microRNA-dependent regulation of biomechanical genes establish tissue stiffness homeostasis

Vertebrate tissues exhibit mechanical homeostasis over time and in response to changing stresses. However, the regulatory pathways that mediate these effects are unclear. To investigate a potential role for microRNAs, we performed a comprehensive identification of Argonaute-2(AGO2)-associated microRNAs and mRNAs in endothelial cells. We discovered a network of 122 microRNA families that target 73 mRNAs encoding cytoskeletal, contractile, adhesive and extracellular matrix (CAM) proteins. These microRNAs showed increased abundance in cells plated on stiff vs. soft substrates, consistent with maintaining homeostasis, and suppressed targets via microRNA recognition elements (MREs) within the 3’UTRs of CAM mRNAs. Inhibition of DROSHA or AGO2, or disruption of MREs within individual target mRNAs such as “Connective Tissue Growth Factor (CTGF)”, induced hyper-adhesive, hyper-contractile phenotypes in multiple cells in vitro, and increased tissue stiffness, contractility and matrix deposition in the zebrafish fin-fold in vivo. Thus, a network of microRNAs buffers CAM expression to mediate tissue mechanical homeostasis.