Effects of Intracerebroventricular Administration of Colony Stimulating Factor 1 Receptor Inhibitor on Microglia

Abstract

BackgroundMicroglia play an important role in innate immunity in the brain and are suggested to be involved in the pathogenesis of cardiovascular diseases, as well as neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Colony stimulating factor 1 (CSF1) regulates the proliferation, differentiation, and survival of microglia and macrophages. Although previous studies have demonstrated that repeated oral administration of a CSF1R inhibitor PLX3397 leads to microglia elimination, systemic administration of PLX3397 affects also peripheral macrophages. Therefore, to establish a method for selective elimination of microglia is needed in order to investigate the roles of microglia independently from peripheral macrophages particularly in systemic diseases, such as cardiovascular diseases. In this study, we evaluated the effects of intracerebroventricular administration of PLX3397 on microglia.Methods and ResultsWe intracerebroventricularly injected PLX3397 (0.45mg/kg) in male 9‐week‐old Wistar‐Hannover rats and collected their brains on 1, 2 and 4 days after administration. Rats without PLX3397 treatment were used as control. We evaluated microglia in hypothalamic paraventricular nucleus, an important nucleus for cardiovascular control, by immunohistochemistry using anti‐Iba1 antibody. The number of microglia was decreased on 1 day after administration (Day 1) and was almost restored to control on Day 4 (control, 32.5±0.8/HPF, n=6; Day 1, 25.8±1.1/HPF, n=2; Day 2, 27.0±1.0/HPF, n=2; Day 4, 31.5±1.5/HPF, n=1). Morphological analyses of surviving microglia revealed a smaller cell size and an increased circularity (cell perimeter: control, 1282±70 μm; Day 1, 758±6 μm; Day 2, 850±30 μm; Day 4, 940±50 μm, cell area: control, 1049±35 μm2; Day 1, 700±35 μm2; Day 2, 798±50 μm2; Day 4, 838±51 μm2, circularity: control, 0.0087±0.00089; Day 1, 0.0174±0.00029; Day 2, 0.0159±0.00041; Day 4, 0.0134±0.0011), which are typically observed in activated microglia, in the PLX3397‐treated rats. These morphological changes tended to be restored as the time elapsed after the PLX3397 administration.Conclusion and PerspectivesSingle intracerebroventricular injection of CSF1R inhibitor PLX3397 reduced the number of microglia. However, the degree of microglial reduction was small and the effect was transient. Multiple injections or continuous infusion of PLX3397 intracerebroventricularly will be needed to robustly eliminate microglia. Further, it should be clarified whether the PLX3397‐induced morphological changes of microglia are resulted from microglial activation or process of microglial apoptosis.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.