title: Mechanically Induced Chromatin Condensation Requires Cellular Contractility in Mesenchymal Stem Cells.
abstract: Mechanical cues play important roles in directing the lineage commitment of mesenchymal stem cells (MSCs). In this study, we explored the molecular mechanisms by which dynamic tensile loading (DL) regulates chromatin organization in this cell type. Our previous findings indicated that the application of DL elicited a rapid increase in chromatin condensation through purinergic signaling mediated by ATP. Here, we show that the rate and degree of condensation depends on the frequency and duration of mechanical loading, and that ATP release requires actomyosin-based cellular contractility. Increases in baseline cellular contractility via the addition of an activator of G-protein coupled receptors (lysophosphatidic acid) induced rapid ATP release, resulting in chromatin condensation independent of loading. Conversely, inhibition of contractility through pretreatment with either a RhoA/Rock inhibitor (Y27632) or MLCK inhibitor (ML7) abrogated ATP release in response to DL, blocking load-induced chromatin condensation. With loading, ATP release occurred very rapidly (within the first 10-20 s), whereas changes in chromatin occurred at a later time point (∼10 min), suggesting a downstream biochemical pathway mediating this process. When cells were pretreated with blockers of the transforming growth factor (TGF) superfamily, purinergic signaling in response to DL was also eliminated. Further analysis showed that this pretreatment decreased contractility, implicating activity in the TGF pathway in the establishment of the baseline contractile state of MSCs (in the absence of exogenous ligands). These data indicate that chromatin condensation in response to DL is regulated through the interplay between purinergic and RhoA/Rock signaling, and that ligandless activity in the TGF/bone morphogenetic proteins signaling pathway contributes to the establishment of baseline contractility in MSCs.
authors: McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Su-Jin
authors: SJ
authors: Heo
authors: Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania.
authors: Woojin M
authors: WM
authors: Han
authors: McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania.
authors: Spencer E
authors: SE
authors: Szczesny
authors: McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania; Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania.
authors: Brian D
authors: BD
authors: Cosgrove
authors: Department of Biomedical Engineering, University of Delaware, Newark, Delaware.
authors: Dawn M
authors: DM
authors: Elliott
authors: Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, London, United Kingdom.
authors: David A
authors: DA
authors: Lee
authors: Department of Biomedical Engineering, University of Delaware, Newark, Delaware; Department of Biological Sciences, University of Delaware, Newark, Delaware.
authors: Randall L
authors: RL
authors: Duncan
authors: McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania; Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania. Electronic address: lemauck@mail.med.upenn.edu.
authors: Robert L
authors: RL
authors: Mauck
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001696:Biomechanical Phenomena; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D002417:Cattle; D002843:Chromatin / Q000737:chemistry* / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D055595:Mechanical Phenomena; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000378:metabolism; D015398:Signal Transduction; D013718:Tensile Strength; D016212:Transforming Growth Factor beta / Q000378:metabolism
chemical_list: D019485:Bone Morphogenetic Proteins; D002843:Chromatin; D016212:Transforming Growth Factor beta; D000255:Adenosine Triphosphate