) Microglia are intimately involved in brain homeostasis and synaptic maturation. Recent studies suggest that developmental brain disorder may induce pathological microglia to impair the neural network. In this project, we will test whether these perinatal injury-induced pathological microglia have a unique lineage origin. The current prevailing view holds that microglia are derived exclusively from early CNS settlers of a yolk sac, and do not receive contributions by peripheral monocytes and derivtatives. Yet, our pilot studies suggested a far more complex situation, which bears great implications for perinatal brain injury/infection-related cognitive derangements. This project will test the hypothesis monocytes readily contribute to the brain microglial pool prenatally, but cease doing so shortly after birth. However, perinatal brain injury or infection widens the window of monocyte-to-microglia conversion to produce chronic pro-inflammatory microglia in adult brains.
Aim 1 : Generate CCR2-CreER mice using BAC recombineering to identify monocyte derivatives. We will produce tamoxifen-inducible CCR2-CreER mice using bacterial artificial chromosome recombineering transgenesis to detect monocyte-derivatives in the R26R-GFP reporter line. We will donate CCR2-CreER mice to the Jackson Laboratory to make this powerful transgenic tool readily available the research community.
Aim 2 : Compare monocyte-derived microglia in normal development or maternal immune activation (MIA) with and without mild hypoxia-ischemia (HI) in the neonatal period. We hypothesize that Monocytes transform to pro-inflammatory microglia to damage nearby synaptic structures after maternal immune activation (MIA) or endotoxin-sensitized hypoxia/ischemia (LPS/HI) in neonates.
Aim 2 a compares the number and morphology of monocyte-derived microglia in normal development and after MIA with and without mild HI injury.
Aim 2 b uses fluorescence-activated cell sorting (FACS) followed by RT- PCR analysis to compare gene expression by monocyte-derived microglia.
Aim 2 c employs confocal imaging analysis to compare the relationship of monocyte-derived microglia with adjacent synapses.
): Perinatal brain injury contributes to cognitive deficits, but the underlying mechanisms remain poorly understood. The recent discovery that (a) microglia survey and modulate the neural circuitry and (b) monocytes normally do not convert to microglia after birth raises an intriguing possibility that perinatal brain injury may recruit monocytes into immature brains to exert both short- and long-term damaging effects. The present project will test this hypothesis in murine models and produce a new transgenic line (CCR2CreERT2) that can be used for fate-mapping and genetic manipulation in monocytes and their derivatives in multiple disease models.
|Sun, Yu-Yo; Lee, Jolly; Huang, Henry et al. (2017) Sickle Mice Are Sensitive to Hypoxia/Ischemia-Induced Stroke but Respond to Tissue-Type Plasminogen Activator Treatment. Stroke 48:3347-3355|