Multiple regression analysis of a comprehensive transcriptomic data assembly elucidates mechanically- and biochemically-driven responses to focused ultrasound blood-brain barrier disruption.

Authors: Mathew AS, Gorick CM, Price RJ

Background: Focused ultrasound (FUS) blood brain barrier disruption (BBBD) permits the noninvasive, targeted, and repeatable delivery of drugs to the brain. FUS BBBD also elicits secondary responses capable of augmenting immunotherapies, clearing amyloid-β and hyperphosphorylated tau, and driving neurogenesis. Leveraging these secondary effects will benefit from an understanding of how they correlate to the magnitude of FUS BBBD and are differentially affected by the mechanical and biochemical stimuli imparted during FUS BBBD. Methods: We aggregated 75 murine transcriptomes in a multiple regression framework to identify genes expressed in proportion to biochemical (i.e. contrast MR image enhancement (CE)) or mechanical (i.e. harmonic acoustic emissions from MB-activation (MBA)) stimuli associated with FUS BBBD. Models were constructed to control for potential confounders, such as sex, anesthesia, and sequencing batch. Results: MBA and CE differentially predicted expression of 1,124 genes 6 h or 24 h later. While there existed overlap in the transcripts correlated with MBA vs CE, MBA was principally predictive of expression of genes associated with endothelial reactivity while CE chiefly predicted sterile inflammation gene sets. Over-representation analysis identified transcripts not previously linked to BBBD, including actin filament organization, which is likely important for BBB recovery. Transcripts and pathways associated with neurogenesis, microglial activation, and amyloid-β clearance were significantly correlated to BBBD metrics. Conclusions: The secondary effects of BBBD may have the potential to be tuned by modulating FUS parameters during BBBD, and MBA and CE may serve as independent predictors of transcriptional reactions in the brain.

Introduction

Purpose Drug delivery with BBB opening

Study Objective To identify transcriptional programs in mouse brain that correlate with and are differentially predicted by mechanical (MBA) versus biochemical (CE) metrics of focused ultrasound–induced blood–brain barrier disruption.

Animal model / Human subject Mouse (murine); strain: not reported; age: not reported; sex: not reported

Disease model Healthy

MRI or image guidance method Contrast-enhanced MRI (CE)

Outcomes and Safety

Summary of Outcomes Contrast enhancement (CE) and microbubble acoustic emissions (MBA) independently predicted differential transcriptional responses to FUS BBBD: CE was chiefly associated with sterile inflammation and transporter changes while MBA preferentially predicted endothelial reactivity/vascular repair, and both predicted actin filament organization, microglial activation, neurogenesis, and amyloid-β clearance signatures at 6 and 24 h. Among tested FUS parameters, higher peak negative pressure (~0.4 MPa, corresponding to ~75% CE), higher microbubble dose, and use of isoflurane (vs ketamine+α2) produced stronger CE/MBA signals and more pronounced transcriptional effects, whereas lower PNPs (0.1–0.2 MPa) produced smaller responses.

Duration of biological effect 24 h

Safety-related matter FUS BBBD elicited sterile inflammation and endothelial activation — upregulation of inflammatory genes (e.g., Nfkb2, Tnf, Tlr2, Icam1, Sele) and leukocyte‑migration signatures proportional to CE/MBA and higher PNP/MB dose. No overt clinical adverse events were reported in these transcriptomic datasets, and albumin or microbubbles alone had negligible transcriptomic effects in the absence of FUS.

Brain Region

Visualization unavailable

Ultrasound Parameters

Focal Characteristics Focal depth: None; Focal length: None; Aperture size: None

Treatment frequency single session

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