Study on the quality evaluation of Yuye decoction and demonstration of aquaporin 9 down-regulation in a transgenic mouse model of Alzheimer's disease associated with beta-amyloid toxicity

Abstract

Alzheimer's disease (AD) is a progressive and irreversible brain disease characterized by progressive cognitive dysfunction. Diabetes mellitus (DM) and its complications are major risk factors in the pathology of AD, and increase AD 1.5-2-fold, regretfully the mechanism has not been well elucidated. Aquaporins (AQPs) are a family of water-selective transporting proteins increasing serum membrane water permeability in various kinds of secretory and absorptive cells. Studies reported that there is a close association between AQP9 and glucose control via the insulin-signaling pathway. The neuronal AQP9 expression was almost exclusively observed in catecholaminergic cells and involved in many cerebral functions. However, the role of AQP9 in the pathogenesis of AD is still undisclosed.

Yuye Decoction (YYD) has long been used for treating DM and its complications. The complex composition makes it difficult to assure the quality of YYD during its long-term clinical use, therefore a practical approach requires to be established to do the quality evaluation of YYD based on both chemical and bioactive markers. In the present project, research focus was drawn on the link between DM and AD pathogenesis, in which AQP9 may be involved and the traditional Chinese prescription YYD may generate potential effect.

First of all, the chemical fingerprint profile of self-made YYD water extract was established by using HPLC/UV and UHPLC-QTOP methods. As a result, 21 compounds were identified in YYD extracts. Particularly, a MEKC method based on the temperature-correlated mobility theory was applied to better analyze lignans from YYD and its compositions. Secondly, the intestinal absorption and brain distribution of YYD components were determined to screen out bioactive components as biomarkers. Thirdly, the anti-diabetic effect of YYD was verified in HepG2 cell model in vitro and STZ-induced diabetic rat model in vivo, results also indicated that the cognitive decline in diabetic rats may be associated with the alteration of the expression of AQP9, APP (Amyloid precursor protein) and BDNF (Brain-derived neurotrophic factor) in the hippocampus and cerebral cortex of the brain. Finally, an age-associated decrease of AQP9 expression was demonstrated in both hippocampus and cerebral cortex from an APPswe/PS1dE9 (Tg) mouse model of AD at 3, 6 and 10 months for the first time. Consistently, a dose-dependent downregulation of AQP9 expression in PC12 cells was observed after treatment with Aβ1-40, and pre-treatment with AQP9 siRNA led to a much more severe neurotoxicity in PC 12 cells in response to Aβ1-40 associated with the alteration of BDNF and APP expression and apoptosis. Collectively, the aforementioned results suggest that AQP9 may play an important role in the shared pathology of DM and AD and may serve as a therapeutic target.