Advanced Optical Microscopic Imaging Techniques for Imaging Amyloid Beta and Deciphering Alzheimer's Disease Pathogenesis

Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive decline in cognitive functions. Given that AD undermines the quality of life for millions and has an extended asymptomatic period, exploring the full AD pathogenesis and seeking the optimal therapeutic solution have become critical and imperative. This allows researchers to intervene, delay, and potentially prevent AD progression. Several clinical imaging methods are utilized routinely to diagnose and monitor AD, such as magnetic resonance imaging (MRI), functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and single photon emission computed tomography (SPECT). Nevertheless, due to their intrinsic drawbacks and restrictions, such as radiation concerns, high cost, long acquisition time, and low spatial resolution, their applications in AD research are limited, especially at the cellular and molecular levels. In contrast, optical microscopic imaging methods overcome these limitations, offering researchers a variety of approaches with distinct advantages to explore AD pathology on diverse models. In this review, we provide a comprehensive overview of commonly utilized optical microscopic imaging techniques in AD research and introduce their contributions to image amyloid beta (Aβ) species. These techniques include fluorescence microscopy (FM), confocal microscopy (CM), two-photon fluorescence microscopy (TPFM), super-resolution microscopy (SRM), expansion microscopy (ExM), and light-sheet fluorescence microscopy (LSFM). In addition, we introduce some related topics, such as the development of near-infrared (NIR) Aβ probes, the Aβ plaque hypothesis, and Aβ oligomer hypothesis, and the roles of microglia and astrocytes in AD progression. We believe optical microscopic imaging methods continue to play an indispensable role in deciphering the full pathogenesis of AD and advancing therapeutic strategies.