Model for Studying the Physiological Role of Non-cell Autonomous Factors on Neuromodulation

Abstract

The intercellular communication in the ventral horn of the spinal cord is essential for the motor function to innervate skeletal muscle. Hence, the progressive pathologies of several neuromuscular diseases (NMDs) are likely to be driven by defects in more than one cellular subtype in the ventral spinal cord. However, current neuro-centric human NMD modeling efforts do not recapitulate the nature of non-cell autonomous neuromodulation occurring upstream of the disease, which significantly limits our pathologic understanding. Therefore, in spite of the recent advancement in developing human induced pluripotent stem cell (hiPSC)-derived neurons, the pathologic mechanism of non-cell autonomous neurodegeneration remains elusive. Moreover, the current differentiation process of iPSC-derived spinal motor neurons does not accurately mirror the transcriptomic trajectories of the native ventral spinal cord development, limiting the application of the differentiated neurons. To address these shortcomings, we studied the role of exogenous physiological inputs on neuromodulation using human iPSC-derived spinal motor neurons, spinal astrocytes, and inflammatory stress factors. We studied the neuroprotective mode of astrocytes in normal tissue and demonstrated that astrocyte-derived extracellular vesicles enhance the longevity and electrophysiological function of immature iPSCneurons. Additionally, we showed that excessive exposure to the pro-inflammatory cytokine interferong, which is secreted from a broad range of immune cells, induces an extensive transcriptomic alteration of iPSC-derived motor neurons toward neurodegeneration, leads to the expression of pathologic hallmarks of ALS. Finally, we assessed the physiological relevance of the iPSC-derived motor neurons we used in this study. We performed a longitudinal transcriptomic analysis of differentiating iPSC-motor neurons at each critical time point of development, to compare it with that of the developing human spinal cord ventral horn. We expect this comprehensive transcriptomic mapping at a single-cell level will provide us invaluable guidance for improving our spinal neuron differentiation strategy. Together, we believe our findings contribute to understanding how the human motor circuit is developing and affected by surrounding factors in normal and diseased conditions, which could lead to developing more reliable human neuromuscular models eventually to identify future therapeutic targets of NMDs.