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Acid sphingomyelinase (ASM) is a lysosomal hydrolase that degrades sphingomyelin into ceramide and phosphocholine. Recent crystallographic studies revealed the functional role of the N-terminal ASM saposin domain. ASM deficiency due to mutations in the ASM-encoding sphingomyelin phosphodiesterase 1 (SMPD1) gene causes an autosomal recessive sphingolipid-storage disorder, known as Niemann-Pick disease Type A (NPA) or Type B (NPB). NPA is an early-onset neuronopathic disorder, while NPB is a late-onset non-neuronopathic disorder. A homozygous one-base substitution (c.398G>A) of the SMPD1 gene was identified in an infant with NPA, diagnosed with complete loss of ASM activity in the patient's fibroblasts. This mutation is predicted to substitute tyrosine for cysteine at amino acid residue 133, abbreviated as p.C133Y. The patient showed developmental delay, hepatosplenomegaly and rapid neurological deterioration leading to death at the age of 3 years. To characterize p.C133Y, which may disrupt one of the three disulfide bonds of the N-terminal ASM saposin domain, we performed immunoblotting analysis to explore the expression of a mutant ASM protein in the patient's fibroblasts, showing that the protein was detected as a 70-kDa protein, similar to the wild-type ASM protein. Furthermore, transient expression of p.C133Y ASM protein in COS-7 cells indicated complete loss of ASM enzyme activity, despite that the p.C133Y ASM protein was properly localized to the lysosomes. These results suggest that the proper three-dimensional structure of saposin domain may be essential for ASM catalytic activity. Thus, p.C133Y is associated with complete loss of ASM activity even with stable protein expression and proper subcellular localization.

Summary The highly lethal brain cancer glioblastoma (GBM) poses a daunting challenge because the blood-brain barrier renders potentially druggable amplified or mutated oncoproteins relatively inaccessible. Here, we identify sphingomyelin phosphodiesterase 1 (SMPD1), an enzyme that regulates the conversion of sphingomyelin to ceramide, as an actionable drug target in GBM. We show that the highly brain-penetrant antidepressant fluoxetine potently inhibits SMPD1 activity, killing GBMs, through inhibition of epidermal growth factor receptor (EGFR) signaling and via activation of lysosomal stress. Combining fluoxetine with temozolomide, a standard of care for GBM, causes massive increases in GBM cell death and complete tumor regression in mice. Incorporation of real-world evidence from electronic medical records from insurance databases reveals significantly increased survival in GBM patients treated with fluoxetine, which was not seen in patients treated with other selective serotonin reuptake inhibitor (SSRI) antidepressants. These results nominate the repurposing of fluoxetine as a potentially safe and promising therapy for patients with GBM and suggest prospective randomized clinical trials.

Increasing evidence suggests that induction of lethal macroautophagy/autophagy carries potential significance for the treatment of glioblastoma (GBM). In continuation of previous work, we demonstrate that pimozide and loperamide trigger an ATG5- and ATG7 (autophagy related 5 and 7)-dependent type of cell death that is significantly reduced with cathepsin inhibitors and the lipid reactive oxygen species (ROS) scavenger α-tocopherol in MZ-54 GBM cells. Global proteomic analysis after treatment with both drugs also revealed an increase of proteins related to lipid and cholesterol metabolic processes. These changes were accompanied by a massive accumulation of cholesterol and other lipids in the lysosomal compartment, indicative of impaired lipid transport/degradation. In line with these observations, pimozide and loperamide treatment were associated with a pronounced increase of bioactive sphingolipids including ceramides, glucosylceramides and sphingoid bases measured by targeted lipidomic analysis. Furthermore, pimozide and loperamide inhibited the activity of SMPD1/ASM (sphingomyelin phosphodiesterase 1) and promoted induction of lysosomal membrane permeabilization (LMP), as well as release of CTSB (cathepsin B) into the cytosol in MZ-54 wild-type (WT) cells. Whereas LMP and cell death were significantly attenuated in ATG5 and ATG7 knockout (KO) cells, both events were enhanced by depletion of the lysophagy receptor VCP (valosin containing protein), supporting a pro-survival function of lysophagy under these conditions. Collectively, our data suggest that pimozide and loperamide-driven autophagy and lipotoxicity synergize to induce LMP and cell death. The results also support the notion that simultaneous overactivation of autophagy and induction of LMP represents a promising approach for the treatment of GBM. Abbreviations: ACD: autophagic cell death; AKT1: AKT serine/threonine kinase 1; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG14: autophagy related 14; CERS1: ceramide synthase 1; CTSB: cathepsin B; CYBB/NOX2: cytochrome b-245 beta chain; ER: endoplasmatic reticulum; FBS: fetal bovine serum; GBM: glioblastoma; GO: gene ontology; HTR7/5-HT7: 5-hydroxytryptamine receptor 7; KD: knockdown; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LAP: LC3-associated phagocytosis; LMP: lysosomal membrane permeabilization; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; RB1CC1: RB1 inducible coiled-coil 1; ROS: reactive oxygen species; RPS6: ribosomal protein S6; SMPD1/ASM: sphingomyelin phosphodiesterase 1; VCP/p97: valosin containing protein; WT: wild-type.

Patient: Male, 45-year-old Final Diagnosis: Niemann-Pick disease type B Symptoms: Hepatosplenomegaly • lung fibrosis Medication: — Clinical Procedure: — Specialty: Pulmonology Objective: Rare disease Background: Niemann-Pick disease is a rare genetic disorder caused by mutations in sphingomyelin phosphodiesterase 1 gene. It results in acid sphingomyelinase deficiency (ASMD) and sphingomyelin intracellular accumulation. Lung disease is diagnosed mostly in chronic visceral ASMD. Ground-glass opacities and smooth interlobular septal thickening are described most frequently. They are localized predominantly in the lower parts of both lungs. Case Report: The authors describe a rare type of lung involvement, composed of emphysema and interstitial lung disease (ILD), in a nonsmoking adult male with chronic visceral ASMD. Areas of ground-glass opacities and lung fibrosis presenting as reticulation and bronchiectasis have been described in high-resolution computed tomography of the lungs. The radiological findings were localized predominantly in the middle and lower parts of both lungs. Large air spaces of marginal emphysema, localized in the upper lobes, were also demonstrated. Foamy macrophages, staining blue with May-Grünwald-Giemsa, were found in bronchoalveolar lavage, confirming lung involvement in the course of ASMD. The course of disease was stable, with no hypoxemia at rest. Nevertheless, because of markedly decreased lung transfer for carbon monoxide and significant desaturation on exertion, further controls have been planned, with qualification for long-term oxygen therapy in case of deterioration. Conclusions: We present a unique type of lung involvement, combined emphysema and ILD, in a nonsmoking adult patient with chronic visceral ASMD. On such occasion chronic obstructive pulmonary disease coexisting with ILD as well as chronic pulmonary fibrosis and emphysema syndrome should be excluded.

Niemann-Pick Disease type B (NPDB) is a rare autosomal recessive disease belonging to the family of lysosomal storage disorders. NPDB is caused by mutations of sphingomyelin phosphodiesterase 1 gene (SMPD1) and is characterized by hepatosplenomegaly, interstitial lung disease, recurrent pulmonary infections, and neurologic disorders. Bronchiectasis are atypical. Until now, only three cases of lung transplantation for severe respiratory impairment have been reported. We describe a case of NPDB that was diagnosed after lung transplantation for cystic bronchiectasis. In 2016, a 31-year-old woman who was experiencing hypoxemic respiratory failure and recurrent pulmonary infections due to cystic bronchiectasis received a double-lung-transplantation. Histopathologic study on removed lungs revealed clusters of CD68 foamy lipid-laden macrophages with concentric and palisade arrangement, compatible with the diagnosis of NPDB, which was confirmed after SMPD1 genetic sequencing. Twenty-three months after transplantation, allograft function is stable (FEV1 was 100% of best-FEV1). The singularity of this case lies in the presence of bronchiectasis, which is an unprecedently described phenotype of NPDB. This finding was accompanied by the detection of a novel SMPD1 mutation (p.Ala46=) of uncertain meaning.

Inhibition of acid sphingomyelinase (ASM), a lysosomal enzyme that catalyzes the hydrolysis of sphingomyelin into ceramide and phosphorylcholine, may serve as an investigational tool or a therapeutic intervention to control many diseases. Specific ASM inhibitors are currently not sufficiently characterized. Here, we found that 1-aminodecylidene bis-phosphonic acid (ARC39) specifically and efficiently (>90%) inhibits both lysosomal and secretory ASM in vitro. Results from investigating sphingomyelin phosphodiesterase 1 (SMPD1/Smpd1) mRNA and ASM protein levels suggested that ARC39 directly inhibits ASM's catalytic activity in cultured cells, a mechanism that differs from that of functional inhibitors of ASM. We further provide evidence that ARC39 dose- and time-dependently inhibits lysosomal ASM in intact cells, and we show that ARC39 also reduces platelet- and ASM-promoted adhesion of tumor cells. The observed toxicity of ARC39 is low at concentrations relevant for ASM inhibition in vitro, and it does not strongly alter the lysosomal compartment or induce phospholipidosis in vitro. When applied intraperitoneally in vivo, even subtoxic high doses administered short-term induced sphingomyelin accumulation only locally in the peritoneal lavage without significant accumulation in plasma, liver, spleen, or brain. These findings require further investigation with other possible chemical modifications. In conclusion, our results indicate that ARC39 potently and selectively inhibits ASM in vitro and highlight the need for developing compounds that can reach tissue concentrations sufficient for ASM inhibition in vivo.

Uncontrolled cardiac fibrosis following myocardial infarction (MI) is a critical pathological change leading to heart failure. Current pharmacotherapies are limited by unsatisfactory efficacy and undesired systemic side effects. Astaxanthin (ASX) is a natural carotenoid with strong antioxidant and anti-inflammatory activities. The effects of ASX on MI-induced cardiac fibrosis and the underlying mechanisms remain largely unknown. In this study, after the establishment of MI model, mice were administrated with ASX (200 mg/kg⋅d) for 4 weeks. We found that ASX treatment attenuated cardiac fibrosis and improved heart function following MI, as evidenced by reduced collagen I/III ratio, hydroxyproline content and left ventricular end diastolic pressure (LVEDP). Lipidomic analysis revealed the overaccumulation of myocardial ceramides in mice with cardiac fibrosis, which was normalized by ASX treatment. Molecular docking analysis showed that ASX produced a tight fit in the pocket of sphingomyelin phosphodiesterase 1 (SMPD1), a key enzyme in the production of ceramides. Western blot analysis confirmed the significant inhibition of SMPD1 expression by ASX. Furthermore, MI-induced overexpression of transforming growth factor β1 (TGF-β1) and phosphorylated SMAD2/3 were attenuated by ASX administration. SMPD1 knockout (KO) abrogated the beneficial effect of ASX. Taken together, our results suggest that the cardioprotective effects of ASX are mediated by SMPD1 through the indirection inhibition of TGF- β1/SMAD signaling cascade.

Key points Membrane rafts (MRs)-redox signalling pathway is activated in response to transforming growth factor-β1 (TGF-β1) stimulation in renal tubular cells. This pathway contributes to TGF-1β-induced epithelial-mesenchymal transition (EMT) in renal tubular cells. The the MRs-redox signalling pathway is activated in renal tubular cells isolated from angiotensin II (AngII)-induced hypertensive rats. Inhibition of this pathway attenuated renal inflammation and fibrosis in AngII-induced hypertension. Abstract The membrane rafts (MRs)-redox pathway is characterized by NADPH oxidase subunit clustering and activation through lysosome fusion, V-type proton ATPase subunit E2 (encoded by the Atp6v1e2 gene) translocation and sphingomyelin phosphodiesterase 1 (SMPD1, encoded by the SMPD1 gene) activation. In the present study, we hypothesized that the MRs-redox-derived reactive oxygen species (ROS) are involved in renal inflammation and fibrosis by promoting renal tubular epithelial-mesenchymal transition (EMT). Results show that transforming growth factor-β1 (TGF-β1) acutely induced MR formation and ROS production in NRK-52E cells, a rat renal tubular cell line. In addition, transfection of Atp6v1e2 small hairpin RNAs (shRNA) and SMPD1 shRNA attenuated TGF-β1-induced changes in EMT markers, including E-cadherin, α-smooth muscle actin (α-SMA) and fibroblast-specific protein-1 (FSP-1) in NRK-52E cells. Moreover, Erk1/2 activation may be a downstream regulator of the MRs-redox-derived ROS, because both shRNAs significantly inhibited TGF-β1-induced Erk1/2 phosphorylation. Further in vivo study shows that the renal tubular the MRs-redox signalling pathway was activated in angiotensin II (AngII)-induced hypertension, as indicated by the increased NADPH oxidase subunit Nox4 fraction in the MR domain, SMPD1 activation and increased ROS content in isolated renal tubular cells. Finally, renal transfection of Atp6v1e2 shRNA and SMPD1 shRNA significantly prevented renal fibrosis and inflammation, as indicated by the decrease of α-SMA, fibronectin, collagen I, monocyte chemoattractant protein-1 (MCP-1), intercellular cell adhesion molecule-1 (ICAM-1) and tumour necrosis factor-α (TNF-α) in kidneys from AngII-infused rats. It was concluded that the the MRs-redox signalling pathway is involved in TGF-β1-induced renal tubular EMT and renal inflammation/fibrosis in AngII-induced hypertension.

Activation of the lysosomal ceramide-producing enzyme, acid sphingomyelinase (ASM), by various stresses is centrally involved in cell death and has been implicated in autophagy. We set out to investigate the role of the baseline ASM activity in maintaining physiological functions of lysosomes, focusing on the lysosomal nutrient-sensing complex (LYNUS), a lysosomal membrane-anchored multiprotein complex that includes mammalian target of rapamycin (mTOR) and transcription factor EB (TFEB). ASM inhibition with imipramine or sphingomyelin phosphodiesterase 1 (SMPD1) siRNA in human lung cells, or by transgenic Smpd1(+/−) haploinsufficiency of mouse lungs, markedly reduced mTOR- and P70-S6 kinase (Thr 389)-phosphorylation and modified TFEB in a pattern consistent with its activation. Inhibition of baseline ASM activity significantly increased autophagy with preserved degradative potential. Pulse labeling of sphingolipid metabolites revealed that ASM inhibition markedly decreased sphingosine (Sph) and Sph-1-phosphate (S1P) levels at the level of ceramide hydrolysis. These findings suggest that ASM functions to maintain physiological mTOR signaling and inhibit autophagy and implicate Sph and/or S1P in the control of lysosomal function.

Niemann-Pick disease (NPD) type B is a rare autosomal recessive disease characterized by variable levels of impairment in sphingomyelin phosphodiesterase 1 (SMPD1) activity. Lung involvement is the most important prognostic factor in NPD-B, with recurrent respiratory infections starting in infancy being the major cause of morbidity and mortality. We hypothesized that decreased SMPD1 activity impaired airway epithelium host defense response. SMPD1 activity was reduced using inducible shRNA. Surprisingly, decreasing SMPD1 activity by 50%, resulted in increased neutrophil recruitment, both at baseline and in response to bacterial stimulation. This correlated with elevated levels of cytokine mRNA shown to contribute to neutrophil recruitment in unstimulated (e.g. IL-8 and GRO-α) and infected cells (e.g. IL-8, GRO-α, GM-CSF and CCL20). Instead of preventing the host defence responses, decreased SMPD1 activity results in an inflammatory response even in the absence of infection. Moreover, decreasing SMPD1 activity resulted in a pro-oxidative shift. Accordingly, expression of an inactive mutant, SMPD1[L225P] but not the WT enzyme increased activation of the antioxidant transcription factor NRF2. Therefore, decreasing SMPD1 activity by 50% in airway epithelial cells, the equivalent of the loss of one allele, results in the accumulation of oxidants that activates NRF2 and a concomitant increased cytokine production as well as neutrophil recruitment. This can result in a chronic inflammatory state that impairs host defence similar to scenarios observe in other chronic inflammatory lung disease such as Chronic Obstructive Pulmonary Disease or Cystic Fibrosis.

Sphingomyelin is an essential cellular lipid that traffics between plasma membrane and intracellular organelles until directed to lysosomes for SMPD1 (sphingomyelin phosphodiesterase 1)-mediated degradation. Inactivating mutations in the SMPD1 gene result in Niemann-Pick diseases type A and B characterized by sphingomyelin accumulation and severely disturbed tissue homeostasis. Here, we report that sphingomyelin overload disturbs the maturation and closure of autophagic membranes. Niemann-Pick type A patient fibroblasts and SMPD1-depleted cancer cells accumulate elongated and unclosed autophagic membranes as well as abnormally swollen autophagosomes in the absence of normal autophagosomes and autolysosomes. The immature autophagic membranes are rich in WIPI2, ATG16L1 and MAP1LC3B but display reduced association with ATG9A. Contrary to its normal trafficking between plasma membrane, intracellular organelles and autophagic membranes, ATG9A concentrates in transferrin receptor-positive juxtanuclear recycling endosomes in SMPD1-deficient cells. Supporting a causative role for ATG9A mistrafficking in the autophagy defect observed in SMPD1-deficient cells, ectopic ATG9A effectively reverts this phenotype. Exogenous C12-sphingomyelin induces a similar juxtanuclear accumulation of ATG9A and subsequent defect in the maturation of autophagic membranes in healthy cells while the main sphingomyelin metabolite, ceramide, fails to revert the autophagy defective phenotype in SMPD1-deficient cells. Juxtanuclear accumulation of ATG9A and defective autophagy are also evident in tissues of smpd1-deficient mice with a subsequent inability to cope with kidney ischemia-reperfusion stress. These data reveal sphingomyelin as an important regulator of ATG9A trafficking and maturation of early autophagic membranes.

International audience; Mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene were reported to be associated with Parkinson's disease and dementia with Lewy bodies. In the current study, we aimed to evaluate the role of SMPD1 variants in isolated rapid eye movement sleep behavior disorder (iRBD). SMPD1 and its untranslated regions were sequenced using targeted next-generation sequencing in 959 iRBD patients and 1287 controls from European descent. Our study reports no statistically significant association of SMPD1 variants and iRBD. It is hence unlikely that SMPD1 plays a major role in iRBD.

Background Acid sphingomyelinase deficiency (ASMD), due to mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, is divided into infantile neurovisceral ASMD (Niemann-Pick type A), chronic neurovisceral ASMD (intermediate form, Niemann-Pick type A/B) and chronic visceral ASMD (Niemann-Pick type B). We conducted a long-term observational, single-center study including 16 patients with chronic visceral ASMD. Results 12 patients were diagnosed in childhood and 4 others in adulthood, the oldest at the age of 50. The mean time of follow-up was approximately 10 years (range: 6 months – 36 years). Splenomegaly was noted in all patients at diagnosis. Hepatomegaly was observed in 88% of patients. Moderately elevated (several-fold above the upper limit of normal values) serum transaminases were noted in 38% of patients. Cherry-red spots were found in five Gypsy children from one family and also in one adult Polish patient, a heterozygote for p.delR610 mutation. Dyslipidemia was noted in 50% of patients. Interstitial lung disease was diagnosed in 44% of patients. Plasmatic lysosphingomyelin (SPC) was elevated in all the patients except one with p.V36A homozygosity and a very mild phenotype also presenting with elevated plasmatic SPC-509 but normal chitotriosidase activity. The most common variant of SMPD1 gene was p.G166R. We found a previously unreported variant in exon 2 (c.491G > T, p.G164 V) in one patient. Conclusions Chronic visceral ASMD could constitute a slowly progressing disease with a relatively good outcome. The combined measurement of lysosphingomyelin (SPC) and lysospingomyelin-509 (SPC-509) is an essential method for the assessment of ASMD course.

Liver dysfunction during sepsis is an independent risk factor leading to increased mortality rates. Specifically, dysregulation of hepatic biotransformation capacity, especially of the cytochrome P450 (CYP) system, represents an important distress factor during host response. The activity of the conserved stress enzyme sphingomyelin phosphodiesterase 1 (SMPD1) has been shown to be elevated in sepsis patients, allowing for risk stratification. Therefore, the aim of the present study was to investigate whether SMPD1 activity has an impact on expression and activity of different hepatic CYP enzymes using an animal model of polymicrobial sepsis. Polymicrobial sepsis was induced in SMPD1 wild-type and heterozygous mice and hepatic ceramide content as well as CYP mRNA, protein expression and enzyme activities were assessed at two different time points, at 24 h, representing the acute phase, and at 28 days, representing the post-acute phase of host response. In the acute phase of sepsis, SMPD1+/+ mice showed an increased hepatic C16- as well as C18-ceramide content. In addition, a downregulation of CYP expression and activities was detected. In SMPD1+/&minus, mice, however, no noticeable changes of ceramide content and CYP expression and activities during sepsis could be observed. After 28 days, CYP expression and activities were normalized again in all study groups, whereas mRNA expression remained downregulated in SMPD+/+ animals. In conclusion, partial genetic inhibition of SMPD1 stabilizes hepatic ceramide content and improves hepatic monooxygenase function in the acute phase of polymicrobial sepsis. Since we were also able to show that the functional inhibitor of SMPD1, desipramine, ameliorates downregulation of CYP mRNA expression and activities in the acute phase of sepsis in wild-type mice, SMPD1 might be an interesting pharmacological target, which should be further investigated.

Background Niemann–Pick disease is caused by reduced level of the lysosomal enzyme acid sphingomyelinase. Children can survive between 2 and 12 years based on the disease type. Two main types are well known: type A and B. Niemann–Pick disease type A is characterized by severe central nervous system deterioration and hepatosplenomegaly while type B is a progressive hypersplenism accompanied with gradual deterioration of pulmonary function. Case presentation We describe an 11-month-old Palestinian baby boy with hepatosplenomegaly, hypotonia, delayed motor development, laryngomalacia, bilateral cherry-red spots, and failure to thrive. Metabolic screening, blood count, differential tests, immunology screen, infectious disease screen, urine, biochemical tests as well as molecular diagnosis were performed. The molecular diagnosis was done by amplifying the whole sphingomyelin phosphodiesterase 1 (SMPD1) gene, followed by deep sequencing. The obtained sequences were aligned, de novo assembled and compared to human reference gene (GenBank GeneID: NG_011780.1, Ensembl version ENSG00000166311 and protein identified as UniProtKB – P17405). Two known mutations were identified in our patient: the pathogenic frameshift mutation NM_000543.4(SMPD1):c.573delT (p.Ser192Alafs) and the benign polymorphism NM_000543.4(SMPD1):c.107T>C (p.Val36Ala). The enzyme study showed a very low level of enzymatic activity of acidic sphingomyelinase (0.1 nmol/ml per hour). Correlations between clinical findings, laboratory data, and sequence analysis are presented. Conclusions In conclusion, this is the first report about a heterozygote frameshift p.Ser192AlafsX65 in a Palestinian patient with Niemann–Pick disease type A, emphasizing the importance of deep sequencing in genetic diagnosis of this rare inherited disease.

Types A and B Niemann-Pick disease (NPD) are autosomal-recessive lysosomal storage disorders caused by the deficient activity of acid sphingomyelinase due to mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene.In order to determine the prevalence and distribution of SMPD1 gene mutations, the genomic DNA of 15 unrelated Iranian patients with types A and B NPD was examined using PCR, DNA sequencing and bioinformatics analysis.Of 8 patients with the p.G508R mutation, 5 patients were homozygous, while the other 3 were heterozygous. One patient was heterozygous for both the p.N385K and p.G508R mutations. Another patient was heterozygous for both the p.A487V and p.G508R mutations. Two patients (one homozygous and one heterozygous) showed the p.V36A mutation. One patient was homozygous for the c.1033-1034insT mutation. One patient was homozygous for the c.573delT mutation, and 1 patient was homozygous for the c.1417-1418delCT mutation. Additionally, bioinformatics analysis indicated that two new p.V36A and p.N385K mutations decreased the acid sphingomyelinase (ASM) protein stability, which might be evidence to suggest the pathogenicity of these mutations.with detection of these new mutations, the genotypic spectrum of types A and B NPD is extended, facilitating the definition of disease-related mutations. However, more research is essential to confirm the pathogenic effect of these mutations.

Background: Types A and B Niemann-Pick disease (NPD) are autosomal-recessive lysosomal storage disorders caused by the deficient activity of acid sphingomyelinase due to mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene. Methods: In order to determine the prevalence and distribution of SMPD1 gene mutations, the genomic DNA of 15 unrelated Iranian patients with types A and B NPD was examined using PCR, DNA sequencing and bioinformatics analysis. Results: Of 8 patients with the p.G508R mutation, 5 patients were homozygous, while the other 3 were heterozygous. One patient was heterozygous for both the p.N385K and p.G508R mutations. Another patient was heterozygous for both the p.A487V and p.G508R mutations. Two patients (one homozygous and one heterozygous) showed the p.V36A mutation. One patient was homozygous for the c.1033–1034insT mutation. One patient was homozygous for the c.573delT mutation, and 1 patient was homozygous for the c.1417–1418delCT mutation. Additionally, bioinformatics analysis indicated that two new p.V36A and p.N385K mutations decreased the acid sphingomyelinase (ASM) protein stability, which might be evidence to suggest the pathogenicity of these mutations. Conclusion: with detection of these new mutations, the genotypic spectrum of types A and B NPD is extended, facilitating the definition of disease-related mutations. However, more research is essential to confirm the pathogenic effect of these mutations.

Parkinson's disease is a common progressive neurodegenerative disorder characterized by predominant degeneration of the dopaminergic neurons in the substantia nigra pars compacta and the presence of intracellular inclusions enriched in α-synuclein, resulting in a variety motor and nonmotor symptoms. Lysosomal storage disorders are a group of disorders including Gaucher disease, Niemann-Pick disease, and neuronal ceroid lipofuscinoses caused by the defective activity of lysosomal and nonlysosomal proteins. In addition to an overlap in some clinical features between lysosomal storage disorders and Parkinson's disease, the two disorders may be also linked pathogenically. There is growing support for the notion that mutations in genes causing lysosomal storage disorders including the glucocerebrosidase gene, the sphingomyelin phosphodiesterase 1 gene, and the NPC1 gene may increase risk for developing Parkinson's disease. In this review, we discuss the recent advances in the genetic convergence of Parkinson's disease and lysosomal storage disorders, shedding new light on the understanding of shared pathogenic pathways.

Acid sphingomyelinase (ASMase)-deficient Niemann-Pick disease (NPD) is caused by mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, resulting in accumulation of sphingomyelin in the lysosomes and secondary changes in cholesterol metabolism. We hypothesized that the oxidation product of cholesterol, 7-ketocholesterol (7-KC), might increase in the plasma of patients with ASMase-deficient NPD. In this study, a rapid and nonderivatized method of measurement of plasma 7-KC by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. Plasma samples from healthy subjects, patients with ASMase-deficient NPD, nonaffected ASMase-deficient NPD heterozygotes, Niemann-Pick type C (NPC) disease, glycogen storage disorder type II (GSDII), Gaucher disease (GD), mucopolysaccharidosis type II (MPSII), Krabbe disease (KD), and metachromatic leukodystrophy (MLD) were tested retrospectively. Markedly elevated 7-KC was found in patients with ASMase-deficient NPD and NPC disease that showed significant differences from ASMase-deficient NPD heterozygotes; patients with GSDII, GD, MPSII, KD, and MLD; and normal controls. The analysis of plasma 7-KC by LC-MS/MS offers the first simple, quantitative, and highly sensitive method for detection of ASMase-deficient NPD and could be useful in the diagnosis of both ASMase-deficient NPD and NPC disease.

The radioprotective effect of amitriptyline, an inhibitor of acid sphingomyelinase (ASMase), on radiation-induced impairment of hippocampal neurogenesis, loss of interneuron, and animal weight changes was investigated in BALB/c mice by immunostaining of biomarkers for cell division (Ki67), immature neurons (doublecortin or DCX), and interneurons (parvalbumin or PV) in the dentate gyrus (DG) of hippocampus. The results indicated that preirradiation (with 10 mg/kg, 2 times per day, for 7 consecutive days) or postirradiation (with 10 mg/kg, 2 times per day, for 14 consecutive days) treatment (pretreatment or posttreatment) with intraperitoneal injection of amitriptyline prevented the loss of newly generated neurons, proliferating cells, and interneurons in the subgranular zone of the DG. At the molecular level, pretreatment or posttreatment inhibited the expression of sphingomyelin phosphodiesterase 1 ( SMPD1) gene which codes for ASMase. The pretreatment for 7 days also prevented radiation-induced weight loss from 2 to 3 weeks, but not within 1 week after irradiation. On the other hand, the posttreatment with amitriptyline for 14 days could improve animal weight gain from 4 to 6 weeks after irradiation. The present study suggests that amitriptyline may be a promising candidate radio-neuroprotective drug to improve radiation-induced impairment of hippocampal neurogenesis and relevant neurological and neuropsychological disorders.

Introduction A founder mutation, p.L302P, in sphingomyelin phosphodiesterase 1, acid lysosomal ( SMPD1 ), causing Niemann-Pick disease, a recessive lysosomal storage disorder, was reported to be associated with increased risk of Parkinson's disease (PD) in Ashkenazi Jewish population. Several other studies about the association between SMPD1 variants and PD were performed afterward in other populations. However, the results on the role of SMPD1 mutations for PD have been conflicting. This study aimed to investigate the role of mutations in SMPD1 in Chinese PD patients. Methods We sequenced all the exons of this gene in 512 Chinese Han cases with sporadic Parkinson's disease and 495 matched healthy control subjects. Results We identified Leu-Ala (Val) repeat variants and six known single nucleotide variants (p.A36V, p.D212D, p.P332R, p.G508R, p.P533L, p.T544T) in SMPD1 in both patients and normal controls. Case-control analysis showed the association between Leu-Ala (Val) repeat variants in SMPD1 and Chinese Han patients with PD (χ 2 = 8.771, p = 0.012), and the allele with less than seven LeuAla (Val) repeats may increase the risk of PD ( p = 0.010). Conclusion We identified association between Leu-Ala (Val) repeat variants in SMPD1 and Chinese Han patients with sporadic Parkinson's disease. Our results provide further support for the role of lysosomal pathways in PD development.

Epithelial ovarian cancer (EOC) is a disease responsible for more deaths among women in the Western world than all other gynecologic malignancies. There is urgent need for new therapeutic targets and a better understanding of EOC initiation and progression. We have previously identified the polypeptide N-acetylgalactosaminyltransferase 3 ( GALNT3 ) gene, a member of the GalNAc-transferases (GalNAc-Ts) gene family, as hypomethylated and overexpressed in high-grade serous EOC tumors, compared to low malignant potential EOC tumors and normal ovarian tissues. This data also suggested for a role of GALNT3 in aberrant EOC glycosylation, possibly implicated in disease progression. To evaluate differential glycosylation in EOC caused by modulations in GALNT3 expression, we used a metabolic labeling strategy for enrichment and mass spectrometry-based characterization of glycoproteins following GALNT3 gene knockdown (KD) in A2780s EOC cells. A total of 589 differentially expressed glycoproteins were identified upon GALNT3 KD. Most identified proteins were involved in mechanisms of cellular metabolic functions, post-translational modifications, and some have been reported to be implicated in EOC etiology. The GALNT3 -dependent glycoproteins identified by this metabolic labeling approach support the oncogenic role of GALNT3 in EOC dissemination and may be pursued as novel EOC biomarkers and/or therapeutic targets. Biological significance Knowledge of the O-glycoproteome has been relatively elusive, and the functions of the individual polypeptide GalNAc-Ts have been poorly characterized. Alterations in GalNAc-Ts expression were shown to provide huge variability in the O-glycoproteome in various pathologies, including cancer. The application of a chemical biology approach for the metabolic labeling and subsequent characterization of O-glycoproteins in EOC using the Ac 4 GalNAz metabolite has provided a strategy allowing for proteomic discovery of GalNAc-Ts specific functions. Our study supports an essential role of one of the GalNAc-Ts — GALNT3, in EOC dissemination, including its implication in modulating PTMs and EOC metabolism. Our approach validates the use of the applied metabolic strategy to identify important functions of GalNAc-Ts in normal and pathological conditions.

Types A and B Niemann-Pick disease (NPD) result from the deficient activity of acid sphingomyelinase (ASM), due to mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene. Here we report the identification, characterization and genotype/phenotype correlations of eight novel mutations in six unrelated NPD patients. These mutations included seven missense mutations: c.631T > C (p.W211R), c.757G > C (p.D253H), c.940G > A (p.V314M), c.1280A > G (p.H427R), c.1564A > G (p.N522S), c.1575G > C (p.Q525H) and c.1729A > G (p.H577R), and a novel frameshift mutation, c.1657delACCGCCT (fsT553). Each missense mutation was expressed in 293T or COS-7 cells; mutant enzymes p.W211R, p.D253H, p.H427R and p.H577R had G mutation obliterated a known N-glycosylation site and its p.N522S mutant enzyme had ~10% of expressed wild-type activity. Western blot analysis revealed that each mutant protein was expressed at near wild-type amounts, despite their differences in residual activity. The novel seven-base deletion occurred at codon 553, leading to a premature truncation after residue 609. The expression studies predicted the clinical phenotypes of the six patients: two type A patients had genotypes with only type A alleles [c.631T > C (p.W211R), c.757G > C (p.D253H) and c.1729A > G (p.H577R)], and the other four type B disease patients had at least one neuroprotective mutant type B allele [c.940G > A (p.V314M), c.1280A > G (p.H427R), c.1564A > G (p.N522S) and c.1575G > C (p.Q525H)] that expressed >5% residual ASM activity. Thus, these new mutations provide novel genotype/phenotype correlations and further document the genetic heterogeneity in types A and B NPD.

Udgivelsesdato: 2010-Jan-28 Heat shock protein 70 (Hsp70) is an evolutionarily highly conserved molecular chaperone that promotes the survival of stressed cells by inhibiting lysosomal membrane permeabilization, a hallmark of stress-induced cell death. Clues to its molecular mechanism of action may lay in the recently reported stress- and cancer-associated translocation of a small portion of Hsp70 to the lysosomal compartment. Here we show that Hsp70 stabilizes lysosomes by binding to an endolysosomal anionic phospholipid bis(monoacylglycero)phosphate (BMP), an essential co-factor for lysosomal sphingomyelin metabolism. In acidic environments Hsp70 binds with high affinity and specificity to BMP, thereby facilitating the BMP binding and activity of acid sphingomyelinase (ASM). The inhibition of the Hsp70-BMP interaction by BMP antibodies or a point mutation in Hsp70 (Trp90Phe), as well as the pharmacological and genetic inhibition of ASM, effectively revert the Hsp70-mediated stabilization of lysosomes. Notably, the reduced ASM activity in cells from patients with Niemann-Pick disease (NPD) A and B-severe lysosomal storage disorders caused by mutations in the sphingomyelin phosphodiesterase 1 gene (SMPD1) encoding for ASM-is also associated with a marked decrease in lysosomal stability, and this phenotype can be effectively corrected by treatment with recombinant Hsp70. Taken together, these data open exciting possibilities for the development of new treatments for lysosomal storage disorders and cancer with compounds that enter the lysosomal lumen by the endocytic delivery pathway.

Aim: Sphingomyelin phosphodiesterase 1 (SMPD1) plays an essential role in initiating the female germ cell death signal. To evaluate whether RNA interference has potential as a new approach in germ cell protection, we tested the effect of SMPD1 knockdown on human granulosa cells in vitro. Methods: We designed and synthesized three small interference RNA (siRNA) sequences targeted on SMPD1 and transfected them into human luteinizing granulosa cells (hGC) in vitro. Forty-eight hours after transfecting with siRNAs, hGC were treated with mitomycin C (MMC) to induce apoptosis. mRNA was detected with quantitative RT-PCR and protein was detected with Western blot. Methyl thiazolyl tetrazolium (MTT) assay was used to measure cell survival rate and detection of apoptotic rate of cells with Annexin V-PI staining by flow cytometer (FCM). Study groups were compared with liposome (lipofectamine 2000), MMC control and negative control siRNA. Results: After treatment with siRNA targeted to SMPD1, significant SMPD1 suppression occurred. After knockdown expression of SMPD1, the survival rate of hGC increased from 32.3% to 40.3%, and the apoptosis rate decreased from 68.3% to 44%. Conclusion: siRNA targeted on SMPD1 can protect hGC cells from apoptosis. These results reveal SMPD1 as a significant and effective target site for RNAi in the protection of human germ cells, which may have a direct bearing on future therapeutic research.

During early gestation in invasively implanting species, the uterine stromal compartment undergoes dramatic remodeling, defined by the differentiation of stromal fibroblast cells into decidual cells. Lipid signaling molecules from a number of pathways are well-established functional components of this decidualization reaction. Because of a correlation in the events that transpire in the uterus during early implantation with known functions of bioactive sphingolipid metabolites established from studies in other organ systems, we hypothesized that uterine sphingolipid metabolism would change during implantation. By a combination of Northern blot, Western blot, and immunohistochemical analyses, we establish that enzymes at each of the major catalytic steps in the sphingolipid cascade become transcriptionally up-regulated in the uterus during decidualization. Each of the enzymes analyzed was up-regulated from Days of Pregnancy (DOP) 4.5-7.5. When comparing embryo-induced decidualization (decidual) with mechanically induced decidualization (deciduomal), sphingomyelin phosphodiesterase 1 (Smpd1) mRNA and sphingosine kinase 1 (SPHK1) protein were shown to be dually regulated in the endometrium by both maternal and embryonic factors. As measured by the diacyl glycerol kinase assay, ceramide levels rose in parallel with Smpd1 gene expression, suggesting that elevated transcription of sphingolipid enzymes results in heightened catalytic activity of the pathway. Altogether, these findings place sphingolipids on a growing list of lipid signaling molecules that become increasingly present at the maternal-embryonic interface.

The aim of this study was to evaluate whether the presence of aberrantly expressed lncRNAs could promote T cell inflammatory responses in patients with RA. The expression levels of 10 potential aberrantly expressed lncRNAs were evaluated in T cells from 39 patients with RA and 17 controls using real-time reverse transcription polymerase chain reaction. The aberrantly expressed lncRNAs were measured in Jurkat cells co-cultured with or without ionomycin and phorbol 12-myristate 13-acetate. Transfection studies using small interfering RNA (siRNA) were conducted for biological functions, and microarray analysis was performed to search for target genes of specific lncRNAs. We confirmed that the expression levels of LOC100652951 and LOC100506036 were higher in RA T cells compared with controls. RA patients treated with biologic agents had lower expression levels of LOC100652951, and female RA patients had lower LOC100506036 expression levels after multivariate analysis. After activation, the expression levels of LOC100506036, but not LOC100652951, increased in Jurkat cells. Transfection of siRNA targeting LOC100506036 inhibited interferon gamma production and the expression of nuclear factor of activated T cells in activated Jurkat cells. After the microarray analysis with validation, inhibition of LOC100506036 expression by siRNA leaded to the decreased expression of sphingomyelin phosphodiesterase 1 (SMPD1). In conclusion, the expression levels of LOC100652951 and LOC100506036 were increased in RA T cells. Treatment with biologic agents could lower the expression of LOC100652951 in RA T cells. LOC100506036 could regulate the expression of SMPD1 and NFAT1 and could contribute to the inflammatory responses in RA.

Mutations in the acid sphingomyelinase (aSMase) coding gene sphingomyelin phosphodiesterase 1 (SMPD1) cause Niemann-Pick disease (NPD) type A and B. Sphingomyelin storage in cells of the mononuclear phagocyte system cause hepatosplenomegaly and severe neurodegeneration in the brain of NPD patients. However, the effects of aSMase deficiency on retinal structure and microglial behavior have not been addressed in detail yet. Here, we demonstrate that retinas of aSMase(-/-) mice did not display overt neuronal degeneration but showed significantly reduced scotopic and photopic responses in electroretinography. In vivo fundus imaging of aSMase(-/-) mice showed many hyperreflective spots and staining for the retinal microglia marker Iba1 revealed massive proliferation of retinal microglia that had significantly enlarged somata. Nile red staining detected prominent phospholipid inclusions in microglia and lipid analysis showed significantly increased sphingomyelin levels in retinas of aSMase(-/-) mice. In conclusion, the aSMase-deficient mouse is the first example in which microglial lipid inclusions are directly related to a loss of retinal function.

Niemann-Pick disease (NPD), an autosomal recessive disorder resulting from mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, is subdivided into the acute, lethal neuronopathic type A, and the chronic visceral type B, explained by the different residual activity levels of acid sphingomyelinase (ASMase). An increasing number of reports on intermediate forms, challenging this traditional clinical classification, have described a broad range of neurological manifestations; however genotype-phenotype correlations have been compromised by relatively small sample sizes and/or allelic heterogeneity. Here we present a genetically homogeneous group of 20 Gypsy patients with intermediate NPD, where we observed a surprising diversity of neurological features. All affected subjects were homozygous for the same ancestral mutation, W391G in SMPD1, yet displayed the entire spectrum of phenotypic variation observed previously in unrelated affected subjects of diverse ethnicity and disease-causing mutations, ranging from subclinical retinal involvement to severe ataxia, cognitive deficits and psychiatric disorders. The clinical heterogeneity of W391G homozygotes points to additional factors, beyond SMPD1 and residual ASMase, which determine the localization, extent and severity of neural involvement. The phenotype similarity of affected relatives suggests a possible role of genetic modifying factors. In practical terms, W391 is common in the Gypsy population and the diagnosis of NPD should be borne in mind despite the atypical course of the disease. Generally, our findings indicate that mutation analysis is of limited value in predicting brain damage, and the option of enzyme replacement therapy should be considered in intermediate NPD.

We have collected demographic and/or mutation information on a worldwide sample of 394 patients with type B Niemann-Pick disease (NPD). The disorder is panethnic, with the highest incidence occurring in individuals of Turkish, Arabic, and North African descent. Only five of the 394 patients were Ashkenazi Jewish, revealing that, unlike the type A form of NPD, type B NPD does not occur frequently within this population. Mutation analysis of the acid sphingomyelinase (ASM) gene (designated "SMPD1") was performed on 228 patients (324 unique alleles), and several novel, "common" mutations were found. Among these were the L137P, fsP189, and L549P mutations, which accounted for approximately 75% of the alleles in Turkish patients, the H421Y and K576N mutations, which accounted for approximately 85% of the alleles in Saudi Arabian patients, the S379P, R441X, R474W, and F480L mutations, which accounted for approximately 55% of the alleles in Portuguese/Brazilian patients, and the A196P mutation, which accounted for approximately 42% of the alleles in Scottish/English patients. The previously reported DeltaR608 mutation occurred on approximately 12% of the alleles studied. Overall, a total of 45 novel mutations were found, and several new genotype/phenotype correlations were identified. In particular, the L137P, A196P, and R474W mutations were consistent with a less severe form of type B NPD, whereas the H421Y and K576N mutations led to an early-onset, more severe form that was specific to Saudi Arabia. These data provide the first extensive demographic assessment of this disorder and describe several new mutations that can be used to predict phenotypic outcome and to gain new insights into the structure and function of ASM.

Niemann–Pick disease type B (NPDB) is a rare, inherited lysosomal storage disorder that occurs due to variants in the sphingomyelin phosphodiesterase 1 (SMPD1) gene and the resultant deficiency of acid sphingomyelinase (ASM) activity. While numerous variants causing NPDB have been described, only a small number have been studied in any detail. Herein, we describe the frequency of the p.(Ala359Asp) variant in the healthy Chilean population, and determine the haplotype background of homozygous patients to establish if this variant originated from a common founder. Genomic DNA samples from 1691 healthy individuals were analyzed for the p.(Ala359Asp) variant. The frequency of p.(Ala359Asp) was found to be 1/105.7, predicting a disease incidence of 1/44 960 in Chile, higher than the incidence estimated by the number of confirmed NPDB cases. We also describe the clinical characteristics of 13 patients homozygous for p.(Ala359Asp) and all of them had moderate to severe NPDB disease. In addition, a conserved haplotype and shared 280 Kb region around the SMPD1 gene was observed in the patients analyzed, indicating that the variant originated from a common ancestor. The haplotype frequency and mitochondrial DNA analysis suggest an Amerindian origin for the variant. To assess the effect of the p.(Ala359Asp) variant, we transfected cells with the ASM-p.(Ala359Asp) cDNA and the activity was only 4.2% compared with the wild-type cDNA, definitively demonstrating the causative effect of the variant on ASM function. Information on common variants such as p.(Ala359Asp) is essential to guide the successful implementation for future therapies and benefit to patients.

WOS: 000323396500060, PubMed ID: 23618813, Niemann-Pick disease (NPD) is a lysosomal storage disorder that results from the deficiency of a lysosomal enzyme, acid sphingomyelinase. Niemann-Pick disease type A and B is caused by mutations in the sphingomyelin phosphodiesterase gene (SMPD1) coding for ASM. The aim of this study was to evaluate the spectrum of SMPD1 gene mutations in Turkish NPD patients and to study genotype-phenotype associations. We present a molecular analysis of 10 Turkish NPD type A/B patients. Four of the patients had type A and six had type B NPD. All mutant SMPD1 alleles were identified, including 5 different mutations, 1 of which was novel. These mutations included three missense mutations: c.409T>C (p.L137P), c.1262 A>G (p.H421R) and c.1552T>C (p.L549P), a common frameshift mutation in codon 189, identified in three patients, is caused by the deletion of the 567T, introducing a stop codon 65 amino acids downstream (p.P189fsX65), and a novel frameshift mutation c.1755delC (p.P585PfsX24) which was not reported previously. (C) 2013 Published by Elsevier B.V.

Plasma secretion of acid sphingomyelinase is a hallmark of cellular stress response resulting in the formation of membrane embedded ceramide-enriched lipid rafts and the reorganization of receptor complexes. Consistently, decompartmentalization of ceramide formation from inert sphingomyelin has been associated with signaling events and regulation of the cellular phenotype. Herein, we addressed the question of whether the secretion of acid sphingomyelinase is involved in host response during sepsis. We found an exaggerated clinical course in mice genetically deficient in acid sphingomyelinase characterized by an increased bacterial burden, an increased phagocytotic activity, and a more pronounced cytokine storm. Moreover, on a functional level, leukocyte-endothelial interaction was found diminished in sphingomyelinase-deficient animals corresponding to a distinct leukocytes' phenotype with respect to rolling and sticking as well as expression of cellular surface proteins.(jlr) We conclude that hydrolysis of membrane-embedded sphingomyelin, triggered by circulating sphingomyelinase, plays a pivotal role in the first line of defense against invading microorganisms. This function might be essential during the early phase of infection leading to an adaptive response of remote cells and tissues.-Jbeily, N., I. Suckert, F. A. Gonnert, B. Acht, C. L. Bockmeyer, S. D. Grossmann, M. F. Blaess, A. Lueth, H.-P. Deigner, M. Bauer, and R. A. Claus. Hyperresponsiveness of mice deficient in plasma-secreted sphingomyelinase reveals its pivotal role in early phase of host response. J. Lipid Res. 2013. 54: 410-424.

Rare loss-of-function mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene are known to dramatically decrease the catalytic activity of acid sphingomyelinase (ASM), resulting in an autosomal recessive lysosomal storage disorder known as Niemann-Pick disease (NPD) type A and B. In contrast to the general low frequency of those deleterious mutations, we found a relatively high frequency for the proposed type B NPD variant c.1460C>T (p.A487V) in our sample of 58 patients suffering from Major Depressive Disorder. We therefore investigated the biochemical consequences of this variant more closely. Our in vivo data derived from blood cell analyses indicated cellular ASM activity levels in the normal range. The secreted ASM activity levels in blood plasma were slightly lower, but still above those levels reported for type B NPD patients. In vitro expression studies of this ASM variant in different cell lines confirmed these results, showing cellular and secreted enzymatic activities equivalent to those of wild-type ASM and similar expression levels. Thus, we conclude that the ASM variant c.1460C>T (p.A487V) is not a rare missense mutation but an SMPD1 sequence variant that yields a protein with functional catalytic characteristics.

Niemann–Pick disease (NPD) types A and B are autosomal recessive disorders caused by acid sphingomyelinase (ASM) deficiency due to mutation in the sphingomyelin phosphodiesterase 1 gene (SMPD1). Although a number of SMPD1 mutations were reported, expression studies were performed for only a small number of missense mutations. We evaluated three unrelated patients with clinical manifestations of NPD. Sequence analysis revealed two previously described (S248R and W391G) and two novel (G247D and F572L) missense mutations. To analyze the effects of the novel mutations on ASM function, cDNA was generated by site-directed mutagenesis and expressed in COS-7 cells. In vitro biochemical assays revealed marked deficiency of ASM activity consistent with the disease phenotype in cells homoallelic for each mutation. We show that each mutation dramatically reduced half-life and catalytic activity of ASM with more pronounced decrease by the G247D mutation. These data suggest that impaired protein stability and decreased enzyme activity are responsible for the disease in sphingomyelinase-deficient patients carrying the G247D and F572L mutations.

Tumor necrosis factor-α (TNF-α) is known as a highly pleiotropic cytokine. Stimulation of TNF-receptor 1 (TNF-R1) by TNF-α elicits the transduction of intracellular signals that on the one side promote cell death by apoptosis. However, TNF-R1 may also transduce non-apoptotic signals that lead to inflammatory responses through the activation of the transcription factor nuclear factor-κB (NF-κB) or to cell proliferation through activation of the mitogen-activated protein kinase (MAPK) cascade. A clue to the understanding of these contradictory biological phenomena may arise from recent findings which reveal a regulatory role of receptor endocytosis and intracellular receptor trafficking in selective transmission of signals, which either promote apoptosis or rather cell survival. Although internalization of cell surface receptors has traditionally been regarded as a means to shut down signaling via receptor degradation, there is now good evidence for an active role of many internalized surface receptors in the continuation of signal transmission along the endocytic pathway. Thus endocytosis may control the quality, intensity, duration, and spatial distribution of signaling events. TNF-induced apoptotic signals lead to an enhanced generation of ceramide by the enzyme sphingomyelin phosphodiesterase 1 (SMPD1, also known as acid sphingomyelinase [A-SMase]). Since TNF-triggered activation of A-SMase is linked to the death domain of TNF-receptor 1 (TNF-R1) and since the death domain adapter proteins FADD and caspase-8 are recruited during internalization of TNF-R1 to endosomes (TNF-receptosomes), we examined the possibility that A-SMase could be activated by caspase-8 within this compartment. Since we observed TNF-induced proteolytic processing and activation of pro-A-SMase that depended on the presence of caspase-8, we propose that activation of A-SMase within TNF-receptosomes requires activation of caspase-8 and probably further downstream proteases. Thus the fusion of internalized TNF-receptosomes with trans-Golgi vesicles containing the proform of A-SMase should be recognized as a novel mechanism to transduce death signals along the endocytic route.

Niemann–Pick diseases are a group of rare autosomal recessive disorders caused by an inherited deficiency of lysosomal storage with similar clinical presentations. At least three different Niemann–Pick (NP) diseases have been described, with NPA and NPB occurring as a result of a deficiency of the acid sphingomyelinase (ASM) enzyme, while NPC as a disorder that cause misregulation in cholesterol and lipids turnover, causing their accumulation in various tissues, including brain. The resulting phenotypic spectrum ranges from a severe infantile type with neurologic degeneration and death, usually by 3 years of age (NPA), to a non-neurologic adult onset form compatible with survival into adulthood (NPB) and a neurovisceral disorder with symptoms that occur at different times and progress independently (NPC). Here, we report on an Italian child born from non-consanguineous healthy parents, with a negative family history, who developed infantile spasms at the age of 5 months and clinical signs of potential storage disease. The genetic screening, performed by means of whole exome sequencing, revealed compound heterozygous mutations in the Sphingomyelin Phosphodiesterase 1 gene ( SMPD1 ), comprising both a homozygous polymorphism (p.V36A) in exon 1 and a new frameshift heterozygous deletion (c.1187delT) in exon 3 generating a premature stop (TAA) at codon 424 (p.L395fsX29). This result appears to corroborate the phenotypic heterogeneity of the symptoms and suggests a correlation between the presence of a truncated SMPD1 polypeptide and the very early onset of the disease. Focal points • Benchside : The comprehension of genotype–phenotype correlations in patients affected by Niemann–Pick disease will accelerate the accuracy of the diagnosis and permit to ameliorate patient follow-up. • Bedside : The coexistence of a homozygous polymorphism and of a new heterozygous frameshift deletion in exon 3 of the SMPD1 gene reveals the presence of infantile spasms, not previously related to mutations in SMPD1 gene. Elucidating the mechanisms associated to this altered gene product could open novel approaches in therapy.

The human acid sphingomyelinase (ASM, EC 3.1.4.12), a lysosomal and secretory protein coded by the sphingomyelin phosphodiesterase 1 (SMPD-1) gene, catalyzes the degradation of sphingomyelin (SM) to ceramide and phosphorylcholine. We examined the structural-functional properties of its carboxyl-terminus (amino acids 462-629), which harbors approximately 1/3 of all mutations discovered in the SMPD-1 gene. We created four naturally occurring mutants (DeltaR608, R496L, G577A, and Y537H) and five serial carboxyl-terminal deletion mutants (N620, N590, N570, N510, and N490). Transient transfection of the His/V5-tagged wild-type and mutant recombinant ASM in Chinese hamster ovary cells showed that all the mutants were normally expressed. Nonetheless, none of them, except the smallest deletion mutant N620 that preserved all post-translational modifications, were found capable of secretion to the medium. Furthermore, only the N620 conserved functional integrity (100% activity of the wild type); all other mutants completely lost the ability to catalyze SM hydrolysis. Importantly, cell surface biotinylation revealed that mutant DeltaR608 transfected CHO cells and fibroblasts from a compound heterozygous Niemann-Pick disease type B (NPD-B) patient (DeltaR608 and R441X) have defective translocation to the plasma membrane. Furthermore, we demonstrated that the DeltaR608 and N590 were trapped in the endoplasmic reticulum (ER) quality control checkpoint in contrast to the wild-type lysosomal localization. Interestingly, while the steady-state levels of ubiquitination were minimal for the wild-type ASM, a significant amount of Lys63-linked polyubiquitinated DeltaR608 and N590 could be purified by S5a-affinity chromatography, indicating an important misfolding in the carboxyl-terminal mutants. Altogether, we provide evidence that the carboxyl-terminus of the ASM is crucial for its protein structure, which in turns dictates the enzymatic function and secretion.

Type A and B forms of Niemann-Pick disease (NPD) are lipid storage disorders caused by deficient activity of the enzyme acid sphingomyelinase (aSMase) and the resulting accumulation of sphingomyelin in tissues. In the present study, we investigated two family members who had been diagnosed with Type B NPD and who had a severe decrease in plasma high density lipoprotein cholesterol (HDL-C). The proband (a 48-year-old male) had an HDL-C of 0.30 mmol/l (12 mg/dl) and his sister had values of 0.45 mmol/l (17 mg/dl) with severe premature coronary artery disease (CAD). Hypertriglyceridemia was found in both cases. aSMase activity measured in skin fibroblasts appeared markedly depressed. The SMPD1 gene, coding for aSMase, was sequenced in affected subjects and all family members. Compound heterozygosity (DeltaR608 and R441X) was identified in both affected patients. Carriers of the DeltaR608 mutation tended to have moderately to severe decreased HDL-C levels, whereas carriers of the R441X mutation, although present only in young subjects (

Endothelial cells represent an important component of the neurogenic niche and may regulate self-renewal and differentiation of neural progenitor cells (NPCs). Whether they have a role in determining the apoptotic fate of NPCs after stress or injury is unclear. NPCs are known to undergo p53-dependent apoptosis after ionizing radiation, whereas endothelial cell apoptosis after irradiation is dependent on membrane acid sphingomyelinase (ASMase) and is abrogated in sphingomyelin phosphodiesterase 1 (smpd1)- (gene that encodes ASMase) deficient mice. Here we found that p53-dependent apoptosis of NPCs in vivo after irradiation was inhibited in smpd1-deficient mice. NPCs cultured from mice, wild type (+/+) or knockout (−/−), of the smpd1 gene, however, demonstrated no difference in apoptosis radiosensitivity. NPCs transplanted into the hippocampus of smpd1−/− mice were protected against apoptosis after irradiation compared with those transplanted into smpd1+/+ mice. Intravenous administration of basic fibroblast growth factor, which does not cross the blood–brain barrier, known to protect endothelial cells against apoptosis after irradiation also attenuated the apoptotic response of NPCs. These findings provide evidence that endothelial cells may regulate p53-dependent apoptosis of NPCs after genotoxic stress and add support to an important role of endothelial cells in regulating apoptosis of NPCs after injury or in disease.

Niemann Pick disease (NPD) is an autosomal recessive lysosomal storage disorder caused by the deficient activity of acid sphingomyelinase due to mutations in the SMPD1 gene. We functionally characterized three novel SMPD1 mutations and 11 already reported in the Italian population. Mutant alleles were studied for enzyme activity and protein processing in transiently transfected COS-1 cells. The c.96G>A, c.100delG, c.565dupC, and c.575dupC (p.W32X, p.G34fsX42, p.P189fsX1, and p.P192fs14) alleles expressed no immunoreactive protein and consequently no enzyme activity. In contrast, cells transfected with mutants c.308T>C, c.389T>C, c.674T>C, c.732G>C, c.841G>A, c.1687G>A, c.1799G>A, and c.1799G>C (p.L103P, p.V130A, p.L225P, p.W244C, p.A281T, p.D563Y, p.R600H, p.R600P) expressed protein levels comparable to wild-type ASM expressing cells. Only three of these constructs, c.389T>C, c.1687G>A, and c.1799G>A (p.V130A, p.D563Y, p.R600H), retained residual activity while the other five expressed very low or no enzyme activity. As expected, the c.1669underscore;1670delGT (p.V557fsX18) mutant expressed a completely inactive truncated protein. Interestingly, the c.2T>G (p.M1_W32del) mutant expressed 26.9% of the wild type activity, even though no ASM protein was detected by Western blot analysis, suggesting that the amount of produced enzyme is below detection levels. The results presented in this study are consistent with the wide phenotype variability found in NP type B patients and provide valuable insights into the molecular basis of the disease. © 2005 Wiley-Liss, Inc.

Background Niemann-Pick disease type A and B is caused by a deficiency of acid sphingomyelinase due to mutations in the sphingomyelin phosphodiesterase-1 (SMPD1) gene. In Niemann-Pick patients, SMPD1 gene defects are reported to be associated with a severe reduction in plasma high-density lipoprotein (HDL) cholesterol. Methods Two common coding polymorphisms in the SMPD1 gene, the G1522A (G508R) and a hexanucleotide repeat sequence within the signal peptide region, were investigated in 118 unrelated subjects of French Canadian descent with low plasma levels of HDL-cholesterol (< 5th percentile for age and gender-matched subjects). Control subjects (n = 230) had an HDL-cholesterol level > the 25th percentile. Results For G1522A the frequency of the G and A alleles were 75.2% and 24.8% respectively in controls, compared to 78.6% and 21.4% in subjects with low HDL-cholesterol (p = 0.317). The frequency of 6 and 7 hexanucleotide repeats was 46.2% and 46.6% respectively in controls, compared to 45.6% and 49.1% in subjects with low HDL-cholesterol (p = 0.619). Ten different haplotypes were observed in cases and controls. Overall haplotype frequencies in cases and controls were not significantly different. Conclusion These results suggest that the two common coding variants at the SMPD1 gene locus are not associated with low HDL-cholesterol levels in the French Canadian population.