Mutations in TMEM76* cause mucopolysaccharidosis IIIC (Sanfilippo C syndrome)

Mucopolysaccharidosis IIIC (MPS IIIC, or Sanfilippo C syndrome) is a lysosomal storage disorder caused by the inherited deficiency of the lysosomal membrane enzyme acetyl-coenzyme A: alpha -glucosaminide N-acetyltransferase (N-acetyltransferase), which leads to impaired degradation of heparan sulfate. We report the narrowing of the candidate region to a 2.6-cM interval between D8S1051 and D8S1831 and the identification of the transmembrane protein 76 gene (TMEM76), which encodes a 73-kDa protein with predicted multiple transmembrane domains and glycosylation sites, as the gene that causes MPS IIIC when it is mutated. Four nonsense mutations, 3 frameshift mutations due to deletions or a duplication, 6 splice-site mutations, and 14 missense mutations were identified among 30 probands with MPS IIIC. Functional expression of human TMEM76 and the mouse ortholog demonstrates that it is the gene that encodes the lysosomal N-acetyltransferase and suggests that this enzyme belongs to a new structural class of proteins that transport the activated acetyl residues across the cell membrane.     

Pentoxifylline reduces fibrin deposition and prolongs survival in neonatal hyperoxic lung injury.

Bronchopulmonary dysplasia is a leading cause of mortality and morbidity in preterm infants despite improved treatment modalities. Pentoxifylline, a phosphodiesterase inhibitor, inhibits multiple processes that lead to neonatal hyperoxic lung injury, including inflammation, coagulation, and edema. Using a preterm rat model, we investigated the effects of pentoxifylline on hyperoxia-induced lung injury and survival. Preterm rat pups were exposed to 100% oxygen and injected subcutaneously with 0.9% saline or 75 mg/kg pentoxifylline twice a day. On day 10, lung tissue was harvested for histology, fibrin deposition, and mRNA expression, and bronchoalveolar lavage fluid was collected for total protein concentration. Pentoxifylline treatment increased mean survival by 3 days (P = 0.0018) and reduced fibrin deposition by 66% (P < 0.001) in lung homogenates compared with untreated hyperoxia-exposed controls. Monocyte chemoattractant protein-1 expression in lung homogenates was decreased, but the expressions of TNF-alpha, IL-6, matrix metalloproteinase-12, tissue factor, and plasminogen activator inhibitor-1 were similar in both groups. Total protein concentration in bronchoalveolar lavage fluid was decreased by 33% (P = 0.029) in the pentoxifylline group. Pentoxifylline treatment attenuates alveolar fibrin deposition and prolongs survival in preterm rat pups with neonatal hyperoxic lung injury, probably by reducing capillary-alveolar protein leakage.     

Phospholipid transfer activities in Morris hepatomas and the specific contribution of the phosphatidylcholine exchange protein

Phospholipid transfer activities for phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine were measured in three hepatomas of increasing growth rate and degree of dedifferentiation, the hepatomas of 9633 and 7777, and compared to the activities found in normal and host liver. A 2-3-fold increase was found in the phosphatidylcholine and phosphatidylinositol transfer activities in the fast-growing 7777 hepatoma, while these activities were moderately or not increased in the 7787 and 9633 hepatomas. Phosphatidylethanolamine transfer was found to be extremely low in all three hepatomas. The possible significance of these findings with respect to the altered phospholipid content and composition of the hepatoma membranes is discussed. The contribution of the phosphatidylcholine specific exchange protein to the total phosphatidylcholine transfer activity was determined in normal and host liver and in the hepatomas 7777 and 9633 with the aid o f a phosphatidylcholine exchange protein specific antiserum. To this end a new procedure for the purification of the phosphatidylcholine exchange protein from rat liver was developed which leads to a final purification factor of 5300 and a high overall yield of 17%. In addition, this protein was chemically and immunologically characterized and its properties were compared to those of the bovine phosphatidylcholine exchange protein purified in our laboratory previously.     

Biosynthesis of phosphatidylcholine from a phosphocholine precursor pool derived from the late endosomal/lysosomal degradation of sphingomyelin

Previous studies suggest that the steps of the CDP- choline pathway of phosphatidylcholine synthesis are tightly linked in a so-called metabolon. Evidence has been presented that only choline that enters cells through the choline transporter, and not phosphocholine administered to cells by membrane permeabilization, is incorporated into phosphatidylcholine. Here, we show that [(14)C]phosphocholine derived from the lysosomal degradation of [(14)C]choline-labeled sphingomyelin is incorporated as such into phosphatidylcholine in human and mouse fibroblasts. Low density lipoprotein receptor-mediated endocytosis was used to specifically direct [(14)C]sphingomyelin to the lysosomal degradation pathway. Free labeled choline was not found either intracellularly or in the medium, not even when the cells were energy-depleted. Deficiency of lysosomal acid phosphatases in mouse or alkaline phosphatase in human fibroblasts did not affect the incorporation of lysosomal [(14)C]sphingomyelin-derived [(14)C]phosphocholine into phosphatidylcholine, supporting our finding that phosphocholine is not degraded to choline prior to its incorporation into phosphatidylcholine. Inhibition studies and analysis of molecular species showed that exogenous [(3)H]choline and sphingomyelin-derived [(14)C]phosphocholine are incorporated into phosphatidylcholine via a common pathway of synthesis. Our findings provide evidence that, in fibroblasts, phosphocholine derived from sphingomyelin is transported out of the lysosome and subsequently incorporated into phosphatidylcholine without prior hydrolysis of phosphocholine to choline. The findings do not support the existence of a phosphatidylcholine synthesis metabolon in fibroblasts.     

Distributed network actions by nicotine increase the threshold for spike-timing-dependent plasticity in prefrontal cortex

Nicotine enhances attention and working memory by activating nicotinic acetylcholine receptors (nAChRs). The prefrontal cortex (PFC) is critical for these cognitive functions and is also rich in nAChR expression. Specific cellular and synaptic mechanisms underlying nicotine's effects on cognition remain elusive. Here we show that nicotine exposure increases the threshold for synaptic spike-timing-dependent potentiation (STDP) in layer V pyramidal neurons of the mouse PFC. During coincident presynaptic and postsynaptic activity, nicotine reduces dendritic calcium signals associated with action potential propagation by enhancing GABAergic transmission. This results from a series of presynaptic actions involving different PFC interneurons and multiple nAChR subtypes. Pharmacological block of nAChRs or GABA(A) receptors prevented nicotine's actions and restored STDP, as did increasing dendritic calcium signals with stronger postsynaptic activity. Thus, by activating nAChRs distributed throughout the PFC neuronal network, nicotine affects PFC information processing and storage by increasing the amount of postsynaptic activity necessary to induce STDP.     

Inhaled nitric oxide attenuates pulmonary inflammation and fibrin deposition and prolongs survival in neonatal hyperoxic lung injury

Administration of inhaled nitric oxide (iNO) is a potential therapeutic strategy to prevent bronchopulmonary dysplasia (BPD) in premature newborns with respiratory distress syndrome. We evaluated this approach in a rat model, in which premature pups were exposed to room air, hyperoxia, or a combination of hyperoxia and NO (8.5 and 17 ppm). We investigated the anti-inflammatory effects of prolonged iNO therapy by studying survival, histopathology, fibrin deposition, and differential mRNA expression (real-time RT-PCR) of key genes involved in the development of BPD. iNO therapy prolonged median survival 1.5 days (P = 0.0003), reduced fibrin deposition in a dosage-dependent way up to 4.3-fold (P < 0.001), improved alveolar development by reducing septal thickness, and reduced the influx of leukocytes. Analysis of mRNA expression revealed an iNO-induced downregulation of genes involved in inflammation (IL-6, cytokine-induced neutrophilic chemoattractant-1, and amphiregulin), coagulation, fibrinolysis (plasminogen activator inhibitor 1 and urokinase-type plasminogen activator receptor), cell cycle regulation (p21), and an upregulation of fibroblast growth factor receptor-4 (alveolar formation). We conclude that iNO therapy improves lung pathology and prolongs survival by reducing septum thickness, inhibiting inflammation, and reducing alveolar fibrin deposition in premature rat pups with neonatal hyperoxic lung injury.     

Quantification of sulfatides and lysosulfatides in tissues and body fluids by liquid chromatography-tandem mass spectrometry

Sulfatides are found in brain as components of myelin, oligodendrocytes, and neurons but are also present in various visceral tissues. Metachromatic leukodystrophy (MLD) is an inherited lysosomal storage disorder caused by a deficiency of arylsulfatase A, leading to severe white matter disease due to the accumulation of sulfatides and lysosulfatides. To study the physiological role of sulfatides, accessible and sensitive quantitative methods are required. We developed a sensitive LC/MS/MS method to quantify total sulfatide and lysosulfatide content as well as individual molecular species in urine and plasma from MLD patients and plasma and tissues from an MLD mouse model. Our results demonstrate that the method can quantify a wide range of sulfatide concentrations and can be used to quantify total sulfatide content and levels of individual molecular species of sulfatides in tissues, cells, and body fluids. Even though plasma sulfatides and lysosulfatides would seem attractive candidate biomarkers that could possibly correlate with the severity of MLD and be of use to monitor the effects of therapeutic intervention, our results indicate that it is unlikely that the determination of these storage products in plasma will be useful in this respect.     

The frequency of lysosomal storage diseases in The Netherlands

We have calculated the relative frequency and the birth prevalence of lysosomal storage diseases (LSDs) in The Netherlands based on all 963 enzymatically confirmed cases diagnosed during the period 1970–1996. The combined birth prevalence for all LSDs is 14 per 100,000 live births. Glycogenosis type II is the most frequent LSD with a birth prevalence of 2.0 per 100,000 live births, representing 17% of all diagnosed cases. Within the group of lipidoses, metachromatic leukodystrophy (MLD) is the most frequent LSD. MLD was diagnosed in 24% of lipidoses and the calculated birth prevalence was 1.42 per 100,000 for all types combined. Krabbe disease, diagnosed in 17% of cases, also belongs to the more frequent lipid storage diseases in The Netherlands with a birth prevalence of 1.35 per 100,000. The birth prevalence of Gaucher disease, commonly regarded as the most frequent lipid storage disease is 1.16 per 100,000 for all types combined. The combined birth prevalence for all lipid storage diseases is 6.2 per 100,000 live births. Within the group of mucopolysaccharidoses (MPSs), MPS I has the highest calculated birth prevalence of 1.19 per 100,000 (25% of all cases of MPS diagnosed), which is slightly more frequent than MPS IIIA with an estimated birth prevalence of 1.16 per 100,000. As a group, MPS III comprises 47% of all MPS cases diagnosed and the combined birth prevalence is 1.89 per 100,000 live births. The birth prevalence of MPS II is 0.67 per 100,000 (1.30 per 100,000 male live births). All other MPSs are rare. The combined birth prevalence for all MPSs is 4.5 per 100,000 live births. Mucolipidoses and oligosaccharidoses are very rare with birth prevalences between 0.04 and 0.20 for individual diseases. Only 49 cases were diagnosed between 1970 and 1996. Their combined birth prevalence is 1.0 per 100,000 live births.     

Conversion of diphosphatidylglycerol to bis(monoacylglyceryl)phosphate by lysosomes

Diphosphatidyl[1',2',3'-14C]glycerol (cardiolipin) is converted to bis(monoacylglyceryl)phosphate when incubated in vitro with rat lysosomes at pH 4.4. The stereochemical configuration of the product is unknown. This reaction probably takes place via lysophosphatidylglycerol, one of the major products of diphosphatidylglycerol hydrolysis by lysosomes. Phosphatidyl[1',2',3'-14C]glycerol was introduced into mitochondrial membranes by incubating mitochondria with [U-14C]sn-glycerol-3-phosphate and cytidine diphosphate diacylglycerol. Membrane-bound phosphatidyl[1',2',3'-14C]glycerol is also converted to bis(monoacylglycerol)phosphate when incubated with lysosomes in a reaction that is dependent on the concentration of lysosomal protein and on incubation time. These results support our previous proposal (Poorthuis, B. J. H. M., and K. Y. Hostetler, 1976. J. Biol. Chem. 251: 4596-4602) that bis(monoacylglyceryl)phosphate formation may require the interaction of lysosomes with other membranes that contain the substrates for the reaction. The stereochemistry of bis(monoacylglyceryl)phosphate biosynthesis is discussed.     

Plasma globotriaosylsphingosine: Diagnostic value and relation to clinical manifestations of Fabry disease

Fabry disease is an X-linked lysosomal storage disorder due to deficiency of alpha-Galactosidase A, causing accumulation of globotriaosylceramide and elevated plasma globotriaosylsphingosine (lysoGb3). The diagnostic value and clinical relevance of plasma lysoGb3 concentration was investigated. All male and adult female patients with classical Fabry disease could be discerned by an elevated plasma lysoGb3. In young pre-symptomatic Fabry heterozygotes, lysoGb3 levels can be normal. Individuals carrying the R112H and P60L mutations, without classical Fabry symptoms, showed no elevated plasma lysoGb3. Multiple regression analysis showed that there is no correlation of plasma lysoGb3 concentration with total disease severity score in Fabry males. However, plasma lysoGb3 concentration did correlate with white matter lesions (odds ratio: 6.1 per 100 nM lysoGb3 increase (95% CI: 1.4–25.9, p = 0.015). In females, plasma lysoGb3 concentration correlated with overall disease severity. Furthermore, plasma lysoGb3 level was related to left ventricular mass (19.5 ± 5.5 g increase per 10 nM lysoGb3 increase; p = 0.001). In addition, it was assessed whether lifetime exposure to lysoGb3 correlates with disease manifestations. Male Fabry patients with a high lysoGb3 exposure (> 10,000 U), were moderately or severely affected, only one mildly. Female patients with a low exposure (< 1000 U) were asymptomatic or mildly affected. A large proportion of the females with an exposure > 1000 U showed disease complications. Plasma lysoGb3 is useful for the diagnosis of Fabry disease. LysoGb3 is an independent risk factor for development of cerebrovascular white matter lesions in male patients and left ventricular hypertrophy in females. Disease severity correlates with exposure to plasma lysoGb3.