Astrocytes contribute to the ReelinApoER2 signalling pathway in the adult brain

Abstract

Reelin is 400 kDa, secreted glycoprotein that signals via the lipoprotein receptors ApoER2 and VLDLR, and the cytosolic adaptor protein Dab1 in target cells. This Reelin signalling pathway has been shown to be essential for the formation of the radial glia scaffold and subsequent layering of the cortex during neural development. Reelin's role in the adult brain has not been clearly established, however, recent studies have implicated Reelin as an obligatory component of LTP in neurons of the adult rodent brain. To investigate a possible role for the Reelin/ApoER2/Dab1 signalling pathway in mature, human astrocytes the NT2 cell model system was utilized. Here we show for the first time, using a combination of molecular and cell biology techniques such as RT-PCR, immunoblotting and immunohistochemistry, the presence of Reelin, its receptor (ApoER2) and downstream signalling components in mature NT2 astrocytes (NT2/A). Treatment of pure 15-week-old NT2/A cells with recombinant Reelin induced the tyrosyl phosphorylation of Dab1 on residues Y198 and Y220. Furthermore, our results showed that the membrane ruffling induced by serum deprivation in NT2/A is significantly reduced in the presence of recombinant Reelin in culture. Our findings support a model in which the secreted glycoprotein Reelin is required in NT2/A cells to maintain astrocytic morphology. In light of recent studies, which have identified the importance of astrocytes in the modulation of synaptic transmission, Reelin signalling in NT2/A cells could potentially play a role in altering the dynamics of synaptic transmission in the adult brain via modulation of the cytoskeleton.