Deletion of Robo4 worsens neuroinflammation in a mouse model of Alzheimer's disease.

Declines in vascular integrity are potential contributors to Alzheimer's disease (AD) as these result in increased blood-brain barrier permeability and, consequently, accelerate neuroinflammation and cognitive impairment. Roundabout guidance receptor 4 (Robo4) is primarily expressed in endothelial cells and stabilizes the vasculature, thereby potentially protecting the brain in AD. To study the effect of Robo4 on neuroinflammation and cognitive function in the context of AD, we compared Robo4 knockout and wild-type mice crossed with mice with and without AD mutations (APP/tau) from heterogeneous age and sex groups. We found that knockout of Robo4 led to greater astrocyte activation, as demonstrated by GFAP content, but this effect depended on the brain region studied. The knockout of Robo4 also led to greater activated microglia, as assessed by Iba1 content, but only in the presence of AD-related mutations. We found that AD mutations, but not Robo4 mutations, were associated with cognitive dysfunction, as measured by a nest-building test. Lastly, there was a non-statistically significant trend toward Robo4 deletion being associated with greater arterial stiffness. In summary, these results demonstrate that Robo4 impacts neuroinflammation and arterial stiffness; however, the impact on neuroinflammation is dependent on the presence/absence of AD-related mutations and the brain region examined.