Dual-domain Flower signaling coordinates extracellular vesicles-mediated fitness selection and cell-intrinsic survival in astrocytes

Cellular fitness surveillance preserves tissue integrity, yet its regulation within the mammalian brain remains poorly understood. We identify a bifurcated mechanism in the transmembrane protein Flower--encoding both survival-promoting ("win") and apoptosis-inducing ("lose") isoforms. We demonstrate that astrocytes secrete specialized extracellular vesicles (EVs), termed "fitness vesicles," carrying Flower to facilitate competitive selection across distal cell populations. The N-terminal Flower domain acts extrinsically via these EVs to drive the elimination of less-fit neighbors. Conversely, the "win"-specific C-terminal domain functions as a cell-intrinsic module; it translocates to the nucleus under stress to repress Caspase-3 and provide resilience. In Alzheimers disease (AD) models and human AD brains, Flower-positive astrocytes accumulate around amyloid-{beta} (A{beta}) plaques. Under A{beta} stress, the "win" isoform reprograms astrocytes toward a neuroprotective state that enhances plaque clearance while ensuring cell-intrinsic survival. Our findings reveal how Flower couples long-range, EV-mediated cellular selection with cell-autonomous protection to coordinate astrocyte quality control and tissue resilience in neurodegeneration.