Chrysin reprograms microglial metabolism and function via targeting SYK to alleviate the symptoms of Alzheimer's disease.

Alpiniae Oxyphyllae Fructus, first documented in Bencao Shiyi, is a classical traditional Chinese herb traditionally used to warm the kidney, invigorate the spleen, consolidate essence and relieve chronic diarrhea. Guided by the TCM theory that kidney essence nourishes brain marrow, modern studies have confirmed its notable neuroprotective and anti-neuroinflammatory activities. Neuroinflammation is a key pathological hallmark of Alzheimer's disease (AD), and spleen tyrosine kinase (SYK) serves as a critical signaling regulator. Our previous work confirmed that Alpiniae Oxyphyllae Fructus extract (AE) exerts notable neuroprotection; nevertheless, its blood-brain barrier-permeable components and detailed mechanisms remain poorly clarified. The purpose of this study is to identify the main active components in AE and clarify its mechanism of improving AD pathology by regulating the SYK signaling pathway. A preliminary dose-finding study with two AE doses (180 mg/kg, 360 mg/kg) was performed via open field test and inflammatory indexes to select the optimal dose for subsequent experiments. Behavioral assays assessed AE-related neurobehavioral improvements. LC-QTOF-MS/MS identified brain-permeable components, while network pharmacology combined with GEO database analysis screened potential targets and underlying mechanisms. Molecular docking was applied to filter SYK-binding candidates, further validated by molecular dynamics simulation and Cellular thermal shift assay (CETSA). In vivo, a piceatannol-induced SYK inhibition model was established to verify whether the candidate component alleviated LPS-triggered behavioral deficits in mice in a SYK-dependent manner. In vitro, BV2 microglia were used to detect microglial polarization, Aβ phagocytosis and migration through qRT-PCR, glucose/ATP/lactate measurement, wound healing assay and immunofluorescence staining. Chrysin was identified as the primary brain-permeable constituents targeting SYK. In AD mice, it significantly ameliorated cognitive deficits and reduced Aβ accumulation. Mechanistically, Chrysin modulated the SYK/BTK/PLCγ2 and NF-κB axes to trigger a microglial M1-to-M2 phenotypic shift. This phenotypic transition is accompanied by metabolic reprogramming-shifting from glycolysis to oxidative phosphorylation, thereby notably enhancing microglial migration capacity and Aβ phagocytosis. These neuroprotective effects were confirmed to be SYK-dependent. Chrysin is the primary brain-permeable constituent of AE. that targets SYK to restore microglial metabolic homeostasis, offering a promising therapeutic strategy for AD.