Baek Jieung, Kumar Sanjay, Schaffer David V
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, CA 94720, USA; Department of Bioengineering, University of California, Berkeley, CA 94720, USA; Division of Mechanical and Biomedical Engineering, Graduate Program in System Health Science and Engineering, Ewha Womans University, Seoul, 03760, Republic of Korea.
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, CA 94720, USA; Department of Bioengineering, University of California, Berkeley, CA 94720, USA.
Biomater Adv. 2024 Jun;160:213836. doi: 10.1016/j.bioadv.2024.213836. Epub 2024 Mar 25.
The behavior of stem cells is regulated by mechanical cues in their niche that continuously vary due to extracellular matrix (ECM) remodeling, pulsated mechanical stress exerted by blood flow, and/or cell migration. However, it is still unclear how dynamics of mechanical cues influence stem cell lineage commitment, especially in a 3D microenvironment where mechanosensing differs from that in a 2D microenvironment. In the present study, we investigated how temporally varying mechanical signaling regulates expression of the early growth response 1 gene (Egr1), which we recently discovered to be a 3D matrix-specific mediator of mechanosensitive neural stem cell (NSC) lineage commitment. Specifically, we temporally controlled the activity of Ras homolog family member A (RhoA), which is known to have a central role in mechanotransduction, using our previously developed Arabidopsis thaliana cryptochrome-2-based optoactivation system. Interestingly, pulsed RhoA activation induced Egr1 upregulation in stiff 3D gels only, whereas static light stimulation induced an increase in Egr1 expression across a wide range of 3D gel stiffnesses. Actin assembly inhibition limited Egr1 upregulation upon RhoA activation, implying that RhoA signaling requires an actin-involved process to upregulate Egr1. Consistently, static-light RhoA activation rather than pulsed-light activation restricted neurogenesis in soft gels. Our findings indicate that the dynamics of RhoA activation influence Egr1-mediated stem cell fate within 3D matrices in a matrix stiffness-dependent manner.
干细胞的行为受其微环境中的机械信号调节，这些信号因细胞外基质（ECM）重塑、血流施加的脉动机械应力和/或细胞迁移而不断变化。然而，机械信号的动态变化如何影响干细胞谱系定向仍不清楚，尤其是在机械传感与二维微环境不同的三维微环境中。在本研究中，我们调查了随时间变化的机械信号如何调节早期生长反应1基因（Egr1）的表达，我们最近发现该基因是机械敏感神经干细胞（NSC）谱系定向的三维基质特异性介质。具体而言，我们使用之前开发的基于拟南芥隐花色素2的光激活系统，对Ras同源家族成员A（RhoA）的活性进行了时间控制，已知RhoA在机械转导中起核心作用。有趣的是，脉冲式RhoA激活仅在刚性三维凝胶中诱导Egr1上调，而静态光刺激则在广泛的三维凝胶硬度范围内诱导Egr1表达增加。肌动蛋白组装抑制限制了RhoA激活时Egr1的上调，这意味着RhoA信号传导需要一个涉及肌动蛋白的过程来上调Egr1。同样，静态光RhoA激活而非脉冲光激活限制了软凝胶中的神经发生。我们的研究结果表明，RhoA激活的动态变化以基质硬度依赖的方式影响三维基质中Egr1介导的干细胞命运。
