Development of a 3D In Vitro Model of the Blood-Brain Barrier in Layered Microfluidic Devices.

Abstract

The endothelial cells lining the capillaries that supply the brain with oxygen and nutrients present a highly regulated transport barrier known as the blood-brain barrier (BBB). These endothelial cells are characterized by thick cell membranes, low number of endocytic vesicles, absence of fenestrae, and highly organized tight junctions that restrict molecular diffusion across the paracellular space. The integrity and function of the BBB is finely regulated by several environmental conditions including endothelial cell-to-cell contact, communication with other neural cells such as astrocytes and pericytes, and the local concentration of secreted chemical factors. Several groups have cultured primary and immortalized brain capillary endothelial cells to develop an in vitro model that mimics the BBB for the purpose of screening transport properties of new drug molecules designed for treatment of central nervous system (CNS) disorders. However, these in vitro models generally failed to mimic the restrictive transport properties of the BBB due to the formation of “loose” tight junctions, lower expression of specific carriers, or limited cell viability. We developed a 3D in vitro model of the BBB by culturing brain endothelial cells with pericytes and astrocytes in layered microfluidic channels. We hypothesized that the proposed model would improve endothelial cell polarization and enhance the formation of tight junctions, provide better endothelial cell-to-cell contact that is important for barrier development, and prevent the dilution of secreted neurotrophic factors, and these conditions collectively led to the development of an in vitro model that can truly mimic the BBB.