Membrane-associated periodic skeleton regulates major forms of endocytosis in neurons through a signaling-driven positive feedback loop

Abstract

Endocytosis is an evolutionarily conserved process that enables neurons to internalize signaling receptors and membrane proteins, maintaining cellular homeostasis and supporting rapid responses to extracellular cues. The neuronal membrane-associated periodic skeleton (MPS), a lattice-like cytoskeletal structure composed of actin and spectrin, has been shown to restrict clathrin-mediated endocytosis (CME) at the axon initial segment (AIS) of neurons, by gating clathrin-coated pit (CCP) formation through membrane-localized "clearing" structures that are devoid of MPS. However, the extent to which the MPS regulates diverse forms of endocytosis across neuronal compartments, and how it is dynamically remodeled to permit trafficking on demand, remain unknown. While CME is relatively well characterized in neurons, the subcellular localization and physiological relevance of caveolin-mediated endocytosis, flotillin-mediated endocytosis, and fast endophilin-mediated endocytosis (FEME) have remained largely unclear. Here, we show that all four major endocytic pathways--CME, caveolin-, flotillin-, and FEME-- are spatially gated by the MPS and occur specifically within MPS-free "clearing" zones distributed across both axonal and somatodendritic compartments of mature neurons. These results, for the first time, map the spatial landscape of these lesser-understood pathways in neurons and reveal a unifying principle of cytoskeletal gating across endocytic mechanisms. Disruption of the MPS markedly enhances both basal and ligand-induced endocytosis across all four pathways, establishing its broad inhibitory role in pit initiation. We further discover that endocytosis can, in turn, remodel the MPS through a novel signaling-driven feedback loop: ligand-triggered endocytosis activates ERK signaling, which promotes calpain- and caspase-mediated spectrin cleavage. This targeted cytoskeletal degradation facilitates further rounds of endocytosis, forming a self-reinforcing circuit that couples membrane trafficking with cortical architecture remodeling. Finally, we show that the MPS limits amyloid precursor protein (APP) endocytosis and thereby suppresses amyloid-{beta} 1-42 (A{beta}42) production and neuronal apoptosis, implicating MPS integrity in the regulation of neurodegenerative processes such as Alzheimers disease. Together, our findings establish the MPS as a dynamic, signal-responsive modulator of endocytosis and neuronal health. This work uncovers a general spatial gating mechanism that applies to diverse endocytic pathways, introduces a cytoskeleton-centered feedback loop for signal-dependent remodeling, and expands the functional significance of the MPS from passive structural support to active regulation of neuronal homeostasis and disease susceptibility. TeaserMembrane skeleton gates endocytosis and remodels in response to signals, linking membrane dynamics to neuronal health and Alzheimers risk.