Prophylactic treatment with the c-Abl inhibitor, neurotinib, diminishes neuronal damage and the convulsive state in pilocarpine-induced mice

The molecular mechanisms underlying seizure generation remain elusive, yet they are crucial for developing effective treatments for epilepsy. The current study shows that inhibiting c-Abl tyrosine kinase prevents apoptosis, reduces dendritic spine loss, and maintains N-methyl-d-aspartate (NMDA) receptor subunit 2B (NR2B) phosphorylated in in vitro models of excitotoxicity. Pilocarpine-induced status epilepticus (SE) in mice promotes c-Abl phosphorylation, and disrupting c-Abl activity leads to fewer seizures, increases latency toward SE, and improved animal survival. Currently, clinically used c-Abl inhibitors are non-selective and have poor brain penetration. The allosteric c-Abl inhibitor, neurotinib, used here has favorable potency, selectivity, pharmacokinetics, and vastly improved brain penetration. Neurotinib-administered mice have fewer seizures and improved survival following pilocarpine-SE induction. Our findings reveal c-Abl kinase activation as a key factor in ictogenesis and highlight the impact of its inhibition in preventing the insurgence of epileptic-like seizures in rodents and humans.

c-Abl Phosphorylates MFN2 to Regulate Mitochondrial Morphology in Cells under Endoplasmic Reticulum and Oxidative Stress, Impacting Cell Survival and Neurodegeneration

The endoplasmic reticulum is a subcellular organelle key in the control of synthesis, folding, and sorting of proteins. Under endoplasmic reticulum stress, an adaptative unfolded protein response is activated; however, if this activation is prolonged, cells can undergo cell death, in part due to oxidative stress and mitochondrial fragmentation. Here, we report that endoplasmic reticulum stress activates c-Abl tyrosine kinase, inducing its translocation to mitochondria. We found that endoplasmic reticulum stress-activated c-Abl interacts with and phosphorylates the mitochondrial fusion protein MFN2, resulting in mitochondrial fragmentation and apoptosis. Moreover, the pharmacological or genetic inhibition of c-Abl prevents MFN2 phosphorylation, mitochondrial fragmentation, and apoptosis in cells under endoplasmic reticulum stress. Finally, in the amyotrophic lateral sclerosis mouse model, where endoplasmic reticulum and oxidative stress has been linked to neuronal cell death, we demonstrated that the administration of c-Abl inhibitor neurotinib delays the onset of symptoms. Our results uncovered a function of c-Abl in the crosstalk between endoplasmic reticulum stress and mitochondrial dynamics via MFN2 phosphorylation.

Understanding the phenotypic variability in Niemann-Pick disease type C (NPC): a need for precision medicine

Niemann-Pick type C (NPC) disease is a lysosomal storage disease (LSD) characterized by the buildup of endo-lysosomal cholesterol and glycosphingolipids due to loss of function mutations in the NPC1 and NPC2 genes. NPC patients can present with a broad phenotypic spectrum, with differences at the age of onset, rate of progression, severity, organs involved, effects on the central nervous system, and even response to pharmacological treatments. This article reviews the phenotypic variation of NPC and discusses its possible causes, such as the remaining function of the defective protein, modifier genes, sex, environmental cues, and splicing factors, among others. We propose that these factors should be considered when designing or repurposing treatments for this disease. Despite its seeming complexity, this proposition is not far-fetched, considering the expanding interest in precision medicine and easier access to multi-omics technologies.

c-Abl tyrosine kinase down-regulation as target for memory improvement in Alzheimer's disease

Background

Growing evidence suggests that the non-receptor tyrosine kinase, c-Abl, plays a significant role in the pathogenesis of Alzheimer's disease (AD). Here, we analyzed the effect of c-Abl on the cognitive performance decline of APPSwe/PSEN1ΔE9 (APP/PS1) mouse model for AD.

Methods

We used the conditional genetic ablation of c-Abl in the brain (c-Abl-KO) and pharmacological treatment with neurotinib, a novel allosteric c-Abl inhibitor with high brain penetrance, imbued in rodent's chow.

Results

We found that APP/PS1/c-Abl-KO mice and APP/PS1 neurotinib-fed mice had improved performance in hippocampus-dependent tasks. In the object location and Barnes-maze tests, they recognized the displaced object and learned the location of the escape hole faster than APP/PS1 mice. Also, APP/PS1 neurotinib-fed mice required fewer trials to reach the learning criterion in the memory flexibility test. Accordingly, c-Abl absence and inhibition caused fewer amyloid plaques, reduced astrogliosis, and preserved neurons in the hippocampus.

Discussion

Our results further validate c-Abl as a target for AD, and the neurotinib, a novel c-Abl inhibitor, as a suitable preclinical candidate for AD therapies.

A Mouse Systems Genetics Approach Reveals Common and Uncommon Genetic Modifiers of Hepatic Lysosomal Enzyme Activities and Glycosphingolipids

Identification of genetic modulators of lysosomal enzyme activities and glycosphingolipids (GSLs) may facilitate the development of therapeutics for diseases in which they participate, including Lysosomal Storage Disorders (LSDs). To this end, we used a systems genetics approach: we measured 11 hepatic lysosomal enzymes and many of their natural substrates (GSLs), followed by modifier gene mapping by GWAS and transcriptomics associations in a panel of inbred strains. Unexpectedly, most GSLs showed no association between their levels and the enzyme activity that catabolizes them. Genomic mapping identified 30 shared predicted modifier genes between the enzymes and GSLs, which are clustered in three pathways and are associated with other diseases. Surprisingly, they are regulated by ten common transcription factors, and their majority by miRNA-340p. In conclusion, we have identified novel regulators of GSL metabolism, which may serve as therapeutic targets for LSDs and may suggest the involvement of GSL metabolism in other pathologies.

c-Abl kinase at the crossroads of healthy synaptic remodeling and synaptic dysfunction in neurodegenerative diseases

Our ability to learn and remember depends on the active formation, remodeling, and elimination of synapses. Thus, the development and growth of synapses as well as their weakening and elimination are essential for neuronal rewiring. The structural reorganization of synaptic complexes, changes in actin cytoskeleton and organelle dynamics, as well as modulation of gene expression, determine synaptic plasticity. It has been proposed that dysregulation of these key synaptic homeostatic processes underlies the synaptic dysfunction observed in many neurodegenerative diseases. Much is known about downstream signaling of activated N-methyl-D-aspartate and α-amino-3-hydroxy-5-methyl-4-isoazolepropionate receptors; however, other signaling pathways can also contribute to synaptic plasticity and long-lasting changes in learning and memory. The non-receptor tyrosine kinase c-Abl (ABL1) is a key signal transducer of intra and extracellular signals, and it shuttles between the cytoplasm and the nucleus. This review focuses on c-Abl and its synaptic and neuronal functions. Here, we discuss the evidence showing that the activation of c-Abl can be detrimental to neurons, promoting the development of neurodegenerative diseases. Nevertheless, c-Abl activity seems to be in a pivotal balance between healthy synaptic plasticity, regulating dendritic spines remodeling and gene expression after cognitive training, and synaptic dysfunction and loss in neurodegenerative diseases. Thus, c-Abl genetic ablation not only improves learning and memory and modulates the brain genetic program of trained mice, but its absence provides dendritic spines resiliency against damage. Therefore, the present review has been designed to elucidate the common links between c-Abl regulation of structural changes that involve the actin cytoskeleton and organelles dynamics, and the transcriptional program activated during synaptic plasticity. By summarizing the recent discoveries on c-Abl functions, we aim to provide an overview of how its inhibition could be a potentially fruitful treatment to improve degenerative outcomes and delay memory loss.

Autophagy Induced by Toll-like Receptor Ligands Regulates Antigen Extraction and Presentation by B Cells

The engagement of B cells with surface-tethered antigens triggers the formation of an immune synapse (IS), where the local secretion of lysosomes can facilitate antigen uptake. Lysosomes intersect with other intracellular processes, such as Toll-like Receptor (TLR) signaling and autophagy coordinating immune responses. However, the crosstalk between these processes and antigen presentation remains unclear. Here, we show that TLR stimulation induces autophagy in B cells and decreases their capacity to extract and present immobilized antigens. We reveal that TLR stimulation restricts lysosome repositioning to the IS by triggering autophagy-dependent degradation of GEF-H1, a Rho GTP exchange factor required for stable lysosome recruitment at the synaptic membrane. GEF-H1 degradation is not observed in B cells that lack αV integrins and are deficient in TLR-induced autophagy. Accordingly, these cells show efficient antigen extraction in the presence of TLR stimulation, confirming the role of TLR-induced autophagy in limiting antigen extraction. Overall, our results suggest that resources associated with autophagy regulate TLR and BCR-dependent functions, which can finetune antigen uptake by B cells. This work helps to understand the mechanisms by which B cells are activated by surface-tethered antigens in contexts of subjacent inflammation before antigen recognition, such as sepsis.

Neuronopathic Gaucher disease: Beyond lysosomal dysfunction

Gaucher disease (GD) is an inherited disorder caused by recessive mutations in the GBA1 gene that encodes the lysosomal enzyme β-glucocerebrosidase (β-GC). β-GC hydrolyzes glucosylceramide (GluCer) into glucose and ceramide in the lysosome, and the loss of its activity leads to GluCer accumulation in different tissues. In severe cases, enzymatic deficiency triggers inflammation, organomegaly, bone disease, and neurodegeneration. Neuronopathic Gaucher disease (nGD) encompasses two different forms of the disease, characterized by chronic or acute damage to the central nervous system (CNS). The cellular and molecular studies that uncover the pathological mechanisms of nGD mainly focus on lysosomal dysfunction since the lysosome is the key organelle affected in GD. However, new studies show alterations in other organelles that contribute to nGD pathology. For instance, abnormal accumulation of GluCer in lysosomes due to the loss of β-GC activity leads to excessive calcium release from the endoplasmic reticulum (ER), activating the ER-associated degradation pathway and the unfolded protein response. Recent evidence indicates mitophagy is altered in nGD, resulting in the accumulation of dysfunctional mitochondria, a critical factor in disease progression. Additionally, nGD patients present alterations in mitochondrial morphology, membrane potential, ATP production, and increased reactive oxygen species (ROS) levels. Little is known about potential dysfunction in other organelles of the secretory pathway, such as the Golgi apparatus and exosomes. This review focuses on collecting evidence regarding organelle dysfunction beyond lysosomes in nGD. We briefly describe cellular and animal models and signaling pathways relevant to uncovering the pathological mechanisms and new therapeutic targets in GD.

c-Abl Activation Linked to Autophagy-Lysosomal Dysfunction Contributes to Neurological Impairment in Niemann-Pick Type A Disease

Niemann-Pick type A (NPA) disease is a fatal lysosomal neurodegenerative disorder caused by the deficiency in acid sphingomyelinase (ASM) activity. NPA patients present severe and progressive neurodegeneration starting at an early age. Currently, there is no effective treatment for this disease and NPA patients die between 2 and 3 years of age. NPA is characterized by an accumulation of sphingomyelin in lysosomes and dysfunction in the autophagy-lysosomal pathway. Recent studies show that c-Abl tyrosine kinase activity downregulates autophagy and the lysosomal pathway. Interestingly, this kinase is also activated in other lysosomal neurodegenerative disorders. Here, we describe that c-Abl activation contributes to the mechanisms of neuronal damage and death in NPA disease. Our data demonstrate that: 1) c-Abl is activated in-vitro as well as in-vivo NPA models; 2) imatinib, a clinical c-Abl inhibitor, reduces autophagy-lysosomal pathway alterations, restores autophagy flux, and lowers sphingomyelin accumulation in NPA patient fibroblasts and NPA neuronal models and 3) chronic treatment with nilotinib and neurotinib, two c-Abl inhibitors with differences in blood-brain barrier penetrance and target binding mode, show further benefits. While nilotinib treatment reduces neuronal death in the cerebellum and improves locomotor functions, neurotinib decreases glial activation, neuronal disorganization, and loss in hippocampus and cortex, as well as the cognitive decline of NPA mice. Our results support the participation of c-Abl signaling in NPA neurodegeneration and autophagy-lysosomal alterations, supporting the potential use of c-Abl inhibitors for the clinical treatment of NPA patients.

Alterations in Lysosome Homeostasis in Lipid-Related Disorders: Impact on Metabolic Tissues and Immune Cells

Lipid-related disorders, which primarily affect metabolic tissues, including adipose tissue and the liver are associated with alterations in lysosome homeostasis. Obesity is one of the more prevalent diseases, which results in energy imbalance within metabolic tissues and lysosome dysfunction. Less frequent diseases include Niemann-Pick type C (NPC) and Gaucher diseases, both of which are known as Lysosomal Storage Diseases (LSDs), where lysosomal dysfunction within metabolic tissues remains to be fully characterized. Adipocytes and hepatocytes share common pathways involved in the lysosome-autophagic axis, which are regulated by the function of cathepsins and CD36, an immuno-metabolic receptor and display alterations in lipid diseases, and thereby impacting metabolic functions. In addition to intrinsic defects observed in metabolic tissues, cells of the immune system, such as B cells can infiltrate adipose and liver tissues, during metabolic imbalance favoring inflammation. Moreover, B cells rely on lysosomes to promote the processing and presentation of extracellular antigens and thus could also present lysosome dysfunction, consequently affecting such functions. On the other hand, growing evidence suggests that cells accumulating lipids display defective inter-organelle membrane contact sites (MCSs) established by lysosomes and other compartments, which contribute to metabolic dysfunctions at the cellular level. Overall, in this review we will discuss recent findings addressing common mechanisms that are involved in lysosome dysregulation in adipocytes and hepatocytes during obesity, NPC, and Gaucher diseases. We will discuss whether these mechanisms may modulate the function of B cells and how inter-organelle contacts, emerging as relevant cellular mechanisms in the control of lipid homeostasis, have an impact on these diseases.

Identification of genetic modifiers of murine hepatic β-glucocerebrosidase activity

The acid β-glucocerebrosidase (GCase) enzyme cleaves glucosylceramide into glucose and ceramide. Loss of function variants in the gene encoding for GCase can lead to Gaucher disease and Parkinson's disease. Therapeutic strategies aimed at increasing GCase activity by targeting a modulating factor are attractive and poorly explored. To identify genetic modifiers, we measured hepatic GCase activity in 27 inbred mouse strains. A genome-wide association study (GWAS) using GCase activity as a trait identified several candidate modifier genes, including Dmrtc2 and Arhgef1 (p=2.1x10⁻⁷), and Grik5 (p=2.1x10⁻⁷). Bayesian integration of the gene mapping with transcriptomics was used to build integrative networks. The analysis uncovered additional candidate GCase regulators, highlighting modules of the acute phase response (p=1.01x10⁻⁸), acute inflammatory response (p=1.01x10⁻⁸), fatty acid beta-oxidation (p=7.43x10⁻⁵), among others. Our study revealed previously unknown candidate modulators of GCase activity, which may facilitate the design of therapies for diseases with GCase dysfunction.

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Hepatic GCase activity significantly differs among mouse strains.

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Genome-wide association study revealed putative modifier genes of GCase activity.

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Bayesian integration of multi-omics identified a regulatory network of GCase activity.

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This study may facilitate the design of therapies for diseases with GCase dysfunction.

Proteomic Analysis of Niemann-Pick Type C Hepatocytes Reveals Potential Therapeutic Targets for Liver Damage

Niemann-Pick type C disease (NPCD) is a lysosomal storage disorder caused by mutations in the NPC1 gene. The most affected tissues are the central nervous system and liver, and while significant efforts have been made to understand its neurological component, the pathophysiology of the liver damage remains unclear. In this study, hepatocytes derived from wild type and Npc1^-/- mice were analyzed by mass spectrometry (MS)-based proteomics in conjunction with bioinformatic analysis. We identified 3832 proteins: 416 proteins had a p-value smaller than 0.05, of which 37% (n = 155) were considered differentially expressed proteins (DEPs), 149 of them were considered upregulated, and 6 were considered downregulated. We focused the analysis on pathways related to NPC pathogenic mechanisms, finding that the most significant changes in expression levels occur in proteins that function in the pathways of liver damage, lipid metabolism, and inflammation. Moreover, in the group of DEPs, 30% (n = 47) were identified as lysosomal proteins and 7% (n = 10) were identified as mitochondrial proteins. Importantly, we found that lysosomal DEPs, including CTSB/D/Z, LIPA, DPP7 and GLMP, and mitocondrial DEPs, AKR1B10, and VAT1 had been connected with liver fibrosis, damage, and steatosis in previous studies, validiting our dataset. Our study found potential therapeutic targets for the treatment of liver damage in NPCD.

Lack of Annexin A6 Exacerbates Liver Dysfunction and Reduces Lifespan of Niemann-Pick Type C Protein-Deficient Mice

Niemann-Pick type C (NPC) disease is a lysosomal storage disorder characterized by cholesterol accumulation caused by loss-of-function mutations in the Npc1 gene. NPC disease primarily affects the brain, causing neuronal damage and affecting motor coordination. In addition, considerable liver malfunction in NPC disease is common. Recently, we found that the depletion of annexin A6 (ANXA6), which is most abundant in the liver and involved in cholesterol transport, ameliorated cholesterol accumulation in Npc1 mutant cells. To evaluate the potential contribution of ANXA6 in the progression of NPC disease, double-knockout mice (Npc1^-/-/Anxa6^-/-) were generated and examined for lifespan, neurologic and hepatic functions, as well as liver histology and ultrastructure. Interestingly, lack of ANXA6 in NPC1-deficient animals did not prevent the cerebellar degeneration phenotype, but further deteriorated their compromised hepatic functions and reduced their lifespan. Moreover, livers of Npc1^-/-/Anxa6^-/- mice contained a significantly elevated number of foam cells congesting the sinusoidal space, a feature commonly associated with inflammation. We hypothesize that ANXA6 deficiency in Npc1^-/- mice not only does not reverse neurologic and motor dysfunction, but further worsens overall liver function, exacerbating hepatic failure in NPC disease.

c-Abl Inhibition Activates TFEB and Promotes Cellular Clearance in a Lysosomal Disorder

The transcription factor EB (TFEB) has emerged as a master regulator of lysosomal biogenesis, exocytosis, and autophagy, promoting the clearance of substrates stored in cells. c-Abl is a tyrosine kinase that participates in cellular signaling in physiological and pathophysiological conditions. In this study, we explored the connection between c-Abl and TFEB. Here, we show that under pharmacological and genetic c-Abl inhibition, TFEB translocates into the nucleus promoting the expression of its target genes independently of its well-known regulator, mammalian target of rapamycin complex 1. Active c-Abl induces TFEB phosphorylation on tyrosine and the inhibition of this kinase promotes lysosomal biogenesis, autophagy, and exocytosis. c-Abl inhibition in Niemann-Pick type C (NPC) models, a neurodegenerative disease characterized by cholesterol accumulation in lysosomes, promotes a cholesterol-lowering effect in a TFEB-dependent manner. Thus, c-Abl is a TFEB regulator that mediates its tyrosine phosphorylation, and the inhibition of c-Abl activates TFEB promoting cholesterol clearance in NPC models.

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c-Abl is a TFEB regulator that mediates its tyr phosphorylation

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c-Abl inhibition promotes TFEB activity independently of mTORC1

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c-Abl inhibition reduces cholesterol accumulation in NPC1 models

Finding pathogenic commonalities between Niemann-Pick type C and other lysosomal storage disorders: Opportunities for shared therapeutic interventions

Lysosomal storage disorders (LSDs) are diseases characterized by the accumulation of macromolecules in the late endocytic system and are caused by inherited defects in genes that encode mainly lysosomal enzymes or transmembrane lysosomal proteins. Niemann-Pick type C disease (NPCD), a LSD characterized by liver damage and progressive neurodegeneration that leads to early death, is caused by mutations in the genes encoding the NPC1 or NPC2 proteins. Both proteins are involved in the transport of cholesterol from the late endosomal compartment to the rest of the cell. Loss of function of these proteins causes primary cholesterol accumulation, and secondary accumulation of other lipids, such as sphingolipids, in lysosomes. Despite years of studying the genetic and molecular bases of NPCD and related-lysosomal disorders, the pathogenic mechanisms involved in these diseases are not fully understood. In this review we will summarize the pathogenic mechanisms described for NPCD and we will discuss their relevance for other LSDs with neurological components such as Niemann- Pick type A and Gaucher diseases. We will particularly focus on the activation of signaling pathways that may be common to these three pathologies with emphasis on how the intra-lysosomal accumulation of lipids leads to pathology, specifically to neurological impairments. We will show that although the primary lipid storage defect is different in these three LSDs, there is a similar secondary accumulation of metabolites and activation of signaling pathways that can lead to common pathogenic mechanisms. This analysis might help to delineate common pathological mechanisms and therapeutic targets for lysosomal storage diseases.

Reduction of Blood Amyloid-β Oligomers in Alzheimer's Disease Transgenic Mice by c-Abl Kinase Inhibition

One of the pathological hallmarks of Alzheimer's disease (AD) is the presence of amyloid plaques, which are deposits of misfolded and aggregated amyloid-beta peptide (Aβ). The role of the c-Abl tyrosine kinase in Aβ-mediated neurodegeneration has been previously reported. Here, we investigated the therapeutic potential of inhibiting c-Abl using imatinib. We developed a novel method, based on a technique used to detect prions (PMCA), to measure minute amounts of misfolded-Aβ in the blood of AD transgenic mice. We found that imatinib reduces Aβ-oligomers in plasma, which correlates with a reduction of AD brain features such as plaques and oligomers accumulation, neuroinflammation, and cognitive deficits. Cells exposed to imatinib and c-Abl KO mice display decreased levels of β-CTF fragments, suggesting that an altered processing of the amyloid-beta protein precursor is the most probable mechanism behind imatinib effects. Our findings support the role of c-Abl in Aβ accumulation and AD, and propose AD-PMCA as a new tool to evaluate AD progression and screening for drug candidates.

Lysosomal and Mitochondrial Liaisons in Niemann-Pick Disease

Lysosomal storage disorders (LSD) are characterized by the accumulation of diverse lipid species in lysosomes. Niemann-Pick type A/B (NPA/B) and type C diseases Niemann-Pick type C (NPC) are progressive LSD caused by loss of function of distinct lysosomal-residing proteins, acid sphingomyelinase and NPC1, respectively. While the primary cause of these diseases differs, both share common biochemical features, including the accumulation of sphingolipids and cholesterol, predominantly in endolysosomes. Besides these alterations in lysosomal homeostasis and function due to accumulation of specific lipid species, the lysosomal functional defects can have far-reaching consequences, disrupting intracellular trafficking of sterols, lipids and calcium through membrane contact sites (MCS) of apposed compartments. Although MCS between endoplasmic reticulum and mitochondria have been well studied and characterized in different contexts, emerging evidence indicates that lysosomes also exhibit close proximity with mitochondria, which translates in their mutual functional regulation. Indeed, as best illustrated in NPC disease, alterations in the lysosomal-mitochondrial liaisons underlie the secondary accumulation of specific lipids, such as cholesterol in mitochondria, resulting in mitochondrial dysfunction and defective antioxidant defense, which contribute to disease progression. Thus, a better understanding of the lysosomal and mitochondrial interactions and trafficking may identify novel targets for the treatment of Niemann-Pick disease.

Mitochondrial GSH replenishment as a potential therapeutic approach for Niemann Pick type C disease

Niemann Pick type C (NPC) disease is a progressive lysosomal storage disorder caused by mutations in genes encoding NPC1/NPC2 proteins, characterized by neurological defects, hepatosplenomegaly and premature death. While the primary biochemical feature of NPC disease is the intracellular accumulation of cholesterol and gangliosides, predominantly in endolysosomes, mitochondrial cholesterol accumulation has also been reported. As accumulation of cholesterol in mitochondria is known to impair the transport of GSH into mitochondria, resulting in mitochondrial GSH (mGSH) depletion, we investigated the impact of mGSH recovery in NPC disease. We show that GSH ethyl ester (GSH-EE), but not N-acetylcysteine (NAC), restored the mGSH pool in liver and brain of Npc1-/- mice and in fibroblasts from NPC patients, while both GSH-EE and NAC increased total GSH levels. GSH-EE but not NAC increased the median survival and maximal life span of Npc1-/- mice. Moreover, intraperitoneal therapy with GSH-EE protected against oxidative stress and oxidant-induced cell death, restored calbindin levels in cerebellar Purkinje cells and reversed locomotor impairment in Npc1-/- mice. High-resolution respirometry analyses revealed that GSH-EE improved oxidative phosphorylation, coupled respiration and maximal electron transfer in cerebellum of Npc1-/- mice. Lipidomic analyses showed that GSH-EE treatment had not effect in the profile of most sphingolipids in liver and brain, except for some particular species in brain of Npc1-/- mice. These findings indicate that the specific replenishment of mGSH may be a potential promising therapy for NPC disease, worth exploring alone or in combination with other options.

MLN64 induces mitochondrial dysfunction associated with increased mitochondrial cholesterol content

MLN64 is a late endosomal cholesterol-binding membrane protein that has been implicated in cholesterol transport from endosomal membranes to the plasma membrane and/or mitochondria, in toxin-induced resistance, and in mitochondrial dysfunction. Down-regulation of MLN64 in Niemann-Pick C1 deficient cells decreased mitochondrial cholesterol content, suggesting that MLN64 functions independently of NPC1. However, the role of MLN64 in the maintenance of endosomal cholesterol flow and intracellular cholesterol homeostasis remains unclear. We have previously described that hepatic MLN64 overexpression increases liver cholesterol content and induces liver damage. Here, we studied the function of MLN64 in normal and NPC1-deficient cells and we evaluated whether MLN64 overexpressing cells exhibit alterations in mitochondrial function. We used recombinant-adenovirus-mediated MLN64 gene transfer to overexpress MLN64 in mouse liver and hepatic cells; and RNA interference to down-regulate MLN64 in NPC1-deficient cells. In MLN64-overexpressing cells, we found increased mitochondrial cholesterol content and decreased glutathione (GSH) levels and ATPase activity. Furthermore, we found decreased mitochondrial membrane potential and mitochondrial fragmentation and increased mitochondrial superoxide levels in MLN64-overexpressing cells and in NPC1-deficient cells. Consequently, MLN64 expression was increased in NPC1-deficient cells and reduction of its expression restore mitochondrial membrane potential and mitochondrial superoxide levels. Our findings suggest that MLN64 overexpression induces an increase in mitochondrial cholesterol content and consequently a decrease in mitochondrial GSH content leading to mitochondrial dysfunction. In addition, we demonstrate that MLN64 expression is increased in NPC cells and plays a key role in cholesterol transport into the mitochondria.

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MLN64 overexpression induces an increase in mitochondrial cholesterol content.

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MLN64 protein expression is increased in NPC cells.

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Down-regulation of MLN64 restores mitochondrial membrane potential and superoxide levels in NPC cells.

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MLN64 overexpression produces mitochondrial dysfunction.

Structural and functional analysis of the ASM p.Ala359Asp mutant that causes acid sphingomyelinase deficiency

Niemann-Pick disease (NPD) type A and B are recessive hereditary disorders caused by deficiency in acid sphingomyelinase (ASM). The p.Ala359Asp mutation has been described in several patients but its functional and structural effects in the protein are unknown. In order to characterize this mutation, we modeled the three-dimensional ASM structure using the recent available crystal of the mammalian ASM as a template. We found that the p.Ala359Asp mutation is localized in the hydrophobic core and far from the sphingomyelin binding site. However, energy function calculations using statistical potentials indicate that the mutation causes a decrease in ASM stability. Therefore, we investigated the functional effect of the p.Ala359Asp mutation in ASM expression, secretion, localization and activity in human fibroblasts. We found a 3.8% residual ASM activity compared to the wild-type enzyme, without changes in the other parameters evaluated. These results support the hypothesis that the p.Ala359Asp mutation causes structural alterations in the hydrophobic environment where ASM is located, decreasing its enzymatic activity. A similar effect was observed in other previously described NPDB mutations located outside the active site of the enzyme. This work shows the first full size ASM mutant model describe at date, providing a complete analysis of the structural and functional effects of the p.Ala359Asp mutation over the stability and activity of the enzyme.

Transgenic overexpression of Niemann-Pick C2 protein promotes cholesterol gallstone formation in mice

BACKGROUND & AIMS

Niemann-Pick C2 (NPC2) is a lysosomal protein involved in the egress of low-density lipoprotein-derived cholesterol from lysosomes to other intracellular compartments. NPC2 has been detected in several tissues and is also secreted from the liver into bile. We have previously shown that NPC2-deficient mice fed a lithogenic diet showed reduced biliary cholesterol secretion as well as cholesterol crystal and gallstone formation. This study aimed to investigate the consequences of NPC2 hepatic overexpression on liver cholesterol metabolism, biliary lipid secretion, gallstone formation and the effect of NPC2 on cholesterol crystallization in model bile.

METHODS

We generated NPC2 transgenic mice (Npc2.Tg) and fed them either chow or lithogenic diets. We studied liver cholesterol metabolism, biliary lipid secretion, bile acid composition and gallstone formation. We performed cholesterol crystallization studies in model bile using a recombinant NPC2 protein.

RESULTS

No differences were observed in biliary cholesterol content or secretion between wild-type and Npc2.Tg mice fed the chow or lithogenic diets. Interestingly, Npc2.Tg mice showed an increased susceptibility to the lithogenic diet, developing more cholesterol gallstones at early times, but did not show differences in the bile acid hydrophobicity and gallbladder cholesterol saturation indices compared to wild-type mice. Finally, recombinant NPC2 decreased nucleation time in model bile.

CONCLUSIONS

These results suggest that NPC2 promotes cholesterol gallstone formation by decreasing the cholesterol nucleation time, indicating a pro-nucleating function of NPC2 in bile.

Metabolic effects of cholecystectomy: gallbladder ablation increases basal metabolic rate through G-protein coupled bile acid receptor Gpbar1-dependent mechanisms in mice

Background & Aims

Bile acids (BAs) regulate energy expenditure by activating G-protein Coupled Bile Acid Receptor Gpbar1/TGR5 by cAMP-dependent mechanisms. Cholecystectomy (XGB) increases BAs recirculation rates resulting in increased tissue exposure to BAs during the light phase of the diurnal cycle in mice. We aimed to determine: 1) the effects of XGB on basal metabolic rate (BMR) and 2) the roles of TGR5 on XGB-dependent changes in BMR.

Methods

BMR was determined by indirect calorimetry in wild type and Tgr5 deficient (Tgr5^-/-) male mice. Bile flow and BAs secretion rates were measured by surgical diversion of biliary duct. Biliary BAs and cholesterol were quantified by enzymatic methods. BAs serum concentration and specific composition was determined by liquid chromatography/tandem mass spectrometry. Gene expression was determined by qPCR analysis.

Results

XGB increased biliary BAs and cholesterol secretion rates, and elevated serum BAs concentration in wild type and Tgr5^-/- mice during the light phase of the diurnal cycle. BMR was ~25% higher in cholecystectomized wild type mice (p <0.02), whereas no changes were detected in cholecystectomized Tgr5^-/- mice compared to wild-type animals.

Conclusion

XGB increases BMR by TGR5-dependent mechanisms in mice.

Spermatozoa from mice deficient in Niemann-Pick disease type C2 (NPC2) protein have defective cholesterol content and reduced in vitro fertilising ability

The cholesterol content of the sperm membrane is regulated during both maturation in the epididymis and capacitation in the female tract, two processes required for the spermatozoa to acquire their fertilising ability. Because Niemann-Pick disease, type C2 (NPC2) protein is one of the most abundant components of the epididymal fluid and contains a functional cholesterol-binding site that can transfer cholesterol between membranes, it has been suggested for years that NPC2 could be involved in the regulation of cholesterol levels in spermatozoa during epididymal maturation. In the present study, western blot and immunohistochemistry analyses demonstrated significant levels of NPC2 in the mouse epididymal epithelium. Epididymal spermatozoa obtained from NPC2(-/-) mice were morphologically normal and had normal motility parameters, but had a reduced cholesterol content compared with that of wild-type (WT) spermatozoa, as determined by both biochemical and by flow cytometry analyses. These results suggest that NPC2 could be involved in regulating cholesterol levels in spermatozoa during epididymal maturation. To understand the relevance of epididymal NPC2 for sperm function, the ability of spermatozoa to undergo events influenced by epididymal maturation, such as capacitation and fertilisation, were compared between WT and NPC2(-/-) mice. Capacitated NPC2(-/-) spermatozoa exhibited defective tyrosine phosphorylation patterns and a reduced ability to fertilise cumulus-oocyte complexes compared with WT spermatozoa, supporting the relevance of mouse epididymal NPC2 for male fertility.

c-Abl stabilizes HDAC2 levels by tyrosine phosphorylation repressing neuronal gene expression in Alzheimer's disease

In Alzheimer's disease (AD), there is a decrease in neuronal gene expression induced by HDAC2 increase; however, the mechanisms involved are not fully elucidated. Here, we described how the tyrosine kinase c-Abl increases HDAC2 levels, inducing transcriptional repression of synaptic genes. Our data demonstrate that (1) in neurons, c-Abl inhibition with Imatinib prevents the AβO-induced increase in HDAC2 levels; (2) c-Abl knockdown cells show a decrease in HDAC2 levels, while c-Abl overexpression increases them; (3) c-Abl inhibition reduces HDAC2-dependent repression activity and HDAC2 recruitment to the promoter of several synaptic genes, increasing their expression; (4) c-Abl induces tyrosine phosphorylation of HDAC2, a posttranslational modification, affecting both its stability and repression activity; and (5) treatment with Imatinib decreases HDAC2 levels in a transgenic mice model of AD. Our results support the participation of the c-Abl/HDAC2 signaling pathway in the epigenetic blockade of gene expression in AD pathology.

The unique case of the Niemann-Pick type C cholesterol storage disorder

Niemann-Pick type C disease (NPC) is a neurovisceral lysosomal cholesterol storage disorder that arises from loss-of-f unction mutations in either the NPCI or NPC2 genes. Both genes code for proteins involved in lysosomal cholesterol efflux. NPC is often diagnosed in early childhood, with patients typically displaying cerebellar ataxia, difficulties in Unfortunately, to date, there is no curative treatment for this devastating and fatal disorder, although several symptomatic manifestations of NPC are treatable. In this review, we discuss the cell biology of the disease, clinical aspects, diagnostic approaches, and current and potential therapeutic strategies against NPC.

Hepatic metabolic response to restricted copper intake in a Niemann–Pick C murine model

Niemann–Pick C disease (NPC) is a vesicular trafficking disorder primarily caused by mutations in theNpc1gene and characterized by liver dysfunction and neuropathology.

Cholinergic abnormalities, endosomal alterations and up-regulation of nerve growth factor signaling in Niemann-Pick type C disease

BACKGROUND

Neurotrophins and their receptors regulate several aspects of the developing and mature nervous system, including neuronal morphology and survival. Neurotrophin receptors are active in signaling endosomes, which are organelles that propagate neurotrophin signaling along neuronal processes. Defects in the Npc1 gene are associated with the accumulation of cholesterol and lipids in late endosomes and lysosomes, leading to neurodegeneration and Niemann-Pick type C (NPC) disease. The aim of this work was to assess whether the endosomal and lysosomal alterations observed in NPC disease disrupt neurotrophin signaling. As models, we used i) NPC1-deficient mice to evaluate the central cholinergic septo-hippocampal pathway and its response to nerve growth factor (NGF) after axotomy and ii) PC12 cells treated with U18666A, a pharmacological cellular model of NPC, stimulated with NGF.

RESULTS

NPC1-deficient cholinergic cells respond to NGF after axotomy and exhibit increased levels of choline acetyl transferase (ChAT), whose gene is under the control of NGF signaling, compared to wild type cholinergic neurons. This finding was correlated with increased ChAT and phosphorylated Akt in basal forebrain homogenates. In addition, we found that cholinergic neurons from NPC1-deficient mice had disrupted neuronal morphology, suggesting early signs of neurodegeneration. Consistently, PC12 cells treated with U18666A presented a clear NPC cellular phenotype with a prominent endocytic dysfunction that includes an increased size of TrkA-containing endosomes and reduced recycling of the receptor. This result correlates with increased sensitivity to NGF, and, in particular, with up-regulation of the Akt and PLC-γ signaling pathways, increased neurite extension, increased phosphorylation of tau protein and cell death when PC12 cells are differentiated and treated with U18666A.

CONCLUSIONS

Our results suggest that the NPC cellular phenotype causes neuronal dysfunction through the abnormal up-regulation of survival pathways, which causes the perturbation of signaling cascades and anomalous phosphorylation of the cytoskeleton.

Alteration of gene expression profile in Niemann-Pick type C mice correlates with tissue damage and oxidative stress

BACKGROUND

Niemann-Pick type C disease (NPC) is a neurovisceral lipid storage disorder mainly characterized by unesterified cholesterol accumulation in lysosomal/late endosomal compartments, although there is also an important storage for several other kind of lipids. The main tissues affected by the disease are the liver and the cerebellum. Oxidative stress has been described in various NPC cells and tissues, such as liver and cerebellum. Although considerable alterations occur in the liver, the pathological mechanisms involved in hepatocyte damage and death have not been clearly defined. Here, we assessed hepatic tissue integrity, biochemical and oxidative stress parameters of wild-type control (Npc1(+/+); WT) and homozygous-mutant (Npc1(-/-); NPC) mice. In addition, the mRNA abundance of genes encoding proteins associated with oxidative stress, copper metabolism, fibrosis, inflammation and cholesterol metabolism were analyzed in livers and cerebella of WT and NPC mice.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed various oxidative stress parameters in the liver and hepatic and cerebellum gene expression in 7-week-old NPC1-deficient mice compared with control animals. We found signs of inflammation and fibrosis in NPC livers upon histological examination. These signs were correlated with increased levels of carbonylated proteins, diminished total glutathione content and significantly increased total copper levels in liver tissue. Finally, we analyzed liver and cerebellum gene expression patterns by qPCR and microarray assays. We found a correlation between fibrotic tissue and differential expression of hepatic as well as cerebellar genes associated with oxidative stress, fibrosis and inflammation in NPC mice.

CONCLUSIONS/SIGNIFICANCE

In NPC mice, liver disease is characterized by an increase in fibrosis and in markers associated with oxidative stress. NPC is also correlated with altered gene expression, mainly of genes involved in oxidative stress and fibrosis. These findings correlate with similar parameters in cerebellum, as has been previously reported in the NPC mice model.

Niemann-Pick C2 protein expression regulates lithogenic diet-induced gallstone formation and dietary cholesterol metabolism in mice

Niemann-Pick C2 protein (NPC2) is a lysosomal soluble protein that is highly expressed in the liver; it binds to cholesterol and is involved in intracellular cholesterol trafficking, allowing the exit of lysosomal cholesterol obtained via the lipoprotein endocytic pathway. Thus, this protein may play an important role in controlling hepatic cholesterol transport and metabolism. The aim of this work was to study the relevance of NPC2 protein expression in hepatic cholesterol metabolism, biliary lipid secretion and gallstone formation by comparing NPC2 hypomorph [NPC2 (h/h)] and wild-type mice fed control, 2% cholesterol, and lithogenic diets. NPC2 (h/h) mice exhibited resistance to a diet-induced increase in plasma cholesterol levels. When consuming the chow diet, we observed increased biliary cholesterol and phospholipid secretions in NPC2 (h/h) mice. When fed the 2% cholesterol diet, NPC2 (h/h) mice exhibited low and high gallbladder bile cholesterol and phospholipid concentrations, respectively. NPC2 (h/h) mice fed with the lithogenic diet showed reduced biliary cholesterol secretion, gallbladder bile cholesterol saturation, and cholesterol crystal and gallstone formation. This work indicates that hepatic NPC2 expression is an important factor in the regulation of diet-derived cholesterol metabolism and disposal as well as in diet-induced cholesterol gallstone formation in mice.

Npc1 deficiency in the C57BL/6J genetic background enhances Niemann-Pick disease type C spleen pathology

Niemann-Pick type C (NPC) disease is an autosomal recessive neurovisceral lipid storage disorder. The affected genes are NPC1 and NPC2. Mutations in either gene lead to intracellular cholesterol accumulation. There are three forms of the disease, which are categorized based on the onset and severity of the disease: the infantile form, in which the liver and spleen are severely affected, the juvenile form, in which the liver and brain are affected, and the adult form, which affects the brain. In mice, a spontaneous mutation in the Npc1 gene originated in the BALB/c inbred strain mimics the juvenile form of the disease. To study the influence of genetic background on the expression of NPC disease in mice, we transferred the Npc1 mutation from the BALB/c to C57BL/6J inbred background. We found that C57BL/6J-Npc1(-/-) mice present with a much more aggressive form of the disease, including a shorter lifespan than BALB/c-Npc1(-/-) mice. Surprisingly, there was no difference in the amount of cholesterol in the brains of Npc1(-/-) mice of either mouse strain. However, Npc1(-/-) mice with the C57BL/6J genetic background showed striking spleen damage with a marked buildup of cholesterol and phospholipids at an early age, which correlated with large foamy cell clusters. In addition, C57BL/6J Npc1(-/-) mice presented red cell abnormalities and abundant ghost erythrocytes that correlated with a lower hemoglobin concentration. We also found abnormalities in white cells, such as cytoplasmic granulation and neutrophil hypersegmentation that included lymphopenia and atypias. In conclusion, Npc1 deficiency in the C57BL6/J background is associated with spleen, erythrocyte, and immune system abnormalities that lead to a reduced lifespan.

Apolipoprotein A-I deficiency does not affect biliary lipid secretion and gallstone formation in mice

BACKGROUND/AIMS

Apolipoprotein A-I (apo A-I) is the main protein component of plasma high-density lipoproteins (HDL) and a key determinant of HDL cholesterol levels and metabolism. The relevance of HDL in controlling the traffic of cholesterol from plasma into bile has been partially addressed. The aim of this study was to evaluate the role of apo A-I expression in controlling the secretion of biliary lipids as well as the risk of gallstone disease in vivo.

METHODS

We evaluated biliary lipid secretion and bile acid homeostasis in mice deficient for apo A-I compared with wild-type animals when fed with low- or high-cholesterol diets. In addition, we assessed the importance of murine apoA-I expression for gallstone formation after feeding a lithogenic diet.

RESULTS

Bile acid pool size and faecal excretion were within the normal range in chow- and cholesterol-fed apo A-I knockout (KO) mice. Basal biliary cholesterol secretion was comparable and increased similarly in both murine strains after cholesterol feeding. Lithogenic diet-fed apo A-I KO mice exhibited an impaired hypercholesterolaemic response owing to a lower increase in cholesterol levels transported in large lipoproteins. However, the lack of apo A-I expression did not affect biliary cholesterol precipitation or gallstone formation in lithogenic diet-fed mice.

CONCLUSIONS

These findings indicate that biliary lipid secretion, bile acid metabolism and gallstone formation are independent of apo A-I expression and plasma HDL cholesterol levels in mice.

Cholecystectomy increases hepatic triglyceride content and very-low-density lipoproteins production in mice

BACKGROUND & AIMS

Bile acid (BA) pool size remains unchanged after cholecystectomy (XGB) but it circulates faster, exposing the enterohepatic system to an increased flux of BA. Triglyceride (TG) and BA metabolisms are functionally inter-related. We investigated whether ablation of the gallbladder (GB) modifies hepatic TG metabolism.

METHODS

Male mice were subjected to XGB and fed a normal diet. In some experiments, mice received a 1% nicotinic acid diet to block lipolysis. Parameters of BA and TG metabolism, and microsomal triglyceride transfer protein (MTTP) activity were measured 1-2 months after XGB. Serum parameters, hepatic lipids and mRNA expression of genes of lipid metabolism were determined.

RESULTS

BA pool size and synthesis were normal, but biliary BA secretion doubled during the diurnal light phase in XGB mice. Serum and hepatic TG concentrations increased 25% (P<0.02), and hepatic very-low-density lipoproteins (VLDL)-TG and apoB-48 productions increased 15% (P<0.03) and 50% (P<0.01), respectively, after XGB. Feeding a 1% nicotinic acid did normalize VLDL production. MTTP activity increased 15% (P<0.005) after XGB. Hepatic free fatty acid (FFA) synthesis and content, and mRNA levels of lipid metabolism-related genes remained normal in XGD mice.

CONCLUSIONS

XGB increased serum and hepatic TG levels, and VLDL production, which were restored to normal by nicotinic acid. The results suggest that FFA flux from adipose tissue to the liver is increased in XGB mice. They support the hypothesis that the GB has a role in the regulation of hepatic TG metabolism and that XGB may favour the accumulation of fat in the liver.

Lack of activation of the unfolded protein response in mouse and cellular models of Niemann-Pick type C disease

BACKGROUND

Niemann-Pick type C (NPC) disease is a fatal lysosomal storage disease related to progressive neurodegeneration secondary to abnormal intracellular accumulation of cholesterol. Signs of endoplasmic reticulum (ER) stress have been reported in other lipidoses. Adaptation to ER stress is mediated by the unfolded protein response (UPR), an integrated signal transduction pathway that attenuates stress or triggers apoptosis of irreversibly damaged cells.

OBJECTIVE

To investigate the possible engagement of ER stress responses in NPC models.

METHODS

We used NPC1 deficient mice and an NPC cell-based model by knocking down the expression of NPC1 to measure several UPR markers through different approaches.

RESULTS

Despite expectations that the UPR will be activated in NPC, our results indicate a lack of ER stress reactions in the cerebellum of symptomatic mice. Similarly, knocking down NPC1 in Neuro2a cells leads to clear cholesterol accumulation without evidence of UPR activation.

CONCLUSION

Our results suggest that cholesterol overload and neuronal dysfunction in NPC is not associated with ER stress, which contrasts with recent reports suggesting the activation of the UPR in other lysosomal storage diseases.

[The metabolic syndrome: from an aggravating condition to a pathogenic risk factor for chronic diseases]

In recent years, a rapidly increasing number of studies have focused on the association between metabolic syndrome and several chronic diseases. However, it is difficult to determine a well defined pathogenic relationship, due to the etiological heterogeneity and comorbidities of these diseases. Research efforts are aiming to identify the convergent biological mechanisms that mediate the effects of hyperinsulinemia, hyperglycemia, dyslipidemia, and hypertension. All these conditions define the metabolic syndrome, that increases the risk for several diseases. The knowledge of these biological mechanisms associated with this syndrome will elucidate the pathogenic association between a variety of chronic diseases, including its pathogenic link with cardiovascular diseases and the most common forms of dementia. The development of new therapeutic and preventive strategies for these diseases will be a corollary of this research.

Deficiency of Niemann-Pick C1 protein protects against diet-induced gallstone formation in mice

BACKGROUND/AIMS

Receptor-mediated endocytosis is a critical cellular mechanism for the uptake of lipoprotein cholesterol in the liver. Because Niemann-Pick C1 (NPC1) protein is a key component for the intracellular distribution of cholesterol originating from lipoprotein endocytosis, it may play an important role in controlling biliary cholesterol secretion and gallstone formation induced by a lithogenic diet.

METHODS

We studied biliary cholesterol secretion, gallbladder lipid composition and gallstone formation in NPC1-deficient mice fed a low-fat lithogenic diet (1.5% cholesterol and 0.5% cholic acid) compared with control animals under the same diet.

RESULTS

The lipid secretion response to the lithogenic diet was impaired in NPC1 (-/-) mice, leading to a decreased cholesterol output and an increased hepatic cholesterol concentration compared with the lithogenic diet-fed wild-type mice. A decreased cholesterol saturation index was found in the gallbladder bile of NPC1 (+/-) and (-/-) mice after lithogenic diet feeding. Consequently, mice with a partial or a total deficiency of NPC1 had a drastically lower frequency of gallbladder cholesterol crystals and a reduced prevalence of gallstones.

CONCLUSION

Hepatic NPC1 expression is an important factor for regulating the biliary secretion of diet-derived cholesterol as well as for diet-induced cholesterol gallstone formation in mice.

Female infertility due to anovulation and defective steroidogenesis in NPC2 deficient mice

Niemann Pick C2 (NPC2) and NPC1 proteins function cooperatively to catalyze cholesterol efflux from lysosomes. NPC1 is expressed in ovarian cells and female NPC1 mice are infertile. This work addressed for the first time the localization and function of murine NPC2 protein in the ovary. Ovarian NPC2 was localized to theca and luteal cells, which use cholesterol as a substrate to produce estradiol and progesterone, respectively. NPC2 deficient (NPC2-/-) females had abnormal estrous cycles and were infertile, with normal folliculogenesis until the antral stage, but a complete absence of corpora lutea and many zonae pellucidae remnants, indicative of anovulation. Serum estradiol was reduced and ovarian cholesterol was accumulated in NPC2-/- mice, suggesting a defect in cholesterol export from intracellular stores. After superovulation, NPC2-/- mice ovulated less eggs than their wild type littermates, showed ovaries with less corpora lutea and numerous unruptured follicles, and lower serum progesterone concentration. Together, these results suggest that NPC2 participates in the traffic of ovarian cholesterol required to provide the substrate for steroid synthesis and support follicle maturation, ovulation and luteinization.

Fecal bile acid excretion and messenger RNA expression levels of ileal transporters in high risk gallstone patients

BACKGROUND

Cholesterol gallstone disease (GS) is highly prevalent among Hispanics and American Indians. In GS, the pool of bile acids (BA) is decreased, suggesting that BA absorption is impaired. In Caucasian GS patients, mRNA levels for ileal BA transporters are decreased. We aimed to determine fecal BA excretion rates, mRNA levels for ileal BA transporter genes and of regulatory genes of BA synthesis in Hispanic GS patients.

RESULTS

Excretion of fecal BA was measured in seven GS females and in ten GS-free individuals, all with a body mass index < 29. Participants ingested the stool marker Cr2O3 (300 mg/day) for 10 days, and fecal specimens were collected on the last 3 days. Chromium was measured by a colorimetric method, and BA was quantitated by gas chromatography/mass spectroscopy. Intake of calories, nutrients, fiber and cholesterol were similar in the GS and GS-free subjects. Mean BA excretion levels were 520 +/- 80 mg/day for the GS-free group, and 461 +/- 105 mg/day for the GS group. Messenger RNA expression levels were determined by RT-PCR on biopsy samples obtained from ileum during diagnostic colonoscopy (14 GS-free controls and 16 GS patients) and from liver during surgery performed at 8 and 10 AM (12 GS and 10 GS-free patients operated on for gastrointestinal malignancies), all with a body mass index < 29. Messenger RNA level of the BA transporter genes for ileal lipid binding protein, multidrug resistance-associated protein 3, organic solute transporter alpha, and organic solute transporter beta were similar in GS and GS-free subjects. Messenger RNA level of Cyp27A1, encoding the enzyme 27alpha-hydroxylase, the short heterodimer partner and farnesoid X receptor remained unchanged, whereas the mRNA level of Cyp7A1, the rate limiting step of BA synthesis, was increased more than 400% (p < 0.01) in the liver of GS compared to GS-free subjects.

CONCLUSION

Hispanics with GS have fecal BA excretion rates and mRNA levels of genes for ileal BA transporters that are similar to GS-free subjects. However, mRNA expression levels of Cyp7A1 are increased in GS, indicating that regulation of BA synthesis is abnormal in Hispanics with GS.

Determinants of transhepatic cholesterol flux and their relevance for gallstone formation

Cholesterol available for bile secretion is controlled by a wide variety of proteins that mediate lipoprotein cholesterol uptake and cholesterol transport and metabolism in the liver. From a disease perspective, abnormalities in the transhepatic traffic of cholesterol from plasma into the bile may influence the risk of cholesterol gallstone formation. This review summarizes some recent progress in understanding the hepatic determinants of biliary cholesterol secretion and its potential pathogenic implications in cholesterol gallstone disease. This information together with new discoveries in this field may lead to improved risk evaluation, novel surrogate markers and earlier diagnosis, better preventive approaches and more effective pharmacological therapies for this prevalent human disease.

Imatinib therapy blocks cerebellar apoptosis and improves neurological symptoms in a mouse model of Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease is a fatal autosomal recessive disorder characterized by the accumulation of free cholesterol and glycosphingolipids in the endosomal-lysosomal system. Patients with NPC disease have markedly progressive neuronal loss, mainly of cerebellar Purkinje neurons. There is strong evidence indicating that cholesterol accumulation and trafficking defects activate apoptosis in NPC brains. The purpose of this study was to analyze the relevance of apoptosis and particularly the proapoptotic c-Abl/p73 system in cerebellar neuron degeneration in NPC disease. We used the NPC1 mouse model to evaluate c-Abl/p73 expression and activation in the cerebellum and the effect of therapy with the c-Abl-specific inhibitor imatinib. The proapoptotic c-Abl/p73 system and the p73 target genes are expressed in the cerebellums of NPC mice. Furthermore, inhibition of c-Abl with imatinib preserved Purkinje neurons and reduced general cell apoptosis in the cerebellum, improved neurological symptoms, and increased the survival of NPC mice. Moreover, this prosurvival effect correlated with reduced mRNA levels of p73 proapoptotic target genes. Our results suggest that the c-Abl/p73 pathway is involved in NPC neurodegeneration and show that treatment with c-Abl inhibitors is useful in delaying progressive neurodegeneration, supporting the use of imatinib for clinical treatment of patients with NPC disease.

Overexpression of the cholesterol-binding protein MLN64 induces liver damage in the mouse

AIM: To examine the in vivo phenotype associated with hepatic metastatic lymph node 64 (MLN64) over-expression.

METHODS: Recombinant-adenovirus-mediated MLN64 gene transfer was used to overexpress MLN64 in the livers of C57BL/6 mice. We measured the effects of MLN64 overexpression on hepatic cholesterol content, bile flow, biliary lipid secretion and apoptosis markers. For in vitro studies cultured CHO cells with transient MLN64 overexpression were utilized and apoptosis by TUNEL assay was measured.

RESULTS: Livers from Ad.MLN64-infected mice exhibited early onset of liver damage and apoptosis. This response correlated with increases in liver cholesterol content and biliary bile acid concentration, and impaired bile flow. We investigated whether liver MLN64 expression could be modulated in a murine model of hepatic injury. We found increased hepatic MLN64 mRNA and protein levels in mice with chenodeoxycholic acid-induced liver damage. In addition, cultured CHO cells with transient MLN64 overexpression showed increased apoptosis.

CONCLUSION: In summary, hepatic MLN64 over-expression induced damage and apoptosis in murine livers and altered cholesterol metabolism. Further studies are required to elucidate the relevance of these findings under physiologic and disease conditions.

Role of plasma and liver cholesterol- and lipoprotein-metabolism determinants in LpX formation in the mouse

Cholestasis is characterized by hypercholesterolemia and the appearance of an abnormal lipoprotein, lipoprotein X (LpX), in plasma. The mechanisms responsible for this cholestatic plasma lipid phenotype are not fully understood. We used ATP-binding cassette A1 (ABCA1)-/- and scavenger receptor class B type I (SR-BI)-/- mice to test the hypothesis that hepatic sinusoidal cholesterol transporters contribute to LpX formation and hypercholesterolemia during cholestasis. Bile-duct ligation (BDL) of both ABCA1-/- and SR-BI-/- mice, as well as their respective controls, induced a dramatic increase in plasma cholesterol and phospholipid concentrations. Plasma fractionation revealed the presence of LpX in plasma of cholestatic mice, irrespective of their genetic background. We observed that the presence of HDL before cholestasis, a decrease in the activity of LCAT, and an increase in VLDL synthesis were not required for hypercholesterolemia and lipoprotein modifications induced by obstructive cholestasis in mice. In addition, murine cholestasis resulted in increased hepatic cholesterol synthesis that may contribute to the higher plasma free cholesterol levels found during the early hours after BDL. Together these findings indicate that hypercholesterolemia and LpX formation associated with obstructive cholestasis are correlated with an increase in hepatic cholesterol synthesis and are independent of plasma HDL levels, LCAT activity, VLDL synthesis, and ABCA1 and SR-BI expression.

Adenovirus-mediated hepatic syndecan-1 overexpression induces hepatocyte proliferation and hyperlipidaemia in mice

BACKGROUND

Heparan sulfate proteoglycans (HSPGs) have been involved in the regulation of cell growth, apoptosis and lipid metabolism in vitro; however, their functional role in vivo remains unknown.

AIM

Here, we describe hepatic tissue and lipid metabolism changes after liver overexpression of syndecan-1 (SDC-1), the main hepatic HSPG, in mice induced by adenoviral gene transfer.

RESULTS

SDC-1 overexpression was associated with marked hepatocyte proliferation, cell-isolated apoptosis and increased plasma alanine aminotransferase (ALT) levels. Additionally, SDC-1 liver overexpression significantly raised plasma cholesterol and triglyceride concentrations due to an increase in all lipoprotein particles, including the appearance of large and apolipoprotein (apo) E-enriched high-density lipoprotein (HDL) particles. Hepatic very low-density lipoprotein (VLDL) production was not affected by SDC-1 overexpression, suggesting a delayed plasma clearance of apo B lipoproteins as the underlying hyperlipidaemic mechanism. These pleotropic effects were qualitatively equivalent, even though less intense, in mice overexpressing a cytoplasmic C-terminal domain-deleted SDC-1.

CONCLUSIONS

This is the first report in vivo of the biological effects induced by a specific HSPG in the liver, with potential implications in both regenerative biology and molecular lipidology.