Precision targeting of C3+ reactive astrocyte subpopulations with endogenous ADAR in an iPSC-derived model.

Astrocytes play pivotal roles in maintaining neural architecture and function. However, their pronounced heterogeneity, especially in reactive states where distinct subtypes can adopt potentially opposing functions (e.g., neuroprotective vs. neuroinflammatory), complicates our understanding of their net contributions to neurological disorders. A critical challenge arises because these functionally distinct subpopulations often coexist, and the lack of precise tools to separately monitor or manipulate them has significantly hindered efforts to dissect their specific roles in disease progression. Here, we address this gap by developing and optimizing fluorescent RNA sensors mediated by endogenous adenosine deaminase acting on RNA (ADAR) for application in induced pluripotent stem cell (iPSC)-derived astrocytes. We employed a streamlined screening methodology to enhance sensor specificity and functionality for complement component 3 (C3), a key marker predominantly associated with neuroinflammatory astrocytes, thus enabling subtype-specific tracking and providing a crucial tool for distinguishing these cells within heterogeneous populations. By integrating the biological complexity of astrocytes with the technological precision of ADAR-mediated sensing, this study establishes a robust framework for investigating astrocyte dynamics.