PPy-coated wire actuators for micromechanostimulation of cells – identification of immediate-early responsive mechanoregulatory genes in osteoblasts

Mechanotransduction, i.e., the conversion of mechanical cues into biochemical signals, is essential for bone development, remodeling, and adaptation. Although mechanical loading is known to regulate osteoblast function and bone homeostasis, dissecting the early and sustained mechanotransductive responses at the microscale remains challenging due to limitations of existing in vitro models. Here, we report the development and application of a mechanostimulation system comprising a polypyrrole (PPy)-based wire actuator that expands and contracts (4 μm in radius) upon electrical actuation and enables precise, localized micromechanical stimulation of a small number of cells within standard culture formats. Using this system, we applied short-term (30 min) cyclic (Cyc30) or static (Stat30), as well as prolonged (120 min) cyclic (Cyc120) stimulations to two osteoblast-like cells (MC3T3-E1 or KUSA-A1). Subsequent transcriptomic profiling and computational network analyses revealed that Cyc30 was not capable of inducing significant changes in mRNA expression, suggesting cellular adaptation to short-term cyclic loading. In contrast, Stat30 induced the upregulation of Fos, Btg2, Egr1, and Fosl1, all known genes associated with mechanotransduction, supporting the validity and reproducibility of our experimental mechanostimulation system. Notably, two long non-coding RNAs (B930036N10Rik and 5430431A17Rik) were identified for the first time as being upregulated in response to Stat30 stimuli. Among the differentially expressed genes (DEGs) upregulated by Cyc120 stimuli, Hmox1, a stress-inducible enzyme known for its roles in maintaining cellular homeostasis and promoting survival, was the only DEG repeatedly observed across the Cyc30/Cyc120 and Stat30/Cyc120 comparisons in both cell types, potentially emerging as a key stress-response gene under prolonged mechanical loading. Collectively, these results establish the PPy-based microactuator as a powerful tool for microscale mechanobiology, and provide molecular insight into immediate-early responsive transcriptional programs underlying osteoblastic mechanoadaptation conserved across different cell types.