Loganin alleviated cognitive impairment in 3×Tg-AD mice through promoting mitophagy mediated by optineurin

Corni Fructus is a traditional Chinese herb and widely applied for treatment of age-related disorders in China. Iridoid glycoside was considered as the active ingredient of Corni Fructus. Loganin is one of the major iridoid glycosides and quality control components of Corni Fructus. Emerging evidence emphasized the beneficial effect of loganin on neurodegenerative disorders, such as Alzheimer's disease (AD). However, the detailed mechanism underlying the neuroprotective action of loganin remains to be unraveled.

To explore the improvement of loganin on cognitive impairment in 3 × Tg-AD mice and reveal the potential mechanism.

Eight-month 3 × Tg-AD male mice were intraperitoneally injected with loganin (20 and 40 mg/kg) for consecutive 21 days. Behavioral tests were used to evaluated the cognition-enhancing effects of loganin, and Nissl staining and thioflavine S staining were performed to analyze neuronal survival and Aβ pathology. Western blot analysis, transmission electron microscopy and immunofluorescence were utilized to explore the molecular mechanism of loganin in AD mice involved mitochondrial dynamics and mitophagy. Aβ_25-35-induced SH-SY5Y cells were applied to verify the potential mechanism in vitro.

Loganin significantly mitigated the learning and memory deficit and amyloid β-protein (Aβ) deposition, and recovered synaptic ultrastructure in 3 × Tg-AD mice. Perturbed mitochondrial dynamics characterized by excessive fission and insufficient fusion were restored after loganin treatment. Meanwhile, loganin reversed the increase of mitophagy markers (LC3II, p62, PINK1 and Parkin) and mitochondrial markers (TOM20 and COXIV) in hippocampus of AD mice, and enhanced the location of optineurin (OPTN, a well-known mitophagy receptor) to mitochondria. Accumulated PINK1, Parkin, p62 and LC3II were also revealed in Aβ_25-35-induced SH-SY5Y cells, which were ameliorated by loganin. Increased OPTN in Aβ_25-35-treated SH-SY5Y cells was further upregulated by loganin incubation, along with the reduction of mitochondrial ROSand elevation ofmitochondrial membrane potential (MMP). Conversely, OPTN silence neutralized the effect of loganin on mitophagy and mitochondrial function, which is consistent with the finding that loganin presented strong affinity with OPTN measured by molecular docking in silico.

Our observations confirmed that loganin enhanced cognitive function and alleviated AD pathology probably by promoting OPTN-mediated mitophagy,. Loganin might be a potential drug candidate for AD therapy via targeting mitophagy.