CELLULAR RESPONSES ELICITED BY THE R451C AUTISM LINK MUTATION IN NLGN3

Mutations linked to autism spectrum disorders are found in genes encoding for the synaptic adhesion proteins Neuroligins (NLGNs). In particular, the R451C mutation in NLGN3 causes a local misfolding followed by the retention of the protein in the Endoplasmic Reticulum (ER). Misfolded protein accumulation in the ER leads to the activation of Unfolded Protein Response (UPR), which aims to restore normal ER function, but has been implicated in the pathogenesis of several neurological diseases. We have used heterologous expression of NLGN3 WT and R451C in HEK-293 and PC12 Tet-On cells to investigate UPR activation. Our data show that NLGN3 R451C activates distinct UPR signaling pathways, as shown by the activation of ATF6, the splicing of XBP1 mRNA, the phosphorylation of eIF2a and the up-regulation of BiP and CHOP. NLGN3 Knock In (KI) mice carrying the NLGN3 R451C substitution have been reported to exhibit autistic-like behaviours and changes in synaptic transmission, not observed in the NLGN3 Knock Out mice. In order to study mutant-induced alterations of neuronal function in culture and a possible correlation with ER stress, we have differentiated PC12 cells to a neuronal phenotype and studied neurotransmitter release. Our data show a reduction in dopamine release in the cells expressing the R451C mutation in comparison to WT expressing cells. Moreover, preliminary data on the expression of UPR markers point toward a different regulation of some UPR target genes in total brain and cerebral cortex of adult R451C KI in the comparison to WT mice.