Clazosentan Attenuates Endothelin-1-Induced ETA Protein Upregulation and Contractile Sensitization in Brain Pericytes

Background/Objectives: Brain pericytes are contractile mural cells of the neurovascular unit whose responses to endothelin-1 (ET-1) are mediated primarily by endothelin type A (ETA) receptors. ET-1/ETA signaling has been implicated in pathological pericyte contraction in neurovascular disorders such as Alzheimer's disease and in cerebrovascular dysfunction after subarachnoid hemorrhage, motivating pharmacological evaluation of selective ETA receptor antagonists at the pericyte level. Clazosentan is a selective ETA receptor antagonist used clinically for cerebral vasospasm; however, its pharmacodynamic effects on brain pericytes remain insufficiently characterized. Methods: Pericyte impedance-based contractile and recovery responses to ET-1 were evaluated by xCELLigence real-time cell index analysis. Pericyte viability, morphology, and ETA protein abundance were examined using Cell Counting Kit-8 assay, immunocytochemistry, and Western blotting. As a secondary barrier-related assessment, transendothelial electrical resistance (TEER) was measured in primary rat brain endothelial cell-based in vitro blood-brain barrier models. Results: ET-1 induced impedance-based contractile responses with a concentration-related trend, followed by recovery responses, and increased ETA protein abundance in a time- and concentration-related manner; clazosentan significantly attenuated ET-1-induced ETA upregulation. Repeated ET-1 exposure was associated with an enhanced subsequent ET-1-induced impedance-based contractile response and a more sustained response, suggesting contractile sensitization; both effects were significantly attenuated by clazosentan. Clazosentan did not overtly disrupt TEER-assessed barrier properties. Conclusions: These findings suggest that ET-1/ETA signaling may shift brain pericytes toward a sensitized contractile response state and that selective ETA blockade by clazosentan attenuates this process without overtly disrupting TEER-assessed barrier properties under the present in vitro conditions. These observations support further pharmacological characterization of clazosentan as a modulator of pericyte ET-1 responses.