Endosomal accumulation of Toll-like receptor 4 causes constitutive secretion of cytokines and activation of signal transducers and activators of transcription in Niemann-Pick disease type C (NPC) fibroblasts: a potential basis for glial cell activation in the NPC brain

Enhanced mGluR5 intracellular activity causes psychiatric alterations in Niemann Pick type C disease

Niemann-Pick disease Type C (NPC) is caused by mutations in the cholesterol transport protein NPC1 leading to the endolysosomal accumulation of the lipid and to psychiatric alterations. Using an NPC mouse model (Npc1nmf164) we show aberrant mGluR5 lysosomal accumulation and reduction at plasma membrane in NPC1 deficient neurons. This phenotype was induced in wild-type (wt) neurons by genetic and pharmacological NPC1 silencing. Extraction of cholesterol normalized mGluR5 distribution in NPC1-deficient neurons. Intracellular accumulation of mGluR5 was functionally active leading to enhanced mGluR-dependent long-term depression (mGluR-LTD) in Npc1nmf164 hippocampal slices. mGluR-LTD was lower or higher in Npc1nmf164 slices compared with wt when stimulated with non-membrane-permeable or membrane-permeable mGluR5 agonists, respectively. Oral treatment with the mGluR5 antagonist 2-chloro-4-((2,5-dimethyl-1-(4-(trifluoromethoxy)phenyl)-1H-imidazol-4-yl)ethynyl)pyridine (CTEP) reduced mGluR-LTD and ameliorated psychiatric anomalies in the Npc1nmf164 mice. Increased neuronal mGluR5 levels were found in an NPC patient. These results implicate mGluR5 alterations in NPC psychiatric condition and provide a new therapeutic strategy that might help patients suffering from this devastating disease.

NPC1 links cholesterol trafficking to microglial morphology via the gastrosome

Microglia play important roles in brain development and homeostasis by removing dying neurons through efferocytosis. Morphological changes in microglia are hallmarks of many neurodegenerative conditions, such as Niemann-Pick disease type C. Here, NPC1 loss causes microglia to shift from a branched to an ameboid form, though the cellular basis and functional impact of this change remain unclear. Using zebrafish, we show that NPC1 deficiency causes an efferocytosis-dependent expansion of the microglial gastrosome, a collection point for engulfed material. In vivo and in vitro experiments on microglia and mammalian macrophages demonstrate that NPC1 localizes to the gastrosome, and its absence leads to cholesterol accumulation in this compartment. NPC1 loss and neuronal cell death synergistically affect gastrosome size and cell shape, increasing the sensitivity of NPC1-deficient cells to neuronal cell death. Finally, we demonstrate conservation of cholesterol accumulation and gastrosome expansion in NPC patient-derived fibroblasts, offering an interesting target for further disease investigation.

A Potential Role for the Amyloid Precursor Protein in the Regulation of Interferon Signaling, Cholesterol Homeostasis, and Tau Phosphorylation in Niemann-Pick Disease Type C

Niemann-Pick disease type C (NPC) is a rare and fatal neurological disorder caused by mutations in Npc1 or Npc2, with Npc1 accounting for 95% of cases. These mutations result in the functional loss of their respective proteins, causing cellular abnormalities characterized by disrupted lipid dysregulation, calcium dysfunction, elevated damage associated molecular patterns (DAMPs), and a pro-inflammatory environment. This cellular pathology ultimately triggers neurodegeneration, with the cerebellum being the earliest and most affected region. We have recently shown atypical activation of interferon signaling in the presymptomatic Npc1-/- mouse cerebellum and, to a lesser extent, in the cerebral cortex. In addition, we reported that the Amyloid Precursor Protein (APP) is an NPC disease modifier. Loss of APP function leads to widespread neurodegeneration in the NPC brain, including exacerbated interferon signaling in the cerebellum. To better understand the role of APP as a disease modifier throughout the NPC brain, here we carried out a transcriptomic analysis of the cerebral cortex and cerebellum from 3-week-old Npc1-/- mice as well as age-matched controls in the presence and absence of APP. We report differential effects of APP loss of function in the cerebral cortex and cerebellum, including cholesterol and tau dysregulation, in both brain regions. Our findings demonstrate a novel link between APP loss and early pathogenic mechanisms in NPC.

Sterol O-Acyltransferase 1 (SOAT1): A Genetic Modifier of Niemann-Pick Disease, Type C1

Niemann-Pick disease type C1 (NPC1) is a lysosomal disorder due to impaired intracellular cholesterol transport out of the endolysosomal compartment.. Marked heterogeneity has been observed in individuals with the same NPC1 genotype, thus suggesting a significant effect of modifier genes. Prior work demonstrated that decreased SOAT1 activity decreased disease severity in an NPC1 mouse model. Thus, we hypothesized that a polymorphism associated with decreased SOAT1 expression might influence the NPC1 phenotype. Phenotyping and genomic sequencing of 117 individuals with NPC1 was performed as part of a Natural History trial. Phenotyping included determination of disease severity and disease burden. Significant clinical heterogeneity is present in individuals homozygous for the NPC1I1061T variant and in siblings. Analysis of the SOAT1 polymorphism, rs1044925 (A>C), showed a significant association of the C-allele with earlier age of neurological onset. The C-allele may be associated with a higher Annualized Severity Index Score as well as increased frequency of liver disease and seizures. A polymorphism associated with decreased expression of SOAT1 appears to be a genetic modifier of the NPC1 phenotype. This finding is consistent with prior data showing decreased phenotypic severity in Npc1-/-:Soat1-/- mice and supports efforts to investigate the potential of SOAT1 inhibitors as a potential therapy for NPC1.

Fabry Disease: Cardiac Implications and Molecular Mechanisms

PURPOSE OF REVIEW

This review explores the interplay among metabolic dysfunction, oxidative stress, inflammation, and fibrosis in Fabry disease, focusing on their potential implications for cardiac involvement. We aim to discuss the biochemical processes that operate in parallel to sphingolipid accumulation and contribute to disease pathogenesis, emphasizing the importance of a comprehensive understanding of these processes.

RECENT FINDINGS

Beyond sphingolipid accumulation, emerging studies have revealed that mitochondrial dysfunction, oxidative stress, and chronic inflammation could be significant contributors to Fabry disease and cardiac involvement. These factors promote cardiac remodeling and fibrosis and may predispose Fabry patients to conduction disturbances, ventricular arrhythmias, and heart failure. While current treatments, such as enzyme replacement therapy and pharmacological chaperones, address disease progression and symptoms, their effectiveness is limited. Our review uncovers the potential relationships among metabolic disturbances, oxidative stress, inflammation, and fibrosis in Fabry disease-related cardiac complications. Current findings suggest that beyond sphingolipid accumulation, other mechanisms may significantly contribute to disease pathogenesis. This prompts the exploration of innovative therapeutic strategies and underscores the importance of a holistic approach to understanding and managing Fabry disease.

Differential Interferon Signaling Regulation and Oxidative Stress Responses in the Cerebral Cortex and Cerebellum Could Account for the Spatiotemporal Pattern of Neurodegeneration in Niemann-Pick Disease Type C

Niemann-Pick disease type C (NPC) is a fatal neurodegenerative condition caused by genetic mutations of the NPC1 or NPC2 genes that encode the NPC1 and NPC2 proteins, respectively, which are believed to be responsible for cholesterol efflux from late-endosomes/lysosomes. The pathogenic mechanisms that lead to neurodegeneration in NPC are not well understood. There are, however, well-defined spatiotemporal patterns of neurodegeneration that may provide insight into the pathogenic process. For example, the cerebellum is severely affected from early disease stages, compared with cerebral regions, which remain relatively spared until later stages. Using a genome-wide transcriptome analysis, we have recently identified an aberrant pattern of interferon activation in the cerebella of pre-symptomatic Npc1-/- mice. Here, we carried out a comparative transcriptomic analysis of cerebral cortices and cerebella of pre-symptomatic Npc1-/- mice and age-matched controls to identify differences that may help explain the pathological progression within the NPC brain. We report lower cerebral expression of genes within interferon signaling pathways, and significant differences in the regulation of oxidative stress, compared with the cerebellum. Our findings suggest that a delayed onset of interferon signaling, possibly linked to lower oxidative stress, may account for the slower onset of cerebral cortical pathology in the disease.

Time-Course Progression of Whole Transcriptome Expression Changes of Trigeminal Ganglia Compared to Dorsal Root Ganglia in Rats Exposed to Nerve Injury

Mechanisms underlying neuropathic pain (NP) are complex with multiple genes, their interactions, environmental and epigenetic factors being implicated. Transcriptional changes in the trigeminal (TG) and dorsal root (DRG) ganglia have been implicated in the development and maintenance of NP. Despite efforts to unravel molecular mechanisms of NP, many remain unknown. Also, most of the studies focused on the spinal system. Although the spinal and trigeminal systems share some of the molecular mechanisms, differences exist. We used RNA-sequencing technology to identify differentially expressed genes (DEGs) in the TG and DRG at baseline and 3 time points following the infraorbital or sciatic nerve injuries, respectively. Pathway analysis and comparison analysis were performed to identify differentially expressed pathways. Additionally, upstream regulator effects were investigated in the two systems. DEG (differentially expressed genes) analyses identified 3,225 genes to be differentially expressed between TG and DRG in naïve animals, 1,828 genes 4 days post injury, 5,644 at day 8 and 9,777 DEGs at 21 days postinjury. A comparison of top enriched canonical pathways revealed that a number of signaling pathway was significantly inhibited in the TG and activated in the DRG at 21 days postinjury. Finally, CORT upstream regulator was predicted to be inhibited in the TG while expression levels of the CSF1 upstream regulator were significantly elevated in the DRG at 21 days postinjury. This study provides a basis for further in-depth studies investigating transcriptional changes, pathways, and upstream regulation in TG and DRG in rats exposed to peripheral nerve injuries. PERSPECTIVE: Although trigeminal and dorsal root ganglia are homologs of each other, they respond differently to nerve injury and therefore treatment. Activation/inhibition of number of biological pathways appear to be ganglion/system specific suggesting that different approaches might be required to successfully treat neuropathies induced by injuries in spinal and trigeminal systems.

Peripheral immune system modulates Purkinje cell degeneration in Niemann-Pick disease type C1

Niemann-Pick disease type C1 (NPC1) is a fatal lysosomal storage disorder characterized by progressive neuronal degeneration. Its key pathogenic events remain largely unknown. We have, herein, found that neonatal BM-derived cell transplantation can ameliorate Purkinje cell degeneration in NPC1 mice. We subsequently addressed the impact of the peripheral immune system on the neuropathogenesis observed in NPC1 mice. The depletion of mature lymphocytes promoted NPC1 phenotypes, thereby suggesting a neuroprotective effect of lymphocytes. Moreover, the peripheral infusion of CD4-positive cells (specifically, of regulatory T cells) from normal healthy donor ameliorated the cerebellar ataxic phenotype and enhanced the survival of Purkinje cells. Conversely, the depletion of regulatory T cells enhanced the onset of the neurological phenotype. On the other hand, circulating inflammatory monocytes were found to be involved in the progression of Purkinje cell degeneration, whereas the depletion of resident microglia had little effect. Our findings reveal a novel role of the adaptive and the innate immune systems in NPC1 neuropathology.

Hypoxia-altered cholesterol homeostasis enhances the expression of interferon-stimulated genes upon SARS-CoV-2 infections in monocytes

Hypoxia contributes to numerous pathophysiological conditions including inflammation-associated diseases. We characterized the impact of hypoxia on the immunometabolic cross-talk between cholesterol and interferon (IFN) responses. Specifically, hypoxia reduced cholesterol biosynthesis flux and provoked a compensatory activation of sterol regulatory element-binding protein 2 (SREBP2) in monocytes. Concomitantly, a broad range of interferon-stimulated genes (ISGs) increased under hypoxia in the absence of an inflammatory stimulus. While changes in cholesterol biosynthesis intermediates and SREBP2 activity did not contribute to hypoxic ISG induction, intracellular cholesterol distribution appeared critical to enhance hypoxic expression of chemokine ISGs. Importantly, hypoxia further boosted chemokine ISG expression in monocytes upon infection with severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). Mechanistically, hypoxia sensitized toll-like receptor 4 (TLR4) signaling to activation by SARS-CoV-2 spike protein, which emerged as a major signaling hub to enhance chemokine ISG induction following SARS-CoV-2 infection of hypoxic monocytes. These data depict a hypoxia-regulated immunometabolic mechanism with implications for the development of systemic inflammatory responses in severe cases of coronavirus disease-2019 (COVID-19).

Investigation of 2-Hydroxypropyl-β-Cyclodextrin Treatment in a Neuronal-Like Cell Model of Niemann-Pick Type C Using Quantitative Proteomics

Niemann-Pick, type C (NPC) is a fatal, neurovisceral lysosomal storage disorder with progressive neurodegeneration and no FDA-approved therapy. Significant efforts have been focused on the development of therapeutic options, and 2-hydroxypropyl-β-cyclodextrin (HP-b-CD) has emerged as a promising candidate. In cell culture, HP-b-CD ameliorates cholesterol storage in endo/lysosomes, a hallmark of the disorder. Furthermore, in animal studies, treatment with HP-b-CD delays neurodegeneration and extends lifespan. While HP-b-CD has been promising in vitro and in vivo, a clear understanding of the mechanism(s) of action is lacking. Utilizing a neuron-like cell culture model of SH-SY5Y differentiated cells and U18666A to induce the NPC phenotype, we report here a large-scale mass-spectrometry-based proteomic study to evaluate proteome changes upon treatment with these small molecules. In this study, we show that differentiated SH-SY5Y cells display morphological changes representative of neuronal-like cells along with increased levels of proliferation markers. Inhibition of the NPC cholesterol transporter 1 protein by U18666A resulted in increased levels of known NPC markers including SCARB2/LIMP2 and LAMP2. Finally, investigation of HP-b-CD treatment was performed where we observe that, although HP-b-CD reduces cholesterol storage, levels of NPC1 and NPC2 are not normalized to control levels. This finding further supports the need for a proteostasis strategy for NPC drug development. Moreover, proteins that were dysregulated in the U18666A model of NPC and normalized to control levels suggest that HP-b-CD promotes exocytosis in this neuron-like model. Utilizing state of the art mass spectrometry analysis, these data demonstrate newly reported changes with pharmacological perturbations related to NPC disease and provide insight into the mechanisms of HP-b-CD as a potential therapeutic.

Defective iron homeostasis and hematological abnormalities in Niemann-Pick disease type C1

Background: Niemann-Pick disease type C1 (NPC1) is a neurodegenerative lysosomal storage disorder characterized by the accumulation of multiple lipids in the late endosome/lysosomal system and reduced acidic store calcium. The lysosomal system regulates key aspects of iron homeostasis, which prompted us to investigate whether there are hematological abnormalities and iron metabolism defects in NPC1. Methods: Iron-related hematological parameters, systemic and tissue metal ion and relevant hormonal and proteins levels, expression of specific pro-inflammatory mediators and erythrophagocytosis were evaluated in an authentic mouse model and in a large cohort of NPC patients. Results: Significant changes in mean corpuscular volume and corpuscular hemoglobin were detected in Npc1 -/- mice from an early age. Hematocrit, red cell distribution width and hemoglobin changes were observed in late-stage disease animals. Systemic iron deficiency, increased circulating hepcidin, decreased ferritin and abnormal pro-inflammatory cytokine levels were also found. Furthermore, there is evidence of defective erythrophagocytosis in Npc1 -/- mice and in an in vitro NPC1 cellular model. Comparable hematological changes, including low normal serum iron and transferrin saturation and low cerebrospinal fluid ferritin were confirmed in NPC1 patients. Conclusions: These data suggest loss of iron homeostasis and hematological abnormalities in NPC1 may contribute to the pathophysiology of this disease.

Exploring Pro-Inflammatory Immunological Mediators: Unraveling the Mechanisms of Neuroinflammation in Lysosomal Storage Diseases

Lysosomal storage diseases are a group of rare and ultra-rare genetic disorders caused by defects in specific genes that result in the accumulation of toxic substances in the lysosome. This excess accumulation of such cellular materials stimulates the activation of immune and neurological cells, leading to neuroinflammation and neurodegeneration in the central and peripheral nervous systems. Examples of lysosomal storage diseases include Gaucher, Fabry, Tay–Sachs, Sandhoff, and Wolman diseases. These diseases are characterized by the accumulation of various substrates, such as glucosylceramide, globotriaosylceramide, ganglioside GM2, sphingomyelin, ceramide, and triglycerides, in the affected cells. The resulting pro-inflammatory environment leads to the generation of pro-inflammatory cytokines, chemokines, growth factors, and several components of complement cascades, which contribute to the progressive neurodegeneration seen in these diseases. In this study, we provide an overview of the genetic defects associated with lysosomal storage diseases and their impact on the induction of neuro-immune inflammation. By understanding the underlying mechanisms behind these diseases, we aim to provide new insights into potential biomarkers and therapeutic targets for monitoring and managing the severity of these diseases. In conclusion, lysosomal storage diseases present a complex challenge for patients and clinicians, but this study offers a comprehensive overview of the impact of these diseases on the central and peripheral nervous systems and provides a foundation for further research into potential treatments.

Loss of NPC1 enhances phagocytic uptake and impairs lipid trafficking in microglia

Niemann-Pick type C disease is a rare neurodegenerative disorder mainly caused by mutations in NPC1, resulting in abnormal late endosomal/lysosomal lipid storage. Although microgliosis is a prominent pathological feature, direct consequences of NPC1 loss on microglial function remain not fully characterized. We discovered pathological proteomic signatures and phenotypes in NPC1-deficient murine models and demonstrate a cell autonomous function of NPC1 in microglia. Loss of NPC1 triggers enhanced phagocytic uptake and impaired myelin turnover in microglia that precede neuronal death. Npc1^−/− microglia feature a striking accumulation of multivesicular bodies and impaired trafficking of lipids to lysosomes while lysosomal degradation function remains preserved. Molecular and functional defects were also detected in blood-derived macrophages of NPC patients that provide a potential tool for monitoring disease. Our study underscores an essential cell autonomous role for NPC1 in immune cells and implies microglial therapeutic potential.

Niemann-Pick type C disease is a rare childhood neurodegenerative disorder predominantly caused by mutations in NPC1, resulting in abnormal late endosomal and lysosomal defects. Here the authors show that NPC1 disruption largely impairs microglial function.

Toll-like receptor mediated lysozyme expression in Niemann-pick disease, type C1

Niemann-Pick type C1 (NPC1) is a rare neurodegenerative disease. In NPC1 mouse cerebella, the antibacterial enzyme, lysozyme (Lyz2), is significantly increased in multiple cell types. Due to its possible role in toxic fibril deposition, we confirmed Lyz2 overexpression in culture in different control and NPC1 cell types including human NPC1 fibroblasts. Lyz2 expression is induced by Toll-like receptors potentially in response to lipid storage but does not play a functional role in NPC disease pathology.

TLR4 and CD14 trafficking and its influence on LPS-induced pro-inflammatory signaling

Toll-like receptor (TLR) 4 belongs to the TLR family of receptors inducing pro-inflammatory responses to invading pathogens. TLR4 is activated by lipopolysaccharide (LPS, endotoxin) of Gram-negative bacteria and sequentially triggers two signaling cascades: the first one involving TIRAP and MyD88 adaptor proteins is induced in the plasma membrane, whereas the second engaging adaptor proteins TRAM and TRIF begins in early endosomes after endocytosis of the receptor. The LPS-induced internalization of TLR4 and hence also the activation of the TRIF-dependent pathway is governed by a GPI-anchored protein, CD14. The endocytosis of TLR4 terminates the MyD88-dependent signaling, while the following endosome maturation and lysosomal degradation of TLR4 determine the duration and magnitude of the TRIF-dependent one. Alternatively, TLR4 may return to the plasma membrane, which process is still poorly understood. Therefore, the course of the LPS-induced pro-inflammatory responses depends strictly on the rates of TLR4 endocytosis and trafficking through the endo-lysosomal compartment. Notably, prolonged activation of TLR4 is linked with several hereditary human diseases, neurodegeneration and also with autoimmune diseases and cancer. Recent studies have provided ample data on the role of diverse proteins regulating the functions of early, late, and recycling endosomes in the TLR4-induced inflammation caused by LPS or phagocytosis of E. coli. In this review, we focus on the mechanisms of the internalization and intracellular trafficking of TLR4 and CD14, and also of LPS, in immune cells and discuss how dysregulation of the endo-lysosomal compartment contributes to the development of diverse human diseases.

Adenovirus Reveals New Pathway for Cholesterol Egress from the Endolysosomal System

In addition to providing invaluable insights to the host response to viral infection, adenovirus continues to be an important model system for discovering basic aspects of cell biology. This is especially true for products of early region three (E3), which have provided the foundation for understanding many new mechanisms regulating intracellular trafficking of host cell proteins involved in the host immune response. Cholesterol homeostasis is vital for proper cellular physiology, and disturbances in cholesterol balance are increasingly recognized as important factors in human disease. Despite its central role in numerous aspects of cellular functions, the mechanisms responsible for delivery of dietary cholesterol to the endoplasmic reticulum, where the lipid metabolic and regulatory machinery reside, remain poorly understood. In this review, we describe a novel intracellular pathway for cholesterol trafficking that has been co-opted by an adenovirus E3 gene product. We describe what is known about the molecular regulation of this pathway, how it might benefit viral replication, and its potential involvement in normal cell physiology. Finally, we make a case that adenovirus has co-opted a cellular pathway that may be dysregulated in various human diseases.

Single Cell Transcriptome Analysis of Niemann-Pick Disease, Type C1 Cerebella

Niemann-Pick disease, type C1 (NPC1) is a lysosomal disease characterized by endolysosomal storage of unesterified cholesterol and decreased cellular cholesterol bioavailability. A cardinal symptom of NPC1 is cerebellar ataxia due to Purkinje neuron loss. To gain an understanding of the cerebellar neuropathology we obtained single cell transcriptome data from control (Npc1^+/+) and both three-week-old presymptomatic and seven-week-old symptomatic mutant (Npc1^-/-) mice. In seven-week-old Npc1^-/- mice, differential expression data was obtained for neuronal, glial, vascular, and myeloid cells. As anticipated, we observed microglial activation and increased expression of innate immunity genes. We also observed increased expression of innate immunity genes by other cerebellar cell types, including Purkinje neurons. Whereas neuroinflammation mediated by microglia may have both neuroprotective and neurotoxic components, the contribution of increased expression of these genes by non-immune cells to NPC1 pathology is not known. It is possible that dysregulated expression of innate immunity genes by non-immune cells is neurotoxic. We did not anticipate a general lack of transcriptomic changes in cells other than microglia from presymptomatic three-week-old Npc1^-/- mice. This observation suggests that microglia activation precedes neuronal dysfunction. The data presented in this paper will be useful for generating testable hypotheses related to disease progression and Purkinje neurons loss as well as providing insight into potential novel therapeutic interventions.

Ultrastructure of spinal anterior horn cells in human Niemann-Pick type C (NPC) patient and mouse model of NPC with retroposon insertion in NPC1 genes

Niemann-Pick disease type C (NPC) is a neurovisceral lipid-storage disease. Although NPC patients show lipid storage in anterior horn cells of the spinal cord, little information is available regarding the electron microscopic analyses of the morphologies of intra-endosomal lipid like-materials in the anterior horn cells of NPC patients. In this study, we elucidated the intra-endosomal ultrastructures in spinal anterior horn cells in an NPC patient, as well as in mutant BALB/c NPC1^-/- mice with a retroposon insertion in the NPC1 gene. These morphologies were classified into four types: vesicle, multiple concentric sphere (MCS), membrane, and rose flower. The percentages of the composition in the NPC patient and NPC1^-/- mice were: vesicle (55.5% and 14.9%), MCS (15.7% and 3.4%), membrane (23.6% and 57.1%), and rose flower (5.2% and 24.6%), respectively. Formation of the intra-endosomal structures could proceed as follows: (i) a vesicle or MCS buds off the endosome into the lumen; (ii) when a vesicle breaks down, a membrane is formed; and (iii) after an MCS breaks down, a rose flower structure is formed. Our new finding in this study is that ultrastructural morphology is the same between the NPC patient and NPC1^-/- mice, although there are differences in the composition.

Complement Component C3 Participates in Early Stages of Niemann-Pick C Mouse Liver Damage

Niemann–Pick type C (NPC), a lysosomal storage disorder, is mainly caused by mutations in the NPC1 gene. Niemann–Pick type C patients and mice show intracellular cholesterol accumulation leading to hepatic failure with increased inflammatory response. The complement cascade, which belongs to the innate immunity response, recognizes danger signals from injured tissues. We aimed to determine whether there is activation of the complement system in the liver of the NPC mouse and to assess the relationship between C3 activation, a final component of the pathway, and NPC liver pathology. Niemann–Pick type C mice showed high levels of C3 staining in the liver which unexpectedly decreased with aging. Using an inducible NPC1 hepatocyte rescue mouse model, we restored NPC1 expression for a short time in young mice. We found C3 positive cells only in non-rescued cells, suggesting that C3 activation in NPC cells is reversible. Then, we studied the effect of C3 ablation on NPC liver damage at two postnatal time points, P56 and P72. Deletion of C3 reduced the presence of hepatic CD68-positive cells at postnatal day 56 and prevented the increase of transaminase levels in the blood of NPC mice. These positive effects were abrogated at P72, indicating that the complement cascade participates only during the early stages of liver damage in NPC mice, and that its inhibition may serve as a new potential therapeutic strategy for the disease.

Maternal immune activation modifies the course of Niemann-pick disease, type C1 in a gender specific manner

Niemann-Pick disease, type C1 (NPC1) is a rare neurodegenerative lysosomal storage disease with a wide spectrum of clinical manifestation. Multiple genetic factors influence the NPC1 mouse phenotype, but very little attention has been given to prenatal environmental factors that might have long-term effects on the neuroinflammatory component of NPC1 pathology. Studies in other mouse models of cerebellar ataxia have shown that developmental exposures lead to Purkinje neuron degeneration later in life, suggesting that environmental exposures during development can impact cerebellar biology. Thus, we evaluated the potential effect of maternal immune activation (MIA) on disease progression in an Npc1 mouse model. The MIA paradigm used mimics viral infection using the toll like receptor 3 agonist polyinosinic-polycytidilic acid during gestation. Through phenotypic and pathologic tests, we measured motor and behavioral changes as well as cerebellar neuroinflammation and neurodegeneration. We observed a gender and genotype dependent effect of MIA on the cerebellum. While the effects of MIA have been previously shown to primarily affect male progeny, we observed increased sensitivity of female mutant progeny to prenatal exposure to treatment with polyinosinic-polycytidilic acid. Specifically, prenatal MIA resulted in female NPC1 mutant progeny with greater motor deficits and a corresponding decrease in cerebellar Purkinje neurons. Our data suggest that prenatal environmental exposures may be one factor contributing to the phenotypic variability observed in individuals with NPC1.

Identification of Novel Pathways Associated with Patterned Cerebellar Purkinje Neuron Degeneration in Niemann-Pick Disease, Type C1

Niemann-Pick disease, type C1 (NPC1) is a lysosomal disease characterized by progressive cerebellar ataxia. In NPC1, a defect in cholesterol transport leads to endolysosomal storage of cholesterol and decreased cholesterol bioavailability. Purkinje neurons are sensitive to the loss of NPC1 function. However, degeneration of Purkinje neurons is not uniform. They are typically lost in an anterior-to-posterior gradient with neurons in lobule X being resistant to neurodegeneration. To gain mechanistic insight into factors that protect or potentiate Purkinje neuron loss, we compared RNA expression in cerebellar lobules III, VI, and X from control and mutant mice. An unexpected finding was that the gene expression differences between lobules III/VI and X were more pronounced than those observed between mutant and control mice. Functional analysis of genes with anterior to posterior gene expression differences revealed an enrichment of genes related to neuronal cell survival within the posterior cerebellum. This finding is consistent with the observation, in multiple diseases, that posterior Purkinje neurons are, in general, resistant to neurodegeneration. To our knowledge, this is the first study to evaluate anterior to posterior transcriptome-wide changes in gene expression in the cerebellum. Our data can be used to not only explore potential pathological mechanisms in NPC1, but also to further understand cerebellar biology.

New Insights to Adenovirus-Directed Innate Immunity in Respiratory Epithelial Cells

The nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) family of transcription factors is a key component of the host innate immune response to infectious adenoviruses and adenovirus vectors. In this review, we will discuss a regulatory adenoviral protein encoded by early region 3 (E3) called E3-RIDα, which targets NFκB through subversion of novel host cell pathways. E3-RIDα down-regulates an EGF receptor signaling pathway, which overrides NFκB negative feedback control in the nucleus, and is induced by cell stress associated with viral infection and exposure to the pro-inflammatory cytokine TNF-α. E3-RIDα also modulates NFκB signaling downstream of the lipopolysaccharide receptor, Toll-like receptor 4, through formation of membrane contact sites controlling cholesterol levels in endosomes. These innate immune evasion tactics have yielded unique perspectives regarding the potential physiological functions of host cell pathways with important roles in infectious disease.

Differential Proteomics Reveals miR-155 as a Novel Indicator of Liver and Spleen Pathology in the Symptomatic Niemann-Pick Disease, Type C1 Mouse Model

Niemann-Pick disease, type C1 (NPC1) is a rare, autosomal recessive, lipid storage disorder caused by mutations in NPC1. As a result, there is accumulation of unesterified cholesterol and sphingolipids in the late endosomal/lysosomal system. Clinically, patients can present with splenomegaly and hepatomegaly. In the current study, we analyzed the differential proteome of the spleen in symptomatic Npc1-/- mice to complement previous studies focused on the differential proteome of the liver, and then evaluated biomolecules that may serve as tissue biomarkers. The proteomic analysis revealed altered pathways in NPC1 representing different functional categories including heme synthesis, cellular regulation and phosphoinositide metabolism in both tissues. Differential proteins included several activators of the ubiquitous and critical protein, Akt, a major kinase involved in multiple cellular processes. Evaluation of Akt revealed decreased expression in both the liver and spleen tissues of symptomatic Npc1-/- mice. Upstream regulation analysis also suggested that miR-155 may modulate the differences of known downstream protein targets observed in our dataset. Upon evaluation of miR-155, we observed an increased expression in the liver and decreased expression in the spleen of symptomatic Npc1-/- mice. Here, we propose that miR-155 may be a novel indicator of spleen and liver pathology in NPC1.

Necroptosis inhibition as a therapy for Niemann-Pick disease, type C1: Inhibition of RIP kinases and combination therapy with 2-hydroxypropyl-β-cyclodextrin

Niemann-Pick disease, type C1 (NPC1) is an inborn error of metabolism that results in endolysosomal accumulation of unesterified cholesterol. Clinically, NPC1 manifests as cholestatic liver disease in the newborn or as a progressive neurogenerative condition characterized by cerebellar ataxia and cognitive decline. Currently there are no FDA approved therapies for NPC1. Thus, understanding the pathological processes that contribute to neurodegeneration will be important in both developing and testing potential therapeutic interventions. Neuroinflammation and necroptosis contribute to the NPC1 pathological cascade. Receptor Interacting Protein Kinase 1 and 3 (RIPK1 and RIPK3), are protein kinases that play a central role in mediating neuronal necroptosis. Our prior work suggested that pharmacological inhibition of RIPK1 had a significant but modest beneficial effect; however, the inhibitors used in that study had suboptimal pharmacokinetic properties. In this work we evaluated both pharmacological and genetic inhibition of RIPK1 kinase activity. Lifespan in both Npc1^-/- mice treated with GSK'547, a RIPK1 inhibitor with better pharmacokinetic properties, and Npc1^-/-:Ripk1^kd/kd double mutant mice was significantly increased. In both cases the increase in lifespan was modest, suggesting that the therapeutic potential of RIPK1 inhibition, as a monotherapy, is limited. We thus investigated the potential of combining RIPK1 inhibition with 2-hydroxypropyl-β-cyclodextrin (HPβCD) therapy HPβCD has been shown to slow neurological disease progression in NPC1 mice, cats and patients. HPβCD appeared to have an additive positive effect on the pathology and survival of Npc1^-/-:Ripk1^kd/kd mice. RIPK1 and RIPK3 are both critical components of the necrosome, thus we were surprised to observe no increase survival in Npc1^-/-;Ripk3^-/- mice compared to Npc1^-/- mice. These data suggest that although necroptosis is occurring in NPC1, the observed effects of RIPK1 inhibition may be related to its RIPK3-independent role in neuroinflammation and cytokine production.

The Role of Efferocytosis in Autoimmune Diseases

Apoptosis happens continuously for millions of cells along with the active removal of apoptotic debris in order to maintain tissue homeostasis. In this respect, efferocytosis, i.e., the process of dead cell clearance, is orchestrated through cell exposure of a set of "find me," "eat me," and "tolerate me" signals facilitating the engulfment of dying cells through phagocytosis by macrophages and dendritic cells. The clearance of dead cells via phagocytes is of utmost importance to maintain the immune system tolerance to self-antigens. Accordingly, this biological activity prevents the release of autoantigens by dead cells, thus potentially suppressing the undesirable autoreactivity of immune cells and the appearance of inflammatory autoimmune disorders as systemic lupus erythematous and rheumatoid arthritis. In the present study, the apoptosis pathways and their immune regulation were reviewed. Moreover, efferocytosis process and its impairment in association with some autoimmune diseases were discussed.

Microglia activation in Niemann-Pick disease, type C1 is amendable to therapeutic intervention

Niemann-Pick disease, type C1 (NPC1) is a neurodegenerative disorder with limited treatment options. NPC1 is associated with neuroinflammation; however, attempts to therapeutically target neuroinflammation in NPC1 have had mixed success. We show here that NPC1 neuroinflammation is characterized by an atypical microglia activation phenotype. Specifically, Npc1-/- microglia demonstrated altered morphology, reduced levels of lineage markers and a shift toward glycolytic metabolism. Treatment with 2-hydroxypropyl-β-cyclodextrin (HPβCD), a drug currently being studied in a phase 2b/3 clinical trial, reversed all microglia-associated defects in Npc1-/- animals. In addition, impairing microglia mediated neuroinflammation by genetic deletion of IRF8 led to decreased symptoms and increased lifespan. We identified CD22 as a marker of dysregulated microglia in Npc1 mutant mice and subsequently demonstrated that elevated cerebrospinal fluid levels of CD22 in NPC1 patients responds to HPβCD administration. Collectively, these data provide the first in-depth analysis of microglia function in NPC1 and suggest possible new therapeutic approaches.

Niemann-Pick Type C2 Protein Regulates Free Cholesterol Accumulation and Influences Hepatic Stellate Cell Proliferation and Mitochondrial Respiration Function

Liver fibrosis is the first step toward the progression to cirrhosis, portal hypertension, and hepatocellular carcinoma. A high-cholesterol diet is associated with liver fibrosis via the accumulation of free cholesterol in hepatic stellate cells (HSCs). Niemann-Pick type C2 (NPC2) plays an important role in the regulation of intracellular free cholesterol homeostasis via direct binding with free cholesterol. Previously, we reported that NPC2 was downregulated in liver cirrhosis tissues. Loss of NPC2 enhanced the accumulation of free cholesterol in HSCs and made them more susceptible to transforming growth factor (TGF)-β1. In this study, we showed that knockdown of NPC2 resulted in marked increases in platelet-derived growth factor BB (PDGF-BB)-induced HSC proliferation through enhanced extracellular signal-regulated kinases (ERK), p38, c-Jun N-terminal kinases (JNK), and protein kinase B (AKT) phosphorylation. In contrast, NPC2 overexpression decreased PDGF-BB-induced cell proliferation by inhibiting p38, JNK, and AKT phosphorylation. Although NPC2 expression did not affect caspase-related apoptosis, the autophagy marker light chain 3β (LC3B) was decreased in NPC2 knockdown, and free cholesterol accumulated in the HSCs. The mitochondrial respiration functions (such as oxygen consumption rate, ATP production, and maximal respiratory capacity) were decreased in NPC2 knockdown, and free cholesterol accumulated in the HSCs, while NPC2-overexpressed cells remained normal. In addition, NPC2 expression did not affect the susceptibility of HSCs to lipopolysaccharides (LPS), and U18666A treatment induced free cholesterol accumulation, which enhanced LPS-induced Toll-like receptor 4 (TLR4), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 phosphorylation, interleukin (IL)-1 and IL-6 expression. Our study demonstrated that NPC2-mediated free cholesterol homeostasis controls HSC proliferation and mitochondrial function.

Gastrointestinal Tract Pathology in a BALB/c Niemann-Pick Disease Type C1 Null Mouse Model

BACKGROUND

Niemann-Pick disease, type C (NPC) is a rare lysosomal storage disorder characterized by progressive neurodegeneration, splenomegaly, hepatomegaly, and early death. NPC is caused by mutations in either the NPC1 or NPC2 gene. Impaired NPC function leads to defective intracellular transport of unesterified cholesterol and its accumulation in late endosomes and lysosomes. A high frequency of Crohn disease has been reported in NPC1 patients, suggesting that gastrointestinal tract pathology may become a more prominent clinical issue if effective therapies are developed to slow the neurodegeneration. The Npc1 nih mouse model on a BALB/c background replicates the hepatic and neurological disease observed in NPC1 patients. Thus, we sought to characterize the gastrointestinal tract pathology in this model to determine whether it can serve as a model of Crohn disease in NPC1.

METHODS

We analyzed the gastrointestinal tract and isolated macrophages of BALB/cJ cNctr-Npc1m1N/J (Npc1-/-) mouse model to determine whether there was any Crohn-like pathology or inflammatory cell activation. We also evaluated temporal changes in the microbiota by 16S rRNA sequencing of fecal samples to determine whether there were changes consistent with Crohn disease.

RESULTS

Relative to controls, Npc1 mutant mice demonstrate increased inflammation and crypt abscesses in the gastrointestinal tract; however, the observed pathological changes are significantly less than those observed in other Crohn disease mouse models. Analysis of Npc1 mutant macrophages demonstrated an increased response to lipopolysaccharides and delayed bactericidal activity; both of which are pathological features of Crohn disease. Analysis of the bacterial microbiota does not mimic what is reported in Crohn disease in either human or mouse models. We did observe significant increases in cyanobacteria and epsilon-proteobacteria. The increase in epsilon-proteobacteria may be related to altered cholesterol homeostasis since cholesterol is known to promote growth of this bacterial subgroup.

CONCLUSIONS

Macrophage dysfunction in the BALB/c Npc1-/- mouse is similar to that observed in other Crohn disease models. However, neither the degree of pathology nor the microbiota changes are typical of Crohn disease. Thus, this mouse model is not a good model system for Crohn disease pathology reported in NPC1 patients.

Contribution of inflammatory pathways to Fabry disease pathogenesis

Lysosomal storage diseases are usually considered to be pathologies in which the passive deposition of unwanted materials leads to functional changes in lysosomes. Lysosomal deposition of unmetabolized glycolipid substrates stimulates the activation of pathogenic cascades, including immunological processes, and particularly the activation of inflammation. In lysosomal storage diseases, the inflammatory response is continuously being activated because the stimulus cannot be eliminated. Consequently, inflammation becomes a chronic process. Lysosomes play a role in many steps of the immune response. Leukocyte perturbation and over-expression of immune molecules have been reported in Fabry disease. Innate immunity is activated by signals originating from dendritic cells via interactions between toll-like receptors and globotriaosylceramide (Gb3) and/or globotriaosylsphingosine (lyso-Gb3). Evidence indicates that these glycolipids can activate toll-like receptors, thus triggering inflammation and fibrosis cascades. In the kidney, Gb3 deposition is associated with the increased release of transforming growth factor beta and with epithelial-to-mesenchymal cell transition, leading to the over-expression of pro-fibrotic molecules and to renal fibrosis. Interstitial fibrosis is also a typical feature of heart involvement in Fabry disease. Endomyocardial biopsies show infiltration of lymphocytes and macrophages, suggesting a role for inflammation in causing tissue damage. Inflammation is present in all tissues and may be associated with other potentially pathologic processes such as apoptosis, impaired autophagy, and increases in pro-oxidative molecules, which could all contribute synergistically to tissue damage. In Fabry disease, the activation of chronic inflammation over time leads to organ damage. Therefore, enzyme replacement therapy must be started early, before this process becomes irreversible.

Activation of PKC triggers rescue of NPC1 patient specific iPSC derived glial cells from gliosis

BACKGROUND

Niemann-Pick disease Type C1 (NPC1) is a rare progressive neurodegenerative disorder caused by mutations in the NPC1 gene. The pathological mechanisms, underlying NPC1 are not yet completely understood. Especially the contribution of glial cells and gliosis to the progression of NPC1, are controversially discussed. As an analysis of affected cells is unfeasible in NPC1-patients, we recently developed an in vitro model system, based on cells derived from NPC1-patient specific iPSCs. Here, we asked if this model system recapitulates gliosis, observed in non-human model systems and NPC1 patient post mortem biopsies. We determined the amount of reactive astrocytes and the regulation of the intermediate filaments GFAP and vimentin, all indicating gliosis. Furthermore, we were interested in the assembly and phosphorylation of these intermediate filaments and finally the impact of the activation of protein kinase C (PKC), which is described to ameliorate the pathogenic phenotype of NPC1-deficient fibroblasts, including hypo-phosphorylation of vimentin and cholesterol accumulation.

METHODS

We analysed glial cells derived from NPC1 patient specific induced pluripotent stem cells, carrying different NPC1 mutations. The amount of reactive astrocytes was determined by means of immuncytochemical stainings and FACS-analysis. Semi-quantitative western blot was used to determine the amount of phosphorylated GFAP and vimentin. Cholesterol accumulation was analysed by Filipin staining and quantified by Amplex Red Assay. U18666A was used to induce NPC1 phenotype in unaffected cells of the control cell line. Phorbol 12-myristate 13-acetate (PMA) was used to activate PKC.

RESULTS

Immunocytochemical detection of GFAP, vimentin and Ki67 revealed that NPC1 mutant glial cells undergo gliosis. We found hypo-phosphorylation of the intermediate filaments GFAP and vimentin and alterations in the assembly of these intermediate filaments in NPC1 mutant cells. The application of U18666A induced not only NPC1 phenotypical accumulation of cholesterol, but characteristics of gliosis in glial cells derived from unaffected control cells. The application of phorbol 12-myristate 13-acetate, an activator of protein kinase C resulted in a significantly reduced number of reactive astrocytes and further characteristics of gliosis in NPC1-deficient cells. Furthermore, it triggered a restoration of cholesterol amounts to level of control cells.

CONCLUSION

Our data demonstrate that glial cells derived from NPC1-patient specific iPSCs undergo gliosis. The application of U18666A induced comparable characteristics in un-affected control cells, suggesting that gliosis is triggered by hampered function of NPC1 protein. The activation of protein kinase C induced an amelioration of gliosis, as well as a reduction of cholesterol amount. These results provide further support for the line of evidence that gliosis might not be only a secondary reaction to the loss of neurons, but might be a direct consequence of a reduced PKC activity due to the phenotypical cholesterol accumulation observed in NPC1. In addition, our data support the involvement of PKCs in NPC1 disease pathogenesis and suggest that PKCs may be targeted in future efforts to develop therapeutics for NPC1 disease.

Bis(monoacylglycero)phosphate inhibits TLR4-dependent RANTES production in macrophages

Toll-like receptor 4 (TLR4) is the receptor for bacterial lipopolysaccharide (LPS) triggering production of pro-inflammatory cytokines which help eradicate the bacteria but could also be harmful when overproduced. The signaling activity of TLR4 is modulated by cholesterol level in cellular membranes, which in turn is affected by bis(monoacylglycero)phosphate (BMP), a phospholipid enriched in late endosomes. We found that exogenously added BMP isomers become incorporated into the plasma membrane and intracellular vesicles of macrophages and strongly reduced LPS-stimulated production of a chemokine RANTES, which was correlated with inhibition of interferon regulatory factor 3 (IRF3) controlling Rantes expression. To investigate the mechanism underlying the influence of BMP on TLR4 signaling we applied Laurdan and studied the impact of BMP incorporation on lipid packing, a measure for membrane order. Enrichment of model and cellular membranes with BMP significantly reduced their order and the reduction was maintained during stimulation of cells with LPS. This effect of BMP was abolished by enrichment of macrophages with cholesterol. In parallel, the inhibitory effect of BMP exerted on the TLR4-dependent phosphorylation of IRF3 was also reversed. Taken together our results indicate that BMP reduces the order of macrophage membranes which contributes to the inhibition of TLR4-dependent RANTES production.

The neuroimmune transcriptome and alcohol dependence: potential for targeted therapies

Transcriptome profiling enables discovery of gene networks that are altered in alcoholic brains. This technique has revealed involvement of the brain's neuroimmune system in regulating alcohol abuse and dependence, and has provided potential therapeutic targets. In this review, we discuss Toll-like-receptor pathways, hypothesized to be key players in many stages of the alcohol addiction cycle. The growing appreciation of the neuroimmune system's involvement in alcoholism has also led to consideration of crucial roles for glial cells, including astrocytes and microglia, in the brain's response to alcohol abuse. We discuss current knowledge and hypotheses on the roles that specific neuroimmune cell types may play in addiction. Current strategies for repurposing US FDA-approved drugs for the treatment of alcohol use disorders are also discussed.

DRABAL: novel method to mine large high-throughput screening assays using Bayesian active learning

Background

Mining high-throughput screening (HTS) assays is key for enhancing decisions in the area of drug repositioning and drug discovery. However, many challenges are encountered in the process of developing suitable and accurate methods for extracting useful information from these assays. Virtual screening and a wide variety of databases, methods and solutions proposed to-date, did not completely overcome these challenges. This study is based on a multi-label classification (MLC) technique for modeling correlations between several HTS assays, meaning that a single prediction represents a subset of assigned correlated labels instead of one label. Thus, the devised method provides an increased probability for more accurate predictions of compounds that were not tested in particular assays.

Results

Here we present DRABAL, a novel MLC solution that incorporates structure learning of a Bayesian network as a step to model dependency between the HTS assays. In this study, DRABAL was used to process more than 1.4 million interactions of over 400,000 compounds and analyze the existing relationships between five large HTS assays from the PubChem BioAssay Database. Compared to different MLC methods, DRABAL significantly improves the F₁Score by about 22%, on average. We further illustrated usefulness and utility of DRABAL through screening FDA approved drugs and reported ones that have a high probability to interact with several targets, thus enabling drug-multi-target repositioning. Specifically DRABAL suggests the Thiabendazole drug as a common activator of the NCP1 and Rab-9A proteins, both of which are designed to identify treatment modalities for the Niemann–Pick type C disease.

Conclusion

We developed a novel MLC solution based on a Bayesian active learning framework to overcome the challenge of lacking fully labeled training data and exploit actual dependencies between the HTS assays. The solution is motivated by the need to model dependencies between existing experimental confirmatory HTS assays and improve prediction performance. We have pursued extensive experiments over several HTS assays and have shown the advantages of DRABAL. The datasets and programs can be downloaded from https://figshare.com/articles/DRABAL/3309562.Graphical abstract

Induction of the type I interferon response in neurological forms of Gaucher disease

Background

Neuroinflammation is a key phenomenon in the pathogenesis of many neurodegenerative diseases. Understanding the mechanisms by which brain inflammation is engaged and delineating the key players in the immune response and their contribution to brain pathology is of great importance for the identification of novel therapeutic targets for these devastating diseases. Gaucher disease, the most common lysosomal storage disease, is caused by mutations in the GBA1 gene and is a significant risk factor for Parkinson’s disease; in some forms of Gaucher disease, neuroinflammation is observed.

Methods

An unbiased gene profile analysis was performed on a severely affected brain area of a neurological form of a Gaucher disease mouse at a pre-symptomatic stage; the mouse used for this study, the Gba^flox/flox; nestin-Cre mouse, was engineered such that GBA1 deficiency is restricted to cells of neuronal lineage, i.e., neurons and macroglia.

Results

The 10 most up-regulated genes in the ventral posteromedial/posterolateral region of the thalamus were inflammatory genes, with the gene expression signature significantly enriched in interferon signaling genes. Interferon β levels were elevated in neurons, and interferon-stimulated genes were elevated mainly in microglia. Interferon signaling pathways were elevated to a small extent in the brain of another lysosomal storage disease mouse model, Krabbe disease, but not in Niemann-Pick C or Sandhoff mouse brain. Ablation of the type I interferon receptor attenuated neuroinflammation but had no effect on GD mouse viability.

Conclusions

Our results imply that the type I interferon response is involved in the development of nGD pathology, and possibly in other lysosomal storage diseases in which simple glycosphingolipids accumulate, and support the notion that interferon signaling pathways play a vital role in the sterile inflammation that often occurs during chronic neurodegenerative diseases in which neuroinflammation is present.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0570-2) contains supplementary material, which is available to authorized users.

Necroptosis in Niemann-Pick disease, type C1: a potential therapeutic target

Niemann–Pick disease, type C1 (NPC1) is a neurodegenerative, lysosomal storage disorder due to mutation of the NPC1 gene. The NPC1 phenotype is characterized by progressive neuronal dysfunction, including cerebellar ataxia and dementia. There is histological evidence of neuroinflammation and progressive neuronal loss, with cerebellar Purkinje cells particularly vulnerable to loss of NPC1 function. Necroptosis was evaluated as a mechanism of neuronal loss. Receptor-interacting protein kinase 1 (RIP1) and RIP3 are key components of the necrosomal complex that regulates necroptotic cell death. We report increased expression of RIP1 and RIP3 in NPC1 fibroblasts, NPC1 iPS cell-derived neuronal precursors, and in cerebellar tissue from both NPC1 mice and patients. Our data suggest a positive correlation between NPC1 neurological disease severity and assembly of the necrosome complex. Furthermore, we demonstrate that pharmacological inhibition of RIP1 decreases cell death both in vitro and in vivo. Treatment of Npc1-mutant mice with necrostatin-1, an allosteric inhibitor of RIP1, significantly delayed cerebellar Purkinje cell loss, progression of neurological symptoms, and death. Collectively, our data identified necroptosis as a key component of the molecular network that contributes to neuronal loss in NPC1 and establish that inhibition of necroptosis is a potential therapeutic intervention.

Extensive macrophage accumulation in young and old Niemann-Pick C1 model mice involves the alternative, M2, activation pathway and inhibition of macrophage apoptosis

We have studied the pathophysiology of lung disease which occurs in two mouse models of Niemann-Pick C1 disease. We utilized Npc1(-/-) mice transgenic for normal gene expression in glia or neurons and glia at ages several fold the usual and a mouse model of the juvenile form of NPC1, a point mutation, at one age to confirm some findings. Lung weights, as per cent of body weight, increase much more than liver and spleen weights. Although pulmonary function parameters only vary for hysteresis between young and older Npc1(-/-) mice, they are markedly different than those found in normal control mice. Cholesterol accumulation continued in the older mice but sphingosine-1-phosphate was not increased. Bronchoalveolar lavage (BAL) showed a massive increase (26×) in the number of macrophages. Histologic examination from the older, transgenic Npc1(-/-) mice showed small foci of alveolar proteinosis and evidence of hemorrhage, as well as dense macrophage accumulation. A large subset of macrophages was immunopositive for Fizz1 or arginase-1, markers of the alternative activation pathway, while no Fizz1 or arginase-1 positive macrophages were found in wild-type mice. The percentage of marker positive macrophages was relatively stable at 5-10% at various ages and within the 2 transgenic models. Phosphohistone H3 and Ki67 showed low levels of proliferation of these macrophages. Apoptosis was prominent within lung capillary endothelial cells, but limited within macrophages. Thus, activation of the alternative pathway is involved in Niemann-Pick C1 associated pulmonary macrophage accumulation, with low proliferation of these cells balanced by low levels of apoptosis.

Role of Toll-like receptor/MYD88 signaling in neurodegenerative diseases

Toll-like receptors (TLRs) are important innate immune proteins, and the activation of the TLRs results in the activation of intracellular signaling pathways, leading to the expression of proinflammatory cytokines that are essential to the identification and clearance of invading pathogens. TLR signaling occurs through adaptor proteins, most commonly myeloid differentiation primary response gene 88 (MyD88). It is now known that immune surveillance and inflammatory responses occur in neurodegenerative diseases and TLR/MYD88 signaling plays a critical role in these diseases. The included studies suggest a contribution for this signaling to the pathophysiology of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple system atrophy, and related disorders. In this review, a discussion of the recent findings in this field is presented.

Proteomic Analysis of ABCA1-Null Macrophages Reveals a Role for Stomatin-Like Protein-2 in Raft Composition and Toll-Like Receptor Signaling

Lipid raft membrane microdomains organize signaling by many prototypical receptors, including the Toll-like receptors (TLRs) of the innate immune system. Raft-localization of proteins is widely thought to be regulated by raft cholesterol levels, but this is largely on the basis of studies that have manipulated cell cholesterol using crude and poorly specific chemical tools, such as β-cyclodextrins. To date, there has been no proteome-scale investigation of whether endogenous regulators of intracellular cholesterol trafficking, such as the ATP binding cassette (ABC)A1 lipid efflux transporter, regulate targeting of proteins to rafts. Abca1(-/-) macrophages have cholesterol-laden rafts that have been reported to contain increased levels of select proteins, including TLR4, the lipopolysaccharide receptor. Here, using quantitative proteomic profiling, we identified 383 proteins in raft isolates from Abca1(+/+) and Abca1(-/-) macrophages. ABCA1 deletion induced wide-ranging changes to the raft proteome. Remarkably, many of these changes were similar to those seen in Abca1(+/+) macrophages after lipopolysaccharide exposure. Stomatin-like protein (SLP)-2, a member of the stomatin-prohibitin-flotillin-HflK/C family of membrane scaffolding proteins, was robustly and specifically increased in Abca1(-/-) rafts. Pursuing SLP-2 function, we found that rafts of SLP-2-silenced macrophages had markedly abnormal composition. SLP-2 silencing did not compromise ABCA1-dependent cholesterol efflux but reduced macrophage responsiveness to multiple TLR ligands. This was associated with reduced raft levels of the TLR co-receptor, CD14, and defective lipopolysaccharide-induced recruitment of the common TLR adaptor, MyD88, to rafts. Taken together, we show that the lipid transporter ABCA1 regulates the protein repertoire of rafts and identify SLP-2 as an ABCA1-dependent regulator of raft composition and of the innate immune response.

Long noncoding RNA SPRY4-IT1 predicts poor patient prognosis and promotes tumorigenesis in gastric cancer

Gastric cancer (GC) is the second common cause of cancer-related death worldwide. Long noncoding RNAs (lncRNAs) are emerging as novel regulators in the cancer paradigm. However, investigation of lncRNAs on GC is still in its infancy. In this study, we focused on lncRNA SPRY4 intronic transcript 1 (SPRY4-IT1) and investigated its expression pattern, clinical significance, biological function, and molecular mechanism in GC. SPRY4-IT1 expression was examined, and its correlation with clinicopathological characteristics and patient prognosis was analyzed. A series of assays were performed to understand the role of SPRY4-IT1 in GC. SPRY4-IT1 expression was elevated in GC tissues and cell lines, and SPRY4-IT1 levels were highly positively correlated with tumor size, invasion depth, distant metastasis, TNM stage, and reduced overall survival (OS) and disease-free survival (DFS). A multivariate analysis showed that SPRY4-IT1 expression is an independent prognostic factor of OS and DFS in patients with GC. Additionally, the results of in vitro assays showed that the suppression of SPRY4-IT1 expression in GC cell line MKN-45 significantly reduced cell proliferation, colony formation, and cell migration/invasion. Moreover, the tumorigenic effects of SPRY4-IT1 were partially mediated by the regulation of certain cyclins and matrix metalloproteinases (MMPs)-related genes. Our data suggest that SPRY4-IT1 plays a critical role in GC tumorigenesis and may represent a novel prognostic marker and potential therapeutic target in patients with GC.

Olfactory deficits in Niemann-Pick type C1 (NPC1) disease

Background

Niemann-Pick type C disease (NPC) is a rare autosomal recessive lipid storage disease characterized by progressive neurodegeneration. As only a few studies have been conducted on the impact of NPC on sensory systems, we used a mutant mouse model (NPC1^−/−) to examine the effects of this disorder to morphologically distinct regions of the olfactory system, namely the olfactory epithelium (OE) and olfactory bulb (OB).

Methodology/Principal findings

For structural and functional analysis immunohistochemistry, electron microscopy, western blotting, and electrophysiology have been applied. For histochemistry and western blotting, we used antibodies against a series of neuronal and glia marker proteins, as well as macrophage markers.

NPC1^−/− animals present myelin-like lysosomal deposits in virtually all types of cells of the peripheral and central olfactory system. Especially supporting cells of the OE and central glia cells are affected, resulting in pronounced astrocytosis and microgliosis in the OB and other olfactory cortices. Up-regulation of Galectin-3, Cathepsin D and GFAP in the cortical layers of the OB underlines the critical role and location of the OB as a possible entrance gate for noxious substances. Unmyelinated olfactory afferents of the lamina propria seem less affected than ensheathing cells. Supporting the structural findings, electro-olfactometry of the olfactory mucosa suggests that NPC1^−/− animals exhibit olfactory and trigeminal deficits.

Conclusions/Significance

Our data demonstrate a pronounced neurodegeneration and glia activation in the olfactory system of NPC1^−/−, which is accompanied by sensory deficits.

Decreased bone formation and increased osteoclastogenesis cause bone loss in mucolipidosis II

Mucolipidosis type II (MLII) is a severe multi-systemic genetic disorder caused by missorting of lysosomal proteins and the subsequent lysosomal storage of undegraded macromolecules. Although affected children develop disabling skeletal abnormalities, their pathogenesis is not understood. Here we report that MLII knock-in mice, recapitulating the human storage disease, are runted with accompanying growth plate widening, low trabecular bone mass and cortical porosity. Intralysosomal deficiency of numerous acid hydrolases results in accumulation of storage material in chondrocytes and osteoblasts, and impaired bone formation. In osteoclasts, no morphological or functional abnormalities are detected whereas osteoclastogenesis is dramatically increased in MLII mice. The high number of osteoclasts in MLII is associated with enhanced osteoblastic expression of the pro-osteoclastogenic cytokine interleukin-6, and pharmacological inhibition of bone resorption prevented the osteoporotic phenotype of MLII mice. Our findings show that progressive bone loss in MLII is due to the presence of dysfunctional osteoblasts combined with excessive osteoclastogenesis. They further underscore the importance of a deep skeletal phenotyping approach for other lysosomal diseases in which bone loss is a prominent feature.

Lysosomal storage diseases--the horizon expands

Since the discovery of the lysosome in 1955, advances have been made in understanding the key roles and functions of this organelle. The concept of lysosomal storage diseases (LSDs)--disorders characterized by aberrant, excessive storage of cellular material in lysosomes--developed following the discovery of α-glucosidase deficiency as the cause of Pompe disease in 1963. Great strides have since been made in understanding the pathobiology of LSDs and the neuronal ceroid lipofuscinoses (NCLs). The NCLs are neurodegenerative disorders that display symptoms of cognitive and motor decline, seizures, blindness, early death, and accumulation of lipofuscin in various cell types, and also show some similarities to 'classic' LSDs. Defective lysosomal storage can occur in many cell types, but the CNS and PNS are particularly vulnerable to LSDs and NCLs, being affected in two-thirds of these disorders. Most LSDs are inherited in an autosomal recessive manner, with the exception of X-linked Hunter disease, Fabry disease and Danon disease, and a variant type of adult NCL (Kuf disease). This Review provides a summary of known LSDs, and the pathways affected in these disorders. Existing therapies and barriers to development of novel and improved treatments for LSDs and NCLs are also discussed.

Lysosomal storage diseases--the horizon expands

Since the discovery of the lysosome in 1955, advances have been made in understanding the key roles and functions of this organelle. The concept of lysosomal storage diseases (LSDs)--disorders characterized by aberrant, excessive storage of cellular material in lysosomes--developed following the discovery of α-glucosidase deficiency as the cause of Pompe disease in 1963. Great strides have since been made in understanding the pathobiology of LSDs and the neuronal ceroid lipofuscinoses (NCLs). The NCLs are neurodegenerative disorders that display symptoms of cognitive and motor decline, seizures, blindness, early death, and accumulation of lipofuscin in various cell types, and also show some similarities to 'classic' LSDs. Defective lysosomal storage can occur in many cell types, but the CNS and PNS are particularly vulnerable to LSDs and NCLs, being affected in two-thirds of these disorders. Most LSDs are inherited in an autosomal recessive manner, with the exception of X-linked Hunter disease, Fabry disease and Danon disease, and a variant type of adult NCL (Kuf disease). This Review provides a summary of known LSDs, and the pathways affected in these disorders. Existing therapies and barriers to development of novel and improved treatments for LSDs and NCLs are also discussed.

Autophagy proteins regulate cell engulfment mechanisms that participate in cancer

Recent evidence has uncovered cross-regulation of mechanisms of cell engulfment by proteins of the autophagy pathway, in what is called LC3-Associated Phagocytosis, or LAP. By LAP, lysosome fusion to phagosomes and the degradation of engulfed extracellular cargo are facilitated by autophagy proteins that lipidate LC3 onto phagosome membranes. Here we discuss the contexts where LAP is known to occur by focusing on potential roles in tumorigenesis, including predicted consequences of LAP inhibition.

Glia maturation factor-γ negatively modulates TLR4 signaling by facilitating TLR4 endocytic trafficking in macrophages

TLR4 signaling must be tightly regulated to provide both effective immune protection and avoid inflammation-induced pathology. Thus, the mechanisms that negatively regulate the TLR4-triggered inflammatory response are of particular importance. Glia maturation factor-γ (GMFG), a novel actin depolymerization factor/cofilin superfamily protein that is expressed in inflammatory cells, has been implicated in mediating neutrophil and T cell migration, but its function in macrophage immune response remains unclear. In the current study, the role of GMFG in the LPS-induced TLR4-signaling pathway was investigated in THP-1 macrophages and human primary macrophages. LPS stimulation of macrophages decreased GMFG mRNA and protein expression. We show that GMFG negatively regulates LPS-induced activation of NF-κB-, MAPK-, and IRF3-signaling pathways and subsequent production of proinflammatory cytokines and type I IFN in human macrophages. We found that endogenous GMFG localized within early and late endosomes. GMFG knockdown delayed LPS-induced TLR4 internalization and caused prolonged TLR4 retention at the early endosome, suggesting that TLR4 transport from early to late endosomes is interrupted, which may contribute to enhanced LPS-induced TLR4 signaling. Taken together, our findings suggest that GMFG functions as a negative regulator of TLR4 signaling by facilitating TLR4 endocytic trafficking in macrophages.

Fabry disease peripheral blood immune cells release inflammatory cytokines: role of globotriaosylceramide

Fabry disease is an X-linked lysosomal disorder (LD) due to deficiency of the enzyme α-galactosidase A (αGal), which leads to the accumulation of neutral glycosphingolipids, mainly globotriaosylceramide (Gb3). Several mechanisms contribute to the diverse physiopathological alterations observed in this disease, and it has been suggested that an underlying proinflammatory state could play a significant role. The aim of this study is to investigate the presence of a proinflammatory state in the different subsets of peripheral blood mononuclear cells (PBMC) and to understand the mechanisms that contribute to its onset and perpetuation. We have shown that cultured PBMC from Fabry patients present a higher proinflammatory cytokine expression and production. Moreover, we determined that among PBMC, dendritic cells and monocytes present a basal proinflammatory cytokine production profile, which is further exacerbated with an inflammatory stimulus. Finally we established that normal, monocyte-derived dendritic cells and macrophages display the same proinflammatory profile when cultured in the presence of Gb3 and an inhibitor of αGal. Furthermore, this effect can be abolished using a TLR4 blocking antibody, indicating that TLR4 is necessary in the process. In summary, our results demonstrate the presence of a proinflammatory state involving two key subsets of innate immunity, and provide direct evidence of Gb3 having a proinflammatory role, likely mediated by TLR4, a finding that could help in the understanding of the underlying causes of the inflammatory pathogenesis of Fabry disease.

Arachidonic acid metabolism via cytosolic phospholipase A2 α induces cytotoxicity in niemann-pick disease type C cells

Niemann-Pick disease type C (NPC) is a neurodegenerative lipid storage disorder caused by mutations in NPC1 or NPC2 genes. Loss of function of either protein results in the endosomal accumulation of cholesterol and other lipids. Here, we report that NPC1-deficient Chinese hamster ovary cells exhibit increased release of arachidonic acid (AA) and synthesis of prostaglandin E(2) compared with wild-type cells. The enhanced release of AA was inhibited by both treatment with the selective inhibitor of cytosolic phospholipase A(2) α (cPLA(2) α) and cultivation in lipoprotein-deficient medium. There was no difference in the expression of both cyclooxygenase-1 and -2 between NPC cells and wild-type cells. U18666A, a cholesterol transport-inhibiting agent commonly used to mimic NPC, also increased the release of AA in L929 mouse fibrosarcoma cells. Furthermore, U18666A-induced formation of reactive oxygen species (ROS) resulted in the induction of cell death and cell cycle delay/arrest in L929 cells. Interestingly, these responses induced by U18666A were much weaker in cPLA(2) α knockdown L929 cells. These results suggest that cPLA(2) α-AA pathway plays important roles in the cytotoxicity and the ROS formation in NPC cells.

Crosstalk between reverse cholesterol transport and innate immunity

Although lipid metabolism and host defense are widely considered to be very divergent disciplines, compelling evidence suggests that host cell handling of self- and microbe-derived (e.g. lipopolysaccharide, LPS) lipids may have common evolutionary roots, and that they indeed may be inseparable processes. The innate immune response and the homeostatic network controlling cellular sterol levels are now known to regulate each other reciprocally, with important implications for several common diseases, including atherosclerosis. In the present review we discuss recent discoveries that provide new insight into the bidirectional crosstalk between reverse cholesterol transport and innate immunity, and highlight the broader implications of these findings for the development of therapeutics.

A high-cholesterol diet exacerbates liver fibrosis in mice via accumulation of free cholesterol in hepatic stellate cells

BACKGROUND & AIMS

Some studies have indicated that dietary cholesterol has a role in the progression of liver fibrosis. We investigated the mechanisms by which dietary cholesterol might contribute to hepatic fibrogenesis.

METHODS

C57BL/6 mice were fed a high-cholesterol diet or a control diet for 4 weeks; liver fibrosis then was induced by bile-duct ligation or carbon tetrachloride administration. Hepatic stellate cells (HSCs) were isolated from mice fed high-cholesterol diets or from Niemann-Pick type C1-deficient mice, which accumulate intracellular free cholesterol.

RESULTS

After bile-duct ligation or carbon tetrachloride administration, mice fed high-cholesterol diets had significant increases in liver fibrosis and activation of HSCs compared with mice fed control diets. There were no significant differences in the degree of hepatocellular injury or liver inflammation, including hepatocyte apoptosis or Kupffer cell activation, between mice fed high-cholesterol or control diets. Levels of free cholesterol were much higher in HSCs from mice fed high-cholesterol diets than those fed control diets. In cultured HSCs, accumulation of free cholesterol in HSCs increased levels of Toll-like receptor 4 (TLR4), leading to down-regulation of bone morphogenetic protein and activin membrane-bound inhibitor (a pseudoreceptor for transforming growth factor [TGF]β); the HSCs became sensitized to TGFβ-induced activation. Liver fibrosis was not aggravated by the high-cholesterol diet in C3H/HeJ mice, which express a mutant form of TLR4; HSCs that express mutant TLR4 were not activated by accumulation of free cholesterol.

CONCLUSIONS

Dietary cholesterol aggravates liver fibrosis because free cholesterol accumulates in HSCs, leading to increased TLR4 signaling, down-regulation of bone morphogenetic protein and activin membrane-bound inhibitor, and sensitization of HSC to TGFβ. This pathway might be targeted by antifibrotic therapies.