Effect Of Amyloid Aβ40 On The Expression Of GABA_Aα6 In Cerebellar Granulosa Cells And Its Developmental Maturation

Beta-amyloid peptide (AP) is thought to play a critical role in the pathogenesis of Alzheimer’s disease (AD). Although studies on its physiological role have been reported recently, its effects on the maturation of central neurons remain largely unexplored. Here we show that recombinant Aβ40significantly increases GABAAAα6receptor mediated outward current in rat cerebellar granule cells (CGCs). Aβ40-induced increase of GABAAα6current is mediated by increasing its protein expression at translational level rather than the transcriptional level. Exposure of CGCs to Aβ40markedly induced the phosphorylation of ERK (pERK) and mammalian target of rapamycin (pmTOR). The increase in GABAAα6current and expression of this protein was attenuated by specific inhibitors of ERK or mTOR, suggesting that ERK and mTOR signaling pathways are required for the Aβ40-induced effect on GABAAα6current and the expression of GABAAα6in CGCs. Pharmacological blockade of p75receptor but not the insulin or a7-nAChR receptor abrogated the effect of Aβ40on the expression of GABAAα6protein and current. Co-IP results suggested the interaction between p75receptor and Aβ40, which in accordance with the results that P75blocking antibody attenuated the phosphorylation of ERK1/2and mTOR.As in the cell cultures, CGCs secret amyloid peptide in the medium without any treatment, we then used APP knockout mice to confirm the role of Aβ40on the expression of GABAAa6. Without amyloid peptide in the cerebellum, these mice showed decreased level of GABAAα6in the early age (younger than P24), and micro-injection of Aβ40recovered it.Since elevated expression of the a6subunit of the GABAA receptor is generally held to be a marker of CGC maturation, we studied the effect of Aβ40on the morphological change of cerebellum which is obvious with the maturation. In the cerebellum organotypic cultures, Aβ40increased the thickness of internal granule layer of cerebellum, which is in accordance with the maturation induced-change. The internal granule cell layer of APP knockout mice’s cerebellum was thinner and obscurer than wild-type ones, which was rescued after micro-injection of Aβ40into the cerebellum of the APP knockout mice.With the result of confocal picture of GFP transfected CGCs, we found out that Aβ40could also increase the dendritic spines of CGCs. NeuroD2is a very important neuronal transcriptional factor in many kinds of neurons, including CGC. The expression of NeuroD2is in association with the development of neurons. with the results of RT-PCR, we found out the mRNA level of5DIC rather than7DIC CGCs was elevated by Aβ40.Together all these results suggest amyloid peptides play an important role in regulating development and maturation of CGC. the understanding of roles of amyloid peptides would be enhanced, and we hope that these finding would help to modifying the amyloid-peptide-targeted-treatment of AD.