Niemann-Pick disease

Precise subcellular targeting approaches for organelle-related disorders

Pharmacological research has expanded to the nanoscale level with advanced imaging technologies, enabling the analysis of drug distribution at the cellular organelle level. These advances in research techniques have contributed to the targeting of cellular organelles to address the fundamental causes of diseases. Beyond navigating the hurdles of reaching lesion tissues upon administration and identifying target cells within these tissues, controlling drug accumulation at the organelle level is the most refined method of disease management. This approach opens new avenues for the development of more potent therapeutic strategies by delving into the intricate roles and interplay of cellular organelles. Thus, organelle-targeted approaches help overcome the limitations of conventional therapies by precisely regulating functionally compartmentalized spaces based on their environment. This review discusses the basic concepts of organelle targeting research and proposes strategies to target diseases arising from organelle dysfunction. We also address the current challenges faced by organelle targeting and explore future research directions.

Pseudorabies virus inhibits progesterone-induced inactivation of TRPML1 to facilitate viral entry

Viral infection is a significant risk factor for fertility issues. Here, we demonstrated that infection by neurotropic alphaherpesviruses, such as pseudorabies virus (PRV), could impair female fertility by disrupting the hypothalamus-pituitary-ovary axis (HPOA), reducing progesterone (P4) levels, and consequently lowering pregnancy rates. Our study revealed that PRV exploited the transient receptor potential mucolipin 1 (TRPML1) and its lipid activator, phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2), to facilitate viral entry through lysosomal cholesterol and Ca2+. P4 antagonized this process by inducing lysosomal storage disorders and promoting the proteasomal degradation of TRPML1 via murine double minute 2 (MDM2)-mediated polyubiquitination. Overall, the study identifies a novel mechanism by which PRV hijacks the lysosomal pathway to evade P4-mediated antiviral defense and impair female fertility. This mechanism may be common among alphaherpesviruses and could contribute significantly to their impact on female reproductive health, providing new insights for the development of antiviral therapies.

Polymer-based drug delivery systems under investigation for enzyme replacement and other therapies of lysosomal storage disorders

Lysosomes play a central role in cellular homeostasis and alterations in this compartment associate with many diseases. The most studied example is that of lysosomal storage disorders (LSDs), a group of 60 + maladies due to genetic mutations affecting lysosomal components, mostly enzymes. This leads to aberrant intracellular storage of macromolecules, altering normal cell function and causing multiorgan syndromes, often fatal within the first years of life. Several treatment modalities are available for a dozen LSDs, mostly consisting of enzyme replacement therapy (ERT) strategies. Yet, poor biodistribution to main targets such as the central nervous system, musculoskeletal tissue, and others, as well as generation of blocking antibodies and adverse effects hinder effective LSD treatment. Drug delivery systems are being studied to surmount these obstacles, including polymeric constructs and nanoparticles that constitute the focus of this article. We provide an overview of the formulations being tested, the diseases they aim to treat, and the results observed from respective in vitro and in vivo studies. We also discuss the advantages and disadvantages of these strategies, the remaining gaps of knowledge regarding their performance, and important items to consider for their clinical translation. Overall, polymeric nanoconstructs hold considerable promise to advance treatment for LSDs.

Influence of sphingomyelin metabolism during epithelial-mesenchymal transition associated with aging in the renal papilla

The renal collecting ducts (CD) are formed by a fully differentiated epithelium, and their tissue organization and function require the presence of mature cell adhesion structures. In certain circumstances, the cells can undergo de-differentiation by a process called epithelial-mesenchymal transition (EMT), in which the cells lose their epithelial phenotype and acquire the characteristics of the mesenchymal cells, which includes loss of cell-cell adhesion. We have previously shown that in renal papillary CD cells, cell adhesion structures are located in sphingomyelin (SM)-enriched plasma membrane microdomains and the inhibition of SM synthase 1 activity induced CD cells to undergo an EMT process. In the present study, we evaluated the influence of SM metabolism during the EMT of the cells that form the CD of the renal papilla during aging. To this end, primary cultures of renal papillary CD cells from young, middle-, and aged-rats were performed. By combining biochemical and immunofluorescence studies, we found experimental evidence that CD cells undergo an increase in spontaneous and reversible EMT during aging and that at least one of the reasons for this phenomenon is the decrease in SM content due to the combination of decreased SM synthase activity and an increase in SM degradation mediated by neutral sphingomyelinase. Age is a risk factor for many diseases, among which renal fibrosis is included. Our findings highlight the importance of sphingolipids and particularly SM as a modulator of the fate of CD cells and probably contribute to the development of treatments to avoid or reverse renal fibrosis during aging.

Potential Composite Digenic Contribution of NPC1 and NOD2 Leading to Atypical Lethal Niemann-Pick Type C with Initial Crohn’s Disease-like Presentation: Genotype-Phenotype Correlation Study

Niemann–Pick disease type C (NPC) is an autosomal recessive neurovisceral disease characterized by progressive neurodegeneration with variable involvement of multisystemic abnormalities. Crohn’s disease (CD) is an inflammatory bowel disease (IBD) with a multifactorial etiology influenced by variants in NOD2. Here, we investigated a patient with plausible multisystemic overlapping manifestations of both NPC and CD. Her initial hospitalization was due to a prolonged fever and non-bloody diarrhea. A few months later, she presented with recurrent skin tags and anal fissures. Later, her neurological and pulmonary systems progressively deteriorated, leading to her death at the age of three and a half years. Differential diagnosis of her disease encompassed a battery of clinical testing and genetic investigations. The patient’s clinical diagnosis was inconclusive. Specifically, the histopathological findings were directed towards an IBD disease. Nevertheless, the diagnosis of IBD was not consistent with the patient’s subsequent neurological and pulmonary deterioration. Consequently, we utilized a genetic analysis approach to guide the diagnosis of this vague condition. Our phenotype–genotype association attempts led to the identification of candidate disease-causing variants in both NOD2 and NPC1. In this study, we propose a potential composite digenic impact of these two genes as the underlying molecular etiology. This work lays the foundation for future functional and mechanistic studies to unravel the digenic role of NOD2 and NPC1.

Combined antioxidants and anti-inflammatory therapies fail to attenuate the early and late phases of cyclodextrin-induced cochlear damage and hearing loss

Niemann-Pick C1 (NPC1) is a fatal neurodegenerative disease caused by aberrant cholesterol metabolism. The progression of the disease can be slowed by removing excess cholesterol with high-doses of 2-hyroxypropyl-beta-cyclodextrin (HPβCD). Unfortunately, HPβCD causes hearing loss; the initial first phase involves a rapid destruction of outer hair cells (OHCs) while the second phase, occurring 4-6 weeks later, involves the destruction of inner hair cells (IHCs), pillar cells, collapse of the organ of Corti and spiral ganglion neuron degeneration. To determine whether the first and/or second phase of HPβCD-induced cochlear damage is linked, in part, to excess oxidative stress or neuroinflammation, rats were treated with a single-dose of 3000 mg/kg HPβCD alone or together with one of two combination therapies. Each combination therapy was administered from 2-days before to 6-weeks after the HPβCD treatment. Combination 1 consisted of minocycline, an antibiotic that suppresses neuroinflammation, and HK-2, a multifunctional redox modulator that suppresses oxidative stress. Combination 2 was comprised of minocycline plus N-acetyl cysteine (NAC), which upregulates glutathione, a potent antioxidant. To determine if either combination therapy could prevent HPβCD-induced hearing impairment and cochlear damage, distortion product otoacoustic emissions (DPOAE) were measured to assess OHC function and the cochlear compound action potential (CAP) was measured to assess the function of IHCs and auditory nerve fibers. Cochleograms were prepared to quantify the amount of OHC, IHC and pillar cell (PC) loss. HPβCD significantly reduced DPOAE and CAP amplitudes and caused significant OHC, IHC and OPC losses with losses greater in the high-frequency base of the cochlea than the apex. Neither minocycline + HK-2 (MIN+ HK-2) nor minocycline + NAC (MIN+NAC) prevented the loss of DPOAEs, CAPs, OHCs, IHCs or IPCs caused by HPβCD. These results suggest that oxidative stress and neuroinflammation are unlikely to play major roles in mediating the first or second phase of HPβCD-induced cochlear damage. Thus, HPβCD-induced ototoxicity must be mediated by some other unknown cell-death pathway possibly involving loss of trophic support from damaged support cells or disrupted cholesterol metabolism.

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.

Spatiotemporal Developmental Upregulation of Prestin Correlates With the Severity and Location of Cyclodextrin-Induced Outer Hair Cell Loss and Hearing Loss

2-Hyroxypropyl-beta-cyclodextrin (HPβCD) is being used to treat Niemann-Pick C1, a fatal neurodegenerative disease caused by abnormal cholesterol metabolism. HPβCD slows disease progression, but unfortunately causes severe, rapid onset hearing loss by destroying the outer hair cells (OHC). HPβCD-induced damage is believed to be related to the expression of prestin in OHCs. Because prestin is postnatally upregulated from the cochlear base toward the apex, we hypothesized that HPβCD ototoxicity would spread from the high-frequency base toward the low-frequency apex of the cochlea. Consistent with this hypothesis, cochlear hearing impairments and OHC loss rapidly spread from the high-frequency base toward the low-frequency apex of the cochlea when HPβCD administration shifted from postnatal day 3 (P3) to P28. HPβCD-induced histopathologies were initially confined to the OHCs, but between 4- and 6-weeks post-treatment, there was an unexpected, rapid and massive expansion of the lesion to include most inner hair cells (IHC), pillar cells (PC), peripheral auditory nerve fibers, and spiral ganglion neurons at location where OHCs were missing. The magnitude and spatial extent of HPβCD-induced OHC death was tightly correlated with the postnatal day when HPβCD was administered which coincided with the spatiotemporal upregulation of prestin in OHCs. A second, massive wave of degeneration involving IHCs, PC, auditory nerve fibers and spiral ganglion neurons abruptly emerged 4–6 weeks post-HPβCD treatment. This secondary wave of degeneration combined with the initial OHC loss results in a profound, irreversible hearing loss.

Apolipoprotein D

ApoD is a 25 to 30 kDa glycosylated protein, member of the lipocalin superfamily. As a transporter of several small hydrophobic molecules, its known biological functions are mostly associated to lipid metabolism and neuroprotection. ApoD is a multi-ligand, multi-function protein that is involved lipid trafficking, food intake, inflammation, antioxidative response and development and in different types of cancers. An important aspect of ApoD's role in lipid metabolism appears to involve the transport of arachidonic acid, and the modulation of eicosanoid production and delivery in metabolic tissues. ApoD expression in metabolic tissues has been associated positively and negatively with insulin sensitivity and glucose homeostasis in a tissue dependent manner. ApoD levels rise considerably in association with aging and neuropathologies such as Alzheimer's disease, stroke, meningoencephalitis, moto-neuron disease, multiple sclerosis, schizophrenia and Parkinson's disease. ApoD is also modulated in several animal models of nervous system injury/pathology.

[Acid sphingomyelinase deficiency (Niemann-Pick disease type B) in adulthood: A retrospective multicentric study of 28 adult cases]

INTRODUCTION

Acid sphingomyelinase deficiency (ASMD) is an autosomal recessive disease with a clinical spectrum ranging from a neurovisceral infantile form (Niemann-Pick disease type A) to a chronic visceral form also encountered in adults (Niemann-Pick disease type B, NP-B).

METHODS

Retrospective multicentric analysis of French adult patients with ASMD over the period 1985-March 2015. Clinical, biological, and imaging data were analyzed.

RESULTS

Twenty-eight patients (19 males, 9 females) were analyzed. Diagnosis was made before the age of 10 years in 16 cases. Main symptoms at diagnosis were spleen/liver enlargement and interstitial lung disease. Biological abnormalities included: thrombocytopenia (platelet count <150 000/mm³) in 24 cases including 4 patients with platelet count <60 000/mm³, constantly low high-density lipoprotein (HDL) cholesterol, polyclonal hypergammaglobulinemia (n=6), monoclonal gammopathy of unknown significance (n=5), normal prothrombin level discordant with low factor V (n=5), elevated chitotriosidase level (n=11). The diagnosis was confirmed in all cases by deficient acid sphingomyelinase enzyme activity. SMPD1 gene sequencing was performed in 25 cases. The frequent p.R610del mutation was largely predominant, constituting 62% of the non-related alleles. During the follow-up period, three patients died before 50 years of age from cirrhosis, heart failure and lung insufficiency, respectively.

CONCLUSION

ASMD in adulthood (NP-B) associates spleen/liver enlargement and interstitial lung disease. Early diagnosis and appropriate management are essential for reducing the risk of complications, improving quality of life, and avoiding inappropriate procedures such as splenectomy. To date, only symptomatic therapy is available. A phase 2/3 therapeutic trial with IV infusion of recombinant enzyme is on-going.

Gene Therapy for the Treatment of Neurological Disorders: Metabolic Disorders

Metabolic disorders comprise a large group of heterogeneous diseases ranging from very prevalent diseases such as diabetes mellitus to rare genetic disorders like Canavan Disease. Whether either of these diseases is amendable by gene therapy depends to a large degree on the knowledge of their pathomechanism, availability of the therapeutic gene, vector selection, and availability of suitable animal models. In this book chapter, we review three metabolic disorders of the central nervous system (CNS; Canavan Disease, Niemann-Pick disease and Phenylketonuria) to give examples for primary and secondary metabolic disorders of the brain and the attempts that have been made to use adeno-associated virus (AAV) based gene therapy for treatment. Finally, we highlight commonalities and obstacles in the development of gene therapy for metabolic disorders of the CNS exemplified by those three diseases.

Macrophage-related diseases of the gut: a pathologist's perspective

The resident macrophages of the gastrointestinal tract represent the largest population of macrophages in the human body and are usually located in the subepithelial lamina propria. This strategic location guarantees a first-line defense to the huge numbers of potentially harmful bacteria and antigenic stimuli that are present in the intestinal lumen. In non-inflamed mucosa, macrophages phagocytose and kill microbes in the absence of an inflammatory response. However, in the event of an epithelial breach and/or microbial invasion, new circulating monocytes and lymphocytes will be recruited to the damaged area of the gut, which will result in the secretion of proinflammatory mediators and engage a protective inflammatory response. Although macrophages are usually not conspicuous in normal mucosal samples of the gut, they can easily be detected when they accumulate exogenous particulate material or endogenous substances or when they become very numerous. These events will mostly occur in pathologic conditions, and this review presents an overview of the diseases which are either mediated by or affecting the resident macrophages of the gut.

Niemann-Pick disease type C: analysis of 7 patients

BACKGROUND

Niemann-Pick disease type C (NP-C), derived from mutation of the NPC1 or NPC2 gene, is one of the recessive lysosomal lipid storage disorders that are difficult to diagnose and treat. Since NP-C has been rarely reported in China, we reviewed 7 patients with NP-C.

METHODS

The 7 patients had been diagnosed with NP-C from 2007 to 2010 at our department and their laboratory and clinical data were analyzed.

RESULTS

The 7 patients, 5 males and 2 females, included 4 patients of late infantile subtype and 3 patients of juvenile subtype, in which patients 2 and 3 were siblings. Their clinical symptoms occurred from 4 to 10 years of age, exhibiting as progressive cognitive and language impairment as well as motor retrogression. Six patients were caught by focal or generalized seizures from 1 to 4 years after the onset of the disease. Vertical supranuclear gaze palsy, dysarthria, dysphagia, internal rotation and adduction of bilateral hands and splenomegaly occurred following the progress of clinical symptoms. Five patients had laughter-cataplexy. MRI showed mild brain atrophy in 6 patients. Reduction of total cholesterol, high density lipoprotein cholesterol and low density lipoprotein cholesterol occurred in 6 patients. Sea-blue cells and Niemann-Pick cells were found in bone marrow smears. The activity of acid sphingomyelin enzyme was normal or only slightly lower. Supporting or symptomatic treatment improved common clinical symptoms.

CONCLUSIONS

NP-C is a rare autosomal recessive inherited lysosomal storage disease that affects the intellectual development of children and may lead to dementia, vegetative state or death. Clinical features of this disease include vertical supranuclear gaze palsy, seizures and cataplexy. Laboratory features include abnormal plasma cholesterol level, and sea-blue cells and Niemann-Pick cells in bone marrow smears. The treatments of the disease include supporting or symptomatic administration.

A role of apolipoprotein D in triglyceride metabolism

Apolipoproteins (apo) are constituents of lipoproteins crucial for lipid homeostasis. Aberrant expression of apolipoproteins is associated with metabolic abnormalities. Here we characterized apolipoprotein D (apoD) in triglyceride metabolism. Unlike canonical apolipoproteins that are mainly produced in the liver, apoD is an atypical apolipoprotein with broad tissue distribution. We show that circulating apoD is present mainly in HDL and, to a lesser extent, in LDL and VLDL and that its plasma levels were reduced in db/db mice with visceral obesity and altered lipid metabolism. Elevated apoD production, derived from adenovirus-mediated gene transfer, resulted in significant reduction in plasma triglyceride levels in mice. This effect was attributable to en-hanced LPL activity and improved catabolism of triglyceride-rich particles. In contrast, VLDL triglyceride production remained unchanged in response to elevated apoD production. These findings were recapitulated in high-fat-induced obese mice. Obese mice with elevated apoD production exhibited significantly improved triglyceride profiles, correlating with increased plasma LPL activity and enhanced postprandial fat tolerance. ApoD was shown to promote LPL-mediated hydrolysis of VLDL in vitro, correlating with its TG-lowering action in vivo. Apolipoprotein D plays a significant role in lipid metabolism. These data provide important clues to clinical observations that genetic variants of apoD are associated with abnormal lipid metabolism and increased risk of metabolic syndrome.

Adult onset familial cherry-red spot myoclonus

We report a case of a 36-year-old woman with progressive generalized myoclonus that first became apparent 9 years ago. Her younger brother had similar problems. Examination of her eyes revealed cherry-red spots. Hexosaminidase A, β-galactosidase and neuraminidase activity were normal. Although the laboratory findings were negative, cherry-red spots, progressive myoclonus and autosomal recessive inheritance pattern suggested that she had an unknown type of lysosomal storage disease.

Proteomic analysis of phospholipidosis in citalopram treated U937 cells--support for the cholesterol biosynthesis hypothesis

Excessive accumulation of phospholipids leads to phospholipidosis (PL), which disrupts cellular functions, in extreme cases leading to acute or chronic disease. Citalopram and many other cationic amphiphilic drugs (CADs) have been shown to cause PL both in vitro and in vivo. Recent toxicogenomic studies suggest four hypothetical mechanisms for PL (lysosomal enzyme transport decrease, lysosomal phospholipase activity decrease, phospholipids biosynthesis increase or cholesterol biosynthesis increase). However, the post-genomic steps remain largely unknown and proteomic analyses hold significant promise for defining mechanisms of PL induction. In this study U937 monoblastoid cells were exposed to citalopram hydrobromide for 24 h (0, 20, 100 or 200 microM as citalopram free base) and then harvested for whole cell proteomic analysis using 2-D gel electrophoresis, or transmission electron microscopy (TEM). Protein spots that were significantly altered versus controls were analysed by MALDI-TOF mass spectrometry. Up-regulated proteins were Glyoxalase-I (Glo 1) and 3-Hydroxy-3-methylglutaryl-Coenzyme A synthase 1 (HMGCS1) in cells with PL shown by TEM (favouring the cholesterol biosynthesis increase hypothesis for citalopram induced PL). Other altered proteins were catalase (up-regulated), beta-actin (up-regulated) and 14-3-3 protein (down-regulated). The function of several of the successfully identified proteins indicates a potential perturbed lipid metabolism.

Potential of neural stem cells for the treatment of brain tumors

Neural stem cells (NSCs) are self-renewing multipotent cells that generate the main phenotypes of the nervous system, neurons, astrocytes and oligodendrocytes. As such they hold the promise to treat a broad range of neurological diseases and injuries. Neural progenitor and stem cells have been isolated and characterized in vitro, from adult, fetal and post-mortem tissues, providing sources of material for cellular therapy. However, NSCs are still elusive cells and remain to be unequivocally identified and characterized, limiting their potential use for therapy. Neural progenitor and stem cells, isolated and cultured in vitro, can be genetically modified and when transplanted migrate to tumor sites in the brain. These intrinsic properties of neural progenitor and stem cells provide tremendous potential to bolster the translation of NSC research to therapy. It is proposed to combine gene therapy and cellular therapy to treat brain cancers. Hence, neural progenitor and stem cells provide new opportunities for the treatment of brain cancers.

Sphingosylphosphocholine effects on cultured astrocytes reveal mechanisms potentially involved in neurotoxicity in Niemann-Pick type A disease

Niemann-Pick type A is a disease characterized by the absence of a functional SMPD1 (acidic sphingomyelinase) gene and the abnormal accumulation of sphingomyelin. Under these conditions, also sphingosylphosphocholine (SPC, a sphingomyelin metabolite) accumulates in various tissues, including the brain, where it might act as a toxic stimulus, contributing to the appearance of the neurological symptoms. We studied the effects of SPC on astrocytic and neuronal cultures from rat. In particular, we investigated the possibility that SPC acts on astrocytes and that this represents the first step leading to neurodegeneration. Our results show that acute administration of SPC to astrocytes in culture promotes Ca2+ responses and a release of glutamate that, in turn, leads to cytosolic [Ca2+] elevation in neurons. We also show that chronic stimulation by SPC leads astrocytes to proliferate, but can also change their phenotype towards an activated state that might contribute to the inflammatory responses. Interestingly, upon acute SPC stimulation, activated astrocytes release more glutamate. In conclusion, we show that both chronic and acute exposure to SPC can constitute harmful signals that may have a role in the sequence of events leading to neurodegeneration.

Disruption of sphingolipid metabolism elicits apoptosis-associated reproductive defects in Drosophila

Sphingolipid signaling is thought to regulate apoptosis via mechanisms that are dependent on the concentration of ceramide relative to that of sphingosine-1-phosphate (S1P). This study reports defects in reproductive structures and function that are associated with enhanced apoptosis in Drosophila Sply05091 mutants that lack functional S1P lyase and thereby accumulate sphingolipid long chain base metabolites. Analyses of reproductive structures in these adult mutants unmasked multiple abnormalities, including supernumerary spermathecae, degenerative ovaries, and severely reduced testes. TUNEL assessment revealed increased cell death in mutant egg chambers at most oogenic stages and in affected mutant testes. These reproductive abnormalities and elevated gonadal apoptosis were also observed, to varying degrees, in other mutants affecting sphingolipid metabolism. Importantly, the reproductive defects seen in the Sply05091 mutants were ameliorated both by a second site mutation in the lace gene that restores long chain base levels towards normal and by genetic disruption of the proapoptotic genes reaper, hid and grim. These data thus provide the first evidence in Drosophila that accumulated sphingolipids trigger elevated levels of apoptosis via the modulation of known signaling pathways.

Inhibitors of sphingolipid metabolism enzymes

Sphingolipids are a family of lipids that play essential roles both as structural cell membrane components and in cell signalling. The cellular contents of the various sphingolipid species are controlled by enzymes involved in their metabolic pathways. In this context, the discovery of small chemical entities able to modify these enzyme activities in a potent and selective way should offer new pharmacological tools and therapeutic agents.

Cellular mechanism of U18666A-mediated apoptosis in cultured murine cortical neurons: bridging Niemann-Pick disease type C and Alzheimer's disease

Neuronal cell death can occur by means of either necrosis or apoptosis. Both necrosis and apoptosis are generally believed to be distinct mechanisms of cell death with different characteristic features distinguished on the basis of their morphological and biochemical properties. The brain is the most cholesterol-rich organ in the body but not much is known about the mechanisms that regulate cholesterol homeostasis in the brain. Recently, several clinical and biochemical studies suggest that cholesterol imbalance in the brain may be a risk factor related to the development of neurological disorders such as Niemann-Pick disease type C (NPC) and Alzheimer's disease (AD). NPC is a fatal juvenile neurodegenerative disorder characterized by premature neuronal death and somatically altered cholesterol metabolism. The main biochemical manifestation in NPC is elevated intracellular accumulation of free cholesterol caused by a genetic deficit in cholesterol trafficking. The pharmacological agent, U18666A (3-beta-[2-(diethylamino)ethoxy]androst-5-en-17-one), is a well-known class-2 amphiphile which inhibits cholesterol transport. Cells treated with this agent accumulate intracellular cholesterol to massive levels, similar to that observed in cells from NPC patients. NPC and AD have some pathological similarities which may share a common underlying cause. AD is one of the most common types of dementia affecting the elderly. However, the molecular mechanisms of neurodegeneration in NPC and AD are largely unknown. This review provides a consolidation of work done using U18666A in the past half century and focuses on the implications of our research findings on the mechanism of U18666A-mediated neuronal apoptosis in primary cortical neurons, which may provide an insight to elucidate the mechanisms of neurodegenerative diseases, particularly NPC and AD, where apoptosis might occur through a similar mechanism.

Les sphingolipides : vecteurs d’agents pathogènes et cause de maladies génétiques

Sphingolipids are present in all eukaryotic cells and share a sphingoid base : sphingosine. They were first discovered in 1884 and for a long time they were thought to participate to membrane structure only. Recently it has been established that they are mainly located in particular areas of the membrane called rafts which are signalling platforms. It has also been demonstrated that sphingolipids are receptors and second messengers. They play a crucial role in cellular functioning and are necessary to maintenance and developing of living organisms. However due to their receptor properties, they are also gateway for penetration of pathogenic agents such as virus (Ebola, HIV) or toxins (botulinium, tetanus). These agents first bind to glycosphingolipids or proteins mainly located in rafts. The complex so formed is required for the crossing of the membrane by the pathogenic agent. Sphingolipids metabolism is regulated by numerous enzymes. A failure in the activity of one of them induces an accumulation of sphingolipids known as sphingolipidoses. These are genetic diseases having severe consequences for the survival of the organism. The precise mechanisms of the sphingolipidoses are still mainly unknown which explains why few therapeutic strategies are available. These particular properties of lipids rafts and sphingolipids explain why a growing number of studies in the medical and scientific fields are devoted to them.

Early pulmonary involvement in Niemann-Pick type B disease: lung lavage is not useful

Niemann-Pick disease (NPD) is a rare, autosomal-recessively inherited lipid storage disease which is characterized by intracellular deposition of sphingomyelin in various body tissues. The disease is heterogeneous and classified into six groups. Pulmonary parenchymal involvement may be a feature of several subtypes of NPD, including type B. Progressive pulmonary involvement in NPD type B is a major cause of morbidity and mortality. It is usually diagnosed at older ages. Only a few cases with early pulmonary involvement have been reported. In this report, a patient with NPD type B, hospitalized with the diagnosis of pneumonia at age 3 months, is presented. Following treatment for pneumonia, she continued to have persistent respiratory symptoms and became oxygen-dependent. High-resolution computed tomography of the chest revealed diffuse interstitial changes. During follow-up, the patient developed hepatosplenomegaly. Lung, liver, and bone marrow biopsies showed characteristic findings for NPD. Biochemical studies also confirmed the diagnosis, and the sphingomyelinase enzyme level of the patient was low. Unilateral lung lavage was performed in order to decrease lipid storage as a treatment modality. However, there was no clinical or radiological improvement. The patient died at age 15 months due to progressive respiratory failure. Pulmonary involvement is a rare entity in early childhood in patients with NPD type B, but should be considered in the differential diagnosis of persistent interstitial lung disease. It may cause progressive respiratory failure, but the treatment options remain limited.

The lipid composition of autophagic vacuoles regulates expression of multilamellar bodies

Multilamellar bodies (MLBs) are responsible for surfactant secretion in type II alveolar cells but also accumulate in other cell types under pathological conditions, including cancer and lysosomal storage diseases such as Niemann-Pick C (NPC), a congenital disease where defective cholesterol transport leads to its accumulation in lysosomes. Mv1Lu type II alveolar cells transfected with Golgi β1,6 N-acetylglucosaminyltransferase V (Mgat5), enhancing the polylactosamine content of complex-type N-glycans, exhibit stable expression of MLBs whose formation requires lysosomal proteolysis within dense autophagic vacuoles. MLBs of Mgat5-transfected Mv1Lu cells are rich in phospholipids and have low levels of cholesterol. In Mv1Lu cells treated with the NPC-mimicking drug U18666A, cholesterol-rich MLBs accumulate independently of both Mgat5 expression and lysosomal proteolysis. Inhibition of autophagy by blocking the PI 3-kinase pathway with 3-methyladenine prevents MLB formation and results in the accumulation of non-lamellar, acidic lysosomal vacuoles. Treatment with 3-methyladenine inhibited the accumulation of monodansylcadaverine, a phospholipid-specific marker for autophagic vacuoles, but did not block endocytic access to the lysosomal vacuoles. Induction of autophagy via serum starvation resulted in an increased size of cholesterol-rich MLBs. Although expression of MLBs in the Mv1Lu cell line can be induced by modulating lysosomal cholesterol or protein glycosylation, an autophagic contribution of phospholipids is critical for the formation of concentric membrane lamellae within late lysosomal organelles.

A model of the acid sphingomyelinase phosphoesterase domain based on its remote structural homolog purple acid phosphatase

Sequence profile and fold recognition methods identified mammalian purple acid phosphatase (PAP), a member of a dimetal-containing phosphoesterase (DMP) family, as a remote homolog of human acid sphingomyelinase (ASM). A model of the phosphoesterase domain of ASM was built based on its predicted secondary structure and the metal-coordinating residues of PAP. Due to the low sequence identity between ASM and PAP (approximately 15%), the highest degree of confidence in the model resides in the metal-binding motifs. The ASM model predicts residues Asp 206, Asp 278, Asn 318, His 425, and His 457 to be dimetal coordinating. A putative orientation for the phosphorylcholine head group of the ASM substrate, sphingomyelin (SM), was made based on the predicted catalysis of the phosphorus-oxygen bond in the active site of ASM and on a structural comparison of the PAP-phosphate complex to the C-reactive protein-phosphorylcholine complex. These complexes revealed similar spatial interactions between the metal-coordinating residues, the metals, and the phosphate groups, suggesting a putative orientation for the head group in ASM consistent with the mechanism considerations. A conserved sequence motif in ASM, NX3CX3N, was identified (Asn 381 to Asn 389) and is predicted to interact with the choline amine moiety in SM. The resulting ASM model suggests that the enzyme uses an SN2-type catalytic mechanism to hydrolyze SM, similar to other DMPs. His 319 in ASM is predicted to protonate the ceramide-leaving group in the catalysis of SM. The putative functional roles of several ASM Niemann-Pick missense mutations, located in the predicted phosphoesterase domain, are discussed in context to the model.

Effects of Acid Sphingomyelinase Deficiency on Male Germ Cell Development and Programmed Cell Death1

Deficiency of acid sphingomyelinase (ASM), an enzyme responsible for producing a pro-apoptotic second messenger ceramide, has previously been shown to promote the survival of fetal mouse oocytes in vivo and to protect oocytes from chemotherapy-induced apoptosis in vitro. Here we investigated the effects of ASM deficiency on testicular germ cell development and on the ability of germ cells to undergo apoptosis. At the age of 20 weeks, ASM knock-out (ASMKO) sperm concentrations were comparable with wild-type (WT) sperm concentrations, whereas sperm motility was seriously affected. ASMKO testes contained significantly elevated levels of sphingomyelin at the age of 8 weeks as detected by high-performance, thin-layer chromatography. Electron microscopy revealed that the testes started to accumulate pathological vesicles in Sertoli cells and in the interstitium at the age of 21 days. Irradiation of WT and ASMKO mice did not elevate intratesticular ceramide levels at 16 h after irradiation. In situ end labeling of apoptotic cells also showed a similar degree of cell death in both groups. After a 21-day recovery period, the numbers of primary spermatocytes and spermatogonia at G2 as well as spermatids were essentially the same in the WT and ASMKO testes, as detected by flow cytometry. In serum-free cultures both ASMKO and WT germ cells showed a significant increase in the level of ceramide, as well as massive apoptosis. In conclusion, ASM is required for maintenance of normal sphingomyelin levels in the testis and for normal sperm motility, but not for testicular ceramide production or for the ability of the germ cells to undergo apoptosis.

Lysenin: A new tool for investigating membrane lipid organization

Sphingomyelin is a major sphingolipid species in animal cells and is a major lipid constituent of plasma membranes. Recent reports have established important roles for sphingomyelin and its metabolites as second messengers in signal transduction events during development and differentiation. Sphingomyelin is also a major component of sphingolipid, cholesterol-rich plasma membrane microdomains, known as 'lipid rafts'. However, little is known about the organization of sphingomyelin in biological membranes. Lysenin is a recently discovered sphingomyelin-specific toxin. In the present review, we summarize the current characterization of this protein and describe our recent attempt to elucidate the organization of sphingomyelin in cellular membranes using lysenin as a unique tool.

Aberrant sphingomyelin/ceramide metabolic-induced neuronal endosomal/lysosomal dysfunction: potential pathological consequences in age-related neurodegeneration

Alterations in the trafficking and function of the endocytic pathway have been extensively documented to be one of the earliest pathological changes in sporadic Alzheimer's disease (AD). Although the pathophysiological consequences of these endosomal/lysosomal changes are currently unknown, several recent studies have suggested that such changes in endocytic function are able to cause a redistribution of several lysosomal hydrolases into early endosomes, leading to the overproduction of neurotoxic amyloid peptide. Recently, we and others have demonstrated that abnormal endocytic pathology within post-mitotic neurons can, in part, be attributed to alterations in sphingomyelin/ceramide metabolism, resulting in the intracellular accumulation of ceramide. Once inside the cell, the ability of ceramide to physically alter membrane structure, formation, and fusion, rather than serving solely as a lipid secondary messenger, may severely compromise normal endocytic trafficking. In this review, we will discuss the potential pathological effects of abnormal sphingomyelin/ceramide metabolism on intracellular vesicular transport in relation to both amyloid accumulation in AD and various neurodegenerative diseases associated with lysosomal abnormalities.

Niemann-Pick type C disease associated with peripheral neuropathy

Niemann-Pick type C disease is an autosomal-recessive, inherited neurovisceral lipid storage disorder. This disease results from either protein NPC1 or HE1 deficiency, which leads to cholesterol metabolism disturbance and is characterized by early hepatosplenomegaly and progressive ataxia, dystonia, cataplexy, dysarthria, and dementia. We describe a 3 1/2-year-old patient with Niemann-Pick type C disease, who presented with regression in both cognitive and motor domains. Almost 10 months before admission to the hospital, the child developed progressive speech and behavioral changes, as well as gait disturbances with frequent falls. The examination demonstrated hepatosplenomegaly, ataxia, and vertical gaze palsy. Nerve conduction velocities demonstrated mild demyelinating peripheral neuropathy. Bone marrow examination revealed foam cells, and cholesterol esterification studies found massive accumulation of unesterified cholesterol and very low intracellular esterification of exogenous lipoprotein-derived cholesterol. These results indicate Niemann-Pick type C disease. Peripheral neuropathy is a rare complication in patients with Niemann-Pick type C disease, which certainly contributes to their neurologic deterioration.

Neuronal endosomal/lysosomal membrane destabilization activates caspases and induces abnormal accumulation of the lipid secondary messenger ceramide

Impairment of endosomal/lysosomal functions are reported as some of the earliest changes in several age-related neurological disorders such as Alzheimer's disease. Dysregulation of the lysosomal system is also accompanied by the accumulation of age-associated pigments and several recent reports have indicated that this age-related lipofuscin accumulation can sensitize cells to oxidative stress and apoptotic cell death. In this study, we have established and evaluated an in vitro age-related pathology paradigm that models lipofuscin accumulation. Our model consists of the treatment of cultured primary mouse neurons with lysosomotropic detergents. We have observed that one of the earliest biochemical changes associated with lysosomotropic detergent-induced membrane instability is a loss of the endosomal/lysosomal proton gradient integrity, followed by an activation of sphingomyelin hydrolysis and ceramide accumulation within enlarged endosomal/lysosomal vesicles. In addition, we demonstrate that ceramide accumulation correlates with the activation of proximal procaspases-8 and -9 as well as distal caspase-3, prior to the appearance of cell death. Taken together, we propose that disturbances of the endosomal/lysosomal system, in addition to the activation of the sphingomyelinase hydrolysis cycle, play essential roles in the course of post-mitotic neuronal aging. The abnormal accumulation of undigested lipids and proteins within dysfunctional endosomal/lysosomal vesicle populations during the process of pathological aging may serve as triggers of the cell death programs that are associated with downstream neurodegeneration.

Seven novel acid sphingomyelinase gene mutations in Niemann-Pick type A and B patients

We have analyzed acid sphingomyelinase (SMPD1; E.C. 3.1.4.12) gene mutations in four Niemann-Pick disease (NPD) type A and B patients of Turkish ancestry and in three patients of Dutch origin. Among four NPD type A patients we found two homozygotes for the g.1421C > T (H319Y) and g.3714T > C (Y537H) mutations and two compound heterozygotes, one for the g.3337T > C (F463S) and g.3373C > T (P475L) mutations and the other for the g.84delC (G29fsX74) and g.1208A > C (S248R) mutations. One of the type B patients was homozygous for the g.2629C>T (P371S) mutation. The last two type B patients were homozygotes for the common g.3927_3929delCGC (R608del) mutation. The G29fsX74, S248R, H319Y, P371S, F463S, P475L and Y537H SMPD1 mutations are all novel and were verified by PCR/RFLP and/or ARMS. All of the identified mutations are likely to be rare or private, with the exception of R608del which is prevalent among NPD type B patients from the North-African Maghreb region. Geographical and/or social isolation of the affected families are likely contributing factors for the high number of homozygotes in our group.

Niemann-Pick disease: a rare problem in anaesthesiological practice

We describe the problems encountered during general anaesthesia in a 2-year-old boy who was suffering from an extremely severe form of Niemann-Pick disease. Attention focused on respiratory difficulties and intubation problems. The usefulness of the lateral position and the limits of the Mallampati score in this case are discussed.

Signaling pathway for radiation-induced apoptosis in the lymphoblasts from neuronopathic (type A) and non-neuronopathic (type B) forms of Niemann-Pick disease

Deficient activity of human lysosomal hydrolase, acid sphingomyelinase (ASM), results in the neuronopathic (type A) and non-neuronopathic (type B) forms of Niemann-Pick disease (NPD). A deficiency of ASM is known to deprive lymphoblasts of their response to apoptotic induction by X-ray irradiation. To elucidate the genetic heterogeneity of apoptotic induction in NPD cells, we investigated radiation-induced apoptosis of lymphoblasts in patients with type A (genotype: IVS3-2A-G/IVS3-2A-G) and type B (genotype: S436R/S436R) NPD. Epstein-Barr virus (EBV)-transformed lymphoblasts established from a patient with type A NPD, a patient with type B NPD and a normal control were irradiated with 20 Gy and incubated for 24 h. The cells were harvested and the morphological features of apoptosis were observed with DNA-specific fluorochrome bis-benzimide. Exposure of lymphoblasts to 20 Gy of radiation resulted in 25-30% apoptosis of total cells in normal lymphoblasts, 8-9% apoptosis in type A NPD and 20-27% apoptosis in type B NPD. The radiation-induced apoptotic response in the lymphoblasts of type A NPD was significantly different from that of the normal lymphoblasts (P<0.0005). On the other hand, the radiation-induced apoptotic response in type B NPD was not markedly different from that in normal lymphoblasts (P=0.624). In the patient with type B NPD, the signaling pathway for radiation-induced apoptosis was preserved in lymphoblasts, which suggests that the extent of cell signaling system disturbance due to ASM deficiency may be related to the phenotypes in types A and B NPD.

Gaucher and Niemann-Pick diseases--enzymatic diagnosis in dried blood spots on filter paper: retrospective diagnoses in newborn-screening cards

BACKGROUND

Gaucher disease (GD) and Niemann-Pick (NP) disease are caused by deficient activity of the lysosomal enzymes acid beta-D-glucosidase (ABG) and acid sphingomyelinase (ASM), respectively. For diagnosis, these enzymes are usually measured in the extracts of leukocytes or cultured fibroblasts. Chitotriosidase (CTE), a chitinolytic enzyme, is markedly increased in the plasma of Gaucher patients. We describe methods for the assay of acid beta-D-glucosidase, acid sphingomyelinase, chitotriosidase, and alpha-N-acetyl-galactosaminidase (NAGA) as a control enzyme in blood spots that were dried onto filter paper.

METHODS

To tubes containing a 3 mm-diameter blood spot, we added elution liquid and substrate solution. After incubation at 37 degrees C, the amount of hydrolyzed product was compared with a calibrator to allow the quantification of enzyme activity. We examined 80 healthy controls, 54 Gaucher patients, 8 Niemann-Pick patients, 27 obligate carriers, and the newborn-screening cards (NSC) from a case of Gaucher and a case of Niemann-Pick disease.

RESULTS AND CONCLUSION

The described methodology is useful to identify Gaucher and Niemann-Pick patients and controls, using samples that are sufficiently stable to be transported to the testing laboratory by mail. The diagnosis of both diseases on a newborn-screening card was clearly established. The newborn-screening card has been added to the biological materials that allow the identification of patients with Gaucher and Niemann-Pick diseases.

Lysosomal disorders

Although most lysosomal storage disorders present in infancy or early childhood with a progressive condition often associated with dysmorphism, considerable genetic heterogeneity exists resulting in a range of illnesses that can include a dramatic neonatal presentation. Whilst some conditions present with a characteristic neonatal phenotype (e.g. Niemann-Pick disease type C), the remainder present in a nonspecific way often with non-immune hydrops fetalis. Diagnosis can be helped by appropriate radiological studies and, in some patients, evidence of the storage phenomena can be seen in peripheral blood smears or bone marrow aspirates. Unfortunately, for the majority of affected patients no effective, curative, treatment is possible. New developments in therapy including enzyme replacement therapy and substrate deprivation may improve prognosis in some disorders. It is important to establish an accurate diagnosis, as prenatal testing can then be offered in future pregnancies.

The role of ceramide in receptor- and stress-induced apoptosis studied in acidic ceramidase-deficient Farber disease cells

The activation of sphingomyelinases leading to the generation of ceramide has been implicated in various apoptotic pathways. However, the role of ceramide as an essential death mediator remains highly controversial. In the present study, we investigated the functional relevance of ceramide in a genetic model by using primary cells from a Farber disease patient. These cells accumulate ceramide as the result of an inherited deficiency of acidic ceramidase. We demonstrate that Farber disease lymphocytes and fibroblasts underwent apoptosis induced by various stress stimuli, including staurosporine, anticancer drugs and gamma-irradiation, equally as normal control cells. In addition, caspase activation by these proapoptotic agents occurred rather similarly in Farber disease and control fibroblasts. Interestingly, Farber disease lymphoid cells underwent apoptosis induced by the CD95 death receptor more rapidly than control cells. Our data therefore suggest that ceramide does not play an essential role as a second messenger in stress-induced apoptosis. However, in accordance with a role in lipid-rich microdomains, ceramide by altering membrane composition may function as an amplifier in CD95-mediated apoptosis.

The amoebapore superfamily

Amoebapores, synthesized by human protozoan parasites, form ion channels in target cells and artificial lipid membranes. The major pathogenic effect of these proteins is due to their cytolytic capability which results in target cell death. They comprise a coherent family and are homologous to other proteins and protein domains found in eight families. These families include in addition to the amoebapores (1) the saposins, (2) the NK-lysins and granulysins, (3) the pulmonary surfactant proteins B, (4) the acid sphingomyelinases, (5) acyloxyacyl hydrolases and (6) the aspartic proteases. These amoebapore homologues have many properties in common including membrane binding and stability. We note for the first time that a new protein, countin, from the cellular slime mold, Dictyostelium discoideum, comprises the eighth family within this superfamily. All currently sequenced members of these eight families are identified, and the structural, functional and phylogenetic properties of these proteins are discussed.