Structure and dynamics of the fenestrae-associated cytoskeleton of rat liver sinusoidal endothelial cells

Abstract

This article describes the cytoskeleton associated with fenestrae and sieve plates of rat liver sinusoidal endothelial cells. Fenestrae control the exchange between the blood and parenchymal cells. We present evidence indicating that several agents that change the fenestrae and sieve plates also cause changes in the cytoskeleton. Cultured liver endothelial cells (LECs) were slightly fixed and treated with cytoskeleton extraction buffer. Detergent-extracted whole mounts of cultured cells were prepared for either scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Extracted cells show an integral intricate cytoskeleton; sieve plates and fenestrae are delineated by cytoskeleton elements. Fenestrae are surrounded by a filamentous, fenestrae-associated cytoskeleton with a mean filament thickness of 16 nm. Sieve plates are surrounded and delineated by microtubuli, which form a network together with additional branching cytoskeletal elements. The addition of ethanol to cultured cells enlarged the diameter for these fenestrae-associated cytoskeleton rings by 5%, whereas serotonin treatment reduced the diameter by 20%. These observations indicate that the fenestrae-associated cytoskeleton probably changes the size of fenestrae after different treatments. After treatment with cytochalasin B the number of fenestrae increased. However, cytochalasin B did not change the structure of the fenestrae-associated cytoskeleton ring, but disperses the microtubuli. In conclusion, LECs have a cytoskeleton that defines and supports sieve plates and fenestrae. Fenestrae-associated cytoskeleton is a dynamic structure and plays a role in maintaining and regulating the size of fenestrae after different treatments. Therefore, the fenestrae-associated cytoskeleton controls the important hepatic function of endothelial filtration.

The size of sinusoidal fenestrae is a critical determinant of hepatocyte transduction after adenoviral gene transfer

“…24 The effect of sodium decanoate on the size of sinusoidal fenestrae may be mediated by modulation of the fenestrae associated cytoskeleton, which has been shown to be involved in regulating the size of fenestrae. 25 Administration of the Kupffer cell blocking agent GdCl 3 or higher viral doses in New Zealand White and Fauve de Bourgogne rabbits only partially overcome the effect of the anatomical barrier constituted by the small fenestrae. A longer circulation time of adenoviral vectors secondary to reduced Kupffer cell phagocytosis or a higher vector dose will allow more vectors to penetrate into the space of Disse via fenestrae with a sufficient diameter for passage of adenoviral vectors.…”

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.…”

oxLDL induces injury and defenestration of human liver sinusoidal endothelial cells via LOX1

“…Liver sinusoidal endothelial cells (LSECs) play important roles in regulating hepatic sinus function. LSECs line the capillaries of the microvasculature and possess fenestrae that facilitate filtration between the liver parenchyma and sinusoids by serving as a selectively permeable barrier (Braet et al 1995. Results have indicated that NAFLD is associated with dysfunction of LSECs .…”