Regulation of endothelin synthesis in hepatic endothelial cells

Abstract

Endothelin (ET) stimulates vasoconstriction and glucose production and mediator synthesis in the liver. Only hepatic endothelial cells express ET-1 mRNA, and during endotoxemia in the intact rat, a ninefold increase in hepatic ET-1 mRNA occurs within 3 h of lipopolysaccharide (LPS) infusion [A. T. Eakes, K. M. Howard, J. E. Miller, and M. S. Olson. Am. J. Physiol. 272 ( Gastrointest. Liver Physiol. 35): G605–G611, 1997]. The present study defines the mechanism by which hepatic ET production is enhanced during endotoxin exposure. Culture media conditioned by exposure to endotoxin-treated Kupffer cells stimulated a twofold increase in immunoreactive ET-1 (irET-1) secretion by liver endothelial cells. Transforming growth factor-β (TGF-β), tumor necrosis factor-α (TNF-α), LPS, and platelet-activating factor (PAF) were tested for their ability to stimulate cultured liver endothelial cells to secrete irET-1. Although TNF-α, LPS, and PAF had no significant effect on ET-1 synthesis, TGF-β increased ET-1 mRNA expression and irET-1 secretion. In coculture experiments, treating Kupffer cells with endotoxin caused a doubling of the ET-1 mRNA level in the liver endothelial cells. This increase in ET-1 mRNA was attenuated by a TGF-β-neutralizing antibody. Hence, a paracrine signaling mechanism operates between Kupffer cells that release TGF-β on endotoxin challenge and hepatic endothelial cells in which TGF-β stimulates ET-1 mRNA expression and ET-1 secretion; this intercellular signaling relationship is an important component in the hepatic responses to endotoxin exposure.

Immunostimulatory CpG-oligodeoxynucleotides (CpG-ODN) induce early hepatic injury, but provide a late window for protection against endotoxin-mediated liver damage

“…Previous studies have indicated that microvascular perfusion failure significantly contributes to the manifestation of endotoxic liver injury [38], as again underlined by the significant negative correlation between hepatocellular excretory function and perfusion failure. The mechanisms, which are involved in the development of sinusoidal perfusion failure in endotoxemia are thought to be based on the action of TNF-a, including intravascular congestion [39], endothelial cell swelling [40], and release of endothelin-1 [41,42]. Thus, the protection from perfusion failure by CpG-ODN observed in our experiments may also be due to the downregulation of the proinflammatory cytokine response.…”

Cell and Molecular Regulation of Endothelin-1 Production during Hepatic Wound Healing

“…Indeed, other cytokines and the extracellular matrix are prominent in many forms of wounding and are likely to be important regulators of ET-1 in this environment. Nonetheless, TGF-␤ has been reported to lead to increased production of ET-1 in other systems (Kurihara et al, 1989;Kanse et al, 1991;Schnermann et al, 1996Eakes andOlson, 1998), consistent with its effect in liver wounding. In these reports and in systems in which other factors stimulate ET-1 synthesis, the effect has been largely via modulation of precursor ET-1 (i.e., preproET-1 mRNA expression), primarily at the level of preproET-1 mRNA transcription.…”

Bone Morphogenetic Protein-9

“…KCs were cultured for 48 h at 37°C in a 10% CO 2 atmosphere prior to conducting all receptor characterization experiments. Kupffer cell and liver endothelial cell primary cultures are known to be highly enriched (95%) for the specified cell type as determined by peroxidase staining (KC marker) and acetylated low-density lipoprotein incorporation (LEC marker) (24). Hepatocytes were isolated as described by Seglen (25) and plated on Corning 24-well plates at 1 ϫ 10 5 cell/well in William's E Medium (Life Technologies, Inc.) supplemented with 10% fetal bovine serum (Hyclone) and 7 mg/liter insulin.…”