Mutations in NPTN could hinder neurodevelopment by impairing the regulation of plasma membrane Ca2+-ATPase (PMCA) levels and Ca2+ transients in brain neurons

Abstract

In recent years, the genetic factors of neurodevelopmental disorders (NDDs) are being explored. Recently, mutations in the Neuroplastin gene (Nptn, NPTN) have been discovered in mice with hearing deficits and in human patients suffering from NDDs. Neuroplastin (Np), is a member of the immunoglobulin superfamily, and its expression is necessary to maintain the expression levels of the calcium pump plasma membrane Ca2+-ATPase (PMCA) and its proper trafficking. This is intimately related to the regulation of intracellular Ca2+ homeostasis. So far, no studies have explored the molecular pathogenesis of NDDs caused by NPTN gene mutations. In this work, by generating expression constructs, transfecting HEK293T cells and primary hippocampal neurons, employing in vitro calcium imaging techniques, and creating mutant Drosophila melanogaster lines, the study identified the expression levels of Np and PMCA for each variant, as well as the dynamics of Ca2+ extrusion under different conditions (overexpression, low frequency stimulation, high frequency stimulation and Np-siRNA knock down conditions). The results indicated that the missense mutations pitch (C315S) and audio-1 (I122N) in Nptn; p.W135R and p.P342L in NPTN impaired the structure and function of the Np protein and the PMCA-neuroplastin complex, leading to impaired cellular Ca2+ homeostasis. This may be the molecular pathological mechanism causing hearing defects in mice and NDDs in human. This study proposed a molecular mechanism underlying the pathological process of outer hair cell degeneration leading to deafness in Nptn mouse mutants and of the NDDs associated NPTN human variants. This work deepens our understanding of NDDs and may provide new insights for early detection and further innovative treatments.