Glutamate transporter expression and function in a striatal neuronal model of Huntington’s disease

• EAAC1 is the primary glutamate transporter in STHdhQ7/Q7 and STHdhQ111/Q111 cells.
• Glutamate uptake is 3.6-fold higher in STHdhQ111/Q111 than in STHdhQ7/Q7 cells.
• Surface expression of EAAC1 is increased in STHdhQ111/Q111 cells.
• The increase in glutamate uptake in STHdhQ111/Q111 cells is mediated by EAAC1.

Excitotoxicity may contribute to the pathogenesis of Huntington’s disease. High affinity Na+ dependent glutamate transporters, residing in the plasma membrane, clear glutamate from the extracellular space and are the primary means of protection against excitotoxicity. Many reports suggest that Huntington’s disease is associated with a decrease in the expression and function of glutamate transporters. We studied the expression and function of these transporters in a cellular model of Huntington’s disease, STHdhQ111/Q111 and STHdhQ7/Q7 cells. We found that only GLT-1b and EAAC1 were expressed in these cell lines and only EAAC1 significantly contributed to the glutamate uptake. Surprisingly, there was an increase in Na+-dependent glutamate uptake in STHdhQ111/Q111 cells accompanied by an increase in surface expression of EAAC1. We studied the influence of the Akt pathway on EAAC1 mediated uptake, since EAAC1 surface expression is influenced by Akt and previous studies have shown increased Akt expression in STHdhQ111/Q111 cells. Glutamate uptake was inhibited by Akt pathway inhibitors in both the STHdhQ7/Q7 and the STHdhQ111/Q111 cell lines. We found no difference in Akt activation between the two cell lines under our conditions of culture. Therefore a difference in Akt activation does not seem to explain the increase in EAAC1 mediated uptake in the STHdhQ111/Q111 cells.