Photostimulation of lymphatic clearance of β-amyloid from mouse brain: a new strategy for the therapy of Alzheimer's disease

Abstract

Alzheimer's disease (AD) is an age-related neurodegenerative disorder that poses a significant burden on socio-economic and healthcare systems worldwide. However, the currently available therapy of AD is limited, and new strategies are needed to enhance the clearance of β-amyloid (Aβ) protein and improve cognitive function. Photobiomodulation (PBM) is a non-invasive and effective therapeutic method that has shown promise in treating various brain diseases. Here, we demonstrate that 1267-nm PBM significantly alleviates cognitive decline in the 5xFAD mouse model of AD and is safe as it does not induce a significant increase in cortical temperature. Moreover, with the combination of 3D tissue optical clearing imaging and automatic brain region segmentation, we show that PBM-mediated reductions of Aβ plaques in different subregions of prefrontal cortex and the hippocampus are different. The PBM-induced lymphatic clearance of Aβ from the brain is associated with improvement of memory and cognitive functions in 5xFAD mice. Our results suggest that the modulation of meningeal lymphatic vessels (MLVs) should play an important role in promoting Aβ clearance. Collectively, this pilot study demonstrates that PBM can safely accelerate lymphatic clearance of Aβ from the brain of 5xFAD mice, promoting improvement of neurocognitive status of AD animals suggesting that PBM can be an effective and bedside therapy for AD.

Keywords: Alzheimer’s disease; Amyloid-β clearance; Meningeal lymphatic vessels; Photostimulation.

Fig. 1

Experimental design. The male 5xFAD mice were subjected to PBM treatment, followed by behavioral tests or Aβ detection

Fig. 2

Effect of different doses of PBM on the changes of temperature on the cortex surface, cognitive functions and the Aβ level in mouse brain. a Average temperature change in the brain’s surface during PBM with different doses. b Maximum temperature difference of individual mouse during PBM treatment with different dose. c Escape latency of mice during MWM training session before and after different doses of PBM. d Escape latency and e typical swimming path in probe trial on day 6. The recognitive index in training f and testing g sessions in NOR test. h Typical movement paths on the testing session in NOR test. i Western blot representative image. j Quantitative analysis of Aβ in the brain. Notes: Data in c, d, f, g and j are presented as mean ± standard deviation, n = 3 for a, n = 8 for c, d, f and g, n = 10 for j, *p < 0.05, **p < 0.01, ***p < 0.001

Fig. 3

PBM-induced Aβ clearance from the prefrontal cortex and the hippocampus. a 3D reconstruction of Aβ in the brain hemisphere after tissue labeling, clearing and imaging, as well as its rendering image after registration and segmentation. b Representative 3D fluorescent images of Aβ in the hippocampus DG, CA1, CA2 and CA3. c Representative 3D fluorescent images of Aβ in the prefrontal cortex ACA, PL, ILA, MOs, ORB and AI. d Clearance of Aβ plaques in the prefrontal cortex and the hippocampus. e Clearance of Aβ plaques in DG, CA1, CA2 and CA3. f Clearance of Aβ plaques in ACA, PL, ILA, MOs, ORB and AI. Data are presented as mean ± standard deviation (n = 5), *p < 0.05, **p < 0.01, ***p < 0.001

Fig. 4

PBM effects on lymphatic clearance of Aβ from the brain of 5xFAD mice. a Representative fluorescent images and b statistical image of Aβ plaques in dcLNs. Scale bar = 20 μm. c Representative fluorescent images of EBD clearance from the right lateral ventricle into the dcLNs in WT, AD and AD + PBM groups. Scale bar = 2 mm. d Quantitative analysis of fluorescence intensity of EBD in dcLNs in WT, AD and AD + PBM groups. e Representative fluorescent images and diameter distribution of basal MLVs (labelled with anti-LYVE-1 and anti-PROX-1) in WT, AD and AD + PBM groups. Scale bar = 50 μm. f Quantitative analysis of average diameter of the basal MLVs in WT, AD and AD + PBM groups. Notes: Data in b, d and e are presented as mean ± standard deviation, n = 10 for b, e and f, n = 3 for d, ns: not significant, *p < 0.05, **p < 0.01, ***p < 0.001