Npc1 acting in neurons and glia is essential for the formation and maintenance of CNS myelin

Potential Use of the Cholesterol Transfer Inhibitor U18666A as a Potent Research Tool for the Study of Cholesterol Mechanisms in Neurodegenerative Disorders

Cholesterol is an essential component of mammalian cell membranes and a precursor for crucial signaling molecules. The brain contains the highest level of cholesterol in the body, and abnormal cholesterol metabolism links to many neurodegenerative disorders. The results indicate that faulty cholesterol metabolism is a common feature among people living with neurodegenerative conditions. The researchers suggest that restoring cholesterol levels may become a beneficial new strategy in treating certain neurodegenerative conditions. Several neurodegenerative disorders, such as Alzheimer's disease (AD), Niemann-Pick type C (NPC) disease, and Parkinson's disease (PD), have been connected to abnormalities in brain cholesterol metabolism. Consequently, using a lipid research tool is vital to study further and understand the effect of lipids in neurodegenerative disorders such as NPC, AD, PD, and Huntington's disease (HD). U18666A, also known as 3-(2-(diethylamino) ethoxy) androst-5-en-17-one, is a pharmaceutical drug that suppresses cholesterol trafficking and is a well-known class-2 amphiphile. U18666A has performed many functions, allowing for essential discoveries in lipid studies and shedding light on the pathophysiology of neurodegenerative disorders. Additionally, U18666A prevented the downregulation of low-density lipoprotein (LDL) receptors that are induced by LDL and led to the buildup of cholesterol in lysosomes. Numerous studies show that U18666A impacts the function of cholesterol trafficking to control the metabolism and transport of amyloid precursor proteins (APPs). Treating cortical neurons with U18666A may provide a new in vitro model system for studying the underlying molecular process of NPC, AD, HD, and PD. In this article, we review the mechanism and function of U18666A as a vital tool for studying cholesterol mechanisms in neurological diseases related to abnormal cholesterol metabolism, such as AD, NPC, HD, and PD.

Endo-lysosomal dysfunction and neuronal-glial crosstalk in Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease is a rare progressive lysosomal lipid storage disorder that manifests with a heterogeneous spectrum of clinical syndromes, including visceral, neurological and psychiatric symptoms. This monogenetic autosomal recessive disease is largely caused by mutations in the NPC1 gene, which controls intracellular lipid homeostasis. Vesicle-mediated endo-lysosomal lipid trafficking and non-vesicular lipid exchange via inter-organelle membrane contact sites are both regulated by the NPC1 protein. Loss of NPC1 function therefore triggers intracellular accumulation of diverse lipid species, including cholesterol, glycosphingolipids, sphingomyelin and sphingosine. The NPC1-mediated dysfunction of lipid transport has severe consequences for all brain cells, leading to neurodegeneration. Besides the cell-autonomous contribution of neuronal NPC1, aberrant NPC1 signalling in other brain cells is critical for the pathology. We discuss here the importance of endo-lysosomal dysfunction and a tight crosstalk between neurons, oligodendrocytes, astrocytes and microglia in NPC pathology. We strongly believe that a cell-specific rescue may not be sufficient to counteract the severity of the NPC pathology, but targeting common mechanisms, such as endo-lysosomal and lipid trafficking dysfunction, may ameliorate NPC pathology. This article is part of a discussion meeting issue 'Understanding the endo-lysosomal network in neurodegeneration'.

Upstream lipid and metabolic systems are potential causes of Alzheimer's disease, Parkinson's disease and dementias

Brain health requires circuits, cells and molecular pathways to adapt when challenged and to promptly reset once the challenge has resolved. Neurodegeneration occurs when adaptability becomes confined, causing challenges to overwhelm neural circuitry. Studies of rare and common neurodegenerative diseases suggest that the accumulation of lipids can compromise circuit adaptability. Using microglia as an example, we review data that suggest increased lipid concentrations cause dysfunctional inflammatory responses to immune challenges, leading to Alzheimer's disease, Parkinson's disease and dementia. We highlight current approaches to treat lipid metabolic and clearance pathways and identify knowledge gaps towards restoring adaptive homeostasis in individuals who are at-risk of losing cognition.

An overview of the role of Niemann-pick C1 (NPC1) in viral infections and inhibition of viral infections through NPC1 inhibitor

Viruses communicate with their hosts through interactions with proteins, lipids, and carbohydrate moieties on the plasma membrane (PM), often resulting in viral absorption via receptor-mediated endocytosis. Many viruses cannot multiply unless the host's cholesterol level remains steady. The large endo/lysosomal membrane protein (MP) Niemann-Pick C1 (NPC1), which is involved in cellular cholesterol transport, is a crucial intracellular receptor for viral infection. NPC1 is a ubiquitous housekeeping protein essential for the controlled cholesterol efflux from lysosomes. Its human absence results in Niemann-Pick type C disease, a deadly lysosomal storage disorder. NPC1 is a crucial viral receptor and an essential host component for filovirus entrance, infection, and pathogenesis. For filovirus entrance, NPC1's cellular function is unnecessary. Furthermore, blocking NPC1 limits the entry and replication of the African swine fever virus by disrupting cholesterol homeostasis. Cell entrance of quasi-enveloped variants of hepatitis A virus and hepatitis E virus has also been linked to NPC1. By controlling cholesterol levels, NPC1 is also necessary for the effective release of reovirus cores into the cytoplasm. Drugs that limit NPC1's activity are effective against several viruses, including SARS-CoV and Type I Feline Coronavirus (F-CoV). These findings reveal NPC1 as a potential therapeutic target for treating viral illnesses and demonstrate its significance for several viral infections. This article provides a synopsis of NPC1's function in viral infections and a review of NPC1 inhibitors that may be used to counteract viral infections. Video Abstract.

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.

The cholesterol transporter NPC1 is essential for epigenetic regulation and maturation of oligodendrocyte lineage cells

The intracellular cholesterol transporter NPC1 functions in late endosomes and lysosomes to efflux unesterified cholesterol, and its deficiency causes Niemann-Pick disease Type C, an autosomal recessive lysosomal disorder characterized by progressive neurodegeneration and early death. Here, we use single-nucleus RNA-seq on the forebrain of Npc1^-/- mice at P16 to identify cell types and pathways affected early in pathogenesis. Our analysis uncovers significant transcriptional changes in the oligodendrocyte lineage during developmental myelination, accompanied by diminished maturation of myelinating oligodendrocytes. We identify upregulation of genes associated with neurogenesis and synapse formation in Npc1^-/- oligodendrocyte lineage cells, reflecting diminished gene silencing by H3K27me3. Npc1^-/- oligodendrocyte progenitor cells reproduce impaired maturation in vitro, and this phenotype is rescued by treatment with GSK-J4, a small molecule inhibitor of H3K27 demethylases. Moreover, mobilizing stored cholesterol in Npc1^-/- mice by a single administration of 2-hydroxypropyl-β-cyclodextrin at P7 rescues myelination, epigenetic marks, and oligodendrocyte gene expression. Our findings highlight an important role for NPC1 in oligodendrocyte lineage maturation and epigenetic regulation, and identify potential targets for therapeutic intervention.

Role of Lipids in Regulation of Neuroglial Interactions

Lipids comprise an extremely heterogeneous group of compounds that perform a wide variety of biological functions. Traditional view of lipids as important structural components of the cell and compounds playing a trophic role is currently being supplemented by information on the possible participation of lipids in signaling, not only intracellular, but also intercellular. The review article discusses current data on the role of lipids and their metabolites formed in glial cells (astrocytes, oligodendrocytes, microglia) in communication of these cells with neurons. In addition to metabolic transformations of lipids in each type of glial cells, special attention is paid to the lipid signal molecules (phosphatidic acid, arachidonic acid and its metabolites, cholesterol, etc.) and the possibility of their participation in realization of synaptic plasticity, as well as in other possible mechanisms associated with neuroplasticity. All these new data can significantly expand our knowledge about the regulatory functions of lipids in neuroglial relationships.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Cholesterol metabolism: Towards a therapeutic approach for multiple sclerosis

Growing evidence points to the importance of cholesterol in preserving brain homeostasis. Cholesterol makes up the main component of myelin in the brain, and myelin integrity is vital in demyelinating diseases such as multiple sclerosis. Because of the connection between myelin and cholesterol, the interest in cholesterol in the central nervous system increased during the last decade. In this review, we provide a detailed overview on brain cholesterol metabolism in multiple sclerosis and its role in promoting oligodendrocyte precursor cell differentiation and remyelination.

Human early-onset dementia caused by DAP12 deficiency reveals a unique signature of dysregulated microglia

The TREM2-DAP12 receptor complex sustains microglia functions. Heterozygous hypofunctional TREM2 variants impair microglia, accelerating late-onset Alzheimer's disease. Homozygous inactivating variants of TREM2 or TYROBP-encoding DAP12 cause Nasu-Hakola disease (NHD), an early-onset dementia characterized by cerebral atrophy, myelin loss and gliosis. Mechanisms underpinning NHD are unknown. Here, single-nucleus RNA-sequencing analysis of brain specimens from DAP12-deficient NHD individuals revealed a unique microglia signature indicating heightened RUNX1, STAT3 and transforming growth factor-β signaling pathways that mediate repair responses to injuries. This profile correlated with a wound healing signature in astrocytes and impaired myelination in oligodendrocytes, while pericyte profiles indicated vascular abnormalities. Conversely, single-nuclei signatures in mice lacking DAP12 signaling reflected very mild microglial defects that did not recapitulate NHD. We envision that DAP12 signaling in microglia attenuates wound healing pathways that, if left unchecked, interfere with microglial physiological functions, causing pathology in human. The identification of a dysregulated NHD microglia signature sparks potential therapeutic strategies aimed at resetting microglia signaling pathways.

The Cerebellum in Niemann-Pick C1 Disease: Mouse Versus Man

Selective neuronal vulnerability is common to most degenerative disorders, including Niemann-Pick C (NPC), a rare genetic disease with altered intracellular trafficking of cholesterol. Purkinje cell dysfunction and loss are responsible for cerebellar ataxia, which is among the prevailing neurological signs of the NPC disease. In this review, we focus on some questions that are still unresolved. First, we frame the cerebellar vulnerability in the context of the extended postnatal time length by which the development of this structure is completed in mammals. In line with this thought, the much later development of cerebellar symptoms in humans is due to the later development and/or maturation of the cerebellum. Hence, the occurrence of developmental events under a protracted condition of defective intracellular cholesterol mobilization hits the functional maturation of the various cell types generating the ground of increased vulnerability. This is particularly consistent with the high cholesterol demand required for cell proliferation, migration, differentiation, and synapse formation/remodeling. Other major questions we address are why the progression of Purkinje cells loss is always from the anterior to the posterior lobes and why cerebellar defects persist in the mouse model even when genetic manipulations can lead to nearly normal survival.

Organ Weights in NPC1 Mutant Mice Partly Normalized by Various Pharmacological Treatment Approaches

Niemann-Pick Type C1 (NPC1, MIM 257220) is a rare, progressive, lethal, inherited autosomal-recessive endolysosomal storage disease caused by mutations in the NPC1 leading to intracellular lipid storage. We analyzed mostly not jet known alterations of the weights of 14 different organs in the BALB/cNctr-Npc1^m1N/-J Jackson Npc1 mice in female and male Npc1^+/+ and Npc1^-/- mice under various treatment strategies. Mice were treated with (i) no therapy, (ii) vehicle injection, (iii) a combination of miglustat, allopregnanolone, and 2-hydroxypropyl-ß-cyclodextrin (HPßCD), (iv) miglustat, and (v) HPßCD alone starting at P7 and repeated weekly throughout life. The 12 respective male and female wild-type mice groups were evaluated in parallel. In total, 351 mice (176 Npc1^+/+, 175 Npc1^-/-) were dissected at P65. In both sexes, the body weights of None and Sham Npc1^-/- mice were lower than those of respective Npc1^+/+ mice. The influence of the Npc1 mutation and/or sex on the weights of various organs, however, differed considerably. In males, Npc1^+/+ and Npc1^-/- mice had comparable absolute weights of lungs, spleen, and adrenal glands. In Npc1^-/- mice, smaller weights of hearts, livers, kidneys, testes, vesicular, and scent glands were found. In female Npc1^-/- mice, ovaries, and uteri were significantly smaller. In Npc1^-/- mice, relative organ weights, i.e., normalized with body weights, were sex-specifically altered to different extents by the different therapies. The combination of miglustat, allopregnanolone, and the sterol chelator HPßCD partly normalized the weights of more organs than miglustat or HPßCD mono-therapies.

Species-specific differences in NPC1 protein trafficking govern therapeutic response in Niemann-Pick type C disease

The folding and trafficking of transmembrane glycoproteins are essential for cellular homeostasis and are compromised in many diseases. In Niemann-Pick type C disease, a lysosomal disorder characterized by impaired intracellular cholesterol trafficking, the transmembrane glycoprotein NPC1 misfolds due to disease-causing missense mutations. While mutant NPC1 has emerged as a robust target for proteostasis modulators, drug development efforts have been unsuccessful in mouse models. Here, we demonstrated unexpected differences in trafficking through the medial Golgi between mouse and human I1061T-NPC1, a common disease-causing mutant. We established that these distinctions are governed by differences in the NPC1 protein sequence rather than by variations in the endoplasmic reticulum-folding environment. Moreover, we demonstrated direct effects of mutant protein trafficking on the response to small molecules that modulate the endoplasmic reticulum-folding environment by affecting Ca++ concentration. Finally, we developed a panel of isogenic human NPC1 iNeurons expressing WT, I1061T-, and R934L-NPC1 and demonstrated their utility in testing these candidate therapeutics. Our findings identify important rules governing mutant NPC1's response to proteostatic modulators and highlight the importance of species- and mutation-specific responses for therapy development.

Heat shock protein amplification improves cerebellar myelination in the Npc1nih mouse model

BACKGROUND

Niemann-Pick disease type C (NPC) is a rare prematurely fatal lysosomal lipid storage disease with limited therapeutic options. The prominent neuropathological hallmarks include hypomyelination and cerebellar atrophy. We previously demonstrated the efficacy of recombinant human heat shock protein 70 (rhHSP70) in preclinical models of the disease. It reduced glycosphingolipid levels in the central nervous system (CNS), improving cerebellar myelination and improved behavioural phenotypes in Npc1^nih (Npc1^-/-) mice. Furthermore, treatment with arimoclomol, a well-characterised HSP amplifier, attenuated lysosomal storage in NPC patient fibroblasts and improved neurological symptoms in Npc1^-/- mice. Taken together, these findings prompted the investigation of the effects of HSP amplification on CNS myelination.

METHODS

We administered bimoclomol daily or rhHSP70 6 times per week to Npc1^-/- (BALB/cNctr-Npc1^m1N/J, also named Npc1^nih) mice by intraperitoneal injection from P7 through P34 to investigate the impact on CNS myelination. The Src-kinase inhibitor saracatinib was administered with/without bimoclomol twice daily to explore the contribution of Fyn kinase to bimoclomol's effects.

FINDINGS

Treatment with either bimoclomol or rhHSP70 improved myelination and increased the numbers of mature oligodendrocytes (OLs) as well as the ratio of active-to-inactive forms of phosphorylated Fyn kinase in the cerebellum of Npc1^-/- mice. Additionally, treatment with bimoclomol preserved cerebellar weight, an effect that was abrogated when co-administered with saracatinib, an inhibitor of Fyn kinase. Bimoclomol-treated mice also exhibited increased numbers of immature OLs within the cortex.

INTERPRETATION

These data increase our understanding of the mechanisms by which HSP70 regulates myelination and provide further support for the clinical development of HSP-amplifying therapies in the treatment of NPC.

FUNDING

Funding for this study was provided by Orphazyme A/S (Copenhagen, Denmark) and a Pathfinder Award from The Wellcome Trust.

Phagocytosing differentiated cell-fragments is a novel mechanism for controlling somatic stem cell differentiation within a short time frame

Stem cells undergo cytokine-driven differentiation, but this process often takes longer than several weeks to complete. A novel mechanism for somatic stem cell differentiation via phagocytosing ‘model cells’ (apoptotic differentiated cells) was found to require only a short time frame. Pluripotent-like Muse cells, multipotent mesenchymal stem cells (MSCs), and neural stem cells (NSCs) phagocytosed apoptotic differentiated cells via different phagocytic receptor subsets than macrophages. The phagocytosed-differentiated cell-derived contents (e.g., transcription factors) were quickly released into the cytoplasm, translocated into the nucleus, and bound to promoter regions of the stem cell genomes. Within 24 ~ 36 h, the cells expressed lineage-specific markers corresponding to the phagocytosed-differentiated cells, both in vitro and in vivo. At 1 week, the gene expression profiles were similar to those of the authentic differentiated cells and expressed functional markers. Differentiation was limited to the inherent potential of each cell line: triploblastic-, adipogenic-/chondrogenic-, and neural-lineages in Muse cells, MSCs, and NSCs, respectively. Disruption of phagocytosis, either by phagocytic receptor inhibition via small interfering RNA or annexin V treatment, impeded differentiation in vitro and in vivo. Together, our findings uncovered a simple mechanism by which differentiation-directing factors are directly transferred to somatic stem cells by phagocytosing apoptotic differentiated cells to trigger their rapid differentiation into the target cell lineage.

Developmental Cues and Molecular Drivers in Myelinogenesis: Revisiting Early Life to Re-Evaluate the Integrity of CNS Myelin

The mammalian central nervous system (CNS) coordinates its communication through saltatory conduction, facilitated by myelin-forming oligodendrocytes (OLs). Despite the fact that neurogenesis from stem cell niches has caught the majority of attention in recent years, oligodendrogenesis and, more specifically, the molecular underpinnings behind OL-dependent myelinogenesis, remain largely unknown. In this comprehensive review, we determine the developmental cues and molecular drivers which regulate normal myelination both at the prenatal and postnatal periods. We have indexed the individual stages of myelinogenesis sequentially; from the initiation of oligodendrocyte precursor cells, including migration and proliferation, to first contact with the axon that enlists positive and negative regulators for myelination, until the ultimate maintenance of the axon ensheathment and myelin growth. Here, we highlight multiple developmental pathways that are key to successful myelin formation and define the molecular pathways that can potentially be targets for pharmacological interventions in a variety of neurological disorders that exhibit demyelination.

Central nervous system cholesterol metabolism in health and disease

Cholesterol is a ubiquitous and essential component of cellular membranes, as it regulates membrane structure and fluidity. Furthermore, cholesterol serves as a precursor for steroid hormones, oxysterol, and bile acids, that are essential for maintaining many of the body's metabolic processes. The biosynthesis and excretion of cholesterol is tightly regulated in order to maintain homeostasis. Although virtually all cells have the capacity to make cholesterol, the liver and brain are the two main organs producing cholesterol in mammals. Once produced, cholesterol is transported in the form of lipoprotein particles to other cell types and tissues. Upon formation of the blood-brain barrier (BBB) during embryonic development, lipoproteins cannot move between the central nervous system (CNS) and the rest of the body. As such, cholesterol biosynthesis and metabolism in the CNS operate autonomously without input from the circulation system in normal physiological conditions. Nevertheless, similar regulatory mechanisms for maintaining cholesterol homeostasis are utilized in both the CNS and peripheral systems. Here, we discuss the functions and metabolism of cholesterol in the CNS. We further focus on how different CNS cell types contribute to cholesterol metabolism, and how ApoE, the major CNS apolipoprotein, is involved in normal and pathophysiological functions. Understanding these basic mechanisms will aid our ability to elucidate how CNS cholesterol dysmetabolism contributes to neurogenerative diseases.

Experience of the NPC Brazil Network with a Comprehensive Program for the Screening and Diagnosis of Niemann-Pick Disease Type C

Niemann-Pick disease type C (NPC) is a lysosomal disorder caused by impaired cholesterol metabolism. Levels of lysosphingomyelin 509 (LysoSM509) have been shown elevated in dried blood spots (DBS) of NPC and acid sphingomyelinase deficiency patients. In this study, we report our experience using a two-tier approach (1st tier is the quantification of lysoSM509 by ultra-performance liquid chromatography tandem mass spectrometry followed by the 2nd tier with next-generation sequencing of the NPC1 and NPC2 genes). DBS samples from 450 suspected patients were received by the NPC Brazil network. Of these, 33 samples had elevated levels of lysoSM509, and in 25 of them, variants classified as pathogenic, likely pathogenic, or of unknown significance were identified in the NPC1 or NPC2 genes by next-generation sequencing. The quantification of lysoSM509 in DBS as a first-tier test for the diagnosis of NPC followed by molecular analysis of the NPC1 and NPC2 genes almost doubled the detection rate when compared to the performance of chitotriosidase activity as a first-tier biomarker, and it could likely be increased with the addition of a third tier with MLPA of the two genes involved. This strategy seems suitable for the neonatal screening (NBS) of NPC if this disease is eventually adopted by NBS programs.

A Glance at the Molecules That Regulate Oligodendrocyte Myelination

Oligodendrocyte (OL) myelination is a critical process for the neuronal axon function in the central nervous system. After demyelination occurs because of pathophysiology, remyelination makes repairs similar to myelination. Proliferation and differentiation are the two main stages in OL myelination, and most factors commonly play converse roles in these two stages, except for a few factors and signaling pathways, such as OLIG2 (Oligodendrocyte transcription factor 2). Moreover, some OL maturation gene mutations induce hypomyelination or hypermyelination without an obvious function in proliferation and differentiation. Herein, three types of factors regulating myelination are reviewed in sequence.

Mass spectrometry-based proteomics in neurodegenerative lysosomal storage disorders

The major function of the lysosome is to degrade unwanted materials such as lipids, proteins, and nucleic acids; therefore, deficits of the lysosomal system can result in improper degradation and trafficking of these biomolecules. Diseases associated with lysosomal failure can be lethal and are termed lysosomal storage disorders (LSDs), which affect 1 in 5000 live births collectively. LSDs are inherited metabolic diseases caused by mutations in single lysosomal and non-lysosomal proteins and resulting in the subsequent accumulation of macromolecules within. Most LSD patients present with neurodegenerative clinical symptoms, as well as damage in other organs. The discovery of new biomarkers is necessary to understand and monitor these diseases and to track therapeutic progress. Over the past ten years, mass spectrometry (MS)-based proteomics has flourished in the biomarker studies in many diseases, including neurodegenerative, and more specifically, LSDs. In this review, biomarkers of disease pathophysiology and monitoring of LSDs revealed by MS-based proteomics are discussed, including examples from Niemann-Pick disease type C, Fabry disease, neuronal ceroid-lipofuscinoses, mucopolysaccharidosis, Krabbe disease, mucolipidosis, and Gaucher disease.

Lipid Dyshomeostasis and Inherited Cerebellar Ataxia

Cerebellar ataxia is a form of ataxia that originates from dysfunction of the cerebellum, but may involve additional neurological tissues. Its clinical symptoms are mainly characterized by the absence of voluntary muscle coordination and loss of control of movement with varying manifestations due to differences in severity, in the site of cerebellar damage and in the involvement of extracerebellar tissues. Cerebellar ataxia may be sporadic, acquired, and hereditary. Hereditary ataxia accounts for the majority of cases. Hereditary ataxia has been tentatively divided into several subtypes by scientists in the field, and nearly all of them remain incurable. This is mainly because the detailed mechanisms of these cerebellar disorders are incompletely understood. To precisely diagnose and treat these diseases, studies on their molecular mechanisms have been conducted extensively in the past. Accumulating evidence has demonstrated that some common pathogenic mechanisms exist within each subtype of inherited ataxia. However, no reports have indicated whether there is a common mechanism among the different subtypes of inherited cerebellar ataxia. In this review, we summarize the available references and databases on neurological disorders characterized by cerebellar ataxia and show that a subset of genes involved in lipid homeostasis form a new group that may cause ataxic disorders through a common mechanism. This common signaling pathway can provide a valuable reference for future diagnosis and treatment of ataxic disorders.

The Antihypertensive Drug Telmisartan Protects Oligodendrocytes from Cholesterol Accumulation and Promotes Differentiation by a PPAR-γ-Mediated Mechanism

Our previous studies have demonstrated that specific peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists play a fundamental role in oligodendrocyte progenitor (OP) differentiation, protecting them against oxidative and inflammatory damage. The antihypertensive drug Telmisartan (TLM) was shown to act as a PPAR-γ modulator. This study investigates the TLM effect on OP differentiation and validates its capability to restore damage in a pharmacological model of Niemann-Pick type C (NPC) disease through a PPAR-γ-mediated mechanism. For the first time in purified OPs, we demonstrate that TLM-induced PPAR-γ activation downregulates the type 1 angiotensin II receptor (AT1), the level of which naturally decreases during differentiation. Like other PPAR-γ agonists, we show that TLM promotes peroxisomal proliferation and promotes OP differentiation. Furthermore, TLM can offset the OP maturation arrest induced by a lysosomal cholesterol transport inhibitor (U18666A), which reproduces an NPC1-like phenotype. In the NPC1 model, TLM also reduces cholesterol accumulation within peroxisomal and lysosomal compartments and the contacts between lysosomes and peroxisomes, revealing that TLM can regulate intracellular cholesterol transport, crucial for myelin formation. Altogether, these data indicate a new potential use of TLM in hypomyelination pathologies such as NPC1, underlining the possible repositioning of the drug already used in other pathologies.

Myelin Defects in Niemann-Pick Type C Disease: Mechanisms and Possible Therapeutic Perspectives

Niemann–Pick type C (NPC) disease is a wide-spectrum clinical condition classified as a neurovisceral disorder affecting mainly the liver and the brain. It is caused by mutations in one of two genes, NPC1 and NPC2, coding for proteins located in the lysosomes. NPC proteins are deputed to transport cholesterol within lysosomes or between late endosome/lysosome systems and other cellular compartments, such as the endoplasmic reticulum and plasma membrane. The first trait of NPC is the accumulation of unesterified cholesterol and other lipids, like sphingosine and glycosphingolipids, in the late endosomal and lysosomal compartments, which causes the blockade of autophagic flux and the impairment of mitochondrial functions. In the brain, the main consequences of NPC are cerebellar neurodegeneration, neuroinflammation, and myelin defects. This review will focus on myelin defects and the pivotal importance of cholesterol for myelination and will offer an overview of the molecular targets and the pharmacological strategies so far proposed, or an object of clinical trials for NPC. Finally, it will summarize recent data on a new and promising pharmacological perspective involving A_2A adenosine receptor stimulation in genetic and pharmacological NPC dysmyelination models.

Psychosis symptoms associated with Niemann-Pick disease type C

Niemann-Pick disease type C (NP-C) is a severe neurovisceral lipid storage disease that results in the accumulation of unesterified cholesterol in lysosomes or endosomes. The clinical presentations of NP-C are variable which include visceral symptoms, neurologic symptoms and psychiatric symptoms. Psychosis is the most common psychiatric manifestation of NP-C and is indistinguishable from a typical psychosis presentation of schizophrenia. The common psychotic presentations in NP-C include visual hallucinations, delusions, auditory hallucinations and thought disorders. Psychosis symptoms are more common in adult or adolescent-onset forms compared with pediatric-onset forms. The underlying pathophysiology of psychosis in NP-C is most probably due to dysconnectivity particularly between frontotemporal connectivity and subcortical structures. NP-C sometimes is mistaken for schizophrenia which causes delay in treatment due to lack of awareness and literature review. This review aims to summarize the relevant case reports on psychosis symptoms in NP-C and discuss the genetics and pathophysiology underlying the condition.

Neurodegeneration in Niemann-Pick Type C Disease: An Updated Review on Pharmacological and Non-Pharmacological Approaches to Counteract Brain and Cognitive Impairment

Niemann–Pick type C (NPC) disease is an autosomal recessive storage disorder, characterized by abnormal sequestration of unesterified cholesterol in the late endo-lysosomal system of cells. Progressive neurological deterioration and the onset of symptoms, such as ataxia, seizures, cognitive decline, and severe dementia, are pathognomonic features of the disease. In addition, different pathological similarities, including degeneration of hippocampal and cortical neurons, hyperphosphorylated tau, and neurofibrillary tangle formation, have been identified between NPC disease and other neurodegenerative pathologies. However, the underlying pathophysiological mechanisms are not yet well understood, and even a real cure to counteract neurodegeneration has not been identified. Therefore, the combination of current pharmacological therapies, represented by miglustat and cyclodextrin, and non-pharmacological approaches, such as physical exercise and appropriate diet, could represent a strategy to improve the quality of life of NPC patients. Based on this evidence, in our review we focused on the neurodegenerative aspects of NPC disease, summarizing the current knowledge on the molecular and biochemical mechanisms responsible for cognitive impairment, and suggesting physical exercise and nutritional treatments as additional non-pharmacologic approaches to reduce the progression and neurodegenerative course of NPC disease.

TDP-43 proteinopathy occurs independently of autophagic substrate accumulation and underlies nuclear defects in Niemann-Pick C disease

AIMS

Neuronal cytoplasmic inclusions of TAR-DNA binding protein of 43 kDa (TDP-43) are a pathological hallmark of diverse neurodegenerative disorders, yet the processes that mediate their formation and their functional significance remain incompletely understood. Both dysfunction in autophagy and neuroinflammation have been linked to TDP-43 mislocalisation. Here, we investigate TDP-43 proteinopathy in Niemann-Pick type C disease (NPC), an autosomal recessive lysosomal storage disease (LSD) distinguished by the accumulation of unesterified cholesterol within late endosomes and lysosomes. NPC is characterised by neurodegeneration, neuroinflammation and multifocal disruption of the autophagy pathway.

METHODS

We utilised immunohistochemistry, confocal microscopy, electron microscopy and biochemical and gene expression studies to characterise TDP-43 pathology and autophagic substrate accumulation in Npc1-deficient mice.

RESULTS

In the NPC brain, cytoplasmic TDP-43 mislocalisation was independent of autophagic substrate accumulation. These pathologies occurred in distinct neuronal subtypes, as brainstem cholinergic neurons were more susceptible to TDP-43 mislocalisation, whereas glutamatergic neurons exhibited hallmarks of autophagic dysfunction. Furthermore, TDP-43 mislocalisation did not co-localise with markers of stress granules or progress to ubiquitinated aggregates over months in vivo, indicating a stable, early stage in the aggregation process. Neither microgliosis nor neuroinflammation were sufficient to drive TDP-43 proteinopathy in the NPC brain. Notably, cytoplasmic TDP-43 co-localised with the nuclear import factor importin α, and TDP-43 mislocalised neurons demonstrated nuclear membrane abnormalities and disruption of nucleocytoplasmic transport.

CONCLUSION

Our findings highlight the relationship between LSDs and TDP-43 proteinopathy, define its functional importance in NPC by triggering nuclear dysfunction, and expand the spectrum of TDP-43 pathology in the diseased brain.

Gender-Specific Effects of Two Treatment Strategies in a Mouse Model of Niemann-Pick Disease Type C1

In a mouse model of Niemann-Pick disease type C1 (NPC1), a combination therapy (COMBI) of miglustat (MIGLU), the neurosteroid allopregnanolone (ALLO) and the cyclic oligosaccharide 2-hydroxypropyl-β-cyclodextrin (HPßCD) has previously resulted in, among other things, significantly improved motor function. The present study was designed to compare the therapeutic effects of the COMBI therapy with that of MIGLU or HPßCD alone on body and brain weight and the behavior of NPC1^−/− mice in a larger cohort, with special reference to gender differences. A total of 117 NPC1^−/− and 123 NPC1^+/+ mice underwent either COMBI, MIGLU only, HPßCD only, or vehicle treatment (Sham), or received no treatment at all (None). In male and female NPC1^−/− mice, all treatments led to decreased loss of body weight and, partly, brain weight. Concerning motor coordination, as revealed by the accelerod test, male NPC1^−/− mice benefited from COMBI treatment, whereas female mice benefited from COMBI, MIGLU, and HPßCD treatment. As seen in the open field test, the reduced locomotor activity of male and female NPC1^−/− mice was not significantly ameliorated in either treatment group. Our results suggest that in NPC1^−/− mice, each drug treatment scheme had a beneficial effect on at least some of the parameters evaluated compared with Sham-treated mice. Only in COMBI-treated male and female NPC^+/+ mice were drug effects seen in reduced body and brain weights. Upon COMBI treatment, the increased dosage of drugs necessary for anesthesia in Sham-treated male and female NPC1^−/− mice was almost completely reduced only in the female groups.

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.

Understanding and Treating Niemann-Pick Type C Disease: Models Matter

Biomedical research aims to understand the molecular mechanisms causing human diseases and to develop curative therapies. So far, these goals have been achieved for a small fraction of diseases, limiting factors being the availability, validity, and use of experimental models. Niemann–Pick type C (NPC) is a prime example for a disease that lacks a curative therapy despite substantial breakthroughs. This rare, fatal, and autosomal-recessive disorder is caused by defects in NPC1 or NPC2. These ubiquitously expressed proteins help cholesterol exit from the endosomal–lysosomal system. The dysfunction of either causes an aberrant accumulation of lipids with patients presenting a large range of disease onset, neurovisceral symptoms, and life span. Here, we note general aspects of experimental models, we describe the line-up used for NPC-related research and therapy development, and we provide an outlook on future topics.

Deregulation of signalling in genetic conditions affecting the lysosomal metabolism of cholesterol and galactosyl-sphingolipids

The role of lipids in neuroglial function is gaining momentum in part due to a better understanding of how many lipid species contribute to key cellular signalling pathways at the membrane level. The description of lipid rafts as membrane domains composed by defined classes of lipids such as cholesterol and sphingolipids has greatly helped in our understanding of how cellular signalling can be regulated and compartmentalized in neurons and glial cells. Genetic conditions affecting the metabolism of these lipids greatly impact on how some of these signalling pathways work, providing a context to understand the biological function of the lipid. Expectedly, abnormal metabolism of several lipids such as cholesterol and galactosyl-sphingolipids observed in several metabolic conditions involving lysosomal dysfunction are often accompanied by neuronal and myelin dysfunction. This review will discuss the role of lysosomal biology in the context of deficiencies in the metabolism of cholesterol and galactosyl-sphingolipids and their impact on neural function in three genetic disorders: Niemann-Pick type C, Metachromatic leukodystrophy and Krabbe’s disease.

Fbxo2 mediates clearance of damaged lysosomes and modifies neurodegeneration in the Niemann-Pick C brain

A critical response to lysosomal membrane permeabilization (LMP) is the clearance of damaged lysosomes through a selective form of macroautophagy known as lysophagy. Although regulators of this process are emerging, whether organ- and cell-specific components contribute to the control of lysophagy remains incompletely understood. Here, we examined LMP and lysophagy in Niemann-Pick type C (NPC) disease, an autosomal recessive disorder characterized by the accumulation of unesterified cholesterol within late endosomes and lysosomes, leading to neurodegeneration and early death. We demonstrated that NPC human fibroblasts show enhanced sensitivity to lysosomal damage as a consequence of lipid storage. Moreover, we described a role for the glycan-binding F-box protein 2 (Fbxo2) in CNS lysophagy. Fbxo2 functions as a component of the S phase kinase-associated protein 1–cullin 1–F-box protein (SKP1-CUL1-SCF) ubiquitin ligase complex. Loss of Fbxo2 in mouse primary cortical cultures delayed clearance of damaged lysosomes and decreased viability after lysosomal damage. Moreover, Fbxo2 deficiency in a mouse model of NPC exacerbated deficits in motor function, enhanced neurodegeneration, and reduced survival. Collectively, our data identified a role for Fbxo2 in CNS lysophagy and establish its functional importance in NPC.

Glycan binding protein Fbxo2 regulates lysophagy in the brain, and its deficiency exacerbates neuronal deficits in a mouse model of Niemann-Pick type C disease.

Lipids in regulating oligodendrocyte structure and function

Oligodendrocytes enwrap central nervous system axons with myelin, a lipid enriched highly organized multi-layer membrane structure that allows for fast long-distance saltatory conduction of neuronal impulses. Myelin has an extremely high lipid content (∼80 % of its dry weight) and a peculiar lipid composition, with a 2:2:1 cholesterol:phospholipid:glycolipid ratio. Inherited neurodegenerative diseases of the lipids (caused by mutations in lipogenic enzymes) often present oligodendrocyte and/or myelin defects which contribute to the overall disease pathophysiology. These phenomena triggered an increasing number of studies over the functions lipid exert to shape and maintain myelin, and brought to the finding that lipids are more than only structural building blocks. They act as signaling molecules to drive proliferation and differentiation of oligodendrocyte progenitor cells, as well as proliferation of premyelinating oligodendrocytes, and their maturation into myelinating ones. Here, we summarize key findings in these areas, while presenting the main related human diseases. Despite many advances in the field, various questions remain open which we briefly discuss. This article is part of a special issue entitled "Role of Lipids in CNS Cell Physiology and Pathology".

Cholesterol and triglyceride levels in first-episode patients with major depressive disorder: A meta-analysis of case-control studies

BACKGROUND

Lipid profile disturbances are frequently observed in major depressive disorder (MDD) and constitute to high mortality rates. However, less is known about whether this risk is present in patients with first-episode MDD. Therefore, this meta-analysis was conducted to examine if lipid parameters differed between healthy controls and first-episode MDD patients.

METHODS

Cochrane Library, PubMed, PsycINFO, EMBASE, Chinese Journal Net, and WanFang databases were searched from inception to October 23, 2018. The primary outcomes were triglycerides, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and total cholesterol levels.

RESULTS

A total of 11 case-control studies compared 690 subjects with first-episode MDD and 614 healthy controls were included and analyzed. Compared to healthy controls, patients with first-episode MDD were significantly associated with higher triglyceride (SMD = 0.29, 95% CI: 0.09, 0.48, P = 0.004) and lower HDL cholesterol levels (SMD = -0.54, 95% CI: -0.86, -0.22, P = 0.001). Subgroup analyses revealed that first-episode MDD patients with higher triglyceride and lower HDL levels were found only in Chinese and plasma group when compared to healthy controls (P < 0.05). Meta-regression analysis showed that the significant heterogeneity for triglyceride and HDL cholesterol was partly explained by the quality of study. No significant difference was found in LDL cholesterol and total cholesterol levels between the two groups.

LIMITATIONS

Heterogeneity was relatively high among the included studies.

CONCLUSIONS

Elevated triglyceride and decreased HDL cholesterol levels may be associated with first-episode MDD. Findings support early lipid monitoring and interventions targeting healthy lifestyle.

Neuron-specific Kv1.1 deficiency is sufficient to cause epilepsy, premature death, and cardiorespiratory dysregulation

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related mortality, but the precise cellular substrates involved remain elusive. Epilepsy-associated ion channel genes with co-expression in brain and heart have been proposed as SUDEP candidate genes since they provide a singular unifying link between seizures and lethal cardiac arrhythmias. Here, we generated a conditional knockout (cKO) mouse with neuron-specific deletion of Kcna1, a SUDEP-associated gene with brain-heart co-expression, to test whether seizure-evoked cardiac arrhythmias and SUDEP require the absence of Kv1.1 in both brain and heart or whether ablation in neurons is sufficient. To obtain cKO mice, we developed a floxed Kcna1 mouse which we crossed to mice with the Synapsin1-Cre transgene, which selectively deletes Kcna1 in most neurons. Molecular analyses confirmed neuron-specific Kcna1 deletion in cKO mice and corresponding loss of Kv1.1 except in cerebellum where Synapsin1-Cre is not highly expressed. Survival studies and electroencephalography, electrocardiography, and plethysmography recordings showed that cKO mice exhibit premature death, epilepsy, and cardiorespiratory dysregulation but to a lesser degree than global knockouts. Heart rate variability (HRV) was increased in cKO mice with peaks during daytime suggesting disturbed diurnal HRV patterns as a SUDEP biomarker. Residual Kv1.1 expression in cKO cerebellum suggests it may play an unexpected role in regulating ictal cardiorespiratory dysfunction and SUDEP risk. This work demonstrates the principle that channelopathies with brain-heart expression patterns can increase death risk by brain-driven mechanisms alone without a functionally compromised heart, reinforcing seizure control as a primary clinical strategy for SUDEP prevention.

Protease Inhibitors, Saquinavir and Darunavir, Inhibit Oligodendrocyte Maturation: Implications for Lysosomal Stress

Despite the introduction of antiretroviral (ARV) therapy (ART), approximately 30-50% of people living with human immunodeficiency virus-1 (HIV-1) will develop a spectrum of measurable neurocognitive dysfunction, collectively called HIV-associated neurocognitive disorder (HAND). While the clinical manifestations of HAND have changed with the advent of ART, certain pathological features have endured, including white matter alterations and dysfunction. The persistence of white matter alterations in the post-ART era suggests that ARV drugs themselves may contribute to HAND pathology. Our group has previously demonstrated that two ARV compounds from the protease inhibitor (PI) class, ritonavir and lopinavir, inhibit oligodendrocyte maturation and myelin protein production. We hypothesized that other members of the PI class, saquinavir and darunavir, could also negatively impact oligodendrocyte differentiation. Here we demonstrate that treating primary rat oligodendrocyte precursor cells with therapeutically relevant concentrations of either ARV drug results in a concentration-dependent inhibition of oligodendrocyte maturation in vitro. Furthermore, we show that acidifying endolysosomal pH via a mucolipin transient receptor potential channel 1 (TRPML1) agonist provides protection against saquinavir- and darunavir-induced inhibition of oligodendrocyte maturation. Moreover, our findings suggest, for the first time, an imperative role of proper endolysosomal pH in regulating OL differentation, and that therapeutic targeting of endolysosomes may provide protection against ARV-induced oligodendrocyte dysregulation. Graphical Abstract Treatment of primary rat oligodendrocyte precursor cells with therapeutically relevant concentrations of either antiretroviral compound of the protease inhibitor class, darunavir or saquinavir, results in a concentration-dependent inhibition of oligodendrocyte maturation in vitro. Additionally, in darunavir or saquinavir-treated cultures we observed a concentration-dependent decrease in the number of acidic lysosomes, via immunostaining with LysoTracker Red, compared with vehicle-treated cultures. Finally, we showed that acidifying endolysosomal pH via a mucolipin transient receptor potential channel 1 (TRPML1) agonist provides protection against saquinavir- or darunavir-induced inhibition of oligodendrocyte maturation. Our findings suggest, for the first time, a critical role of proper endolysosomal pH in regulating OL differentation, and that therapeutic targeting of endolysosomes may provide protection against antiretroviral-induced oligodendrocyte dysregulation.

Addressing neurodegeneration in lysosomal storage disorders: Advances in Niemann Pick diseases

Most lysosomal storage disorders (LSDs) cause progressive neurodegeneration leading to early death. While the genetic defects that cause these disorders impact all cells of the body, neurons are particularly affected. This vulnerability may be explained by neuronal cells' critical dependence on the lysosomal degradative capacity, as they cannot use division to eliminate their waste. However, mounting evidence supports the extension of storage beyond lysosomes to other cellular compartments (mitochondria, plasma membrane and synapses) as a key event in pathogenesis. Impaired energy supply, oxidative stress, calcium imbalance, synaptic failure and glial alterations may all contribute to neuronal death and thus could be suitable therapeutic targets for these disorders. Here we review the pathological mechanisms underlying neurodegeneration in Niemann Pick diseases and therapeutic strategies developed in animal models and patients suffering from these devastating disorders. This article is part of the special issue entitled 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.

Lipid-Binding Proteins in Brain Health and Disease

A proper lipid management is paramount for a healthy brain. Lipid homeostasis alterations are known to be causative or risk factors for many neurodegenerative diseases, or key elements in the recovery from nervous system injuries of different etiology. In addition to lipid biogenesis and catabolism, non-enzymatic lipid-binding proteins play an important role in brain function and maintenance through aging. Among these types of lipoproteins, apolipoprotein E has received much attention due to the relationship of particular alleles of its gene with the risk and progression of Alzheimer's disease. However, other lipid-binding proteins whose role in lipid homeostasis and control are less known need to be brought to the attention of both researchers and clinicians. The aim of this review is to cover the knowledge of lipid-managing proteins in the brain, with particular attention to new candidates to be relevant for brain function and health.

Do heterozygous mutations of Niemann-Pick type C predispose to late-onset neurodegeneration: a review of the literature

BACKGROUND/METHODS

Monogenic diseases are important models for the study of neurodegenerative diseases, such as Parkinson's disease (PD) and dementia. Notably, for some disorders, homozygosity is associated with a complex metabolic disease, while heterozygosity predisposes to late-onset neurodegeneration. For instance, biallelic glucocerebrosidase gene mutations cause Gaucher's disease, while heterozygous mutations are a common genetic risk factor for late-onset PD. Little is known about similar risks of related diseases, such as Niemann-Pick type C (NPC). Given that both conditions map into related, i.e., lysosomal, pathways, we hypothesize a similar risk of single-NPC gene mutations. Indeed, there is increasing evidence based on clinical observations in humans and animal studies. Here we review the current knowledge of NPC heterozygosity.

RESULTS

Family history studies suggest a high proportion of late-onset neurodegenerative diseases in NPC families. We identified 19 cases with heterozygous NPC mutations in the literature who presented with a neurodegenerative disease, including levodopa-responsive PD, atypical parkinsonism (PSP, CBD), dystonia or dementia with a mean age at onset of about 57 years (range 8-87). Consistent splenomegaly and mildly abnormal filipin staining results have also been reported in heterozygous gene mutation carriers. Imaging and pathological data support this notion.

DISCUSSION/CONCLUSION

This finding has wider implications in so far as NPC-related forms of Parkinsonian syndromes, dementia, motor neuron disease and other neurodegenerative disorders may benefit from NPC-mechanistic therapies, in particular related to lysosomal dysfunction. Further research is warranted to generate systematic data of heterozygous mutation carriers, including longitudinal data.

Adenosine A2A receptor stimulation restores cell functions and differentiation in Niemann-Pick type C-like oligodendrocytes

Niemann Pick type C (NPC) disease is a rare neurovisceral disorder. Mutations in npc1 gene induce an intracellular accumulation of unesterified cholesterol in the endosomal/lysosomal system causing cell death. We recently showed that stimulation of adenosine A_2A receptors (A_2AR) restores cholesterol accumulation in late endosomes/lysosomes in human NPC fibroblasts and neural cell lines transiently transfected with NPC1 siRNA, suggesting that these receptors might be targeted to contrast the disease. Since NPC1 disease is characterized by dysmyelination and maturational arrest of oligodendrocyte progenitors (OPs), in this study, we investigated whether A_2AR stimulation could promote oligodendrocyte differentiation and myelin formation, thus overcoming these important neurological abnormalities. We developed a NPC1 pharmacological model, in which primary cultures of OPs are exposed to a cholesterol transport inhibitor to induce a NPC1-like phenotype characterized by several typical features such as (i) cholesterol accumulation, (ii) altered mitochondrial morphology and membrane potential, (iii) defect of autophagy and (iv) maturation arrest. The A_2AR agonist CGS21680 normalized all NPC1-like features. The ability of CGS21680 of rescuing OP from maturational arrest and promoting their differentiation to mature OL, suggests that A_2AR stimulation might be exploited to correct dysmyelination in NPC1, further supporting their therapeutic potential in the disease.

Modeling neuronopathic storage diseases with patient-derived culture systems

Lysosomes are organelles involved in the degradation and recycling of macromolecules, and play a critical role in sensing metabolic information in the cell. A class of rare metabolic diseases called lysosomal storage disorders (LSD) are characterized by lysosomal dysfunction and the accumulation of macromolecular substrates. The central nervous system appears to be particularly vulnerable to lysosomal dysfunction, since many LSDs are characterized by severe, widespread neurodegeneration with pediatric onset. Furthermore, variants in lysosomal genes are strongly associated with some common neurodegenerative disorders such as Parkinson's disease (PD). To better understand disease pathology and develop novel treatment strategies, it is critical to study the fundamental molecular disease mechanisms in the affected cell types that harbor endogenously expressed mutations. The discovery of methods for reprogramming of patient-derived somatic cells into induced pluripotent stem cells (iPSCs), and their differentiation into distinct neuronal and glial cell types, have provided novel opportunities to study mechanisms of lysosomal dysfunction within the relevant, vulnerable cell types. These models also expand our ability to develop and test novel therapeutic targets. We discuss recently developed methods for iPSC differentiation into distinct neuronal and glial cell types, while addressing the need for meticulous experimental techniques and parameters that are essential to accurately identify inherent cellular pathologies. iPSC models for neuronopathic LSDs and their relationship to sporadic age-related neurodegeneration are also discussed. These models should facilitate the discovery and development of personalized therapies in the future.

Animal models for Niemann-Pick type C: implications for drug discovery & development

INTRODUCTION

Niemann-Pick type C (NPC) is a neurovisceral, progressively detrimental lysosomal storage disease with very limited therapeutic options and no approved treatment available in the US. Despite its rarity, NPC has seen increased drug developmental efforts over the past decade, culminating in the completion of two potential registration trials in 2018. Areas covered: This review highlights the many available animal models that have been developed in the field and briefly covers classical and new cell technologies. This review provides a high-level evaluation and prioritization of the various models with regard to efficient and clinically translatable drug development, and briefly discusses the relevant developments and opportunities pertaining to this. Expert opinion: With a number of in vitro and in vivo models available, and with having several drugs, all with various mechanisms of action, either approved or in late stage development, the NPC field is in an exciting time. One of the challenges for researchers and developers will be the ability to make use of the lessons learnt from existing late-stage programs as well as the incorporation not only of the opportunities but also the limitations of the many models into successful drug discovery and translational development programs.

Proteomics of the corpus callosum to identify novel factors involved in hypomyelinated Niemann-Pick Type C disease mice

Hypomyelination in the central nerves system (CNS) is one of the most obviously pathological features in Niemann-Pick Type C disease (NPC), which is a rare neurodegenerative disorder caused by mutations in the NPC intracellular cholesterol transporter 1 or 2 (Npc1 or Npc2). Npc1 plays key roles in both neurons and oligodendrocytes during myelination, however, the linkage between the disturbed cholesterol transport and inhibited myelination is unrevealed. In this study, mass spectrometry (MS)-based differential quantitative proteomics was applied to compare protein composition in the corpus callosum between wild type (WT) and NPC mice. In total, 3009 proteins from both samples were identified, including myelin structural proteins, neuronal proteins, and astrocyte-specific proteins. In line to hypomyelination, our data revealed downregulation of myelin structural and indispensable proteins in Npc1 mutant mice. Notably, the reduced ceramide synthase 2 (Cers2), UDP glycosyltransferase 8 (Ugt8), and glycolipid transfer protein (Gltp) indicate the altered sphingolipid metabolism in the disease and the involvement of Gltp in myelination. The identification of most reported myelin structural proteins and proteins from other cell types advocates the use of the corpus callosum to investigate proteins in different cell types that regulate myelination.

Psychiatric and Cognitive Symptoms Associated with Niemann-Pick Type C Disease: Neurobiology and Management

Niemann-Pick disease type C (NPC) is a lysosomal storage disorder that presents with a spectrum of clinical manifestations from infancy and childhood or in early or mid-adulthood. Progressive neurological symptoms including ataxia, dystonia and vertical gaze palsy are a hallmark of the disease, and psychiatric symptoms such as psychosis and mood disorders are common. These latter symptoms often present early in the course of NPC and thus these patients are often diagnosed with a major psychotic or affective disorder before neurological and cognitive signs present and the diagnosis is revised. The commonalities and characteristics of psychotic symptoms in both NPC and schizophrenia may share neuronal pathways and mechanisms and provide potential targets for research in both disorders. The neurobiology of NPC and its relationship to the pattern of neuropsychiatric and cognitive symptoms is described in this review. A number of neurobiological models are proposed as mechanisms by which NPC causes psychiatric and cognitive symptoms, informed from models proposed in schizophrenia and other metabolic disorders. There are a number of symptomatic and illness-modifying treatments for NPC currently available. The current evidence is discussed; focussing on two medications which have shown promise, miglustat and hydroxypropyl-β-cyclodextrin.

Targeting Smoothened as a New Frontier in the Functional Recovery of Central Nervous System Demyelinating Pathologies

Myelin sheaths on vertebrate axons provide protection, vital support and increase the speed of neuronal signals. Myelin degeneration can be caused by viral, autoimmune or genetic diseases. Remyelination is a natural process that restores the myelin sheath and, consequently, neuronal function after a demyelination event, preventing neurodegeneration and thereby neuron functional loss. Pharmacological approaches to remyelination represent a promising new frontier in the therapy of human demyelination pathologies and might provide novel tools to improve adaptive myelination in aged individuals. Recent phenotypical screens have identified agonists of the atypical G protein-coupled receptor Smoothened and inhibitors of the glioma-associated oncogene 1 as being amongst the most potent stimulators of oligodendrocyte precursor cell (OPC) differentiation in vitro and remyelination in the central nervous system (CNS) of mice. Here, we discuss the current state-of-the-art of studies on the role of Sonic Hedgehog reactivation during remyelination, referring readers to other reviews for the role of Hedgehog signaling in cancer and stem cell maintenance.

Improvement of impaired electrical activity in NPC1 mutant cortical neurons upon DHPG stimulation detected by micro-electrode array

Niemann-Pick Type C1 (NPC1) disease is an autosomal recessive neurodegenerative disease characterized by an excessive accumulation of unesterified cholesterol in late endosomes/lysosomes. Patients with NPC1 disease show a series of symptoms in neuropathology, including a gradually increased loss of motor control and seizures. However, mechanism of the neurological manifestations in NPC1 disease is not fully understood yet. In this study, we utilized the micro-electrode array (MEA) to analyze the spontaneous extracellular electrical activity in cultivated cortical neurons of the NPC1 mutant (NPC1^-/-) mouse. Our results show a decrease of the spontaneous electrical activity in NPC1^-/- neuronal network when compared to wild type neurons, as indicated by the decreased spike rate, burst rate, event rate, and the increased burst period and event period. Application of 3,5-dihydroxyphenylglycine (DHPG), a specific agonist of group I metabotropic glutamate receptors, improved the electrical activity of the NPC1^-/- neuronal network, suggesting that DHPG can be used as a potential therapeutic strategy for recovery of the electrical activity in NPC1 disease.

Tolerance of chronic HDACi treatment for neurological, visceral and lung Niemann-Pick Type C disease in mice

Histone deacetylase (HDAC) inhibitors are of significant interest as drugs. However, their use to treat neurological disorders has raised concern because HDACs are required for brain function. We have previously shown that a triple combination formulation (TCF) of the pan HDACi vorinostat (Vo), 2-hydroxypropyl-beta-cyclodextrin (HPBCD) and polyethylene glycol (PEG) 400 improves pharmacokinetic exposure and entry of Vo into the brain. TCF treatment significantly delayed both neurodegeneration and death in the Npc1^nmf164 murine model of Niemann-Pick Type C (NPC) disease. The TCF induces no metabolic toxicity, but its risk to normal brain functions and potential utility in treating lung disease, a major NPC clinical complication, remain unknown. Here we report that TCF administered in healthy mice for 8–10 months was not detrimental to the brain or neuromuscular functions based on quantitative analyses of Purkinje neurons, neuroinflammation, neurocognitive/muscular disease symptom progression, cerebellar/hippocampal nerve fiber-staining, and Hdac gene-expression. The TCF also improved delivery of Vo to lungs and reduced accumulation of foamy macrophages in Npc1^nmf164 mice, with no injury. Together, these data support feasibility of tolerable, chronic administration of an HDACi formulation that treats murine NPC neurological disease and lung pathology, a frequent cause of death in this and possibly additional disorders.

Integrated Systems Approach Reveals Sphingolipid Metabolism Pathway Dysregulation in Association with Late-Onset Alzheimer's Disease

Late-onset Alzheimer’s disease (LOAD) and age are significantly correlated such that one-third of Americans beyond 85 years of age are afflicted. We have designed and implemented a pilot study that combines systems biology approaches with traditional next-generation sequencing (NGS) analysis techniques to identify relevant regulatory pathways, infer functional relationships and confirm the dysregulation of these biological pathways in LOAD. Our study design is a most comprehensive systems approach combining co-expression network modeling derived from RNA-seq data, rigorous quality control (QC) standards, functional ontology, and expression quantitative trait loci (eQTL) derived from whole exome (WES) single nucleotide variant (SNV) genotype data. Our initial results reveal several statistically significant, biologically relevant genes involved in sphingolipid metabolism. To validate these findings, we performed a gene set enrichment analysis (GSEA). The GSEA revealed the sphingolipid metabolism pathway and regulation of autophagy in association with LOAD cases. In the execution of this study, we have successfully tested an integrative approach to identify both novel and known LOAD drivers in order to develop a broader and more detailed picture of the highly complex transcriptional and regulatory landscape of age-related dementia.

Lovastatin promotes myelin formation in NPC1 mutant oligodendrocytes

Niemann-Pick Type C (NPC) disease is a rare neurovisceral disorder caused by mutations of either NPC1 or NPC2 gene and characterized by defective intracellular transport of cholesterol and glycosphingolipids, leading to neuron loss and myelin aberration in the central nervous system. In this study, by comparing protein expression in the cortical white matter tracts from mice at different postnatal days, we identified that in the NPC1 mutant (NPC1^-/-) mice, the onset of myelination is delayed and the amount of the major myelin protein MBP and PLP, and oligodendrocyte regulatory factor Olig1 and Olig2, but not NG2 and Sox10, decreased significantly, suggesting a disruption of oligodendrocyte differentiation. Furthermore, in in vitro oligodendrocyte cultivation, NPC1^-/- oligodendrocytes showed less response to the stimulation of neuron-conditioned medium (CdM), indicating a defect of oligodendrocyte per se. Interestingly, lovastatin restores the number of mature myelin-forming oligodendrocytes by increasing Olig1 and Olig2 expressions. Our data suggest a potential strategy for improving myelination using lovastatin in NPC disease.