Mirodenafil improves cognitive function by reducing microglial activation and blood-brain barrier permeability in ApoE4 KI mice.

Introduction: Alzheimer's disease (AD) has significant public health concerns in the aging society. AD can compromise brain function and lead to severe neurological abnormalities associated with dementia. The human Apolipoprotein E (ApoE4) gene is a strong risk factor for AD. However, comprehensive analyses and improvements of mouse models expressing ApoE4 remain largely unexplored.

Methods: ApoE4 knock-in (KI) mice were used to investigate the role of humanized ApoE4 in hippocampal histological changes and cognitive impairment. Cerebrovascular perfusion, blood-brain barrier (BBB) integrity, microgliosis, and amyloid-beta 42 (Aβ₄₂) accumulation were examined. Cognitive functions were assessed using the Morris water maze, Y-maze, and novel object recognition tests. Mirodenafil, a potent and selective phosphodiesterase 5 inhibitor (PDE5i), was orally administered to ApoE4 KI mice for 4 weeks. An in vitro BBB model and BV2 microglial cells were used to investigate endothelial permeability and inflammation.

Results: ApoE4 KI mice exhibited not only reduced cerebrovascular perfusion and CLN-5 expression but also increased microgliosis and Aβ₄₂ accumulation in the hippocampus. These phenomena were accompanied by impaired cognitive functions. Mirodenafil administration reversed the histological and behavioral alterations induced by ApoE4 KI. In vitro, mirodenafil treatment mitigated Aβ₄₂-induced endothelial permeability and lipopolysaccharide-induced microglial inflammation.

Discussion: These findings suggest that mirodenafil enhances cerebrovascular function, preserves BBB integrity, and mitigates neuroinflammation in ApoE4 KI mice, leading to cognitive improvement. PDE5 inhibition may serve as a promising therapeutic approach for addressing ApoE4-associated cerebrovascular and cognitive dysfunction.