Hepatic stellate cells require a stiff environment for myofibroblastic differentiation

Area of Science:

• Cell Biology
• Biophysics
• Hepatology

Background:

• Hepatic stellate cell (HSC) differentiation into myofibroblasts is central to liver fibrosis and cirrhosis.
• The precise molecular drivers of HSC activation remain incompletely understood.
• Liver tissue stiffening is a hallmark of fibrotic liver disease.

Purpose of the Study:

• To investigate the role of substrate mechanical properties in HSC differentiation.
• To determine if matrix stiffness is a principal factor in HSC activation.
• To elucidate the physical versus chemical determinants of HSC myofibroblastic phenotype.

Main Methods:

• Primary rat HSC cultured on polyacrylamide gels of defined stiffness.
• Coating gels with extracellular matrix proteins or poly-L-lysine.
• Assessing HSC differentiation via morphology, immunofluorescence, and gene expression.

Main Results:

• HSC differentiation progressively increased with substrate stiffness across various coatings.
• HSC activation degree, not speed, correlated with stiffness; intermediate stiffness yielded stable phenotypes.
• Quiescent HSC on soft substrates could differentiate upon transfer to stiff substrates.
• Stiffness-dependent differentiation required cell adhesion and mechanical tension generation.
• Transforming growth factor-β enhanced differentiation on stiff substrates but was not essential.

Conclusions:

• HSC differentiation to myofibroblasts in vitro is primarily governed by substrate physical properties (stiffness) rather than chemical properties.
• Mechanically stiff substrates, coupled with cell adhesion and tension, are necessary for HSC differentiation.
• Liver stiffness is a critical factor driving the progression of liver fibrosis.