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RhoA inactivation enhances endothelial barrier function.

J M Carbajal1, R C Schaeffer

  • 1Department of Physiology, University of Arizona, The Benjamin W. Zweifach Microcirculation Laboratories, Department of Veterans Affairs Medical Center, Tucson, Arizona 85723, USA.

The American Journal of Physiology
|November 24, 1999
PubMed
Summary

This study investigated how RhoA, a small GTP-binding protein, influences endothelial barrier function. Using C3 transferase to inhibit RhoA, researchers observed a reduction in stress fibers and focal adhesions in bovine pulmonary artery endothelial cells. These structural changes correlated with improved barrier function, as measured by permeability assays. The study also found that RhoA inhibition led to cytoskeletal reorganization and enhanced junctional integrity. These findings suggest that RhoA activity is necessary for maintaining stress fibers and focal adhesions, and its inhibition mimics cAMP-like effects on endothelial structure.

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Area of Science:

  • Endothelial cell biology in vascular physiology
  • Cytoskeletal regulation in cell signaling
  • GTPase signaling in barrier function studies

Background:

Endothelial barrier integrity is a key determinant of vascular function. Prior research has shown that cytoskeletal organization, particularly actomyosin stress fibers and focal adhesions, influences endothelial permeability. However, the role of RhoA in this process remains unclear. While it is known that RhoA regulates cytoskeletal dynamics, no prior work had resolved how its inhibition affects barrier function. This gap motivated the use of C3 transferase to investigate RhoA's role in endothelial structure and function. The uncertainty surrounding RhoA's influence on stress fibers and focal adhesions drove the need for direct experimental validation. Researchers have proposed that RhoA inhibition could alter barrier function, but the exact mechanisms remain unexplored. This study aims to clarify how RhoA activity affects endothelial permeability through cytoskeletal changes. By focusing on RhoA's role in stress fiber organization, the study addresses a specific gap in understanding cytoskeletal signaling. The research builds on established knowledge of cytoskeletal signaling to explore novel regulatory pathways.

Keywords:
RhoA inhibitionendothelial barriercytoskeletal regulationstress fibersendothelial permeability

Frequently Asked Questions

RhoA inhibition via C3 transferase reduced stress fibers and improved barrier function by reorganizing F-actin and junctional proteins.

C3 transferase inhibits RhoA, leading to disassembly of stress fibers and focal adhesions in endothelial cells.

Phosphotyrosine levels in paxillin and p125(FAK) decreased, suggesting reduced focal adhesion signaling after RhoA inhibition.

The 170–300% increase in cell surface area suggests cytoskeletal relaxation and improved barrier function.

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Purpose Of The Study:

This study aimed to test the hypothesis that RhoA activity regulates endothelial barrier function through cytoskeletal organization. The specific problem addressed was how RhoA inhibition affects stress fibers and focal adhesions in endothelial cells. The motivation stemmed from the need to clarify RhoA's role in barrier function regulation. The authors sought to determine whether RhoA inhibition could reduce stress fibers and improve barrier integrity. The study focused on bovine pulmonary artery endothelial cells to model these effects. By using C3 transferase, the researchers aimed to dissect RhoA's influence on cytoskeletal structures. The goal was to assess how RhoA inhibition impacts endothelial permeability and junctional organization. This approach allowed the team to investigate the direct effects of RhoA on barrier function mechanisms.

Main Methods:

The study used bovine pulmonary artery endothelial cells treated with C3 transferase to inhibit RhoA. A size-selective permeability assay measured barrier function changes. Digital imaging tracked stress fiber and focal adhesion disassembly. The researchers compared C3-treated cells with thrombin-treated and untreated controls. Myosin II immunostaining was used to assess cytoskeletal reorganization. Phosphotyrosine levels in paxillin and p125(FAK) were quantified to evaluate signaling changes. Cell surface area and F-actin content were measured to assess structural alterations. The study also evaluated thrombin-induced effects in C3-treated cells to confirm RhoA dependency.

Main Results:

C3 treatment reduced stress fibers and focal adhesions in endothelial cells. Myosin II staining became diffuse, indicating cytoskeletal reorganization. Phosphotyrosine levels in paxillin and p125(FAK) decreased significantly. F-actin content dropped by 60–85%, while cell surface area increased by 170–300%. These changes correlated with improved endothelial barrier function. Beta-catenin-containing junctions showed increased F-actin and phosphotyrosine localization. C3 prevented thrombin-induced myosin ribbon formation and stress fiber assembly. The results suggest RhoA inhibition mimics cAMP-like effects on cytoskeletal structure.

Conclusions:

The authors propose that RhoA inhibition reduces stress fibers and focal adhesions in endothelial cells. They suggest that this leads to improved barrier function through cytoskeletal reorganization. The study shows that C3 treatment mimics cAMP-like effects on endothelial structure. The findings indicate that RhoA activity is necessary for thrombin-induced cytoskeletal changes. The data support the idea that RhoA inhibition enhances junctional organization. The authors state that RhoA is essential for maintaining stress fibers and focal adhesions. They conclude that RhoA signaling directly influences endothelial permeability. These results align with prior work on cytoskeletal regulation in barrier function.

Thrombin failed to induce myosin ribbons or stress fibers in C3-treated cells, showing RhoA dependency.

These junctions showed increased F-actin and phosphotyrosine, indicating enhanced cell-cell adhesion after RhoA inhibition.