Study on the role of Dihuang Yinzi in regulating the AMPK/SIRT1/PGC-1α pathway to promote mitochondrial biogenesis and improve Alzheimer's disease

Ethnopharmacological relevance: Dihuang Yinzi (DHYZ) is a classic prescription in traditional Chinese medicine. Its therapeutic effect on Alzheimer's disease (AD) has been widely validated. However, the underlying molecular mechanisms of DHYZ in AD treatment remain unclear and require further research. Aim of the study: Elucidating DHYZ's promotion of mitochondrial biogenesis through the AMPK/SIRT1/PGC-1 alpha pathway improves neuronal loss, mitochondrial damage, and memory deficits in AD. Materials and methods: Administering DHYZ by gavage to SAMP8 mice, after completing behavioral tests, the effects of DHYZ on hippocampal neuron loss and mitochondrial structural damage in AD model mice were assessed using Nissl staining and transmission electron microscopy. Western blot was used to detect the expression of mitochondrial biogenesis-related proteins PGC-1 alpha, CREB, mitochondrial fusion protein MFN2, and mitochondrial fission proteins DRP1 and FIS1. At the same time, immunofluorescence (IF) was employed to measure the relative fluorescence intensity of mitochondrial fusion protein MFN1. After determining the optimal dose of DYHZ for treating AD, we conducted mechanistic studies. By intraperitoneally injecting SAMP8 mice with the AMPK inhibitor (Compound C) to inhibit AMPK protein expression and subsequently treating them with DHYZ, the impact of DHYZ on hippocampal neurons in AD model mice was evaluated using Nissl and hematoxylin-eosin staining. Western blot was used to detect the protein expression of AMPK, p-AMPK, SIRT1, PGC-1 alpha, NRF1, and TFAM. In contrast, IF was used to measure the relative fluorescence intensity of PGC-1 alpha, NRF1, and TFAM proteins in the hippocampal CA1 region. Results: DHYZ significantly improved AD model mice's cognitive impairment and memory deficits and mitigated hippocampal neuron loss and degeneration. Additionally, it ameliorated mitochondrial morphological structures. DHYZ upregulated the protein expression of mitochondrial biogenesis-related proteins PGC-1 alpha, CREB, and mitochondrial fusion proteins MFN1 and MFN2 while inhibiting the expression of mitochondrial fission proteins DRP1 and FIS1. Further studies revealed that DHYZ could upregulate the expression of the AMPK/SIRT1/PGC-1 alpha pathway proteins and their downstream proteins NRF1 and TFAM. Conclusion: DHYZ promotes mitochondrial biogenesis by activating the AMPK/SIRT1/PGC-1 alpha signaling pathway, thereby improving memory deficits, neuronal loss, and mitochondrial dysfunction in AD.