Sphingomyelin is an abundant constituent of the plasma membranes of mammalian cells. Ceramide, its primary catabolic intermediate, is released by either acid sphingomyelinase or neutral sphingomyelinase (nSMase) and has emerged as a potential lipid signaling molecule. nSMase is regarded as a key enzyme in the regulated activation of the “sphingomyelin cycle” and cell signaling. We report here the cloning, identification, and functional characterization of murine and human nSMase, a ubiquitously expressed integral membrane protein, which displays all established properties of the Mg 2+ -dependent nSMase of the plasma membrane. Stably nSMase-overexpressing U937 and human embryonic kidney cell lines have been generated for the study of the role of nSMase in signal transduction pathways. Their stimulation by tumor necrosis factor α leads only to a moderately elevated ceramide concentration. Activation of Jun kinase and NFκB and poly(ADP-ribose) polymerase cleavage are identical in mock- and nSMase-transfected cells. Tumor necrosis factor α triggers the ERK1 pathway in none of the cell lines. The cloned nSMase will facilitate further controlled experiments aiming at the definition of a possible role of ceramide as signal transduction molecule.

PurposeAge-related macular degeneration (AMD) is a frequent, complex disorder in elderly of European ancestry. Risk profiles and treatment options have changed considerably over the years, which may have affected disease prevalence and outcome. We determined the prevalence of early and late AMD in Europe from 1990 to 2013 using the European Eye Epidemiology (E3) consortium, and made projections for the future.DesignMeta-analysis of prevalence data.ParticipantsA total of 42 080 individuals 40 years of age and older participating in 14 population-based cohorts from 10 countries in Europe.MethodsAMD was diagnosed based on fundus photographs using the Rotterdam Classification. Prevalence of early and late AMD was calculated using random-effects meta-analysis stratified for age, birth cohort, gender, geographic region, and time period of the study. Best-corrected visual acuity (BCVA) was compared between late AMD subtypes; geographic atrophy (GA) and choroidal neovascularization (CNV).Main Outcome MeasuresPrevalence of early and late AMD, BCVA, and number of AMD cases.ResultsPrevalence of early AMD increased from 3.5% (95% confidence interval [CI] 2.1%–5.0%) in those aged 55–59 years to 17.6% (95% CI 13.6%–21.5%) in those aged ≥85 years; for late AMD these figures were 0.1% (95% CI 0.04%–0.3%) and 9.8% (95% CI 6.3%–13.3%), respectively. We observed a decreasing prevalence of late AMD after 2006, which became most prominent after age 70. Prevalences were similar for gender across all age groups except for late AMD in the oldest age category, and a trend was found showing a higher prevalence of CNV in Northern Europe. After 2006, fewer eyes and fewer ≥80-year-old subjects with CNV were visually impaired (P = 0.016). Projections of AMD showed an almost doubling of affected persons despite a decreasing prevalence. By 2040, the number of individuals in Europe with early AMD will range between 14.9 and 21.5 million, and for late AMD between 3.9 and 4.8 million.ConclusionWe observed a decreasing prevalence of AMD and an improvement in visual acuity in CNV occuring over the past 2 decades in Europe. Healthier lifestyles and implementation of anti–vascular endothelial growth factor treatment are the most likely explanations. Nevertheless, the numbers of affected subjects will increase considerably in the next 2 decades. AMD continues to remain a significant public health problem among Europeans.

Neutral sphingomyelinases sphingomyelin phosphodiesterase (SMPD)2 and -3 hydrolyze sphingomyelin to phosphocholine and ceramide. smpd2 is expressed ubiquitously, and smpd3 is expressed predominantly in neurons of the CNS. Their activation and the functions of the released ceramides have been associated with signaling pathways in cell growth, differentiation, and apoptosis. However, these cellular responses remain poorly understood. Here we describe the generation and characterization of the smpd3 ؊/؊ and smpd2 ؊/؊ smpd3 ؊/؊ double mutant mouse, which proved to be devoid of neutral sphingomyelinase activity. SMPD3 plays a pivotal role in the control of late embryonic and postnatal development: the smpd3-null mouse develops a novel form of dwarfism and delayed puberty as part of a hypothalamus-induced combined pituitary hormone deficiency. Our studies suggest that SMPD3 is segregated into detergent-resistant subdomains of Golgi membranes of hypothalamic neurosecretory neurons, where its transient activation modifies the lipid bilayer, an essential step in the Golgi secretory pathway. The smpd3 ؊/؊ mouse might mimic a form of human combined pituitary hormone deficiency.

Genetic and epidemiologic studies have shown that lipid genes and High Density Lipoproteins (HDL) are implicated in age-related macular degeneration (AMD). We studied circulating lipid levels in relation to AMD in a large European dataset, and investigated whether this relationship is driven by certain sub fractions. Design: (Pooled) analysis of cross-sectional data. Participants: 30,953 individuals aged 50+ participating in the E3 consortium; and 1530 individuals from the Rotterdam Study with lipid sub fraction data. Methods: In E3, AMD features were graded per eye on fundus photographs using the Rotterdam Classification. Routine blood lipid measurements were available from each participant. Data on genetics, medication and confounders such as body mass index, were obtained from a common database. In a subgroup of the Rotterdam Study, lipid sub fractions were identified by the Nightingale biomarker platform. Random-intercepts mixed-effects models incorporating confounders and study site as a random-effect were used to estimate the associations. Main Outcome Measures: early, late or any AMD, phenotypic features of early AMD, lipid measurements. Results: HDL was associated with an increased risk of AMD, corrected for potential confounders (Odds Ratio (OR) 1.21 per 1mmol/L increase (95% confidence interval[CI] 1.14-1.29); while triglycerides were associated with a decreased risk (OR 0.94 per 1mmol/L increase [95%CI 0.91-0.97]). Both were associated with drusen size, higher HDL raises the odds of larger drusen while higher triglycerides decreases the odds. LDL-cholesterol only reached statistical significance in the association with early AMD (p=0.045). Regarding lipid sub fractions: the concentration of extra-large HDL particles showed the most prominent association with AMD (OR 1.24 [95%CI 1.10-1.40]). The CETP risk variant (rs17231506) for AMD was in line with increased-HDL levels (p=7.7x10-7); but LIPC risk variants (rs2043085, rs2070895) were associated in an opposite way (p=1.0x10-6 and 1.6x10-4). Conclusions: Our study suggests that HDL-cholesterol is associated with increased risk of AMD and triglycerides negatively associated. Both show the strongest association with early AMD and drusen. Extra-large HDL sub fractions seem to be drivers in the relation with AMD, variants in lipid genes play a more ambiguous role in this association. Whether systemic lipids directly influence AMD or represent lipid metabolism in the retina remains a question to be answered.

Sphingomyelinases (SMases) catalyze the hydrolysis of sphingomyelin, an essential lipid constituent of the plasma membrane, lysosomal membranes, endoplasmic reticulum, and the Golgi membrane stacks of mammalian cells. In this study, we report the biochemical and functional characterization and subcellular localization of magnesium-dependent nSMase1 from overexpressing human embryonic kidney (HEK293) cells. Site-directed mutagenesis of conserved residues probably involved in the enzymatic sphingomyelin cleavage as well as the removal of one or both putative transmembrane domains lead to the complete loss of enzymatic activity of human nSMase1 expressed in HEK293 cells. Polyclonal antibodies raised against recombinant mammalian nSMase1 immunoprecipitated and inactivated the enzyme in membrane extracts of overexpressing HEK293 cells and different murine tissues. Cell fractionation combined with immunoprecipitation studies localized the nSMase1 protein predominantly in the microsomal fraction. The enzyme colocalized with marker proteins of the endoplasmic reticulum and the Golgi apparatus in immunocytochemistry. Anti-nSMase1 antibodies did not affect the nSMase activity in the plasma membrane fraction and membrane extracts from murine brain. Our study leads to the conclusion that nSMase1 is one of at least two mammalian neutral sphingomyelinases with different subcellular localization, tissue specificity, and enzymatic properties.