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

Abstract

Hepatic endothelial fenestrae are dynamic structures that act as a sieving barrier to control the extensive exchange of material between the blood and the liver parenchyma. Alterations in the number or diameter of fenestrae by drugs, hormones, toxins, and diseases can produce serious perturbations in liver function. Previous studies have shown that disassembly of actin by cytochalasin B or latrunculin A caused a remarkable increase in the number of fenestrae and established the importance of the actin cytoskeleton in the numerical dynamics of fenestrae. So far, however, no mechanism or structure has been described to explain the increase in the number of fenestrae. Using the new actin inhibitor misakinolide, we observed a new structure that appears to serve as a fenestrae-forming center in hepatic endothelial cells.

An in vitro assay reveals a role for the diaphragm protein PV-1 in endothelial fenestra morphogenesis

“…The potent effect of microfilament disassembly on fenestra induction in bEND5 cells and the spatial and temporal correlation between stress fiber disassembly and sieve plate formation highlighted the importance of actin microfilaments. Whereas previous studies had addressed the role of actin disassembly in sustaining or modulating the number of pores in fenestrated liver endothelial cells (31)(32)(33)35) and isolated kidney glomeruli (36), we demonstrated a role for actin disassembly in de novo fenestra formation. Our observations of a rearrangement of large actin filaments during fenestra induction by the physiological stimulus VEGF and the prevention of such rearrangements and fenestra induction by the F-actin-stabilizing drug phalloidin further supported a role for actin remodeling in fenestra formation.…”

New anti-actin drugs in the study of the organization and function of the actin cytoskeleton

“…8A). As illustrated in Figure 8 B-F, treatment with all five compounds at the indicated concentrations caused loss of F-actin bundles without adverse effects on cell shape and viability, but each of the compounds induced distinctive actin staining patterns in LSECs (Braet et al, 1996(Braet et al, , 1998a. Maximal effects for all compounds, except for JASPA, were obtained within 10-15 minutes, and further incubation did not result in additional alterations in actin organization.…”

“…However, only by treating LSECs with MISA were we able to visualize the process of fenestrae formation and to identify a new structure involved in the process of fenestrae formation (Braet et al, 1998a). This new structure comprises a special cytoskeletal domain (small unfenestrated area) from which nascent fenestrae are fanning out into the surrounding cytoplasm.…”

Glomerular Endothelial Cells Form Diaphragms during Development and Pathologic Conditions

“…BASIC RESEARCH www.jasn.org polymerization of actin filaments, 43,44 but the pathway linking VEGF and the depolymerization of actin filaments in GEnC remains to be elucidated.…”