Brain pathology in Niemann Pick disease type A : insights from the acid sphingomyelinase knockout mice

Severe neurological involvement characterizes Niemann Pick disease (NPD) type A, an inherited disorder caused by loss of function mutations in the gene encoding acid sphingomyelinase (ASM). Mice lacking ASM, which mimic NPD type A, have provided important insights into the aberrant brain phenotypes induced by ASM deficiency. For example, lipid alterations, including the accumulation of sphingolipids, affect the membranes of different subcellular compartments of neurons and glial cells, leading to anomalies in signalling pathways, neuronal polarization, calcium homeostasis, synaptic plasticity, myelin production or immune response. These findings contribute to our understanding of the overall role of sphingolipids and their metabolic enzymes in brain physiology, and pave the way to design and test new therapeutic strategies for type A NPD and other neurodegenerative disorders. Some of these have already been tested in mice lacking ASM with promising results

Secondary Alterations of Sphingolipid Metabolism in Lysosomal Storage Diseases

In several neurodegenerative diseases, sphingolipid metabolism is deeply deregulated, leading to the expression of abnormal membrane sphingolipid patterns and altered plasma membrane organization. In this paper, we review the potential importance of these alterations to the pathogenesis of these diseases and focus the reader's attention on some secondary alterations of sphingolipid metabolism that have been sporadically reported in the literature. Moreover, we present a detailed analysis of the lipid composition of different central nervous system and extraneural tissues from the acid sphingomyelinase-deficient mouse, the animal model for Niemann-Pick disease type A, characterized by the accumulation of sphingomyelin. Our data show an unexpected, tissue specific selection of the accumulated molecular species of sphingomyelin, and an accumulation of GM3 and GM2 gangliosides in both neural and extraneural tissues, that cannot be solely explained by the lack of acid sphingomyelinase

Lipid contents of brain, of brain membrane lipid domains and of neurons from acidic sphingomyelinase deficient mice (ASMKO)

The cholesterol, sphingolipid, and glycerophospholipid content of total brain, of detergent-resistant membranes prepared from the total brain, and of cerebellar granule cells differentiated in culture from wild type (WT) and acid sphingomyelinase knockout (ASMKO) were studied. Brains derived from 7-month-old ASMKO animals showed a fivefold higher level of sphingomyelin and a significant increase in ganglioside content, mainly because of monosialogangliosides GM3 and GM2 accumulation, while the cholesterol and glycerophospholipid content was unchanged with respect to WT animals. An increase in sphingomyelin, but not in gangliosides, was also detected in cultured cerebellar granule neurons from ASMKO mice, indicating that ganglioside accumulation is not a direct consequence of the enzyme defect. When a detergent-resistant membrane fraction was prepared from ASMKO brains, we observed that a higher detergent-to-protein ratio was needed than in WT animals. This likely reflects a reduced fluidity in restricted membrane areas because of a higher enrichment in sphingolipids in the case of ASMKO brain

Nitric oxide boosts chemoimmunotherapy via inhibition of acid sphingomyelinase in a mouse model of melanoma

Cisplatin is one of the most effective anticancer drugs, but its severe toxic effects, including depletion of immune-competent cells, limit its efficacy. We combined the systemic treatment with cisplatin with intratumor delivery of dendritic cells (DC) previously treated ex vivo with a pulse of nitric oxide (NO) released by the NO donors (z)-1-[2-(2-aminoethyl)-N-(2- ammonioethyl)amino]-diazen-1-ium-1,2-diolate or isosorbide dinitrate. We found that this chemoimmunotherapy, tested in the B16 mouse model of melanoma, was significantly more efficacious than cisplatin alone, leading to tumor regression and animal survival at low doses of cisplatin that alone had no effect. Tumor cure was not observed when combining cisplatin with DCs not exposed to NO donors, indicating the key role of the pretreatment with NO. We investigated the mechanisms responsible for the synergic effect of NO-treated DCs and cisplatin and found that NO-treated DCs were protected both in vitro and in vivo from cisplatin-induced cytotoxicity. Cisplatin triggered DC apoptosis through increased expression and activation of acid sphingomyelinase; pretreatment of DCs with NO donors prevented such activation and inhibited activation of the downstream proapoptotic events, including generation of ceramide, activation of caspases 3 and 9, and mitochondrial depolarization. The effects of NO were mediated through generation of its physiologic messenger, cyclic GMP. We conclude that NO and NO gener ating drugs represent promising tools to increase the efficacy of chemoimmunotherapies in vivo, promoting the survival and increasing the function of injected cells by targeting a key pathway in cisplatin-induced cytotoxicity