PIEZO1 REGULATES MICROGLIAL MOTILITY AND RESPONSES TO EXTRACELLULAR MATRIX REMODELING DURING ZEBRAFISH BRAIN DEVELOPMENT

Microglia rely on dynamic interactions with their physical environment, including the extracellular matrix (ECM), to survey the developing brain and respond to injury. Here, we investigate the role of the mechanoreceptor ion channel Piezo1 in regulating microglial physiology during early zebrafish development. Using CRISPR/Cas9-mediated knockdown, we generated piezo1 crispants in Tg(mpeg1:eGFP) and Tg(mpeg1:mScarlet) reporter zebrafish lines and evaluated microglial motility and navigation, as well as phagocytosis of ablated neurons in a context of Poly I:C-induced inflammation. To further probe mechanosensitive responses to ECM remodeling, hyaluronic acid was enzymatically degraded using hyaluronidase. Our results revealed that, under basal conditions, piezo1 crispant microglia move faster and further than control. However, when challenged with Poly I:C-induced inflammation, these cells showed significantly reduced directionality, indicating impaired navigation, while phagocytosis assays showed a downward trend in the phagocytic index following neuronal ablation. Notably, upon ECM degradation, piezo1-deficient microglia displayed reduced speed and directionality, frequently halting their movement and adopting an amoeboid morphology. This response is striking, as amoeboid morphology is typically associated with a non-homeostatic, highly motile state, suggesting a decoupling between microglial reactivity and motility in the absence of Piezo1. Together, these findings suggest that Piezo1 is required for the proper integration of mechanical cues that modulate microglial motility and navigation in the developing brain in response to inflammation, underscoring the essential role of Piezo1-mediated sensing in innate immune responses in the vertebrate central nervous system.