Immobilization after injury alters extracellular matrix and stem cell fate
Amanda K. Huber, … , Aaron W. James, Benjamin Levi
Amanda K. Huber, … , Aaron W. James, Benjamin Levi
Published July 16, 2020
Citation Information: J Clin Invest. 2020;130(10):5444-5460. https://doi.org/10.1172/JCI136142.
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Research Article Bone biology Stem cells

Immobilization after injury alters extracellular matrix and stem cell fate

Abstract

Cells sense the extracellular environment and mechanical stimuli and translate these signals into intracellular responses through mechanotransduction, which alters cell maintenance, proliferation, and differentiation. Here we use a mouse model of trauma-induced heterotopic ossification (HO) to examine how cell-extrinsic forces impact mesenchymal progenitor cell (MPC) fate. After injury, single-cell (sc) RNA sequencing of the injury site reveals an early increase in MPC genes associated with pathways of cell adhesion and ECM-receptor interactions, and MPC trajectories to cartilage and bone. Immunostaining uncovers active mechanotransduction after injury with increased focal adhesion kinase signaling and nuclear translocation of transcriptional coactivator TAZ, inhibition of which mitigates HO. Similarly, joint immobilization decreases mechanotransductive signaling, and completely inhibits HO. Joint immobilization decreases collagen alignment and increases adipogenesis. Further, scRNA sequencing of the HO site after injury with or without immobilization identifies gene signatures in mobile MPCs correlating with osteogenesis, and signatures from immobile MPCs with adipogenesis. scATAC-seq in these same MPCs confirm that in mobile MPCs, chromatin regions around osteogenic genes are open, whereas in immobile MPCs, regions around adipogenic genes are open. Together these data suggest that joint immobilization after injury results in decreased ECM alignment, altered MPC mechanotransduction, and changes in genomic architecture favoring adipogenesis over osteogenesis, resulting in decreased formation of HO.

Authors

Amanda K. Huber, Nicole Patel, Chase A. Pagani, Simone Marini, Karthik R. Padmanabhan, Daniel L. Matera, Mohamed Said, Charles Hwang, Ginny Ching-Yun Hsu, Andrea A. Poli, Amy L. Strong, Noelle D. Visser, Joseph A. Greenstein, Reagan Nelson, Shuli Li, Michael T. Longaker, Yi Tang, Stephen J. Weiss, Brendon M. Baker, Aaron W. James, Benjamin Levi

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Figure 1

MPCs at the extremity injury site demonstrate increased mechanotransductive genes before aberrant cell fate change.

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MPCs at the extremity injury site demonstrate increased mechanotransduct...
(A) Schematic of burn/tenotomy (BT) injury model denoting where the cells were harvested (blue box). (B) Canonical correlation analysis of the HO site defines 16 clusters, including 3 MPC subsets based on expression of Pdgfra, Prrx1, and Clec3b. (C) Feature plot of the MPC clusters displaying expression of Ptk2, Wwtr1, and Yap1 across the different time points of the canonical analysis. (D) Trajectory analysis of gene expression changes in cells across pseudotime.