S-021 | Characterization of GPM6a and Neuroplastin Interactions in Neuronal Morphogenesis

Cellular and Molecular Neurobiology
Author: Gutierrez Fuster Rocio | Email: rgutierrezfuster@iib.unsam.edu.ar

Rocio Gutierrez Fuster^1°2°, Antonella León^1°2°, Gabriela Ines Aparicio^3°,  Facundo Brizuela Sotelo^1°2°, Karl Heinz Smalla^4°, Camila Scorticati^1°2°

^1° Instituto de Investigaciones Biotecnológicas, Universidad Nacional de San Martín (UNSAM) – Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) , San Martín, Buenos Aires, Argentina
^2° Escuela de Bio y Nanotecnologías (EByN), Universidad Nacional de San Martín. San Martín, Buenos Aires, Argentina.
^3° Department of Neurosurgery, College of Medicine, University of Kentucky, Lexington, USA.
^4° Leibniz Institute for Neurobiology, Research Group Neuroplasticity, Magdeburg, Germany

The molecular mechanisms governing neuronal morphogenesis remain incompletely understood. Neuronal membrane glycoprotein GPM6a promotes neuronal differentiation, though the underlying mechanisms remain elusive. The importance of elucidating these mechanisms is underscored by the association of GPM6A gene variants or dysregulated expression levels with neuropsychiatric disorders such as schizophrenia, depression, Alzheimer’s disease, and claustrophobia. Given that the extracellular loops (ECs) of GPM6a play a critical role in its function, prior studies from our laboratory revealed that the adhesion molecule neuroplastin (NPTN) co-immunoprecipitates with GPM6a using its ECs as bait. This study aimed to explore the potential functional interaction between GPM6a and NPTN in hippocampal neurons and cell lines. We observed that endogenous NPTN and GPM6a colocalize at the neuronal membrane during different developmental stages. The NPTN ectodomain and GPM6a ECs interact in a trans configuration, inducing cell aggregation in live HEK293 cells. This aggregation was inhibited by the addition of a calcium chelator (EGTA) or neutralizing GPM6a monoclonal antibodies. Notably, an NPTN isoform lacking one of the IgG domains (NPTN55) failed to aggregate with GPM6a, and a GPM6a mutant deficient in EC2 folding did not aggregate with wild-type NPTN. Collectively, these findings validate the association between GPM6a and NPTN65, likely mediated through their extracellular domains.