Disruptions of occludin and claudin‐5 in brain endothelial cells in vitro and in brains of mice with acute liver failure†

Abstract

Brain edema in acute liver failure (ALF) remains lethal. The role of vasogenic mechanisms of brain edema has not been explored. We previously demonstrated that matrix metalloproteinase-9 (MMP-9) contributes to the pathogenesis of brain edema. Here, we show that MMP-9 mediates disruptions in tight junction (TJ) proteins in vitro and in brains of mice with ALF. We transfected murine brain endothelial cells (ECs) with MMP-9 complementary DNA (cDNA) using pc DNA3.1 (؉)/Myc-His A expression vector. Tissue inhibitor of matrix metalloproteinases (TIMP-1) cDNA transfection or GM6001 was used to inhibit MMP-9. ALF was induced in mice with azoxymethane. Endogenous overexpression of MMP-9 in brain ECs resulted in significant degradation of the TJ proteins occludin and claudin-5. The alterations in TJ proteins correlated with increased permeability to fluorescein isothiocyanate-dextran molecules. The degradation of TJ proteins and the increased permeability were reversed by TIMP-1 and GM6001. Similar results were found when MMP-9 was exogenously added to brain ECs. We also found that TJ protein degradation was reversed with GM6001 in the brains of mice with ALF. In acute liver failure (ALF), brain edema and sepsis are the two leading causes of death. 2 ALF occurs when there is a sudden loss of hepatic function in a person without preexisting liver disease. The mechanisms responsible for the development of brain edema in ALF remain inadequately characterized. Although the cytotoxic mechanism of brain edema is commonly known, 3 the role of a vasogenic mechanism in ALF is not known.Others have reported that vasogenic BBB failure in ALF results in increased selective permeability to small molecules. [4][5][6] However, light and electron microscopy have shown that in subjects with ALF, the BBB and its TJs are grossly intact. [4][5][6][7][8] These findings are consistent with the emerging concept that a vasogenic brain edema results from subtle modifications of TJ proteins without an obvious disruption of the BBB. 9 Consistent with a leaky BBB that lacks obvious structural breakdown, a perturbation in the extracellular loops of occludin can disturb the barrier function. [10][11][12] Similarly, a deletion in claudin-5 results in increased BBB permeability to molecules Ͻ800 Da despite an intact BBB ultrastructure. 13 Matrix metalloproteinases play significant roles in highly complex processes, including regulating cell behavior, cell-cell communication, and tumor progression. 14,15 Matrix metalloproteinases mediate many different proteolytic reactions involving cellular surface elements, in-

Metformin protects against the development of fructose-induced steatosis in mice: role of the intestinal barrier function

“…As earlier results of our group suggest that the effect of fructose on occludin protein levels in the duodenum is not dependent upon an alteration of occludin mRNA expression 20 and as results of recent studies suggest that occludin protein levels are also regulated through MMPs, 21,22 we determined mRNA expression of MMP-9 and MMP-13 as well as protein levels of TIMP-1 in the duodenum. Expressions of MMP-9 ( Figure 7a) and MMP-13 ( Figure 7b) were considerably induced in the duodenum of fructose-fed groups; however, a similar effect of the fructose feeding was not detected in metformin-treated mice.…”

“…Indeed, it has been suggested before by the results of in-vitro and in-vivo studies of others that MMPs are involved in the degradation of occludin. 21,22 Furthermore, it has been shown that MMPs and TIMPs levels are altered in situations of insulin resistance. 34,35 However, mechanisms involved in these alterations and the protective effects of metformin herein remain to be determined.…”

Brain edema in acute liver failure and chronic liver disease: Similarities and differences

“…In the same models, alterations in the expression of the major BBB tight junction proteins (occludin, claudin-5, zonula occludens 1 and 2) have been observed (Chen et al, 2009, Lv et al, 2010, Sawara et al, 2009and Shimojima et al, 2008. However, in galactosamine-induced ALF in the rabbit, it was reported that capillary endothelial cells appeared normal, and no evidence of brain extravasation to horseradish peroxidase was observed (Traber et al, 1987), contradicting the anterior data.…”

Neuropathological changes in the brain of pigs with acute liver failure

“…This treatment concept is based upon the presumption of an intact BBB, which may not be the case in severe ALF with high HE score [7,21]. The present results should therefore lead to a discussion about the Kristiansen, R.G.…”