Functional implications of disrupting GPM6a–NPTN cis and trans interactions using a synthetic peptide targeting the extracellular domains of GPM6a

Neuronal architecture is shaped by the formation of diverse protein complexes, including those involving neuronal glycoprotein M6a (GPM6a) and neuroplastin (NPTN). GPM6a and NPTN individually contribute to neuronal morphogenesis, promoting neurite and filopodia outgrowth and synapse formation. We previously demonstrated that co-expression of GPM6a and NPTN decreases neurite outgrowth in N2a cells, although the molecular mechanism underlying this effect remains unknown. Here, we investigated the role of GPM6a extracellular loops in this interaction using a recombinant peptide targeting both GPM6a extracellular domains, previously generated in our laboratory (GPM6a-loops). In N2a cells, treatment with GPM6a-loops restored neurite outgrowth that was abolished by GPM6a–NPTN co-expression for both NPTN isoforms (NPTN65 and NPTN55). Furthermore, cell aggregation assays in HEK293 cells showed that GPM6a-loops prevented aggregate formation between GPM6a- and NP65-overexpressing cells, suggesting interference with their trans interaction. Together, these results suggest that the extracellular loops of GPM6a participate in both cis and trans interactions with NPTN and underscore the essential contribution of these regions to its biological function. These results provide new insight into the molecular mechanisms regulating neurite development and identify the GPM6a–NPTN interaction as a potential target for modulating neuronal morphogenesis.