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Neurosurgeon Forum

Trauma

Synaptic Connectivity of Human Brain Organoid Grafts with the Rat Motor System

Friday, May 3, 2024
3:05 PM – 3:09 PM CT
Location:  S401ab
Disclosure(s):
Shikha Singh, B.S.: No financial relationships to disclose
Introduction: Brain injury can result in irreparable damage to neurological structure and function. Current therapeutics are constrained by inherent limitations of brain regeneration. Here, we propose a novel technique for repairing cortical injury through transplantation of human stem cell-derived brain organoids. This project characterizes how human cortical organoids grown at 2 timepoints can structurally integrate with the rat motor system after injury.

Methods: Organoids were generated using human induced pluripotent stem cells expressing Cre-GFP. 16 rats underwent transplantation of day 20-25 or day 55-60 organoids immediately after motor cortex aspiration lesions. Two months after transplantation, organoids were injected with H129ΔTK-TT, a polysynaptic anterograde tracer with Cre-dependent expression of a tdTomato fluorescent marker. After 1 week, GFP and tdTomato signals were localized in the CNS and quantified using ABBA, QuPath, and Renyi Entropy software to identify downstream synaptic targets of the organoid graft.

Results: In day 20-25 organoid grafts, tdTomato signal localized to the lateral/dorsolateral orbital area, basal forebrain, olfactory bulb, primary motor area, striatum, nucleus accumbens, ventral tegmental area, substantia nigra pr, reticular prethalamic nucleus, primary somatosensory cortex, and thalamus. Signal also localized to ventral horn motor neurons and white matter tracts of the spinal cord. In day 55-60 organoid grafts, tdTomato localized to the primary somatosensory cortex, primary motor area, and red nucleus.

Conclusion : Organoid grafts synaptically integrated with the host motor system, including through polysynaptic connections with the rat spinal cord by 2 months post-transplantation. Moreover, younger organoids demonstrated increased structural integration with the host brain compared to older organoids. These results suggest that human brain organoids could facilitate the restoration of motor function by tapping into pre-existing neural pathways of the host rather than by regrowing axonal tracts. Thus, this study shows the potential of cortical organoids as a powerful therapeutic tool for brain repair.