TGFβ-Induced Phosphorylation of Usp9X Stabilizes Ankyrin-G and Regulates Dendritic Spine Maintenance

Abstract

Signaling by the cytokine TGFβ has been implicated in a multitude of biological functions outside and within the nervous system. While canonical TGFβ signaling is mediated by Smad-dependent regulation of gene expression, non-canonical TGFβ signaling, in particular in the central nervous system, remains largely unexplored. ANK3 variants (encoding ankyrin-G) are associated with bipolar disorder, intellectual disability, and autism spectrum disorder, while mutations in USP9X, which encodes a deubiquitinase, are associated with X-linked intellectual disability and autism in humans. Here we show that TGFβ signaling promotes Usp9X phosphorylation, which enhances its interaction with ankyrin-G, and stabilizes ankyrin-G in spines, leading to spine enlargement. Using in situ proximity ligation combined with structured illumination super-resolution microscopy we characterize the postsynaptic spatial organization of phosphorylation-dependent regulation of Usp9X/ankyrin-G interaction in dendrites and its quantitative relationship with spine morphology and number. These data reveal a cytokine-mediated mechanism regulating protein stability in spines, and suggest a role for deubiquitination and TGFβ signaling in neurodevelopmental disorder pathogenesis and treatment.