Info
Background:
Spatiotemporal optical imaging of tau pathology is critical for understanding Alzheimer’s disease progression and evaluating therapeutics,1 yet remains challenging due to the lack of probes that combine deep tissue penetration with high specificity for pan-tau species. While clinical modalities such as MRI and PET are routinely employed, the cost-effective and easily accessible 3D optical imaging techniques have not yet achieved widespread application.2
Hypothesis/Objective:
Building on the success of 3D chemiluminescence imaging of Aβ plaques,3 it was hypothesized that optimizing a probe’s structure to achieve both tau selectivity and near-infrared (NIR) emission would enable precise monitoring of tau pathology and tau propagation deep within the brain.
Methods:
Molecular Design Strategy: Guided by cryo-EM structures of tau filaments and POVME-based pocket analysis, a key dimensional disparity was identified: tau binding pockets are significantly larger than those of Ab.4, 5 To exploit this, a series of chemiluminescent probes, ADLumin-Xs (X = 22-24, Figure 1a), was designed featuring curved configurations to match tau protein pockets, contrasting with linear probes that fit both Ab and tau. A cyano group was strategically introduced to serve a dual function: forming a robust hydrogen bond with the pivotal Lys353 residue to enhance binding affinity, and extending electronic delocalization to induce a bathochromic shift into the NIR region (>700 nm). In vitro, ADLumin-23 showed nanomolar affinity for tau fibrils (Kd = 45 nM) and oligomers (Kd = 93 nM), with a >22-fold turn-on response and high selectivity over Ab or a-synuclein. Tissue penetration depths of up to 4 cm were achieved in biological tissues, providing a foundation for accurate 3D signal localization (Figure 1b).
Results:
Whole-brain 3D Tomographic Imaging. When combined with optimized IVIS imaging system parameters, ADLumin-23 enabled non-invasive, longitudinal monitoring of tau pathology progression from 16 to 28 weeks of age, with signal intensity correlating with disease stage. Furthermore, 3D whole-brain tomographic imaging was successfully reconstructed, allowing for the volumetric quantification of tau burden in vivo.
Longitudinal Monitoring Tau Propagation. By optimizing the IVIS DLIT algorithm for ADLumin-23’s specific emission spectrum, we achieved the first dynamic visualization of PFF-mediated tau pathology propagation in PS19 mice, capturing the spatiotemporal migration of tau aggregates from the primary injection site in the right hippocampus to contralateral brain regions over a 3-month longitudinal study (Figure 1b). To our knowledge, this represents the first report of a molecular probe capable of capturing the spatiotemporal evolution of tau pathology in vivo.
Whole-body 3D Imaging of Brains and Guts. Given the important role of the gut–brain axis in AD, we leveraged the dual-responsiveness of ADLumin-23 to tau species and reactive oxygen species (ROS) and performed whole-body 2D/3D imaging simultaneously across various cohorts, including rTg4510, PS19 models, drug-treated mice and their respective controls. These studies not only confirmed that the cerebral signals primarily originate from tau expression rather than elevated ROS levels, but also provide direct visual evidence for the interaction along the gut-brain axis, revealing that cerebral tau pathology significantly correlates with elevated intestinal oxidative stress (Figure 1b).
Conclusion:
Collectively, this work establishes ADLumin-23 as a powerful molecular probe for spatiotemporal monitoring of tau pathology, offering new avenues for early diagnosis, mechanistic investigation of prion-like propagation, and longitudinal assessment of therapeutic interventions in tauopathies, and exploration of the pathological contribution of the brain-gut axis in disease models.
Image/Figure:
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Image/Figure Caption:
Figure 1. Schematic diagram of tau probe design and in vivo imaging application. a) Strategic flow chart for design chemiluminescent probes to achieve near-infrared emission and tau-specificity via integrating POVME-assisted quantitative structural analysis, configurational modulation, and atomic-level affinity optimization. b) Schematic illustration of ADLumin-23 for whole-body 3D imaging and dynamic 3D imaging of tau pathology and propagation in the mouse brain, and brain-gut axis in mouse models. Cartoon icons of mice and organs were created in BioRender (biorender.com) using a paid subscription license.
Author
Zhiyong Jiang
MGH/Harvard