Involvement of Mas in Neuroinflammation

Abstract

Alzheimer’s disease (AD) is a neurodegenerative disease that is characterized by cognitive decline in memory and behavior. Targeting the common pathologies associated with AD (amyloid-beta (Aβ) plaques and intraneuronal neurofibrillary tangles (NFTs)) have yielded little success in improving cognition in AD patients. Research has turned to exploration of other AD pathologies, including neuroinflammation caused by chronically activated microglia. In the following studies, decreasing microglial activation through modulation of the anti-inflammatory Mas receptor of the Renin-Angiotensin system (RAS) in the brain was explored. First, using an AD mouse model, mice were treated with Mas receptor agonists (the native ligand angiotensin (1-7), in addition to two small molecules, RASRx1902 and RASRx1911). Expression of hippocampal RAS receptors and microglial activation markers was explored using RT-qPCR. Mas receptor expression was found to be positively correlated to expression of both the pro-inflammatory RAS receptor At1r-1b and the microglial activation marker Cd68. Cd68 expression was negatively correlated to novel object recognition (NOR) score. These results indicate a possible relationship among Mas receptor expression, microglial activation, and cognition that will be explored further in future studies. Next, the HMC3 cell line was used as an in vitro model of human microglia, and the resting and activated states of the cells were characterized by measuring the microglial activation markers CD68, HLA-DR, CD11b, reactive oxygen species, and cell size. After activating the cells with IFN-gamma, they were treated with RASRx1902 and a significant decrease in microglial activation occurred. These results indicate that RASRx1902 might be effective in decreasing neuroinflammation caused by microglial activation in AD. Lastly, in preparation for future experiments to study signaling pathways modulated by the Mas agonists, efforts to overexpress the Mas receptor in cell lines were made. CHO-K1 cells were transfected with human Mas, and the cells were selected with an antibiotic and cloned. Using RT-qPCR, it was found that the cells overexpressed human Mas RNA; however, when cells were stained with antibodies and viewed with flow cytometry, immunofluorescence imaging, and western blot, no protein was found. Current work on overexpressing the Mas receptor in HMC3 cells is also described. Overall, it was found that decreasing microglial activation using Mas receptor agonists has promise to be an effective treatment of neuroinflammation in AD.