Effects of Red Liriope platyphylla on NGF secretion ability, NGF receptor signaling pathway and γ-secretase components in NSE/hAPPsw transgenic mice expressing Alzheimer's Disease

Abstract

Liriope platyphylla (LP) has long been regarded as a curative herb for the treatment of diabetes, asthma, and neurodegenerative disorders. To examine the therapeutic effects of Red LP (RLP) manufactured by steaming process on neurodegenerative disorders, significant alteration of the key factors influencing Alzheimer's Disease (AD) was detected in NSE/hAPPsw transgenic (Tg) mice after RLP treatment. The concentration of nerve growth factor (NGF) in serum increased in RLP-treated NSE/hAPPsw Tg mice compared with vehicle-treated Tg mice. However, downstream effectors of the NGF receptor signaling pathway, including TrkA and p75(NTR) proteins, were suppressed in RLP-treated NSE/hAPPsw Tg mice. Especially, Tg mice showed decreased levels of TrkA, p75(NTR), and RhoA expression. Production of Aβ-42 peptides was lower in RLP-treated NSE/hAPPsw Tg mice than in vehicle-treated Tg mice. Further, analysis of γ-secretase components showed that Aβ-42 peptide expression was downregulated. Of the four components, the expression of APH-1 and Nicastrin (NCT) decreased in RLP-treated NSE/hAPPsw Tg mice, whereas expression of PS-2 and Pen-2 was maintained or increased within the same group. Overall, these results suggest that RLP can help relieve neurodegenerative diseases, especially AD, through upregulation of NGF secretion ability, activation of NGF signaling pathway, downregulation of Aβ-42 peptide deposition, and alteration of γ-secretase components.

Keywords: Aβ-42; NGF; NGF signaling pathway; Red L. platyphylla; γ-secretase.

Figure 1

Identification of Tg mice and NGF secretion. (A) pNSE/hAPPsw harbors the encoding hAPPsw gene under control of the NSE promoter. In the identification of Tg mice, PCR was performed on genomic DNA isolated from tails of founder mice, and the resulting products (512-bp) are shown. (B) NGF concentration in blood serum of NSE/hAPPsw Tg mice was measured using an anti-NGF ELISA kit. Data are reported as the mean±SD of three experiments. ^*P<0.05 is the significance level relative to vehicle-treated group.

Figure 2

Effects of RLP on downstream signaling pathway of NGF receptor, including (A) TrkA signaling pathway and (B) p75^NTR signaling pathway. Total cell lysates were prepared from brain cortex of NSE/hAPPsw Tg mice treated with vehicle or RLP as described in the Materials and Methods. Fifty micrograms of protein per sample was immunoblotted with antibodies for each protein. Three samples were assayed in triplicate by Western blotting. Data are reported as the mean±SD. ^*P<0.05 is the significance level compared to cells treated with vehicle.

Figure 3

Effects of RLP on production of Aβ-42 peptides. Immunostaining analysis of Aβ-42 peptide accumulation. Production of Aβ-42 peptides in brains of 10-month-old NSE/hAPPsw Tg mice was detected by immunostaining (A), dot blot assay (B), and Aβ-42 ELISA assay (C). In immunostaining analysis, low intensity was observed in the hippocampus (CA1-3) and DG of RLP-treated NSE/hAPPsw Tg mice (Ae), as compared with vehicle-treated mice (Aa), at 200× magnification. Detailed histological features of several regions of the hippocampus are shown in three rectangles at 400× magnification (Ab-d and f-h). Left column of Aβ-42 ELISA assay shows the correlation between optical density at 450 nm and concentration of Aβ-42 peptides. Data are reported as the mean±SD. ^*P<0.05 is the significance level compared to mice treated with vehicle.

Figure 4

Expression of γ-secrease components in brain cortex of NSE/hAPPsw Tg mice. Cortex region was prepared from brain tissues of vehicle- and RLP-treated Tg mice. Fifty micrograms of protein per sample was immunoblotted with antibody for each protein. Expression levels of the four γ-secretase components were measured with specific antibody and horseradish peroxidase-conjugated goat anti-rabbit IgG, as described in the Materials and Methods section. The intensity of each protein was calculated using an imaging densitometer. Data are reported as the mean±SD from three replicates. ^*P<0.05 is the significance level compared to the vehicle-treated group.