Evidence strongly suggests that the inflammatory dysfunction of the innate immune cells of the brain known as microglia contributes to neurodegenerative conditions. There is a way to clear microglia from the brain, which is the use of CSF1R inhibitors such as PLX5622. A few weeks of treatment dramatically reduce the population of microglia, which will rebuild itself within a further few weeks after treatment has stopped. Researchers have observed that the new population is much less inflammatory than the old one. Researchers here note that this therapy fails to improve measures of Alzheimer's pathology in a mouse model by the end of a short ten day study - more time is required for effects to emerge.
While moderately activated microglia in Alzheimer's disease (AD) are pivotal in clearing amyloid beta (Aβ), hyperactivated microglia perpetuate neuroinflammation. Prior investigations reported that the elimination of ~80% of microglia through inhibition of the colony-stimulating factor 1 receptor (CSF1R) during the advanced stage of neuroinflammation in 5xFamilial AD (5xFAD) mice mitigates synapse loss and neurodegeneration. Furthermore, prolonged CSF1R inhibition diminished the development of parenchymal plaques. Nonetheless, the effects of short-term CSF1R inhibition during the early stages of neuroinflammation on residual microglia are unknown. Therefore, we investigated the effects of 10-day CSF1R inhibition using PLX5622 in three-month-old female 5xFAD mice, a stage characterized by the onset of neuroinflammation and minimal Aβ plaques.
We observed ~65% microglia depletion in the hippocampus and cerebral cortex. The leftover microglia displayed a noninflammatory phenotype with reduced NLRP3 inflammasome complexes. Moreover, plaque-associated microglia were reduced with diminished Clec7a expression. Additionally, phosphorylated S6 ribosomal protein and the protein sequestosome 1 analysis suggested reduced mechanistic targets of rapamycin (mTOR) signaling and autophagy in microglia and neurons within the hippocampus and cerebral cortex. Biochemical assays validated the inhibition of NLRP3 inflammasome activation, decreased mTOR signaling in the hippocampus and cerebral cortex, and enhanced autophagy in the hippocampus. However, short-term CSF1R inhibition did not influence Aβ plaques, soluble Aβ-42 levels, astrocyte hypertrophy, or hippocampal neurogenesis.
Thus, short-term CSF1R inhibition during the early stages of neuroinflammation in 5xFAD mice promotes the retention of homeostatic microglia with diminished inflammasome activation and mTOR signaling, alongside increased autophagy.
Link: https://doi.org/10.1111/acel.14398
View the full article at FightAging
