Porphyromonas gingivalis disrupts hippocampal circadian clock via PI3K/AKT pathway, exacerbating Alzheimer‐like pathology

INTRODUCTION Periodontal pathogen Porphyromonas gingivalis is epidemiologically linked to Alzheimer's disease (AD), yet how oral infection disrupts the central circadian clock to drive hippocampal neurodegeneration remains unknown. METHODS C57BL/6 mice received oral P. gingivalis for 6 months; hippocampal clock gene oscillations, phosphorylated protein kinase B (p‐AKT), glial fibrillary acidic protein (GFAP)/Ionized calcium‐binding adapter molecule 1 (Iba1), and amyloid beta (Aβ) load were quantified. C8‐D1A astrocytes and BV2 microglia were infected with P. gingivalis ± phosphatidylinositol 3‐kinase/protein kinase B (PI3K/AKT inhibitor or agonist; Bmal1 (brain and muscle ARNT‐like 1)/ Clock (circadian locomotor output cycles kaput) were knocked down by lentivirus. RESULTS P. gingivalis ‐induced periodontitis dampened hippocampal Bmal1 rhythms, lowered p‐AKT, activated glia, and elevated Aβ and interleukin 1β (IL‐1β). In glial cells, P. gingivalis flattened Bmal1 oscillation; PI3K blockade mimicked these effects, whereas AKT agonist restored rhythms and suppressed GFAP/Iba1/IL‐1β. Bmal1 knockdown alone triggered glial activation and cytokine release. DISCUSSION P. gingivalis oral infection suppresses PI3K/AKT signaling, destabilizing glial circadian clocks and unleashing neuroinflammation that fosters hippocampal AD‐like pathology; rescuing PI3K/AKT or clock function may mitigate the oral–brain axis in AD.