Resumo

Neuro-glial interactions play key roles in synaptic transmission. Recently, molecules secreted by astrocytes were identified as promoters of synaptogenesis in the central nervous system. Here, we investigated the role of transforming growth factor beta 1 (TGF-beta1) on the formation of synapses of cerebral cortex neurons in vitro. Primary cultures of cortical neurons were treated with TGF-beta1 (10ng/mL) on days 0, 3, 6, 9 and analyzed after 12 days in vitro. Immunocytochemistry assays for presynaptic (synaptophysin) and post-synaptic (PSD-95) proteins revealed a 113% and 37% increase in the puncta numbers of synaptophysin and PSD-95, respectively. Moreover, a 145% increase in synaptophysin/PSD-95 double labeled punctas was observed in TGF-beta1 treated group, indicating an increase in structural functional synapses. These data were supported by identification of 100% increase in the levels of synaptophysin and PSD-95 proteins in TGF-beta1-treated neurons by western blotting assays. Morphological data were followed by electrophysiological results, which showed increase in spontaneous current and sodium channels activity in TGF treated neurons. Concurrent with these data, we previously found that TGF-beta1 induced secretion of D-serine, the major co-agonist of NMDA receptors, in neurons and astrocytes from the cerebral cortex. Treatment of neuronal cultures with 0.4 mM of D-Serine increased synaptophysin, PSD-95 and colocalizing synaptophysin/PSD-95 puncta numbers by 122%, 40% and 218%, respectively. Addition of a specific D-serine blocker, the enzyme D-amino acid oxidase, to TGF-beta1-treated cells completely impaired TGF-beta 1 synaptic induction. Together, our data demonstrate that TGF-beta 1 induces synaptogenesis of cerebral cortical neurons through modulation of D-serine levels. Our data shed light on glial-derived molecules as potential compounds for synaptic deficit diseases and for improvement of cellular therapy efficacy in the central nervous system.