Thymosin β4 stabilizes hypoxia induced brain microvascular endothelial cell dysfunction through S1PR1 dependent mechanisms

Acute ischemic injury causes impairment of blood brain barrier (BBB) permeability and is considered as secondary insult in the brain after traumatic brain injury (TBI). The mechanisms underlying these events are incomprehensible and therefore therapeutic opportunities are limited. Although drugs have been showing some promise in TBI outcome, the restoration of BBB damage remain elusive. Thymosin β4 (Tβ4) is a secreted 43 amino acid peptide showed beneficial outcome in cerebral ischemia or TBI, however, it's role in hypoxia-induced BBB damage remains elusive. We hypothesize that Tβ4 protect hypoxia-induced BBB disruption via Sphingosine 1-phosphate receptor 1 (S1PR1) modulation. In the current study, we investigated the beneficial effects of Tβ4 in hypoxia induced gene expression of several tight junction proteins, S1PR1, endothelial cell permeability and tight junction dynamics in human brain microvascular endothelial cells (hBMVECs), one of the important cell types in the BBB integrity. The data suggests that pretreatment with Tβ4 reversed the hypoxia-induced damage of BBB components in hBMVECs. Furthermore, results identify S1PR1, a possible target for Tβ4. Inhibition of S1PR1 showed that Tβ4 failed to offer protection. Together, data provided evidence that S1PR1 is pivotal and Tβ4 can serve as a protective agent in BBB integrity and may offer a promising therapeutic target. In conclusion, we propose that depletion of S1PR1signaling is vital in hypoxia-induced BBB pathophysiology and Tβ4 may be tested as a potential treatment modality and warrant further investigation.