Abstract
Degeneration of the corticospinal tract is a central feature in a number of neurodegenerative disorders and leads to significant disability. However, modeling corticospinal neuron (CSN) pathology and corticospinal connectivity in neurological disorders is particularly challenging. While rodent models are important for understanding early degeneration of CSN, interspecies differences in corticospinal connectivity and challenges of in vivo study suggest that human in vitro models of corticospinal biology may be ripe for development. Human induced pluripotent stem cells (hiPSC) are promising tools for overcoming intrinsic limitations that arise from physiological differences between rodents and humans. We have developed an innovative hiPSC-based microfluidic platform for modeling human CSN and spinal motor neuron (SpMN) connectivity. The incorporation of regionally specific astrocyte subtypes (cortical and spinal) in addition to CSNs and SpMNs in this newly designed system allows for the modeling of both regional and neural cell-subtype interactions. Using this model, multielectrode array electrophysiology reveals the maturation of both cortical and spinal motor neurons over the time course of 12 weeks. Retrograde labeling methods demonstrate synaptic connectivity between corticospinal and spinal motor neurons. Optogenetic strategies to selectively activate excitatory CNs attenuated by glutamate receptor antagonism confirms the functional relevance of the model. Incorporating morphological, electrophysiological and physiological measures of corticospinal connectivity, this platform is a versatile model for use in neurodegenerative disease research and for the future development of targeted CSN therapies. SIGNIFICANCE STATEMENT: Degeneration of the corticospinal tract is a key feature of numerous neurodegenerative diseases, yet current in vitro models lack the anatomical and functional fidelity to study this system. We developed a human iPSC-derived "Corticospinal Tract-on-a-Chip" using a multielectrode array platform that incorporates regionally patterned cortical and spinal neurons and astrocytes. This model demonstrates structural and functional synaptic connectivity and enables longitudinal electrophysiological recordings. Critically, it supports compartment-specific manipulation and real-time analysis of CST network dynamics, capabilities lacking in existing systems. By mimicking human corticospinal physiology in vitro , this platform offers a novel tool for mechanistic investigation and preclinical testing of CST-targeted therapies. It holds broad relevance for studying disorders such as ALS, hereditary spastic paraplegia, and primary lateral sclerosis.