Streptozotocin Causes Blood-Brain Barrier and Astrocytic Dysfunction In Vitro

Streptozotocin (STZ) is an alkylating agent that has neurotoxic effects when injected into the cerebral ventricles (ICV) and also models many other features of Alzheimer's disease. However, the mechanisms of STZ neurotoxicity are not well understood. In this study, we hypothesized that some of the neurotoxic effects of STZ could be due to direct activities on brain endothelial cells and astrocytes, which are key in forming and supporting the functions of the blood-brain barrier (BBB), respectively. To test this hypothesis, we characterized the changes induced by STZ either in cultures of human-induced pluripotent stem cell (iPSC)-derived brain endothelial-like cells (iBECs), which form an in vitro BBB model, or in primary human astrocytes. We found that STZ at a dosage of 5 mM caused a delayed reduction in the transendothelial electrical resistance (TEER) of iBECs at 7-11 days post-treatment, indicating induction of BBB leakage. Additionally, we observed significant increases in albumin leakage across the monolayer, altered iBEC morphology, and reductions in tight junction proteins, suggesting that STZ causes BBB disruption. We further found that the BBB glucose transporter GLUT-1 was reduced in iBECs, as was the total number of iBECs. In astrocytes, the 5 mM dose of STZ reduced the GFAP signal and total number of cells, suggesting that STZ has anti-proliferative and/or toxic effects on astrocytes. Together, these data support that STZ's neurotoxic effects could be due, in part, to its direct toxic activities on brain endothelial cells and astrocytes.