Neuronal dependency of the glycine transporter GLYT1 expression in glial cells.

Two membrane-localized transporter proteins (GLYT1 and GLYT2) are responsible for removal of extracellular glycine in the mammalian CNS. Whereas GLYT1 seems to be expressed mainly in glial cells, GLYT2 is neuronal. The highest concentrations of both transporters are found in glycinergic areas of the nervous system. The expression of these proteins may be under regulatory control. We demonstrate here that GLYT1 is not expressed in pure glial cultures, but it is expressed by diverse types of glial cells in mixed neuronal/glial cultures. In these mixed cultures, the glial expression of GLYT1 is down-regulated after selective elimination of the neurons. The absence of expression in pure glial cultures and the observed reduction in the GLYT1 expression after neuronal loss support the existence of a regulatory cross-talk between neurons and glia to initiate and sustain the glial expression of GLYT1.