LRRK2 deficiency mitigates amyloid β deposition-mediated pathology in a murine Alzheimer’s disease model by reprogramming microglia

Leucine-rich repeat kinase 2 (LRRK2), primarily expressed in microglia, is responsible for the modulation of innate immune responses and associated with various immunological disorders. Available evidence documents that though as the predominant etiological factor for familial Parkinson’s disease, LRRK2 mutations rarely occur in Alzheimer’s disease (AD) and that LRRK2 polymorphism is potentially associated with late-onset AD. However, the role of LRRK2 in AD immunopathogenesis remains unknown. In this study, we investigated the impact of LRRK2 deficiency on cognitive function, Aβ plaque accumulation, and plaque-associated neuropathology in AD mice. The results revealed that compared with the 5xFAD mice, the 8-month-old 5xFAD;LRRK2-/- mice reported improved learning and memory, reduced cerebral and hippocampal Aβ plaque burden, and decreased microglia and astrocytes within the central region of hippocampal Aβ plaques. The 5xFAD;LRRK2-/- mice also showed a decrease in several complement and proinflammatory cytokines in the brain, indicating an altered microglial phenotype. Furthermore, the absence of LRRK2 prevented synaptic loss and restored the disrupted equilibrium between excitatory and inhibitory synapses in the 5xFAD mice. These findings suggest that LRRK2 may play an essential role in Aβ plaque pathology, glial responses to plaques, and neuronal dysfunction in the brain of the 5xFAD mice and that a genomic transgene-blockade of LRRK2 may reprogram the microglial responsivity, thus mitigating the neuropathological and behavioral deficits in AD mice.