Astrocyte-Derived TGFβ1 Facilitates Blood–Brain Barrier Function via Non-Canonical Hedgehog Signaling in Brain Microvascular Endothelial Cells

Abstract

The blood–brain barrier is a specialized structure in mammals, separating the brain from the bloodstream and maintaining the homeostasis of the central nervous system. The barrier is composed of various types of cells, and the communication between these cells is critical to blood–brain barrier (BBB) function. Here, we demonstrate the astrocyte-derived TGFβ1-mediated intercellular communication between astrocytes and brain microvascular endothelial cells (BMECs). By using an in vitro co-culture model, we observed that the astrocyte-derived TGFβ1 enhanced the tight junction protein ZO-1 expression in BMECs and the endothelial barrier function via a non-canonical hedgehog signaling. Gli2, the core transcriptional factor of the hedgehog pathway, was demonstrated to modulate ZO-1 expression directly. By the dual-luciferase reporter system and chromatin immunoprecipitation, we further identified the exact sites on Smad2/3 that bound to the gli2 promotor and on Gli2 that bound to the zo-1 promotor. Our work highlighted the TGFβ1-mediated intercellular communication of astrocytes with BMECs in BBB, which shall extend current knowledge on the BBB homeostasis physiologically, and more importantly suggests TGFβ1 as a potential effector for future prevention and amelioration of BBB dysfunction.

Meningitic Escherichia coli α-hemolysin aggravates blood–brain barrier disruption via targeting TGFβ1-triggered hedgehog signaling

“…The α-hemolysin HlyA in meningitic E. coli was shown to decrease the TGFβ1 receptor TGFBRII and the key transcription factor Gli2 of hedgehog signaling, which finally led to BBB disruption. Together with our recent conclusion that astrocytes-derived TGFβ1 facilitates BBB function via activating non-canonical hedgehog signaling in BMECs [ 13 ], we here revealed a novel strategy for meningitic E. coli induction of BBB dysfunction by disturbing the regular astrocytes-endothelium cross-talking. This finding could largely extend the current knowledge of bacterial-caused CNS dysfunction from perspective of intercellular communication within BBB, and shall be beneficial for future prevention and control of bacterial meningitis.…”

“…1 B). Noticeably, we have recently evidenced that astrocytes-derived TGFβ1 could facilitate the BBB barrier function by increasing ZO-1 expression in BMECs via a non-canonical hedgehog signaling [ 13 ]. We therefore presumed that such TGFβ1-mediated intercellular communication between astrocytes and endothelium was largely disturbed during meningitic E. coli infection.…”

“…Previously we have evidenced that astrocytes-derived TGFβ1 facilitated the BBB barrier function in BMECs via a non-canonical hedgehog signaling [ 13 ]. Here, our in vivo assay also demonstrated that the hedgehog signaling transcription factor Gli2 in mice BMECs was largely reduced in response to RS218 infection (Fig.…”

“…Since we have evidenced the importance of TGFβ1-triggered hedgehog signaling in astrocytes-endothelium communication and BBB function maintaining [ 13 ], we thus hope to see whether activating hedgehog signaling by the known agonist SAG could show some protective effects against bacterial challenge. Here, we firstly tested the possible effects of SAG treatment on the hBMECs barrier function in vitro .…”

“…Also, Ang1/Tie2 and Flk1 were reported to promote the capillary tube-like formation of BMECs [ 12 ]. We previously demonstrated that astrocytes-derived transforming growth factor-β1 (TGFβ1) enhanced the endothelial ZO-1 expression and maintained the BBB integrity by triggering a non-canonical hedgehog signaling in BMECs, indicating that the TGFβ1-mediated intercellular communication between astrocytes and BMECs is beneficial for BBB integrity maintaining [ 13 ], and exogenous TGFβ1 addition would exhibit a protective effect on BBB. However, whether such TGFβ1-mediated intercellular cross-talking within BBB could be hijacked during meningitic E. coli infection is entirely unknown.…”