A Chemical Strategy for Imaging and Manipulating the Brain's Astrocytes

PROJECT SUMMARY The active participation of the brain’s astrocytes in normal and pathological brain function is now well established. Astrocytes adjust synaptic strength, mediate synaptogenesis, and participate directly in neural signaling on a breadth of timescales that would be otherwise inaccessible with neuron-centric signaling.

Gaining a better understanding of astrocyte function will have wide-ranging implications for human health. The technologies for visualizing and manipulating astrocytes generally, and neuron-to-astrocyte interactions in particular, are limited, especially in comparison to the repertoire of strategies for visualizing neuron anatomy

and physiology. By bridging the fields of chemistry and neuroscience, we have designed a chemical strategy that will enable the direct visualization and manipulation of astrocytes globally, and, potentially, neural- astrocyte connectivity specifically. Our strategy for chemical imaging of astrocytes and neuron-astrocyte interactions employs a chemical tag

that, when appended to structurally diverse chemical scaffolds, targets molecules to astrocytes when delivered systemically to an organism. Here, we will further evaluate the properties of this astrocyte targeting tags and expand on their capabilities, for example, delivering fluorescent reporters of cell physiology, drugs for

modulating astrocyte function, or transcription activators to control gene expression, directly to astrocytes. Further, in preliminary experiments, we found that when fluorescent molecules with the astrocyte targeting tag are introduced directly into neurons of larval zebrafish, they specifically label astrocytes proximal to the

neuron’s axonal projections, potentially serving as a marker for the population of astrocytes that interact with a given neuron. In preliminary results, we have chemically synthesized an array of candidate neuron-astrocyte probes and characterized the specificity and mechanism of their labeling in larval zebrafish and mammalian

astrocytes. In this application, we describe projects that will broaden the reach of the described probes for systemic astrocyte imaging and manipulation. We describe alterations to the neuron-glia label’s chemical structure in order to explore possibilities for astrocyte specific drug delivery, cell-type specific labeling, and

transgene expression in labeled astrocyte populations. Ultimately, the ability to interrogate astrocytes with tunable chemical scaffolds, and, specifically, to visualize select neuron-astrocyte interactions, will be a valuable tool for understanding the brain.