Extracellular Matrix Viscoelasticity Regulates Mammary Branching Morphogenesis

Area of Science:

• Biomedical Engineering
• Developmental Biology
• Cellular Mechanics

Background:

• Extracellular matrix (ECM) mechanical properties are crucial for tissue morphogenesis.
• Existing ex vivo models have limitations in controlling and mimicking ECM mechanics.
• The role of matrix stress relaxation rate in mammary branching morphogenesis remains largely unexplored.

Purpose of the Study:

• To investigate how matrix stress relaxation rate influences mammary branching morphogenesis.
• To elucidate the underlying cellular and mechanical mechanisms.
• To establish a more physiologically relevant model for studying tissue development.

Main Methods:

• Utilized 3D alginate-collagen matrices with tunable stress relaxation properties.
• Cultured human mammary epithelial cell spheroids within these matrices.
• Analyzed branching patterns, ECM fiber alignment, cellular contractions, and focal adhesion signaling.
• Employed pharmacological inhibitors (Rac1, non-muscle myosin II) and osmotic pressure to modulate cellular behavior.

Main Results:

• Slow stress-relaxing matrices promoted mammary branching morphogenesis.
• Branching in slow-relaxing matrices correlated with collagen fiber alignment, intermittent ECM pulling, and focal adhesion signaling.
• Fast stress-relaxing matrices resulted in isotropic pushing forces on the ECM.
• Inhibition of Rac1 or non-muscle myosin II abolished branching irrespective of matrix relaxation rate.
• Restricting cell expansion via osmotic pressure impeded branching even in slow-relaxing matrices.

Conclusions:

• Matrix stress relaxation rate is a critical regulator of mammary branching morphogenesis.
• Cellular contractility and cytoskeletal dynamics (Rac1, myosin II) are essential for branching.
• The ability of the matrix to relax stress influences the type of forces cells exert and receive, directing morphogenesis.