Novel Function of Ceramide for Regulation of Mitochondrial ATP Release in Astrocytes

We reported that amyloid β peptide (Aβ42) activated neutral SMase 2 (nSMase2), thereby increasing the concentration of the sphingolipid ceramide in astrocytes. Here, we show that Aβ42 induced mitochondrial fragmentation in wild-type astrocytes, but not in nSMase2-deficient cells or astrocytes treated with fumonisin B1 (FB1), an inhibitor of ceramide synthases. Unexpectedly, ceramide depletion was concurrent with rapid movements of mitochondria, indicating an unknown function of ceramide for mitochondria. Using immunocytochemistry and super-resolution microscopy, we detected ceramide-enriched and mitochondria-associated membranes (CEMAMs) that were codistributed with microtubules. Interaction of ceramide with tubulin was confirmed by cross-linking to N-[9-(3-pent-4-ynyl-3-H-diazirine-3-yl)-nonanoyl]-D-erythro-sphingosine (pacFACer), a bifunctional ceramide analog, and binding of tubulin to ceramide-linked agarose beads. Ceramide-associated tubulin (CAT) translocated from the perinuclear region to peripheral CEMAMs and mitochondria, which was prevented in nSMase2-deficient or FB1-treated astrocytes. Proximity ligation and coimmunoprecipitation assays showed that ceramide depletion reduced association of tubulin with voltage-dependent anion channel 1 (VDAC1), an interaction known to block mitochondrial ADP/ATP transport. Ceramide-depleted astrocytes contained higher levels of ATP, suggesting that ceramide-induced CAT formation leads to VDAC1 closure, thereby reducing mitochondrial ATP release, and potentially motility and resistance to Aβ42. Our data also indicate that inhibiting ceramide generation may protect mitochondria in Alzheimer’s disease

A2B5+/GFAP+ Cells of Rat Spinal Cord Share a Similar Lipid Profile with Progenitor Cells : A Comparative Lipidomic Study

The central nervous system (CNS) harbors multiple glial fibrillary acidic protein (GFAP) expressing cell types. In addition to the most abundant cell type of the CNS, the astrocytes, various stem cells and progenitor cells also contain GFAP+ populations. Here, in order to distinguish between two types of GFAP expressing cells with or without the expression of the A2B5 antigens, we performed lipidomic analyses on A2B5+/GFAP+ and A2B5-/GFAP+ cells from rat spinal cord. First, A2B5+/GFAP- progenitors were exposed to the leukemia inhibitory factor (LIF) or bone morphogenetic protein (BMP) to induce their differentiation to A2B5+/GFAP+ cells or A2B5-/GFAP+ astrocytes, respectively. The cells were then analyzed for changes in their phospholipid, sphingolipid or acyl chain profiles by mass spectrometry and gas chromatography. Compared to A2B5+/GFAP- progenitors, A2B5-/GFAP+ astrocytes contained higher amounts of ether phospholipids (especially the species containing arachidonic acid) and sphingomyelin, which may indicate characteristics of cellular differentiation and inability for multipotency. In comparison, principal component analyses revealed that the lipid composition of A2B5+/GFAP+ cells retained many of the characteristics of A2B5+/GFAP- progenitors, but their lipid profile was different from that of A2B5-/GFAP+ astrocytes. Thus, our study demonstrated that two GFAP+ cell populations have distinct lipid profiles with the A2B5+/GFAP+ cells sharing a phospholipid profile with progenitors rather than astrocytes. The progenitor cells may require regulated low levels of lipids known to mediate signaling functions in differentiated cells, and the precursor lipid profiles may serve as one measure of the differentiation capacity of a cell population.Peer reviewe

Brain Gangliosides of a Transgenic Mouse Model of Alzheimer's Disease with Deficiency in GD3-Synthase: Expression of Elevated Levels of a Cholinergic-Specific Ganglioside, GT1aα

In order to examine the potential involvement of gangliosides in AD (Alzheimer's disease), we compared the ganglioside compositions of the brains of a double-transgenic (Tg) mouse model [APP (amyloid precursor protein)/PSEN1 (presenilin)] of AD and a triple mutant mouse model with an additional deletion of the GD3S (GD3-synthase) gene (APP/PSEN1/GD3S −/– ). These animals were chosen since it was previously reported that APP/PSEN1/GD3S −/– triple-mutant mice performed as well as WT (wild-type) control and GD3S −/– mice on a number of reference memory tasks. Cholinergic neuron-specific gangliosides, such as GT1aα and GQ1bα, were elevated in the brains of double-Tg mice (APP/PSEN1), as compared with those of WT mice. Remarkably, in the triple mutant mouse brains (APP/PSEN1/GD3S −/– ), the concentration of GT1aα was elevated and as expected there was no expression of GQ1bα. On the other hand, the level of c-series gangliosides, including GT3, was significantly reduced in the double-Tg mouse brain as compared with the WT. Thus, the disruption of the gene of a specific ganglioside-synthase, GD3S, altered the expression of cholinergic neuron-specific gangliosides. Our data thus suggest the intriguing possibility that the elevated cholinergic-specific ganglioside, GT1aα, in the triple mutant mouse brains (APP/PSEN1/GD3S −/– ) may contribute to the memory retention in these mice