Expression of the bumetanide-sensitive Na-K-Cl cotransporter BSC2 is differentially regulated by fluid mechanical and inflammatory cytokine stimuli in vascular endothelium.

In vascular endothelium, the electroneutral Na-K-Cl cotransport system is thought to function in the maintenance of a selective permeability barrier in certain vascular beds (e.g., brain), as well as in the preservation of endothelial homeostasis in the face of fluctuating osmotic conditions that may accompany certain pathophysiological conditions (e.g., diabetes mellitus). Here we demonstrate that the gene encoding the bumetanide-sensitive cotransporter BSC2, one of the two major isoforms of Na-K-Cl cotransporters present in mammalian cells, can be differentially regulated by inflammatory cytokines and fluid mechanical forces in cultured endothelium. Interleukin-1beta and tumor necrosis factor-alpha significantly upregulate expression of BSC2 mRNA and protein in human umbilical vein endothelial cells, a response that is inhibited by pretreatment with interferon-gamma. Steady laminar fluid shear stress, at a physiologic magnitude (10 dyn/cm2), is also able to induce and maintain elevated expression of BSC2 in cultured human umbilical vein endothelial cells, while a comparable time-averaged magnitude of turbulent fluid shear stress is not. In vivo, BSC2 mRNA is upregulated after intraperitoneal administration of bacterial endotoxin (LPS) in murine lung and kidney, but not in cardiac tissue. These results provide the first experimental evidence that the BSC2 gene can be selectively regulated by different inflammatory cytokine and fluid mechanical stimuli in endothelium, and support a role for BSC2 in vascular homeostasis and inflammation.