Abstract
Autism spectrum disorder is a complex neurodevelopmental disease characterized by altered cortical network excitability. Recent genetic studies have identified deep layer V cortical pyramidal neurons in the frontal cortex as central to autism pathophysiology, yet the cortical circuits, plasticity mechanisms and molecular signalling pathways involved remain poorly understood. Layer V pyramidal neurons consist of two main types with distinct functional roles: intratelencephalic neurons, which respond to low-frequency stimulation and project within the cortex and striatum, and pyramidal tract neurons, which are tuned to theta-frequency inputs and convey information to subcortical structures. Determining which of these two neuron types is more critical to autism pathophysiology and whether disruptions in their synaptic connectivity or intrinsic excitability contribute to autism-related dysfunctions would significantly advance our understanding of the disorder. Integrins, a family of cell adhesion molecules, are vital for neuronal function. The gene encoding β3 integrin (ITGB3) is genetically linked to autism spectrum disorder, with rare mutations identified in affected individuals, while Itgb3 knockout mice exhibit autism-like behaviours, including impaired social memory and increased grooming. However, it remains unclear why loss of β3 integrin is associated with autism spectrum disorder, how it disrupts cortical circuits, and which plasticity mechanisms and molecular pathways are involved. Here, we demonstrate that β3 integrin selectively regulates the excitability of pyramidal tract neurons in the medial prefrontal cortex. Using electrophysiology, proteomics and molecular approaches, we show that β3 integrin regulates the gain, adaptation and precision of action potential discharge by controlling the surface expression of Ca2+-activated SK2 channels. Genetic ablation of Itgb3 impaired intrinsic excitability and SK2 channel function in pyramidal tract neurons, with no effects in intratelencephalic neurons. Furthermore, we identified Tau, a protein traditionally linked to neurodegenerative diseases, as part of the SK2 channel interactome. Proteomic analyses revealed altered protein kinase A-dependent phosphorylation of Tau in Itgb3 knockout mice, while protein kinase A inhibition restored SK2 channel currents, thereby connecting phosphorylation changes to excitability deficits. Our findings expand the current mechanistic framework linking signalling pathway dysfunctions to cortical excitability deficits, highlighting the dysregulation of pyramidal tract neuron excitability as a core feature of autism pathophysiology and demonstrating the involvement of β3 integrin, SK2 channels, Tau and PKA in this process. Because pyramidal tract neurons serve as final integrators of cortical computations before relaying information outside the cortex, their impaired excitability may disrupt communication with subcortical targets, contributing to the complex pathophysiology of autism spectrum disorder.
Keywords:
PKA; SK2 channels; intrinsic excitability; layer V pyramidal neurons; medial prefrontal cortex; spike frequency adaptation.