PT  - JOURNAL ARTICLE
AU  - Zachary I. Blume
AU  - Jared M. Lambert
AU  - Anna G. Lovel
AU  - Diana M. Mitchell
TI  - Microglia in the developing retina couple phagocytosis with the progression of apoptosis via P2RY12 signaling
AID  - 10.1101/2020.01.30.925859
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.01.30.925859
4099  - http://biorxiv.org/content/early/2020/01/31/2020.01.30.925859.short
4100  - http://biorxiv.org/content/early/2020/01/31/2020.01.30.925859.full
AB  - Background Microglia colonize the developing vertebrate central nervous system coincident with detection of developmental apoptosis. Our understanding of apoptosis in intact tissue in relation to microglial clearance of dying cells is largely based on fixed samples, which is limiting given that microglia are highly motile and mobile phagocytes. Here, we used a system of microglial depletion and in vivo real-time imaging in zebrafish to directly address microglial phagocytosis of apoptotic cells during normal retinal development, the relative timing of phagocytosis in relation to apoptotic progression, and the contribution of P2RY12 signaling to this process.Results Depletion of microglia resulted in accumulation of numerous apoptotic cells in the retina. Real-time imaging revealed precise timing of microglial engulfment with the progression of apoptosis, and dynamic movement and displacement of engulfed apoptotic cells. Inhibition of P2RY12 signaling delayed microglial clearance of apoptotic cells.Conclusions Microglial engulfment of dying cells is coincident with apoptotic progression and requires P2RY12 signaling, indicating that microglial P2RY12 signaling is shared between development and injury response. Our work provides important in vivo insight into the dynamics of apoptotic cell clearance in the developing vertebrate retina and provides a basis to understand microglial phagocytic behavior in health and disease.Bullet PointsLevels and location of developmental apoptosis in the zebrafish retina are elusive due to rapid and efficient clearance by microgliaMicroglial clearance of apoptotic cells is timed with the progression of apoptosis of the engulfed cell so that many cells are cleared in relatively early apoptotic stagesP2RY12 signaling is involved in microglial sensing and clearance of cells undergoing normal developmental apoptosis, indicating shared signals in microglial responses to cell death in both healthy and injured tissueGrant Sponsors NIH NIGMS Grant No. P20 GM103408