HUMAN CORTICO-HIPPOCAMPAL ASSEMBLOIDS.<EM> </EM><EM>A NOVEL TOOL FOR ALZHEIMER’S DISEASE RESEARCH</EM>

The cortico-hippocampal pathway plays a crucial role in memory formation. Despite recent advances, the mechanisms involved in the establishment of the cortico-hippocampal connectivity and its alterations in Alzheimer’s disease (AD) remain poorly understood, being the lack in vitro models one of the major challenges. We have developed a reliable in vitro model that replicates the development and functionality of the cortico-hippocampal pathway.
We derived and characterized cortical and hippocampal organoids from human induced pluripotent stem cells (hiPSCs). To model the cortico-hippocampal pathway, we combined these region-specific organoids into assembloids. Interregional connectivity was assessed using axonal projection analysis and monosynaptic tracing, revealing the formation of reciprocal projections and the establishment of functional circuits between cortical and hippocampal regions. Neuronal activity analysis showed robust spontaneous activity and high connectivity in cortical organoids, whereas hippocampal organoids exhibited minimal activity when cultured alone, consistent with the input-dependent nature of hippocampal circuits. Notably, integration into cortico-hippocampal assembloids led to a marked increase in hippocampal neuronal activity driven by cortical input, closely mirroring in vivo hippocampal dynamics and highlighting the physiological relevance of the model. To further enhance biological fidelity, microglial cells were incorporated into the organoids, where they successfully integrated, remained active and modulated neuronal activity. Finally, tau pathology is being induced to investigate circuit-level vulnerability and mechanisms of tau spreading in AD.
In summary, we present a robust and reproducible model of the cortico-hippocampal pathway that provides a powerful platform to investigate AD and support the development of new therapeutic strategies.