For too long, studies of the Blood-Brain Barrier (BBB) have ignored the blood component of this interface, focusing almost exclusively on the cells of the Neurovascular Unit (NVU). The goal of the FOA to which we are responding aims to change this: ?The intent of this FOA is to stimulate the development of a new field of blood-based science by re-defining the neurovascular unit as a component of the blood-brain interface. This will facilitate development of human- based neurovascular-blood models to identify targets for diagnostics and regulation of the blood-brain interface?? The NVU is comprised of endothelial cells (EC), pericytes and astrocytes, and a complex basement membrane, which work together to severely limit the free movement of molecules from the blood into the brain parenchyma. In response to local signals during development BBB EC develop tight junctions and have very low rates of transcytosis. The side-effect of this is that access of potentially therapeutic drugs into the brain is also compromised. In this proposal we will build on our well-established human Vascularized Micro-Organ (VMO) platform to create a novel blood-brain interface model, the VMO-B. In this model a network of human microvessels anastomoses to microfluidic channels representing an artery and a vein and are induced to a BBB phenotype by Wnt signaling. The vessels are invested by pericytes and contacted by astrocyte foot-processes. Importantly, we will run a blood substitute ? VMOBlood ? through the vessels that will mimic the composition of blood, including protein and lipid content. We will then use the VMO-B to investigate the process of BBB breakdown in the pathogenesis of Huntington?s disease. We already have preliminary data suggesting that expression of mutant HTT protein in EC causes BBB deficits. We will investigate crosstalk between blood and the cells of the NVU, and how expression of mHTT in each cell type affects cell-cell communication and barrier function. In the R61 phase we will pursue three aims:
Aim 1 Develop a stable MPS BBB model with perfused microvasculature;
Aim 2 Incorporate flow of blood into BBB microfluidic model; and, Aim 3 Characterize key transporters at the blood-brain interface. In the R33 phase we will use this platform to examine the role of the blood-brain interface in the pathology of HD through an additional two aims:
Aim 4 Test the hypothesis that expression of mHTT in EC disrupts transport across the BBB leading to changes in the neural micro-environment; and, Aim 5 Test the hypothesis that expression of mHTT disrupts multiple cell-to-cell interactions at the blood- brain interface. Completion of this project will not only shed light on the neuropathology of Huntington?s disease, but will also yield a platform ideally suited to drug development and investigating the role of the blood- brain interface in numerous neurological diseases including Alzheimer?s disease, Multiple Sclerosis, Parkinson?s disease, stroke, CADASIL, and traumatic brain injury.
This proposal will seek to develop a novel microfluidic (?organ-on-chip?) model of the human blood-brain interface. Breakdown of this interface in several neurological diseases, including Huntington?s disease, Alzheimer?s disease, stroke and traumatic brain injury is thought to contribute to disease progression. Our platform will allow testing of new therapeutic approaches in an entirely human, animal free, model system.