Exploration of the Effects of Substrate Stiffness on Biological Responses of Neural Cells and Their Mechanisms.

Substrate stiffness, as a critical mechanical factor, has been proven to be an important regulator of biological responses, cellular functions, and disease occurrence. However, the effects of substrate stiffness on the phenotypes and drug responses of neural cells remain largely unknown. In this study, polydimethylsiloxane (PDMS) substrates with different stiffnesses were employed to establish the mechanical microenvironment of tissues of different organs. We studied the influences of stiffness on neural cell phenotypes, including cell viability, cell cycle, cytoskeleton structures, cell stiffness, and drug responses of neural cells for hormesis and therapeutic efficacy in neurodegenerative disorders (NDD). The results showed that the greater the range of maximum stimulatory responses, the bigger the width of the stimulatory dosage and the higher the range of maximum neuroprotective activities of hormetic chemicals in neural cells grown on the soft substrate commensurable to the stiffness of the brain, indicating that neural cells on a rigid substrate are resistant to hormetic and neuroprotective effects of hormetic chemicals against 6-hydroxydopamine (6-OHDA)-induced Parkinson's disease (PD) model. The sensitivity of neural cells on the soft substrate to drug response was attributed to the increased cell viability rate, cell cycle progression, actin stress fibers, focal adhesion formation, and decreased cell stiffness. The promoting effect of the soft substrate and the enhanced hormetic and neuroprotective effect of hormetic chemicals on soft substrates in PC12 cells were confirmed to be mediated by the upregulated EGFR/PI3K/AKT signaling pathway by RNA-Seq and bioinformatics analysis. This study demonstrates that the biomechanical properties of the neural microenvironment play important roles in cell phenotypes and drug responses of neural cells in vitro and suggests that substrate stiffness should be considered in the anti-NDD drug design and treatment.