Decreased Substrate Stiffness Promotes a Hypofibrotic Phenotype in Cardiac Fibroblasts.

Area of Science:

• Cardiovascular Biology
• Mechanobiology
• Fibrosis Research

Background:

• Cardiac fibroblasts (CFs) from a volume overload heart failure model (aortocaval fistula - ACF) exhibit a paradoxical hypofibrotic phenotype, characterized by reduced extracellular matrix (ECM) synthesis despite elevated TGF-β.
• The ACF model results in decreased cardiac tissue stiffness compared to control (sham) hearts, suggesting a potential role for mechanical environment in modulating CF behavior.

Purpose of the Study:

• To investigate whether substrate stiffness influences the hypofibrotic phenotype observed in CFs isolated from ACF.
• To determine if mechanical memory of a softer environment contributes to the observed hypofibrotic characteristics of ACF CFs.

Main Methods:

• CFs were isolated from ACF and sham hearts and cultured on polyacrylamide gels with varying stiffness (2 kPa to 50 kPa).
• Key markers of cytoskeletal and fibrotic proteins were measured to assess cellular responses to different stiffness levels.
• Nuclear translocation of transcriptional regulators MRTF-A and YAP was analyzed.

Main Results:

• Sham CFs cultured on soft substrates recapitulated aspects of the hypofibrotic phenotype seen in ACF CFs.
• Similar expression levels of CTGF and transgelin mRNA were observed in sham CFs on soft gels and ACF CFs on stiff gels.
• Decreased nuclear translocation of MRTF-A and YAP was observed in ACF CFs, correlating with reduced CTGF and transgelin expression across all tested stiffnesses.

Conclusions:

• Substrate stiffness plays a significant role in modulating the fibrotic phenotype of cardiac fibroblasts.
• ACF CFs exhibit a 'mechanical memory' of a softer environment, leading to an overall hypofibrotic phenotype.
• Reduced nuclear localization of YAP and MRTF-A may underlie the stiffness-dependent hypofibrotic response in cardiac fibroblasts.