The stiffness-sensitive transcriptome of human tendon stromal cells

Abstract

Matrix stiffness and its effects on tensional homeostasis act as major regulators of cellular states in health and disease. Stiffness-sensing studies are typically performed using cells that have acquired "mechanical memory" through prolonged propagation in rigid mechanical environments, e.g. tissue culture plastic (TCP). This may potentially mask the full extent of the stiffness-driven mechanosensing programs. To address this, we developed a biomaterial system composed of two-dimensional mechano-variant silicone substrates that is permissive to large-scale cell culture expansion processes. We broadly mapped the stiffness-mediated mechano-responses by performing RNA sequencing on human tendon-derived stromal cells. We find that matrix rigidities approximating tendon microscale stiffness range (E. ~35 kPa) distinctly favor programs related to chromatin remodeling and Hippo signaling; whereas more compliant stiffnesses (E. 2 kPa) were enriched in responses related to pluripotency, synapse assembly and angiogenesis. We also find that tendon stromal cells undergo dramatic phenotypic drift on conventional TCP, with near-complete suppression of tendon-related genes and emergence of expression signatures skewed towards fibro-inflammatory and metabolic activation. Strikingly, mechano-variant substrates abrogate fibroblasts activation, with tenogenic stiffnesses inducing a transcriptional program that strongly correlate with established tendon tissue-specific signatures. Computational inference predicted that AKT1 and ERK1/2 are major signaling hubs mediating stiffness-sensing in tendon cells. Together, our findings highlight how the underlying biophysical cues may dictate the transcriptional identity of resident cells, and how matrix mechano-reciprocity regulates diverse sets of previously underappreciated mechanosensitive processes in tendon stromal fibroblasts.