Microglia increases the proliferation of retinal precursor cells during postnatal development

PURPOSE: In mice, retinal development continues throughout the postnatal stage accompanied by the proliferation of retinal precursor cells. Previous reports showed that during the postnatal stage microglia increase from postnatal day 0 (P0) to P7. However, how microglia are associated with retinal development remains unknown. METHODS: The involvement of microglia in retinal development was investigated by two approaches, microglial activation and loss, using lipopolysaccharide (LPS) and PLX3397 (pexidartinib), respectively. RESULTS: LPS injection at 1 mg/kg, intraperitoneally (i.p.) in the neonatal mice increased the number of retinal microglia at P7. 5-Bromo-2´-deoxyuridine (BrdU)-positive proliferative cells were increased by LPS treatment compared to the control group. The proliferative cells were mainly colocalized with paired box 6 (Pax6), a marker of retinal precursor cells. However, the depletion of microglia by treatment with PLX3397 decreased the BrdU-positive proliferative cells. Moreover, progranulin deficiency decreased the number of microglia and retinal precursor cells. CONCLUSIONS: These findings indicated that microglia regulate the proliferation of immature retinal cells.