Diseases of gut inflammation such as neonatal necrotizing enterocolitis (NEC) result after an injury to the mucosal lining of the intestine, leading to translocation of bacteria and endotoxin (lipopolysaccharide). Intestinal mucosal defects are repaired by the process of intestinal restitution, during which enterocytes migrate from healthy areas to sites of injury. In an animal model of NEC, we determined that intestinal restitution was significantly impaired compared with control animals. We therefore sought to determine the mechanisms governing enterocyte migration under basal conditions and after an endotoxin challenge. Here we show that the cytoskeletal reorganization and stress fiber formation required for migration in IEC-6 enterocytes requires RhoA. Enterocytes were found to express the endotoxin receptor Toll-like receptor 4, which served to bind and internalize lipopolysaccharide. Strikingly, endotoxin treatment significantly inhibited intestinal restitution, as measured by impaired IEC-6 cell migration across a scraped wound. Lipopolysaccharide was found to increase RhoA activity in a phosphatidylinositol 3-kinasedependent manner, leading to an increase in phosphorylation of focal adhesion kinase and an enhanced number of focal adhesions. Importantly, endotoxin caused a progressive, RhoA-dependent increase in cell matrix tension/contractility, which correlated with the observed impairment in enterocyte migration. We therefore conclude that endotoxin inhibits enterocyte migration through a RhoA-dependent increase in focal adhesions and enhanced cell adhesiveness, which may participate in the impaired restitution observed in experimental NEC.Necrotizing enterocolitis (NEC) 1 is the leading cause of death from gastrointestinal disease in neonates and is second to respiratory disease as the overall leading cause of morbidity and mortality in this population (1-3). Clinical manifestations of NEC include abdominal distention, feeding intolerance, and systemic sepsis, which result from the destruction of the intestinal barrier (4, 5). Mucosal breakdown may occur as a result of a perinatal insult, such as hypoxia, which allows bacteria and bacterial by-products to breach the normally impermeable mucosal barrier and initiate a local and systemic inflammatory response (4,6,7,9). This causes the release of proinflammatory cytokines, including tumor necrosis factor, platelet-activating factor, nitric oxide, and endotoxin, which lead to further epithelial injury (10 -13). Following mucosal damage, healing occurs initially through the process of epithelial restitution, in which healthy enterocytes adjacent to the sites of injury migrate toward the denuded mucosa to bridge the defect (14 -18). We hypothesize that the intestinal barrier defect in NEC does not result from epithelial injury alone but also from impaired restitution. This paper focuses specifically on the process of enterocyte migration, which is the sine qua non of epithelial restitution and mucosal healing.Although a variety of cytokines may be importan...
Sinusoidal endothelial cell (SEC) porosities were compared between the periportal (zone 1) and pericentral (zone 3) regions of the rat liver during regeneration following partial hepatectomy (PHx). SEC porosities and fenestration diameters were measured in control livers, as well as at 5 minutes, 24, 48, 72, 96, 120 hours, and 14 days following PHx. Bimodal maximums in both porosity and fenestration diameters were observed in both zones at 5 minutes and 5 days following PHx. SEC porosities increased significantly in both zones 1 and 3 within 5 minutes following PHx, but the increase was maintained only in zone 1 at 24 hours after resection. Following the initial rise, both zones displayed a gradual decrease to less than half their porosity values at 72 hr post-PHx. After 72 hours, porosities increased to over control levels and remained elevated until 14 days after PHx. The decrease in porosity at 72 hr post-PHx is accompanied by ultrastructural changes within the sinusoid at this time. Vascular corrosion casting and transmission electron microscopy (TEM) show sinusoid compression resulting from increased hepatic plate widths due to hepatocyte proliferation in the absence of SEC proliferation. Also at this time, we observed many SEC completely enveloped by stellate cells. The zonal variations observed for porosities throughout regeneration did not correlate with changes in laminin, collagen I and IV, or fibronectin deposition within the space of Disse. Taken together, the data reveal that SEC are dynamic regulators of porosity that respond rapidly and locally to environmental zonal stimuli during liver regeneration. (HEPATOLOGY 2001;33:363-378.)Following chemical or mechanical injury, the liver has the extraordinary capacity to regenerate back to its normal mass within a short time. During regeneration, the same physiologic functions required by the organism must be performed with less metabolic "equipment," and therefore the liver must continuously adapt its metabolic output to its rapidly changing architecture. As a result of tissue loss, the concentrations of many factors, including growth factors, cytokines, and proteases, rise in the blood and liver to promote temporal and spatial proliferation and migration of the various cells to efficiently reconstitute the liver mass (reviewed by Michalopoulos 1 and Fausto 2 ). Following 70% partial hepatectomy (PHx) in the rat, hepatocyte DNA synthesis peaks abruptly at 24 hours after PHx, and essentially terminates DNA synthesis by 72 hours following resection. 3 Sinusoidal endothelial cells (SEC), the open, fenestrated, discontinuous endothelial cells that line the vessels supplying the parenchymal plates, do not initiate DNA synthesis until 48 to 72 hours after resection, peaking at 4 d post-PHx, but continue to proliferate at least until 8 days following PHx. [3][4][5] This cellular order of proliferative events results in the formation of avascular hepatic islands throughout the liver lobule. 6 Subsequent proliferation and migration of the sinusoidal endothelium i...
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