Tumor necrosis factor-α impairs cerebral blood flow in pregnant rats: role of vascular β-epithelial Na channel.

Preeclampsia is a pregnancy-related disorder characterized by hypertension, vascular dysfunction and an increase in circulating inflammatory factors including the cytokine, tumor necrosis factor-α (TNF-α). Studies have shown that placental ischemia is associated with ) increased circulating TNF-α, ) attenuated pressure-induced cerebral vascular tone, and ) suppression of β-epithelial Na channel (βENaC) protein in cerebral vessels. In addition to its role in epithelial Na and water transport, βENaC is an essential signaling element in transduction of pressure-induced (aka "myogenic") constriction, a critical mechanism of blood flow autoregulation. While cytokines inhibit expression of certain ENaC proteins in epithelial tissue, it is unknown if the increased circulating TNF-α associated with placental ischemia mediates the loss of cerebrovascular βENaC and cerebral blood flow regulation. Therefore, the purpose of this study was to test the hypothesis that increasing plasma TNF-α in normal pregnant rats reduces cerebrovascular βENaC expression and impairs cerebral blood flow (CBF) regulation. In vivo TNF-α infusion (200 ng/day, 5 days) inhibited cerebrovascular expression of βENaC and impaired CBF regulation in pregnant rats. To determine the direct effects of TNF-α and underlying pathways mediating vascular smooth muscle cell βENaC reduction, we exposed cultured VSMCs (A10 cell line) to TNF-α (1-100 ng/mL) for 16-24 h. TNF-α reduced βENaC protein expression in a concentration-dependent fashion from 0.1 to 100 ng/mL, without affecting cell death. To assess the role of canonical MAPK signaling in this response, VSMCs were treated with p38MAPK or c-Jun kinase (JNK) inhibitors in the presence of TNF-α. We found that both p38MAPK and JNK blockade prevented TNF-α-mediated βENaC protein suppression. These data provide evidence that disorders associated with increased circulating TNF-α could lead to impaired cerebrovascular regulation, possibly due to reduced βENaC-mediated vascular function. This manuscript identifies TNF-α as a possible placental-derived cytokine that could be involved in declining cerebrovascular health observed in preeclampsia. We found that infusion of TNF-α during pregnancy impaired cerebral blood flow control in rats at high arterial pressures. We further discovered that cerebrovascular β-epithelial sodium channel (βENaC) protein, a degenerin protein involved in mechanotransduction, was reduced by TNF-α in pregnant rats, indicating a potential link between impaired blood flow and this myogenic player. We next examined this effect in vitro using a rat vascular smooth muscle cell line. TNF-α reduced βENaC through canonical MAPK-signaling pathways and was not dependent on cell death. This study demonstrates the pejorative effects of TNF-α on cerebrovascular function during pregnancy and warrants future investigations to study the role of cytokines on vascular function during pregnancy.