Substrate compliance versus ligand density in cell on gel responses

Area of Science:

• Cell biology
• Biophysics
• Biomaterials science

Background:

• Substrate stiffness is a critical physical cue influencing cell behavior.
• Aortic smooth muscle cells (ASMCs) respond to substrate properties like stiffness and adhesion.
• Previous studies show ASMCs spread and organize on rigid substrates more than soft ones.

Purpose of the Study:

• To investigate how substrate stiffness and collagen density affect ASMC spreading.
• To explore the role of the cytoskeleton and specific proteins in overriding substrate limitations.
• To model the relationship between ligand density, substrate stiffness, and cell spreading.

Main Methods:

• ASMCs were cultured on gels of varying stiffness and collagen densities.
• Cell spreading, cytoskeleton organization, and focal adhesions were analyzed.
• Green fluorescent protein (GFP) tagged actin, paxillin, or control GFP were overexpressed in ASMCs.
• Mathematical modeling was used to describe cell spreading curves.

Main Results:

• ASMCs spread and organized cytoskeletons more on stiff substrates than soft ones.
• Spreading on soft gels was insensitive to collagen density, unlike on stiffer substrates.
• Overexpression of GFP-actin, but not GFP or GFP-paxillin, rescued cell spreading on soft gels.
• GFP-actin expression led to organized filamentous cytoskeletons, overriding soft gel effects.

Conclusions:

• The cytoskeleton plays a key structural role in driving cell membrane outward during spreading.
• Cytoskeletal signaling networks can override typical spreading limitations imposed by soft substrates.
• Actin dynamics are crucial for cell adaptation to substrate stiffness, with implications for tissue engineering and mechanobiology.