Toxoplasma gondii infects astrocytes, neurons and microglia cells in the CNS and, after acute encephalitis, persists within neurons. Robust astrocyte activation is a hallmark of Toxoplasma encephalitis (TE); however, the in vivo function of astrocytes is largely unknown. To study their role in TE we generated C57BL/6 GFAP-Cre gp130fl/fl mice (where GFAP is glial fibrillary acid protein), which lack gp130, the signal-transducing receptor for IL-6 family cytokines, in their astrocytes. In the TE of wild-type mice, the gp130 ligands IL-6, IL-11, IL-27, LIF, oncostatin M, ciliary neurotrophic factor, B cell stimulating factor, and cardiotrophin-1 were up-regulated. In addition, GFAP+ astrocytes of gp130fl/fl control mice were activated, increased in number, and efficiently restricted inflammatory lesions and parasites, thereby contributing to survival from TE. In contrast, T. gondii- infected GFAP-Cre gp130fl/fl mice lost GFAP+ astrocytes in inflammatory lesions resulting in an inefficient containment of inflammatory lesions, impaired parasite control, and, ultimately, a lethal necrotizing TE. Production of IFN-γ and the IFN-γ-induced GTPase (IGTP), which mediate parasite control in astrocytes, was even increased in GFAP-Cre gp130fl/fl mice, indicating that instead of the direct antiparasitic effect the immunoregulatory function of GFAP-Cre gp130fl/fl astrocytes was disturbed. Correspondingly, in vitro infected GFAP-Cre gp130fl/fl astrocytes inhibited the growth of T. gondii efficiently after stimulation with IFN-γ, whereas neighboring noninfected and TNF-stimulated GFAP-Cre gp130fl/fl astrocytes became apoptotic. Collectively, these are the first experiments demonstrating a crucial function of astrocytes in CNS infection.

Pyruvate dehydrogenase reaction utilizing glucose-derived pyruvate is an almost exclusive source of acetyl-CoA in different cell mitochondrial compartments of the brain. In neuronal mitochondria, the largest fraction of acetyl-CoA is utilized for energy production and the much smaller one for N-acetyl-L-aspartate (NAA) synthesis. Cholinergic neurons, unlike others, require additional amounts of acetyl-CoA for acetylcholine synthesis. Therefore, several neurotoxic signals, which inhibit pyruvate dehydrogenase, generate deeper shortages of acetyl-CoA and greater mortality of cholinergic neurons than noncholinergic ones. NAA is considered to be a marker of neuronal energy status in neuropathic brains. However, there is no data on putative differential fractional distribution of the acetyl-CoA pool between energy producing and NAA or acetylcholine synthesizing pathways in noncholinergic and cholinergic neurons, respectively. Therefore, the aim of this study was to investigate whether zinc-excess, a common excitotoxic signal, may evoke differential effects on the NAA metabolism in neuronal cells with low and high expression of the cholinergic phenotype. Differentiated SN56 neuronal cells, displaying a high activity of choline acetyltransferase and rates of acetylcholine synthesis, contained lower levels of acetyl-CoA and NAA, being more susceptible to ZnCl2 exposition that the nondifferentiated SN56 or differentiated dopaminergic SHSY5Y neuronal and astroglial C6 cells. Differentiated SN56 accumulated greater amounts of Zn2 + from extracellular space than the other ones, and displayed a stronger suppression of pyruvate dehydrogenase complex activity and acetyl-CoA, NAA, ATP, acetylcholine levels, and loss of viability. These data indicate that the acetyl-CoA synthesizing system in neurons constitutes functional unity with energy generating and NAA or acetylcholine pathways of its utilization, which are uniformly affected by neurotoxic conditions.

Toxoplasma (T.) gondii infects astrocytes, neurons and microglia cells in the CNS and, after acute encephalitis, persists within neurons. Robust astrocyte activation is a hallmark of Toxoplasma encephalitis (TE); however, the in vivo function of astrocytes is largely unknown. To study their role in TE, we generated C57BL/6 GFAP-Cre gp130 fl/ fl mice, which lack gp130, the signal transducing receptor for IL-6 family cytokines, in their astrocytes. In TE of wildtype mice, the gp130 ligands IL-6, IL-11, IL-27, LIF, oncostatin M, ciliary neurotrophic factor, B cell stimulating factor, and cardiotrophin-1 were upregulated. In addition, GFAP + astrocytes of gp130 fl/fl control mice were activated, increased in number, and efficiently restricted inflammatory lesions and parasites, thereby, contributing to survival from TE. In contrast, T. gondii-infected GFAPCre gp130 fl/fl mice lost GFAP + astrocytes in inflammatory lesions resulting in an inefficient containment of inflammatory lesions, impaired parasite control and, ultimately, a lethal necrotizing TE. Production of IFN-gamma and IGTP, which mediate parasite control in astrocytes, were even increased in GFAP-Cre gp130 fl/fl mice indicating that instead of the direct anti-parasitic effect the immunoregulatory function of GFAP-Cre gp130 fl/fl astrocytes was disturbed. Correspondingly, in vitro infected GFAP-Cre gp130 fl/fl astrocytes inhibited growth of T. gondii efficiently after stimulation with IFN-gamma, whereas neighbouring non-infected and TNF-stimulated GFAP-Cre gp130 fl/fl astrocytes became apoptotic. Collectively, these are the first experiments demonstrating a crucial function of astrocytes in CNS infection.from Infectious diseases of the nervous system: pathogenesis and worldwide impact Paris,