Three-dimensional (3D) tissue-engineered models of the blood-brain barrier (BBB) recapitulate in vivo shear stress, cylindrical geometry, and cell-ECM interactions. Here we address four issues associated with BBB models: cell source, barrier function, cryopreservation, and matrix stiffness. We reproduce a directed differentiation of brain microvascular endothelial cells (dhBMECs) from two fluorescently labeled human induced pluripotent stem cell lines (hiPSCs) and demonstrate physiological permeability of Lucifer yellow over six days. Microvessels formed from cryopreserved dhBMECs show expression of BBB markers and maintain physiological barrier function comparable to non-cryopreserved cells. Microvessels displaying physiological barrier function are formed in collagen I hydrogels with stiffness matching that of human brain. The dilation response of microvessels was linear with increasing transmural pressure and was dependent on matrix stiffness. Together these results advance capabilities for tissue-engineered BBB models.

Brain microvascular endothelial cells derived from induced pluripotent stem cells (dhBMECs) are a scalable and reproducible resource for studies of the human blood−brain barrier, including mechanisms and strategies for drug delivery. Confluent monolayers of dhBMECs recapitulate key in vivo functions including tight junctions to limit paracellular permeability and efflux and nutrient transport to regulate transcellular permeability. Techniques for cryopreservation of dhBMECs have been reported; however, functional validation studies after long-term cryopreservation have not been extensively performed. Here, we characterize dhBMECs after 1 year of cryopreservation using selective purification on extracellular matrix-treated surfaces and ROCK inhibition. One-year cryopreserved dhBMECs maintain functionality of tight junctions, efflux pumps, and nutrient transporters with stable protein localization and gene expression. Cryopreservation is associated with a decrease in the yield of adherent cells and unique responses to cell stress, resulting in altered paracellular permeability of Lucifer yellow. Additionally, cryopreserved dhBMECs reliably form functional three-dimensional microvessels independent of cryopreservation length, with permeabilities lower than non-cryopreserved two-dimensional models. Long-term cryopreservation of dhBMECs offers key advantages including increased scalability, reduced batch-to-batch effects, the ability to conduct well-controlled follow up studies, and support of multisite collaboration from the same cell stock, all while maintaining phenotype for screening pharmaceutical agents.

The blood–brain barrier (BBB) plays a pivotal role in brain health and disease. In the BBB, brain microvascular endothelial cells (BMECs) are connected by tight junctions which regulate paracellular transport, and express specialized transporter systems which regulate transcellular transport. However, existing in vitro models of the BBB display variable accuracy across a wide range of characteristics including gene/protein expression and barrier function. Here, we use an isogenic family of fluorescently-labeled iPSC-derived BMEC-like cells (iBMECs) and brain pericyte-like cells (iPCs) within two-dimensional confluent monolayers (2D) and three-dimensional (3D) tissue-engineered microvessels to explore how 3D microenvironment regulates gene expression and function of the in vitro BBB. We show that 3D microenvironment (shear stress, cell-ECM interactions, and cylindrical geometry) increases BBB phenotype and endothelial identity, and alters angiogenic and cytokine responses in synergy with pericyte co-culture. Tissue-engineered microvessels incorporating junction-labeled iBMECs enable study of the real-time dynamics of tight junctions during homeostasis and in response to physical and chemical perturbations.

Oxidative stress is a shared pathology of neurodegenerative disease and brain injuries, and is derived from perturbations to normal cell processes by aging or environmental factors such as UV exposure and air pollution. As oxidative cues are often present in systemic circulation, the blood–brain barrier (BBB) plays a key role in mediating the effect of these cues on brain dysfunction. Therefore, oxidative damage and disruption of the BBB is an emergent focus of neurodegenerative disease etiology and progression. We assessed barrier dysfunction in response to chronic and acute oxidative stress in 2D and 3D in vitro models of the BBB with human iPSC-derived brain microvascular endothelial-like cells (iBMECs). We first established doses of hydrogen peroxide to induce chronic damage (modeling aging and neurodegenerative disease) and acute damage (modeling the response to traumatic brain injury) by assessing barrier function via transendothelial electrical resistance in 2D iBMEC monolayers and permeability and monolayer integrity in 3D tissue-engineered iBMEC microvessels. Following application of these chronic and acute doses in our in vitro models, we found local, discrete structural changes were the most prevalent responses (rather than global barrier loss). Additionally, we validated unique functional changes in response to oxidative stress, including dysfunctional cell turnover dynamics and immune cell adhesion that were consistent with changes in gene expression.

The blood-brain barrier (BBB) plays a pivotal role in brain health and disease. In the BBB, brain microvascular endothelial cells (BMECs) are connected by tight junctions which regulate paracellular transport, and express specialized transporter systems which regulate transcellular transport. However, existing in vitro models of the BBB display variable physiological accuracy across a wide range of characteristics including gene/protein expression and barrier function. Here, we use an isogenic family of fluorescently-labeled iPSC-derived BMEC-like cells (iBMECs) and brain pericyte-like cells (iPCs) within two-dimensional confluent monolayers (2D) and three-dimensional (3D) tissue-engineered microvessels to explore how 3D microenvironment regulates gene expression and function of the in vitro BBB. We show that 3D microenvironment (shear stress, cell-ECM interactions, and cylindrical geometry) increases BBB phenotype and endothelial identity, and alters angiogenic and cytokine responses in synergy with pericyte co-culture. Tissue-engineered microvessels incorporating junction-labeled iBMECs enable study of the real-time dynamics of tight junctions during homeostasis and in response to physical and chemical perturbations.

Huntington’s disease (HD) is an inherited neurodegenerative disease caused by expansion of cytosine–adenine–guanine (CAG) repeats in the huntingtin gene, which leads to neuronal loss and decline in cognitive and motor function. Increasing evidence suggests that blood–brain barrier (BBB) dysfunction may contribute to progression of the disease. Studies in animal models, in vitro models, and post-mortem tissue find that disease progression is associated with increased microvascular density, altered cerebral blood flow, and loss of paracellular and transcellular barrier function. Here, we report on changes in BBB phenotype due to expansion of CAG repeats using an isogenic pair of induced pluripotent stem cells (iPSCs) differentiated into brain microvascular endothelial-like cells (iBMECs). We show that CAG expansion associated with juvenile HD alters the trajectory of iBMEC differentiation, producing cells with ~ two-fold lower percentage of adherent endothelial cells. CAG expansion is associated with diminished transendothelial electrical resistance and reduced tight junction protein expression, but no significant changes in paracellular permeability. While mutant huntingtin protein (mHTT) aggregates were not observed in HD iBMECs, widespread transcriptional dysregulation was observed in iBMECs compared to iPSCs. In addition, CAG expansion in iBMECs results in distinct responses to pathological and therapeutic perturbations including angiogenic factors, oxidative stress, and osmotic stress. In a tissue-engineered BBB model, iBMECs show subtle changes in phenotype, including differences in cell turnover and immune cell adhesion. Our results further support that CAG expansion in BMECs contributes to BBB dysfunction during HD.

Real-time, cellular resolution imaging is essential for probing the highly dynamic functions of the lung at the interface of physics, biology, and immunology. CT and MRI modalities have low spatial resolution, and histological approaches provide only snapshots of fixed lungs with little temporal information. Existing intravital imaging approaches cannot include and manipulate the physical and spatiotemporal changes involved in respiratory function. Here, we describe the development of a platform, termed "LungEx", to visualize and mechanistically probe the dynamics of a functioning lung at optical resolutions. LungEx is equipped with a novel transparent ribcage, termed "crystal" ribcage, that provides physiological conditions for a functioning lung and allows high-resolution and real-time optical imaging of nearly the entire lung surface. This imaging capability is obtained while LungEx preserves the complex 3-D architecture, cellular diversity, and integrative function of the ex vivo ventilated and perfused lung at near in vivo conditions. Utilizing LungEx in health and key lung diseases such as metastasis, pneumonia, and fibrosis, we probed a wide range of lung dynamic functions and remodeling at multiple spatial scales including alveolar deformation and elasticity, circulation-respiration coupling at the capillary level, cellular deformation, immune cell motility, and vascular transport. By modulating the biophysical environment of LungEx, we discovered that intravascular and interstitial, but not intra-alveolar neutrophils are highly and reversibly responsive to vascular pressure. Thus, by allowing high spatiotemporal imaging coupled with controlled biophysical interventions, LungEx, provides a powerful platform to mechanistically probe dynamic and multiscale lung functions in health and disease.

Huntington’s disease (HD) is an inherited neurodegenerative disease caused by expansion of cytosine–adenine–guanine (CAG) repeats in the huntingtin gene, which leads to neuronal loss and decline in cognitive and motor function. Increasing evidence suggests that blood-brain barrier (BBB) dysfunction may contribute to progression of the disease. Studies in animal models, in vitro models, and post-mortem tissue suggest that disease progression is associated with increased microvascular density, altered cerebral blood flow, and loss of paracellular and transcellular barrier function. Here we report on changes in BBB phenotype due to expansion of CAG repeats using an isogenic pair of induced pluripotent stem cells (iPSCs) differentiated into brain microvascular endothelial-like cells (iBMECs). We show that CAG expansion alters the trajectory of iBMEC differentiation, producing cells with ~ 2-fold lower purity of adherent endothelial cells. CAG expansion is associated with lower transendothelial electrical resistance, lower tight junction protein expression, and unique gene expression profiles, but no significant changes in paracellular permeability. In addition, CAG expansion results in unique responses to pathological and therapeutic perturbations including angiogenic factors, oxidative stress, and osmotic stress. In a tissue-engineered BBB model, iBMECs show subtle changes in phenotype, including differences in cell turnover and immune cell adhesion. Our results further support that CAG expansion in BMECs may alter BBB phenotype during HD.