Amphiphysin-1 protein level changes associated with tau-mediated neurodegeneration

Abstract

Tauopathies are a family of neurodegenerative diseases that have the pathological hallmark of intraneuronal accumulation of filaments composed of hyperphosphorylated tau proteins that tend to aggregate in an ultrastructure known as neurofibrillary tangles. The identification of mutations on the tau gene in familial cases of tauopathies underscores the pathological role of the tau protein. However, the molecular process that underlines tau-mediated neurodegeneration is not understood. Here, a proteomics approach was used to identify proteins that may be affected during the course of tau-mediated neurodegeneration in the tauopathy mouse model JNPL3. The JNPL3 mice express human tau proteins bearing a P301L mutation, which mimics the neurodegenerative process observed in humans with tauopathy. The results showed that the protein amphiphysin-1 (AMPH1) is significantly reduced in terminally ill JNPL3 mice. Specifically, the AMPH1 protein level is reduced in brain regions known to accumulate aggregates of hyperphosphorylated tau proteins. The AMPH1 protein reduction was validated in Alzheimer's disease cases. Taken together, the results suggest that the reduction of the AMPH1 protein level is a molecular event associated with the progression of tau-mediated neurodegeneration.

Fig. 1

Amphiphysin-1 (AMPH1) protein level is reduced in the JNPL3 mouse brain. (a) Two-dimensional gel electrophoresis of brainstem protein extracts from nontransgenic and JNPL3 mice. The black circle shows the same region on both gels. The arrowheads point to reference proteins indicating similar protein abundance in both gels. The ranges for pH and molecular weight are shown. (b) Western blot analysis was used to validate the identification of the protein AMPH1. Ponceau S stain shows equal loading on both nontransgenic and JNPL3 samples. Anti-AMPH1 antibodies labeled a protein band of the corresponding molecular weight (*). Tau13 antibodies specific to human tau proteins were used to confirm the sample from the transgenic JNPL3 mouse. The opened arrow indicates the hyperphosphorylated tau (64 kDa) form.

Fig. 2

The reduction in the amphiphysin-1 (AMPH1) protein level is brain region specific. Densitometry analysis was used to quantify the difference in the AMPH1 protein level. The AMPH1 protein level was corrected for loading error using the level of GAPDH protein per sample. The white and grey bars indicate the AMPH1 level in nontransgenic and JNPL3 mice, respectively. The number of mice used in the statistical analysis is indicated on the graph. Error bars are represented as ±SEM (**P=0.0067; ***P=0.0008). OD, optic density

Fig. 3

Amphiphysin-1 (AMPH1) protein level reduction in Alzheimer’s disease (AD) brain. Densitometry analysis of the results obtained from western blot analyses was carried out. The white and gray bars indicate the AMPH1/GAPDH ratio plotted as the mean value obtained from normal-aging and AD cases, respectively. Error bars are presented as ±SEM (**P=0.0069).