains with similar dinucleotide binding folds with a deep cleft at the interface. The structure reveals homology to alanine dehydrogenase, despite low primary sequence similarity. A model of the ternary complex of SDH, NAD, and saccharopine identifies residues Lys77 and Glu122 as potentially important for substrate binding and/or catalysis, consistent with a proton shuttle mechanism. Furthermore, the model suggests that a conformational change is required for catalysis and that residues Lys99 and Asp281 may be instrumental in mediating this change. Analysis of the crystal structure in the context of other homologous enzymes from pathogenic fungi and human sources sheds light into the suitability of SDH as a target for antimicrobial drug development.

Characterization of function and activity of domains A, B and C of xylanase C from Fibrobacter succinogenes S85

Xylanase C from the ruminant bacterium Fibrobacter succinogenes is comprised of two catalytic domains, A and B, and a third domain, C, of unknown function. The DNA coding for domains A and B of xylanase C were separately cloned and expressed in Escherichia coli as fusion proteins with glutathione-S:-transferase. The fusion proteins were isolated by affinity chromatography on glutathione-Sepharose 4B, cleaved with thrombin and the released xylanase C catalytic domains A and B were purified to apparent homogeneity by anion-exchange chromatography on Mono Q. Electrospray mass spectrometry provided a molecular mass of 27 818 Da (expected, 27 820 Da) for domain B. The pH and temperature optima for activity of domain B on oat spelt xylan were 5.0 and 52 degrees C, respectively. A kinetic analysis of the activity of the catalytic domain A on oat spelt xylan, birch wood xylan and xylooligomers at pH 6.5 and 37 degrees C provided data significantly different to those obtained previously with a protease-derived form of the enzyme [Zhu et al. (1994) J. Bacteriol. 176, 3885-3894]. The isolated domain A was more active on barley-glucan than the protease-derived form and its affinity for birch wood xylan was enhanced resulting in greater overall catalytic efficiency as reflected by k(cat)/K:(M) values. Likewise, significant differences in the Michaelis-Menten parameters K:(M), k(cat) and k(cat)/K:(M) were obtained with domain B compared with values previously reported with this domain attached to domain C. In general, the presence of domain C appeared to decrease the overall efficiency of domain B 7- and 36-fold with birch wood xylan and xylopentaose as substrates, respectively, as reflected by values of k(cat)/K:(M). The removal of domain C also affected the mode of action of domain B such that it more closely resembled that of catalytic domain A. However, no change in either pH and temperature optima or stability were found with domain B compared with the combined domains B and C. The function of domain C remains unknown, but hydrophobic cluster analysis indicated that it may belong to a class of dockerin domains involved in the protein-protein interactions of cellulolytic and xylanolytic complexes.

The role of tryptophan residues in substrate binding to catalytic domains A and B of xylanase C from Fibrobacter succinogenes S85

Oxidation of the isolated catalytic domain B of xylanase C (XynC-B) from Fibrobacter succinogenes with N-bromosuccinimide (NBS) resulted in the modification of five of the seven Trp residues present in the enzyme. Hydrolytic activity of the enzyme was rapidly lost upon initiation of oxidation as a molar ratio of about two NBS molecules per molar equivalent of protein was sufficient to cause 50% inhibition of enzyme activity, and the addition of five molar equivalents of NBS resulted in less than 10% activity. Pre-incubation of XynC-B with the competitive inhibitor D-xylose resulted in the apparent protection of two Trp residues from oxidation. Xylose protection of the enzyme also resulted in a maintenance of activity, with 60% activity still evident after addition of 8-9 molar equivalents of NBS. This protection from inactivation was enhanced by the inclusion of xylohexaose in reaction mixtures. Under these conditions, however, a further Trp residue was protected from NBS oxidation. The three protected Trp residues were identified as Trp135, Trp161 and Trp202 by differential labelling and peptide mapping of NBS-oxidized preparations of the xylanase employing a combination of electrospray mass spectroscopic analysis and N-terminal sequencing. By analogy to the known structures of the family 11 xylanases, the fully conserved Trp202 residue is located on the only alpha-helix present in the enzymes, at the interface between it and the back of the beta-sheet which forms the active site cleft. Trp135 represents a highly conserved aromatic residue in family 11, but it is replaced with Thr in domain A of F. succinogenes xylanase C. To investigate the role of Trp135 in conferring the different activity profile of domain B relative to domain A, the Trp135Thr and Trp135Ala derivatives of domain B were prepared by site-directed mutagenesis. However, the kinetic parameters of the two domain B derivatives were not significantly different compared to the wild-type enzyme as reflected by K(M) and k(cat) values and product distribution profiles. Similar results were obtained with the Trp161Ala derivative of domain B, indicating that these two residues do not directly participate in the binding of substrate but likely form the foundation for binding subsite 2.

Lysine: N6-hydroxylase: stability and interaction with ligands

Recombinant lysine:N6-hydroxylase, rIucD, which is isolated as an apoenzyme, requires FAD and NADPH for its catalytic function. rIucD preparations have been found to undergo time-dependent loss in monooxygenase function due to aggregation from the initial tetrameric state to a polytetrameric form(s), a process which is reversible by treatment with thiols. Ligand-induced conformational changes in rIucD were assessed by monitoring its CD spectra, DSC profile, and susceptibility to both endo- as well as exopeptidases. The first two methods indicated the absence of any significant conformational change in rIucD, while the last approach revealed that FAD, and its analog ADP, can protect the protein from the deleterious action of proteases. NADPH was partially effective and L-lysine was ineffective in this regard. Deletion of the C-terminal segment, either by treatment with carboxypeptidase Y or by mutagenesis of iucD, results in the loss of rIucD's monooxygenase activity. These findings demonstrate the crucial role of the C-terminal segment in maintaining rIucD in its native conformation.

Suppression of protein synthesis in brain during hibernation involves inhibition of protein initiation and elongation

Protein synthesis (PS) has been considered essential to sustain mammalian life, yet was found to be virtually arrested for weeks in brain and other organs of the hibernating ground squirrel, Spermophilus tridecemlineatus. PS, in vivo, was below the limit of autoradiographic detection in brain sections and, in brain extracts, was determined to be 0.04% of the average rate from active squirrels. Further, it was reduced 3-fold in cell-free extracts from hibernating brain at 37 degreesC, eliminating hypothermia as the only cause for protein synthesis inhibition (active, 0.47 +/- 0.08 pmol/mg protein per min; hibernator, 0.16 +/- 0.05 pmol/mg protein per min, P < 0.001). PS suppression involved blocks of initiation and elongation, and its onset coincided with the early transition phase into hibernation. An increased monosome peak with moderate ribosomal disaggregation in polysome profiles and the greatly increased phosphorylation of eIF2alpha are both consistent with an initiation block in hibernators. The elongation block was demonstrated by a 3-fold increase in ribosomal mean transit times in cell-free extracts from hibernators (active, 2.4 +/- 0.7 min; hibernator, 7.1 +/- 1.4 min, P < 0.001). No abnormalities of ribosomal function or mRNA levels were detected. These findings implicate suppression of PS as a component of the regulated shutdown of cellular function that permits hibernating ground squirrels to tolerate "trickle" blood flow and reduced substrate and oxygen availability. Further study of the factors that control these phenomena may lead to identification of the molecular mechanisms that regulate this state.

Effect of selective cysteine --> alanine replacements on the catalytic functions of lysine: N6-hydroxylase

Recombinant lysine: N6-hydroxylase, rIucD, catalyzes the conversion of L-lysine to its N6-hydroxy derivative. Re-examination of the nucleotide sequence of iucD, the gene encoding for the enzyme, has revealed a few discrepancies in the data documented in literature and the corrected version is presented. The revised nucleotide sequence predicts the presence of five cysteine residues in the primary structure of IucD. Two of these residues, cysteine 51 and cysteine 158 are alkylatable by iodoacetate in the native conformation of the protein resulting in a loss of monooxygenase activity while their replacement with alanine has no such adverse effect. Site directed mutagenesis studies have enabled an assessment of the reactivity of these cysteine residue(s) towards thiol modifying agents.