Role for caveolin-mediated transcytosis in facilitating transport of large cargoes into the brain via ultrasound.

The blood-brain barrier (BBB) is a dynamic diffusional barrier regulating the molecular and chemical flux between the blood and brain, thereby preserving cerebral homeostasis. Endothelial cells form the core anatomical component of the BBB based on properties such as specialized junctional complexes between cells, which restricts paracellular transport, and extremely low levels of vesicular transport, restricting transcytosis. In performing its protective function, the BBB also constrains the entry of therapeutics into the brain, hampering the treatment of various neurological disorders. Focused ultrasound is a novel therapeutic modality that has shown efficacy in transiently and non-invasively opening the BBB for the targeted delivery of therapeutics to the brain. Although the ability of ultrasound to disrupt the junctional assembly of endothelial cells has been partially investigated, its effect on the transcellular mode of transport has been largely neglected. In this study, we found that ultrasound induces a pronounced increase in the levels of the vesicle-forming protein caveolin-1. In order to investigate the role of vesicle-mediated transcytoplasmic transport, we compared the leakage of various cargo sizes between a mouse model that lacks caveolin-1 and wild-type mice following sonication of the hippocampus. The absence of caveolin-1 did not lead to overt abnormalities in the cerebral vasculature in the mice. We found that caveolin-1 has a critical role specifically in the transport of large (500 kDa), but not smaller (3 and 70 kDa) cargoes. Our findings indicate differential effects of therapeutic ultrasound on cellular transport mechanisms, with implications for therapeutic interventions.