Increase in the number of fenestrae in mouse endothelial liver cells by altering the cytoskeleton with cytochalasin B

Abstract

Endothelial cells of the hepatic sinusoid isolated from mice livers and maintained in culture display typical fenestrae grouped in sieve plates. Treatment with cytochalasin B led to no significant change in the mean diameter of the fenestrae but to an increase in their number and in the porosity of the cells (percentage of the cellular surface opened by the fenestrae) which attained up to 300% of that of the controls. Scanning electron microscopic observations of Triton-extracted cells revealed that these modifications were related to an alteration of the cytoskeleton. The effect of cytochalasin B could be reversed; 3 hr after removal of the drug, the cells recovered their original aspect with sieve plates scattered over their surface. These observations demonstrate that endothelial fenestrae are inducible structures and that the cytoskeleton seems to be involved in their formation.

Sinusoidal Ultrastructure Evaluated During the Revascularization of Regenerating Rat Liver

“…This is believed to be accomplished by adjusting the diameter and/or number of fenestrae via an actin-based contraction system. 13,16,17 Compelling data from several laboratories have documented the exquisite zonal variation of sinusoidal porosity as a function of fenestration diameter and number along the portal-central axis of the lobule. 9,23-25 In FIG.…”

“…(See also vitro and in vivo studies have also shown that fenestrae can modulate their diameter in response to soluble agents as well as a variety of environmental conditions, including changes in shear stress and portal pressure, and pathological ECM deposition. [10][11][12][13][14][15][16][17][18][19] We sought to investigate the trends in porosity expression in the SEC within and between lobule zones throughout the revascularization process following PHx. We believed that such changes may play a critical role in the sieving function of the sinusoids and contribute to the progression of the regenerative process.…”

“…9 Fenestrations are thought to regulate flow of these agents by modulating porosity throughout the sinusoidal wall. Therefore, fenestrations are not passive sieves, but are most probably very dynamic structures whose size and density have been shown to be affected by physical factors such as portal pressure and shear stress 10,11 ; soluble substances such as alcohol, 12 serotonin, 13 endotoxin, 14 and nicotine 15 ; and cytoskeletal disruption agents like cytochalasin B, 16,17 as well as the composition of the ECM. 18,19 Given the fact that SEC fenestrations can modulate their diameters in response to a variety of factors and events, we sought to examine fenestration size and sinusoidal porosity index with respect to ultrastructural changes taking place within the regenerating lobule.…”

A novel structure involved in the formation of liver endothelial cell fenestrae revealed by using the actin inhibitor misakinolide

“…The increase in endothelial porosity, induced by microfilament-disrupting drugs may perhaps be exploited therapeutically to improve the extraction of atherogenic lipoproteins from the circulation (3) and to enhance the efficiency of liposome-mediated gene or drug delivery to liver parenchymal cells (30). These possible therapeutic implications are supported by the fact that cytochalasin B is able to increase the porosity of the liver sieve in vivo (14) and that polyanionized proteoliposomes can be targeted with high efficiency to hepatic endothelial cells in vivo (31). Therefore, this opens up attractive possibilities to modulate the liver sieve of hepatic endothelial cells with liposome-encapsulated microfilamentdisrupting drugs.…”

“…Contractile bundles of actin and myosin around fenestrae seem to regulate fenestrae diameter under the control of intracellular calcium levels (9). Cytochalasin B, a widely used fungal metabolite disrupting actin filaments by complex mechanisms (10,11) and latrunculin A, a marine sponge-derived macrolide disassembling actin filaments by sequestration of actin monomers (12,13), both induce a substantial and rapid increase in fenestrae number (14,15). These data indicate that fenestrae are inducible structures and that the organization of actin plays an important role in their numerical dynamics.…”