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The developed multisite BBB chip is expected to be used for screening drug by more accurately predicting their permeability through BBB as well as their toxicity.

Neuroinflammation and increased production of tumor necrosis factor (TNF) in the CNS have been implicated in many neurological diseases including white matter disorders periventricular leukomalacia and multiple sclerosis. However, the exact role of TNF in these diseases and how it mediates oligodendrocyte injury remain unclear. Previously, we demonstrated that lipopolysaccharide (LPS) selectively kills oligodendrocyte precursors (preOLs) in a non-cell autonomous fashion through the induction of TNF in mixed glial cultures. Here, we report that activation of oligodendroglial, but not astroglial and microglial, TNFR1 is required for LPS toxicity, and that astrocytes promote TNF-mediated preOL death through a cell contact-dependent mechanism. Microglia were the sole source for TNF production in LPS-treated mixed glial cultures. Ablation of TNFR1 in mixed glia completely prevented LPS-induced death of preOLs. TNFR1-expressing preOLs were similarly susceptible to LPS treatment when seeded into wildtype and TNFR1 Using an in vitro model for inflammatory injury to preOLs, we demonstrated that LPS induces selective preOL death indirectly by activating microglia (Li et al. , 2008. We further identified that peroxynitrite underlies the potent direct killing capability of activated microglia and that astrocytes can shift the killing mechanism to one dependent on TNF signaling (Li et al. 2008). However, neither the cellular source for TNF production nor the TNF receptor mediating preOL death was identified. As primary glial cells all express TNF receptors (Dopp et al. 1997), they can all engage in TNF signaling. Here, we systematically dissected the cellular source for TNF production, determined the TNF receptor required for LPS toxicity, and further identified an essential role for oligodendroglial TNFR1 in TNF-mediated killing of preOLs in mixed glial cultures. Most importantly, we provided the first evidence demonstrating that astrocytes sensitize preOLs to TNF toxicity in a contact-dependent manner. Materials and methodsAnimals and reagents Wildtype B6.129SF2/J and C57BL/6J mice, transgenic eGFP mice (003291, background C57BL/6J), and TNF (background B6.129SF2/J) and TNFR1 (background C57BL/6J) knockout mice were obtained from the Jackson Laboratory (Bar Harbor, ME, USA). Recombinant TNF was obtained from R&D Systems (Minneapolis, MN, USA). Platelet-derived growth factor and basic fibroblast growth factor were from PeproTech (Rocky Hill, NJ, USA). Recombinant green fluorescent protein (GFP) adenovirus was from Gene Transfer Vector Core, University of Iowa. Rabbit polyclonal antibodies against Iba1 were purchased from Wako Chemicals (Richmond, VA, USA). Rat anti-mouse TNF (clone MP6-XT22) was obtained from eBioscience (San Diego, CA, USA). Olig2 antibody was a generous gift from Dr. Richard Lu (University of Texas Southwestern Medical Center). Lactate dehydrogenase (LDH) cytotoxicity kit was from Roche Applied Science (Indianapolis, IN, USA). Unless specified otherwise, all other reagents were from Sigma (St. Lou...

Oligodendroglial injury is a pathological hallmark of many human white matter diseases, including multiple sclerosis and periventricular leukomalacia. Critical regulatory mechanisms of oligodendroglia destruction, however, remain incompletely understood. Ceramide, a bioactive sphingolipid pivotal to sphingolipid metabolism pathways, regulates cell death in response to diverse stimuli and has been implicated in neurodegenerative disorders. We report here that ceramide accumulates in reactive astrocytes in active lesions of multiple sclerosis and periventricular leukomalacia, as well as in animal models of demyelination. Serine palmitoyltransferase, the rate-limiting enzyme for ceramide de novo biosynthesis, was consistently upregulated in reactive astrocytes in the cuprizone mouse model of demyelination. Mass spectrometry confirmed the upregulation of specific ceramides during demyelination and revealed a concomitant increase of sphingosine as well as a suppression of sphingosine-1-phosphate, a potent signaling molecule with key roles in cell survival and mitogenesis. Importantly, this altered sphingolipid metabolism during demyelination was restored upon active remyelination. In culture, ceramide acted synergistically with tumor necrosis factor leading to apoptotic death of oligodendroglia in an astrocyte-dependent manner. Taken together, our findings implicate that disturbed sphingolipid pathways in reactive astrocytes may indirectly contribute to oligodendroglial injury in cerebral white matter disorders.

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