Rg1 improves Alzheimer's disease by regulating mitochondrial dynamics mediated by the AMPK/Drp1 signaling pathway

Ethnopharmacological relevance: Alzheimer's disease (AD) is the most prevalent form of dementia, characterized by a complex pathogenesis that includes Aβ deposition, abnormal phosphorylation of tau protein, chronic neuroinflammation, and mitochondrial dysfunction. In traditional medicine, ginseng is revered as the 'king of herbs'. Ginseng has the effects of greatly tonifying vital energy, strengthening the spleen and benefiting the lungs, generating fluids and nourishing the blood, and calming the mind while enhancing intelligence. Ginsenoside Rg1 (Rg1) is a well-defined major active component found in ginseng, known for its relatively high content. It has been demonstrated to exhibit neuroprotective effects in both in vivo and in vitro models, capable of ameliorating Aβ and tau pathology, regulating synaptic function, and reducing inflammation, oxidative stress, and apoptosis. However, the potential of Rg1 to improve AD pathology through the regulation of mitochondrial dynamics is still uncertain.

Aim of the study: Despite the active research efforts on drugs for AD, the currently available anti-AD medications can only slow disease progression and manage symptoms, yet unable to provide a cure for AD. Furthermore, some anti-AD drugs failed phase III and IV clinical trials due to significant side effects. Therefore, there is an urgent need to further investigate the pathogenesis of AD, to identify new therapeutic targets, and to explore more effective therapies. The aim of this study is to evaluate the potential therapeutic effects of Rg1 on APP/PS1 double transgenic mice and Aβ₄₂-induced HT22 cell models, and to investigate the potential mechanisms through which it provides neuroprotective effects.

Materials and methods: This study investigates the effects of Rg1 in treating AD on APP/PS1 double transgenic mice and Aβ₄₂-induced HT22 cells. In the in vivo experiments, APP/PS1 mice were divided into a model group, Rg1-L group, Rg1-H group, and donepezil group, with C57BL/6 mice serving as the control group (n = 12 per group). The Rg1-L and Rg1-H groups were administered Rg1 at doses of 5 mg/kg/d and 10 mg/kg/d, respectively, while the donepezil group received donepezil at a dose of 1.3 mg/kg/d. Both the control and model groups received an equal volume of physiological saline daily for 28 days. Learning and spatial memory were assessed by the Morris water maze (MWM) and novel object recognition (NOR) tests, and neuronal damage by Nissl staining. Aβ deposition was analyzed through immunohistochemistry and Western blot, while the expression levels of synaptic proteins PSD95 and SYN were evaluated via immunofluorescence staining and Western blot. The dendritic spines of neurons was observed by Golgi staining.The ultrastructure of neuronal mitochondria and synapses was examined by transmission electron microscopy (TEM). Mitochondrial function was assessed through measurements of Reactive oxygen species (ROS), Superoxide Dismutase (SOD), and Adenosine Triphosphate (ATP), and Western blot analysis was performed to detect the expression levels of AMPK, p-AMPK, Drp1, p-Drp1, OPA1, Mfn1, and Mfn2, thereby investigating the protective effects of Rg1 on mitochondrial dysfunction and cognitive impairment in APP/PS1 double transgenic mice. In vitro experiments, HT22 cells were treated with Aβ₄₂ of 10 μM for 24 h to verify the therapeutic effects of Rg1. Flow cytometry was used to detect ROS and JC-1, biochemical methods were employed to measure SOD and ATP, immunofluorescence staining was used to detect the expression levels of PSD95 and SYN, and Western blot analysis was conducted to elucidate its potential mechanisms of action.

Results: The findings suggest that after 28 days of Rg1 treatment, cognitive dysfunction in APP/PS1 mice was improved. Pathological and immunohistochemical analyses demonstrated that Rg1 treatment significantly reduced Aβ deposition and neuronal loss. Rg1 can improve synaptic dysfunction and mitochondrial function in APP/PS1 mice. Rg1 activated AMPK, enhanced p-AMPK expression, inhibited Drp1, and reduced p-Drp1 levels, which led to increased expression of OPA1, Mfn1, and Mfn2, thereby inhibiting mitochondrial fission and facilitating mitochondrial fusion. Additionally, Rg1 effectively reversed the decrease in mitochondrial membrane potential (MMP) and the increase in ROS production induced by Aβ₄₂ in HT22 cells, restoring SOD and ATP levels. Furthermore, Rg1 regulated mitochondrial fission mediated by the AMPK/Drp1 signaling pathway, promoting mitochondrial fusion and improving synaptic dysfunction.

Conclusion: Our research provides evidence for the neuroprotective mechanisms of Rg1 in AD models. Rg1 modulates mitochondrial dynamics through the AMPK/Drp1 signaling pathway, thereby reducing synaptic and mitochondrial dysfunction in APP/PS1 mice and AD cell models.