Brain cellular localization of endothelin receptors A and B in a rodent model of diffuse traumatic brain injury

Endothelin-1 exerts potent vasoconstrictor and vasodilatory effects through its actions on its receptors A (ETrA) and B (ETrB), respectively. While ETrA and B have classically been thought to be expressed on vascular cell types, more recent evidence suggests that, particularly following brain injury, their expression may be seen in other, non-vascular cell types. To date no studies have comprehensively studied the cellular location of endothelin receptors following traumatic brain injury (TBI). Therefore, this study investigates the cellular localization of ETrA and B in normal and traumatized brains using an impact acceleration device. Adult male Sprague-Dawley rats were subjected to TBI by weight drop (450 g) from either 1.5, a distance known to elicit mild TBI in the absence of changed in cerebral blood flow (CBF) or 2 m, a distance shown to cause a significant reduction in CBF. One set of impacted brains were processed for Western determination of ETrA and B expression. Another set were processed for immunofluorescence (IF). For IF, ETrA and ETrB antibodies were combined with cell markers for neurons, astrocytes, microglia, oligodendrocytes, smooth muscle cells and endothelial cells of blood vessels. While ETrA and B was upregulated after more moderate to severe injury (2 m) overall receptor expression was unchanged in response to mild trauma (1.5 m). Double labeling IF confirmed prominent ETrA and ETrB labeling in NeuN labeled pyramidal neurons and interneurons in sensorymotor cortex (smCx) and hippocampus (hipp) post TBI. ETrA rather than ETrB was preferentially co-localized in vascular smooth muscle cells. After injury, a subpopulation of astrocytes in white matter co-localized ETrA but not ETrB. Localization of either receptor in endothelial cells was sparse. No prominent IF was detected in microglia and oligodendrocytes. Taken together with previous findings in other pathological states that show an apparent shift in the localization of ETrA and B, the observed receptor shifts in this work may underlie the ET-1-mediated pathotrajectory of TBI including hypoperfusion.