Cerebral cortical astroglia from the trisomy 16 mouse, a model for down syndrome, produce neuronal cholinergic deficits in cell culture

Abstract

Trisomy 21 (Down syndrome) is associated with a high incidence of Alzheimer disease and with deficits in cholinergic function in humans. We used the trisomy 16 (Ts16) mouse model for Down syndrome to identify the cellular basis for the cholinergic dysfunction. Cholinergic neurons and cerebral cortical astroglia, obtained separately from Ts16 mouse fetuses and their euploid littermates, were cultured in various combinations. Choline acetyltransferase activity and cholinergic neuron number were both depressed in cultures in which both neurons and glia were derived from Ts16 fetuses. Cholinergic function of normal neurons was significantly down-regulated by coculture with Ts16 glia. Conversely, neurons from Ts16 animals could express normal cholinergic function when grown with normal glia. These observations indicate that astroglia may contribute strongly to the abnormal cholinergic function in the mouse Ts16 model for Down syndrome. The Ts16 glia could lack a cholinergic supporting factor present in normal glia or contain a factor that down-regulates cholinergic function.

Figure 1

Cultures from normal (A, B_1, and B₂) and Ts16 fetuses (C, D₁ and D₂) stained with an antibody to ChAT. (Bars = 50 μm; A, B₁, C, and D_1, ×200; B₂ and D_2, ×100). Note the thicker, more elaborate processes in normal than in Ts16 neurons.

Figure 2

The relative cholinergic expression (number of ChAT-containing neurons) in homologous and heterologous cultures as a function of the number of neurons in the cultures. The open circles show the cholinergic function as the ratio of normal neurons on trisomic glia to trisomic neurons on normal glia. The circles with crosses show that ratio of expression for trisomic neurons on trisomic glia to that for normal neurons on normal glia. Note that at low neuronal density, the heterologous cultures containing Ts16 glia have relatively low numbers of cholinergic neurons, whereas at high neuronal density the heterologous cultures having Ts16 neurons have the lower number of cholinergic neurons.

Figure 3

Plots of the ChAT enzyme levels and cholinergic neuron number in homologous and heterologous cultures expressed as % of NG+NN. For the homologous cultures, the values are taken from Table 1; for the heterologous cultures (TG+NN and NG+TN), the data are taken from cultures with the lowest neuron density in each series of experiments.