Browsing by Subject "Acid sphingomyelinase"

Now showing 1 - 4 of 4
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    Exocytosis of acid sphingomyelinase by wounded cells promotes endocytosis and plasma membrane repair
    (Rockefeller University Press, 2010-06-07) Tam, Christina; Idone, Vincent; Devlin, Cecilia; Fernandes, Maria Cecilia; Flannery, Andrew; He, Xingxuan; Schuchman, Edward; Tabas, Ira; Andrews, Norma W.; Medicine, School of Medicine
    Rapid plasma membrane resealing is essential for cellular survival. Earlier studies showed that plasma membrane repair requires Ca2+-dependent exocytosis of lysosomes and a rapid form of endocytosis that removes membrane lesions. However, the functional relationship between lysosomal exocytosis and the rapid endocytosis that follows membrane injury is unknown. In this study, we show that the lysosomal enzyme acid sphingomyelinase (ASM) is released extracellularly when cells are wounded in the presence of Ca2+. ASM-deficient cells, including human cells from Niemann-Pick type A (NPA) patients, undergo lysosomal exocytosis after wounding but are defective in injury-dependent endocytosis and plasma membrane repair. Exogenously added recombinant human ASM restores endocytosis and resealing in ASM-depleted cells, suggesting that conversion of plasma membrane sphingomyelin to ceramide by this lysosomal enzyme promotes lesion internalization. These findings reveal a molecular mechanism for restoration of plasma membrane integrity through exocytosis of lysosomes and identify defective plasma membrane repair as a possible component of the severe pathology observed in NPA patients.
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    Functional inhibition of acid sphingomyelinase disrupts infection by intracellular bacterial pathogens
    (Life Science Alliance, 2019-03-22) Cockburn, Chelsea L.; Green, Ryan S.; Damle, Sheela R.; Martin, Rebecca K.; Ghahrai, Naomi N.; Colonne, Punsiri M.; Fullerton, Marissa S.; Conrad, Daniel H.; Chalfant, Charles E.; Voth, Daniel E.; Rucks, Elizabeth A.; Gilk, Stacey D.; Carlyon, Jason A.; Department of Microbiology and Immunology, Indiana University School of Medicine
    Intracellular bacteria that live in host cell-derived vacuoles are significant causes of human disease. Parasitism of low-density lipoprotein (LDL) cholesterol is essential for many vacuole-adapted bacteria. Acid sphingomyelinase (ASM) influences LDL cholesterol egress from the lysosome. Using functional inhibitors of ASM (FIASMAs), we show that ASM activity is key for infection cycles of vacuole-adapted bacteria that target cholesterol trafficking-Anaplasma phagocytophilum, Coxiella burnetii, Chlamydia trachomatis, and Chlamydia pneumoniae. Vacuole maturation, replication, and infectious progeny generation by A. phagocytophilum, which exclusively hijacks LDL cholesterol, are halted and C. burnetii, for which lysosomal cholesterol accumulation is bactericidal, is killed by FIASMAs. Infection cycles of Chlamydiae, which hijack LDL cholesterol and other lipid sources, are suppressed but less so than A. phagocytophilum or C. burnetii A. phagocytophilum fails to productively infect ASM-/- or FIASMA-treated mice. These findings establish the importance of ASM for infection by intracellular bacteria and identify FIASMAs as potential host-directed therapies for diseases caused by pathogens that manipulate LDL cholesterol.
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    Homeostatic role of acid sphingomyelinase in mtor signaling and autophagy
    (2017-04) Justice, Matthew Jose; Petrache, Irina; Roach, Peter J.; Dong, X. Charlie; Yin, Xiao-Ming
    Key regulatory decisions of protein synthesis and autophagy are controlled by the lysosomal nutrient sensing complex (LYNUS). To engage protein synthesis signaling, LYNUS requires cellular availability of amino acids, adenosine triphosphate (ATP), growth factors, and docking at the lysosomal membrane. The molecular determinants of LYNUS signaling and docking are not completely elucidated and may involve regulators of the lipid membrane structure and function of the lysosome. Since ceramides are both bioactive second messengers and determinants of lipid membrane stiffness, we investigated the role of the ceramide-producing lysosomal acid sphingomyelinase (ASM) in the homeostatic function of mammalian target of rapamycin (mTOR) signaling and autophagy. Using ASM inhibition with either imipramine or siRNA against SMPD1, in primary human lung cells or Smpd1+/- mice, we demonstrated that ASM is an endogenous inhibitor of autophagy. ASM was necessary for physiological mTOR signaling and maintenance of sphingosine levels. Whereas overstimulation of ASM has been shown to trigger autophagy with impaired flux, inhibition of ASM activity during homeostatic, non-stressed conditions triggered autophagy with degradative potential, associated with enhanced transcription factor EB (TFEB), a master regulator of autophagy and lysosomal biogenesis genes, translocation to the nucleus and decreased sphingosine levels. These findings suggest LYNUS signaling and autophagy are partially regulated by ASM.
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    Increase in acid sphingomyelinase level in human retinal endothelial cells and CD34+ circulating angiogenic cells isolated from diabetic individuals is associated with dysfunctional retinal vasculature and vascular repair process in diabetes
    (Elsevier, 2017-05) Kady, Nermin; Yan, Yuanqing; Salazar, Tatiana; Wang, Qi; Chakravarthy, Harshini; Huang, Chao; Beli, Eleni; Navitskaya, Svetlana; Grant, Maria; Busik, Julia; Ophthalmology, School of Medicine
    BACKGROUND: Diabetic retinopathy is a microvascular disease that results from retinal vascular degeneration and defective repair due to diabetes-induced endothelial progenitor dysfunction. OBJECTIVE: Understanding key molecular factors involved in vascular degeneration and repair is paramount for developing effective diabetic retinopathy treatment strategies. We propose that diabetes-induced activation of acid sphingomyelinase (ASM) plays essential role in retinal endothelial and CD34+ circulating angiogenic cell (CAC) dysfunction in diabetes. METHODS: Human retinal endothelial cells (HRECs) isolated from control and diabetic donor tissue and human CD34+ CACs from control and diabetic patients were used in this study. ASM messenger RNA and protein expression were assessed by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. To evaluate the effect of diabetes-induced ASM on HRECs and CD34+ CACs function, tube formation, CAC incorporation into endothelial tubes, and diurnal release of CD34+ CACs in diabetic individuals were determined. RESULTS: ASM expression level was significantly increased in HRECs isolated from diabetic compared with control donor tissue, as well as CD34+ CACs and plasma of diabetic patients. A significant decrease in tube area was observed in HRECs from diabetic donors compared with control HRECs. The tube formation deficiency was associated with increased expression of ASM in diabetic HRECs. Moreover, diabetic CD34+ CACs with high ASM showed defective incorporation into endothelial tubes. Diurnal release of CD34+ CACs was disrupted with the rhythmicity lost in diabetic patients. CONCLUSION: Collectively, these findings support that diabetes-induced ASM upregulation has a marked detrimental effect on both retinal endothelial cells and CACs.