Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by the loss-of-function of fragile X mental retardation protein (FMRP). The loss of FMRP function in neurons abolishes its suppression on mGluR1/5-dependent dendritic protein translation, enhancing mGluR1/5-dependent synaptic plasticity and other disease phenotypes in FXS. In this study, we describe a new activation function of FMRP in regulating protein expression in astroglial cells. We found that astroglial glutamate transporter subtype glutamate transporter 1 (GLT1) and glutamate uptake is significantly reduced in the cortex of fmr1(-/-) mice. Correspondingly, neuronal excitability is also enhanced in acute fmr1(-/-) (but not in fmr1(+/+) control) cortical slices treated with low doses (10 μm) of the GLT1-specific inhibitor dihydrokainate (DHK). Using mismatched astrocyte and neuron co-cultures, we demonstrate that the loss of astroglial (but not neuronal) FMRP particularly reduces neuron-dependent GLT1 expression and glutamate uptake in co-cultures. Interestingly, protein (but not mRNA) expression and the (S)-3,5-dihydroxyphenylglycine-dependent Ca(2+) responses of astroglial mGluR5 receptor are also selectively reduced in fmr1(-/-) astrocytes and brain slices, attenuating neuron-dependent GLT1 expression. Subsequent FMRP immunoprecipitation and QRT-PCR analysis showed that astroglial mGluR5 (but not GLT1) mRNA is associated with FMRP. In summary, our results provide evidence that FMRP positively regulates translational expression of mGluR5 in astroglial cells, and FMRP-dependent down-regulation of mGluR5 underlies GLT1 dysregulation in fmr1(-/-) astrocytes. The dysregulation of GLT1 and reduced glutamate uptake may potentially contribute to enhanced neuronal excitability observed in the mouse model of FXS.

In mice bearing transplantable mammary carcinomas, serum levels of sialic acid-containing glycolipids were elevated 2.5-fold in pooled serum samples from which gangliosides were purified by column chromatography. A method is also described by which ganglioside content was estimated on as little as 1.0 ml of whole blood to permit studies with individual tumor-bearing mice and age-and litter-matched controls. Using this method, we observed similar elevations in ganglioside levels that were independent of age and sex of the animal and appeared in advance of palpable tumors. Following excision of the tumors, the glycolipid sialic acid values dropped below control levels and remained there. Serum sialic acid of the glycolipid fraction was elevated nearly 2-fold in human carcinoma patients and appeared to decline after surgery. taneous implantation of tumor fragments into male or female syngeneic recipients. Age-matched controls of the same strain were injected with an equivalent amount of saline but received no tumor implant and were otherwise treated exactly as the principals. Tumor masses were examined for degree of vascularization and then were excised and weighed. Determination of Gangliosides. Groups of 25 carcinomabearing mice were exsanguinated 60 days after implantation of tumor fragments. Sera were pooled following centrifugation. Gangliosides were extracted with chloroform/methanol and further purified by chromatography on DEAE-Sephadex and Unisil silicic acid (16). Sialic acid assays (17) were on purified gangliosides. By this method recovery of [6-3H]galactose-Nacetylgalactosamine-(N-acetylneuraminic acid)-galactoseglucose-ceramide ([3H]GM1) added to samples averaged 96%.Individual mice bearing tumors were exsanguinated at 3-90 days after implantation of tumors along with litter-matched control mice as described above. The sera (0.5-1 ml) obtained following centrifugation were extracted with chloroform/ methanol (1:1 vol/vol) overnight. The extracts were filtered and the residue was extracted a second time with chloroform/ methanol (2:1) overnight. The combined extracts were concentrated and adjusted to 3 ml. To precipitate sialic acid-containing lipo-and glycoproteins (not elevated in sera of tumor bearers), 100 ,ul of a 0.1% solution of tripotassium citrate (18) was added and the resulting precipitate was removed by centrifugation. The supernatant after citrate treatment was analyzed for sialic acid (17) using values calculated by the Warren (17) formula to correct for variation due to unspecific absorbance. With this method recovery of [3H]GM1 added to serum samples averaged 92%. RESULTS Animal modelThe level of total gangliosides, determined on the basis of sialic acid, was elevated about 2.5 times above control values in sera of both male and female recipient mice carrying a transplantable mammary carcinoma of spontaneous origin (Table 1). Similar elevations were observed at 11, 21, and 35 days after transplantation; at 11 days palpable tumor masses were not detected. These increases were no...