Dynamic light-responsive RhoA activity regulates mechanosensitive stem cell fate decision in 3D matrices

Area of Science:

• Biomedical Engineering
• Stem Cell Biology
• Mechanobiology

Background:

• Stem cell behavior is influenced by dynamic mechanical cues in their niche.
• Understanding how these dynamics affect stem cell lineage commitment in 3D is crucial.
• The early growth response 1 gene (Egr1) is a 3D matrix-specific mediator of neural stem cell (NSC) mechanosensitive lineage commitment.

Purpose of the Study:

• To investigate how temporally varying mechanical signaling regulates Egr1 expression in 3D.
• To elucidate the role of RhoA signaling dynamics in mechanotransduction and stem cell fate.
• To determine the influence of matrix stiffness on RhoA-mediated Egr1 regulation.

Main Methods:

• Utilized an optoactivation system based on Arabidopsis thaliana cryptochrome-2 to control RhoA activity temporally.
• Investigated Egr1 expression in 3D gels of varying stiffness under static and pulsed RhoA activation.
• Assessed the role of actin assembly in RhoA-mediated Egr1 upregulation.
• Examined the effect of static vs. pulsed RhoA activation on neurogenesis in soft 3D gels.

Main Results:

• Pulsed RhoA activation specifically upregulated Egr1 in stiff 3D gels.
• Static light stimulation increased Egr1 expression across a broad range of 3D gel stiffnesses.
• Actin assembly inhibition impaired Egr1 upregulation following RhoA activation.
• Static RhoA activation, unlike pulsed activation, restricted neurogenesis in soft gels.

Conclusions:

• The dynamics of RhoA activation critically influence Egr1-mediated stem cell fate in 3D matrices.
• This influence is dependent on the mechanical properties, specifically stiffness, of the 3D microenvironment.
• RhoA signaling requires actin-dependent processes for Egr1 upregulation and subsequent stem cell fate determination.