Reorganization of Gap Junctions after Focused Ultrasound Blood–Brain Barrier Opening in the Rat Brain

Abstract

Ultrasound-induced opening of the blood-brain barrier (BBB) is an emerging technique for targeted drug delivery to the central nervous system. Gap junctions allow transfer of information between adjacent cells and are responsible for tissue homeostasis. We examined the effect of ultrasoundinduced BBB opening on the structure of gap junctions in cortical neurons, expressing Connexin 36, and astrocytes, expressing Connexin 43, after focused 1-MHz ultrasound exposure at 1.25 MPa of one hemisphere together with intravenous microbubble (Optison, Oslo, Norway) application. Quantification of immunofluorescence signals revealed that, compared with noninsonicated hemispheres, small-sized Connexin 43 and 36 gap-junctional plaques were markedly reduced in areas with BBB breakdown after 3 to 6 hours (34.02 ± 6.04% versus 66.49 ± 2.16%, P = 0.02 for Connexin 43; 33.80 ± 1.24% versus 36.77 ± 3.43%, P = 0.07 for Connexin 36). Complementing this finding, we found significant increases in large-sized gap-junctional plaques (5.76 ± 0.96% versus 1.02 ± 0.84%, P = 0.05 for Connexin 43; 5.62 ± 0.22% versus 4.65 ± 0.80%, P = 0.02 for Connexin 36). This effect was reversible at 24 hours after ultrasound exposure. Western blot analyses did not show any change in the total connexin amount. These results indicate that ultrasound-induced BBB opening leads to a reorganization of gap-junctional plaques in both neurons and astrocytes. The plaque-size increase may be a cellular response to imbalances in extracellular homeostasis after BBB leakage.

Pericytes are involved in the pathogenesis of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy

“…31 Other groups reported the reorganization of connexin-43 in astrocytic gap junctions but no change in connexin-43 protein levels in response to injury. 32,33 Therefore, connexin-43 may be reorganized in CADASIL mice, which would correlate nicely with the reorganization of polarized markers of astrocytic end-feet. Using in vivo imaging, we also found that cerebral flood flow is not altered in TgNotch3 R169C mice at 7 months of age, despite significant changes in microvascular morphology changes at this age.…”

The Size of Blood–Brain Barrier Opening Induced by Focused Ultrasound is Dictated by the Acoustic Pressure

“…Several potential cellular mechanisms for FUS-enhanced paracellular transport have been proposed, such as disassembling of tight junction proteins, 29 disruption of the interaction between tight junction proteins, 30 or reorganization of gap junction proteins. 31 The effect of FUS upon tight junctions has been reported to be transient and reversible. [29][30][31] Future studies are needed to elucidate how FUS and MBs interact at the molecular level of the BBB.…”

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