Study of Nedd4L in Periventricular Nodular Heterotopia - PROJECT SUMMARY/ABSTRACT Periventricular nodular heterotopia (PNH) is a rare neurological disorder caused by impaired cortical neuron migration during early development. While individuals with PNH typically have normal intelligence, many develop seizures during adolescence, and some may exhibit learning disorders. Neural precursor cell expressed developmentally down-regulated gene 4-like (Nedd4L, also known as Nedd4-2) is a PNH-associated gene with multiple loss-of-function missense mutations identified in affected individuals. Unlike other PNH-associated genes that encode cytoskeleton proteins, however, Nedd4L has not shown a clear connection to neuronal migration. To approach this question, our recent work (Lee et al., EMBO Rep. 2021) showed that knocking out Nedd4L in forebrain excitatory neurons leads to reduced phosphorylation of cofilin, an actin-depolymerizing protein. Dephosphorylation of cofilin enhances its actin-binding affinity, thereby reducing the elongation of actin filaments, as we have observed in Nedd4L knockout neurons (Lee et al., EMBO Rep. 2021). Based on these findings, we hypothesize that Nedd4L, which is an E3 ubiquitin ligase, ubiquitinates certain phosphatases to promote cofilin phosphorylation, and PNH-associated missense mutations on Nedd4L impair this process and neuronal migration. In Aim 1, we will first search for the phosphatase that is associated with Nedd4L-dependent cofilin phosphorylation. We will follow this by determining whether and how the loss of two major isoforms of Nedd4L impacts neuronal migration and whether promoting cofilin phosphorylation can restore any defects in neuronal migration. In Aim 2, we will study the mechanism by which three reported PNH-associated missense mutations in Nedd4L lead to elevated degradation. We will follow this by testing whether stabilizing mutant Nedd4Ls can restore their functions in promoting neuronal migration and improve other PNH-associated neuronal phenotypes such as neuronal hyperexcitability. Completion of this project will provide a mechanistic understanding of how mutations of Nedd4L lead to PNH and will introduce cofilin as a therapeutic target for Nedd4L-associated PNH.
