Caveolar transport at BBB

The blood-brain barrier (BBB) tightly regulates substance and cell exchange between neural tissue and the systemic environment. For its full functionality, cerebral blood vessels rely on a network of endothelial and mural cells, referred to as neurovascular unit (NVU). Caveolae are membrane lipid rafts and multifunctional cell signalling and sensing platforms that also have vesicular transport capability. Previous work in our lab has shown that the central nervous system (CNS) stimulant methamphetamine (METH) induces hyperpermeability in cultures of BBB endothelial cells (ECs) via endothelial nitric oxide synthase (eNOS)-mediated vesicular transport. Here, I hypothesise that caveolar transport operates at the intact NVU and that transport-competent caveolae can be used for CNS drug delivery. Our data shows that METH induces a high number of transport-competent vesicles with ultrastructural features of caveolae in rodent brains ex vivo. This leads to vessel leakage, which was absent at 4°C and in caveolae-deficient mice, indicating that caveolar transport can be induced at the NVU. Mechanistically, activation of eNOS, p38 and AMPK is required for METH-induced leakage, as are phosphorylation of Caveolin-1 (Cav-1) and upregulation of plasmalemma vesicle associated protein (PLVAP). Interestingly, transport-incompetent caveolae are induced at the BBB by lysophosphatidic acid (LPA), a permeability mediator that exclusively triggers paracellular transport. Lastly, low dose METH markedly enhances the BBB penetration of doxorubicin (DOX) and aflibercept (AFL). In a mouse xerograph model of human glioblastoma (GBM), METH significantly improved the therapeutic efficacy of DOX with a 25% increase in median survival time. In conclusion, caveolae transport occurs at the intact BBB and could be exploited for CNS drug delivery.