Ginsenoside Compound K Inhibits Complement C1qA/C3-CR3-Mediated Microglial Synaptic Pruning and Neuronal Pyroptosis

Ginseng (Panax ginseng C.A. Meyer), a classic traditional Chinese medicine, has long been used for "calming the mind and enhancing intelligence" to combat cognitive decline. Its major metabolite, ginsenoside compound K (CK), exerts neuroprotection, but the molecular mechanisms against Alzheimer's disease (AD) remain unclear.

This study investigated the molecular mechanism by which CK attenuates microglial aberrant synaptic phagocytosis and neuronal pyroptosis via inhibiting the complement C1qA cascade.

APP/PS1 mice were used as AD models and treated with CK (20 or 40 mg/kg/d) or memantine (MH, 3 mg/kg/d) by gavage once daily for 14 weeks. Morris water maze and open field tests were used to assess cognitive function and anxiety-like behavior, respectively. HE, Nissl and Golgi staining detected neuronal damage and synaptic integrity. Immunofluorescence and ELISA measured microglial polarization, activation and synaptic phagocytosis. Molecular docking and dynamics simulations analyzed the CK-C1qA interaction. Western blot, immunofluorescence and ELISA detected complement components (C1qA, C3, CR3) and pyroptosis-related proteins (NF-κB, NLRP3, ASC, caspase-1, GSDMD-N, IL-18). In vitro cellular experiments, including BV2 cell monoculture and BV2-HT22 transwell co-culture systems, were further performed to validate the causal role of C1qA.

CK improved cognitive and anxiety behaviors in APP/PS1 mice, attenuated hippocampal neuronal damage, increased Nissl-positive neurons, restored dendritic complexity and spine density, and upregulated PSD95 and SYP. CK induced microglial M1-like-to-M2-like polarization and reduced Iba1⁺/CD68⁺ microglia colocalization with PSD95⁺ synapses, indicating suppressed synaptic engulfment. CK was predicted to bind to the C1qA globular head domain, reduced C1qA deposition at synapses, inhibited C3, and CR3 expression, suppressed NF-κB phosphorylation, downregulated NLRP3, ASC, cleaved-caspase-1, and GSDMD-N, decreased IL-18 release, and alleviated neuronal pyroptosis. In vitro, CK suppressed C1qA expression in BV2 cells and reduced synaptic C1qA deposition in HT22 cells.

CK ameliorated cognitive and synaptic deficits in APP/PS1 mice by inhibiting the C1qA/C3-CR3 pathway to suppress aberrant microglial synaptic phagocytosis and blocking NF-κB/NLRP3/GSDMD-mediated neuronal pyroptosis. These findings elucidate CK's neuroprotective mechanisms and provide scientific evidence for ginseng's traditional cognitive benefits.