Light-based modulation of astrocytic calcium for regulation of organelle dynamics and morphogenesis.

Astrocytes are essential for neuronal homeostasis, and synaptic modulation and development. While astrocytes exhibit distinct Ca2+ signaling patterns, decoding their physiological roles remains challenging because conventional approaches generate nonphysiological, spatially imprecise Ca2+ surges that obscure endogenous signals. Here, we developed a tunable light-based tool to modulate astrocytic Ca2+ activity, mimicking localized spikes and global waves elicited by graded glutamate through endogenous mGluR-Gq-IP3R signaling. IP3R triple knockout abolished light-evoked Ca2+ elevations, indicating elevated Ca2+ requires ER-IP3Rs. Using this modulation platform, we found that local Ca2+ spikes enhance organelle entry into astrocytic processes, whereas global Ca2+ waves arrest organelle movement. FKBP-FRB motor recruitment assays showed that global Ca2+ elevations acutely suppress motor-driven transport when cargo adaptors are bypassed. Combining our method with astrocyte process outgrowth analysis showed that Ca2+-dependent distal organelle accumulation promotes process elongation. Together, this light-based strategy provides a versatile platform for eliciting endogenous-like astrocytic Ca2+ patterns and reveals how distinct Ca2+ patterns differentially control organelle dynamics and astrocytic structural remodeling.