Evidence for Drop-Like Nuclear Deformation in Sheared Endothelial Monolayers.

Area of Science:

• Cell Biology
• Biophysics
• Mechanobiology

Background:

• Endothelial cells respond to blood flow shear stress by altering nuclear morphology.
• The mechanical underpinnings of flow-induced endothelial cell smoothing and nuclear shape changes are not fully understood.

Purpose of the Study:

• To investigate the mechanical basis of shear stress-induced nuclear shape changes in human umbilical vein endothelial cells (HUVECs).
• To test the nuclear drop model's predictions regarding nuclear volume and surface area constancy under shear stress.
• To elucidate the mechanisms driving shear-induced YAP nuclear localization.

Main Methods:

• Subjecting HUVECs to physiological shear stress.
• Analyzing nuclear morphology using microscopy.
• Depleting lamin A/C and lamin B1 to assess their role in nuclear mechanics.
• Utilizing computational modeling to predict nuclear shapes.
• Quantifying cell spreading, focal adhesion assembly, and cytoskeletal tension.

Main Results:

• Shear stress reduced the frequency of tall, wrinkled nuclei, leading to population-level decrease in nuclear height.
• Nuclear volume and surface area remained constant under shear stress, supporting the nuclear drop model.
• Lamin A/C depletion resulted in irregular nuclei that failed to recover shape post-indentation, indicating its role in nuclear surface tension.
• Shear-induced YAP nuclear localization was driven by increased cell spreading and cytoskeletal tension, not nuclear deformation, in remaining cells.

Conclusions:

• Shear stress-induced endothelial cell smoothing is primarily mediated by increased cell spreading and cytoskeletal tension, leading to YAP nuclear localization.
• The nuclear drop model, with constant nuclear volume and surface area, accurately predicts nuclear shape changes under shear stress.
• Lamin A/C is crucial for maintaining nuclear shape and surface tension in endothelial cells.