Detection, Comparative Validation And Spectral Characteristics Of Senile Plaque Autofluorescence In APP/PS1 Transgenic Mouse Model Of Alzheimer’s Disease

Alzheimer’s disease (AD) is a prevalent neurodegenerative disease which has been classically viewed as the accumulation of amyloid-β (Aβ) generated by precursor protein (APP) and formed senile plaque (SP). So SP is one of the hallmark pathological lesions in AD. Nowadays, there is no efficient way to cure AD, only a few drugs can slow disease progression to a certain extent. Therefore, early diagnosis become important for early intervention treatment.Nowadays, several traditional methods have been employed for histological demonstration of SP, such as immunohistochemistry (IHC), silver stain, Congo red stain, Thioflavine S (Th-S) stain and so on. Congo red and Th-S stain are the two major histological methods used to detect any form of SP by binding to the characteristic β-sheet conformation of SP. However, each method has it’s own disadvantages, such as low sensitivity, low specificity, complex operation, long duration and so on. While accuracy is important for neuropathological examination as well as diagnosis. So there are strong incentives to develop a sensitve, reliable, simple and easy method for detection of SP.Actually, there may be a simple and sensitive method that the SP have been shown to exhibit blue autofluorescence (Auto-F) under ultraviolet (UV) light. Since SP has been claimed to show some Auto-F (no details) in 1970, there have been several articles were published about the SP Auto-F. However, observation of the SP Auto-F was not widely used. The limitation may be mainly atributed to no details of the Auto-F has been uncovered.In order to popularize the application of the SP Auto-F, we have performed the detection, comparative validation and spectral characteristics of SP Auto-F in APP/PS1 transgenic mouse model of AD. Frozen brain slices were washed, mounted on glass slides. The unstained sections were examined using Olympus fluorescence microscope (BX-53) or laser scanning confocal microscope (LSCM) for detection of the SP Auto-F. And after that, the slices were stained or performed triple-labelling IHC of 6E10, GFAP and Ibal for comparative validation with Auto-F. Moreover, fluorescence excitation spectrum and emission spectrum of SP were imaged for understanding their optical properties and providing experimental basis for clinical diagnosis. Our results are as follows:1. The Auto-F of unstained slices of APP/PS1 transgenic mice can be induced by UV and visible light, and especially under 405nm BV, we can see compact plaques and loosed fibrous structure.2. In view of the morphology of the Auto-F regions, it was concluded that most and possibly all of these were derived from the amyloid component of SP. And the blue Auto-F under 405 nm laser positively stained with Congo red and Th-S, which show that the composition containing Aβ. And we verified that the Auto-F is based on β folding structure, which has nothing to do with DNA.3. By scanning a single plaque using a TPM, we obtained a clear excitation spectrum of the Auto-F. The excitation spectrum is broad and the peak is less than or equal to 350 nm. And blue Auto-F under 405 nm laser is strong and specific, which was clearly visible against the background fluorescence without-SP. Compared with 350 nm UV light,405 nm BV allows imaging of deeper tissue and less damage to the organization.4. We have characterized the emission spectrum of SP Auto-F by scanning a single plaque using a LSCM, the emission spectrum is broad, mainly from 420 to 550nm and peaks at about ～440 and ～465 nm. Taking advantage of the emission spectrum will be useful for disguishing DAPI-DNA complexes and backgroud fluorescence. And we found the second peaks of SP is similar to the peak of DAPI-DNA complexes (-460 nm).5. Compared with the traditional pathological detection methods, such as silver stain, Congo red stain and Th-S stain, method of Auto-F detection has absolute advantages——without staining or marking slices, we can get a clear, specific image with high resolution and high sensitive. And the operation is simple and easy as well as low cost.6. So we can use the Auto-F detection of extracellular Aβ deposition, rather than the expensive Aβ antibody.The above results show that the Auto-F detection method is simple, rapid, sensitive and specific, and can replace traditional pathological detection methods in basic research and clinical diagnosis. In addition, the AutoF of SP has a characteristic emission spectrum, which provides experimental evidence for the application of SP Auto-F detection.