PLX-5622

Transplantation of microglia into the embryonic brain could provide a powerful approach to trace microglial fate and test their functional contribution during development. However, embryonic microglial transplantation remains technically challenging because only a limited number of donor cells can be obtained and transplantation efficiency is low. Here, we investigated whether transient depletion of endogenous microglia could improve the engraftment of transplanted microglia in the embryonic mouse brain. Pregnant mice were fed a diet containing a colony-stimulating factor 1 receptor inhibitor (PLX5622) in advance to reduce resident microglia in the embryos. CD11b-positive cells isolated from embryonic day (E) 12.5 CX3CR1-GFP donor brains were transplanted into the lateral ventricles of E12.5 embryos, and brains were analyzed at E14.5. In embryos fed a normal diet, most transplanted cells remained in the ventricular space, whereas PLX5622-treated embryos showed a marked increase in GFP-positive cells within the brain parenchyma, suggesting improved engraftment. Furthermore, early microglial depletion caused enlargement of cavities in the cortico-striato-amygdalar boundary (CSA), a developmental boundary region in the ganglionic eminence. Microglial transplantation significantly reduced the size of these cavities. These results suggest that transient depletion of host microglia enhances embryonic microglial transplantation and that transplanted microglia can partially restore structural abnormalities caused by microglial loss.

Microglia, the intrinsic immune cells of the brain, play a crucial role in maintaining neuronal health and circadian rhythms. BMAL1 is a core transcriptional regulator of the molecular circadian clock that coordinates daily rhythms in physiology and behavior. In this study, we investigated the impact of microglial modulation on circadian disruptions and behavioral abnormalities observed in bmal-/- mice. Our results revealed disruptions in circadian rhythms and microglial activation in bmal-/- mice, characterized by altered activity patterns and increased microglia numbers. Inhibiting microglia with PLX5622 effectively ameliorated circadian disruptions and improved behavioral performance in bmal-/- mice, as observed in open field and elevated plus-maze tests. Additionally, microglia inhibition restored structural and functional abnormalities in neurons of bmal-/- mice, including dendritic spine reduction and impaired long-term potentiation (LTP). Furthermore, we observed a normalization of proinflammatory cytokine levels (IL-1β and TNF-α) upon PLX5622 treatment, indicating a potential link between microglial modulation and neuroinflammation. Our findings highlight the intricate interplay between circadian rhythms, microglia, and neuronal health, offering insights into potential therapeutic interventions for circadian-related and neuroinflammatory disorders.