Repeated low-intensity focused ultrasound led to microglial profile changes in TgF344-AD rats

Alzheimer’s disease (AD), the most common cause of dementia, represents one of the main clinical challenges of the century as the number of patients is predicted to triple by 2050. Despite the recent approval of three monoclonal antibodies targeting Amyloid β (Aβ) aggregates by the Food and Drug Administration (FDA), immunotherapies still face challenges due to the difficulty of antibodies crossing the blood-brain barrier (BBB). This necessitates administering large doses of drugs to achieve their therapeutic effects, which is associated with significant side effects. In this context, low-intensity focused ultrasound (LiFUS) appears as an innovative and non-invasive method which, in association with intravenous injection of microbubbles (MB), leads to a transient BBB opening. This innovative strategy has been extensively studied in different preclinical models and more recently in human clinical trials, particularly in the context of AD. LiFUS+MB seems to increase the inflammatory response at short term, but the time course of this response is not consistent between studies, certainly due to the discrepancy between LiFUS protocols used. Moreover, the impact at longer term is understudied and the mechanisms underlying this effect are still not well understood. In our study, we therefore used the TgF344-AD rat model of AD, to investigate the effect of a single or multiple exposures to LiFUS+MB in the entire brain, on inflammatory response and amyloid load. The ultrasound attenuation through the skull was corrected to apply a peak negative acoustic pressure of 450 kHz in all treated animals. Single LiFUS+MB exposure induces a slight astrocyte and microglial response 24 hours post-treatment whereas repeated LiFUS treatment seems to induce microglial reprogramming, leading to the adaptation of gene expression related to key functions such as inflammatory response, mitochondrial and energetic metabolism. In our rat model and LiFUS+MB protocol conditions, multiple exposures did not modulate soluble/poorly aggregated forms nor the highly aggregated forms of Aβ ₄₀ and Aβ ₄₂ . For therapeutic AD management, LiFUS+MB could be combined with drugs such as immunotherapies. In a proof-of-concept experiment, we validated that LiFUS was also efficient to improve the brain entry of the anti-Aβ antibody, Aducanumab.