Reconstruction of the human blood–brain barrier in vitro reveals a pathogenic mechanism of APOE4 in pericytes

The Religious Orders Study and Rush Memory and Aging Project are both ongoing longitudinal clinical-pathologic cohort studies of aging and Alzheimer's disease (AD).

There has been considerable progress in identifying signaling pathways directing the differentiation of human pluripotent stem cells (hPSCs) into specialized cell types including neurons. However, extrinsic factor-based differentiation of hPSCs is a slow, step-wise process mimicking the protracted timing of normal human development. Using a small molecule screen we identified a combination of five small molecule pathway inhibitors sufficient to yield hPSC-derived neurons at >75% efficiency within 10 days of differentiation. The resulting neurons express canonical markers and functional properties of human nociceptors including TTX-resistant, SCN10A-dependent sodium currents and response to nociceptive stimuli including ATP and capsaicin. Neuronal fate acquisition occurs three-fold faster than during in vivo 1 development suggesting that use of small molecule pathway inhibitors could develop into a general strategy for accelerating developmental timing in vitro. The quick and high efficiency derivation of nociceptors offers unprecedented access to this medically relevant cell type for studies of human pain.

The highly impermeable tight junctions between endothelial cells forming the capillaries and venules in the central nervous system (CNS) of higher vertebrates are thought to be responsible for the blood-brain barrier that impedes the passive diffusion of solutes from the blood into the extracellular space of the CNS. The ability of CNS endothelial cells to form a blood-brain barrier is not intrinsic to these cells but instead is induced by the CNS environment: Stewart and Wiley demonstrated that when avascular tissue from 3-day-old quail brain is transplanted into the coelomic cavity of chick embryos, the chick endothelial cells that vascularize the quail brain grafts form a competent blood-brain barrier; on the other hand, when avascular embryonic quail coelomic grafts are transplanted into embryonic chick brain, the chick endothelial cells that invade the mesenchymal tissue grafts form leaky capillaries and venules. It is, however, not known which cells in the CNS are responsible for inducing endothelial cells to form the tight junctions characteristic of the blood-brain barrier. Astrocytes are the most likely candidates since their processes form endfeet that collectively surround CNS microvessels. In this report we provide direct evidence that astrocytes are capable of inducing blood-brain barrier properties in non-neural endothelial cells in vivo.