Aloe-emodin attenuated Aβ-induced tau phosphorylation by autophagy-NLRP3 inflammasome pathway

Anthraquinone derivative aloe-emodin, extracted from Chinese herbs has been confirmed with various pharmacological effects, including anti-inflammatory and neuroprotective properties, particularly in Alzheimer's disease, but the exact mechanism of action remains unclear.

In this study, the PC12 cells were induced by amyloid β-protein (Aβ) to establish an in vitro model of Alzheimer's disease. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide, 5-ethynyl-2'-deoxyuridine staining, transmission electron microscopy, real-time quantitative PCR, western blot, ELISA, coimmunoprecipitation (Co-IP), and immunofluorescence were employed to evaluate effect of aloe-emodin on the survival and expression of related genes and proteins in PC12 cells induced by Aβ.

We found that 5 μM aloe-emodin significantly enhanced cell survival and proliferation. It also increased the mRNA and protein expression of Beclin-1 and LC3II, while decreasing the mRNA expression of P62, PI3K, AKT, mechanistic target of rapamycin (mTOR), NOD-like receptor protein 3 (NLRP3), and caspase-1, as well as the protein expression of P62, NLRP3, cleaved-caspase-1, p-PI3K, p-AKT, p-mTOR, interleukin-18 (IL-18), and IL-1β. Additionally, aloe-emodin reduced the intensity of p-tau fluorescence. The Co-IP results demonstrated a direct interaction between NLRP3 and LC3. Interestingly, aloe-emodin exhibited effects comparable to those of RAPA, an mTOR inhibitor.

These findings demonstrate that aloe-emodin offers neuroprotective benefits by reducing NLRP3-mediated inflammation and promoting autophagy, thereby providing a novel perspective on the treatment of Alzheimer's disease.