Background: For neuronal replacement therapies to succeed we need to understand how the integration of nascent neurons is regulated in CNS disease.
Hypothesis: The interaction of nascent neurons with local and recruited immune cells is a critical checkpoint for circuit integration.
Strategy: Implant neurons in CNS disease models with distinct neuronal pathologies and immune responses using circuit tracing, in vivo imaging and molecular interference to investigate how their interactions shape circuit integration.
Neuronal replacement therapy is urgently needed for many neurological disease conditions that cause loss of neurons or their connections. However, the correct functional integration of transplanted neurons is a fundamental prerequisite for re-establishing physiological circuit function and preventing maladaptive distortion of the neuronal circuitry. Notably, fully adequate functional integration of transplanted neurons with exquisitely appropriate brain-wide connectome and highly specific receptive field function was recently achieved in a selective neuronal ablation model. These findings now set the stage to move neuronal replacement therapy towards more clinically relevant models. This project thus aims to utilize such models of traumatic and inflammatory grey matter pathology to determine the cellular and molecular checkpoints regulating adequate circuit integration of nascent neurons. Here we want to track the structural requirements, cellular interactions and molecular signals that determine the appropriate and stable integration of transplanted neurons in the cortical circuitry. In particular, we plan to address the following specific aims:
Aim ❶ Structural requirements for circuit integration of nascent neurons
We will transplant neurons in disease models characterized by distinct neuronal damage and immune response patterns. We will then follow neuronal integration by chronic live in vivo imaging of single transplanted neurons and monitor the brain-wide connectome using monosynaptic rabies virus tracing and clearing techniques. In particular we will pursue the hypothesis that initial integration of new neurons is governed by previous synapse loss.
Aim ❷ Cellular checkpoints for circuit integration of nascent neurons
We will use in vivo microscopy to track the main glial and immune cell populations that interact with transplanted neurons and confocal and ultrastructural analysis to monitor their synapse uptake. Defined immune and glial cell populations will then be specifically targeted to identify the cellular mechanisms of initial integration and synapse turn-over and pruning in TBI.
Aim ❸ Molecular checkpoints for circuit integration of nascent neurons
Transcriptome and proteome analysis will be used to identify receptor-ligand pairs or signalling pathways associated with the integration and pruning. These candidates will be probed by inducible and cell-type-specific genetic manipulations to identify key determinants that regulate the balance between circuit integration and disconnection in the injured brain.